Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Patent
1996-06-14
1998-09-29
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
2502521, 25039003, G01T 308, H01L 31115, H01L 3100
Patent
active
RE0359084
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE TECHNOLOGY
The present invention relates to a portable neutron dose meter for use by individuals who are engaged in radiation handling in radiation handling facilities such as nuclear power plants, reprocessing facilities and the like, a neutron exposure dose rate meter for monitoring neutrons within the compounds of neutron handling facilities, and a neutron detector which serves as their detection element, and more specifically it relates to such that employs a semiconductor detector as its neutron detection element.
BACKGROUND TECHNOLOGY
As prior art neutron individual dose meters using semiconductor detection elements, there are such that have been described in Radiation Protection Dosimetry, Vol. 27, No. 3, pp145-156 (1989) (hereinafter referred to as the prior art 1) and in U.S. Pat. No. 322787 as the prior art 2). Because the (hereinafter referred to semiconductor detection elements cannot detect neutrons directly, they manage to detect indirectly the neutrons by means of detecting charged particles which are generated by the interaction of the neutrons with other substances. For this purpose, the structure of the neutron detector in the prior art referred to in the former has a boron layer on the surface of the semiconductor detection element for detecting low energy thermal neutrons, and a polyethylene layer formed on the boron layer for detecting high energy fast neutrons. Further, in front of them, neutron moderator material is disposed to moderate neutron energy. The neutron detector in the prior art referred to in the latter case has a boron layer formed on the surface of a semiconductor detection element likewise the former example, the periphery of which layer is further surrounded by neutron moderator material in order to detect fast neutrons.
On the other hand, many of the prior art neutron exposure dose rate meters for monitoring neutrons in radiation handling facilities employ BF.sub.3 counters or .sup.3 He counters as described in the Japanese Patent Publication 63-235646 (1988) (hereinafter referred to as the prior art 3). It is disclosed, further, in the same publication that, in order to cut thermal neutrons and detect only fast neutrons, said counter is surrounded by neutron moderator, the surface of which is further surrounded by thermal neutron absorber, still further the surface of which is covered by neutron moderator, respectively.
Each country concerned is required to provide for various radiation detectors which satisfy energy response characteristics so that the effective dose equivalent evaluation conforming to the recommendation of the International Committee on Radiological Protection (ICRP) may be performed. Also in Japan, in accordance with the ICRP recommendation, the domestic radiation hazard prevention laws and regulations have been revised in April, 1989. Generally, radiation damages (dose quantities) differ depending on materials, even when they are exposed to radiation of the same energy. The so-called effective dose equivalent refers to a dose value for evaluation which precisely reflects an exposure quantity to neutrons of a human body. In order to implement this effective dose equivalent, it is necessary to survey and evaluate respective quantities of dose of each energy in a human body over a wider spectrum range of energy existing in radiation handling facilities. The range of energy includes a region for thermal neutrons having energy in the thermal neutron region below 0.5 eV, to fast neutrons ranging above 0.5 eV up to 10 MeV. Here, a sensitivity curve with respect to each specific energy is called a response. Since the difference in the effective dose equivalent responses in terms of sensitivities between the thermal neutron region and the MeV region is as large as more than 50 times, it is extremely difficult to implement this required response. The required response will be called as a dose equivalent response hereinunder. In order to satisfy the dose equivalent response, it is important (1) to make the shapes of sensitivity curves to c
REFERENCES:
patent: 4074136 (1978-02-01), Heinzelmann et al.
patent: 4489315 (1984-12-01), Falk et al.
Dale E. Hankins, "Phantoms for Calibrating Albedo Neutron Dosimeters." Health Physics, vol. 39, No. 3 pp. 580-584, Pergamon Press Ltd. Sep. 1980.
Izumi Shigeru
Kaihara Akihasa
Kitaguchi Hiroshi
Hannaher Constantine
Hitachi , Ltd.
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