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Neutron Test Sources Po210+Be or U238+Be?

Posted: Wed Jan 09, 2019 8:24 am
by Enzo Carter
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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Re: Neutron Test Sources Po210+Be or U238+Be?

Posted: Wed Jan 09, 2019 8:52 am
by Enzo Carter
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?

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

Posted: Wed Jan 09, 2019 10:58 am
by Bruce Meagher
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

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

Posted: Wed Jan 09, 2019 11:33 am
by Luke Harrill
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

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

Posted: Wed Jan 09, 2019 5:08 pm
by Richard Hull
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

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

Posted: Wed Jan 09, 2019 6:14 pm
by Rich Feldman
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.
Picture here: viewtopic.php?f=18&t=10004&p=68240#p68240

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

Posted: Thu Jan 10, 2019 7:08 pm
by Dennis P Brown
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.

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

Posted: Thu Jan 10, 2019 8:14 pm
by Enzo Carter
thanks everyone for your constructive feedback
Dennis P Brown wrote: Thu Jan 10, 2019 7:08 pm 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 5:08 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 10:58 am 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 10:58 am 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 10:58 am 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

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

Posted: Fri Jan 11, 2019 2:49 am
by Bruce Meagher
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

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

Posted: Fri Jan 11, 2019 5:40 pm
by Richard Hull
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

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

Posted: Sat Jan 12, 2019 2:49 pm
by Dan Knapp
Dennis stated in an earlier reply that a neutron source could be rented. I don't think one could rent a neutron source without an NRC license. Can he be more specific about this? Was he referring to the Polonium alpha source that Staticmaster leases?

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

Posted: Sun Jan 13, 2019 12:14 am
by Richard Hull
I am sure he was. No single person can get an NRC license for a home neutron source.

Richard Hull

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

Posted: Sun Jan 13, 2019 7:14 am
by Dennis P Brown
Unless rules have changed, the commercial polonium source was available for rental (6 months.) But it was three years ago I looked into it. So, they might not allow it anymore. The neutron flux wasn't dangerous at all. I even saw someone use one to calibrate their neutron detector selling He tubes on ebay. Again, a few years ago so the rules might have changed - still, they didn't discus with me any licence requirement when I discussed ordering one. Again, times might have changed or they forgot to mention that and that would then come up later. I can only talk about what happen when I talked to the company to order one. Then, of course, didn't since I obtained a fusor level power supply. As for who rented it, I assumed (now) it was the Polonium alpha source that Staticmaster leases.

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

Posted: Sun Jan 13, 2019 4:16 pm
by Richard Hull
Polonium is not a neutron source..... Period! Any polonium source over 300uCi (static master) must be controlled leased as a large anti-static alpha source. Each year it must be re-leased as the old source is dead, per se and an exchange unit is sent out to the end user and the old one must be returned to the original seller. No license is required when on lease.

You are not leasing a neutron source.

Richard Hull

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

Posted: Sun Jan 13, 2019 4:45 pm
by John Myers
Sealed sources and/or exempt amounts don't require a license for the person receiving it. I just spent a little time on the NRC site and I don't see anything specific to neutron sources that prevents a licensee from distributing a sealed neutron source to the public.

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

Posted: Sun Jan 13, 2019 6:28 pm
by Dan Knapp
There is no exempt quantity for any neutron source. I spent some time a year or so ago interacting with the NRC on this issue. We were talking with the NRC people about petitioning for establishment of an exempt quantity for Californium-252 (the most commonly used neutron source). This was involved with a company that sells Cf-252 sources. They take back decayed sources from customers, which becomes a nuisance for them in that they have to track them forever. If there were an exempt quantity of Cf-252, they could easily get rid of the decayed sources (sell them as exempt test sources, give them away for a tax writeoff, or even just discard them). The problem is that Cf-252 doesn't just emit neutrons; it is also an alpha source. This is not normally an issue with a Cf-252 neutron source, which is contained in a double welded stainless steel capsule, but for the purpose of establishing an exempt quantity of the isotope, the alpha production becomes the limiting thing. I don't recall the exact numbers, but if you consider that 50 microcuries is a typical exempt amount, the amount of Cf-252 to yield 50 microcuries of neutrons would be many times that amount in terms of alpha activity. If you consider an exempt amount of Cf-252 in terms of alpha activity, it is such a small amount that the neutron flux is uselessly small. We gave up on the issue. Unless someone discovers a new isotope that emits a neutron as a fission fragment with no other radiation production, there will never be an exempt quantity for a neutron emitter.

A Cf-252 source that has decayed to the point of no longer being useful for its original purpose, can still be useful as a test source if one has the required NRC license. But even a general license like a University, for example, would typically have is not sufficient and must still be amended to cover a neutron source. Life is unfortunately never simple. The only neutron test source an amateur is ever likely to be able to have access to would be one improvised from the aforementioned polonium antistatic device with a piece of beryllium.

There is one exception I know of if you by some chance happen to be VERY good friends with a major paving contractor. The big operators use pavement moisture measuring instruments that contain a neutron source (typically Americium/Beryllium). These are very strictly controlled by the NRC for obvious reasons. A paving contractor, unless you are a VERY close friend, is not likely to even admit that they own one; so don't bother asking unless you have a very close friend in the business.

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

Posted: Sun Sep 06, 2020 4:02 pm
by keelan
@richard hull
Dear Richard, if I understand you correctly, the longest lasting most efficient alpha emitter for a neutron source it americium, because it has more activity than uranium and a longer half life than polonium.

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

Posted: Sun Sep 06, 2020 6:45 pm
by Richard Hull
Americium is the best but is not available in the strengths needed to the private individual by NCR regs.

Richard Hull