Radioactive_Manganese.avi

This 10-minute video follows a home experiment in which radioactive manganese-56 is produced from natural manganese-55 by neutron capture, and detected by gamma spectroscopy and decay-rate analysis. Neutron activation experiments can be accomplished without much difficulty by enterprising amateur scientists, perhaps surprising folks under the impression that access to a nuclear reactor or a major accelerator is required for this kind of thing.

The reactions:
Mn-55(n,g)Mn-56 (production)
Mn-56 = Fe-56 + beta + gamma (decay)

The video has four parts:

(0:00) Two similar manganese dioxide targets are prepared. One target will be irradiated for ~24 hours in a plastic flux trap that will also contain an AmBe source producing about 2000 n/s; the other is marked "B" for "background" and will not be irradiated.

(2:13) The detector and counting system are discussed. In this system, a sodium iodide (NaI:Tl) scintillator is the detector of gamma radiation. A Canberra 556 AIM module is used to gather counts from two sources simultaneously. On "ADC1" is a multichannel scaler that is set to a dwell time of 15 minutes per channel. On "ADC2" is an analog-to-digital converter that digitizes the amplitude of pulses from the detector and bins them accordingly. Both channels are fed by the detector through a common delay-line amplifier. The computer screen simultaneously displays both the time and energy spectra, and I show the calibration of the energy spectrum using check sources.

(5:20) It's now the day after the video started. The irradiated MnO2 target is removed from the neutron flux trap and placed under the scintillation detector. The energy and time spectra are recorded. Some raw data is shown five hours into the count, with telltale features of Mn-56 decay in evidence. Later, off camera, the "background" MnO2 target is counted. The background spectra will be subtracted from those for the irradiated target.

(7:05) Finally, the processed data (with backgrounds subtracted) are shown and discussed. The gamma energy spectrum has a very large and statistically-significant peak at 850 keV, consistent with Mn-56 decay. A smaller peak may be seen at 1800 keV; this is also associated with Mn-56, but is a lower-probability decay product. Also visible are a low-energy continuum from the Compton effect and other downscattering processes. The time spectrum has a decay half-life of 2.6 hours, consistent with Mn-56 decay.

Thanks for watching!

Category:

Science & Technology

Tags:

• neutron
• gamma radiation
• gamma spectroscopy
• scintillation
• radiation
• neutron activation
• nuclear engineering
• physics
• nuclear

[glastheim]

Radiation level high, but not toxic! :)

[Thallium208]

@promet247 The Am-241 sources should be in direct contact with the beryllium. Ideally, you would have a homogenous mixture of the alpha emitter in the beryllium metal, but that is not practical with sealed sources.

[promet247]

@Thallium208 I would like to know if the construction of the neutron source is important in regard to the way the beryllium foil and Am241 are put together --is it better to layer the two together --or better to completely surround the Am241 with the Beryllium or the other way around? also if foil better than solid slabs of Beryllium? Thanks much

[KarbineKyle]

SPECTACULAR! I LOVE your videos! Educational, interesting, informative, professional, and radioactive! Keep up the AWESOME work! =D

- Kyle

[Thallium208]

@promet247 The quantity of radioactivity produced in this experiment is so low that only a shielded detector, a long count time, and the energy spectroscopy technique shown produce statistically significant Mn-56 counts relative to background. I'm afraid trying this with a bare NaI probe and a non-energy-selective counter like a Ludlum 3 would have poor results. Of course, you could always find a stronger source of neutrons...

[promet247]

@Thallium208 would this 24 hr. activation be detectable real time with a Ludlum model 3 with a NaI probe? Would this work as well with manganese metal (powder)?

[ryanlak1234]

@Thallium208 is maganese-56 safe enough to handle with your bare hands?

[Thallium208]

@ryanlak1234 The details of the "neutron oven" aren't really important to its function. Fundamentally all you want is to surround the source and activation sample with as much of a moderating reflector as possible. Polyethylene, wax, and water are very similar in their effectiveness. It depends mostly on what materials are easily at your disposal. The "neutron oven" is part of an old neutron detector, actually, but you could do as well with blocks of polyethylene.

[ryanlak1234]

@Thallium208 Oh by the way could you show us how to build this neutron oven please? Your description of the oven wasn't very specific.

[Thallium208]

@ryanlak1234 Yes, in principle. Of course, the neutron source is very weak, and the only reliable way to detect this reaction would be through gamma rays emitted in the decay of short-lived grandparent U-239. That is probably possible to do with a careful experiment using an HPGe detector, but it would be barely out of the noise.