November 30, 2022, 07:13:00 PM
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Topic: gamma rays from various isotopes as a forensic tool  (Read 2911 times)

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Offline Babcock_Hall

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gamma rays from various isotopes as a forensic tool
« on: November 09, 2021, 10:32:51 AM »
https://doi.org/10.1073/pnas.1903481116

I teach a little bit of basic nuclear chemistry as it relates to forensic chemistry.  My textbook mentioned that the ratio of cesium-134 (at 605 and796 KeV)  to cesium-137 (662 KeV) and the ratio of iodine-133 to iodine-131 can be used to determine whether the cause of radioactivity was a nuclear bomb or the meltdown of a nuclear reactor.  It also mentioned that there was a handheld device that could be plugged into a cell phone that could be used in this regard but gave almost no specifics.  I did a quick search that turned up the paper above.  It deals with cesium-137 years after nuclear tests were done.

I am looking for a source of basic information that deals with how one identifies and quantitates various radioactive isotopes, especially these four; it seems plausible that the energy of emission is a characteristic property.  If the reading were too advanced for my class, I might be able to summarize it for them.

Offline Corribus

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Re: gamma rays from various isotopes as a forensic tool
« Reply #1 on: November 09, 2021, 11:14:05 AM »
I guess ICP-MS is gradually replacing traditional spectrometric methods of detecting fission products.

E.g., https://pubs.rsc.org/en/content/articlehtml/2017/ja/c6ja00334f , https://pubmed.ncbi.nlm.nih.gov/19542689/ , https://pubs.rsc.org/en/content/articlelanding/2014/ja/c3ja50291k etc.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline marquis

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Re: gamma rays from various isotopes as a forensic tool
« Reply #2 on: December 14, 2021, 08:47:37 PM »
From the look of it, they are using a wavelength dispersive XRF (WDXRF).  I've used many EDXRF and they don't have the resolution needed to tell the difference between the energies of different atoms ( ie 137 Cs vs any other Cs). It's been a while since I used a WD XRF,too.  But according to Wiki, their resolution has improved greatly over the last few years.

Offline Babcock_Hall

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Re: gamma rays from various isotopes as a forensic tool
« Reply #3 on: December 15, 2021, 08:16:48 AM »
marquis, Thank you.  I will look into this more.

Offline kriggy

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Re: gamma rays from various isotopes as a forensic tool
« Reply #4 on: February 21, 2022, 10:30:03 AM »
First, Im not convinced there is a "phone based" device for that. In my lab we have handheld radiation detectors with solid scintilator which are able to detect and measure around 7 various isotopes and price of one is around 10 000 USD. And they are size of clothes iron.

Im not 100% sure how the intrument they used works but looks like a portable gamma spectroscope. Im not really versed in how those work but they are able to detect the radiation with specific energies (which are given for each isotope)

Offline Jotaro

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Re: gamma rays from various isotopes as a forensic tool
« Reply #5 on: September 15, 2022, 05:22:16 AM »
Sorry for bumping an old thread.

But its true that various ratios can tell what the source are. Also, depending on the "fingerprint" (what radionuclides are seen) it can tell what temperatures might be relevant. Especially in nuclear power plant accidents, some elements are released relatively easy, such as noble gases, krypton, xenon and whatnot, but also Iodine. But some elements require relatively high temperatures to be released, and of course, if you see like plutonium or uranium in the measurement, then you have fuel fragments, and that is pretty much an indication of an explosion that just blasted away all kinds of stuff.

As for the source, well, I cant provide one. This stuff is not really mainstream science, and perhaps there are either no desire to spread info on this further (to avoid teaching how things can be detected) or no one is interested and have asked the questions :)

As for the measurement of these radionuclides, you measure them by gamma spectrometry using a high purity germanium detector (HPGe). All countries should have some air monitoring system, they take the filter, and then measure it (137,134Cs and I-isotopes are gamma emitters) and can be seen in the spectrum.

As for a plug-in detector to phones, could work maybe. There are some semi conductor detector system (including electronics) that can be powered from an usb port. But the resolution on these semi conductors operating in room temperature (in contrast to liquid nitrogen for HPGe) is really bad, so might be difficult to see all 4 radionuclides clearly.

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