Condensed matter nuclear reaction products observed in Pd/D co-deposition experiments

Abstract

Pd/D co-deposition has been used by a number of researchers to explore the condensed matter nuclear reactions occurring within the palladium lattice by generating highly loaded layers of lattice over the cathode. Reaction products that have been observed include heat, transmutation, tritium, energetic charged particles and neutrons. The results of these experi-ments are discussed here.

Full text

SPECIAL SECTION: LOW ENERGY NUCLEAR REACTIONS
CURRENT SCIENCE, VOL. 108, NO. 4, 25 FEBRUARY 2015
656
*For correspondence. (e-mail: pboss@san.rr.com)
Condensed matter nuclear reaction products
observed in Pd/D co-deposition experiments
P. A. Mosier-Boss1,*, L. P. Forsley2, F. E. Gordon3, D. Letts4, D. Cravens5,
M. H. Miles6, M. Swartz7, J. Dash8, F. Tanzella9, P. Hagelstein10,
M. McKubre9 and J. Bao9
19112 Fermi Ave., San Diego, CA, USA
2JWK Corp., 5101B Backlick Road, Annandale, VA 22003, USA
3SPAWAR Systems Center Pacific, San Diego CA, USA
412015 Ladrido Lane, Austin, TX 78727, USA
5Cloudcroft, NM 88317, USA
6University of La Verne, La Verne, CA 91750, USA
7JET Energy, Inc., Wellesley, MA 02481, USA
8Portland State University, Portland, OR 97207, USA
9SRI International, Menlo Park, CA 94025, USA
10Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA
Pd/D co-deposition has been used by a number of
researchers to explore the condensed matter nuclear
reactions occurring within the palladium lattice
by generating highly loaded layers of lattice over the
cathode. Reaction products that have been observed
include heat, transmutation, tritium, energetic charged
particles and neutrons. The results of these experi-
ments are discussed here.
Keywords: Energetic particles, excess heat, Pd/D
codeposition, transmutation.
Introduction
IN the typical Pd/D co-deposition experiment, the cathode
and anode are immersed in a solution of palladium chlo-
ride and lithium chloride in deuterated water. The cath-
ode is comprised of either palladium or a metal that does
not absorb hydrogen isotopes. The difference between
these cathodes is shown in Figure S1 (see Supplementary
Information online). Palladium is then electrochemically
reduced onto the surface of the cathode in the presence of
evolving deuterium gas. In the co-deposition process, an
ever-expanding electrode surface is created that assures
the existence of non-steady-state conditions and local
high loading (D/Pd ratio  1), as shown by cyclic voltam-
metry1,2 and galvanostatic pulsing3 experiments. More
importantly, Pd/D co-deposition eliminates long charging
times and prevents lattice cracking. The resultant Pd
deposit has a uniform ‘cauliflower’-like structure consist-
ing of aggregates of spherical micro-globules and has a
large surface area. In this article, results of Pd/D co-
deposition experiments conducted by several researchers
are discussed.
Results and discussion
One of the earliest Pd/D co-deposition experiments4 in-
volved measuring the temperature of the cathode and the
solution during the course of the reaction. It was found
that the temperature of the cathode was 2–4C hotter than
the solution indicating that the heat source was the cath-
ode and not Joule heating. This was further confirmed by
real-time infrared imaging of the cathode5. Not only did
the infrared imaging show that the cathode was hotter
than the solution, the steepness of the temperature gradi-
ents indicated that the heat sources were located in close
proximity to the electrode–solution contact surface.
Miles was the first to report on calorimetric measure-
ments of Pd/D co-deposition6. In addition to palladium
chloride, Miles’ electrolyte also contained ND4Cl and
ND4OD, but no LiCl. He used an open, isoperibolic, Dewar
calorimetry cell that was tall enough to keep the Pd deposit
from reaching the gas–liquid interface, thereby preventing
D2 and O2 recombination from occurring. Miles conducted
three co-deposition experiments using the Dewar cells. The
results, summarized in Figure 1 a, show that all three exper-
iments produced excess heat. The amount of excess heat
produced by co-deposition was comparable to that ob-
tained using bulk Pd cathodes. Additional electrochemi-
cal studies showed that the excess heat was not due to
any shuttle reactions7. Periodically in these experiments,
calibration heating pulses were applied that cause an in-
crease in cell temperature. When no excess power was
present or when the excess power remained constant, the
cell temperature relaxed back to the expected baseline
upon termination of the heating pulse. The positive feed-
back effect (Figure 1 b) is observed when the cell temper-
ature did not relax back to the original baseline upon
cessation of this added thermal input. While the cell tem-
perature increased, the cell potential at constant current

SPECIAL SECTION: LOW ENERGY NUCLEAR REACTIONS
CURRENT SCIENCE, VOL. 108, NO. 4, 25 FEBRUARY 2015
657
decreased. This positive feedback effect is the simplest
and clearest indication of excess power.
Letts8 designed a Seebeck calorimeter with an output
power variation of  0.01 W, a precision within 1%, and
a sensitivity of 5 mW. This calorimeter was used in a
series of Pd/D co-deposition experiments that were con-
ducted with a recombiner and in the presence of a 675 G
magnetic field at the cathode. The cell contained a gold-
plated copper cathode inside a Pt anode coil as well as Ti
cathode placed outside of the Pt anode coil. Because Pd
does not plate out on Ti, the latter is an ideal inert cathode
that can be used for calibration purposes. Consequently,
both the inert Ti cathode and the gold plated Cu cathode/
Pt anode assembly were placed in the PdCl2/LiCl electro-
lyte at the same time. The calorimeter and cell were de-
signed to permit changing or repositioning of the
electrodes and removal/replacement of the electrolyte
while the experiment was running. Figure S2 (see Sup-
plementary Information online) shows the output of this
experiment9. Up to point 800, the inert Ti cathode was
electrolysed at 3 W outside the anode coil. During this
time the cell was in power balance to within 1%, i.e. no
excess heat production was observed. At point 800,
Figure 1. a, Excess power measurements in three co-deposition
experiments done using an open cell. The Cu cathode used for co-
deposition was placed inside a Pt coil anode. b, The cell temperature
and cell potential curves, during the application of a resistive heater
calibration pulse for 6 h. This illustrates the positive feedback effect.
electrolysis was diverted to the gold-plated copper cath-
ode inside the Pt anode coil. Pd/D co-deposition was then
done on the gold-plated copper cathode. An excess power
signal of 250 mW appeared quickly and cell temperature
increased at the same time by 4–5C. The excess power
signal and cell temperature remained elevated, producing
~ 7 kJ of excess energy. At point 1100, a pump was acti-
vated to remove the deuterium-based electrolyte and re-
place it with hydrogen-based electrolyte of identical
volume and concentrations of PdCl2 and LiCl used at the
start of the D2O experiment. As seen in Figure S2 (see
Supplementary Information online), the excess power
signal declined over a 9 h period after replacing D2O with
H2O, which demonstrated an isotopic dependence. Letts
also discovered that geometry made a difference whether
or not excess heat was observed. In Pd/D co-deposition
experiments done with the gold-plated copper cathode
placed outside the Pt coil, no excess heat generation was
observed. This demonstrates the need for good symmetry
between the anode and cathode in experiments.
Cravens and Letts10 explored using chemical additives
to trigger excess heat in Pd/D co-deposition. In these ex-
periments, a 0.636 cm diameter copper tube was used as
the cathode. The copper tube was sealed by crimping.
Gold was plated on the tube and then masked with Teflon
tape leaving a 0.6 cm wide, unmasked region available
for co-deposition. A thermistor was inserted inside the
tube. The cathode was first plated with palladium for use
in a series of laser stimulation trials using 660 nm excita-
tion. As shown in Figure S3 (see Supplementary Infor-
mation online), no significant excess thermal output was
observed. Then about 10 drops of a separate plating mate-
rial was used that contained additional metal ions. The
plating additive was derived from Pd, Rh, Ce, La and U
salts in acidified D2O. U and Rh increase the absorption
of D within the palladium black. La and Ce mischmetal
were added to allow for spin exchanges to aid spin con-
servation terms for wave functions in the D + D  He
nuclear channel. The addition of Ce also increases the
diffusion rate of deuterium within Pd. The addition of U
and La created a convoluted surface. It is worth noting
that the rationale for the addition of U (natural abun-
dance) and Ce mischmetal was to supply metals with a
non-zero quadrupole. Such materials are required for
coupling of the nuclear spins to the phonon states, as is
known within the area of nuclear acoustics resonance.
This is thought to provide pathways for both spin polari-
zation of the deuterium and for thermal energy release.
The results of the deposition of the additive components
are shown in Figures S3 and S4 (see Supplementary
Information online). The excess reached approximately
2 W from the small 0.6 cm length of plated area and per-
sisted for a day before the experiment was terminated.
Figure S4, supplementary material, shows that the cath-
ode temperature response is faster than the electrolyte.
This indicates the source of the heat is the cathode.

SPECIAL SECTION: LOW ENERGY NUCLEAR REACTIONS
CURRENT SCIENCE, VOL. 108, NO. 4, 25 FEBRUARY 2015
658
Swartz and Verner11,12 prepared spiral-wound palladi-
um cathodes (see Figure S5 Supplementary Information
online). In their experiments, the Pd cathode and Pt anode
were immersed in low electrical conductivity D2O (with
no additional electrolyte) that contained 8.2 mM PdCl2.
The spiral cathode system, with its open helical cylindri-
cal geometry, on a high electrical resistance solution, cre-
ated a unique and unusual electric field distribution that
resulted in asymmetric electrolysis on one side of the
cathode. This caused deuteron flux inside the metal lat-
tice. Excess heat was measured using a modified dual
ring calorimeter with redundant thermometry (Figure
S6 a, see Supplementary Information online), waveform
reconstruction, full thermal controls, and time integration
(Figure S6 b, see Supplementary Information online).
Figure S6 a shows the input electrical power and ther-
mometry of a Pd co-deposition done on the spiral Pd
cathode and an ohmic thermal resistor as control. For the
same power input to the ohmic control and the cold
fusion component, there is a higher temperature resultant
in the latter. Figure S6 b shows the calorimetry of the
same experiment. Four curves are shown in Figure S6 b,
two of which involve power. It can be seen that the ob-
served power output is much greater for the deuterium-
loaded system. Two additional curves on Figure S6 b con-
firm that the excess heat is not simply stored energy. It can
be seen that for the ohmic joule (thermal) control, the inte-
grated energies of the input and output arise in parallel. In
contrast, in the deuterium-loaded heavy water system, there
is a gap, which increases with time. This shows excess heat
of the co-deposition system (more than 100,000 joules ex-
cess energy over ~ 15 h compared to the ohmic resistor).
Tanzella et al.13 loaded and stabilized 50–250 m
diameter PdDx and PdHx wires. Deuterium loading of the-
se wires was determined by measuring the resistance of
the wires using the four-point probe method. They also
did co-deposition on 50–250 m diameter PdDx, PdHx,
and Ag wires, which they also stabilized. They then
placed these wires in a cryogenic calorimeter and meas-
ured the energy released from destructive electro-
diffusion of these wires. Generally, the D-loaded metals
yielded greater and more reliable excess energy than the
H-loaded metals, The co-deposited PdDx on highly load-
ed PdDx wires yielded greater excess energy than the bulk
metal hydrides. The co-deposition process generated
many point vacancies in the co-deposited layer and these
vacancies were stabilized by co-deposited D/H. These
vacancies were able to host molecular D2. These vacan-
cies, along with high loading of D and its flux, are neces-
sary for excess heat generation.
In yet another variation on co-deposition, Dash and
Ambadkar14 used Pd as the anode and Pt as the cathode.
Both electrodes were immersed in a D2O–H2SO4 electro-
lyte in a cell with a recombiner. When a constant current
was applied, Pd dissolved from the Pd anode and co-
deposited with hydrogen isotopes on the Pt cathode. After
229 h of electrolysis, the excess thermal power output
was 0.93  0.1 W. No excess power was measured in a
closed control cell comprised of two Pt electrodes
immersed in a H2O–H2SO4 electrolyte. At the end of the
experiment, the Pt/Pd cathode was subjected to SEM/
EDS analysis. The results are summarized in Figure S7
(see Supplementary Information online). The EDS spec-
trum, Figure S7 b, of the bright dendritic particles in Fig-
ure S7 a, shows the presence of Pd. The ratio of the Pd
L

X-ray peak at 2.84 KeV to the Pd L

X-ray peak at
2.99 KeV was 0.45. The ratio of these two peaks in the
EDS spectrum (Figure S7 c) obtained for the black area
shown in Figure S7 a was 0.71. This increase is caused by
the overlap of Ag L

with Pd L

. Since the presence of
Ag was not homogeneous over the surface of the cathode,
this Ag is not due to contamination.
Additional co-deposition experiments by other research
groups have shown evidence of transmutation as well as
tritium production and the emission of energetic particles.
Szpak et al.15 conducted Pd/D co-deposition experiments
in the presence of an external electric field that had a 6%
AC ripple which allowed the electric field to couple into
the cathode. Upon termination of the experiments, the
cathodes were subjected to SEM analysis which showed
the presence of craters and other features indicative of
localized melting of the Pd deposit (Figure S8 a–c, see
Supplementary Information online). EDX analysis of the-
se features showed the presence of elements such as Ca,
Mg, Si, Zn and Al in addition to Pd (Figure S8 d). These
new elements are not due to contamination as their distri-
bution over the cathode was not homogeneous.
Using a recombiner in a separate chamber, Bockris et
al.16 measured the tritium content, as a function of time,
in the liquid and gas phases of co-deposition experiments.
The results are summarized in Figure S9 (see Supplemen-
tary Information online). Bursts of tritium production
were observed in both the gas and liquid phases when
low tritiated water was used. However, when highly triti-
ated water was used, an overall decrease in tritium was
observed. Similar results were reported by Lee et al.17
using closed cells and measuring the tritium content of
the electrolyte.
Mosier-Boss et al.18 used CR-39, a solid-state nuclear
track detector, to measure the emissions of energetic parti-
cles in Pd/D co-deposition experiments. It was found that
when Pd/D co-deposition was done on a Ni screen cath-
ode, in the absence of an external electric/magnetic (E/B)
field, no tracks due to energetic particles were measured.
Instead the impression of the Ni screen was observed on
the CR-39 detector. Similar damage was observed when a
CR-39 detector was wrapped with Cu screen and exposed
to a 137Cs

-ray source, suggesting that this damage is due
to X-rays. Tracks were observed for co-deposition on Ni
screen done in the presence of an external E/B field. In
contrast, for Pd/D co-deposition done on either Au, Ag or
Pt cathodes, tracks were obtained in both the presence

SPECIAL SECTION: LOW ENERGY NUCLEAR REACTIONS
CURRENT SCIENCE, VOL. 108, NO. 4, 25 FEBRUARY 2015
659
and absence of an external E/B field. These results led to
the following composite cathode experiment in which Au
was electroplated on half of the Ni screen, as shown in
Figure S10 (see Supplementary Information online). This
composite cathode was placed in contact with a CR-39
detector and used in a Pd/D co-deposition experiment. At
the end of the experiment, the detector was etched and
analysed. The results show that no tracks were obtained
on the bare Ni half of the cathode. The impression of the
Ni screen was observed. However, tracks were observed
on the Au-coated Ni screen. Both halves of the cathode
experienced the same chemical and electrochemical envi-
ronment at the same time. If the pitting in CR-39 was due
to chemical attack, those reactions would have occurred
on both the bare Ni and Au-coated Ni halves of the cath-
ode and both halves would have shown pitting of the
CR-39 detector. But this was not observed. Therefore, the
tracks observed in the CR-39 detector were not the result
of chemical attack.
In addition to tracks due to energetic particles, Mosier-
Boss et al.19 also reported triple tracks in CR-39 detec-
tors. These triple tracks are diagnostic of the 12C(n, n)3

carbon break-up reaction due to the reaction of >9.6 MeV
neutrons with a carbon atom in the detector. Examples of
these triple tracks as well as their corresponding DT
neutron generated triple tracks are shown in Figure S11
(see Supplementary Information online). No triple tracks
were observed in CR-39 detectors used in control
experiments.
Conclusions
Several researchers have used Pd/D co-deposition to in-
vestigate the phenomenon of condensed matter nuclear
reactions within a Pd lattice. The emphasis of many of
these investigations has been on heat production. In these
particular experiments, excess heat has been measured
using different variations of co-deposition as well as dif-
ferent kinds of calorimeters, both open and closed. In ad-
dition to heat, other reaction products that have been
observed include new elements, tritium, energetic parti-
cles and neutrons.
1. Szpak, S. et al., Charging of the Pd/nH system: role of the inter-
phase. J. Electroanal. Chem., 1992, 337, 147–163.
2. Szpak, S. et al., Cyclic voltammetry of Pd + D codeposition.
J. Electroanal. Chem., 1995, 380, 1–6.
3. Szpak, S., Mosier-Boss, P. A. and Smith, J. J., Deuterium uptake
during Pd–D codeposition. J. Electroanal. Chem., 1994, 379, 121–
127.
4. Szpak, S., Mosier-Boss, P. A. and Smith, J. J., On the behavior of
Pd deposited in the presence of evolving deuterium. J.
Electroanal. Chem., 1991, 302, 255–260.
5. Mosier-Boss, P. A. et al., Review of twenty years of LENR
research using Pd/D co-deposition. J. Condens. Matter Nucl. Sci.,
2011, 4, 173–187.
6. Szpak, S. et al., Thermal behavior of polarized Pd/D electrodes
prepared by co-deposition. Thermochim. Acta, 2004, 410, 101–
107.
7. Miles, M. H., Investigations of possible shuttle reactions in
co-deposition systems. J. Condens. Matter Nucl. Sci., 2012, 8,
12–22.
8. Letts, D., Codeposition methods: a search for enabling factors.
J. Condens. Matter Nucl. Sci., 2011, 4, 81–92.
9. Letts, D. and Hagelstein, P. L., Modified Szpak protocol for
excess heat. J. Condens. Matter Nucl. Sci., 2012, 6, 44–54.
10. Cravens, D. J. and Letts, D. G., Practical techniques in CF
research-triggering methods. In Proceedings of the Tenth Interna-
tional Conference on Condensed Matter Nuclear Science, Cam-
bridge, MA, 2003.
11. Swartz, M. and Verner, G., Excess heat from low electrical con-
ductivity heavy water spiral-wound Pd/D2O/Pt and Pd/D2O–
PdCl2/Pt devices. In Proceedings of the Tenth International Con-
ference on Condensed Matter Nuclear Science, Cambridge, MA,
2003.
12. Swartz, M. R., Codeposition of palladium and deuterium. Fusion
Technol., 1997, 32, 126–130.
13. Tanzella, F. et al., Stimulation of PdDx wires at cryogenic
temperatures. In Proceedings of the Sixteenth International
Conference on Condensed Matter Nuclear Science, Chennai,
India, 2011.
14. Dash, J. and Ambadkar, A., Co-deposition of palladium with
hydrogen isotopes. In Proceedings of the Eleventh International
Conference on Condensed Matter Nuclear Science, Marseille,
France, 2004.
15. Szpak, S. et al., Evidence of nuclear reactions in the Pd lattice,
Naturwissenschaften, 2005, 92, 394–397.
16. Bockris, J. O’M. et al., Tritium and helium production in palladi-
um electrodes and the fugacity of deuterium therein. In Proceed-
ings of the Third International Conference on Condensed Matter
Nuclear Science, Nagoya, Japan, 1992.
17. Lee, K.-H., Jang, H. and Kim, S.-J., A change of tritium content in
D2O solutions during Pd/D co-deposition. In Proceedings of the
Seventeenth International Conference on Condensed Matter
Nuclear Science, Daejeon, Korea, 2012.
18. Mosier-Boss, P. A. et al., Use of CR-39 in Pd/D co-deposition
experiments. Eur. Phys. J. Appl. Phys., 2007, 40, 293–303.
19. Mosier-Boss, P. A. et al., Comparison of Pd/D co-deposition and
DT neutron generated triple tracks observed in CR-39 detectors.
Eur. Phys. J. Appl. Phys., 2010, 51, 20901.

Proof
Supplementary Information
Figure S1. Local D/Pd loading ratios for the three types of LANR/LENR systems (provided by M. Swartz).
Figure S2. Calorimetry results obtained by Letts. No excess heat was observed when the Ti cathode was undergoing electrolysis. Excess heat was ob-
served when Pd/D co-deposition was done on a Au/Cu cathode. When the isotope was changed from deuterium to ordinary hydrogen, the excess power
declined to baseline, suggesting that the anomalous thermal power was nuclear in origin. This experiment was done using a closed cell. The Ti cathode
was placed outside the Pt anode coil. The 5 mm × 10 mm × 0.6 mm Au/Cu cathode used for co-deposition was placed inside the Pt anode coil.

Proof
Figure S3. Results of a Pd/D co-deposition experiment done by Cravens and Letts. The onset of excess heat was initiated after the addition of the mixed
salt additive at the 2400 min mark. The excess reached approximately 2 W from the small 0.6 cm length of plated area and persisted for a day before the
experiment was terminated. This experiment was done using a closed cell. The Cu/Au cathode was 0.6 cm in length and 0.47 cm in diameter. This cathode
was placed inside the Pt coil anode.
Figure S4. Cathode temperature rise after addition of Pd, Rh, Ce, La, U solution. This was the same cathode that gave the excess heat results
shown in Figure 3S. The cathode temperature responded faster than the electrolyte. This indicates the source of the heat is the cathode.

Proof
Figure S5. Photograph of a spiral-wound palladium cathode showing asymmetric bubbling on one side of the cathode. The cathode was wound
[palladium wire, 1.0 mm diameter, 99.98+%, Alfa Aesar, Ward Hill, MA] and was 3.3 square centimeters, with an active volume circa 0.083 cm3.
The anode was platinum wire (1 mm diameter, 99.998), mass 2.01 g, an active area of ~3 cm2. The gap separation was 6 mm. In the experiments,
the Pd cathode and Pt anode were immersed in low electrical conductivity D2O (deuterium oxide, low paramagnetic, 99.99%, Cambridge Isotope
Laboratories, Andover MA) to minimize unwanted reactions of electrolysis, that contained 8.2 mM PdCl2. The volume of the heavy water solution
was 40 cm3 and was sealed with parafilm to minimize entry of ordinary water from the atmosphere.

Proof
Figure S6. a, Thermometry of, and electrical input power to, a spiral wound Pd/PdCl2–D2O/Pt and an ohmic control – shown are the reaction con-
tainer's core temperature (T1), the next compartment’s temperature (T2), the ambient temperature (T3)and the input electrical power (Pin). b, Calo-
rimetry of a spiral wound Pd/PdCl2–D2O/Pt and an ohmic control to input electrical power – shown are the input and output power and energy.

Proof
Figure S7. (a) SEM micrograph obtained by Dash for a Pt/Pd cathode. (b) X-ray spectrum for the spot labeled 1 in (a) showing the Pd L
α
peak at
2.84 keV and the Pd L
β
peak at 2.99 keV. The intensity ratio, Pd L
β
/L
α
, is 0.45 (this ratio is expected to be 0.42). (c) ) X-ray spectrum for the spot
labeled 3 in (a). The intensity ratio, Pd L
β
/L
α
, is 0.71. The increase in the ratio, compared to (b) is caused by overlap of Ag L
α
with Pd L
β
. This
experiment was done using a closed cell where the Pd and Pt electrodes were parallel to one another.
Figure S8. Results of Pd/D co-deposition done on a Au substrate in the presence of a 6000 V external electric field. (a) and (b) are SEM images
of the deposit showing localized melting, (c) is an SEM of a ‘blister’ like formation. (d) X-ray spectrum of the ‘blister’ showing the presence of Zn,
Mg, Al, Si, and Ca.

Proof
Figure S9. Tritium measurements in the liquid and gas phases of Pd/D co-deposition experiments. When low tritiated heavy water was used
(Isotec D2O), bursts of tritium production was observed in both the liquid and gas phases. When high tritiated heavy water was used (Cambridge
D2O), an overall decrease in tritium was observed.
Figure S10. CR-39 results for Pd/D co-deposition done on a Ni/Au composite cathode. The middle photograph is of the composite electrode used
in a Pd/D co-deposition experiment done in the absence of an external electric/magnetic field. The top half of the cathode is bare Ni screen, the bot-
tom half is Au-plated Ni screen. Photomicrograph on the right is of CR-39 in contact with the bare Ni half, 20× magnification. The impression of
the Ni screen is observed. The photomicrograph on the left is of CR-39 in contact with the Au-coated Ni half, 1000× magnification. Tracks are ob-
served.

Proof
Figure S11. Photomicrographs of triple tracks observed in CR-39 detectors used in Pd/D co-deposition experiments and their corresponding DT
neutron tracks, magnification 1000×. The left hand images were obtained by focusing the optics on the surface of the CR-39 detector while the
right hand images are overlays of two images taken at two different focal lengths (surface and bottom of the pits).