JPS59108367A - Semiconductor radiation dosimeter - Google Patents

Abstract

PURPOSE:To magnify moreover the extent of linearity of a radiation dose rate by an SSD of one piece, and to contrive to enhance reliability of the semiconductor radiation dosimeter by a method wherein a loop type control electrode is provided in the shape to surround a main electrode, and a means to change a voltage to be applied to the main electrode and a means to control a voltage to be applied to the control electrode in relation to the respective voltages thereof are provided. CONSTITUTION:A main electrode 2 and a loop type control electrode 3 are formed on the surface on one side of a P type silicon element 1, and an electrode 4 to make ohmic contact is formed on the surface on another side. At this time, in the case when the bias voltage of the main electrode is 5V and 100V, for example, the loop type electrode is controlled respectively, and a depletion layer 5 or 6 is formed. When gamma-rays are entered in the depletion layer 5 or 6 having different volume according to the dose rate, pulses are separated to be counted by a count circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor radiation detector, and in particular to a semiconductor radiation (gamma ray) dosimeter with improved dose linearity.

In general, this type of dosimeter is more reliable as the range in which the count rate is linear with respect to the irradiation gamma ray dose rate, that is, the wider the range of dose direct linearity. is required to be small, lightweight, and low cost.

Conventionally, as this type of dosimeter, one using a GM counter tube as an element for detecting gamma rays is generally known. However, in this case, the region where the dose linearity falls within ±15% is the dose rate range of 10 m R/h to 5 FL/h. When replaced with
Expand to the range R,/h.

In order to further expand this range, it is necessary to prepare dedicated SSDs for each of the low-dose region and the high-dose region.

Therefore, an object of the present invention is to further expand the range of the above-mentioned dose linearity with - SSDs and provide a more reliable gamma-ray dosimeter.

Here, the structure of the 08SD, which describes the operating principle of the SSD, includes a PN junction type and a surface barrier type, both of which are used by forming a depletion layer by applying a reverse bias voltage. When γ-rays pass through the depletion layer of γ-rays, secondary electrons are generated through the photoelectric effect, Compton effect, or electron pair generation, and these secondary electrons further interact with lattice atoms to become electron-positive. A hole pair is generated, which is detected as a current pulse.

Dose linearity means that the number of pulses per unit time (counting rate) generated from the SSD increases in proportion to the magnitude of the dose rate of γ-rays incident on the SSD. That is, the dose rate R is R = 4 j; B μair where 1: constant f: γ-ray flux density E: γ-ray energy μaIr: total Ir: number coefficient, so the counting efficiency f is f = (1-e-μ5il-) where μsi: the absorption coefficient of si, t: the thickness of the depletion layer, the counting rate C is C=fi8=, 2R, S, where S: the surface area of the depletion layer, 2: a constant. , therefore proportional to R.

When the dose rate increases, before the electrons and holes generated in the depletion layer reach the electrode, stains and holes are generated in the next incoming gamma ray, and pulses generated by these electron-hole pairs. A pile-up phenomenon occurs in which individual gamma rays cannot be separated, such as when the next pulse enters the counting circuit before it is counted as one pulse by the counting circuit. Therefore, in order to separate and count the gamma rays that successively enter on the high-dose side, the depletion layer region should be made smaller. but,
In that case, the problem arises that counting efficiency on the low dose side decreases and measurement errors increase.

In order to solve this problem and achieve a reduction in cost, size, and weight, it is sufficient to change the depletion layer volume between the high-dose region and the low-dose region. For this purpose, a method has been considered to expand the range of dose linearity by changing the bias voltage, for example, by changing the bias voltage to 5 V and 100 V to change the depletion layer region. No. 93737)
. In addition, in an SSD equipped with a main electrode that forms a depletion layer sensitive to γ-rays, a ring-shaped control electrode is provided to surround the main electrode, and the voltage applied to this control electrode is applied to the main electrode. It has been found that when the voltage is increased or decreased, the depletion layer region changes in accordance with the voltage change, and an SSD with this configuration is described in a patent application filed on the same date by the present applicant.

In particular, in the 8SD with the above configuration, if the voltage applied to the main electrode is changed to, for example, 5V and 100V, and the voltage of the annular control electrode is adjusted for each voltage, the range of dose direct linearity can be changed. was found to further expand.

According to the present invention, in a semiconductor radiation dosimeter equipped with a secondary main electrode that forms a depletion layer sensitive to radiation, an annular control electrode is provided to surround the main electrode, and the main electrode and means for adjusting the voltage applied to the control electrode for each of the voltages, thereby expanding the range of υ dose linearity. A semiconductor radiation dosimeter (SSD) is provided.

In the SAD according to the present invention, the annular control electrodes are formed around the main electrode on the semiconductor element and spaced apart electrically at a predetermined distance. The rotation electrode can be formed by a method commonly used in semiconductor technology, such as a vacuum evaporation method or a sputtering method. Here, the annular shape does not necessarily have to be circular, but also includes a shape that changes depending on the shape of the main electrode. Therefore, if the main electrode is square, the control electrode is also formed as a square ring.

The control electrode may be in the form of a ring-shaped body or may consist of a plurality of arc-shaped electrode sections. In the latter case, the voltage of each electrode piece can be increased or decreased.

Both a PN junction structure and a surface barrier type structure are effective as the semiconductor element of the SSD of the present invention. Particularly preferred is P-type or N-type silicon.

Varying the bias voltage applied to the main electrode can be accomplished by reverse bias power supplies of different voltages and transfer switches, and increasing or decreasing the voltage applied to the control electrode can be accomplished by conventional means.

Hereinafter, the present invention will be described in detail with reference to the drawings. In the SSD shown in FIGS. 1(a) and 1(b), P
A main electrode 2 and an annular control electrode 3 are formed on one side of the shaped silicon element 1, and an electrode 4 in ohmic contact is formed on the other side. Here, when the bias voltage of the main electrode is, for example, 5V and 100V, the depletion layer 5 or 6 is formed by adjusting the annular control electrode, respectively. Figure 1 (
a) shows the change in the depletion layer due to adjustment of the annular control electrode voltage VB2 when the main electrode voltage vB1 is low. Figures ib show the annular control electrode voltage VB when the main electrode voltage Vold is high.
2 shows the change in the depletion layer due to adjustment of 2. When γ-rays enter the depletion layer 5 or 6, which has a different volume depending on the dose rate, the pulses are separated and counted by the counting circuit 7. show. The radiation source is 137C3. The voltage of each electrode is as follows.

Curve 8-a: VB1=100V VB2=10V 8b: VBI=]00V VB2=200V 9-a: VBI=5V VB2=OV 9-b: VBI=5V vB2-20V Shown in Figure 2 The measurement results show that the range of dose linearity is further expanded by the configuration of the SSD of the present invention.

In particular, since this effect can be obtained with a single SSD, it is expected to be smaller, lighter, and cheaper than the conventional method of connecting multiple SSDs in parallel and increasing or decreasing the number of parallel SSDs depending on the dose rate. can.

Although the present invention has been mainly described with respect to a γ-ray dosimeter, it can also be applied to a β-ray dosimeter.

[Brief explanation of the drawing]

FIG. 1(a) and FIG. 1(b) show an SSD according to the present invention.
3 shows changes in the depletion layer due to voltage adjustment in one specific example. FIG. 2 is a graph showing the measurement results of dose linearity at different voltages. 1... P-type silicon element, 2... Main electrode, 3...
Annular control electrode, 4... electrode, 5, 6... depletion layer, 7
... Counting circuit patent applicant Fuji Electric Research Institute Co., Ltd. Fuji Electric Manufacturing Co., Ltd.

Claims (1)

[Claims] 1) In a semiconductor radiation dosimeter equipped with a main electrode that forms a depletion layer sensitive to radiation, an annular control electrode is provided to surround the main electrode, and the main electrode is provided with an annular control electrode. It is characterized by being configured to include means for changing the applied voltage and means for adjusting the voltage applied to the control electrode for each of the voltages, thereby expanding the range of dose linearity. Semiconductor radiation dosimeter. 2. The dosimeter according to claim 1, wherein the radiation is gamma rays.