Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
Conner Ruhl
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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Conner Ruhl » Thu Aug 30, 2012 2:01 pm

I don't want to produce pure isotopes in volumes that can be used, I just want to show that the isotopes are present (even if just barely detectable). I keep reading about silver activation on here. If silver can be activated why not other elements?

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Frank Sanns
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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Frank Sanns » Thu Aug 30, 2012 2:27 pm

It is all about detection. The average lab could never detect by weight or chemical method, the levels of activation going on with a fusor. The number of atoms are just too low. Yes, there are methods to do so but short half lives and low concentrations are against you. With radiation detection though, single decays can be detected. This make it a perfect measuring tool for radioisotopes. The activation with a fusor has more to do with proving unequivocally that neutrons were produced and electrical noise from the fusor is eliminated. Quite and elegant detection scheme it is but for any real quantity of isotope it is not.

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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Conner Ruhl » Thu Aug 30, 2012 3:02 pm

If I can show there is radioactivity from an originally stable element, I will have proven that there is now some quantity of isotope in the material. Is this not possible?

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Frank Sanns
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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Frank Sanns » Thu Aug 30, 2012 3:19 pm

It is easily possible with even a feeble neutron source, a moderator like water or polyethylene and a pancake detector.

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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Conner Ruhl » Thu Aug 30, 2012 3:22 pm

Very cool, thanks for the responses!

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Jim Kovalchick
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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Jim Kovalchick » Thu Aug 30, 2012 4:14 pm

It's a common exageration among the high school science fair folks to claim that medical isotope production is a practical use of a fusor.

I believe that IEC fusors by current design concepts don't come close to that. Just because you activated a few atoms to the point of convincing them to whisper to a sensitive radiation detector doesn't mean you changed lead to gold enough that you can see it shine.

Medical isotope production takes some significant fluence. A typical research reactor has a thermal flux on the order of 10+14 n/cm2-sec. That's many orders of magnitude greater than even the big IEC devices that the University of Wisconsin has tinkered with. The flux just isn't there, and no one has a design that comes close to that.

Trying to boost the flux using a subcritical uranium capsule is further along, but still, to make enough stuff to demonstrate practical use as a concept still means fluxes that are a significant challenge. There are certainly regulatory implications of doing that with uranium and ultimately the uranium if exposed enough to do something like this will still end up like fuel out of a fission reactor...very messy.

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Richard Hull
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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Richard Hull » Thu Aug 30, 2012 4:18 pm

You are looking for two things is selecting a neutron activation target when working with a fusor.

1. An element of large cross section for thermal neutrons
2. An element that matches the above criterion and, in its activated state, has a very short half life.

At any given neutron flux you need about 5 half-lives exposure time of the activated element to saturate it to its maximum radioactivity. Elements with activated isotopes with half lives of seconds to a few minutes are all that the average fusor run can deal with. As the fusor has a pitifully low net flux, we seek to saturate what we are bombarding.

Elements that satisfy the above requirements are tough to find.

I have prepared a listing in order of ease of activation with the fusor that can just make about 1 million neutrons isotropic per second. All activation materials are best presented to the neutron bombardment as a metal foil. Some, like number 3 below, are gamma emitters and can do well dissoved in water as a saturated soluable compound.

1. Silver
2. Indium
3. Manganese

Rhodium foil would be the ideal, but is far too costly.

Silver is the easiest and cheapest of all to activate and detect, even with a weak fusor. This is why it is so talked about here. Those who can't afford a neutron detector can use silver activation as proof of performance, but they need to be making over 250,000n/s for easy detection, though 100,000n/s is certainly possible with good technique.

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Fusion is the energy of the future....and it always will be
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Carl Willis
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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Carl Willis » Thu Aug 30, 2012 4:37 pm

The following elements have been activated using amateur fusors and are discussed in this site's archives (search for "activation" in the Neutron Detection forum). Jon Rosenstiel's experiments are the lion's share, and mine pick up most of the remaining handful. The discussions on this subject are quite detailed about instrumentation and technique.

(in no particular order)
Aluminum
Gold
Rhodium
Europium
Silver
Indium
Iodine
Vanadium
Magnesium
Arsenic
Hafnium
Scandium
Selenium
Holmium
Neodymium
Ytterbium
Lanthanum
Germanium
Gallium
Molybdenum
Bromine
Sodium
Samarium
Tungsten
Copper
Manganese
Uranium

(Am I missing any?)

There's more than a decade of good, solid information in the archives.

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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Conner Ruhl » Thu Aug 30, 2012 4:40 pm

Thank you for this! Molybdenum is what is important. I am always astounded by the wealth of information available at this site!

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Re: Medical Isotope Production Using a Neutron Moderator and a Fissionable Capsule

Post by Richard Hull » Thu Aug 30, 2012 6:07 pm

Carl's list includes elements that are tough to activate unless you have a fusor producing well over 1 million n/s or can run your fusor for many minutes to an hour. Not the norm at all!...especially for a newbie.

Some activations in Carl's list are impossible to detect following activation even with a plus ultra fusor without special detection gear and techniques.

If you have a superior, plus ultra fusor that ranks among the best ever run here, working at its peak and a Ge-Li, HpGe detector, all the elements in Carl's list are open to you. Superior fusor = lots of $$$.... Special detectors = lots of $$$. If you are working on a truly low budget or out of a scrap heap for parts and have only a GM counter, you are pretty much stuck with silver and indium.

As Carl noted in an earlier post, you might be able to borrow or use more sophisticated gear if you hook up with some college or professional organization avoiding a number of costs.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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