Interesting report on nuclide Body Burdens

[Richard Hull]

This is a report of an interesting and ongoing experiment based on a startling initial finding. I seek to have comments from others on this report.

I recently obtained a Ludlum 44-99 scintillation detector with mating Ludlum 3534 detector electronics box removed from a working medical waste portal sold by Ludlum. This portal contained four of these detectors and two of the 3534/3532 electronic boxes.

Thus, I have a mated detector and electronics produced for the purpose of detecting very low levels of radioactive waste, (urem/hr - microrem/hr), passing through a controlled portal point.

A discussion will be built around the detection of people with a radio-nuclide body burden and what might be an interesting finding related to same.

The Detector

It consists of a 2” PMT optically coupled to a 3” diameter by 1” deep NaI:Tl crystal.
To warrant only a forward looking detector, the crystal is backed by a 1” thick lead backing and surrounded by a 1.5” thick lead doughnut. This pretty much obviates detection of much gamma radiation from the sides and rear. The entire detector head is encased in a light-tight, hermetically sealed, aluminum housing. The detector has a single BNC “C” type connector often used by Ludlum. See Image #1 below.


The Electronics

The electronics box is the height of simplicity and economy of design. There is a simple HF oscillator and voltage multiplier that is regulated and adjustable to power the detector’s PMT.

A preamp-amp combo couples into an integrator and the user merely controls a “set point” to just below the alarm point desired. Should radiation rise above this point a piercing audible alarm sounds and a read light comes on. A front panel meter that is calibrated in urem/hr provides a calibrated radiation reading when coupled to the 44-99 detector head.

The Setup

I decided that since my lab is a bit “noisy” radiologically, I would preload the system to a steady forward-looking background of about 80% of full scale, (approx 17urem/hr). This was done by placing a number of pieces of uranium ore about 40 inches from the detector face on a bench top opposite the bench that contained the detector arrangement.
See Image #2 below.

I carefully set the threshold alarm detect to sound off at the slightest advance over background. This was a ragged edge setting such that any material within the 40” distance could be analyzed. This included shielding testing as well as source testing.

Body Burden Detection

Once this setup was made, I found that I could set the alarm off when about 6-12 inches from the detector which was at belly level on the bench. I found I could set it off with my back or front facing the detector. I became immediately concerned that I had a body burden due to my youthful and continuing activities around U ore, fusion work and the like. I told a few of my friends about this. One suggested that my clothing might be loaded with radon daughters.

I showered really well, paying particular attention to my back and stomach. I then faced the device in the nude and still set the device off. So, radon daughters are out of the mix.

I also considered scattering due to interposing myself between the ore load 40 inches away and the detector. I interposed a number of materials and thicknesses between the detector’s face and varied the distance between the materials and the detector. They all had a net shielding effect which is what my body should have done also.

It was looking more and more like I had a permanent internal body burden. Sadly, this was confirmed when a friend and fellow member of the Virginia chapter of the American Nuclear Society visited my lab with his fiancée last weekend. Both he and his girl friend stood in virtual contact with the detector head both front and rear and could not make it alarm. I, on the other hand, could cause an immediate alarm at about 9 inches!

Somewhat despondent, I accepted that I would carry this burden with me for the rest of my days. I comforted myself with the knowledge that I am in relatively good health for my 64 years and let it go. I decided to leave this setup intact.

Later Developments

Last Friday, a 72 year old friend and HEAS member visited me and I asked him to step into the detector’s sensitive area after showing him how I could set it off. Upon standing only 12” away, the alarm sounded on him as well! He is somewhat of a “health nut” and lives about 100 miles from here and has never been involved in any self directed radiation experiments, nor does he collect any radioactive minerals.

More calls to more rad-wise friends were made and I posited, based on having had only four people face the device, that this was detecting body burdens received as children due to atmospheric testing when hundreds of atomic and hydrogen devices were set off in the atmosphere during the 1940’s, 50’s and early 60’s.

I noted that young bodies pick the stuff up rapidly due to the growth spurt when the body stashes a lot of minerals needed to enlarge and maintain the active child. We “Baby Boomers” were active, too! There was no TV except in the evenings, no Internet and no Game Boys. We were out playing war, Cowboys and Indians, baseball, football, riding our bikes 10 miles a day exploring the world and getting dirty, dusty, and cut and bruised. Polio and TB were the big killers of young kids. Atomic and Hydrogen bombs were going off like fire crackers. There were some weeks at school when milk could not be had due to increased Sr-90 uptake in cows. The Cold War was in full swing.

One of my friends suggested having my wife step into the breech. I took this advice and she also set off the device. She is 61 years of age.

My ANS member friend and his fiancée who were mentioned earlier and tested negative before the Ludlum are in their 30’s and were thus born well after the Atmospheric Test Ban Treaty of the early 1960’s.

All of this made me feel much better, but I need to expand this test to many other people of varying ages who were raised in different localities to see if my surmise based on this limited testing holds any water.



More Tests, Different Instruments

My friend and fellow uranium hunter, Bill Kolb suggested we try our TSA scintillators. He has two of the large, PRM 4400 units and I have the more modern, smaller PRM 475B. Both instruments are very complex and highly capable with built in CPU chips and advanced features which make them the “plus ultra” choice for uranium hunting and field work. I was doubtful as these are “sigma set” units and can’t be placed on a precipitous edge as can the continuously variable, simple Ludlum 3532/34 monitor units.

As it turned out, I was right. In both cases the unshielded plastic scintillators picked background from a 4 pi environment due to their complete lack of shielding. Thus, in both cases, our bodies acted as shielding from the background count over the plastic’s broad flat face and failed to satisfy the sigma demanded for an alarm even if we did add a trifle more radiation. We had just taken the background down too far.

Other methods are now being sought, other than using the qualitative Ludlum, especially to determine the nuclide involved. We suspect that uptake of Cs137 or Am-241 found in fallout residues, due to atmospheric testing, is the culprit.



Summary

I hope to have this setup at HEAS #21 in October where a number of folks might pass in front of the detector and allow for a much expanded data point review.

I have had a number of humorous, yet appropriate names advanced by myself and others on this setup, among them are….. “Nuclear Age Detector”, “A Detector For The Nuclear Aged”, “Baby Boomer Detector”, “Old Fart Detector”.



Appendix A

Using only myself as the source, as noted above, and at Bill Kolb’s suggestion, I made up a “go”, “no-go” table of items and thicknesses that passed the radiation from my body and tripped the alarm versus those that did not set off the alarm or acted as effective shielding. I supply this table for what it is worth. All dimensions are in inches.

Allowed radiation to pass and set off alarm

0.020 Styrene
0.060 Aluminum
0.006 Brass
0.225 Plexiglass/Perspex
1.87 of Wood
0.40 Phenolic

Caused the alarm to sputter or go on and off. Partial effective shielding

0.105 Aluminum
0.625 Phenolic

Stopped enough radiation to keep the alarm completely silent.

.004 Lead foil
0.125 Aluminum
0.025 Copper
0.040 Iron
0.75 Phenolic

I am tempted to surmise that the .004 lead foil stop might mean most of the burden is the 59kev Am241, though I bet there is some Cs137 there in the background as well.

As noted in the past, when I first was given a GM counter in the mid 50’s, I used to drain and then evaporate my folk’s bird bath water every week for the contained nuclides that fell like manna from the heavens during rain storms.

Richard Hull

[David D Speck MD]

Richard,

Perhaps parking in front of a MCA for an hour or two would provide more information on the offending entities.

Dave

[Jon Rosenstiel]

Very cool Richard, can't wait to get myself checked-out at the upcoming HEAS. There is a chance that I may have ingested a little nuclear fallout... I grew up on a farm in northern Illinois during the 50's.

Jon Rosenstiel

[Richard Hull]

Dave,

I hope to bring this setup to Ed's big bash this coming weekend for a first pass at getting a gang o' folks to give me some additional data.

Oh, and good luck taking meaningful readings within 100 meters of my home with hour long MCA gamma spec runs. Even Bill kolb has issues at his home and his advanced setup is the cat's PJs.

I have been offered a chance for a formal whole body scan for free at the nuclear power plant by one of my ANS pals who works there. I might just have to take him up on that as my MCA is impotent to help out.

We'll talk this coming weekend.

Jon, I will test your aged carcus this October!

Richard Hull

[Richard Hester]

What you need is someone who grew up in Nevada during those oh-so-active times. I was in Norfolk, VA at the time, so I don't know how many nasties I picked up there. I won't find out, either, as my carcass is staying out on the West coast this year.

[David D Speck MD]

Richard,

I wonder if you took a longish MCA run without your physical presence, and then took a similar length run with you in proximity, then subtracted the background scan from the body scan, if you would get any sort of identifiable peaks.

It will be interesting to see what results you get from the professional systems. I underwent a total body scan measuring the amount of K40 in me back during medical school. It was an interesting, if rather claustrophobic, experience. I wish I had paid more attention to the counting electronics.

Look forward to seeing you Friday.

Dave

[Steven Sesselmann]

Richard,

You posing naked in front of that detector was a missed photo opportunity

Are you observing the no eating or drinking in the lab rule?

With that much radioactive stuff around your lab, it would be pretty hard to avoid some intake.

I for one am not particularly shocked that Mr. Hull has a somewhat glowing personality.

Steven

[Frank Sanns]

Looking at your shielding materials, two quick possibilities which would be ubiquitous are carbon14 and potassium40. The C14 would be a possible choice as the carbonaceous materials seemed to not shield but it could be because they also emitted. The exception was the thick section of pheonolic that did shield so it can not be C14 and also because it is a beta emitter.

The K40 has my bet. There are around 150 g of potassium in the body at any given time. At the isotopic ratio (0.012%) of the K40 this puts it at around 0.1 uCi or around 3,000 desintegrations per second. It should be very detectable with such a set up as you have Richard.

There would also be differences amongst people based on fat content. Fat has less water and thus less potassium so lean body mass most likely makes a difference with K40.

Frank Sanns

[chad ramey]

Richard,

Both my father and I will definitely be willing to be tested at HEAS. I'm pretty interested in his results; he's near fifty (and I definitely didn't mention that here....oops!) and grew up in/near Oak Ridge. I've always lived in Georgia but perhaps being the offspring of a linage that is centered in Oak Ridge might have a slight effect. Your post was extremely interesting by the way!

-Chad Ramey

[Richard Hull]

I will speak to a number of comments.

Frank, I have a 10uCi C-14 source and the betas will not penetrate heavy duty Reynolds wrap foil. The betas are extremely weak.

I did place a 5 lb bag of pure KCL in contact with the detector and nothing. The thin crystal (1") is not good for detecting the high energy gammas. the Al housing I thought might put out some x-rays from the gamma or betas but apparently not enough to trigger at my set point.

We have had my tubby self and tubby wife set the thing off and my 72 year old friend who is a skinny bean pole set it off. The non-alarmers were both of medium smallish build. Thus far, age seems to set it off.

We just don't have enough data yet, but this weekend may tell more of a tale. I have already prepared a data sheet to record the info. No names, of course.

Data

1. Alarm or no alarm
2. Age
3. Build
4. Childhood place of growth
5. Details - A separate section for what might seem additional useful data.

Thanks for all those suggestions. I will follow all this up. I appreciate the discussions.

It is important to note that anyone could pass through the Ludlum portal that this was part of and not be detected as my wife, Larry and I were. You must have the detector set on its ragged edge, (never set here in a medical portal setting), and I find that you must be within 6-12 inches of the head in all cases. This is never the case in a portal which is usually 5 feet or more wide so that carts and equipment can also pass through

Bill Kolb reports some tests done last night that indicate scattering of x-rays in the body mass may be the culprit. More mass, more scattering. However, the flyer in my limited data set is 72 year old Larry, the lightest, and thinest person to stand and yet he was detected.

I found that Am-241 can be detected at rather great ranges... 2 feet or more, while a 10uCi Cs137 source is detected at 1 foot. I figure this is, again due to the thinish crystal not detecting the 660 keV Ba137 gammas well, but halting and detecting everyone of the 59 keV Am241 gammas nicely. It might be remembered that medical waste is usually made up of lower energy short lived gammas and this is what the portal electronics is setup for.

I'll try a few more tests this evening.

Richard Hull

[billwcf]

Hi, I will look forward to taking the test. Would any of these be useful additional questions:
Do you smoke? Do you or have you ever farmed tobacco (apatite fertilizer) Do you eat a lot of Brazil or other nuts ? Are you vegetarian? Have you ever worked in the nuclear industry? -bill

[Richard Hull]

Such things are to be in the "Details" box (#5). Questions like these would never be asked unless a young person sets the alarm off. Or if a baby boomer or older person fails to set the alarm off. These "flyers" would demand greater detail.

Richard Hull

[Frank Sanns]

I will answer any question and do just about anything in the name of science but please don't make us look at your bare belly and bum at the HEAS!

FS

[SkyPuppy]

As a former health physics tech and manager, I might be able to help here.
1. Very few body burdens remain in the body for years. One has to consider the nuclide(s) of interest and lookup their effective half-life. That amount of time is based upon the physical half-life of the radionuclide in combination with the biological half-life of the radionuclide (based entirely upon the chemical nature of the element in question. If there are more than one radionuclide in the body at one time, you combine all the effective half-lives to derive the total dose to the body.

It is very interesting that both you and your wife give positive counts. It is most likely due to improper handling of your radioactive materials in your home. You can't really just play around with this stuff.

Many nuclides can be enticed to get out of your bodies faster than they would normally, sometimes by drinking lots of beer and sometimes other methods. A doctor is the best person to determine what to do.

I am seriously concerned that your bodies set off your new sodium iodide detector, especially if it is calibrated in mrem/hour as I understand your post. That indicates that your wife and you have dangerously high levels of radionuclides in your bodies and you need to get this looked into immediately. Take the offer of your friend that works at a power plant to get that body count. (I used to do those, too.) If your detector is calibrated to just look for disintegrations per second (dps) then I would not be as alarmed. Please see to this right away.

[SkyPuppy]

another possibiity. Have either of you had any nuclear medicine procedures performed recently? How about enhanced MRI or CT scan? Procedures such as those will put stuff into your body.

Another thought: if your system is calibrated in mrem/hour and you got it during the nuke testing era, you'd already be dead.

[billwcf]

Well, This ought to keep this post going: http://blogs.houstonpress.com/eating/edible_science/ Maybe we can do a before and after Anthony & George's scan at HEAS. Banana Equivalent Dose; Really? -bill

[Richard Hull]

Sky Puppy......Wish you had a real name as requested in recent postings.

The Ludlum portal monitor unit is calibrated in urem/hr, (micro rem) not mr/h (millirem.hr). The unit has only one range 0-20 urem/hr on its meter. Thus, neither I, my wife, nor my friend Larry are loaded to any great degree if at all. The image in the original posting shows the meter face clearly to be in urem/hr. Sorry about the mixup.

Being manufactured as a medical waste Portal monitor there would be zero use for something so gross as a mr/hr reading unit. If the thing goes off at 12urem/hr while wheeling through a laundry hopper, they only then call the CHP's with cutie pies to locate the hot sauce spilled on the lab coat.

All this body burden biz may be moot due to work done by my friend Bill Kolb. It looks as if low energy background scatter may be at work here. I worked with Bill remotely by phone last night and I am leaning towrds his hypothesis, but will still do bulk people testing this weekend.

I will post Bill's recent e-mail before commenting below it.............I attach his pdf

******************************************************

Richard,

I ran two experiments using a 5 inch Bicron FIDLER detector to see if I could reproduce your results. This detector has a beryllium window on a 1/16 thick NaI(Tl) crystal and is designed for low energy measurements in the range of 10 to 100 keV. The usual application is field detection of Am-241.

A preliminary 1000-second background collection was compared to a 1000-second collection of my gut at a distance of 2.5 inches. The total gut measurement was 12% higher than the total background measurement over the width of a 10 to 200 keV window--clearly a statistically significant increase. Counts were higher at lower energies but there was no well-defined peak.

I made second set of measurements with a wall consisting of two 5"x5"x8" paraffin blocks placed 2.5 inches from the detector. Another background count and the paraffin run were each 7200 seconds to reduce sampling error. I also made a 7200 second run with an Am-241 smoke detector source at a distance of 9.5 inches for comparison. (A C-14 source had no effect on the detector because it is a pure beta emitter.) These data are plotted in the attached PDF and show an overall increase in background of 9.5%. A well defined peak forms around 25 keV then tapers off to background levels by 90 keV. My paraffin may have been around during above ground nuclear testing but it is unlikely that it is contaminated. After confirming your results and looking at the effects of the various shielding materials you tried, I think backscattering is the likely explanation for what is happening.

Three things can occur when a low energy gamma ray or x-ray photon interacts with matter: it pass through, its absorbed or its scattered. Materials with low atomic numbers, e.g., paraffin and people, scatter x-rays more strongly than lead, aluminum and iron because they are less likely to absorb the photons. Z-backscatter technology based on this principle is actually being developed and used in the defense industry. There is a good explanation and some excellent photos illustrating this principle at

http://www.as-e.com/products_solutions/ ... catter.asp

which leads me to believe the differences between test subjects may have more to do with their diet than fallout.

Bill

***********************************

Following this up, I took a gallon jug of water and placed it in contact with the detector head. It set the detector off, just barely, but not a ~15 pound 12x12 inch by 3" thick paraffin block. The paraffin block did make the alarm sputter on and off a bit, but it never stayed on. A large graphite plank 1.5 inches thick and 14X9 inches in width and length also refused to set it off.

I tuned the water out of alarm mode to a hairs breadth, but I could still set the device off, raising the detected background by 1 urem/hr when in contact with the Lublum 44-99 face.

I have a full Canberra/Bicron Gamma spec setup similar to Bills, as most of you know, but I did not have the thin crystal, Beryllium windowed head like Bill had as a low energy spare to his normally used 5"X5" NaI:Tl head. Our larger Crystals would have just had a larger load of noise to deal with.

So, it is still up in the air with a judgement leaning towards some sort of yet to be determined scatter source.

We will see, as I will be at Bill's home on Thursday for more tests. I am carrying the setup with me. Then I am off to New York with Bill on Friday to return on Monday.

More later.

Richard Hull

[Doug Coulter]

Richard,

having been in your lab and verified how high your background is there compared to here, might I suggest you try with the other detectors in a place where the background is much lower than anywhere near your place? They might tell you more in that case with the 4 pi ones. But I also like the idea of doing the spectra with background subtract to see any possible changes with you there vs pure background.

As we didn't test Richmond as a whole (who knows, the general background might be higher there than it is here in the mountains?) we don't know if it was your place only, or the whole area. Here we are only a little nearer the cosmic rays and some large U deposits, and it's kind of quiet radiologically compared to what we measured at your lab last year.
(roughly 5x quieter, depending on which measurement tool we used in both places, less with a geiger tube than with a scintillator)

I'm not so sure I'd be extremely worried, though -- at our ages a slight increase in the probability of getting cancer in the next 20-30 years out may not mean squat. Were we 19, I'd worry more, maybe.
At our ages, the probability is that something else gets you first anyway.

[Richard Hull]

I really wasn't all that worried based on a 1 urem differential against background for my presence. I was far more surprised that the Ludlum was a variable people detector. Now, as mentioned, it looks like backscatter is the issue based on body mass as opposed to body burden. Still there is "string bean" Larry setting it off.

I figure I might carry a very slight and intrinsically insignificant, but possibly measurable burden due to all my time as an Atoms for Peace "user" back in the 50's and 60's.

The lab is only about 3 times above open background by GM readings here which is nothing, of course. Probably hormetic, even. The lab, with its concrete floor, is at a variable 6-8pCi/l (which is fine, of course) While the wooden house is at 3pCi/l. So, no daughters issues.

What you noted about us oldsters and cancer after 65 is a virtual given as even the alara nutballs write us off and allow massive doses, figuring we are on our way out anyway and...What's a little extra rad load among the geriatrics anyhow?

Richard Hull

[Frank Sanns]

Is it possible that some capacitive coupling is going on when you are in close proximity to the detector? This could change the count rate.

The other possibility is the moderation of high energy gammas. As you have stated, your detector is a low energy detector and it could be that the body is shifting and spreading one of the lower of the higher energy peaks down into the range that the detector is more sensitive.

Frank Sanns

[Richard Hull]

Frank,

What you posit is a form of scattering and it is what Bill and I are now latching onto to explain what is going on. Backscatter classically assumes that you launch an x-ray source or there is a source of x-ray photons directed at low z targets and you look at the return photonic reflection. Scattering is a 4pi thingy based on enviromental background. In my lab, there is a bit of both.

Bill and I will be noodling a bit of this out via experiment this evening at his place. I will try and report back on Monday on what we found. As I noted, I am leaning towards Bill's findings of the other night.

We are looking at uni-directional, virtual 2 pi deltas of +/- one micro rem. Few have insturments that can look at these levels. However, such an instrument would be easy to gin up and construct by the average rad-head who is decently geared up.

Richard Hull

[Doug Coulter]

Yeah, even though your background freaked out BillF, I didn't see any big issues with it (when your fusor wasn't running!). Here's it's just really quiet except for cosmics -- my whole radioactives collection fits in a big lunch pail in pigs and isn't even kept indoors. But here we see some extra counts near the ground compared to on the second floor -- there's U in these here hills!

We have run into backscattering a lot here from fusor rad sources (even off the wood ceiling) and it makes some measurements a pain -- you simply must shut down the fusor to see activations for example. I've been learning about "good geometry" experiments from the literature around that topic. Seems you either have to do things in almost empty space or get truly crazy with multi-mode shielding to get good readings.

I also notice some interesting effects of nearby mass on cosmics -- makes showers that with a fast phototube counter get resolved into a lot of counts per cosmic ray sometimes, and the mass of "one human nearby" is noticeable in that regard and makes counts go up, as does a thin lead sheet over a geiger or scint counter -- which doesn't increase the count if you turn the whole mess sideways nearly as much! To me that means it's showers from cosmics hitting things.

Taking the TSA or even a geiger up on the roof, they count less on cosmics -- fewer showers above than below the roof!

All of this is making me like plain counters less and less -- you just lose too much information by thresholding and just counting to be sure what a simple count means (basic signal processing theory). Give me a scope, a PHA, or even just audio and I like it a lot better for nearly everything. Even audio can give a kind of hint on pulse sizes -- more bass on the big ones and a moderately trained ear can get a lot more out of that than just a counter gives you. This is particularly true on the 3He as it makes much larger pulses when it gets a burst vs just one neutron -- if you don't just clip and count it, thereby throwing useful information out the window.

We get such fierce bursts of cosmics sometimes I've now gone to a two counter system so I know which count intervals to remove from my data -- when the second counter goes nuts, I can assume that many of the counts on the one counting activation are just garbage, for example. We've seen second(s) long bursts of huge count rates sometimes with nothing but counters turned on in here.
Obvious it's bogus on audio, you'd never know from a counter reading.

We call Bill's TSA the "henny penny" as it goes off on seemingly anything and starts beeping -- as you say, great for prospecting in some cases -- but he took it to the new big U find near here and it was useless due to all the radon coming out of the ground -- it just read continuously everywhere around there, so it was blinded by that and couldn't find any hot spots.

He says he got a lot of stares trying to scout out things at hamfests as many the older guys there had "seeds" in their prostrates and he was beeping at them from many feet away! Here, it sees my torbermite sample inside a thick lead pig at a few paces, for example -- that thing is touchy indeed and seems to have a very low energy threshold -- very soft X rays make it "go" where any geiger tube is sitting there counting background, either thick or thin wall types. It will also see X rays from a pure alpha source if the alphas hit any medium or high Z stuff inside their range in air, which in some cases includes other parts of the source packaging itself.

Although I'm no "true believer" in hormesis, I just don't worry about that too much. I've already survived a lifetime of smoking, drinking, and red meat, auto and high explosive accidents, and lived through the "butter or eggs are bad for you, oh no, now they aren't" bunch of foolery the diet freaks go on about. I don't go out of my way to catch rads, but hey -- seems like a few in the name of science isn't much of an issue.

Hope I'm not posting I have cancer anytime soon -- but if I do -- it would more likely have been due to one of the other things I "expose myself to". Already had some pulled out of my lower GI tract long before any of this work or rad exposure.

Interesting the huge amount of lead we put over our fusor rig makes a geiger counter just stop completely noticing its running state -- no square law needed, but that thing makes henny penny go completely nuts anywhere in the building -- do we think these see neutrons in the plastic scint in them? I've not yet been able to make a measurement that convinces me either way. I do have a nicely working neutron detector made here of the same stuff -- you just stop all the X rays and what gets through is neutrons that make it count -- not as good as a 3He tube, but a heck of a lot smaller as it doesn't need (or want) a moderator. I am working on a directional detector based on that one, using a hole through a moderator to get directionality -- it doesn't notice slow neutrons, so no need to actually stop them -- and trying to stop them does make gammas that it sees -- bad idea.

[Richard Hull]

Report from Trip to Bill Kolb's:

We have determined beyond any reasonable doubt that the body detection associated with the depicted detector in the original post is due, 100%, to low energy gamma scattering by low Z materials from a hydrogenous target. The amount of scattering is related to the background gamma levels and the surface area and thickness of the target placed in front of the detector.

I nor anyone measured in the prior tests has any demonstrable body burden based on the tests made with the depicted instrumentation.

The instrument, however, has been determined to be extremely sensitive to lower energy gamma rays and x-rays.

In a rather stunning test, in a zone of backbround measuring on the order of 3.75 urem/hr, I could not set the instrument off nor could Bill or his wife. Placing a small box of very rich uranium ore ~5 feet from the detector and slightly forward of it caused the reading to jump to 6 urem/hr. Upon reseting the alarm very close to the edge of the reading, we could all approach from a somewhat oblique, opposite angle to the source over 6 feet away from the source and, at 6 inches from the detector face, set the detector off.

Placing the box of hot U ore just beside the detector, (6" away to side), raised the detector, again, to only 6urem/hr due to the heavy shielding surrounding the detector and PMT, mentioned in the original post. Reseting the alarm, Bill or I could set the detector off over 4 feet away! His slender wife needed to be about 2 feet away.

Finally Bill placed his small radio barium source in place of the box of U rock. Barium is a rich source of low energy gammas. In this scenario, a person within 7 or 8 feet of the face of the detector would reflect enough low energy gamma back into the face of the detector to set off the device. The source, itself, could be detected in another room!

While 4 pi scattering was the culprit in my lab, most likely due to the wide placement and dispersion of possible sources, the tests at Bill's were purely backscatter.

Thus, I did not take the device to the large Rochester event to take further data.

While discussion may continue, I feel that my original surmise was wrong based on the above tests and Bill's previously supplied gamma spectrum diagram.

I want to thank all who offered comment and ideas throughout the process. The secret was to locate a relatively quiet, uniform background zone without the complication of surrounding sources even though they contributed only a tiny amount of elevation to natural background.

The scattering of low energy gammas by people is considerable, perhaps as much as 12% of such incident gammas are back scattered from single sources in close proximity to a detector. With multiple sources or a uniformly elevated background of low to medium energy gammas, 4pi scattering can contribute to trigger a tightly adjusted alarm on the instrument shown in the original posting.

In a gamma spectrogram, taken with the properly constructed detector head, such scattering would show up as a broad, band of increased noise in the lower end of the resulting plot.

Richard Hull