High speed detection of thermonuclear neutrons with solid state detectors

Abstract

I n e r t i a l confinement fusion experiments generate thermonuclear neutrons on subnanosecond time scales. To understand the burning o f DT f u e l , we have developed a 14 MeV neutron detector w i t h subnanosecond time response. bulk GaAs w i t h electron-hole recombination times o f 60 ps. by the energy deposited by the neutrons i n t e r a c t i n g i n the detector t h a t create f r e e c a r r i e r s . The f a s t electron hole recombination time o f t h i s material q u i c k l y removes these r a d i a t i o n generated c a r r i e r s from the conduction process r e s u l t i n g i n extremely f a s t response times. The measurements and calculations o f the s e n s i t i v i t y o f these detectors t o 14 MeV neutrons are i n good agreement. The detectors are made o f neutron damaged, The conductivity o f the detector i s modulated I n t r o d u c t i o n The design, construction and t e s t i n g o f subnanosecond neutron detection systems i s a formidable task, but t h i s c a p a b i l i t y i s important t o the understanding o f the physics of i n e r t i a l confinement fusion (ICF) implosion experiments which can produce subnanosecond bursts o f 14 MeV neutrons. consisting o f a high speed detector and s i n g l e shot recording system which record pulses o f neutrons w i t h less than 200 ps time resolution. The detector i s bulk GaAs t h a t has been neutron damaged t o decrease the e l e c t r o n and hole recombination times. This i s important because the speed of response i s a d i r e c t r e s u l t of the recornbination o f r a d i a t i o n induced c a r r i e r s i n the detector, 1.e.. the conductivity o f the detector i s modulated by the i n c i d e n t r a d i a t i o n . c a l c u l a t e the s e n s i t i v i t y of these detectors, one must c a l c u l a t e the power deposition by the neutrons i n the detectors and the f r a c t i o n of t h i s power t h a t i s used t o generate f r e e c a r r i e r s (free c a r r i e r generation r a t e ) . I n addition, the electron and hole recombination times and m o b i l i t i e s must be known and the detector placed i n an environment t h a t mfnimizes the gamma-ray and scattered neutron background. W e have b u i l t a system To The Desian of the Detector System The goal o f t h i s e f f o r t was t o produce a detector t h a t could measure the temporal h i s t o r y o f the thermonuclear burn i n an ICF experiment, not t o measure s i n g l e neutrons w i t h high speed. Computer simulations i n d i c a t e t h a t i d e a l implosions w i l l produce neutron pulses w i t h the FWHM i n the range o f 30 t o 200 ps. This pulse width i s a s e n s i t i v e measure o f the q u a l i t y o f an implosion. demonstrated t h a t we can bui I d sol id-state detectors w i t h FWHM o f less than 60 ps f o r electro-magnetic r a d i a t i o n . This technology has been used d i r e c t l y t o f a b r i c a t e the detector used t o measure neutrons. The detector i s 1 x 1 x 3 mm piece o f GaAs. The damaging was done t o the material...

Neutron penumbral imaging of laser-fusion targets

“…Our recent numerical and theoretical calculations verified the feasibility of neutron penumbral imaging described by Nugent andLuther-Davies (1985, 1986). The advantages over other imaging techniques are that the size of the aperture is large relative to the desired resolution and that the image signal-to-noise ratio (SNR) for small sources improves relative to a pinhole.…”

The physics of solid-state neutron detector materials and geometries

“…In elastic neutron diffraction [35], where the physical and/or magnetic structure of a solid may be determined, tremendous gains [36] in structural refinement and reduced collection times (with usually less sample damage) can be made with a twodimensional channel plate detector [37], analogous to the advances in x-ray diffraction and photoemission techniques with the discovery and use of the two-dimensional channel plate with delay-line detectors [38][39][40]. High-efficiency neutron detection with spatial, temporal and/or energy resolution is important to the amelioration of high-energy physics [41,42], neutron forensics [43], non-proliferation of special nuclear materials [44], nuclear energy [45,46], oil-well logging [47], H 2 O/CO 2 exploration [48], the search for dark matter [49] and inelastic neutron scattering [50]. In these applications, cumbersome and costly post-scattering monochromators, time-of-flight or low-resolution traditional Bonner spectrometer methods could be replaced by compact, portable and low-voltage solidstate detectors that operate at room temperature.…”

“…All solid-state devices that generate and separate e-h pairs do so through a heterostructure geometry [131]. In the context of a solid-state neutron detector, a heterostructure device may be as simple as a single neutron-sensitive dielectric sandwiched between two metallic contacts [46, or as complicated as a stack of gadolinium-coated p-n junctions with back surface field space charge regions. Figure 4 illustrates three heterostructure classes commonly used in solid-state neutron Table 1.…”

Laser Program annual report 1987

“…381). This limitation also limits the area of the detector, 382 and the active volume V of the detector is restricted by the combination of the transit-time limit and capacitance. The active volume can be written as…”