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Zamboni

Thu Jun 17 2010, 12:58AM

Registered Member #2836 Joined: Fri Apr 30 2010, 01:24PM
Location:
Posts: 41

I am very interested in building a "radium Clock". Such as the one at the link below.

I was thinking of using a mason jar and vacuum sealing it.

I was going to use Americium-241 instead of Radium.

My idea was to put the Americium in a small aluminum foil box and then attach a piece of faux gold leaf to the foil. My hope was that the foil would be repelled from the Aluminum foil box because the alpha emission from the A-241 would charge the foil box and the leaf positive.

The design would include a ground wire. As the foil leaf separated from the foil box, it would eventually touch the ground wire and lose it's charge and collapse onto the foil box to start the process again.

My concern was the possibility of creating neutrons from the A-241/Aluminum foil interaction. I am unsure if that is in any way dangerous. Hence, I thought I would seek the counsel of those who know more about radiation than I do.

I plan on using a standard smoke detectors worth of A-241.

So my question is:
1. Will neutrons be created?
2. If so, Is that dangerous?
3. Is there a better type of foil to use that would not create the neutrons?

I believe that the alpha radiation will all be stopped by the foil.
I don't believe that the small amount of Beta will do any harm.

Thank You,
Paul

plazmatron

Thu Jun 17 2010, 01:40AM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Theoretically neutrons will be created by the interactions of Alpha particles with Aluminium foil.

The good news is that with the source you describe, the neutron count produced would be so small as to be undetectable.

Even a deliberately manufactured neutron source using Beryllium and the Am out of a smoke detector, would produce a count so low, it would take hours to measure it accurately.

Am-241, produces just Alpha particles, and a little Gamma at 60keV. Sealed in a mason jar it would be perfectly safe. More so than as a smoke detector

That is actually a pretty cool looking toy, I will be most interested to see if it can be done at home

Les

Conundrum

Thu Jun 24 2010, 06:20PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

heh.. i have some silver leaf here.

Another amusing trick you can do is use a small amount of phosphor next to the Am241 source, and image the resultant glow with a night vision tube.
Note, will need to be at least a Gen 1 or better, the unamplified IR converters do not work

(but might be useable as homemade 'scope tubes with external coils)
-A

Zamboni

Wed Dec 08 2010, 03:04AM

Registered Member #2836 Joined: Fri Apr 30 2010, 01:24PM
Location:
Posts: 41

Just a sad update. I could not get the required vacuum and the device didn't work. ;=(

Bjørn

Wed Dec 08 2010, 04:28AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Am-241, produces just Alpha particles, and a little Gamma at 60keV. Sealed in a mason jar it would be perfectly safe. More so than as a smoke detector.

I got a 20 year old Am-241 source and it is emitting radiation that passes through thin aluminium plates but is stopped by more than 5 mm aluminium. I am pretty sure it is Beta particles.

Steve Conner

Wed Dec 08 2010, 09:24AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, as any atomic boy scout knows, americium-241 emits alpha particles, not beta particles. But it also emits gamma rays, according to the Wikipedia article.

wrote ...
Americium-241 decays to 237Np emitting alpha particles of 5 different energies, mostly at 5.486 MeV (85.2%) and 5.443 MeV (12.8%). Because many of the resulting states are metastable, they also emit gamma-rays with the discrete energies between 26.3 and 158.5 keV.

Those energies are really more X-rays than gamma rays, they seem in the ballpark for being stopped by 5mm of aluminium.

Scott Fusare

Wed Dec 08 2010, 09:38AM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

Steve McConner wrote ...

Those energies are really more X-rays than gamma rays, they seem in the ballpark for being stopped by 5mm of aluminium.

IIRC gamma photons are differentiated from X-ray photons by their source (nuclear vs. electronic), not their energies.

That said, Americium gamma is located in a range usually associated with lower energy X-rays. This likely accounts for its use in portable XRF equipment.

Proud Mary

Wed Dec 08 2010, 09:47AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

BjÃ¸rn wrote ...

Am-241, produces just Alpha particles, and a little Gamma at 60keV. Sealed in a mason jar it would be perfectly safe. More so than as a smoke detector.

I got a 20 year old Am-241 source and it is emitting radiation that passes through thin aluminium plates but is stopped by more than 5 mm aluminium. I am pretty sure it is Beta particles.

As Steve says, no betas.

Here is the gamma ray spectrum of 241Am, including gammas of the disintegration products which build up over time in any Am sample starting from the date of its isolation and purification. Thus we can calculate the date of purification of An sample by the strength of its Np emissions.

1291801541 543 FT0 241am Gamma Spectrum High Energy

1291801561 543 FT0 241am Gamma Spectrum Low Energy

This link will give you an intuitive understanding of the 241Am spectrum better than words, with the heavy percussion in the final section representing the alphas:

Steve Conner

Wed Dec 08 2010, 10:17AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Are those fancy charts saying that the gamma radiation gets stronger as the source ages and decay products build up? That would explain Bjorn's finding. The first chart goes up to 10^6 counts, the second one goes to 10^9.

Proud Mary

Wed Dec 08 2010, 10:45AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Steve McConner wrote ...

Are those fancy charts saying that the gamma radiation gets stronger as the source ages and decay products build up? That would explain Bjorn's finding. The first chart goes up to 10^6 counts, the second one goes to 10^9.

Yes.

Of more domestic concern is the build up of decay products in thoriated gas mantles - in countries where they are still widely used - which become significantly more radioactive as time goes by from the date of isolation and purification of the thorium feedstock.

________________________________________________ __________________________________________________ ______________________________

Radiation Protection Dosimetry vol 71, issue 1, pp. 53-56
Estimation of Thorium in Gas Mantles to Ascertain Regulatory Compliance

1. G. Sadagopan,
2. K.S.V. Nambi,
3. G. Venkataraman,
4. V.K. Shukla and
5. S. Kayastha

Abstract

In India, stipulated limits for the use of thorium in gas mantles are 600 mg for less than 400 cd rating and 800 mg for greater than 400 cd rating. Although measurements of radioactivity are easily done there are uncertainties in assessing the mass of thorium present because of the age of the thorium, and hence the degree of radioactive disequilibrium in the sample, is unknown. This paper describes the detailed non-destructive gamma spectrometric measurements performed on mantle samples from 18 different manufacturers and verification by neutron activation analysis and presents estimates of thorium in them. Five of these samples were also subjected to gravimetric analysis and good agreement was obtained. All of the mantles contained thorium in amounts well within the prescribed limits. The results show that about 1/8 by weight of the mantle accounts for the mass of thorium. This factor may be used for a rapid preliminary estimation of thorium in gas mantles in the Indian context.

________________________________________ __________________________________________________ __________________________________

Thorium daughters are removed during initial refining, but start to build up again immediately. 224Ra, 212Bi and 212Pb are vapourised into the surrounding air when the mantle is burning, but start to build up again when the mantle is cold. Were gas mantles still widely used in Britain, I believe the thoriated type would have been banned by now.

I often dream of visiting India to see the famous monazite sands of Ganjam beach, and go to the Koovagam Festival, and perhaps I will get there one of these days.

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