252Cf fission-neutron spectrum using a simplified time-of-flight setup: An advanced teaching laboratory experiment
Decay scheme of 252Cf with branching ratios indicated (see Ref. 10 ).
The neutron-ToF setup. (a) Schematic, detectors not shown. (b) Picture with detectors in place, neutron flight path of 79 cm. The lead shielding normally placed around the source region has been removed for the schematic and the photograph. The brass bar shown alongside the box in the picture is the neutron shadow bar (see text).
(a) Schematic of electronics setup for n-ToF utilizing standard NIM electronics modules and a gated 1-D MCA with computer-based data acquisition and display. HV = PMT high-voltage supply; CFD = constant fraction discriminator; Delay = variable pulse delay module, 1–100 ns; TAC = time-to-analog converter; MCA = multi-channel pulse-height analyzer. (b) Picture of NIM electronics setup, AC isolation transformer, USB MCA, and data acquisition computer display.
Calculated neutron detection efficiency for typical 2-in. diameter × 2-in. long plastic scintillator (Eljen EJ-200) as a function of the electronic threshold setting in electron-equivalent energy units (see text). Tabulated values are given in Table I .
Typical -ToF spectra using the setup shown in Figs. 2 and 3 : (a) initial ToF spectrum; (b) ToF spectrum with shadow bar inserted.
The 252Cf fission-neutron energy spectrum deduced from the measured n-ToF spectrum: (a) measured spectrum compared with the shape obtained using a Maxwell-Boltzmann-type fission neutron spectrum [Eq. (1) ] for 252Cf with T = 1.4 MeV (see Refs. 11 and 12 ), including the detector efficiency (Fig. 5 ) for the detector size and electronic threshold. The curves have been arbitrarily normalized near ; (b) same as (a) but for a Watt spectral function [Eq. (2) , see Ref. 11 ] with fixed spectral parameters taken from Ref. 30 .
Illustration of PSD using short and long pulse-integration timing gates on the scintillator PMT anode signal input to the CAMAC QDCs.
A 2-D display of the liquid scintillator n-ToF detector PSD, using the multi-parameter nuclear data acquistion program KMAX (see Ref. 24 ), showing separation of the -ray and neutron signals.
Tabulated scintillator efficiency for a 2-in. diameter × 2-in. long plastic Eljen EJ-200 scintillator.
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