Manti has asked some really good questions about the radiation report. It probably is best to address the test moratorium and non-proliferation geopolitics in another thread.
I raised this in another thread and actually was convinced it's not the case, but what is your opinion on the scenario that gamma radiation was "not tested" as opposed to being tested but not detected?
First off, my Russian is extremely limited, and I don't even try to read the original case files, making do with the translations. Anyone who can read the original Russian and can provide an opinion on the exact phrasing of the original would be appreciated.
From sheet 372:
Samples of solid biosubstrates and clothes combined in groups under Nos 1, 2, 3, 4 were submitted to the radio-isotope laboratory of the Sverdlovsk Sanitary epidemiological station and were analyzed for presence of radioactive materials.
Dosimetric measurements of clothes showed excessive radioactivity (Betaemission only, no Alpha or Gamma-quanta) of 200–300 counts per minute (cpm) over the natural background.
This language implies to me that all were tested, only beta was detected, and alpha and gamma ruled out. Testing only for beta makes no sense when dealing with unknown radioactive material. Geiger counters typically are always sensitive to gammas. Also, gamma is by far the most dangerous type of radiation for external exposure, so failing to test for it makes absolutely no sense.
Thin-wall metal Geiger tubes are sensitive to hard (high energy) betas and gammas. A quick way to categorize radiation is to use such a counter, measure the sample (collecting beta + gamma), then insert a metal shield between the Geiger tube and the sample, and test again. Gamma radiation would largely pass through thin metal, while beta radiation would be almost completely blocked.
Gamma can also be detected via a scintillator, such as NaI(Tl), which is a very sensitive method of detection. Alpha can be detected by specialized Geiger tubes that have thin mica windows, which would be sensitive to alpha, beta, and gamma. A sheet of paper can shield alphas, so a drop in count rate after introducing a sheet of paper indicates their presence. Alphas can also be detected via a ZnS scintillator, which has the benefit of being sensitive almost exclusively to alpha and almost completely insensitive to beta and gamma, so there would be no need to shield and subtract.
We don't know what equipment was used, but I don't believe that language would have been used if some test for each of alpha, beta, and gamma was made and the lab technician had not ruled the other two out.
Both alpha scintillators and mica window Geiger tubes are very sensitive to alpha. If this were natural uranium or thorium (say, from a lantern mantle) then detecting it would be trivial.
Gamma is a different matter. We don't know how gamma was ruled out. As I've mentioned elsewhere, fission products contain, among other things, a mix of Cs-137 and Sr-90, which collectively emit a lot of gamma and beta. Thin-wall metal Geiger tubes are not terribly sensitive to gamma. So it is possible that, for a low enough activity sample of fission products, beta would be above the threshold for detection and gamma would be below it. For 200-300 cpm beta above background, this is an interesting question, which is why I can't completely rule out fission products. If I knew they tested for gamma with a NaI(Tl) scintillator, the gamma level of detection would be low enough that there is no question the gammas from fission products having 200-300 cpm beta could be detected, and I would definitely rule out fission products. They also have a "lead castle" to lower background. Taking a measurement in such a lead castle with a shielded Geiger tube would be more likely to reveal gammas from fission, if they were there, than simply waving a shielded Geiger probe over a low gamma activity sample and simply listening for differences in cpm by ear.
To this end, I would say that an alpha emitter like U or Th can be ruled out, a hard beta emitter like Sr-90 is definitely possible, and the blend of fission products that includes Cs-137 and Sr-90 may or may not be ruled out depending on the equipment used.
Also another thing that I've always wondered about the radiation report is, was relatively high contamination only detected in specific areas on the clothing, or were these simply random areas that were tested and other parts weren't?
That's a very good question, and the answer is that we don't know. This is a question of sampling bias. All 9 samples were well above background, and several were above Soviet nuclear worker occupational limits. The real question is whether the 9 samples of clothing were picked without bias, or whether some "cherry picking" happened, e.g. all the clothing was frisked with a Geiger counter and only the hottest parts were analyzed.
Ivanov's resolution for testing, in case files sheet 370, states:
At the disposal of the expert to present all the clothes of Zolotaryov, Dubinina, Kolevatov and Thibeaux-Brignolle, as well as part of their bodies.
I interpret this to mean that the Sverdlovsk lab had all of the clothing of the four hikers in the ravine. The lab definitely has Geiger counters, so they could have done a preliminary scan and intentionally picked 9 definitely hot pieces of the clothing to work with. They also could have taken pieces at random. Unfortunately, we don't know.
Still, even with sampling bias, it can be said that all four hikers wore at least one piece of clothing contaminated significantly above background, which is not what one would ever expect from natural sources and global atmospheric nuclear testing.
You're right; radiation count rates are normalized to counts per 150 cm^2 to account for differences in sizes of samples.
Anyway are there other plausible contaminants apart from strontium? One thing that maybe be a candidate is tritiated rust which I believe is a welding product (for example could be present on the stove). It has a half-life of 12 years, but it's probably much too weak to account for the contamination.
Here is a complete a list of beta-only emitters: http://homepages.cae.wisc.edu/~blanchar/purebeta.htm I guess those can be excluded that have half-lives too short, or decay products that are alpha/gamma emitters because then gamma radiation would have been detected too, also gases like Kr-85. Still, leaves a lot of possibilities..
Another thought: strontium is not water-soluble, but it is stated that the contamination decreased with washing. Or does solubility not matter if it's in dust form?
The contaminant does NOT have to be Sr-90. I mention it because it is an easily obtained and measured hard beta emitter. It is produced in significant quantity in nuclear fission. Later period Soviet Geiger counters include a small amount of Sr-90, safely embedded in epoxy resin, as an operational check and calibration source.
However, we know from the report that the quantitative testing on clothing was done with STS-6 Geiger tubes. These can still be purchased, and data sheets are available. These are thin-walled hard beta and gamma sensitive tubes. Sr-90 can easily be detected with such tubes. But Sr-90 has a maximum and average beta energy of 546 and 196 keV, respectively. This is enough to get through the thin metal wall of the STS-6 Geiger tube and register a count. Tritiated rust can be ruled out, as the max and avg energy is 18.6 and 5.7 keV. Even C-14 (max/avg 157/50 keV) is probably too soft to be counted on an STS-6. Something like P-32 is plenty energetic, but with a half-life of 14 days, it would be gone by the time the bodies were discovered (assuming exposure was approximately concurrent with death.) So the list of suspects can be limited.
The question of solubility is a good one. Insoluble particles can be trapped in the cloth fibers. Running water through or over the cloth can mechanically dislodge and carry away particles. So something insoluble in water like Sr would tend to remain in the clothing unless the mechanical action of the water washed the particles out. I definitely would expect washing in running water to reduce the activity on the cloth samples.