Radioactivity in public

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Cosmic
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Radioactivity in public

Post by Cosmic » 12 Oct 2019, 20:33

Hello,

I'd like to share a spectrum and a short story with you:

Some days ago in the morning, when I went to work and entered the bus my dosimeter (Atom Fast + smartphone) alarmed me and the alarm didn't go off. I had troubles setting the sound off, because I first had to buy a ticket. Suddenly I was awake and sat down, analyzing what was going on. As the readings were still over 1 micro Sv/h I was searching for the source. It was a passenger, who was sitting alone and as I moved closer the Atom Fast showed up to 60 micro Sv/h! Fortunatelly I had the Mirion PDS-100G with me, startet recording a spectrum, put it in my backpack, placed it on the seat behind the person and backed off to a "safer" location.
I had two similar experiences before, one person told me, that he had got a radio-iodine-tretment, readings were around 50 micro Sv/h, unfortunately I had no gamma spectrometer with me.
So I suspected a medical application, but I didn't ask the person what treatment she got because I didn't want to worry her or spread panic in the bus.

And here is the spectrum (prepared with Interspec, log y), it doesn't look as I expected.
The vertical red line indicates 140.5keV, which corresponds to Tc99m (half life 6h) that is quite commonly used in medical diagnosis.

But as I am a complete noob to gamma spectroscopy, what do the experts mean?
Is my "analysis" correct, the peak is a bit off at 137keV, or might it have been a completely different isotope?
There are a lot of counts at lower energies, is this the compton continuum?
There is a broad peak at around 230keV (grey), I couldn't find a corresponding isotope. I think this might be the sum peak of the Tc99m with itself together with energies from the compton continuum because the count rate at around 4000cps was possibly way to high. I didn't think about that when I recorded the spectrum.
20191008_Tc99m.PNG
20191008_Tc99m.PNG (48 KiB) Viewed 123 times
Stefan

luuk
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Re: Radioactivity in public

Post by luuk » 12 Oct 2019, 22:06

Hi Stefan,
Tc-99m is used in diagnostics sometimes in real high doses, so very easy to detect even after a few day.
My colleague got a scan some years ago and was injected with Tc-99m, the next day when he got back to work my dosimeter got almost to the maximum alarm level and I was sitting about 3 meter away.
A 3x3" NaI(Tl) was able to measure the radiation from Tc-99m after 7 day's when held close to his body, so yes I think you did measured Tc-99m.
Luuk

ipelupessy
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Re: Radioactivity in public

Post by ipelupessy » 13 Oct 2019, 05:23

The amount of radioactivity used in medical diagnostic applications is surprisingly high, often >300 MBq (this corresponds to gamma fluxes of ~ thousand per cm**2 at skin level). with half lifes measured in hours this means ~ 1 gamma ray for every 10 cells in the body or so (and a large part is indeed absorbed) .. If you compare the dose rate for the patient with the natural background its about a million times the natural background! And a person sitting next to such patient encounters (momentarily) a radioactivity higher than much of the hot zone around Tjernobyl. The total dose for e.g. a PET scan is I think something like 0.0001 the letal dose..

I don't think you should mention any of this to a random person you encounter though..they have enough to worry about...please be considerate!!

gwgw
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Re: Radioactivity in public

Post by gwgw » 13 Oct 2019, 06:23

Not sure how much of the Tc99m is getting excreted out of the organism, but I guess some of it remains in the bones (bone accumulation of Tc99m is a desired effect for scintigraphy bone scans). It then decays to Tc99 which has a very long half life of over 200,000 years and I guess Tc99 stays in the bones as well. Wondering how safe that is. I've been told it's very safe. I've never had such procedure, but this year I had a pelvis x-ray scan and to get to the X-ray room, you go through a long corridor in the hospital. In the corridor there was a "nuclear medicine / scintigraphy" room and they made sure it looks scary - it had a big "ionizing radiation" sign plus another "radioactive materials, restricted access" one. I remember joking "this can't be any worse than the dose I just received in my genitals", hehe.
Regards,
Milen Rangelov

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Go-Figure
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Re: Radioactivity in public

Post by Go-Figure » 13 Oct 2019, 08:46

So I am not the only one going around with a PDS 100G always in my pocket!
Talking about Tc99m you could be interested in this video https://www.youtube.com/watch?v=Mj0HDN82Pfo

Another example is the dose from I131 people get from Thyroid cancer therapy, I couldn't believe it when I learned it, it makes all my samples look like moderately sparkling water.

Massimo

ipelupessy
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Re: Radioactivity in public

Post by ipelupessy » 14 Oct 2019, 02:22

@gwgw I think even if Tc99 stys in the body, its activity decreases by the ratio of the half lifes (6hr/200kyr), so what remains of a typical 400 MBq dose is about 1 Bq...

btw the more I think about this, the more I think there is an ethical issue with scanning a person in public this way .. its quite a bit of medically sensitive information you get, so so its a bit of an invasion of privacy to do this...

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Svilen
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Re: Radioactivity in public

Post by Svilen » 14 Oct 2019, 20:36

@ipelupessy Speaking about ethical issues, could you please add a signature with your real name since this is one of the few rules we all should follow here. You signed your introduction with "Inti", but it would be kind if we can see it under your posts too, thank you in advance.
Svilen

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Cosmic
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Re: Radioactivity in public

Post by Cosmic » 14 Oct 2019, 21:32

Hi,
Go-Figure wrote:
13 Oct 2019, 08:46
Talking about Tc99m you could be interested in this video https://www.youtube.com/watch?v=Mj0HDN82Pfo
Thanks, I already re-discovered that video from famous Bionerd23!
Go-Figure wrote:
13 Oct 2019, 08:46
Another example is the dose from I131 people get from Thyroid cancer therapy, I couldn't believe it when I learned it, it makes all my samples look like moderately sparkling water.
For medical therapy they are talking about doses of 1 to 2 Gy per session and 50 to 80 Gy in total - if I'm not totally wrong, as a rule of thumb Grays translate to Sieverts!
Another interesting video from Bionerd23 on that subject would be https://www.youtube.com/watch?v=xJaJUtHO4bI
At 3:50 in the video when the reading on the geiger counter is over 3 mSv and Bionerd gets slightly excited, the doctor in the background says (in German) "That's only 3 mSv PER HOUR, just half the yearly dose, you could stand there at the window for an hour and you wouldn't have to worry about it!".
ipelupessy wrote:
14 Oct 2019, 02:22
btw the more I think about this, the more I think there is an ethical issue with scanning a person in public this way .. its quite a bit of medically sensitive information you get, so so its a bit of an invasion of privacy to do this...
That's indeed an aspect that should be considered.
Stefan

cicastol
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Re: Radioactivity in public

Post by cicastol » 21 Oct 2019, 04:27

ipelupessy wrote:
14 Oct 2019, 02:22
its quite a bit of medically sensitive information you get, so so its a bit of an invasion of privacy to do this...
Maybe for sure, but this can be valid also for the neighbor people who don't want being irradiated ….
Here in Italy my mother, after scintigraphy with Tc99m, doctors said to not stand near people , at least for the first 24h.
Ciro

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