317) About CR-39 detectors

Ludwik Kowalski; 12/1/2006
Department of Mathematical Sciences
Montclair State University, Upper Montclair, NJ, 07043

Introduction
Unit #314 was devoted to exciting developments in San Diego. The name I invented for the new effect, based on first names of SPAWAR researchers did not catch on; most researchers, on the CMNS list continue using the SPAWAR identifier, as Steven Krivit did in reporting the discovery on 11/10/06. In issue #19 of New Energy Times, at

http://newenergytimes.com/news/2006/NET19.htm

, referring to a recent meeting in Washington D.C., he reported: “The chips that the SPAWAR Systems Center scientists had brought to Washington were slices of CR-39 plastic, a common, transparent polymer that resists fogging and abrasions and is used to make eyeglass lenses, among other things. The researchers had placed the small pieces of plastic inside several of their electrochemical LENR test cells to capture and preserve any fleeting evidence of nuclear events.

"We heard about the use of CR-39 detectors from other LENR researchers at the 11th International Conference on Condensed Matter Nuclear Science in Marseilles, , in 2004," Mosier-Boss said.

She and her colleagues later learned that these same simple detectors have long been used by researchers in inertial confinement fusion (a form of hot fusion) and other areas of nuclear science to record the passage of neutrons, protons, and alpha particles (the two-proton nuclei of helium atoms stripped of their electrons). The traveling particles’ charges shatter the bonds linking the plastic’s polymers, leaving pits or “tracks” in the plastic.

After a CR-39 detector is exposed to a source of nuclear emissions, the detector is bathed in a sodium hydroxide solution, typically for six or seven hours, at a temperature between 65 and 73 degrees C. . . . The bath scours away the collision’s debris, and the resulting tracks are visible with a microscope or, if they’re present in sufficient densities, with the unaided eye.”

That is a good general introduction. Structural damage is created along the paths of nuclear a particle in certain solids. Called latent track, it is like a tunnel that is too narrow to be seen through an ordinary microscope, even at the highest magnification. Keeping the chips in a hot sodium hydroxide solution is called etching. The etching solution penetrates the tunnel and enlarges it. After that a track can be seen under the common microscope. Quoting Frank Gordon, Steven writes: “ ‘CR-39 detectors are ideal for detecting particles in LENR experiments because we can put them right inside the cell where the placement of electronics would otherwise be highly impractical, . . . You don’t need complicated instrumentation like you do with calorimetry or tritium analysis, . . . It’s an easy detection tool that’s very straightforward.’ ”

That is certainly true. How were CR-39 detectors used in SPAWAR experiments? This question is answered in two pictures; they were drawn by P. Boss and S. Krivit. The cathode is a gold wire, presumably coated with codeposited metals (Pd and Li) and loaded with deuterium. The wire is simply wrapped around the CR-39 chip. This method of recording, if I understand it correctly, has one serious limitation. If alpha particles are emitted from the cathode then only a very small fraction of them would be seen; most of them would be stopped in the electrolyte before reaching the detector. If particles were observed on the entire surface of the CR-39 detector (Krivit’s report does not say that this was the case) then the unavoidable conclusion would be that they are emitted from the electrolyte.

Let me assume that tracks are observed only where the wire and the detector are in contact. In a situation like this I would use a different approach. I would evaporate a thin layer of gold on the CR-29; it would still be transparent to track-forming particles. The layer of gold would be my cathode. After the experiment I would remove the layer, etched the CR-39 chip and looked for tracks. That would be a detector inside the cathode. About 25% of all particles would be detected as tracks. An ideal detector would record 50% of emitted particles, i.e. all particles emitted into its direction. A real CR-39 detector, on the other hand, does not display tracks of particle that are intercepted at grazing angles.

In future experiments, if the SPAWAR claim is confirmed by using CR-39 detectors, people will probably use the idea of the “detector inside the cathode” for electronic detectors. I am thinning about a box with a thin wall containing a silicon detector. The advantages of the silicon detector are obvious, they should allow us to measure the energy spectra of particle, and to determine their identity. Protons, for example, could be distinguished from alpha particles by using foils of appropriate thickness. Furthermore, a silicon detector could provide information on the rate of emission, and on its dependence on various parameters, such as time, electric field, magnetic field, etc. But all this will be possible if results are reproducible, as in other areas of science. The mechanism of the process (or processes) by which a nuclear activity results from a chemical activity will probably be identified in less than a year, once the importance of that topic is recognized agencies supporting research.

Below I will show messages (or extracts from messages) about CR-39 detection that I posted on the restricted Internet list for CMNS researchers since the SPAWAR discovery was first presented at the Navy Science and Technology conference in Washington, D.C. on August 2. I really believe that something very significant is going to happen in the controversial CMNS field very soon; may be as soon as two or three months.

Message 1 (posted on 11/14/06)

Last year i had a chance of examining the CR-39 that had a very low background, typically, 2 to 5 tracks per cm^2, The thickness was 2 mm, which is very convenient for microscopic examination. You focus on the side facing you and what id on the other side is not visible at all. People with more experience, especially Lipson, Roussetski and Orin, will probably have something to say about this. I do not recall the Japanese vender; ask Jiro Kasagi <kasagi@lns.tohoku.ac.jp>. Perhaps he will post this information, and the current price on the list.

To count tracks I recommend the magnification 40 (x4 objective and x10 eyepiece). To examine individual tracks magnification 100 will probably be sufficient.
(x10 objective with the same eyepiece). In principle, any traditional microscope should be OK. But I prefer a microscope equipped with a digital camera connected to a computer. That is how Orin works. This offers several obvious advantages. One of them is that counting tracks on a printed picture s more accurate, especially when track density is high (you circle tracks after they are counted, to avoid double-counting). For extremely low counting rates magnification 20 would probably be more convenient -- each picture covers four times larger area.

Message 2 (posted on 11/14/06)
Here is how I just replied to a private message. The reply might be useful to other beginners; that is why I am posting it here. Diameters 10 to 15 microns are good enough for easy counting of tracks. It is often frustrating to wait much longer. Typical track diameters depend on the etching time, as shown below

1) Etching at 65 C
================
3 hrs 5 microns
5 hrs 10 microns
10 hrs 22 microns
15 hrs 35 microns The CR-39 chip become translucent (foggy), but that does not interfere with counting large tracks

2) Etching at 70 C
================
3 hrs15 microns
5 hrs 25 microns
10 hrs 37 microns The CR-39 chip become translucent (foggy), but that does not interfere with counting large tracks
15 hrs 45 microns Even more foggy, but tracks are clearly identifiable. Did someone looked at them through a good magnifying glass? I didn't.

I suspect that some tracks might be etched away when etching is too long. Keep in mind that my measurements of diameters were not very accurate. But that was good enough for my purpose.

Message 3 (posted on 11/14/06)
In a private message someone pointed to a paper of Frenje et al. in the Review of Scientific Instruments -- July 2002 -- Volume 73, Issue 7, pp. 2597-2605. To get the article go to Google and type this into the search box:

CR-39 Frenje “Absolute measurements of neutron yields from DD”

A short description of the track formation process in CR-39 (in section IIA) is probably sufficient for the intelligent use of detectors. For a much more detailed description see the long paper of Nikezic and Yu, to which George Miley referred two days ago. The main purpose of the paper, by Frenje et al., is to describe how CR-39 are used to detect neutrons. As mentioned by Krivit, CR-39 are widely used to detect neutrons, when yields are large, in the range of 10^6 to 10^13. What is the difference between detection of alpha particles (or protons) and detection of neutrons? Any alpha particle intercepted by the CR-39, will create a track, provided the incidence angle is not too large. For neutrons, on the other hand, the probability of forming a track is usually much smaller than unity. To get the general 2002 review of track detectors by Nikozic and Yu, go to Google and type this into the search box:

Nikozic “Formation and growth of tracks”

Message 4 (posted on 11/15/06)
. . . Consider a 222Rn atom in air; it emits an alpha particle and the recoiling nucleus, 218Po, becomes a positive ion. Yes, outer electrons are often lost when an atom is pushed suddenly. The 218Po ion, or an ion of 214Pb, or an ion of 214Bi, etc. slowly drifts toward the electrically-charged screen. That is why dust collected from a TV screen (on a tissue) contains radioactive atoms. This can easily be checked with a simple Geiger counter. About ten years ago I convinced myself that the measured decrease in activity was consistent with the above explanation. The motivation for the experiment was a message posted on a discussion list for physics teachers. The author advised us to use TV screens as extremely inexpensive radioactive sources for classroom demonstrations.

But this is not a list for teachers. Why do I think that users of CR-39 should be aware of what I write here? Because it is very easy to charge a CR-39 chip electrostatically, most likely when the protective plastic is peeled off. An electrically charged CR-39 chip, if left in air for a long time, will have more tracks than a similar chip left in distilled water, for the same time. I checked this last year because I was aware of the TV screen effect. Fortunately static charges can easily be removed, for example by touching CR-39 surfaces with wet finger. Keep this in mind while looking for CMNS particles.

Message 5 (posted on 11/16/06)
In New Energy Times Steven also reported: “During the plating process, the cathode is in contact with a CR-39 detector in the cell to which the scientists had applied an external electric or magnetic field. After the experiments had completed their runs of eight to 11 days, Mosier-Boss and Szpak saw dense, cloudy areas on the portions of the detector near the cathode.

‘The fact that the cloudy areas are observed where the detector was in close proximity to the cathode suggests that the cathode caused the cloudiness,’ Mosier-Boss said. As a control, Mosier-Boss also exposed CR-39 detectors to electrolysis in a lithium solution without palladium in it. The result: only a sprinkling of tracks, randomly distributed and so few in number that they could be accounted for by background radiation. She also immersed the detectors in the usual solution of palladium chloride and lithium chloride in deuterium but without applying the external electric current. The outcome was the same: no unusual shower of tracks from high-energy particles.”

An easy way to produce a cloudy area on a CR-39 is to expose it to a source of alpha particles. A small 241Am source I used was form an old radiation-type smock detector (a new one costs about $10, for example, in Home Depot or Radio Shack). Exposing it to CR-39 -- with about 5 mm of air between the surfaces -- produced many well separated tracks. A ten times longer exposure produced proportionally more tracks, with frequent overlapping. Much longer exposures produced cloudy surfaces (after etching) visible to naked eye. I do not recall seeing cloudiness before etching. But it would not surprise me to see it after much longer exposures.

My suggestion is to expose a CR-39 chip to an alpha source for an hour or two. Would it become cloudy? Would it resemble the chip removed from the co-deposition cell after 11 days? Perhaps cloudiness, after 11 days of exposure, was an indication of many "giant showers" mentioned by John Fisher. But such test should be performed far away from the room in which the electrolysis experiments are performed. (One advantage of a smock detector source, over a piece of depleted uranium, [or over a welding electrode containing thorium], is that Americium is most likely coated by a very thin layer of something, to prevent contamination of air etc.) By the way, 241Am is also a source of 59 keV X-rays.

Message 6 (posted on 11/19/06)
. . . My experience was that only rarely (up to several % of cases -- when 241Am tracks were examined) did mechanical defects look like nuclear tracks. Most cases can be definitely resolved by refocusing in depth. When I worked with Orin, one year ago, he suggested uncertain tracks be ignored. In particular we ignored cases in which more than four (often more that ten) adjacent pits were on straight segments. We believed that these track-looking defects were due to mechanical scratches. I do not know how discrimination between tracks and non-tracks is handled by counting software. But visual examination is highly reliable, after some experience, when one sees more that ten randomly distributed tracks, (or clusters of tracks) per view.

By the way, Oriani's CR-39 chips were often precounted. Such time-consuming approach is justified only when background track are nearly as frequent as tracks attributed to CMNS reactions. That seems not be the case in the PamStan effect. (Precounting involves two etchings, First a chip is etched before being used in an experiment and background tracks are counted. Then it is etched again, after the experiment. Suppose the difference is 25-7=18. Then no statistical error is associated with 7. Measuring background with another chip is not as reliable as measuring it with the same chip. One can go one step further -- old tracks can be recognized by their relative locations, and by larger diameters. Fortunately, all this is not necessary when background corrections are small.)

Message 7 (posted on 11/27/06)
. . . I started to suspect that static charges on CR-39 surfaces (that could possibly be created by removing the protecting plastic) attracted positive alpha-radioactive ions. Such ions are always present in air. I already mentioned that, in most basements, dust removed from a TV screen is alpha radioactive. This can be checked by using a Geiger counter with a sufficiently thin window. Leave the TV on for a week or two and then remove as much dust as you can with a small piece of wet paper towel. I shared my suspicion with Orin and he said he will make sure charges are removed from CR-39 surfaces. Did this eliminate the effect? I do not know. Most recently Orin was studying cathodes after the electrolysis. CR-39 chips were applied to surfaces that were wet during the electrolysis, as described here in one of his recent messages. His results are shown in unit #314 at my CMNS website.

Message 8 (posted on 11/30/06)

On Nov 30, 2006, at 12:58 PM, Scott Little wrote:
I”n the recent "Extraordinary Evidence" article in New Energy Times

http://www.newenergytimes.com/news/2006/NET19.htm#ee

There is a photo entitled, "Ag wire/Pd/D in Magnetic Field" with a caption below the photo that reads, "Dr. Gary Phillips: "They show a number of double tracks which you would see from a reaction that emits two particles of similar mass and energy."

The photo does show an abnormal incidence of double tracks...i.e. more than you'd expect from simple coincident landings of individual particles. But my limited understanding of nuclear physics suggests that two-particle reactions would normally send the two particles off in opposite directions....to conserve momentum.

Is there such a thing as a nuclear reaction that emits two particles in the
same direction?”

That could be a troublesome signature. I am thinking about tiny grains of uranium or radium codeposited on the electrode. The best way to check for this would be run the electrolysis for much longer than ten days. Suppose the percentage of doubles increases significantly, or triples start to appear. In that case one would have a proof of contamination. It did not occur for me that this could be the second independent test showing that contamination is not responsible for observed tracks. Steven already reported the first convincing test -- track formation stops when the external field is turned off. But, having a second test would be desirable, in the present situation.
P.S.
On the other hand, one can say doubles and triples do not necessarily prove that contamination is present; they prove that NAE is not uniformly distributed over the surface

Message 9 (posted on 11/30/06)
On Nov 30, 2006, at 6:22 PM, Scott Little wrote:

I'm wondering what to expect from CR-39 as an alpha detector. Will every alpha that hits normal* to the surface of the detector make a track?

Yes, and this track will be round. There is a critical incidence angle above which tracks would be so shallow that etching would destroy them. Roussetski and Lipson reported it. Perhaps one of them will reply to this message. My rule of thumb is that a CR-39 chip, located on top of cathode, detects about 25% of all particles as tracks. But that is only a quick estimate.

If not, what is the mechanism for an alpha striking normal to the surface and not making a track? Backscattering from near-surface nuclei seems possible in principle
but wouldn't the cross-section for that be very small?

I expect it to be extremely small. Rutherford scattering formula is highly reliable at at low energies. My guess that no more than one out billion alpha particles will be scattered into the backward hemisphere. Perhaps someone will theoretically confirm this intuitive guess

Is there any other mechanism besides backscattering that will cause an alpha particle NOT to make a track in CR-39? *Low angle incidence alphas will certainly make nascent tracks but the track will be completely etched off during the etching process so you see nothing.

P.S.
Assuming that NAE is distributed uniformly over the 1 cm^2 of the cathode (below a CR-39 chip, also 1 cm^2), and assuming that N tracks are recorded, what is the probability of finding two tracks very close to each other? The answer depends on two factors: the total number of tracks, N, and the definition of the "very close." I expect the issue raised by Scott to be noticed by referees. That is why it should be
addressed. Here is my rather trivial contribution. It is based on a Monte Carlo program I wrote today. I am assuming that a given number of
tracks, for example, N=10000, are recorded at randomly selected points on the 1 cm^2 of the CR-39. That fixes the track density. By changing N, I can simulate any density I want. The program compares location of each point with locations of all other points. If the distance between two points turns out to be smaller than d then my counter of coincidences is incremented by one. Any value of d can be imposed. As expected, for a chosen track density, the percentage of coincidences increases with d.

Diameters of tracks are probably 10 microns. With this in mind, my first choice was d=20 microns, for N=1000. Results collected during the debugging are shown below. I will run the program for N=1000, for d=20, several more times. This will give me the mean percentage and the standard deviation.

N=1000 tracks, d=20 microns; Ncoinc=5 (this is only 0.5%)
N=1000 tracks, d=50 microns; Ncoinc=35
N=1000 tracks, d=80 microns; Ncoinc=104
N=2000 tracks, d=80 microns; Ncoinc=446

For very large N every track will have a close neighbor.
P.S.
In running the first case 30 times, the mean turned out to be 6.5 coincidences; standard deviation 2.0 coincidences. Each run, for N=1000, takes only about 30 seconds on my old Mac. I would be happy to run the program with other N and d, if needed. the listing of the program is shown below; the code is in True Basic, but it should easily be translated into another computer language. Exclamation sign are beginnings of comments (up to the end of the line). I am dividing by 2, in the last print statement because each coincidence was counted twice in my primitive code.

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
program TRACKS
! 11/30/06 dim xx(100000), yy(100000) ! random locations (maximum 100000)
randomize
let N=1000
let dmin=0.002 ! in cm (10 microns is 0.001 cm)
let dmin2=dmin^2 ! to avoid slow sqr() calculations
for i=1 to N
let xx(i)=rnd
let yy(i)=rnd
next i
let cnt=0 ! counter of coincidences
for i=1 to N ! compare with all previous points
for k=1 to N
let d2=(xx(i)-xx(k))^2 + (yy(i)-yy(k))^2 ! avoiding the sqr
if d2<dmin2 and (k<i or k>i) then let cnt=cnt+1
end if
next k
next i
print "coinc=";cnt/2;" out of N=";N;". dmin=";dmin; "cm"
END
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

Message 10 (posted on 12/1/06)
Scott Little wrote asked: “I'm wondering what to expect from CR-39 as an alpha detector. Will every alpha that hits normal* to the surface of the detector make a track?” I can now be more specific about the CR-39 efficiency.

According to a long review paper of Nikezic and Yu [Materials Science and Engineering R 46 (2004) 51–123] the critical angle depends on the energy of alpha particles. It decreases from about 60 degrees for the 6 MeV alpha particles to 45 degrees for the 10 MeV particles. This refers to etching for 6 hrs. Also note that the angles are between the particle's trajectory and the CR-39 surface.

How does the 60 degrees compare with my 25% rule of thumb? Their 60 degrees translates into the incidence angle of 30 degrees (with respect to the normal, as in optics). The solid angle corresponding to an incidence angle A is 2*Pi*(1-cosA). It is always a fraction of the total solid angle, 4*Pi. For A=45 the fraction is close to 0.15, or
15%. I expect this fraction to double when etching time is reduced to 3 hours. Note that all tracks would disappear for really very long etching. That would be 0% efficiency (a lot of nuclear particles but no tracks at all). The efficiency for protons should be much better than for alpha particles. Why? Because their latent tracks are longer than those of alpha particles of the same energy. My guess is that the efficiency, for 10 MeV protons, will be nearly ideal. i.e. 50%. Why am I guessing? Because I trust my intuition based on knowledge of ranges of charged particles in matter. The actual answer, after spending many hours, would nearly certainly be higher than 40%. To be more accurate I would have to perform calculations based on rates of etching, etc. Or I would have to look for references in published papers. This is also a lot of work, in such cases.

I recommend etching for 3 hrs. It has three advantages: (a) efficiency is higher, (b) tracks are smaller (but still clearly visible and recognizable), and (c) time is saved. Note that two nearby tracks might overlap after 6 hrs of etching but not after 3 hrs of etching. Orin drills tiny holes in CR-39 chips and suspends the chips into the etching solution, with nickel wires. My approach was different; I just dropped the chip into the etching solution which was constantly stirred with a rotating magnet. Stirring is important when the beaker is sitting on a thermostat-controlled hot plate. Small chips are never at the bottom. Without stirring chips would stay at the bottom and their
temperature could be unacceptably high (overetching).

Low magnification, such as 4*10 (objective 4 and the rest 10) is desirable when tracks are rare. In fact, I would prefer 2*10 when densities are below ~100 tracks per square centimeter. But low magnifications make visual counting impossible when track densities are very high, which, I suspect, was the case in SPAWAR experiments. At the extreme, when tracks are too numerous, with frequent overlapping (for example, when track densities exceed ~100000/cm^2, instead of ~10/cm^2 background) one might use traditional optical densitometry. It would be simply a matter of comparing chips exposed to NAE with chips exposed to known numbers of aloha particles from a calibrated source. Let us hope that future experimental data will force us to abandon counting of tracks in favor of densitometry. ;-)
P.S.
The 2004 review of solid track detectors, by Nikezic and Yu, that was mentioned above can be downloaded from my website as:

http://blake.montclair.edu/~kowalskil/cf/cr39nikezic.pdf

Message 11 (posted on 12/2/06)
On Dec 1, 2006, at 7:04 PM, Michel Jullian wrote:

. . . Thinking back to my proposal of letting the alphas escape through the cell bottom so they can be detected outside, I recall you doubted that a sufficiently alpha-transparent material could stand the ~5 cm water column. And then I remembered your own proposal of coating the CR-39 detector with a few microns of Ni (~9 g/cm3), wouldn't a 10 microns "plastic wrap" for household use (LDPE, 0.9g/cm3 i.e. 10 times less dense than Ni), which definitely could stand the water column, be just as alpha-transparent as a 1 micron Ni layer? Or isn't density the only factor to take into account?

That seems to be a good solution. I am assuming you are suggesting a thin metallic coating on the plastic wrap (on the wet side) to be the cathode. That is better than wires you first suggested. The path seems to be open to use a Si detector after SPAWAR results are confirmed by people involved in the Galileo project initiated by Krivit. When will we know about the results? It is a matter of following a protocol already tested by SPAWAR people. I do not expect any problems with CR-39 detectors. But everything should be tested and this takes time.

Let me show range-energy relations in several materials. That information would probably be useful to those who are planing to implement the idea. R is the range in mg/cm^2. Illustrations on how to use range-energy information will be shown below.

10 MeV alphas in gold: R=45.5
8 MeV alphas in gold: R=33.4
6 MeV alphas in gold: R=22.8
5 MeV alphas in gold: R=18.0
4 MeV alphas in gold: R=13.6
3 MeV alphas in gold: R=9.6
2 MeV alphas in gold: R=6.1
1 MeV alphas in gold: R=3.2

10 MeV alpha in nickel: R=22.6
8 MeV alphas in nickel: R=16.3
6 MeV alphas in nickel: R=10.9
5 MeV alphas in nickel: R=8.5
4 MeV alphas in nickel: R=6.4
3 MeV alphas in nickel: R=4.5
2 MeV alphas in nickel: R=2.9
1 MeV alphas in nickel: R=1.6

10 MeV alphas in aluminum: R=16.5
8 MeV alphas in aluminum: R=11.6
6 MeV alphas in aluminum: R=7.5
5 MeV alphas in aluminum: R=5.8
4 MeV alphas in aluminum: R=4.2
3 MeV alphas in aluminum: R=2.9
2 MeV alphas in aluminum: R=1.8
1 MeV alphas in aluminum: R=1.0

10 MeV alphas in carbon: R=12.4
8 MeV alphas in carbon: R=5.6
6 MeV alphas in carbon: R=5.4
5 MeV alphas in carbon: R=4.1
4 MeV alphas in carbon: R=2.9
3 MeV alphas in carbon: R=1.9
2 MeV alphas in carbon: R=1.2
1 MeV alphas in carbon: R=0.6

10 MeV alphas in hydrogen: R=4.19
8 MeV alphas in hydrogen: R=2.81
6 MeV alphas in hydrogen: R=1.70
5 MeV alphas in hydrogen: R=1.24
4 MeV alphas in hydrogen: R=0.85
3 MeV alphas in hydrogen: R=0.53
2 MeV alphas in hydrogen: R=0.28
1 MeV alphas in hydrogen: R=0.11

In planning for an experiment it would be sufficient to use carbon as a representative for a plastic material (unless very accurate calculations are needed)..

Plot the R=f(E) curve and use the smooth curve to solve a problem. Here are two illustrations. How much energy will an alpha particle of 6 MeV have after traversing the Al foil of 2.5 mg/cm^2. The range of 6 MeV alpha is 6.5 mg/cm^2; thus it will pass through the foil. Its energy will be reduced. Subtract 2.5 from 6.5. The result is 4 mg/cm^2. What energy does it correspond to on your plotted curve for aluminum? My curve shows it is close to 3.9 MeV. That is the is the energy of the the alpha particle after traversing the foil perpendicularly.

Another typical problem is to chose the foil thickness for a desired output energy. For example, I want the 6 MeV alpha particle to emerge with 3.5 MeV. How much nickel would I need? Use the R=f(E) curve for In. It shows that 3.5 MeV corresponds to R=5.3 mg/cm^2. What is the range of the 6 MeV alphas in In? It is 10.9 mg/cm^2. Thus the foil you need is 10.9-5.3 = 5.6 mg/cm^2. How to convert this mass per unit area into the thickness in cm? The density of In is 7.9 g/cm^3. Therefore 5.6 mg/cm^2 translates into 0.00071 cm; this is 7.1 microns.

Message 12 (posted on 12/2/06)
Responding to my request for permission to be quoted (that is a rule on the private CMNS list) and to what I added, Michel I wrote: “Indeed coating the cathode on the transparent window (by CVD?) might be better than loose wires, but keeping it in the shape of wires would be better than a uniform coating as it allows correlating track density with wire proximity as Pam noted”


Message 13 (posted on 12/2/06)
Changing from uniform coating (uniform wet cathode) from nonuniform coating (strips simulating wires) would be only one of many parameters to explore. For the time being I am assuming that the purpose of gold wires (inside the electrolyte) was to become NAE. In that case concentration of tracks near wires is natural. If I recall correctly, they also had a picture with silver wire. Let us wait for results that Steve Krivit will report at the termination of Galileo project. In that project the task is to replicate the SPAWAR protocol and to describe the results. That might lead to many interesting experiments, deviating from the working protocol, one parameter at a time or in different directions, according to expectations. Our theoreticians will finally have reliable experimental data for validating theories. It would not take too long before the mystery of NAE is solved. Will this end the the dark age of discrimination? Will CMNS will become normal science? Let us hope so.

I would appreciate if someone could send me ranges for alphas in one or two plastic materials, and for water. An electrolyte is mostly water.