JPS6045833B2 - Radiation measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation measuring device that measures the dose rate in the atmosphere of a radiation detector, and in particular, the present invention relates to a radiation measuring device that measures the dose rate in the atmosphere of a radiation detector, and in particular, to determine the dose rate based on the drift of equipment placed on the front stage side and the half-life of a reference radiation source. The present invention relates to a radiation measuring device having a correction means for correcting attenuation of radiation energy.

When determining the γ-ray dose rate using a radiation detector such as a Nal(Ti) scintillation detector, Nal(Ti)
) The incident gamma ray energy to the crystal is E.

If the pulse distribution function of the energy E from the radiation detector obtained from this is υ (E, Eo), and the dose rate in that atmosphere is D, then D = fυ (E, Eo)G
(E) dE...It is determined by an integral formula such as (1).

It is known that once the operator fG(E) is determined, the dose rate D due to Eo can be found from the spectrum υ(E, Eo). Further, as another example, there is a method of determining υ(E, Eo) using a multi-channel pulse height analyzer to obtain the dose rate D. In this case, D■ΣN(I)G(I)
It is also known to calculate the dose rate using the equation (2).

Here, I is the channel number, N(I) is the counting rate of the I channel, and G(1) is the weight function value for the energy of the I channel. However, even if it is possible to calculate the dose rate D using the above formula, as a practical matter NaI(T
Drift exists in radiation detectors, multichannel pulse hightonalizers, and subsequent equipment, and this appears as changes in characteristics over time, making it impossible to stably and accurately determine dose rates over long periods of time. .

The present invention has been made in view of the above-mentioned circumstances, and is intended to solve the problem of drift of equipment arranged at the front stage in order to obtain a dose rate by adding a reference radiation source that forms a reference spectrum to a radiation detector. The object of the present invention is to provide a radiation measuring device that can stably and accurately determine the dose rate over a long period of time based on the method of equation (2) described above while automatically correcting the above factors.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 10 is a radiation detector such as a NaI (T) scintillation detector, and is provided with a reference radiation source 11 to form a reference spectrum. Because it is necessary to correct the drift of equipment such as power supplies, proportional pulse amplifiers, and multichannel wave height analyzers, we will provide a radioactive substance whose nuclide and intensity are known for the NaI (T) crystal. The source 11 does not necessarily have to be a γ-ray emitter, and a loaded particle radiator such as α-rays and β-rays is provided in an appropriate arrangement with the NaI (T) crystal, giving an apparent γ-ray emitter.
Any reference spectrum may be used as long as it is the same as the radiation dose rate and is easily distinguishable from the spectrum of the object to be measured. For example, the reference radiation source 11 that emits alpha rays with only a single energy is Na
One example is doping into I(T1) crystal.
12 is a high-voltage power supply that is applied to the radiation detector 10; 13 is a proportional pulse amplifier that proportionally amplifies the combined output pulse of the spectrum of the object to be measured and the reference spectrum into a pulse signal that can be processed by subsequent equipment; Reference radiation source 1
This is a multi-channel pulse height analyzer that calculates the number of pulses for one pulse height (energy).

15 stores in advance a reference spectrum radiation dose (hereinafter abbreviated as reference spectrum) of the reference radiation source 11 that does not include drift due to equipment (proportional pulse amplifier 13, etc.) placed before the multiplex height analyzer 14, and this reference a comparison calculator that compares the spectral radiation dose and the spectral radiation dose (hereinafter abbreviated as spectrum) including the drift from the reference radiation source 11 and outputs a deviation amount proportional to the drift;
Reference numeral 16 denotes a weighting function storage device that stores a constant weighting function G(E) for the radiation energy input to the radiation detector 10.

17 is a multi-channel pulse height analyzer 14, a comparison calculator 1
5 and the output signal of the weight function memory 16.

18 is an output device.

Next, the operation of the device configured as above will be explained.

First, the radiation energy of the object to be measured and the reference radiation source 11
The reference radiation energy is supplied as a composite pulse from the radiation detector 10 to the multichannel pulse height analyzer 14 via the proportional pulse amplifier 13. The multi-channel pulse height analyzer 14 specifically extracts reference radiation energy from the combined radiation energy and inputs it into the comparison calculator 15 . On the other hand, the subsequent dose rate calculator 17 is supplied with the combined radiation energy spectrum. In this case, assuming that the reference spectrum of the reference radiation source 11 is N''(1) and the combined total spectrum is N(1), the net γ-ray dose rate D! is obtained.

In this equation (3), G(1) is the energy EI corresponding to the I channel from the weighting function G(E) (where E=0 to Max) prepared in advance by the weighting function memory 16. The value G(EI) is selected and stored. 1
1:d. Since the correspondence of EI varies depending on the radiation detector 10, amplifier 13, etc., this is compared with the reference spectrum radiation dose of the reference radiation source 11 predetermined by the comparator 5 and the reference radiation of 11 channels from the multiple wave height analyzer 14. The spectral radiation dose including the drift of the source 11 is compared, and the amount of deviation corresponding to the drift is extracted and supplied to the dose rate calculator 17.

Now, as shown in FIG. 2, the reference spectrum of the reference radiation source 11 is a, the spectrum of the object to be measured is b, and their combined spectrum is c.

In this reference spectrum a, the peak energy E1 remains unchanged since the reference is known, but due to drift, channel 11 changes to 1.
:I) The weighting function value G(EI) of the energy EI corresponding to the I channel can be found. That is, G(EI) is
●●Mu11A1,LJJLI It is assumed that the weighting function determined by MU11A1, LJJLI is selected as the weighting function for the spectrum c(7)N(1).

This weight function is then supplied to the dose rate calculator 17, where the above-mentioned equation (3) is calculated as follows.

That is, this equation allows accurate measurement of the dose rate D of the object to be measured by calculation that removes the drift of equipment placed before the multichannel pulse height analyzer 14.
Next, FIG. 3 is a block diagram showing another embodiment of the apparatus of the present invention. This device not only performs the drift correction described in FIG. 1, but also corrects the attenuation of the radiation dose due to the half-life of the reference radiation source 1. For this purpose, a clock device 20 is provided in the dose rate calculator 17, and the half-life of the reference radiation source 11 is known in advance.
A time signal is input to the dose rate calculator 17 to correct the attenuation of the reference radiation dose. Next, FIG. 4 shows an example in which the spectrum of the object to be measured and the reference spectrum of the reference radiation source 11 completely overlap.

In this figure, since the peak value 7 of the reference spectrum of the reference radiation source 11 is known in advance, it is set in the comparator 15 as the reference value. On the other hand, if drift occurs in the equipment, the peak value @ of the synthesized spectrum will shift, so if this shift is extracted by the comparator 15, the drift can be easily extracted, and an accurate dose rate excluding the drift can be obtained. be able to. FIG. 5 is a spectrum diagram of the radiation energy of the object to be measured without the reference radiation source 11.

That is, this figure is a spectrum diagram when the reference spectrum is removed from FIG. 4. It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention.

For example, the radiation detector 10 is not limited to a NaI (T1) scintillation detector, but may be any device that faithfully converts incident radiation energy into an electrical signal and outputs it. It is also possible to replace any number or all of the subsequent devices 15 to 18, 20 connected to the multichannel pulse height analyzer 14 with a computer for processing. As described in detail above, according to the present invention, a radiation detector is provided with a known reference radiation source that forms a reference spectrum, and the spectral radiation dose of a specific channel including drift is extracted from the composite spectrum of these detectors and the radiation source. This is compared with a previously known standard spectral radiation dose to determine the amount of deviation corresponding to the drift, and the counting rate is determined from this and a pre-memorized weight function. It is possible to remove the deviation in the spectrum of the measured object due to the equipment and obtain the dose rate stably and accurately over a long period of time.

Moreover, since the half-life of the reference radiation source is known and the attenuation of the radiation dose is also corrected, it becomes possible to correct everything automatically and accurately determine the dose rate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the radiation measuring device according to the present invention, FIG. 2 is a diagram showing a spectrum of count rate with respect to energy, and FIG. 3 is a block diagram illustrating another invention. 4 and 5 are diagrams showing spectra with and without a reference radiation source. 10...Radiation detector, 11...Reference radiation source, 14...Multi-channel pulse height analyzer,
15... Comparison calculator, 16... Load function storage device, 17... Dose rate calculator, 20... Clock device.

Claims (1)

[Claims] 1. A radiation detector that detects a spectrum of radiation energy of an object to be measured, a known reference radiation source that is installed in this radiation detector and forms a reference spectrum, and a radiation detector that generates the reference spectrum from the composite spectrum output from the radiation detector. The amount of drift is determined by comparing a reference spectrum including the drift of a device placed before the analyzer outputted from this analyzer with a reference spectrum of the reference radiation source stored in advance. a comparator to obtain, a weighting function memory for storing a weighting function to be obtained by the radiation energy in a channel of the composite spectrum that is approximately equal to the channel of the peak of the reference spectrum, and attenuation of the radiation dose due to the half-life of the reference radiation source. A clock device that outputs a time signal to correct for A radiation measuring device comprising: a dose rate calculator that corrects and calculates the total dose rate of the radiation detector atmosphere.