Sketch of a thermal neutron detector consisting of a silicon detector coupled with a 6LiF neutron converter layer. As the neutron energy is very low, the reaction products are emitted in opposite directions in the laboratory frame. (a) The triton is detected, the alpha is not. (b) The alpha is detected, the triton is not.
Sample calibration spectrum, with a triple alpha source 239Pu, 241Am, 244Cm, placed in front of the silicon detector.
The silicon detector with a neutron converter on top, installed in its frame inside a cardboard box. The box was then sealed with black tape and wrapped in an aluminum foil, for visible light and electromagnetic shielding.
Deposited energy spectrum in the neutron detector with (Si+6LiF) and without (Si) the 1.5 μm 6LiF converter on polystyrene, normalized to the live data acquisition time. The (Si) data are due to gamma background which can be subtracted.
Difference between the two spectra of Fig. 4 , representing the deposited energy spectrum for thermal neutron detection events only. For the meaning of the continuous line see the text.
Test performed six months later, with another identical sample of neutron converter. We used the same calibration parameters of the previous test, and the results are exactly the same as before.
Semi-quantitative GEANT4 simulation (line) of thermal neutrons and gamma interaction with the neutron detector, as compared to measured data (squares).
A sketch of the polyethylene moderator with dimensions.
The polyethylene moderator castle.
Test with a high intensity neutron source. Deposited energy spectrum in the neutron detector, normalized to the live data acquisition time, with two 6LiF converters: 1.5 μm on polystyrene and 1.8 μm on glass. The error bars are within the symbols.
Deposited energy spectrum, in log scale, for three different source configurations: AmBe, 137Cs and 60Co, AmBe and 137Cs and 60Co.
Comparison of spectra taken under three different conditions, namely without neutron source, with source, with source and no LiF converter.
Same spectra of Fig. 12 in log scale. The presence of percent traces of LiF powder onto the silicon detector is proved by the triton peak two orders of magnitude below the true one.
Comparison of spectra taken with one and two LiF converters (one on each Si detector face). During the measurement with one converter some heavy material, close to the silicon detector, was causing gamma scattering. It was removed before the measurement with two converters.
Comparison in log scale between spectra taken with and without scattering material (two PMTs with scintillators) close to the silicon detector.
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