研究実績の概要 |
A gas-type Cylindrical Ion-Pulse Ionization Chamber (CIPIC) was constructed during first year of the project (2 units). The CIPIC is made to register α-particles directly from the 222Rn decay in a filled air sample. The energy resolution of a 2.1% (FWHM) was achieved for the 5.49 MeV α-line from the 222Rn decay. It will be further improved after construction of a protective cover against an acoustic noise and vibration. However, already with the currently achieved resolution the 5.49 MeV α-peak is clearly separated from neighbor peaks from decay of 218Po and 210Po. A typical signal amplitude is about 400mV, and duration is about 8ms. Signals from the CIPIC were fed to a 12bit waveform digitizer La-n10-12USB. The thermal neutron detector was made based on a 0.32mm-thick EJ-426 scintillator sheets (a mixture of LiF and ZnS:Ag ; the Lithium is enriched in 6Li to a 95%; the 6LiF to ZnS:Ag mass ratio is 1:2) produced by Eljen Technology, U.S.A. The thermal neutron detection uses the nuclear reaction 6Li (n,α)3H + 4.78MeV with a cross-section of 941 barns. The light emitted by ZnS:Ag scintillator is detected by a 5-inch Hamamatsu R1250 photomultiplier with wavelength sensitivity that matches well the EJ-426 emission spectrum. Between the EJ-426 sheets and the PMT a light collecting pyramid covered with light reflector sheets (Tyvek paper) was placed. Data acquisition is done using a 14bit CAEN waveform digitizer N6724F.The GEANT4 model of the fast neutron detector (a pseudocumene-based liquid scintillator loaded with 6Li) was prepared.
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