Speaker
Dr
Feng LI
(USTC)
Description
In recent years, the increasing neutron yields of ICF implosions have made it possible to attempt measurements of low yield secondary neutrons. The secondary neutron energy spectra from ICF targets can be used to diagnose the temperature or areal density (ρR) of the fuel. Because the neutron emission time is short (≤1 ns), the spectra can be obtained from time-of-flight (TOF) measurements. But the yields from these secondary reactions are too low for accurate spectra from conventional current-mode TOF detectors. Single-hit neutron detector arrays are used to increase sensitivity while maintaining good time resolution for low-yield targets.
A 960-channel detector array is designed to obtain neutron spectra from targets on SG-III prototype laser facility in China. It consists of 960 channels of a neutron sensitive plastic scintillator (BC422 type) coupled to a photomultiplier tube (PMT) and data acquisition electronics. Every PMT is followed by a discriminator, TDC, Shaper and ADC to allow the measurement of neutron arrival time as well as pulse amplitude. The array is capable of measuring yields as low as 4×105 DT neutrons (100 detected hits) with resolution of 1.0 ns (90 keV for 14.1MeV DT neutrons with 16.67-m flight path).
In the ICF experiments, the secondary neutrons arrive at the detector array after X and gamma rays, and before the primary neutrons. All these uninterested particles can produce pulses in scintillators and PMTs. And they can not be shielded completely. To ensure the proper functioning of the single-hit-mode neutron detectors array, a timing controller module is in need either. It will supply relevant control signals for the electronics system.
The whole system should be properly designed, tested and calibrated to obtain the accurate secondary neutron spectra.
Author
Dr
Feng LI
(USTC)
