FAQ - Activation? - What detection gear is needed or desired

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Richard Hull
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FAQ - Activation? - What detection gear is needed or desired

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Let us assume you are doing activation. It is expected that, just like fusion, you are expected to prove that you have, indeed, via neutron bombardment, made the non-radioactive material radioactive by creating a radioactive isotope within it.

What will I have to detect? What are the ideals detectors? How do you get the best shot at detecting and reporting your activation to advantage?

What will I have to detect?

For the most part, as an amateur, you will have two activation radiations that will herald successful activation. Beta particle radiation and Gamma-ray radiation. Neutron activated materials typically emit...
1. Beta particles only
2. Gamma rays only
3. Beta and Gamma rays

The third emission is the most common in activated isotopes of the neutron bombarded material. For those who have lots of neutrons or decent flux, you can pick and choose from a larger group of materials to activate than folks with lower output fusors. Thus, you can choose what particles or rays you wish to sniff out of the reaction.

1. Beta Particles are the easiest and cheapest to detect when investing in detection gear.
2. Gamma rays are the most expensive and difficult to detect in a highly accurate reporting manner.

What are the ideal detectors?

Beat particles - These are easily detected by a Geiger counter and its probe. With low energy betas, a 2-inch diameter mica windowed pancake probe is ideal. However, low energy betas are not the norm in activated isotopes. Such Betas are usually a large fraction of a million electron volts in energy or more, (.5MeV - 2.5MeV). As such, a thin metal-walled GM detector like the Victoreen 1B85 tube or one of the many SB-20 or CTC-5 Russian GM tubes are just fine.

Gamma rays - A photomultiplier tube, (PMT), with suitable attached scintillation crystal is the norm here. For just counting gammas one of the low cost plastic scintillators is fine. However if you wish to identify, by gamma ray spectroscopy, specific energy gamma rays, your scintillator must typically be a sodium iodide crystal that is thallium activated. (NaI:Tl). Gammas can be detected with a good GM counter, but as Beta particles are often associated with activation product radiation, (#3 above), a special lead or plastic beta absorber must shield the GM tube from the betas. In addition, GM tube detectors are horribly inefficient gamma detectors allowing 95% or more of the gammas to go right through them without detection.

How do I get the best shot at detecting and reporting my activation effort.

Beta Particles - In the case of Beta particles, an analog meter on a standard GM detector is an integrated guess at the beta emission rate. A digital counter readout with a timed period of collection is much better but adds to the expense if added to an already extant GM counter, externally. For fabulous reporting of beta particles one might employ a data gathering system that counts for small intervals of time and stores the counts over that period and then continues to count for similar intervals over a span of time. This can then be downloaded as a series of counts collected over time and placed an Excel type graph to show the decay of the isotope you have produced. This proof of activation of a specific isotope can be shared with others. I supply such a chart below.Note: left click on image to enlarge

The complexity of detailed and explicit Beta recording and reporting can become moderately expensive and require skills on the part of the experimenter. The beauty of Beta recording is that it can be the least expensive method of detecting and proving activation of all. It is up to you if you use a simple metered GM counter and report your initial CPM reading or go for a much more detailed effort.

Gamma rays - Regardless of method of detection, only the grossly inefficient GM detection method will be inexpensive. A simple plastic scintillator on a PMT hooked to a preamp and digital counter will be complex and somewhat expensive, but capture and count a large fraction of the gamma rays. Unfortunately, such systems have a high background level of detection and this must be taken into consideration in reporting your results. The ideal is to own a good gamma ray spectrometer and report the specific and expected peaks of gamma ray energy associated with the isotope your activation has produced. The expense here can border on $2000-$4000 if you buy new gear for such detection efforts. Most fusioneers with this gear purchase it as working surplus for under $1000

There you have it! The two easiest and least expensive metals to activate are Silver and Indium. Both emit both beta and gamma rays. As such, they are always first choice activation materials.

All the best of luck...

Richard Hull
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A beta decay curve of Rhodium 104 collected on a home built Arduino based, data collection and storage counting system of 5 second interval counts over 10 minutes (600 seconds.) Rhodium 104 half-life = ~46 seconds.
A beta decay curve of Rhodium 104 collected on a home built Arduino based, data collection and storage counting system of 5 second interval counts over 10 minutes (600 seconds.) Rhodium 104 half-life = ~46 seconds.
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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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