Low Level Gamma Radiation

Mike Monett wrote:
> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> Mike Monett wrote:
> 
> [...]
> 
>>> I'm not planning on heavy use. The idea is to compare the scintillator
>>> againt the Radiacode, and try to measure any Radon gas in the basement.
>>> Then it will probably go into storage.
>>
>> It ought to work fine for light-duty use like that, though you'll need
>> the PMT supply and bias string.  If you know the tube P/N, I can
>> probably tell you what to use.
>>
>> Cheers
>>
>> Phil Hobbs
> 
> I don't think the PMT P/N is available. I also assume the bias string is
> buried inside the assembly. I'll probably have to find the operating voltage
> by experimenting, a time-honored tradition among hackers.
> 

Turns out the p/n is (more or less) in the listing title: it's some 
flavour of R7400, whose datasheet is here, courtesy of Jeroen & Co:
<https://ctf3-tbts.web.cern.ch/instr/PMT/R7400U_TPMH1204E07.pdf>.

CsI(Tl) emits in the visible (the peak is around 550 nm), so the tube is 
probably an R7400-02 or -20.

It's an 8-stage tube that likes about 75-100V per stage, and is 
interestingly fast at 800 ps FWHM.  That's fast like an APD, and much 
faster than a SiPM/MPPC.  I ordered a few of them to try out, probably 
without the scintillator.

For scintillation counting, you don't need brilliant linearity, so a 
resistor string is probably fine for the dynode bias.  I'd start with a 
current-limited -1 kV variable supply and some 1M resistors, with a 
2.2-nF cap across each of the bottom two or three resistors.  That way, 
at 800V you'll be dissipating about 80 mW.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

[...]

> Turns out the p/n is (more or less) in the listing title: it's some 
> flavour of R7400, whose datasheet is here, courtesy of Jeroen & Co:
> <https://ctf3-tbts.web.cern.ch/instr/PMT/R7400U_TPMH1204E07.pdf>.
> 
> CsI(Tl) emits in the visible (the peak is around 550 nm), so the tube is
> probably an R7400-02 or -20.
> 
> It's an 8-stage tube that likes about 75-100V per stage, and is 
> interestingly fast at 800 ps FWHM.  That's fast like an APD, and much 
> faster than a SiPM/MPPC.  I ordered a few of them to try out, probably 
> without the scintillator.
> 
> For scintillation counting, you don't need brilliant linearity, so a 
> resistor string is probably fine for the dynode bias.  I'd start with a 
> current-limited -1 kV variable supply and some 1M resistors, with a 
> 2.2-nF cap across each of the bottom two or three resistors.  That way, 
> at 800V you'll be dissipating about 80 mW.
> 
> Cheers
> 
> Phil Hobbs

Very valuable information. Thanks.



-- 
MRM

On Sunday, June 26, 2022 at 5:23:43 PM UTC-7, Mike Monett wrote:
> I will send my name and address to your gmail address. Again, thanks. 

Go ahead and send your address to me at john (at) miles.io if you'd 
still like one, and I'll throw one in a padded envelope next time I go to
the post office.  My GMail account is almost unusable due to people 
confusing their email address with mine and signing me up for
all kinds of junk mail.  Right now there are 217,959 unread messages
and I don't see yours anywhere. :(

I powered one up just now and took a video:

http://www.ke5fx.com/r7400u.htm

Hopefully I'm looking at a lot of dark counts or other PMT artifacts, 
because jeez, that sure seems like a lot of pulses.

-- john, KE5FX

"John Miles, KE5FX" <jmiles@gmail.com> wrote:

> On Sunday, June 26, 2022 at 5:23:43 PM UTC-7, Mike Monett wrote:
>> I will send my name and address to your gmail address. Again, thanks. 
> 
> Go ahead and send your address to me at john (at) miles.io if you'd 
> still like one, and I'll throw one in a padded envelope next time I go to
> the post office.  My GMail account is almost unusable due to people 
> confusing their email address with mine and signing me up for
> all kinds of junk mail.  Right now there are 217,959 unread messages
> and I don't see yours anywhere. :(
> 
> I powered one up just now and took a video:
> 
> http://www.ke5fx.com/r7400u.htm
> 
> Hopefully I'm looking at a lot of dark counts or other PMT artifacts, 
> because jeez, that sure seems like a lot of pulses.
> 
> -- john, KE5FX

Hi John,

Very nice page !

That is a very nice offer. Thanks.

Various sources say the PMT voltage is critical and must be adjusted 
individually for each PMT. One way to do this is to find a known 
radioactive source and generate a spectrum, then adjust the PMT voltage so 
the source lines up with the known energies in KeV or Mev.

Getting samples of thorium has turned out to be impossible, except for 
traces in welding rods. However, radium is readily available in the form of 
watch hands painted with radium. These are for sale extremely cheap on 
Ebay.

The watch hands no longer glow in the dark since the phosphor will have 
worn out. However, the radium will still be active since it has a half-life 
of 1600 years. Below is the radioactive series of radium-226. You can see 
the first step is radon, which releases alpha particles and gamma 
radiation:

https://www.ld-
didactic.de/software/524221en/Content/Appendix/Ra226Series.htm

Radon gas is extremely dangerous. There is a small amount in every 
basement. You breath it into your lungs, where it emits alpha particles, 
which are the nucleus of helium-4. This causes lung cancer and you die.

We need to be able to monitor the amount of radon in our basements and be 
certain it doesn't increase, such as during the winter when most 
ventilation is shut off.

So it pays to learn a bit about gamma spectrometers to be able to protect 
yourself and your family.

Regular radon detectors are very expensive, but gamma spectrometers can be 
quite modest in cost. You can get the Radiacode, which is a very nice unit, 
or build the Hamamatsu R7400U PMT version as a backup and verification.



-- 
MRM

On Saturday, July 16, 2022 at 8:25:08 PM UTC+10, Mike Monett wrote:
> "John Miles, KE5FX" <jmi...@gmail.com> wrote:
> > On Sunday, June 26, 2022 at 5:23:43 PM UTC-7, Mike Monett wrote: 
> >> I will send my name and address to your gmail address. Again, thanks. 
> > 
> > Go ahead and send your address to me at john (at) miles.io if you'd 
> > still like one, and I'll throw one in a padded envelope next time I go to 
> > the post office. My GMail account is almost unusable due to people 
> > confusing their email address with mine and signing me up for 
> > all kinds of junk mail. Right now there are 217,959 unread messages 
> > and I don't see yours anywhere. :( 
> > 
> > I powered one up just now and took a video: 
> > 
> > http://www.ke5fx.com/r7400u.htm 
> > 
> > Hopefully I'm looking at a lot of dark counts or other PMT artifacts, 
> > because jeez, that sure seems like a lot of pulses. 
> 
> Very nice page ! 
> 
> That is a very nice offer. Thanks. 
> 
> Various sources say the PMT voltage is critical and must be adjusted 
> individually for each PMT. One way to do this is to find a known 
> radioactive source and generate a spectrum, then adjust the PMT voltage so 
> the source lines up with the known energies in KeV or Mev. 

The photomultiplier voltage just adjusts the gain of the photomultiplier tube - photons hitting the photocathode produce electrons in the cathode space, and the voltage drop across the dynode chain just adjusts the number of electrons that each electron hitting the first dynode ends up delivering to the anode.

Getting the energy of individual particles coming out of the radiation source takes rather more than fiddling with the gain of the electron multiplication stages inside the photomultiplier tube. Because you've got a lot of stages of multiplication - anything from 10 to 14 - you can vary that gain a lot.
 
> Getting samples of thorium has turned out to be impossible, except for 
> traces in welding rods. However, radium is readily available in the form of 
> watch hands painted with radium. These are for sale extremely cheap on 
> Ebay. 
> 
> The watch hands no longer glow in the dark since the phosphor will have 
> worn out. However, the radium will still be active since it has a half-life 
> of 1600 years. Below is the radioactive series of radium-226. You can see 
> the first step is radon, which releases alpha particles and gamma 
> radiation: 
> 
> https://www.ld- 
> didactic.de/software/524221en/Content/Appendix/Ra226Series.htm 
> 
> Radon gas is extremely dangerous. There is a small amount in every 
> basement. 

If your house is built above granite rocks, or any other kind of rock that contains uranium, you can get radon gas leaking into the basement. If it is, put in an extractor fan to move it out before it can drift up to diffuse through the floor into the rest of the house.

> You breath it into your lungs, where it emits alpha particles,  which are the nucleus of helium-4. This causes lung cancer and you die. 

Helium four won't do any damage at all, but energetic alpha particles can cause mutations in any cell that they hit, and some mutations can make cell cancerous
 
> We need to be able to monitor the amount of radon in our basements and be 
> certain it doesn't increase, such as during the winter when most 
> ventilation is shut off. 

If there's uranium - or the like  - in the rocks under your basement it makes sense to monitor for radon. If there is, it makes sense to ventilate that space, even in winter.
 
> So it pays to learn a bit about gamma spectrometers to be able to protect yourself and your family. 

Learning about geology is cheaper.

> Regular radon detectors are very expensive, but gamma spectrometers can be 
> quite modest in cost. You can get the Radiacode, which is a very nice unit, 
> or build the Hamamatsu R7400U PMT version as a backup and verification. 

Radon itself decays by emitting a 4.6 Mev alpha particle. This isn't any kind of gamma ray, but it is energetic enough that if it hits an adjacent atom it may generate a gamma ray (an energetic photon) which is likely to have a longer range.

The Radiacode 101 monitor uses a scintillation detector - the chunk of thallium doped cesium iodide - which produces a flash of light when hit by a gamma ray photon (or anything else that can get at it).

   > crystal CsI (Tl) of cesium iodide doped with thallium in a sealed container;
   > silicon photomultiplier;

Also called an avalanche photodiode.

  >  optical interface between scintillator and photomultiplier;

A window, so the photons emerging from the transparent can get at the sensitive face of the photodiode

   > precision temperature-compensated power supply for photomultiplier;

Avalanche photodiodes are tricky to bias. 

   > high-speed analog-digital circuit for processing pulses from a photomultiplier.

The pulses do tend to be narrow. You need fast op amps and comparators, but they are widely available and not that expensive.

https://ctf3-tbts.web.cern.ch/instr/pmt/r7400u_tpmh1204e07.pdf

The minature Hamamatsu R7400U photomultiplier tubes are pretty compact (but not as compacts as an avalanche photodode) and  need a higher voltage supply, but they aren't quite as tricky to bias as an avalanche photodiode.

-- 
Bill Sloman, Sydney

In article <XnsAED63FC6A8982idtokenpost@88.198.57.247>,
Mike Monett  <spamme@not.com> wrote:
>Getting samples of thorium has turned out to be impossible, except for 
>traces in welding rods. However, radium is readily available in the form of 
>watch hands painted with radium. These are for sale extremely cheap on 
>Ebay.

Also on eBay, you can find "quantum energy" or "scalar energy" or
"negative ion" pendants made out of a black volcanic rock.  They're
often touted as a way of protecting oneself from the (supposed)
harmful effects of electromagnetic radiation.

They do generate "negative ions", in the form of beta-decay
electrons... these are not your gentle after-the-rainstorm negative
ions by any means!

By one report the radiation level is high enough that wearing one next
to the skin for a year can exceed safe exposure levels and might even
cause a mild radiation burn.  I understand that Singapore has banned
the import of such products for this reason.

The rock from which they are made appears to be rich in thorium and
its decay products (perhaps something like monazite?).

I measured one on my home-made gamma spectrometry system and got
a very recognizable thorium-decay signature (the isotope markers
are from a best-efforts calibration).

https://www.radagast.org/~dplatt/gamma/quantum-pendant.png

Another useful calibration source (for higher-energy gammas from
potassium-40) is a sack of potassium chloride water-softener recharge
crystals from your local big-box home/hardware store (or, on a smaller
scale, a box of Morton "Lite Salt" which is about half potassium
chloride).

And, one can still find orange Fiestaware and green uranium glass at
the occasional estate or garage sale or antique store.

On Saturday, 16 July 2022 at 16:16:38 UTC+2, Dave Platt wrote:
> In article <XnsAED63FC6A8...@88.198.57.247>,
> Mike Monett <spa...@not.com> wrote: 
> >Getting samples of thorium has turned out to be impossible, except for 
> >traces in welding rods. However, radium is readily available in the form of 
> >watch hands painted with radium. These are for sale extremely cheap on 
> >Ebay.
> Also on eBay, you can find "quantum energy" or "scalar energy" or 
> "negative ion" pendants made out of a black volcanic rock. They're 
> often touted as a way of protecting oneself from the (supposed) 
> harmful effects of electromagnetic radiation. 
> 
> They do generate "negative ions", in the form of beta-decay 
> electrons... these are not your gentle after-the-rainstorm negative 
> ions by any means! 
> 
> By one report the radiation level is high enough that wearing one next 
> to the skin for a year can exceed safe exposure levels and might even 
> cause a mild radiation burn. I understand that Singapore has banned 
> the import of such products for this reason. 
> 
> The rock from which they are made appears to be rich in thorium and 
> its decay products (perhaps something like monazite?). 
> 
> I measured one on my home-made gamma spectrometry system and got 
> a very recognizable thorium-decay signature (the isotope markers 
> are from a best-efforts calibration). 
> 
> https://www.radagast.org/~dplatt/gamma/quantum-pendant.png 
> 
> Another useful calibration source (for higher-energy gammas from 
> potassium-40) is a sack of potassium chloride water-softener recharge 
> crystals from your local big-box home/hardware store (or, on a smaller 
> scale, a box of Morton "Lite Salt" which is about half potassium 
> chloride). 
> 
> And, one can still find orange Fiestaware and green uranium glass at 
> the occasional estate or garage sale or antique store.
-Low Level Gamma Radiation is all fake

On Saturday, July 16, 2022 at 7:16:38 AM UTC-7, Dave Platt wrote:
> I measured one on my home-made gamma spectrometry system and got 
> a very recognizable thorium-decay signature (the isotope markers 
> are from a best-efforts calibration). 
> 
> https://www.radagast.org/~dplatt/gamma/quantum-pendant.pn

Resolution of that setup looks really good -- is it written up anywhere?

-- john, KE5FX

dplatt@coop.radagast.org (Dave Platt) wrote:

> In article <XnsAED63FC6A8982idtokenpost@88.198.57.247>,
> Mike Monett  <spamme@not.com> wrote:
>>Getting samples of thorium has turned out to be impossible, except for 
>>traces in welding rods. However, radium is readily available in the form
>>of watch hands painted with radium. These are for sale extremely cheap
>>on Ebay.
> 
> Also on eBay, you can find "quantum energy" or "scalar energy" or
> "negative ion" pendants made out of a black volcanic rock.  They're
> often touted as a way of protecting oneself from the (supposed)
> harmful effects of electromagnetic radiation.
> 
> They do generate "negative ions", in the form of beta-decay
> electrons... these are not your gentle after-the-rainstorm negative
> ions by any means!
> 
> By one report the radiation level is high enough that wearing one next
> to the skin for a year can exceed safe exposure levels and might even
> cause a mild radiation burn.  I understand that Singapore has banned
> the import of such products for this reason.
> 
> The rock from which they are made appears to be rich in thorium and
> its decay products (perhaps something like monazite?).
> 
> I measured one on my home-made gamma spectrometry system and got
> a very recognizable thorium-decay signature (the isotope markers
> are from a best-efforts calibration).
> 
> https://www.radagast.org/~dplatt/gamma/quantum-pendant.png
> 
> Another useful calibration source (for higher-energy gammas from
> potassium-40) is a sack of potassium chloride water-softener recharge
> crystals from your local big-box home/hardware store (or, on a smaller
> scale, a box of Morton "Lite Salt" which is about half potassium
> chloride).
> 
> And, one can still find orange Fiestaware and green uranium glass at
> the occasional estate or garage sale or antique store.

Thanks for the information. I will try to find the black volcanic rock 
products. I recall an article describing these that got them kicked off 
Amazon (I think).

Your gamma spectrometry system sounds very interesting. Can you supply more 
information, such as what kind of scintillator crystal do you use, how big 
is it, and do you use a PMT or diode for the detector, what software do you 
use to generate the spectrum, how do you drive it, and any other details 
that might be interesting.

I use pure potassium chloride (KCl) in the form of Windsor Salt Free 
seasoning, but my Radiacode is not sensitive enough to detect the decay 
products. I left it sitting on three containers for several days but had no 
luck. I need a more sensitive detector, which is why yours is so 
interesting.

On a related topic, I have been trying to find out why the background gamma 
spectrum has a sharp rise at low energies, and where does it come from? Do 
you have any ideas?

Thanks,

Mike



-- 
MRM

On 16.07.22 20:43, John Miles, KE5FX wrote:
> On Saturday, July 16, 2022 at 7:16:38 AM UTC-7, Dave Platt wrote:
>> I measured one on my home-made gamma spectrometry system and got
>> a very recognizable thorium-decay signature (the isotope markers
>> are from a best-efforts calibration).
>>
>> https://www.radagast.org/~dplatt/gamma/quantum-pendant.pn
>
> Resolution of that setup looks really good -- is it written up anywhere?
>
> -- john, KE5FX
>
why did somebody snip off the last letter of .PNG????