JPS6135385A - Neutron detector - Google Patents

Abstract

PURPOSE:To measure a neutron ray energy spectral image in real time by imposing a moderator around a detector formed by combining a hetero junction deposited with an amorphous semiconductor on the surface of a single crystal semiconductor and a thin boron film. CONSTITUTION:The amorphous silicon film 2 is deposited by a plasma CVD method on the substrate surface of P type single crystal silicon. The thin boron film 3 contg. <10>B at a high concn. is formed on the rear thereof by a plasma CVD method. A metal is thereafter deposited by evaporation thereon as electrodes 5, 6. A reverse bias voltage is impressed to the electrodes 5 and 6 to form a depletion layer in the single crystal silicon substrate. Neutron rays 6 come into said layer and generate <10>B reaction in the film 3 thus generating alpha rays 7. The alpha rays 7 are detected as electric current pulses in the depletion layer. The detecting element 10 is covered by the modulator 11 by which the devie capable of measuring the fast neutron rays is obtd. When the neutron rays 6 come in, the rays arrive at the element 10 by the locus shown in the figure with the moderator 11. The measurement of the neutron ray energy spectral image in real time is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a neutron detection device using a boron thin film.

[Prior art and its problems]

The principle of a semiconductor radiation detector is to form a diode structure using any method such as a PN junction, a semiconductor-metal Schottky junction, or a crystalline semiconductor-amorphous semiconductor heterojunction.
A reverse bias voltage is applied to the diode, thereby expanding a depletion layer in the semiconductor, and electron-hole pairs generated by radiation flying into the depletion layer are counted and detected as current pulses.

Semiconductor materials include germanium (Ge) and silicon (
Currently, silicon (Si) is overwhelmingly used in industrial radiation dosimeters because the material is easily available. Recently, high-purity, high-resistivity silicon has come to be used due to the demand for low-voltage operation.

Regarding radiation, X-rays, α-rays, β-rays, and γ-rays directly generate electron-hole pairs within the semiconductor depletion layer, and can be detected using conventional methods. Since it has no electric charge, it does not have any effect on the orbital electrons or the Coulomb field of the atomic nucleus other than nuclear reactions, and therefore no electron-hole pairs are generated within the semiconductor depletion layer, making it impossible to detect neutron beams using conventional methods. It is. Therefore, as a neutron beam detection method, neutron beams are transmitted through a material with a large neutron absorption cross section, and α rays are generated from the neutron transmutation reaction ζ.
There is a method in which the ray generates electron-hole pairs in the conductor depletion j-, and this is detected to detect the neutron beam.

As a specific example, JOB (n.

There is a method using the α) reaction to detect α rays generated from boron when a neutron beam is incident, according to the reaction shown in the following equation.

'. B(n,α) reaction: '%B+ %n-+;L+
+: He However, boron has an extremely high melting point of 2000° C. or higher, and it is difficult to easily form a single layer of boron. Even if a boron layer could be formed, there was a problem in that the substrate itself, which should detect the alpha rays, would be destroyed or deteriorated due to the high temperature.

Particularly in semiconductor radiation detectors ζ, there is a problem that thermal distortion occurs at high temperatures, resulting in deterioration of device characteristics. In particular, since semiconductors used in radiation detectors have high purity and high specific resistance, a low-temperature process is required in the manufacturing process. In high-purity high-resistivity silicon,
It is said that thermal strain begins to occur at temperatures above 400°C. Therefore, the 800
High temperature processes above °C are not suitable for semiconductor radiation detectors.

For example, a neutron detector combining a boron phosphide layer and a semiconductor PN junction is known, but this has problems in the following points.

■ Because a pyrolysis method is used to form the boron phosphide layer 9
Since the semiconductor substrate is exposed to a high temperature of 00° C., deterioration of semiconductor characteristics is unavoidable for the reasons mentioned above.

(2) Boron isotope 10B is found in nature (IO
B: IIBζ1:4), but even if IOB is added to a higher concentration, phosphine (PH
1) because phosphorus is included in the boron phosphide layer.

The concentration of JOB decreases. Therefore, neutron detection sensitivity decreases.

(2) Since the thickness of the prepared boron phosphide layer is as much as 20 μm, the generated α rays are reduced by self-absorption, and therefore the neutron detection sensitivity is reduced.

As described above, a neutron detection device that combines a boron oxide layer and a semiconductor has problems.

In addition, neutron detectors that do not use semiconductors have complex structures, lack stability, and have low detection sensitivity and poor counting characteristics.Furthermore, neutron detectors that do not use semiconductors are extremely large and heavy. It also has the following drawbacks.

Neutron detection elements have the above-mentioned drawbacks, so if you try to use a moderator to detect fast neutron beams, etc., unless you use a semiconductor detector, the detection part is large and cannot be mounted around it. The moderator installed there is also extremely large and heavy, making it difficult to put it into practical use.

In order to measure fast neutrons of each energy using a moderator, it is necessary to place a moderator with a thickness corresponding to each energy, but the detection element must be miniaturized like a semiconductor. In this case, the amount of moderator will be enormous.

Recently, with the increase in neutron sources such as nuclear reactors and accelerators, we are investigating what kind of neutron beams are being generated, that is, what kind of energy neutron beams are being generated, and are investigating the effects of neutron beams on the human body. There is an urgent need to take appropriate measures.

However, as mentioned above, it is currently difficult to accurately detect fast neutron beams in real time, so a device called a Bonner ball is actually used to detect fast neutron energy spectrum images.

This uses gold (7Au) for the neutron detection part, and surrounding it are several moderators such as polyethylene with different thicknesses to correspond to each energy.
A neutron beam spectrum image is detected using gold activation (19'Au→'''Au).

This will be miniaturized to some extent, but it will only become clear after being irradiated with carbon neutron beams.

It is not measured in real time.

[Purpose of the invention]

The present invention is based on the boron isotope JOB l0B(n, α)
This is a semiconductor neutron detector that uses reactions. This is 10B
Using a boron thin film containing a high concentration of The purpose is to provide a device that can be obtained.

[Key points of the invention]

The present invention has developed the boron isotope 10B, which was previously considered difficult.
A thin boron film containing a high concentration of is formed on the surface of a semiconductor substrate at a low temperature of 200°C or lower, and an amorphous silicon film is deposited on a high resistivity silicon surface at a low temperature of 200°C or lower to form a heterojunction diode structure. In this way, all detection elements were fabricated using a low-temperature process. As a result, a high-sensitivity neutron beam detection element was fabricated without thermally straining the semiconductor substrate or deteriorating its characteristics, and a shape in which moderators of various types with different properties were placed around this element was created. This system uses several or more devices to obtain energy spectrum images of fast neutron beams in real time.

This neutron beam detection part is highly sensitive and small.

Since it has become possible to make it lightweight, it has also become possible to make the moderator smaller and lighter.

[Embodiments of the invention]

FIG. 1 is a cross-sectional view of a neutron beam detection element portion. P-type nest crystal silicon substrate surface! (Amorphous silicon film 2 was deposited by plasma CVD under the following conditions.

・Plasma CVD method gas used: Monosilane (SiH2 (10-H2 base)
[Substrate temperature: 200°C Pressure: 10.0 Torr Applied pressure: 700 V (D, C,) Also, on the back side, a boron thin film 3 containing a high concentration of t(IB) was formed by plasma CVD method.The conditions were as follows. Shown below.

Used Kasunijihora 7 (”BzHs (1000ppmH
2 base)] Substrate temperature: 200℃ Pressure Crab 2. OTorr Applied voltage: 560V (D, C,) After this, metal is deposited as electrodes 5 and 6. A reverse bias voltage is applied to electrodes 5 and 6 to form a depletion layer in the single crystal silicon substrate. Here, the neutron beam 6 enters, causing a B(n1α) reaction in the boron thin film 3, generating α rays 7, which are detected as current pulses within the depletion layer.

In FIG. 2, the detection element 10 of FIG. 1 is covered with a moderator 11 to form a device capable of measuring fast neutron beams. When the neutron beam 6 comes, it causes the moderator 11 to reach the detection element 10 along a trajectory as shown in FIG.

In this example, the measurement neutron beam energy range is 0.0
It was found that 25 eV to 14 MeV is possible.

〔Effect of the invention〕

According to this invention, a neutron beam energy spectrum image can be measured in real time. In addition, it can be used as a monitor to indicate the influence of neutron beams on the human body by changing the thickness of the moderator in several types in accordance with the ICRP recommendations indicating the degree of influence of neutron beams on the human body.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a neutron beam detection element, and FIG. 2 is a sectional view of a detection device using the element of FIG. 1. 1...P-type nest crystal silicon, 2...Amorphous silicon. 3... Boron thin film, 4, 5... Electrode, 6... Neutron beam, 7... α ray, 10... Detection element, 11...
moderator. 'f1 genius 21

Claims (1)

[Claims] 1) A neutron detection device characterized by a detector combining a heterojunction in which an amorphous semiconductor is deposited on the surface of a single crystal semiconductor and a thin boron film, and a moderator placed around the detector.