CN102636804B - Method for measuring gamma/X radiation field intensity and current type semiconductor detection structure - Google Patents

Abstract

The present invention relates to a method for measuring γ/X radiation field intensity and a current-type semiconductor detection structure, which comprises the following steps: 1) using a stray electron filter to filter the stray electrons generated by the interaction between γ/X rays and substances around the detector; The stray electron filter is a low atomic number insulating dielectric material; 2) Measure the electron beam and γ/X rays passing through the stray electron filter with a current-type semiconductor detector, and record the output current of the current-type semiconductor detector; 3 ) Calculate and determine the γ/X radiation field intensity according to the output current of the current-mode semiconductor detector and the current sensitivity of the detector. The invention solves the technical problem in the prior art that the radiation sensitivity of the semiconductor detector cannot be accurately calibrated in the current working mode, so that it cannot be used for the absolute measurement of the gamma/X-ray intensity. The invention realizes accurate calibration of gamma/X radiation sensitivity and absolute measurement of radiation field intensity based on the detection structure of the current type semiconductor detector.

Description

Method for Measuring γ/X Radiation Field Intensity and Current Type Semiconductor Detection Structure

technical field

The invention belongs to radiation detection technology, and in particular relates to a method for measuring γ/X radiation field intensity and a semiconductor detector adopting a current working mode.

Background technique

Semiconductor detectors have outstanding advantages such as fast time response, good energy resolution, high sensitivity, and convenient use. Especially the CVD diamond film detectors developed in recent years (high temperature resistance, working temperature up to 500°C; radiation resistance, 3 orders of magnitude higher than Si-PIN semiconductor detectors), CZT detectors (high Z; gamma High sensitivity), GaN detector (sub-nanosecond time response) with its excellent performance and low noise, become the stable state detector for deep space exploration, synchrotron radiation, strong neutrons, gamma rays, electrons, heavy charged particles and X-rays And pulsed radiation field and complex environment pulsed radiation detection research hotspots, new semiconductor detectors and their applications have become a frontier topic in the current radiation detection field and one of the more ideal detection devices.

Semiconductor detectors have two modes of operation: pulse counting mode and current mode of operation. Compared with the counting semiconductor detector, the semiconductor detector in the current working mode is an ohmic contact type, and has a linear current output above ampere. For weaker radiation fields, detectors in pulse counting mode are usually used. At this time, the detector is directly placed in the radiation field, and the radiation field intensity and energy spectrum distribution are measured through the preamplifier, main amplifier and multi-channel analysis system. When the radiation field is strong or in a pulse state, the pulse counting mode cannot meet the measurement requirements, and a detector with a current working mode is required. At this time, this type of detector is connected with a small current measuring instrument or an oscilloscope to perform time-intensity measurement. Measurement. Regardless of the counting mode or the current mode, when the semiconductor detector measures the radiation field strength, its radiation sensitivity must be calibrated in advance, and then the intensity information is given. However, in the experimental research of gamma/X-ray measurement, it is found that when the gamma/X-ray energy is above 200KeV, it is difficult to obtain accurate sensitivity when the semiconductor detector working in current mode is directly placed in the radiation field to measure gamma/X-ray result. The main reason is that the stray electrons generated by the interaction between γ/X rays and the surrounding materials of the detector enter the detector, making it impossible to carry out accurate experimental calibration of its radiation sensitivity. This difficulty has been perplexing the research and application of semiconductor detectors in current mode. For this reason, since the discovery of semiconductor detectors, it is rare to see semiconductor detectors working in a single current mode for measuring high-current γ/X Reporting of radiation field strength or pulsed gamma/X-ray beam strength. Through years of research, we have found that in such experiments, the strays generated by the surrounding materials of γ/X rays and current type semiconductor detectors (Si-PIN detectors, CZT detectors, GaN detectors, CVD diamond thin film detectors, etc.) The interference signal generated by the electrons entering the detector is the main reason for the increase of the output signal and the inaccurate calibration of the sensitivity. These stray electronic interference signals are sometimes 1 to 3 times higher than the intrinsic response of the detector to the incident γ/X rays. Moreover, the strength of the interference signal is closely related to the measurement environment and the layout of the experiment, making each measurement result different. In order to solve this problem, the use of current-type semiconductor detectors for absolute measurement of γ/X-ray intensity must filter out the interference of external stray electrons in the experiment, and design and adopt a new detection structure based on semiconductor detectors.

Contents of the invention

The purpose of the present invention is to provide a method and a current-type semiconductor detector capable of measuring γ/X radiation field strength, which solves the problem that the semiconductor detector in the prior art cannot accurately calibrate its radiation sensitivity in the current working mode, so that it cannot be used for γ /Technical issues of absolute measurement of X-ray intensity.

Technical solution of the present invention is:

A method for measuring the field strength of gamma/X radiation, which is special in that it includes the following steps:

1] Use a stray electron filter to filter the stray electrons generated by the interaction between γ/X rays and the surrounding substances of the detector; the stray electron filter is an insulating dielectric material with a low atomic number;

2] Measure the electron beam and gamma/X-ray passing through the stray electron filter with the current semiconductor detector, and record the output current of the current semiconductor detector;

3] Calculate and determine the γ/X radiation field intensity according to the output current of the current-mode semiconductor detector and the current sensitivity of the detector.

The thickness of the stray electron filter is determined by adjusting the thickness of the stray electron filter until the signal current output by the detector no longer increases and enters the saturation region.

The thickness of the above-mentioned stray electron filter is determined by the following method: through theoretical calculation and experimental measurement, the thickness of the stray electron filter that can filter the extraneous stray electrons is initially selected, and the Si-PIN detector is used as the calibration detector. The charge collection efficiency of the Si-PIN detector is measured to verify the theoretical calculation and experimental structure, and finally determine the thickness of the stray electron filter.

The above-mentioned stray electron filter is an insulating material, and the insulating material includes polyethylene or polytetrafluoroethylene or bakelite.

The two electrodes of the above-mentioned current type semiconductor detector are in ohmic contact, and its pulse linear current output is greater than 300mA.

A current-type semiconductor detection structure for measuring the intensity of the γ/X radiation field, including a semiconductor detector 2 operating in a current mode, and a stray detector that is close to the front surface of the semiconductor detector 2 and completely covers the sensitive area of the semiconductor detector 2. Electronic filter 1.

It includes an insulating material encapsulation shell 3 for embedding stray electron filter 1 and current-type semiconductor detector 2; two collimation channels 4 are arranged on the encapsulation shell 3, and the semiconductor detector 2 is located in two between collimated channels 4.

Above-mentioned current mode semiconductor detector 2 comprises current mode Si-PIN detector, current mode CZT detector, current mode GaN detector or current mode CVD diamond film detector; described stray electron filter sheet 1 is insulating material, and described The insulating material is polyethylene or polytetrafluoroethylene or bakelite.

The two electrodes of the above-mentioned current type semiconductor detector are in ohmic contact, and its pulse linear current output is greater than 300mA.

The advantages that the present invention has:

The present invention proposes a method for measuring the intensity of the γ/X radiation field and a current-type semiconductor detection structure. It only needs to stick a stray electron filter with a suitable thickness in front of the existing semiconductor detector to eliminate the γ/X radiation field intensity. The influence of stray electrons generated by X-rays around the detection medium on the detection signal, and the influence of the stray electron filter on the signal can be accurately determined through theoretical calculations and experimental measurements. The invention realizes the accurate calibration of the detection structure based on the current-type semiconductor detector to the gamma/X radiation sensitivity and the absolute measurement of the gamma/X radiation field strength, and solves the problem that the semiconductor detector in the prior art cannot be used in the current working mode. The problem of absolute measurement of γ/X radiation field strength.

Description of drawings

Fig. 1 is the structure schematic diagram of the current type semiconductor detection structure based on the current type semiconductor detector of the present invention to measure the gamma/X radiation field strength;

Fig. 2 is a schematic diagram of a calculation model for theoretically calculating the net deposition energy of γ/X radiation in a semiconductor detector.

Figure 3 is the theoretical calculation result of the net deposition energy of 1.25MeV unit γ-ray in a 300μm thick detector (Si-PIN detector and CVD diamond detector) as a function of the thickness of the stray electron filter.

Fig. 4 is the theoretical calculation result of the thickness of the required stray electron filter changing with γ/X-ray energy when the stray electron filter is polytetrafluoroethylene.

In the figure, 1-stray electron filter; 2-semiconductor detector; 3-package shell; 4-collimation channel.

Detailed ways

The present invention proposes a method for measuring γ/X radiation field strength, comprising the following steps:

1] Use a stray electron filter to filter the stray electrons generated by the interaction between γ/X rays and the surrounding materials of the detector; the stray electron filter is a low atomic number insulating medium material, generally polyethylene or polytetrafluoroethylene or bakelite; The low atomic number insulating dielectric material is an insulating dielectric material with an average atomic number less than or equal to 9. The thickness of the required stray electron filter corresponds to the net deposition energy of the unit γ/X ray in the detector, which can be adjusted by adjusting the stray electron The thickness of the electronic filter is determined by measuring the signal current output by the detector at the same time. When the signal current no longer increases with the thickness, the detector signal current reaches the saturation value; when the signal current output by the detector is in the saturation region, The corresponding thickness is the thickness of the required stray electron filter. The thickness of the required stray electron filter can also be determined by the following methods: through theoretical calculation and experiments, the thickness that can filter the extraneous stray electrons is initially selected, and the Si-PIN detector is used as a calibration detector, and by measuring its charge collection Efficiency Theoretical calculations and experimental configurations are verified to determine the required thickness of the stray electron filter.

2] Measure the gamma/X-rays and electron beams passing through the stray electron filter with a current-type semiconductor detector; both electrodes of the current-type semiconductor detector used in the measurement are good ohmic contacts (not Schottky contacts) , its pulse linear current output is greater than 300mA.

Record the output current of the current type semiconductor detector;

Current-mode semiconductor detectors include current-mode Si-PIN detectors, current-mode CZT detectors, current-mode GaN detectors or current-mode CVD diamond film detectors and other current-mode semiconductor detectors.

3] Calculate and determine the γ/X radiation field intensity according to the output current of the current-mode semiconductor detector and the current sensitivity of the detector.

The present invention is a current-type semiconductor detection structure for measuring γ/X radiation field strength, including a semiconductor detector 2 working in a current mode, a stray gas that is close to the front end of the semiconductor detector 2 and completely covers the sensitive area of the semiconductor detector 2 Electronic filter sheet 1, packaging case 3 made of insulating material for embedding stray electronic filter sheet 1 and semiconductor detector 2; packaging case 3 is provided with front and rear two collimation channels 4; the front collimation channel is located in stray The front of the electronic filter 1, the rear collimation channel is located at the back of the semiconductor detector 2, the cross-sectional shape of the collimation channel is consistent with the sensitive area of the semiconductor detector 2 and the area is less than or equal to the sensitive area of the semiconductor detector 2.

为信号电流实验测量值，I_mth为假设载流子被完全收集时的信号电流理论计算值，当聚乙烯杂散电子过滤片厚度小于4mm时，由于干扰信号的存在，输出信号的测量值比计算值大，无法获得正确的实验结果，而聚乙烯杂散电子过滤片厚度取4mm以上值时，可以获得η_Si-PIN为100％，测量结果正确，表明设计的探测结构正确可行。The radiation response sensitivity of the detector can be calculated from its charge collection efficiency to radiation. Si-PIN semiconductor detector, the technology is mature, the substrate Si is a single crystal structure, the purity can reach more than 99.9999%, the probability of the carrier being captured during the transport under the action of the electric field is very small, so it can be approximated that its charge collection The efficiency is 100%. The Si-PIN detector can be used as a calibration detector, and the theoretical calculation and experimental structure can be verified by measuring its charge collection efficiency. Table 1 shows the Si-PIN detector pair with ⁶⁰ The response measurement results of Coγ-rays, where

is the experimental measurement value of the signal current, I _mth is the theoretical calculation value of the signal current when the carrier is completely collected, when the thickness of the polyethylene stray electron filter is less than 4mm, due to the existence of the interference signal, the measured value of the output signal is higher than The calculated value is large, and the correct experimental results cannot be obtained, but when the thickness of the polyethylene stray electron filter is above 4mm, the η _Si-PIN can be obtained as 100%, and the measurement results are correct, indicating that the designed detection structure is correct and feasible.

Table 1

Principle of the present invention:

The core point of the present invention is to put a stray electron filter of appropriate thickness in front of the current-type semiconductor detector, which is mainly used to filter the stray electrons generated by the interaction between gamma/X rays and the surrounding materials of the detector, so that they cannot enter the detector Sensitive media, the thickness of the stray electron filter increases with the increase of γ/X-ray energy. The electrons generated by γ/X rays on the stray electron filter can be accurately determined by calculation and experiment, so that the influence of interference signals on the measurement can be effectively eliminated, and the field intensity of γ/X radiation can be controlled by the semiconductor detector in the current working mode. Measure accurately. The method of determining the thickness of the stray electron filter is as follows: through theoretical calculation and experimental measurement, the thickness of the stray electron filter that can filter the extraneous stray electrons is initially selected, and the Si-PIN detector with a charge collection efficiency of 100% is used as a verification The detector is used to verify the theoretical calculation and experimental structure, and finally determine the required stray electron filter thickness. The stray electron filter thickness is determined by the incident gamma/X-ray energy spectrum and the highest energy. In principle, the higher the ray energy, the thicker the thickness of the stray electron filter required. For a γ/X-ray beam with a given energy distribution, the thickness of the stray electron filter can be given by theoretical calculation and experimental measurement results, corresponding to the net deposition energy of γ/X-ray in the detector or the signal output by the detector The stray electron filter thickness in the saturation region of the current is the required thickness of the stray electron filter.

Claims (7)

1. method of measuring γ/X radiation field intensity is characterized in that: may further comprise the steps:

1] stray electron that produces with stray electron filter filtration γ/X ray and the effect of detector ambient substance; Described stray electron filter is low atomic number insulating medium material;

2] measure electron beam and the γ/X ray that passes from the stray electron filter, the output current of record current type semiconductor detector with the current mode semiconductor detector;

3] according to the output current of current mode semiconductor detector and the current sensitivity calculative determination γ of detector/X radiation field intensity;

The thickness of described stray electron filter is determined in the following way: adjust the thickness of stray electron filter, until the marking current of detector output no longer increases, enter the saturation region;

Perhaps can filter the stray electron filter thickness of external stray electron by theory calculating and experiment measuring initial option, with the Si-PIN detector as the verification detector, theory is calculated and tested structure by the charge collection efficiency of measuring the Si-PIN detector and carry out verification, finally determine the thickness of stray electron filter.

2. the method for measurement according to claim 1 γ/X radiation field intensity, it is characterized in that: described stray electron filter is insulating material, described insulating material comprises tygon or teflon or bakelite.

3. the method for measurement according to claim 1 and 2 γ/X radiation field intensity, it is characterized in that: described current mode semiconductor detector two electrodes are Ohmic contact, its pulse linear current output is greater than 300mA.

4. current mode semiconductor detecting structure of measuring γ/X radiation field intensity, comprise the semiconductor detector (2) that is operated in current-mode, it is characterized in that: also comprise the front end face of being close to semiconductor detector (2) and cover the stray electron filter (1) of semiconductor detector (2) sensitive volume fully;

The thickness of described stray electron filter is determined in the following way: adjust the thickness of stray electron filter, until the marking current of detector output no longer increases, enter the saturation region;

Perhaps can filter the stray electron filter thickness of external stray electron by theory calculating and experiment measuring initial option, with the Si-PIN detector as the verification detector, theory is calculated and tested structure by the charge collection efficiency of measuring the Si-PIN detector and carry out verification, finally determine the thickness of stray electron filter.

5. the current mode semiconductor detecting structure of measurement γ/X radiation field intensity according to claim 4 is characterized in that: also comprise for the insulating material package casing (3) that embeds stray electron filter (1) and current mode semiconductor detector (2); Be provided with former and later two collimation passages (4) on the described package casing (3), described semiconductor detector (2) is positioned between two collimation passages (4).

6. according to claim 4 or the current mode semiconductor detecting structures of 5 described measurement γ/X radiation field intensities, it is characterized in that: described current mode semiconductor detector (2) comprises current mode Si-PIN detector, current mode CZT detector, current mode GaN detector or current mode CVD diamond thin film detector; Described stray electron filter (1) is insulating material, and described insulating material is tygon or teflon or bakelite.

7. according to claim 4 or the current mode semiconductor detecting structures of 5 described measurement γ/X radiation field intensities, it is characterized in that: described current mode semiconductor detector two electrodes are Ohmic contact, and its pulse linear current output is greater than 300mA.

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