JPH0634762A - Semiconductor type beta-ray measuring device - Google Patents

Abstract

PURPOSE:To easily detect a beta-ray emitting nucleide having a power of energy without using a high degree of technology by measuring a beta-ray emitting gas to be detected, with the use of a semiconductor radioactive ray detector adapted to detect beta-rays having a low power of energy, after the beta-ray emitting gas permeates under a membrane separating process. CONSTITUTION:A plurality of semiconductor type beta-ray detectors are arranged in series on the posterior stage of a separating membrane permeated by a beta-ray emitting gas to be measured and provided in an inflow part in which radioactive fluid flows. Semiconductor detecting elements 3, 4 which become sensitive only to beta-rays having a low power of energy are applied on the inner surface of the housing 3 of each of the detectors, facing together so as to extract beta-ray detection signals by means of electrodes 7, 7'. The detection signals are transmitted through coupling capacitors 10, 10' to preamplifiers 11, 11 and linear amplifiers 12, 12' so as to be amplified. An anticoincidence circuit 13 is connected thereto on the posterior stage thereof, and is then connected thereto with a radioactivity computing means 14 which is then connected to a display 14 for indicating thereon a detected value. The circuit 13 delivers beta-rays only when a unit output is present, so as to largely eliminate affection by background radioactive rays.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring low energy β-ray emitting nuclides using a semiconductor element such as silicon.

[0002]

2. Description of the Related Art Conventional low-energy β-ray emitting nuclides such as "tritium ( ³ H) and carbon ( ¹⁴ C)" are measured by a liquid scintillator after β-ray emission after concentration and separation treatment accompanied by condensation and isotope exchange. It was common to measure the emitted nuclide. This method complicates the concentration and separation process of condensation and isotope exchange, that the measuring device of the liquid scintillator is expensive,
Further, the application range was limited due to the requirement of advanced concentration and separation technology and measurement technology.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-energy low-energy β-ray emission nuclide measuring device that does not require the high-level concentration and separation techniques and measuring techniques that have been conventionally required. is there.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor radiation detector for selectively measuring low energy β-rays after performing a membrane separation process for selectively transmitting a β-ray emission gas to be measured. It can be achieved by measuring at.

[0005]

In the measurement of low energy β-ray emitting nuclides ( ³ H, ¹⁴ C, etc.), how to remove the influence of the interfering nuclides of the measurement is an important point. In the present invention, a gas membrane separation technique is used to simply separate ³ H, ¹⁴ C, etc., and a β-ray measurement has a cell structure in which two semiconductor detection elements facing each other are sensitive only to low-energy β-rays to be measured. Selectively measure β-rays. Further, in the measurement of β rays, an inverse coincidence counting process of two semiconductor detection elements is added to exclude other background radiation (γ rays, cosmic rays, etc.). With this configuration,
It is possible to provide a low-cost low-energy β-ray emission nuclide measuring device that does not require advanced concentration and separation or measurement technology.

[0006]

EXAMPLES The detailed description of the present invention will be given below with reference to examples. FIG. 1 shows an embodiment of the semiconductor low energy β-ray measuring device of the present invention. In this measuring device, semiconductor detecting elements 3 and 4 are provided on the inner surface of a measuring cell composed of a measuring fluid inlet / outlet 1 and a housing 2. The electrode extraction structure of the detection element is not shown (details will be described later). The semiconductor detection elements 3 and 4 are provided in a structure facing the sensitive surface of β rays. Fig. 2 shows the range of β rays in the air. It can be seen that the β-ray energy of ³ H is 18.6 keV and its range is about 5 mm. Therefore, when measuring ³ H, the surface distance (5 in FIG. 1) of the semiconductor detection elements 3 and 4 in FIG. 1 is 5 to 10 mm (1 to 2 times the range).
It means that the structure set to (double) is optimal. That is, since the β-rays emitted from the radionuclide are isotropic, if the interplanar distance between the semiconductor detection elements 3 and 4 is larger than this dimension, the sensitivity to the measurement volume will be significantly reduced.

FIG. 3 shows a semiconductor detection element structure. The pn junction 6 of the semiconductor detection element 3 provided on the inner surface of the housing 2
A reverse bias is applied to the electrode 7 via the electrode 7 and the extraction electrode 7 '. The extraction electrode 7 ′ and the housing 2 are insulated by the insulating material 8. In this reverse bias applied state, the depletion layer 9 spreads adjacent to the pn junction 6. The principle of β-ray detection is that β-ray is depleted layer 9
Charge (electron-hole pair) generated by incident on
To use. Β range of ³ H in silicon is about 2.5μ
m, and if the thickness of the depletion layer 9 can be set to this value, ³ H
Therefore, the β ray of can be selectively measured. The thickness of the pn junction 6 and the electrode 7, which are insensitive layers for β-ray detection, is 0.2 μm.
The following can be produced and can be ignored. The thickness t of the depletion layer depends on the applied bias voltage V and is determined by the following relationship.

[0008]

[Equation 1]

Ρ: Resistivity of semiconductor (Ω · cm) C: Constant When an n-type semiconductor is used, a depletion layer of several μm can be formed by applying a resistance of 50 Ω · cm and a reverse bias of 1V. Background radiation (γ-rays, cosmic rays, etc.) that becomes an obstacle has a large penetrating power, and the influence of the disturbing radiation can be suppressed to a low level by this thin depletion layer.

FIG. 4 shows a block diagram of the measuring circuit of the present invention. A β-ray detection signal is taken out from the semiconductor detection elements 3 and 4 provided facing the inner surface of the housing 2 through the extraction electrode 7 '. V ₁ and V ₂ represent reverse bias applying sections. The respective output signals are passed through the coupling capacitors 10 and 10 'to the preamplifiers 11 and 11' and the linear amplifiers 12 and 1, respectively.
Connect 2 '. An inverse coincidence counting circuit 13, a radioactivity calculator 14, and a display 15 for both output signals are provided at the subsequent stage. The background radiation having a large penetrating power is detected by the semiconductor detection element 3,
Since it passes through both No. 4 and No. 4, there is a high probability that the output signals are simultaneously output from both detection elements. Inverse coincidence counting processing, in which β selection output is performed only when there is a single output, largely eliminates background radiation. By this processing, the influence of disturbing radiation can be further reduced.

FIG. 5 shows a device configuration of the present invention. A separation membrane 21 (a discharge pipe for a substance other than the measurement target is not shown) that allows only the measurement target to permeate is provided in the inflow part of the radioactive fluid, and the semiconductor β-ray measuring instruments 20A, 20B, ... 20
n are arranged in series. With this configuration, sensitivity can be improved n times. As the separation film 21, a palladium alloy film for ³ H, a polyimide film (polymer film) for ¹⁴ C (carbon dioxide), and the like can be applied.

FIG. 6 shows a modification of the present invention, which is a β-ray measuring device 2
0A, 20B, ..., 20n are arranged in parallel to increase the sensitivity. With this configuration, the same high sensitivity can be easily achieved.

The fluid to be measured described above can be designed in the same idea in both gas and liquid. In addition, although the above description uses a silicon semiconductor as an example,
Of course, other semiconductor detection elements such as cadmium telluride can be easily replaced.

By using this embodiment, it is possible to provide a low energy β-ray emitting nuclide measuring device having a simple structure, high sensitivity and low cost.

[0015]

Industrial Applicability According to the present invention, it is possible to provide a practical β-ray emission nuclide measuring device which does not require a high-level concentration and separation technique and a measuring technique and is low in cost.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a semiconductor type low energy β ray measuring device of the present invention.

FIG. 2 is a characteristic diagram showing a β-ray range in air.

FIG. 3 is an explanatory diagram showing a semiconductor detection element structure.

FIG. 4 is a block diagram of a measuring circuit of the present invention.

FIG. 5 is an explanatory diagram showing a device configuration of the present invention.

FIG. 6 is an explanatory diagram showing a modified example of the present invention.

[Explanation of symbols]

2 ... Housing, 3, 4 ... Semiconductor detection element, 7 '... Electrode, 10, 10' ... Coupling capacitor, 11, 1
1 '... Preamplifier, 12, 12' ... Linear amplifier, 13 ...
Inverse coincidence counting circuit, 14 ... Radioactivity calculator, 15 ... Display.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsutoshi Sato 1168 Moriyama-cho, Hitachi-shi, Ibaraki Pref.

Claims (4)

[Claims] 1. A semiconductor device characterized by comprising a β-ray measuring device having a cell structure in which the sensitive surfaces of a plurality of semiconductor detecting elements are faced to each other, and a circuit for simultaneously and inversely measuring output signals of the facing sensing elements. Beta-ray measuring device. 2. The interplanar distance of a cell structure, in which the sensitive surface of the semiconductor detection element faces, according to claim 1, wherein β is a measurement target.
A semiconductor β-ray measuring device that uses a β-ray measuring device that is set within twice the range of rays. 3. The semiconductor type β ray measuring apparatus according to claim 1, wherein a device for introducing a sample through a separation membrane for separating the β ray emitting substance is added. 4. The semiconductor β-ray measuring device according to claim 1, wherein a plurality of β-ray measuring devices are arranged in series or in parallel and a sample is simultaneously introduced.