This is old-hat to those with neutron-generating fusors. But waiting for Carl's Jr. to come on line in the years since the end of my Guilford College fusor has been like recovering from a stroke in many ways: slowly getting all those basic capabilities back again. So it is with activation, where I've repeated the first grade with a simple indium activation last night. Here it is. A piece of indium was irradiated in a stack of polyethylene bricks behind Carl's Jr. and then counted in a gamma spectroscopy setup. The graph shows the resulting background-subtracted spectrum as well as where the expected peaks should be (red = strong peak, blue = weaker peak). The radio-indium peaks show up where expected.
Indium is mostly In-115, whose thermal neutron capture cross-section for neutrons of a room-temperature Maxwellian distribution is 181.6 b and whose resonance integral is about 3 kb. The capture products include In-116m2 (2.18 s) and In-116m1 (54.4 m) in fairly equal proportions, and a smaller amount of In-116 (14 s). In-116m2 decays by isomeric transition to In-116m1; In-116m1 decays by beta emission to tin.
Expected strong gamma radiation from In-116m1 (courtesy of www.nndc.bnl.gov):
416.9 keV (27.7%)
818.7 keV (11.5%)
1097 keV (56%)
1294 keV (84%)
1507 keV (10%)
2112 keV (16%)
Details:
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Irradiation time: 15 min.
Neutron source rate: 450,000 / s
Power: 250 W (50 kV, 5 mA)
Ion Source: magnetron, ~ 20 mA
Sample: ~ 7 g indium metal hammered into a plate about the size of a quarter dollar
Moderator: UHMW polyethylene flux trap, still under construction
Counting equipment: 1 x 1.5" NaI(Tl) scintillator and TN-1705 MCA, calibrated with Co-60 and Cs-137, LabVIEW data retrieval program
Counting interval: 3000 s. immediately following irradiation
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2006-12-15 15:06 Activation of Indium 
(Carl Willis) [Latest: 2006-12-15 16:31]