Neutron Test Sources Po210+Be or U238+Be?

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Enzo Carter
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Neutron Test Sources Po210+Be or U238+Be?

Post by Enzo Carter » Wed Jan 09, 2019 1:24 pm

i have read here that beryllium will produce neutrons if irriated by alphas which are just He nucleuses. i read that Po210 works reasonably well as an alpha source. I googled Po210 and it looks like its alphas are 5.3MeV.

So why don't people use hot U238 and Be. U238 does emit alpha particles at 4-5 MeV not to much of a difference than Po210

I have 6lbs of hot U238 the highest rock at 62,000 cpm

so why don't poeple use the most commen radioactive element (U238) instead of the most dangeruos radioactive element(Po210 is 250000x more toxic than hydrogen cianide.)?
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Enzo Carter
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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Enzo Carter » Wed Jan 09, 2019 1:52 pm

so after thinking about it the answer may be in the half life

U238 is 4.7billion years

Po210 is 138 days

4.7B years / 138 days is 15.6 BILLION times more frequent.

could this be the issue?

Bruce Meagher
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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Bruce Meagher » Wed Jan 09, 2019 3:58 pm

Yes. Look up the specific activity of U238 and Po210. What does this tell us about the two substances? How much U238 would you need to create 1 million alphas/second? Can you find out approximately how many 4 - 5 MeV alphas/second are needed to create one neutron/second with the type of beryllium you purchased? What is the fusion reaction that creates the neutrons in this setup?

Bruce

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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Luke Harrill » Wed Jan 09, 2019 4:33 pm

Really this should have been asked in the new user area, as this is already explained in the FAQ.

viewtopic.php?f=31&t=5316
viewtopic.php?f=31&t=5504

I'm unsure of what you measured it with, but 62kcpm isn't exactly a hot rock.

-Luke Harrill

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Richard Hull
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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Richard Hull » Wed Jan 09, 2019 10:08 pm

This has been answered above, but here is a carry-on.

While 62k is hot enough, that 62 k is not all alpha. Regardless of your GM detection tube, almost 100% of those 62K are Betas! Unless you have a mica windowed GM tube and have it under 1-inch from the rock, you will count 0 alphas and nearly zero gammas. You need to read a lot of books and understand everything about GM tubes before a lot of this becomes clear.

Next, any alphas coming off the rock are surface generated only. Any alpha emission that occurs a few microns below the surface are trapped as helium gas within the rock for millions of years. However, in many porous rock forms, over time, the harmless helium gas can leak out. U rock is fairly safe even at over 150,000 cpm as you will be handling it and close it only on very rare occasions, as needed.

Even radon will be limited for the same reason helium emission is limited. However, if a large enough collection of hot U rock is present (over 25-30 pounds), it is advisable to store it in gasket sealed ammo boxes to avert radon build up in a dwelling, but it is advisable never to even store this sealed up amount inside a home. An outside shed would be far more advisable and desirable.

Few people here would ever need more than a couple of U rock samples to use as check sources. So most of the radon issue vanishes if you just store them in a small jar with a good sealed lid. This can be safely stored in your bedroom in a corner.

100 micorcuries of polonium in a static master is right there going full blast alpha issuing no radon, beta or significant gamma. This is the beauty of Po as it is also virtually totally dead within a year. The hottest possible sample of U rock can never come within 6 orders of magnitude of a static master's alpha emission rate.

Richard Hull
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Rich Feldman
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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Rich Feldman » Wed Jan 09, 2019 11:14 pm

Adding to what RIchard said about alpha particles generated inside of rocks
(or inside of, say, a chunk of Pu-238 oxide in a heat source for RTG).

Alpha particle sources found in consumer products (e.g. Po in Staticmasters, and Am in smoke detectors) have the radioisotope in very thin films, sometimes protected by a very thin non-active film, so nearly half of the alpha emission escapes into air.

Commercial neutron sources (Am-Be or Pu-Be) have the alpha-emitting isotope and the beryllium intimately mixed together, so neutron generating reactions can and do happen at any place within the bulk of the mixture.

Of the alpha sources discussed in this thread, Po-210 has by far the shortest half-life and the highest specific activity. As Enzo discovered already.

A few years ago, I mentioned finding a Staticmaster brush that had contained 50 microcuries of Po-210, when new in 1965.
Had some fun with statistics, looking at tail end of the decay curve.
At some point in 1982 or 1983, the remaining amount of Po-210 decreased from 1 atom to none at all.
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Dennis P Brown
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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Dennis P Brown » Fri Jan 11, 2019 12:08 am

Once again, I will be the person talking safety of materials - beryllium is toxic and should only be handled with gloves (that are disposed of after a single use) and still, wash your hands. The beryllium should be stored in a sealed plastic bag. Disposal is an issue; I assume you have studied that question and have a plan.

Remember, a proper beryllium/polonium source can be rented and has a fair number of neutrons emitted. I considered it, callled the company (they had no issues with a private rental) but I decided to build a fusor instead. Someone here did obtain the source (search the forum) and used it to semi-calibrate their neutron detector. The rented source is sealed and very safe to use. After six months, the source must be returned to the company.

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Enzo Carter
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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Enzo Carter » Fri Jan 11, 2019 1:14 am

thanks everyone for your constructive feedback
Dennis P Brown wrote:
Fri Jan 11, 2019 12:08 am
Once again, I will be the person talking safety of materials - beryllium is toxic and should only be handled with gloves (that are disposed of after a single use) and still, wash your hands. The beryllium should be stored in a sealed plastic bag. Disposal is an issue; I assume you have studied that question and have a plan.
1. plastic bags block alphas
2. disposal will likely be on eBay
3.We go through more gloves than a nurse
Enzo-Gloves-IMG_5212.jpg
Richard Hull wrote:
Wed Jan 09, 2019 10:08 pm
While 62k is hot enough, that 62 k is not all alpha
good point Richard did not think of that
Bruce Meagher wrote:
Wed Jan 09, 2019 3:58 pm
activity of U238 and po210. What does this tell us about the two substances?
specific activity is the activity per quantity
Po210=166 T bq/g
U238=12 k bq/g
So Trillion beats Thousand by a 10 Orders of magnitude. i see now!!!!!
Bruce Meagher wrote:
Wed Jan 09, 2019 3:58 pm
How much U238 would you need to create 1 million alphas/second?
half life u238 = 4.4 ^9 years
how many grams of u238 do we need to release 1M alphas every second?
31.5M sec in year times half life of U238 is 138,758 trillion
that times avagodros number 6.02^23 times atomic weight of U238
= 14 zeros plus 23 zeros is 37 zeros
answer; about 1^37 grams
i suppose Po210 would be 10 orders of magnitude better?
Bruce Meagher wrote:
Wed Jan 09, 2019 3:58 pm
What is the fusion reaction that creates the neutrons in this setup?
Po210 releases alphas of 5 MeV that make contact with the beryllium9 creating Be8 + N

I had to ask google assistant about 210-238 questions

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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Bruce Meagher » Fri Jan 11, 2019 7:49 am

Great job trying to answer my questions. The specific activities you found are accurate, and you correctly observed the huge difference. One thing you might not fully understand yet is what the units mean. A becquerel (Bq) is the unit of radioactivity. 1 Bq = one radioactive disintegration (decay) per second. Specific activity units are radioactivity per unit mass (e.g. Bq / g).

U238’s specific activity of ~12k Bq/g means one gram of U238 will emit 12k alpha particles per second (each disintegration of U238 emits one alpha particle). You would need ~80g of U238 to produce 1 million alpha particles per second. That's about the same mass as 3 silver dollars. Po210 only needs ~6 ng for the same 1 million alpha particles per second. That’s about the same mass as 1/10th of an eyelash. (edit: Oops I made a mistake by 3 orders of magnitude! I believe it's more like 1/10000th of an eyelash)

In physics it’s easy to mess up on the units and be off by orders of magnitude. I do it all the time. It’s wise to think about the answer to see if it makes sense. For example 10^37 grams is larger than the sun.

Finally your fusion reaction is incorrect, but that’s explained in the FAQs linked above.

Admins: feel free to move this thread to the new user chat area if so desired.

Bruce

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Re: Neutron Test Sources Po210+Be or U238+Be?

Post by Richard Hull » Fri Jan 11, 2019 10:40 pm

Bruce noted the physics of things, but then there is the real world.....

That 80 grams of U238 would need to be in a hyper thin shelled, hollow sphere of immense volume with its interior fully evacuated to an interstellar vacuum. With your detector at the center of this sphere, you might actually have 100,000 or less alphas hit the detector each second. Again, a nasty habit of the dense U238 to absorb its own alphas. You would never, under any circumstances, be able to have those 1 million alphas/sec from 80 grams of uranium to actually interact with Be.

Finally, your U238, if in the form of ore is probably 95%++ silicon dioxide. Whatever U238 is in there is also in there with 4-6 other hot alpha emitters, (daughters) and buried so deep that no alphas from 99.99% of all the radioactives in the ore will ever exit the rock.

However, with the little gold strip of Po210 covered with Be foil and pressed against it, you stand a half-way decent chance of having about 40% of all the alphas in that strip actually enter the Be foil and even then.... not all would create neutrons.

It is a tough real world out there and calculation will only take you so far. Material science coupled with a full understanding of nuclear issues helps a lot.

As you enter the work place, you will see this in your paycheck as the U.S. Government, the State, creditors, the power and water companies, etc. take what is a nice salary and whittle it down to scraps you can actually use. The same is true in physics and engineering mathematics the seemingly final math figure is not necessarily the final result.

Richard Hull
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Fusion is the energy of the future....and it always will be
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