Characterizing isotopic composition of post-accident/incident fallout

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juliemac
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Characterizing isotopic composition of post-accident/incident fallout

Post by juliemac » 27 Jan 2020, 07:14

Hi,

New here, an amateur from the west coast of the USA. I have a reasonably good layperson's understanding of radioactivity, isotopic decay chains, types of radiation, KeV spectra, principles of shielding, etc. Mostly with reference to nuclear safety concerns from reactor accidents (fuku / chernobyl / TMI / Windscale) and to possible nuclear war or terrorism. (Anything from isolated nuclear terrorism incident up to major nuclear exchange between major powers.)

At present I have a NukAlert ER rad detector. It's designed and tested to go all the way from single counts to 1 (one) full Sievert per hour without saturating.

In the unlikely event that I happen to be living in a place that ends up in the path of significant fallout from any sort of nuclear materials release, whether accidental or otherwise, I'm hoping to provide myself with usable data on the isotopic composition of fallout at my exact location. (Typically it's many days to weeks from the release incident until much solid info is released by government agencies, and even then it's only very general in nature.)

I've reviewed a good amount of the lower-cost (<$2000 USD) gamma spectroscopy equipment available for sale and have a general notion that a gam-spec setup could be very useful for characterizing post-accident/incident fallout composition. The main roadblock appears to be the low saturation threshold. Fallout particles or contaminated soil collected "shortly" after the incident (anything from hours to possibly months) is likely to be so active that it quickly saturates unshielded gam-spec equipment.

I assume that with a properly-calibrated reverse shielding setup (i.e. where the shield is configured to attenuate the sample material itself, rather than blocking out background radiation) I'd be able to take a pretty "hot" fallout sample and get usable data on its isotopic composition.

Assume for the purposes of this discussion that I would have already planned and prepared for relatively safe handling of said sample: For example: I emerge from a fallout shelter 48 hours post-incident and measure a radiation field averaging about 0.01 Sievert /hour. Low enough that I can afford to spend 5 minutes outdoors to collect a soil sample. I use a long-handled scoop to carefully put 10 mL's of soil into a clean ZipLoc sample bag, taking care to avoid even the slightest contam. of the outside of the bag. The sealed ZipLoc bag then goes into a small, portable, covered-top lead pig of perhaps no more than 20 kilos total weight, which itself had been set down temporarily on a piece of clean, disposable plastic sheeting. I take the covered lead pig & sample back into the shelter and attempt to perform gamma-spec measurements on it. (Assume also that I had already configured & tested my fallout shelter with a reasonably low BGR workstation area and that I had taken all necessary precautions to avoid tracking any soil or fallout back into the shelter, e.g. with proper donning & removal of tyvek bunny suit and shoe covers during sample collection, doing a careful radiation survey around the inside of the shelter with a rad meter to check for sources of stray emissions, etc.)

Is this a workable idea from a data-collection standpoint? I'm thinking that in principle it should be possible, either with just the portable lead pig itself or if need be with additional lead shielding, to attenuate the radiation to a level the gamma-spec equipment can handle. What I'm less certain about is whether the fallout would be so rich with a wide variety of isotopes that it might prove difficult or impossible to distinguish among the many different species in the mix.

Interested to hear comments & suggestions.

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Steven Sesselmann
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Re: Characterizing isotopic composition of post-accident/incident fallout

Post by Steven Sesselmann » 27 Jan 2020, 17:28

juliemac wrote:
27 Jan 2020, 07:14
Hi,

New here, an amateur from the west coast of the USA.
Great, welcome to the forum, but please pay attention to the forum rules. You need to introduce yourself in the introductions forum and you need to post using your real name. That's the rule, no exceptions.
I have a reasonably good layperson's understanding of radioactivity, isotopic decay chains, types of radiation, KeV spectra, principles of shielding, etc. Mostly with reference to nuclear safety concerns from reactor accidents (fuku / chernobyl / TMI / Windscale) and to possible nuclear war or terrorism. (Anything from isolated nuclear terrorism incident up to major nuclear exchange between major powers.)
Always good to understand radiation, that way you don't need to fear it, however if you worry about conflicts between nations, you would be better off putting your efforts into politics.
At present I have a NukAlert ER rad detector. It's designed and tested to go all the way from single counts to 1 (one) full Sievert per hour without saturating.
In the unlikely event that I happen to be living in a place that ends up in the path of significant fallout from any sort of nuclear materials release, whether accidental or otherwise, I'm hoping to provide myself with usable data on the isotopic composition of fallout at my exact location. (Typically it's many days to weeks from the release incident until much solid info is released by government agencies, and even then it's only very general in nature.)
In such an unlikely event, radiation is probably going to be one of your lesser concerns, unless you happen to be at point zero, in which case I wouldn't worry, but sure if you survive the fight for food at the supermarket, and the fight for clean bottled water, a geiger counter might be useful.

I've reviewed a good amount of the lower-cost (<$2000 USD) gamma spectroscopy equipment available for sale and have a general notion that a gam-spec setup could be very useful for characterizing post-accident/incident fallout composition. The main roadblock appears to be the low saturation threshold. Fallout particles or contaminated soil collected "shortly" after the incident (anything from hours to possibly months) is likely to be so active that it quickly saturates unshielded gam-spec equipment.
I assume that with a properly-calibrated reverse shielding setup (i.e. where the shield is configured to attenuate the sample material itself, rather than blocking out background radiation) I'd be able to take a pretty "hot" fallout sample and get usable data on its isotopic composition.
I have made well over 1,000 spectrometers and none of my clients have reported the count rate being a serious issue, most people have the opposite issue where they need a lot of lead to shield out background because the sample is so weak.
Assume for the purposes of this discussion that I would have already planned and prepared for relatively safe handling of said sample: For example: I emerge from a fallout shelter 48 hours post-incident and measure a radiation field averaging about 0.01 Sievert /hour. Low enough that I can afford to spend 5 minutes outdoors to collect a soil sample. I use a long-handled scoop to carefully put 10 mL's of soil into a clean ZipLoc sample bag, taking care to avoid even the slightest contam. of the outside of the bag. The sealed ZipLoc bag then goes into a small, portable, covered-top lead pig of perhaps no more than 20 kilos total weight, which itself had been set down temporarily on a piece of clean, disposable plastic sheeting. I take the covered lead pig & sample back into the shelter and attempt to perform gamma-spec measurements on it. (Assume also that I had already configured & tested my fallout shelter with a reasonably low BGR workstation area and that I had taken all necessary precautions to avoid tracking any soil or fallout back into the shelter, e.g. with proper donning & removal of tyvek bunny suit and shoe covers during sample collection, doing a careful radiation survey around the inside of the shelter with a rad meter to check for sources of stray emissions, etc.)Is this a workable idea from a data-collection standpoint? I'm thinking that in principle it should be possible, either with just the portable lead pig itself or if need be with additional lead shielding, to attenuate the radiation to a level the gamma-spec equipment can handle. What I'm less certain about is whether the fallout would be so rich with a wide variety of isotopes that it might prove difficult or impossible to distinguish among the many different species in the mix.
Interested to hear comments & suggestions.
Well, you seem to have it all worked out, but you seem to lack hands on experience, so I suggest getting a good scintillator and a spectrometer and learn more about gamma spectrometry and it's limitations. The nuclear accidents we have experience with are well documented, so you should read about how radiation affected people living in the area, probably less than you imagine, first responders and firefighters seem to be the group most at risk.

In any case you are reaching out to learn more which is the right way to deal with your concerns.

Steven

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Cosmic
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Re: Characterizing isotopic composition of post-accident/incident fallout

Post by Cosmic » 27 Jan 2020, 21:36

Hi Julie (?),

in a post-apocalyptic scenario as you described, I agree with Steven, radiation won't be your biggest problem. And figuring out what isotopes are in the fallout will not help very much, maybe you can identify some isotopes with short half lives (i.e. in the range of a few days) and get an idea how long you have to stay in the shelter till they have decayed away. But there will be isotopes with long(er) half-lives Cs137 (hl 30 years) and for them do decay you would have to wait at least hundreds of years.

If the sample is too hot for a measurement you could always take a smaller sample, increase distance, and ... use shielding. But let's face it: if your sample you took from outside the shelter was that hot, you wouldn't survive opening the door to take the sample.

here is a video about a hot piece of "nuclear fallout" - I personally would use gloves ;)
https://www.youtube.com/watch?v=ejZyDvtX85Y
Stefan

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