This Captured Lightning® sculpture was created by injecting trillions of
electrons into a block of
acrylic using a 5 million
volt particle accelerator. Electrons were first injected from the left
side, the specimen rotated 180 degrees, and additional electrons
were injected through the opposite side. This created two
intensely-charged layers of excess electrons inside the specimen, each
one-half inch below the
surface. The charge layer on the right side was then manually
discharged. The escaping electrons created a brilliant flash of
"lightning" that propagated upward through the nearest
layer. Additional discharges then grew from the right layer
to the left layer, forming a complex, beautifully
interconnected 3D structure. The entire discharge event
than 100 billionths of a second! The resulting sculpture is illuminated
by blue light emitting diodes (LED's). Each of our Captured Lightning
sculptures contains an incredibly detailed fractal discharge pattern.
Unlike laser art, every one of our sculptures is a one-of-a-kind
treasure. As they
branch, the discharge channels become increasingly smaller, and the
hair-like tips ultimately disappear into the acrylic. The smallest
discharges are thought
to extend down to the molecular level. See our Frequently Asked Questions (FAQ) or our one-page explanation for a quick overview of how these beautiful objects are created, or you can learn about all the details from this web page.
(Sculpture size: 3 x 3 x 2 inches or 7.6 x 7.6 x 5 cm)
What are Lichtenberg figures?
"Lichtenberg figures" are branching, tree-like patterns that
are created by the passage of high voltage electrical discharges along the surface or through
electrically insulating materials (dielectrics).
The first Lichtenberg figures were actually 2-dimensional "dust figures"
that formed when dust in the air settled on the surface of electrically-charged
plates of resin in the laboratory of their discoverer, German
physicist Georg Christoph Lichtenberg
(1742-1799). Professor Lichtenberg made this observation in 1777,
demonstrating the phenomenon to his physics students and peers. He
reported his findings in his memoir (in Latin): De Nova Methodo Naturam Ac Motum Fluidi Electrici Investigandi (Göttinger
Novi Commentarii, Göttingen, 1777). The translated title of
Lichtenberg's paper is, "Concerning the New Method Of Investigating the
Nature and Movement of Electric Fluid". The physical principles involved
in forming Lichtenberg figures eventually evolved to become the
modern-day science of plasma physics.
Lichtenberg used various high voltage electrostatic devices to electrically charge
the surfaces of various insulating materials including resin, glass, and
rubber). He then sprinkled a mixture of finely powdered
sulfur (yellow) and minium (called red lead, or lead tetroxide) onto the
charged surface. He
found that powdered sulfur (which became negatively-charged
through friction with its container) was more strongly attracted to the
positively-charged regions. Similarly, frictionally-charged red lead
powder acquired a positive charge and was attracted to negatively-charged regions. The colored powders
made previously hidden regions of stranded surface charge, and their
polarity, clearly visible. We now know that these charged regions on the surface were
previously deposited by small sparks of static electricity. Once deposited, electrical charges can remain stranded on the
surface of electrical insulators for a very long time since the insulating
material prevents them from
easily moving and dissipating. Lichtenberg also discovered that the shapes of
positively and negatively charged figures were significantly different.
Figures created by discharges from a positively-charged high-voltage
terminal were star-like with long, branching paths, while figures
created by discharges from negatively-charged terminals were shorter, rounded, and
shaped like a fan or
shell. By carefully pressing a piece of paper onto the dusted
surface, Lichtenberg was able to transfer these dust images onto paper,
demonstrating what eventually became the modern processes of xerography and laser printing. Drawings of positive and negative figures created by Lichtenberg are shown below.
Positive Lichtenberg figure
Negative Lichtenberg figure
following demonstration video replicates Lichtenberg's experiments
using a mixture of powdered red lead and sulfur to highlight positive
(yellow) and negative (red) Lichtenberg figures. In the video a more modern Wimshurst electrostatic generator is used as the high voltage source instead of an electrophorus,
as originally used by Lichtenberg, but the principles are otherwise the
same. In the video, branching positive Lichtenberg figures are created first,
shell-shaped negative Lichtenberg figures.
number of other physicists and experimenters investigated Lichtenberg
figures over the next two hundred years. Notable 19th and 20th century
researchers included physicists Gaston Planté and Peter T. Riess (mid-1850's), French artist and scientist Etienne Leopold Trouvelot, Thomas Burton Kinraide (late 1800's), and professors Carl Edward Magnusson, Maximilien Toepler, P. O. Pedersen, and Arthur Von Hippel
(1920's-30's). Modern researchers used photographic film to
directly capture the faint light emitted by the electrical
discharges. A wealthy English industrialist and
electricity researcher, Lord William G. Armstrong, published two beautiful full-color books showing some his high
voltage and Lichtenberg Figure studies. Although these books have become quite scarce, an online copy of Armstrong's
first book, "Electric Movement in Air and Water, with Theoretical Inferences", was recently made available through the kind efforts of Jeff Behary at the Turn of the Century Electrotherapy Museum.
In the mid-1920's, Von Hippel discovered that Lichtenberg figures were
actually created through complex interactions between corona discharges
or small electrical sparks, called streamers,
and the dielectric surface below. The electrical discharges deposited
matching patterns of electrical charge onto the dielectric surface
below, where they became temporarily stranded. Von Hippel also
discovered that increasing the applied voltage, or reducing the
surrounding gas pressure, caused the length and diameter of
the individual paths to increase.
Riess discovered that the diameter of a positive Lichtenberg figure was about 2.8
times the diameter of an equal-voltage negative figure. The relationships between the length of Lichtenberg figures versus voltage
and polarity were utilized in early measuring and recording instruments, such as
to measure the peak voltage and polarity of
high voltage impulses. Klydonographs photographically recorded the size
and shape of Lichtenberg figures that were generated by abnormal
electrical surges on electrical power lines created by nearby or direct
strikes. These measurements allowed lightning researchers and power
system designers in the 1930's and 1940's to
accurately measure lightning-induced voltages, thus providing critical
information about the electrical characteristics of lightning strikes.
This information allowed power engineers to create
"man-made lightning" with similar characteristics under controlled
laboratory conditions so that they could test the effectiveness of
various lightning-protection approaches.
Lightning protection evolved to become an essential part of the design in all
electrical transmission and distribution systems. A schematic
diagram of the active parts of a klydonograph is shown on the leftmost
along with examples of "klydonograms" from positive and
high voltage transients of equal size. Notice how the positive Lichtenberg figure is
considerably longer than the negative figure even though the peak voltages were identical.
Schematic view of a klydonograph showing the position of the
photographic film and high voltage electrode. Light from the high
voltage discharges creates a photographic record of the event.
From W.W. Lewis, "The Protection of Transmission Systems
Against Lightning", John Wiley & Sons, 1950
Lichtenberg figures are now known to occur during electrical breakdown
processes within gases, insulating liquids, and solid dielectrics.
Lichtenberg figures may be created within billionths of a second (nanoseconds)
when dielectrics are subjected to very high electrical stress, or they may develop over
a period of years through a progressive series of small, low-energy, partial discharges.
Countless partial discharges on the surface or interior of solid
dielectrics often create growing, partially-conductive 2D surface
Lichtenberg figures or internal 3D "electrical trees".
2D electrical trees are often found along the surfaces of contaminated
insulators. 3D trees can also form, hidden from view, inside dielectrics
due to the presence of small internal defects or voids, or at points
where an insulator has been physically damaged. Since these
partially-conductive trees will eventually cause
complete electrical failure of the insulator, preventing
their formation and growth is critical to long-term reliability of
The study of electrical trees and tree formation has been critical to
the reliable design of the high-voltage power transmission systems that
transfer electrical power to our homes and businesses.
The first large 3D Lichtenberg figures inside transparent plastic were
created by physicists Arno Brasch and Fritz Lange in the late 1940's.
their newly-invented electron accelerator, they injected trillions of
free electrons into plastic specimens, causing internal electrical breakdown and the formation of carbonized internal
Lichtenberg figures. Electrons are tiny, negatively charged particles that orbit the positively-charged
nucleus of the atoms that make up all condensed matter. The scientists used high voltage pulses from a
multimillion volt Marx Generator
to drive a pulsed electron beam accelerator.
An article about their research and their accelerator (which they
"Capacitron") originally appeared in the March 10, 1947 issue of LIFE
Magazine. The Capacitron could deliver a three-million volt pulse, and
generate a powerful beam of free electrons with a peak current of
100,000 amperes! The glowing region of ionized air created by the
beam of electrons resembled a bluish-violet rocket engine flame. A complete set of previously unpublished B&W pictures,
including Lichtenberg figures inside a clear block of plastic, has
recently become available online, as has another article with color pictures
from the April, 1951 issue of Popular Mechanics. In 1944, Brasch
founded the Electronized Chemicals Corporation (ECC), a pioneering researcher of
cross-linking monomers and polymers to improve their electrical and
physical properties. ECC was purchased by the 3M Company in
The first formal scientific study of charge movement and charge trapping within
dielectrics was conducted by a Brazilian physicist, Dr.
Bernhard Gross, in the early 1950's. Dr. Gross confirmed that internal Lichtenberg figures could be created within a number of different polymers and glasses by injecting them with high-energy electrons. The techniques that we use to make our sculptures are built upon
the theoretical work and experimental techniques originally developed by Brasch, Lange, and Gross. 3D acrylic Lichtenberg figures are sometimes
called "electron trees" or "beam trees" - we call our state of the art creations Captured Lightning®sculptures.
How do we make our Captured Lightning® sculptures?
Over the last decade, we have developed and refined irradiation and fabrication
techniques to create a wide variety of beautiful 2D and 3D sculptures.
We begin by carefully cutting and polishing various shapes from a clear, glass-like polymer called polymethyl methacrylate (or PMMA).
This material, commonly known as acrylic, is sold under various trade
names such as Lucite, Plexiglas, or Perspex (UK). Acrylic has a unique combination of
high optical clarity and superior electrical
and mechanical properties. Besides being an excellent electrical insulator,
acrylic is actually clearer than glass! A number of other clear polymers, such as polycarbonate
(PC), polystyrene (PS) , polyethylene terephthalate (PET), and polyvinyl
chloride (PVC) can also make Lichtenberg figures with varying
degrees of success. However, most other materials tend to form dark gray or black discharge patterns instead
of the attractive, mirror-like figures seen within acrylic. Lichtenberg figures can also be
created within glass. However, glass Lichtenberg figures often explosively shatter upon discharge or, unpredictably, days or weeks later, so we no longer make them.
We inject electrons into our specimens using a 5 million volt, 150 kW particle accelerator called a Dynamitron.
The heart of this device is the accelerator tube - a huge three-story
high "vacuum tube" that operates at voltages between one and
five million volts. At the top of the tube, electrons are emitted by a
small, white-hot tungsten filament. The filament is connected to
the negative output terminal of a
multimillion volt power supply, while the bottom of the tube is
connected to ground and the positive terminal
of the high voltage supply. This configuration creates a very strong
field that accelerates electrons emitted from the filament to a very
high velocity as they "fall" though the large potential difference
towards ground. The
bottom of the vacuum tube has very thin (only 2.3 thousandths of an inch thick!) titanium
window that separates the high vacuum on the inside
from air, at atmospheric pressure, on the outside. The high velocity electrons pass right through
the titanium window, almost as though it wasn't even there! The electrons then emerge
from the outside surface of the window, and then travel through another 24 inches of air before
crashing into our acrylic specimens on the movable carts below. Although the typical lifetime of free electrons in
air is only 11 billionths of a second, that's more than enough
time for them to work their magic.
The energy of electrons leaving the accelerator is measured in millions of electron volts (or MeV).
Most of our sculptures were created using electrons with energies
between 2 and 5 MeV. At these energies, electrons are traveling at relativistic velocities - between 98.5% and 99.6% of the speed of light. During irradiation,
these energetic electrons burrow deeply inside the
acrylic before finally coming to a stop. The penetration depth is a function of
the energy of the electron beam, the target material's
dielectric properties, and its atomic density. The higher the energy of
the electron beam, the deeper the electrons
will penetrate. For example, electrons with an energy of five MeV will
penetrate about one-half inch through acrylic, but a sheet of lead only
1/16" thick will completely stop them.
a thick piece of acrylic is irradiated, huge numbers of electrons
inside the specimen, creating a strongly-charged cloud-like layer called
charge. Because acrylic is an excellent electrical insulator, injected
electrons become temporarily trapped inside the acrylic. By passing
through the electron beam in two or more passes, changing specimen
orientation between passes or rotating them while they're
being irradiated, complex 3-dimensional space charge regions can be
created. As the number of electrons accumulate during irradiation, the
electrical stress (called the electrical field or "E-field") inside
the acrylic dramatically rises, reaching several million volts
centimeter. We normally charge our specimens to just below the point
where they'll break down. We then force the charged specimen to release
("discharge") the electrons at the desired location by poking it with a
metal tool. This creates a small fracture that concentrates the electrical
stress at that point. The electrical field at the tip of the fracture overcomes the dielectric strength of the acrylic, initiating electrical breakdown of the acrylic. During breakdown, chemical
bonds that hold the acrylic molecules together rapidly break, stripping away free electrons in a process
These newly-freed electrons become accelerated by the
extreme electric field, colliding with, and ionizing additional acrylic
molecules. In an instant, portions of the acrylic abruptly become electrically
conductive in a runaway process called avalanche breakdown.
billionths of a second, a network of branching, white-hot, plasma channels form within
the acrylic and, with a bright flash and a loud BANG, the
material suddenly undergoes dielectric breakdown.
The previously-trapped electrical charges rush out in a river-like
torrent as thousands of smaller tributaries dump their
share of stored charge into larger channels that eventually merge into a
single, brilliant discharge path that exits the acrylic. Although images
and videos may appear as though we're injecting high voltage into each specimen, we're
actually removing excess
charges that were previously trapped inside. Dielectric breakdown occurs with incredible speed - the main electrical discharge
within a 4 inch square specimen lasts less than 120
billionths of a second (120 nanoseconds)! Some physicists think that dielectric
breakdown within a charge-injected solid may be the most energetic
(explosive) chemical reaction known, vastly greater than high explosives.
The following image shows a 12 x 12 x 1 inch
specimen being discharged. In the image, a neutral density filter
reduced the brilliance of the discharge so that the individual paths can be
seen. Note the bright high-current discharge that exits from the discharge point
jumping along the top surface of the specimen to the grounded
metal table below:
(Photo courtesy of Terry Blake)
As the miniature lightning bolts blast their way through the acrylic,
create millions of microscopic tubes and fractures, leaving behind a
permanent "lightning fossil" deep inside the acrylic. The peak current
within the electrical discharge reaches several hundred, to several
amperes depending upon the size of the specimen. The temperature of the hot plasma in the
confined discharge channels may exceed 10,000 degrees, and the
combination of heat and high pressure causes nearby acrylic to vaporize and fracture.
Higher-current "roots" may even char the surrounding acrylic. The
exit point of the discharge creates a small crater on the surface.
Surprisingly, although we inject a huge amount of negative charge into
our specimens, the electrical discharges originate from points which are
more electrically positive (versus the space charge layer), so all of
our Captured Lightning® sculptures are actually "positive" Lichtenberg
Some specimens self-discharge while they are being irradiated. This
is usually caused by a small surface scratch, residual
manufacturing stress, or an internal defect (a small bubble or invisible manufacturing stresses) in the acrylic. A
specimen will continue to discharge numerous times as long as its being
irradiated as the electron beam continues to inject new charge into the
specimen. However, unlike the neatly branched structures seen in
manually-triggered sculptures, self-triggered sculptures develop a
thicker, mat-like tangle of chaotic discharges, or a complex combination of
dendritic and chaotic patterns. Because of their complexity,
self-discharged specimens are often among some of our most fascinating
Video clip of a huge 15 x 20 x 2 inch sculpture being discharged:
is a short video clip showing a huge 15" x 20" x 2" specimen being
discharged. The specimen was first
charged on one surface by a 5 MeV electron beam. The electrically-charged
specimen was then (very carefully!) flipped over and irradiated once
again on the opposite side. This created two independent charge planes,
each located about 1/2" below the large surfaces. Prior to discharging,
the estimated potential of these internal charge planes was about 2.6
million volts. Because of the two charge planes and large size, this
specimen stored significantly more electrostatic energy than most of our
other specimens - more than four kilojoules! Safety precautions were
necessary to prevent the possibility of receiving a painful and potentially dangerous electrical
Although the main discharge is quite brief (under 500 billionths
of a second for this specimen), the video successfully captured the brilliance of the 4
kilojoule electrical discharge in a single video frame (below). Numerous
secondary discharges continued to flash after the main discharge. These
continued sporadically for over 30 minutes. This video is courtesy of
Bill Hathaway, GCL Laboratories. The resulting sculpture, cradled within
a custom walnut light base and illuminated by an array of white and
blue LED's, is also shown below.
(Click on above image for high-resolution image)
The resulting Lichtenberg Figure is a series of branching hollow tubes surrounded by conchoidal
(shell-shaped) fractures. Conchoidal fractures are characteristic of the way glassy (amorphous)
materials fracture when stressed beyond their breaking point. Since the
fractures behave as tiny mirrors, illuminating a figure through one or
more edges causes the entire Lichtenberg figure to glow brilliantly
with the reflected colors of the external light source.
Lichtenberg figures are fractals
branching pattern of a Lichtenberg figure looks similar at various scales of
magnification - a property called "self-similarity". This property suggests that Lichtenberg
figures can be mathematically described through a recently-developed branch of mathematics called Fractal Geometry.
Unlike most common geometric forms, fractal objects do not have
even-integer dimensions. Instead, they
have dimensions that lie between 1 and 2 (for 2-dimensional fractals) or between 2
and 3 (for 3-dimensional fractals). Lichtenberg figures
may be one of the first fractal-like forms created by man. Our
branching 2D Lichtenberg figures have a
fractal dimension of about 1.5 (for thin, sparsely branching discharges) to 1.9 for
our densest discharges. Most of our standard 2D sculptures have figures with a
fractal dimension of about 1.7, and our
standard 3D figures have a fractal dimension of about 2.5. The appearance of
Lichtenberg figures depends upon how much charge was injected into the
acrylic and when the specimens are discharged. The technical terms for
these branching figures are dendritic or ramified (tree-like). If a larger amount of electrical charge is injected
into a specimen, very dense dendritic discharges can be created such as
in Figure 1 below. These very dense discharges are similar in appearance
to fern fronds ("filiciform") or dendritic plume agates.
Specimens exhibiting this
form were heavily charged to just below the point of self-breakdown and
then immediately discharged. If the amount of injected charge is
more classical, lightning-like or tree-like discharges are created
(Figure 2). If premature breakdown occurs as we are actively irradiating
a specimen, the resulting discharges form a thicker, densely tangled mat of "chaotic"
(Figure 3). In these specimens, after the initial discharge, newly-injected electrons from
the accelerator recharge smaller nearby regions, causing them to
repetitively discharge in random directions. The rapidly changing
internal electrical fields create a much thicker mat of densely chaotic
are reminiscent of interconnected nerve cells and neural networks.
Some of the most complex and fascinating patterns
occur when a specimen self-discharges about halfway through the
process, creating dramatic discharges that evolve from densely dendritic
to densely chaotic from one end of a sculpture to the other.
(Click for larger image)
Figure 1. Dense (filiciform or fern-like) Discharges
Maximum charge density
Fractal dimension ~1.8-1.9.
Figure 3. Chaotic Discharges
while being irradiated)
Unknown fractal dimension
self-similarity of dendritic discharges can easily be seen in the
following sequence of zooms from a 12" x 12" Lichtenberg Figure.
Although the branches become finer and hairlike, the overall branching
structure remains similar until the finest tips ultimately disappear at
the very edges of the discharge structure.
Similar fractal patterns are prevalent in nature. They are seen in
aerial views of rivers and their tributaries, and organic structures
such as branching tree limbs, your body's circulatory system, and within
various organs such as lungs, kidneys, and the liver. The satellite
view in the left image below shows the fractal pattern of a river
drainage system near Grand Junction, Colorado, USA. The rightmost image is a
casting of the bronchial tree of a human lung (courtesy Paul Cazeaux,
PhD student at Laboratoire Jacques-Louis Lions (LJLL), Paris, France).
The similar branching structure of all of these systems may be a
consequence of a recently proposed new law of physics, the Constructal Law,
which states that Nature tends to develop a hierarchical branching
network of paths that result in most efficient flow. The flowing
material can be water, air... or even electrons!
Lichtenberg figures can be mathematically modeled using an iterative growth process called "Diffusion Limited Aggregation" (DLA). A more accurate model, that combines an electric field with DLA, is called the Dielectric Breakdown Model (DBM).
The DBM appears to accurately describe the forms of Lichtenberg
figures that occur under various electrical field intensities on the
surface or within solid, liquid, and gaseous insulators.
Other interesting properties: fluorescence, solarization, birefringence, and discharge-free zone
acrylic is irradiated by high-energy electrons, it glows brilliantly
with a blue-white color. Radiation chemistry studies suggest that this
is mainly due to luminescence that peaks at a wavelength of about 435 nm. However, acrylic also generates fainter glows from X-ray fluorescence, and Cherenkov radiation
as high velocity electrons interact with acrylic molecules. The
detailed light-producing mechanisms for electron-irradiated acrylic are
yet fully understood.
Newly-irradiated specimens develop an amber-colored layer in the region
between the surface(s) that were irradiated by the electron beam and the
discharge layer. This phenomenon, called solarization, appears to be caused by various interactions between high
speed electrons and the acrylic's molecular structure. During
irradiation, electrons in the beam are initially traveling at over 99%
of the speed of light. As they penetrate the specimen, they collide with
acrylic molecules, rapidly coming to a stop within a fraction of an
inch. Electrons in the beam have lot of kinetic energy,
and as they collide with the atoms in the acrylic they release this energy
as heat, x-rays, and gamma rays.
In acrylic, most solarization seems to occur in the regions directly
hit by the electrons. However, it has recently been found that
regions that are intentionally covered by sheet lead (to prevent
electrons from hitting some areas of the acrylic) may also exhibit
solarization in deeper regions of the acrylic. As electrons crash into
the lead mask, they radiate very intense x-rays and gamma rays that
often create darker solarization in the acrylic underneath the mask.
Energetic collisions with electrons, x-rays, and excess electrons
injected into the acrylic's molecular structure stimulate chemical and
physical reactions that alter the physical and optical properties of the
acrylic. Deeply-trapped electrons may remain stranded within the acrylic for years,
creating color centers
which also contribute to solarization. While some of these changes last
for only minutes or hours, others persist for months or years after
irradiation. And, some changes appear to be permanent. Although all of the specific causes
of solarization are not completely understood, there is evidence that
irradiation creates longer-lived unstable ("metastable")
compounds that preferentially absorb light at the blue end of the
spectrum (250 - 400 nm). Since part of the blue portion of ambient light
is absorbed by the solarized regions, irradiated specimens appear green, brownish, or
amber colored when illuminated by white light.
Most acrylic specimens turn a lime-green color immediately
after irradiation. Once discharged, the color changes to
brownish-amber, then more slowly fading to a lighter amber color. The
amber region then typically fades away over several months to several
years. Fading can
often be accelerated by gently heating
block in the presence of air or oxygen or by leaving the specimen
in bright sunlight for an extended period of time. As oxygen diffuses
acrylic from the outside surfaces and the porous discharge layer,
slowly bleaches the solarized region, causing the solarized layer in between to
gradually become thinner until it eventually disappears.
Most Lichtenberg figures older than 2-3 years are completely bleached. Although older
specimens may no longer show any solarization, many exhibit various
degrees of "fogging" from electron collisions and X-radiation damage to the acrylic's molecular structure.
Some PMMA specimens exhibit
comparatively little initial solarization, while a small percentage of
specimens permanently retain their amber color. Permanently-colored specimens
appear to be solarized via a different, deeper penetrating mechanism,
such as X-radiation, since these specimens also tend to be uniformly
solarized throughout their entire thickness. These differences may be due to subtle variations in the acrylic blends and the specific catalytic agents used by various suppliers to polymerize the acrylic.
It has also been discovered that the solarization layer is often fluorescent.
An amateur scientist from Australia, Daniel Rutter, discovered that monochromatic light from a green laser pointer apparently changes color
when passed through the solarized layer of a Lichtenberg figure. More
recently, we have discovered that the light from a near-ultraviolet
source, such as a 405 nm Blu-ray laser or bright blue LED's, also causes the
solarized region to fluoresce with a yellow-green color. Both effects
appear to be due to the presence of semi-stable fluorescent components within the
solarization layer. As the solarization fades over time, so does the
Most specimens also exhibit slight changes in the
in the regions near the discharge layer. This may be due to residual mechanical stresses near the discharge
stresses near the Lichtenberg figures can sometimes be seen as
multicolored regions near the discharge plane when a sculpture is
illuminated by polarized
light and then viewed through a second polarizing filter (a configuration called crossed polarizers). When physically stressed,
acrylic exhibits a property called birefringence.
When viewed through crossed polarizers, stress-induced birefringence
causes changes in color that are directly related to the amount and
distribution of otherwise hidden stresses. An electrically charged
specimen clearly shows internal compressive forces created by the high
internal electrical field. These forces are then relieved when the
discharged. Following are images of the same specimen prior to charging,
fully charged, and then after discharging. Little internal stress is
seen in the initially uncharged specimen. The specimen was then charged
by injecting electrons from the left side. The injected charge forms an
intensely negative layer of charge near the center of the specimen. At
the same time, positive ions are strongly attracted to the external
surfaces of the specimen. partially neutralizing the overall external
charge outside the specimen. Attraction between the internal negative
layer and the positively-charged outer surfaces create significant
compressive stresses within the acrylic. For the specimens below, the
calculated compressive force created by the internal electrical field was in the range of 400 pounds per square inch (PSI).
The compression can easily be seen as
colored regions on either side of the center in the middle image. After
the specimen is discharged, the electrical stresses are greatly relieved
as can be seen in the rightmost image. There are still residual
mechanical stresses near the discharge zone due to fracturing. Click on
any of the individual images to see full-size images.
Initially uncharged specimen
Fully charged specimen
(electrons were injected from left side)
Finally, you may notice that all of our sculptures have a discharge-free
boundary along the outside edges. This is thought to be caused by a
combination of dielectric leakage and reduced electrical fields due to
the presence of positive surface charges. Because acrylic is not a
insulator, some of the internal charge leaks away along all the
edges. The rate that excess charges leaks away is highest where the
internal electrical field is greatest - i.e., in the region between the
sharper edge of the internal space charge region and the perimeter of
specimen. In these regions, the amount of stored charge is reduced to
the point where it can no longer break down the acrylic. In addition,
the presence of large numbers of positive charges on the outer surfaces
reduce the electrical field seen by advancing streamer tips as they
approach the edges which effectively stops them at a relatively fixed
distance from the edges.
"Iced 'bergs" and negative Lichtenberg figures. Do we get curved figures in a magnetic field?
From studies done by other researchers, we knew that acrylic specimens
could retain their injected
charge for weeks, or even months, when
chilled, charged, and maintained at dry ice
(-109F/-78.5C) temperatures. One of our team members, Todd
Johnson, has christened these frozen objects as "Iced 'bergs". At room temperature,
injected charge leaks away exponentially over a few minutes to a few
hours for commercial acrylic. Chilling acrylic
significantly reduces the speed that free charges can move inside the
acrylic, and this dramatically increases the time that trapped charges
can be stored. At dry ice temperatures, trapped charges can apparently
be stored indefinitely. We have confirmed virtually full charge
several weeks, and
other researchers have demonstrated charge storage for up to six months.
When later discharged, these specimens behave in a fashion similar to
freshly-charged specimens. The lime-green color is also retained in
chilled specimens until they are discharged. This suggests that the green color
related to the high density of electrons that remain
trapped before discharging. Once discharged, chilled specimens rapidly
lose their green color, changing to an amber color.
Chilled specimens also develop a heavy layer of frost when
exposed to humid air. When we discharge a specimen, we produce a "positive"
Lichtenberg figure inside the acrylic. Photographic evidence confirms
that the exiting spark "wraps around" and covers the exterior surfaces of the
specimen, discharging a layer of positive charges that have attached themselves to the
specimen's outer surfaces. The external surface discharge produces a
"negative" Lichtenberg figure along the large surfaces of the specimen.
However, the negative surface discharges are considerably fainter than the
brilliant internal discharges, so they're usually very
difficult to see or photograph. We accidentally discovered that, when a
charged specimen is coated with frost, the negative discharges along the acrylic
surface blast away the frost layer immediately above the discharges,
making the paths taken by the negative discharges clearly visible. The following "iced 'berg" was discharged by Todd
Johnson and Dr. Timothy Koeth during our 2010 production run. As
can be seen, the resulting negative Lichtenberg
figures blasted through the frost show considerably less branching than positive
internal figures... just as professor Lichtenberg observed
over 200 years ago.
We also wondered if an externally-applied magnetic
field might cause discharge paths inside the acrylic to become curved.
It was known that Lichtenberg figures created within gases along
dielectric surfaces become curved due to Lorentz force acting on the
moving charged particles within the electrical discharges. The stronger
the magnetic field, the greater the curvature:
Since we could chill charged specimens to dry ice temperatures and keep them charged indefinitely, it became possible to perform
tests on charged specimens in a more controlled laboratory environment.
Following our Fall, 2007 production run, Dr. Timothy Koeth placed a
chilled and charged specimen within the poles of a 1.5T (15,000 Gauss)
cyclotron electromagnet in his lab and then discharged it while it was
within the magnetic field. The blue-white flash of the electrical discharge
can be easily seen along the edge of the specimen in the photo below:
It was found that the paths of the resulting
Lichtenberg figure showed no evidence of any curvature - the paths
looked completely identical to control specimens discharged with no
applied field. It's possible that the 1.5T magnetic field was simply not
strong enough to show any effect. Or perhaps the net velocity of the
electrons within the discharges inside acrylic is
considerably slower than within gases, and the resulting Lorentz force
is lower and the degree of curving is much less. Perhaps a future
experiment, using a stronger electromagnet, may allow us to create
Discharge speed and current measurements... and a paradox During our 2007 and 2009 production runs, we
measured and recorded discharge current waveforms for a number of 4" x
4" x 3/4" specimens. We designed a special holding fixture with copper
foil plates that made physical contact with the large outer surfaces of a
charged acrylic specimen. A heavily-insulated wire connected the pair of
foil plates to a pointed discharge tool. This wire was also passed
through the center of a Pearson Model 411 wideband Current Transformer
(CT). When the specimen was discharged, the main current pulse flowed
from the interior charge layer,
through the wire (and center of the CT), to the oppositely-charged outer
surfaces of the specimen. The resulting discharge current was converted
to a voltage pulse via the CT - the conversion factor for this
particular CT was 0.1 volt per amp. So, every 100 amps of discharge
current would show up as 10 volts of output from the CT. The resulting
waveform was captured and stored by a Tektronix TDS3034B
300 MHz digital storage oscilloscope (DSO). An image and schematic of the experimental configuration can be seen below:
Specimens were previously charged by injecting a cumulative charge of ~2.7 microCoulombs/cm2 using an electron beam with a nominal energy of 4.0 MeV. Charged specimens were then placed inside the test fixture and manually discharged. The discharge current waveforms from one of the specimens is shown below. We found that this main discharge event occurred in less than
120 billionths of a second (120 ns), the peak current reached almost 600
amperes in 45 ns, and the waveform contained four discrete current
peaks. Discharges from five subsequent specimens showed similar discharge intervals with three
and seven discrete current peaks. Overall, the peak discharge currents declined as the time between irradiation and discharge increased. This decline was expected because the injected charge slowly leaks away, reducing the amount of remaining energy and the peak discharge current. Subsequent peak current measurements on the other specimens ranged from 526 to 404 amperes.
The occurrence of multiple current peaks suggests that the electrical trees may progress via a
series of larger breakdown events. Each current peak reflects a
surge of newly conducting channels ("streamers" and "leaders") as newer channels blast
their way into previously untapped reservoirs of charge within the
acrylic, pause briefly, then surge again, etc. The average discharge
velocity was between 8.5 x 105 and 1.3 x 106 meters/second (526 and 790
miles/second, or around 0.3% the speed of light). However, pauses
between successive current surges suggest that the peak discharge
velocity during the propagation phases are significantly faster. Surprisingly,
the average streamer velocity within the specimen was found to be 10-100 times
greater than the velocity of positive lightning leaders in air! This is
thought to be due to the extreme electrical field (estimated to exceed
20 million volts/cm) at the tips of the propagating discharges.
high streamer velocities within PMMA create a paradox, since they are
over 800 times the speed of sound within PMMA. This is completely
inconsistent with Griffith's theory of crack propagation within solids,
which predicts that the maximum speed that cracks can propagate within a
solid is limited to the speed of sound within the material (about
1.6 x 103 meters/second for PMMA). The current waveform clearly
demonstrated that the breakdown process (the complete formation of
chains of cracks and gas channels across the specimen) for our
Lichtenberg figures propagated at speeds that were almost 1000 times
FASTER than the maximum predicted by classical fracture theory! A
series of independent electro-optical measurements were taken by Dr. Timothy
Koeth in his laboratory at the University of Maryland. Dr. Koeth
measured the time delay between optical (light) emissions at the
beginning and ends of propagating discharges within 6" x 6" x 1"
specimens. His optical measurements also confirmed streamer velocities ranging between 7.4 x 105 and 1.55 x 106 m/s.
Some insights into this paradox may come from a Russian researcher, Yu
N. Vershinin. Dr. Vershinin explored how electrostatic energy is
and released within solid dielectrics during electrical breakdown.
Specifically, he studied how
energy is stored within acrylic when electrical charge is slowly
injected into the material ("charge trapping"), and the effects of
rapidly releasing these trapped charges ("charge detrapping") during
breakdown processes. Vershinin proposed that, when a dielectric contains
significant trapped space charge, the stored electrostatic potential
energy may be rapidly liberated, contributing to explosive formation and
growth of crack tips. As chemical bonds in the surrounding material are
ruptured, some of the material breaks down into its constituents,
liberating high pressure gases that rapidly expanding the channels
behind the propagating crack tips, forcing the crack forward. Vershinin
experimentally confirmed) that for very high internal electrical fields
(E-fields), the potential energy initially stored within the E-field was
rapidly converted into kinetic and thermal energy that drove crack
propagation at hypersonic velocities. When mechanically shocked, a
dielectric material that is highly stressed by an electrical field can
down, releasing energy previously stored within the electrical field,
causing larger molecules to break into into smaller, gaseous
byproducts. Breakdown occurs along rapidly propagating reaction fronts
(streamers), accompanied by shock waves.
Vershinin speculated that dielectric breakdown might be closely related to the process of detonation.
He found that "electronic detonation" did indeed occur within solid
dielectrics, but only for propagating positive discharges within highly
E-fields - the same conditions we create when making acrylic
Lichtenberg figures! An American researcher, Dr. Paul Budenstein,
developed a theory of dielectric breakdown in solids that seems to
explain many of these observations at a more fundamental level. Based
upon the rate of channel
expansion, Budenstein concluded that dielectric breakdown may be the
fastest known chemical reaction in nature. During
the breakdown process,
disassociating dielectric molecules create a network of
electrically-conductive gaseous channels that initially have nearly the
same density as the surrounding solid material. Budenstein estimated
that the initial temperature
of the gases inside these highly-compressed channels reached 100,000 K
they supersonically expanded to create a network of hollow tubules and
fractures that eventually form the resulting Lichtenberg figure. The
breakdown process along each channel appears to progress in a series of
discontinuous steps: gas pressure creates and expands a crack into the
virgin material ahead, stops temporarily, then repeats as gas expands in
the newly-created crack.
Some evidence for the above theories of breakdown and discharge
can be seen within Captured Lightning Lichtenberg figures. Under a
microscope, the discharge channels that make up the figures are found
to be hollow tubes, surrounded by countless small fractures that
scatter light. Some paths clearly exhibit periodic structures along the
discharge channel, similar to beads along a string, and higher current
paths may also exhibit charring of the surrounding material. These
structures are observed during dielectric breakdown of various polymers
as well as crystalline ionic salts. The theories predict that the
electrical field ruptures the chemical bonds within the acrylic. The
resulting electronic breakdown processes
liberate gases as some of the insulating material is decomposed into its
atomic constituents. Dr. Koeth has confirmed that a significant volume
of gas exits from the discharge point when an acrylic specimen is
under water. Other researchers have determined that the evolved gases
consist primarily of hydrogen, carbon monoxide, carbon dioxide, and
methane. "Beading" appears to reflect a repetitive sequence of electronic
decomposition, evolution of gases under high pressure, and formation/growth of
new cracks ahead of the expanding gas zone. Following is an example of a
beaded channel captured in one of our Captured Lightning sculptures by Dr. Bill Hathaway (GCL Laboratories).
We have experimentally confirmed that "electronic detonation" during the main discharge is 10 to 100 times faster than the detonation
velocity of the fastest known chemical explosive.
The stored electrostatic energy in larger specimens can exceed several
kilojoules. Since this energy is discharged in less than a microsecond, the
instantaneous power liberated when creating a Captured Lightning
sculpture can easily exceed one gigawatt
(109 watts)! Not surprisingly, the discharge
creates a very loud
BANG(!) as the brilliant, lightning-like spark channels wreak havoc inside the acrylic, blasting countless fractures
and tubes all along the space charge layer(s). The abrupt release of
previously-trapped space charge (a process called charge detrapping) is
now known to play a major role in the degradation and breakdown of
all solid dielectrics when subjected to long-term high voltage
sudden voltage changes, or abrupt polarity reversals. In many respects,
charge detrapping within a solid dielectric is analogous to a
high-voltage capacitor discharge that occurs entirely within the insulating material.
After the main discharge, hundreds of smaller secondary electrical
discharges continue to flash throughout the specimen as small pockets of
residual charge redistribute themselves across the specimen.
Immediately after the main discharge, large
sculptures sparkle and sizzle, making a sound similar to frying bacon.
IN large specimens, intermittent sparking has been observed over 30
minutes after the main
discharge. Harmless secondary discharges often sting our fingers
when we handle recently-discharged specimens. Click on the following
image to see some high resolution video captured during one of our
production runs that shows primary and secondary discharges.
(Photo and video courtesy of Mike Walker and Theodore Gray) Click on the Above image to see a video clip
of many Lichtenberg figures being discharged
Natural Lichtenberg figures - fulgurites, natural tattoos, and fractal lightning
Occasionally, nature creates also "fossilized lightning", called fulgurites
(from the Latin word "fulgur", or lightning). These are hollow, glass-lined tubes that are formed when the powerful
electrical current from a lightning strike creates underground discharge
channels within poorly-conducting sandy or sandy-clay soils. The
intense heat from the arc-like channels melts the surrounding sand
and soil particles, forming hollow glassy tubes in the soil. Larger fulgurites often exhibit
fractal characteristics as they split into smaller diameter root-like
branches at further distances from the site of the main strike.
Lichtenberg figures, sometimes called "lightning flowers" or "skin feathering", often form
beneath the skin of unfortunate humans who have been struck by lightning. The victim often has one
or more reddish radiating feathery patterns that branch outward from
the entry and exit points of the strike. Here's an example of an electrical tattoo from a lucky lightning survivor:
OUCH! A temporary lightning tattoo on a "lucky" survivor
From "Lichtenberg Figures Due to a Lightning Strike" by Yves Domart, MD, and Emmanuel Garet, MD,
New England Journal of Medicine, Volume 343:1536, November 23, 2000
terms for this phenomenon include arborescent lightning burn,
arborescent (tree-like) erythema, keraunographic markings, or ferning
patterns. Although the exact causes are subject to some debate, the markings
appear to be the result of physical damage to capillaries under the
skin, perhaps caused by the flow of electrical current, or by shock wave
bruising from external flashovers just above the skin. These reddish
marks fade away over a period of hours or days. They are recognized by
forensic pathologists as clear evidence that a victim has been struck by
lightning. The patient above survived with no permanent injuries, and
the lightning flowers completely faded within a few days. A small
Lichtenberg figure has also been observed at the entry point where a
high voltage spark penetrated the skin of an unfortunate (but surviving)
local electrical experimenter who was accidentally zapped by a homemade
60,000 volt Marx Generator. No... it wasn't me!
A similar phenomenon is sometimes seen when lightning
hits a grassy field, as in this picture where lightning struck a
golf course flagpole, leaving this beautiful 25 foot Lichtenberg figure on the
(From "Lightning and Lichtenberg Figures" by Cherington, Olson and Yarnell, Injury, Volume 34, Issue 5, May 2003)
Note the similarity between the figure above and the Lichtenberg figure below (illuminated from below by blue LED's):
High voltage discharges to the surface of water can also create Lichtenberg figures. Some beautiful examples of
both positive and negative Lichtenberg figures on water surfaces can be seen on Dr. Colin Pounder's Lichtenberg figures web site. Natural lightning often creates transient "Lichtenberg figures" in the sky. Air is an excellent dielectric and, although the physical breakdown
mechanisms for air and Plexiglas are considerably different, the appearance of the
branching discharges is quite similar. So it should not be surprising that the branching forms of propagating lightning leaders also have fractal
characteristics. This similarity can clearly be observed during "anvil crawler" and horizontal "spider lightning".
Spider lightning follows a thin, positively charged cloud layer that
sometimes forms in dissipating storms. These slowly propagating discharges
can crawl across the sky for 30 - 70 miles
- literally spanning from horizon to horizon! On a much smaller scale, transient Lichtenberg figures
(sometimes mistakenly called St. Elmo's Fire) sometimes appear on the outer
surface of cockpit windows of airplanes as they fly through
Similar branching fractal patterns also occur when thunderstorms generate electrically conductive leaders that
propagate downward from a charged cloud to the ground below. When one
of these leaders connects with an unfortunate object on the ground, a high current pulse (called the return stroke) surges back upward through the completed path, resulting in a Cloud-to-Ground (CG) lightning
strike. The peak current is typically tens of thousands of amperes, and large positive bolts may reach several hundred thousand amperes. Exceptional examples of downward propagating positive leaders have been captured by South Dakota lightning
researcher, Tom Warner. Using high speed video imaging equipment, he
was able to capture the downward progression of leaders and the return
strokes from a positive lightning bolt. Positive lightning
is a significantly rarer, and considerably more dangerous, form of lightning than negative lightning. Tom's "slow motion" videos show the air breaking down, forming
glowing conductive plasma paths (called leaders) that fan
downward from a huge reservoir of excess charge within the cloud
above. The brightly glowing tips of the positive leaders smoothly propagate,
unlike negative leaders which propagate in a series of discrete jumps (called stepped leaders). The first descending leader to finally connect with the Earth below
completes the circuit, resulting in a powerful Cloud-to-Ground (CG) lightning discharge. See Tom's web site to see his spectacular gallery of images and videos of positive and negative lightning.
Under special conditions lightning also creates transient upward-growing
tree-like Lichtenberg figures. This phenomenon often occurs when
broadcast antennas or mountain tops generate positive leaders that
propagate upward into heavily-charged negative regions above. As the
ground-based positive leaders propagate into the negatively-charged
regions, they form densely-branched positive Lichtenberg figures that,
except for their massive scale, look quite similar to the positive Lichtenberg figures inside our Captured
Lightning sculptures. This fascinating phenomenon has been
captured in another slow-motion video by Tom Warner - click on the
following image to see the YouTube clip.
Lichtenberg figures can also be seen at some high energy pulsed
power facilities, especially where deionized water is used as a dielectric to briefly store large amounts of electrical energy. The following photo is from Sandia National Laboratory's mighty Z
Machine, the world's most powerful electrical pulse generator.
After the completion of a high energy experiment, the water breaks down
huge electrical stress, becoming an electrical conductor that safely
residual energy from the system. The filamentary breakdown paths form
Lichtenberg figures that dance across the water's surface. If you look
closely, you'll notice that many of the
paths actually trace out high voltage electrical field lines along the
surface of the water. Although
impressive, this display is only dissipating "left over" energy after
the experiment is over. The discharges below represent ~5% of the initial energy that was used during the
previous pulsed-power experiment.
(Click for a higher resolution image)
Are there practical uses for Lichtenberg figures?
of the form and origination points of Lichtenberg figures can be a powerful
tool for diagnosing, and subsequently preventing, high voltage
solid dielectrics. By examining these figures in high voltage equipment, experts can diagnose and
prevent future electrical faults within a variety of devices including high voltage power transformers,
capacitors, and insulators. Historically,
Lichtenberg figures (created by HV measuring equipment such as Klydonographs)
were a powerful tool for measuring the polarity and
magnitude of high voltage surges on power lines caused by lightning
strikes. These early measurements were critical for the development of
reliable electrical power transmission and distribution
systems. Lichtenberg figures are still used as a forensic clue for
the cause of injury or death of human and animal lightning victims.
Recent studies of Lichtenberg figures and charge detrapping in polymers
important details on the mechanisms that are involved in the
degradation and electrical breakdown of solid insulating materials.
There may be future medical applications as well. In 2009, a team of researchers at Texas A&M University proposed using
3D Lichtenberg figures created within various polymeric materials as
"templates" for growing blood vessels (vascular tissue).
There are significant similarities between branching Lichtenberg figures
and animal circulatory systems - a fact not lost on many
medical researchers. The hope is that, by creating branching 3D
Lichtenberg figures inside a biodegradable polymer, such as polylactic acid (PLA), scientists can then use these as "molds" to support the development and growth of vascular tissue. Vascularization
is essential for growing functional replacement tissues and organs. It's quite possible that the 18th century technology
of Lichtenberg figures may ultimately play a critical role in organ growth and replacement therapy during the 21st century!
Captured Lightning sculptures are "fossilized lightning bolts"
Lightning is an accurate description for our sculptures, and holding a
Captured Lightning sculpture is about the closest you can come to
holding a fossilized lightning bolt.
Each Lichtenberg figure is unique - a one-of-a
kind treasure, sculpted in exquisite detail by the same electrical forces unleashed by natural lightning. Captured Lightning sculptures are completely
safe - they are completely discharged and are not radioactive.
Two-dimensional photos cannot begin to capture the beauty and exquisite
detail of our 3D Captured Lightning
sculptures. Following are a pair of 3D images that can be rotated 360
degrees so that you can more fully appreciate the detail within some of
our doubly-irradiated sculptures. Once the images have been completely
downloaded, you can drag your mouse over the image to rotate each for a
full 360 degree view. [Note: large size - a high speed Internet connection is recommended].
3D Rotatable Image
3D Rotatable Image
(Courtesy of Theodore Gray)
(Courtesy of Theodore Gray)
Very few people have actually seen or held one of these rare objects of
scientific art. Far fewer have had the
opportunity to own sculptures as beautiful and spectacular as these.
Stoneridge Engineering is proud to be the world's most experienced
provider of these rare treasures.
Can I make my own Lichtenberg Figures?
Unfortunately, since electrons must be injected deep into the acrylic,
it takes a
multimillion-volt electron accelerator to make 3D
Captured Lightning sculptures. Even my patient, understanding spouse
won't let me install one of these at home. However, 2D Lichtenberg
figures can be
made on the surfaces of some materials, such as carbonized
Lichtenberg figures on wood or cardboard, or as dust figures on the
surfaces of some
plastics. Some artists have used this technique to make 2D works of art. To make carbonized figures, a high voltage (HV) power source, such as an
ignition coil or neon sign transformer (NST), is required. The experiment
should be done outside since it generates a significant amount of smoke and some small
flames. Two nails or pins are driven into the wood with a gap of 4 - 10 inches.
The surface is then lightly sprayed with a saltwater solution to make it
partially conductive, and the high voltage source is connected across
the two nails. When high voltage is applied, carbonized
paths begin to form near the nails. Accompanied by lots of smoke, they begin branching as they grow towards each other.
The heat from the process dries out the nearby surface, causing the branches to continuously change direction, often heading away from the opposite nail. The carbonized paths eventually grow to form Lichtenberg figures with "roots" at each
nail. This technique must be done VERY carefully, since it
involves using dangerously high voltages and water
together. A method to adjust the voltage (such as a variable
autotransformer) helps to control the discharge process and will improve
shape of the resulting figure. The following video clip shows this
technique using a 9,000 volt 30 mA NST as the high voltage source:
How can I get a Captured Lightning sculpture of my very own?
We offer a wide selection of Captured Lightning sculptures that range in size from
affordable 2 inch specimens through museum-quality two inch thick blocks as large as 15 inches by 20 inches. Please visit Gallery 1 or Gallery 2
to select a sculpture at the right price for you. We also offer a wide
variety of lighted bases with white, blue, and multi-color
color changing options. Many of these are also available with UK,
Australian, or EC power options. Our light bases illuminate the delicate
patterns within, causing the discharge channels to glow so that even
the finest hair-like details become visible. We also offer a variety of
attractively-priced factory 2nd sculptures discounted to 50% off regular price. Be sure to visit our Eye Candy page to see some of the best artistic and experimental work by Stoneridge Engineering and some of our very creative friends.
More fun with electrons: Glowing rocks, flashing crystals, going to the dark side, and the "Rad-Cam"
High-energy electrons, x-rays, and gamma rays cause many fascinating effects within crystalline solids. One particularly interesting phenomenon is called thermoluminescence (TL). In thermoluminescent materials, high energy electromagnetic radiation (such
as x-rays) may temporarily drive some atoms within the crystalline
structure into higher, semi-stable energy states. When these excited atoms revert back to their normal state, they radiate electromagnetic energy, often within the visible light spectrum.
Thermoluminescent materials are usually triggered into releasing their stored
energy by applying heat. Sensitive light detectors, such as photomultipliers, are used to detect the faint light emitted by most specimens. The light output versus temperature is called a "glow curve" and its shape tells much about the nature of the material and its cumulative radiation history.
The emitted radiation is often in the infrared (IR) or ultraviolet
(UV) portion of the electromagnetic spectrum, and thus not directly
visible. Many thermoluminescent materials also require the application
of relatively high temperatures to release their thermoluminescence.
Some minerals radiate visible light at room temperature. An outstanding
example is the mineral Calcite
(CaCO3), which often glows brilliantly after being irradiated by a
powerful electron beam or X-rays. However, the TL glow is not from the
calcite itself, but from traces of impurity elements such
as manganese. Manganese is one of many known activators, and is responsible for the characteristic yellow-orange glow seen in many calcite specimens. Other common TL activators include lead, copper, cobalt, magnesium, iron, nickel, and silver. Very clear calcite (called "Iceland Spar)
typically shows relatively little thermoluminescence since the purer crystals
contain fewer impurities (i.e., fewer activator atoms).
The degree of luminescence is proportional to the amount of cumulative
radiation seen by the specimen. Passing a
manganese-activated calcite crystal through a high-energy electron beam several
times will cause the specimen to glow brightly for several hours at room
temperature. Although the glow curve for electron-irradiated calcite
peaks at about 110 degrees Celsius, significant light is emitted at
room temperature. The amount of light rapidly decreases as
the temperature of the calcite is lowered, and virtually disappears below 0
degrees Celsius. So, if we irradiate a frozen specimen
of calcite, its thermoluminescent properties will not be immediately obvious. However,
if we keep it cold and then warm it up to room
temperature some time later, it will then glow brightly. The
following image shows Dr. Timothy Koeth admiring a spectacular
glowing calcite crystal brought by Dr. David Speck during our 2010 Lichtenberg run.
Common table salt (NaCl) is also thermoluminescent. However, unlike calcite, it doesn't
glow at room temperature. When irradiated with high-energy electrons,
NaCl changes to a cinnamon color due to the trapping of electrons in defects, called F-Centers. These are vacancies inside the crystalline lattice that makes up salt crystals. Irradiated salt will remain this color as
long as it is kept cool, dry, and protected from UV light. When
irradiated salt crystals are dropped onto a hot surface (250 C or above), each emits a
brilliant green flash as it changes back to its normal (clear/white)
color. When dropped into distilled water, the cinnamon color also
and the dissolving salt emits a pale bluish-green glow (called aquoluminescence)
as previously-trapped electrons liberate their energy.
After exposure to light, irradiated salt changes from cinnamon to a
dark blue or dark purple color. This is thought to be caused by
trapped F-center electrons combining with Na+ ions, reducing them to
atoms of metallic sodium. The resulting colloidal
dispersion of atomic sodium throughout the crystal causes the color
change. When dissolved in distilled water, the purple color also
disappears. We may offer
small amounts of irradiated salt ("Flashing Crystals") to interested
amateur experimenters and physics instructors in the future.
Another interesting salt is potassium chloride (KCl). This material is
normally a white powder. However, when subjected to high-energy
electrons or X-radiation, it changes to a dark purple color. Applying
heat or UV (sunlight) turns it back to its normal color. This property
is actually a relatively rare phenomenon in nature. KCl is a "scotophor". Unlike a phosphor, which emits light when excited by ionizing radiation, a scotophor darkens when irradiated. This process is called reversible photochromism or tenebrescence.
Another example are photochromic eyeglass lenses that automatically
darken from UV in sunlight, and then bleach back to their normal
transparency in lower light. KCl was used in some early radar cathode ray tube (CRT) displays since it could be quickly "written" by an electron beam, creating an image with very
long persistence. The recorded image could then be erased by applying a bit of heat to the material.
Only a few minerals exhibit reversible photochromism - these include hackmanite, scapolite and tugtupite.
The following image shows KCl and NaCl that have changed from being
white powders (before irradiation) to dark purple and cinnamon-colored
crystals after irradiation by multiple passes through a 5 MeV electron
During an experimental run in June 2013, Andrew Seltzman, a guest and
graduate-level physics student from the University of Wisconsin, built a
protective "cave" for his older Sony Cyber-Shot DSC-P72 3.2 MP camera
using sheet lead topped with a one inch thick piece of high-density polyethylene (HDPE) to reduce production of gamma rays. Andrew mounted his camera
inside the cave and positioned it so that it could record a "cart's-eye
view" of various objects being irradiated
with the 3 to 5 million volt electron beam. We were thinking that the
first pass through the beam might be a one-way trip, since the scattered
electron and radiation levels were so intense. We were amazed to
discover that the "Rad-Cam" not only survived, it faithfully recorded
its journey through the beam - not just once, but for a dozen trips! The
only obvious problem was that the microphone seemed to become less
sensitive after every pass. However, the camera fully recovered a few days after the run.
The following video clip shows boxes of various minerals, and a large calcite crystal becoming energized by ionizing radiation
from the beam. The crystal brilliantly fluoresces with a yellow-orange
color while being irradiated, then softly glows from orange
thermoluminescence afterwards. The acrylic sphere in front of the
calcite fluoresces blue-white as the beam hits it, then briefly flashes
as it self-discharges a short time later. Speckles in the
image and static in the audio are caused by high-energy electrons,
x-rays, and gamma rays impacting the camera's image sensor and audio
The loud buzzing sound is from high-energy x-rays directly interfering
camera's electronics as the beam scans across the width of the cart at
100 cycles per second. The camera's video and audio systems finally
become overwhelmed as the camera passes directly under the electron
beam. Although the radiation and ozone
levels in the room would be lethal to living things, this tough
little camera just shook off all the abuse and came back for more!
physical experiment which makes a bang is always worth more than a
quiet one. Therefore a man cannot strongly enough ask of Heaven: if it
wants to let him discover something, may it be something that makes a
bang. It will resound into eternity.”
– Lichtenberg, Georg Christoph, and Albert Leitzmann. 1906. "Georg Christoph LichtenbergsAphorismen: nach den Handschriften.
Drittes Heft, 1775-1779," page 326. Originally in German, from Lichtenberg's Booklet F, Aphorism 1138, Oct 11-13, 1778.
(Thanks to Fermilab scientist and author, Bill Higgins for researching the source of the above quote)
"Thunder is good; thunder is impressive. But it is the lightning that does the work." - Mark Twain
References and Further Reading:
1. Gross, Bernard, "Irradiation Effects in Plexiglas", Journal of Polymer Science, Volume 27, 1958, Issue 115, Pages 135 - 143
2. Hashishes. Yuzo, "Two Hundred Years of Lichtenberg Figures", Journal
of Electrostatics, Volume 6, Issue 1 , February 1979, Pages 1-13
3. Chadwick, K. H., "The Effect of Light Exposure on the Optical Density
of Irradiated Clear Polymethylmethacrylate", 1972 Phys. Med.
Biol. 17, Pages 88-93
4. Chadwick, K. H., and Leenhouts, H. P., "Fading of radiation-induced
optical density in polymethylmethacrylate on oxygen diffusion", Phys.
Med. Biol. 15 No 4 (October, 1970), Pages 743-744
5. L. Niemeyer, L. Pietronero*, and H. J. Wiesmann, "Fractal Dimension
of Dielectric Breakdown", Phys. Rev. Lett. 52, Pages 1033–1036 (1984)
6. Gardner, Donald G., et. al., "Radiation-induced changes in the index
of refraction, density, and dielectric constant of
poly(methylmethacrylate)", Journal of Applied Polymer Science, Volume
7,July 1967, Pages 1065-1068
7.Akishin, A.A.; Tseplyaev, L.I., "Edge effect in radiation-charge
dielectric materials", Physics and Chemistry of Materials Treatment, v
31, n 1, Jan.-Feb. 1997, p 30-1. A similar paper is also contained
within the book "Effects of Space Conditions on Materials", Akishin, A.
I., Nova Science Publishers, 2001, ISBN 590330285
8. Fothergill, J.C.; Dissado, L.A.; Sweeney, P.J.J., "A
discharge-avalanche theory for the propagation of electrical trees. A
physical basis for their voltage dependence", Dielectrics and Electrical
Insulation, IEEE Transactions on, Volume 1, Issue 3 , June 1994, Pages 474 - 486
9. R. A. Galloway, T. F. Lisanti and M. R. Cleland, "A new 5 MeV – 300
kW Dynamitron for radiation processing", Radiation Physics and
Chemistry, Volume 71, Issues 1-2, September-October 2004, Pages 551-553
10. Sessler, G.M.. "Charge distribution and transport in polymers", IEEE
Transactions on Dielectrics and Electrical Insulation, Volume 4, Issue 5, Oct. 1997, Pages 614 - 628
11. Karczmarczuk, Jerzy, "Dendrites in Nature and in Computer", Foton 84/SPECIAL ISSUE, Spring 2006
C. M. Foust, General Electric Review: Instruments for Lightning
Measurements (Includes Klydonograph and Lichtenberg Figures), Volume 34,
#4, April, 1931, Pages 235 - 246
13. Watson, Alan and Dow, Julian, "Emission Processes Accompanying
Megavolt Electron Irradiation of Dielectrics", Journal of Applied
Physics, December 1968, Volume 39, Issue 13, pages 5935-5940 14. Fujimori, S., "Fractal properties of breakdowns", Properties and
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