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252Cf fission-neutron spectrum using a simplified time-of-flight setup: An advanced teaching laboratory experiment
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Image of Fig. 1.
Fig. 1.

Decay scheme of 252Cf with branching ratios indicated (see Ref. 10 ).

Image of Fig. 2.
Fig. 2.

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).

Image of Fig. 3.
Fig. 3.

(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.

Image of Fig. 4.
Fig. 4.

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 .

Image of Fig. 5.
Fig. 5.

Typical -ToF spectra using the setup shown in Figs. 2 and 3 : (a) initial ToF spectrum; (b) ToF spectrum with shadow bar inserted.

Image of Fig. 6.
Fig. 6.

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 .

Image of Fig. 7.
Fig. 7.

Illustration of PSD using short and long pulse-integration timing gates on the scintillator PMT anode signal input to the CAMAC QDCs.

Image of Fig. 8.
Fig. 8.

NIM-CAMAC electronics (see Refs. 4 and 5 ) used for 2-D computer-based n-ToF data acquisition and a liquid scintillator (Ref. 6 ). Notation is the same as in Fig. 3 , with added CAMAC modules where “ADC” ( = QDC) = charge-to-digital converter.

Image of Fig. 9.
Fig. 9.

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.

Image of Fig. 10.
Fig. 10.

The n-ToF spectrum obtained using the electronics shown in Fig. 7 with a neutron ToF spectrum projected out from the PSD 2-D spectrum (Fig. 9 ).


Generic image for table
Table I.

Tabulated scintillator efficiency for a 2-in. diameter × 2-in. long plastic Eljen EJ-200 scintillator.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: 252Cf fission-neutron spectrum using a simplified time-of-flight setup: An advanced teaching laboratory experiment