Calibration and operation of a neutron time-of-flight scintillator array on nova Page: 3 of 12
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The neutron energy spectrum from inertial confinement fusion (ICF) targets provides
important information about the distribution function of the reacting deuterium or tritium
ions. For example, the spectrum may contain information about the temperature,' areal
density,2,3 and fluid motion of the reacting ions." Because the neutron production time is
typically ; 1 ns, the spectrum can be obtained from time-of-flight (TOF) measurements. In
many ICF targets, the yield is too low to obtain accurate spectra using conventional current-
mode TOF detectors.' Single-neutron-interaction detector arrays', can be used to increase
sensitivity while maintaining good time resolution in order to extend neutron spectroscopy
to low-yield targets.
The Tion ("Tee-ion") detector array was designed to obtain neutron spectra from targets
on the Nova laser at Livermore. Each detector channel consists of a scintillator, photomul-
tiplier, constant-fraction discriminator, and time-to-digital convertor (TDC) connected to
a data acquisition system. Details of the detector and electronics are available elsewhere.8
Tion covers neutron yields from 2 x 106 to 2 x 109 using three interchangeable sets of 1020
scintillators with volumes of 0.16, 0.79, or 3.53 cm3, thus spanning the gap between the
Large Neutron Scintillator Array7 (LaNSA) and nTOF detectors on Nova.' In this paper,
we describe the detector calibration and data analysis procedure, and compare Tion results
with those of a current-mode TOF detector.
The detector calibration includes the detector response time, deadtime correction, time
differences between channels, and neutron scattering effects. The TDCs (LeCroy model
1879) are operated with 2.8-ns sampling in order to record x-rays as well as d-d neutrons
within their 512-bin memory. X-rays provide a time fiducial and resolution check on most
Nova shots. The width of the x-ray peak is typically 4 ns FWHM.
After receiving a "hit," a TDC channel cannot record another signal for an interval2
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Chrien, R. E.; Klare, K. A. & Murphy, T. J. Calibration and operation of a neutron time-of-flight scintillator array on nova, article, December 31, 1995; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc667123/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.