JPH05341047A - Effective method for simultaneous measuring of alpha and beta@(3757/24)gamma) ray and associate sensor - Google Patents

Abstract

PURPOSE:To make measurement upon discriminating perfectly alpha and beta(gamma) rays of the gross at the same time with one run of measuring using a waveform discriminating method. CONSTITUTION:A sensor is equipped with composite scintillator consisting of a double combination of ZnS (Ag) scintillator, plastic having a gored short rising (falling) time, stilbene, and BGO or NaI (Tl) scintillator, in which the ZnS (Ag) scintillator is first arranged for a ray source, and then plastic, stilnbene, and BGO or NaI (Tl) scintillator are arranged. Another sensor is fitted with a composite scintillator consisting of a treble combination of ZnS (Ag) scintillator, plastic or stilnbene having a good short rising (falling) time, and BGO or NaI (Tl) scintillator, in which the ZnS (Ag) scintillator is first arranged for a ray source, and then plastic or stilbene is arranged, and finally BGO or NaI (Tl) is arranged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector for measuring the .alpha. And .beta. Three
In the case of multiple combinations, gross α-rays, mainly β-rays, and mainly γ-rays can be measured almost simultaneously at the same time. These measuring methods and detectors are effective in the measurement in which the energy of a solid, liquid, or gas sample is not particularly strict. For example, it can be used as a detector for a radiation monitor such as a survey meter for radiation control, an area monitor, a radioactive gas monitor, and a radioactive dust monitor.

[0002]

2. Description of the Related Art Normally, α and β (γ) rays are measured using dedicated detectors. But,
When it is necessary to simultaneously measure α and β (γ) rays using one detector, a method to obtain from the energy difference using a radiation detector including various scintillators, α ray and β (γ) ray There is a method using a single scintillator or the like (for example, CsI (Tl) or stilbene crystal) capable of discriminating the waveform of the above.

[0003]

When simultaneously measuring α and β (γ) rays with one detector, the method of measuring from the wave height, that is, the difference in energy, is used for both single and compound scintillators. It is difficult to completely distinguish and measure β (γ) rays. On the other hand, as a method for simultaneously measuring α and β (γ) rays by the waveform discrimination method, only an example using a single scintillator has been reported. CsI (Tl) and CsI (N), which are known as scintillators capable of most effectively discriminating the waveform of α and β (γ) rays.
a), stilbene, etc., have about 2-3 FOM (Figure o
f merit) values have been reported. However, at this level, it is not possible to expect stable measurement because the difference in energy, fluctuations in temperature and measurement conditions, etc. affect the discrimination of α and β (γ) rays. That is, the problem to be solved in the present invention is that, when α and β (γ) rays are simultaneously measured, a sufficiently large resolution (F
The purpose is to develop a detector with OM value).

[0004]

A radiation detector using a ZnS (Ag) thin film is almost insensitive to β and γ rays, but extremely sensitive to α rays. Moreover, it has a characteristic that the rising (or falling) time is long. Therefore, it is sensitive to β and γ rays and ZnS (A
Rising (or falling) of β (γ) ray compared to g)
A composite scintillator with a combination of plastic, stilbene, BGO or NaI (Tl) scintillator, whose time is considerably short, is much larger than a single scintillator capable of particle discrimination by waveform discrimination. It is possible to obtain the resolution of α and β (γ) rays. Since a plastic or stilbene scintillator that detects β (γ) rays is composed of elements with a low atomic number, a detector consisting of ZnS (Ag) scintillator and a combination of these scintillators is suitable for simultaneous measurement of α rays and mainly β rays. .. Moreover, since the average atomic number of BGO or NaI (Tl) scintillator is high, the detection efficiency of γ-rays and X-rays is quite high, and the detector consisting of a combination of these scintillators simultaneously measures α-rays and mainly γ-rays and X-rays. Suitable for Moreover, the rise (or fall) time of BGO or NaI (Tl) scintillators is approximately midway between that of ZnS (Ag) scintillators and that of plastic or stilbene scintillators. Therefore, a composite scintillator that combines these scintillators in triplicate is
It becomes possible to measure the lines, mainly β-rays (including γ-rays) and mainly γ-rays (including β-rays) almost simultaneously at the same time.

As an example, ZnS (Ag) thin film and NE1
Fig. 1 shows an overview of the detector when a 02A plastic scintillator (Nuclear Enterprise) is used.
Shown in. Fluorescence emitted by the ZnS (Ag) scintillator by α rays is introduced into the photomultiplier tube (PMT) through the NE102A scintillator. Since the range of α rays is extremely short and is completely absorbed by the ZnS (Ag) thin film,
Only β (γ) rays are absorbed by the NE102A plastic scintillator. At that time, NE10 is generated by β (γ) rays.
The fluorescence emitted by the 2A scintillator is directly introduced into the PMT. Since the rise times (or fall times) of the pulses due to both radiations are considerably different, the two can be easily distinguished by the waveform discrimination method. That is, the rise (or fall) time spectrum is analyzed by the pulse height analyzer (P
MA) or α and β (γ)
The α and β (γ) rays are simultaneously measured by outputting count values from two single channel analyzers (SCA) prepared in the area.

FIG. 1 shows ZnS (Ag) and NE102A.
It is a general view of a detector when using it in combination with a scintillator. Each element is a system in which it is contacted with silicone oil or an optical adhesive, and the whole is used by housing it in an aluminum container or the like except for the window portion of the detector.

In FIG. 1, the thin aluminum evaporation Mylar film has the functions of blocking (blocking) light from the outside, reflecting the fluorescence from the scintillator to improve efficiency, and further protecting the scintillator. Further, when the detector is contaminated, the membrane can be replaced for simple and effective decontamination.

[0008]

EXAMPLE FIG. 2 shows an example of rise time spectra of α and β (γ) rays by the above detector. That is, FIG.
Is a dual combination of ZnS (Ag) / NE102A
3 is a rise time spectrum of α and β (γ) rays measured using a composite scintillator. The horizontal axis represents the channel (rise time: nsec), and the vertical axis represents the number of counts per channel. Discrimination between α rays and β (γ) rays has a very large resolution and is completely performed. The waveform discrimination method is a method developed by Kinbara and Kumahara [S. Kinbara,
T. Kumahara: “A General Purpose Pulse Shape Disc
riminating Circuit ", Nucl. Instr. Methods, 70 , 173
-182 (1969)] was used. The measurement samples are α-radioactivity standard body ( ²⁴⁴ Cm) and β (γ) -radioactivity standard body ( ¹³⁷ Cs).
Table 1 summarizes the measurement results. The resolution (FOM) of the α and β (γ) ray peaks was an extremely large value of about 10. The tailing is almost negligible (about 10 ^-4 or less). The α ray detection efficiency was 44.6% when measured almost in contact with the detector. Moreover, since a ZnS (Ag) scintillator is used,
The background in the α region was extremely low.

[0009]

Further, in the detector in which ZnS (Ag) and stilbene are combined, the FOM of α and β (γ) ray peaks is obtained.
The value was about 8, and a characteristic almost equivalent to that of the above detector obtained by combining with the plastic scintillator was obtained.

On the other hand, the detector in which ZnS (Ag) and BGO are combined is inferior to the above-mentioned detector in resolution (FOM: about 4), but the detection efficiency of γ-rays and X-rays is several times higher. .. In addition, ZnS (Ag) and NaI (T
The detector combining l) is also ZnS (Ag) and BGO.
Has almost the same performance and characteristics as the combined detector.

In FIG. 3, ZnS (A
g) / NE102A / BGO composite scintillator
An example of rise time spectra of α, mainly β and mainly γ rays of ²⁴¹ Am and ⁶⁰ Co is shown. That is, FIG. 3 is a rise time spectrum of α, mainly β and mainly γ rays by a ZnS (Ag) / NE102A / BGO composite scintillator in triple combination. The horizontal axis represents the channel (rise time: nsec), and the vertical axis represents the number of counts per channel. Discrimination between α rays and β and γ rays is almost complete, and discrimination between mainly β rays and mainly γ rays is almost performed. The FOM value of α and mainly β ray peaks was about 5, and the FOM value of β and mainly γ ray peaks was about 4.

[0013]

EFFECTS OF THE INVENTION By discriminating α and β (γ) rays with an extremely large resolution, the following has become possible.

Gross α and β (γ) with one detector
Accurately measure lines at the same time. The background of α rays is extremely low. They are not affected by the magnitude of energy and the influence of each other's radiation (tailing). It is not affected by changes in detector characteristics due to temperature fluctuations.

[Brief description of drawings]

FIG. 1 is a schematic view of a ZnS (Ag) / NE102A composite scintillator detector.

FIG. 2 is a rise time spectrum diagram of α and β (γ) rays measured by using a ZnS (Ag) / NE102A composite scintillator.

FIG. 3 is a rise time spectrum diagram of α, mainly β and mainly γ rays measured by using a ZnS (Ag) / NE102A / BGO composite scintillator.

Claims (4)

[Claims] 1. A ZnS (Ag) scintillator and a plastic, stilbene, BGO or NaI (T) having a considerably short rise (or fall) time by a waveform discrimination method.
l) A method of simultaneously and almost completely distinguishing between the α and β (γ) rays of the gross by using a composite scintillator in which the scintillators are combined doubly. 2. A composite scintillator in which ZnS (Ag) scintillator, plastic or stilbene, BGO or NaI (Tl) scintillator is triple-combined is used to produce gross α rays, mainly β rays (including γ rays), A method to measure γ-rays (including β-rays) almost simultaneously. 3. A ZnS (Ag) scintillator and a plastic, stilbene, BGO or NaI (T) having a considerably short rise (fall) time by a waveform discrimination method.
l) A detector for simultaneously and almost completely distinguishing gross α and β (γ) rays by using a composite scintillator in which a scintillator and a scintillator are combined in a dual manner, and ZnS (Ag) A detector characterized by arranging a scintillator and then a plastic, stilbene, BGO or NaI (Tl) scintillator. 4. A ZnS (Ag) scintillator, a plastic or stilbene having a considerably short rise (fall) time, and BGO or NaI by a waveform discrimination method.
Using a composite scintillator in which (Tl) scintillators are combined in three layers, gross α rays, mainly β rays (including γ rays), and mainly γ rays (including β rays) are almost simultaneously distinguished and measured. The detector is a ZnS (A
g) A detector characterized by arranging a scintillator, then plastic or stilbene, and then BGO or NaI (Tl).