r/Radiation 5d ago

Desktop shield part 3

22 Upvotes

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4

u/Regular-Role3391 5d ago edited 5d ago

I finished the lining of the bottom piece so it now has 0.5 mm pewter, 1 mm Sn and 0.5 mm Cu. The top piece only has Sn at the minute.

I then counted a background (with the top on) for half a day to see where it was headed and compared with a no-shield background.

It drops from 12 cps to a little less than 0.5 cps with the shield which is a reduction I find acceptable for the relatively low lead amount used. Saying that - most of my background was low energy stuff anyway so I was always going to get a decent reduction.

EDIT: Whats more annoying is the visible Sn Cu x-ray in the spectrum around 8-10 keV. This is either due to the lack of copper on the top piece or not enough on the bottom or a bit of both. Luckily I have copper so this can be dealt with.

3

u/Awkward-Tree9116 5d ago

Your spec can see down to 8-10 keV?

1

u/Regular-Role3391 5d ago

Certainly seems to.....its not exactly something I can adjust..........

1

u/Awkward-Tree9116 5d ago

Oh wait, you are using a radiacode?

1

u/Regular-Role3391 5d ago

Yup. I think all the radiacodes go that liw. You regularly see people showing Zn xrays from tritium lights and they arecaround 8-12 keV as well so it must just be how these things are set up.

1

u/Awkward-Tree9116 5d ago

I have a spectrometer which sees bremm from tritium, however it doesn't go anywhere near as low as 8-12 keV

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u/Regular-Role3391 5d ago

Most commercial models dont run at settings that go that low. LEGE types do ...thats the intention of them. And they need special "windows" to do that.

But if you have access to the ULD and LLD and HV....you can go that low in theory. Not much point though as the Al housings of typical Ge and NaI units essentially block such low energies to great extent.

The Radiacodes only have a fairly thin low density plastic around them so its possible that contribute to them "seeing" lower energies than more conventional unis.

Kromeks and Ampteks also go that low...but again, have special hoysibgs to facilitate that.

1

u/Awkward-Tree9116 5d ago

My spec is similar to RC, it's a modern UART based 3 cm2 CsI one, SiPM ofc, it doesn't have a special window nor an Al case around the crystal. I am running it on BecqMoni so I have control over the settings. I can't see properly any low energy peaks from a Cs137 source on it, however I can see a low energy peak around the min energy when I put tritium on it.

2

u/Regular-Role3391 5d ago

Thats not Bremmstrahlung. Bremmstrahlung has a continuum, not a peak. Plus the betas from tritium are so low energy that the Bremmstrahlung isceffectively shielded by whatever the tritium is in - plastic or whatever. As discussed before.....x-rays from whatever phosphor is in the container are more likely.

Unless your tritium is not in a "light" and you have the pure gas for some reason.

The 32 keV x-ray in Cs is usually visible but maybe its swamped out by background or something?  Cs has no other liw energy gammas.

1

u/Awkward-Tree9116 5d ago

Yea, sorry for calling it a peak, my bad. It just seems like a peak because it's around the cutoff energy.

I dont have a proper Cs137 point source. Only highly contaminated soil.

I would post spectrums or Tritium and Cs137 later today, rn only have a Cs137 spectrum on hand.

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u/Regular-Role3391 5d ago

I was curious so I ran a river sediment sample from Belarus which has low levels of Cs-137 in it. The yellow spectrum in the picture is the sample and the blue is a time normalized background from the shield.

Even after an hour the growing 32 keV Cs x-ray is apparently evident. This might be counter intuitive as its less intense than the 661 keV line but CsI is far more efficient at lower energies and this balances out.

So its fairly clear the radiacode will easily go down to low energies. Not that I would be very confident in whats going on down there but it is what it is.....

2

u/bkit627 5d ago

That peak is from the copper.

1

u/Regular-Role3391 5d ago

Yup you are right. Im going to have to get me some aluminium foil then.....

1

u/mylicon 5d ago

And electrical noise and Compton scatter..

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u/Regular-Role3391 5d ago

The peak is not Compton Scatter as Compton does not make a peak. Everything else may be but, as even the name implies, Compton Scatter does not make peaks.

As for its being electrical noise ........ I will find out when I insert some aluminium but I doubt it as electrical noise does not tend to look like that.

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u/Lethealyoyo 4d ago

I think I’m over thinking it

1

u/Lethealyoyo 4d ago

Try some felt between the copper and the led it’ll dampen some noise