Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-11-22
2002-11-12
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370040, C250S472100, C250S390010
Reexamination Certificate
active
06479826
ABSTRACT:
BACKGROUND OF THE INVENTION
Semiconductor particle detectors coated with neutron reactive films have shown promise as potential neutron detectors. The device operation is simple and involves a semiconductor diode detector coated with a neutron reactive film that spontaneously emits ionizing radiation upon the interaction with a neutron. The ionizing radiation, preferably in the form of charged particles, can enter the diode detectors and be detected.
Generally, the methods used to recognize neutron interactions within a detector rely on second-order effects. Two very common neutron interactions that are used for a variety of thermal neutron detectors, i.e., neutrons; having energies less than approximately 0.5 eV, are the
10
B(n,&agr;)
7
Li reaction and the
6
Li(n,&agr;)
3
H reaction. The charged-particle reaction products emitted as a result of neutron interactions in B-10 and Li-6 can be easily detected with a charged-particle detector. At higher neutron energies, fission chambers, ionization chambers, devices using He-3, and other arrangements are commonly used. The sensitivity of the detection devices at these higher neutron energies is limited because of the reduced cross section for interactions.
Low atomic number materials such as hydrogen tend to have relatively high elastic scattering cross sections for fast neutrons, and often (n,p) reactions from fast neutrons, i.e., neutrons having energies greater than approximately 500 KeV, interacting in hydrogen-filled materials are manipulated for fast neutron detection.
Semi-insulating (Si) bulk GaAs has been studied as a radiation detector for a variety of applications, but has suffered difficulties due to electric field perturbations in Schottky-based diodes fabricated from the material. Reverse-biased Schottky barrier diodes fabricated from undoped Si GaAs that has been compensated with the deep level EL2 demonstrate an unusually truncated electric field distribution. The electric field in reverse biased Si GaAs diodes is clearly divided into a high electric field region (approximately 10
4
V/cm) and a low electric field region (negligible voltage). The present invention is based on the heretofore unrecognized fact that only a small region near the rectifying contact is actually active under low reverse bias, and secondly, the active region increases in width linearly with applied voltage. The active region width increases on the average as 1 V/m, although the dependence has been observed to range between 0.5-2.0 V/m. Termed the “truncated electric field effect”, the present invention takes advantage of this physical phenomenon.
The present invention addresses the limitations of the prior art in detecting high energy neutrons by providing a GaAs device coated with a hydrogen-rich material such as a polymer having a large cross section for epithermal neutrons.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a device for detecting high energy neutrons, i.e., greater than approximately 500 KeV, even in high radiation fields.
It is another object of the present invention to provide a highly sensitive neutron detector capable of discriminating from other forms of radiation for improved detection accuracy.
Yet another object of the present invention is to provide a neutron detector for use in real-time neutron radiography in high gamma fields, digital fast neutron radiography, and fissile material identification.
A further object of the present invention is to provide a coated semiconductor neutron detector which affords improved detection efficiency at specific neutron energies, spatial resolution of the detected neutrons, neutron energy discrimination, radiation hardness and ease of operation.
This invention contemplates apparatus for detecting neutrons comprising: a semiconductor substrate having first and second opposed surfaces; a layered metal arrangement disposed on the first surface of the semiconductor substrate and forming a rectifying junction; a low resistivity contact layer disposed on the second opposed surface of the semiconductor substrate; a voltage source connected between the layered metal arrangement and the low resistivity contact layer for reverse-biasing rectifying junction; and a thin neutron responsive layer disposed on the low resistivity contact layer and responsive to energetic neutrons incident thereon for providing positive charged particles to the semiconductor substrate.
REFERENCES:
patent: 4419578 (1983-12-01), Kress
patent: 5969359 (1999-10-01), Ruddy et al.
“Semi-Insulating Bulk GaAs as a Semiconductor Thermal-Neutron Imaging Device”, D.S. McGregor et.al., Nuclear Instruments and Methods in Physics Research, 1996, 271-275.
Klann Raymond T.
McGregor Douglas S.
Dvorscak Mark P.
Gottlieb Paul A.
Hannaher Constantine
Israel Andrew
Smith Bradley W.
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