JPH11142521A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radiation detector in which a counting omission caused by a dead time can be corrected with good accuracy with reference to a radiation whose intensity is changed in terms of time. SOLUTION: Radiation counting rates from radiation measuring parts 2, 4 provided with semiconductor detectors 10, 12 whose sensing area is different are input to a computing circuit 6. The computing circuit 6 compares the counting rates from both radiation measuring parts 2, 4 in the form of their ratio or difference so as to find a corrected counting rate. In a process in which their ratio or difference is found, the degree of a reduction in the counting rate caused by a counting omission provided at the respective counting rates is cancelled, and the correction accuracy of the counting omission is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detecting apparatus for measuring a radiation counting rate, and more particularly, to correction of radiation count-down caused by dead time of a radiation measuring section after detecting radiation.

[0002]

2. Description of the Related Art Generally, a radiation detecting apparatus used for measuring a radiation counting rate utilizes an ionization phenomenon or a light emission phenomenon caused by an interaction between radiation and a substance.
For example, the radiation detection device generates an electric pulse by collecting an electric charge generated by ionization by applying an electric field or detecting light emission by a photomultiplier tube, and counts the electric pulse by an electric circuit. Find the radiation count rate.

For example, in a semiconductor radiation detector, a charge depletion layer is provided in a semiconductor, and charges generated in the depletion layer due to the passage of radiation are collected to obtain a pulse output. The pulse has a certain time width in accordance with the distribution position of the electric charge, not at one point, but along the radiation passage path and the moving speed of the electric charge in the semiconductor. Therefore, if the second radiation is incident during the charge collection by the first radiation, the pulses of both radiations cannot be distinguished as two, and the number of detected output pulses is smaller than the number of incident radiation. Can occur. That is, there is a possibility that radiation that has entered in close proximity in time within a certain time (decomposition time) may be counted down.

Further, in a counter tube such as a GM tube, a phenomenon occurs that ions generated by radiation weaken the electric field between the electrodes, making it difficult for discharge to occur. In particular, cations have a larger mass and a lower mobility than electrons, so that the time required for sweeping is longer. Due to such a phenomenon, even in a GM tube or the like, there is a decomposition time in which radiation incident at time intervals shorter than that is counted down.

[0005] Assuming that the count rate obtained by the measurement is N and the decomposition time is τ, the time during which the radiation detection device cannot perform the count operation (dead time) is Nτ, and the ratio of the measurement time to the count rate N is the count rate N. The larger, the higher. In other words, in the measurement of a strong radiation sample, the rate of counting down becomes particularly large.

Assuming that the true count rate without counting down is N ₀ , conventionally, N ₀ is obtained by using the following equation.
Correction of counting down was performed.

N ₀ = N + NN ₀ τ (1) N ₀ = N / (1−Nτ) (2) Note that the measured value N affected by counting down is obtained by modifying equation (1). It is expressed by the following equation obtained by

N = N ₀ / (1 + N ₀ τ) (3)

[0009]

However, the above equation holds under the premise that radiation is incident at regular time intervals. That is, when the count rate changes during the measurement time, there is a problem that an error generally increases. This will be shown using specific numerical examples.

Here, the decomposition time is given by τ = 1.0 × 10
⁻⁴ [seconds], from equation (3), N ₀ = 1.0 × 10
Measurement value N in the case of ³ [cps] N = 9.1 × 10 ² [cp
s] and N ₀ = 1.0 × 10 ⁴ [cps], N = 5.
It becomes 0 × 10 ³ [cps]. When these N are corrected by the equation (2), naturally, each of N ₀ =
1.0 × 10 ³ [cps], N ₀ = 1.0 × 10 ⁴ [cp
s] is obtained.

A problem arises when the counting rate changes during the measurement time. For example, N ₀ = 1.0 × 10 ³ [cps] and N ₀ = 1.
Consider the case of 0 × 10 ⁴ [cps]. In this case, as can be easily understood, N ₀ = 5.5 × 10 ³ [cps] (4) over the entire measurement time. However, the measured value N over the entire measuring time is as follows: N = 9.1 × 10 ² × 0.5 + 5.0 × 10 ³ × 0.5 ≒ 3.0 × 10 ³ [cps] (5) Become. By substituting this value into equation (2) and performing correction, N ₀ = 4.3 × 10 ³ [cps] (6) This value has a large error with respect to the correct value shown by the equation (4). Thus, the conventional correction method for the case where the counting rate changes within the measurement time does not produce a correct result even with the theoretical calculation for the simple case as described above. This is due to the fact that equation (2) is non-linear.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and has as its object to provide a radiation detection apparatus in which the accuracy of correction for counting down caused by dead time of a radiation measurement unit is improved. Improve safety in such areas.

[0013]

According to the present invention, there is provided a radiation detecting apparatus for detecting radiation with different sensitivities and outputting radiation count rates, respectively, and a radiation detecting unit which is caused by dead time of the radiation measuring unit. A count rate correction operation unit for obtaining a dead correction count rate that is a radiation count rate corrected for counting down of radiation, wherein the count rate correction operation unit compares the radiation count rates from the radiation measurement units. And calculating the dead correction count rate.

According to the present invention, when the radiation measuring section detects one radiation, it is accompanied by a dead time in which the radiation cannot be detected for a short time after that. The dead time here is a time interval in which even if a plurality of radiations are incident, only a single event is counted. Therefore, not only the dead time in a narrow sense that the detector does not respond to radiation at all, but also the output pulse wave height is insufficient due to insufficient recovery of the detector from the state where the previous radiation was incident, and electric circuit This includes up to a decomposition time in which the pulse counting operation is not performed.

In the present invention, at least two radiation measuring units having different sensitivities are provided. In a preferred aspect of the present invention, in the plurality of radiation measurement units, the sensitivities differ due to different sizes of sensitive regions for detecting radiation. For example, when the radiation measurement unit employs a semiconductor radiation detector, the size of the sensitive area depends on the area of the semiconductor substrate forming the detection unit. The means for making the sensitivity of the radiation measurement unit different is not limited to the one based on the size of the sensitive area as described above. For example, it is also possible to make the voltage applied to the detection unit different or to use a different detection mechanism. It is possible.

Since the plurality of radiation measurement units have different sensitivities, the radiation counting frequency differs even under the same radiation environment. Therefore, the ratio of the dead time to the measurement time is also different, and therefore, the degree of counting down is also different. In the present invention, the radiation count rates obtained from the plurality of radiation measurement units are compared, and an insensitive correction count rate, which is a radiation count rate in which counting is corrected, is obtained. Generally, the higher the radiation density and the higher the sensitivity of the radiation measurement unit, the greater the rate of counting down. So, for example, standardizing the radiation count rate of each radiation measurement unit based on sensitivity,
These differences increase with radiation density. In the present invention, the dead correction count rate is obtained from such a difference. According to the present invention, in the process of determining the insensitive correction count rate by comparing a plurality of radiation count rates, it is possible to obtain an effect of canceling out or mitigating the influence of the above-described non-linearity of counting.

In the radiation detection apparatus according to the present invention, the count rate correction operation unit obtains a ratio between the radiation count rates output from the plurality of radiation measurement units, based on the ratio of the radiation count rates. The insensitive correction counting rate is obtained.

According to the present invention, the ratio between radiation count rates from a plurality of radiation measurement units is determined. A theoretical value corresponding to the ratio obtained by this measurement can be obtained. The theoretical value is expressed as a function that is monotonic with respect to the true radiation count rate (ie, either a monotonically decreasing function or a monotonically increasing function), and therefore, as a ratio obtained by measurement, as a true radiation count rate. The insensitive correction count rate to be adopted can be uniquely determined.

[0019]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram of a gamma-ray survey meter according to an embodiment of the present invention. The apparatus has two radiation measuring units 2 and 4 for detecting and counting radiation and outputting a radiation counting rate. Radiation measurement unit 2,
The respective radiation count rates output from 4 are calculated by an arithmetic circuit 6
Is input to The processing result in the arithmetic circuit 6, for example, the measurement result such as the radiation count rate is displayed on the display unit 8. The radiation measurement units 2 and 4 have semiconductor detectors 10 and 12, respectively.

These semiconductor detectors use a semiconductor having a planar PN junction parallel to the sensitive surface inside as a sensor. A reverse bias voltage is applied to the PN junction to form a charge depletion layer, and when γ-rays generate pairs of electrons and holes in the charge depletion layer, they move according to the potential gradient in the semiconductor and generate a current. These are respectively output as pulse-like electric signals.

An amplifier 14 is connected to each of the semiconductor detectors 10 and 12. The electric signals amplified by the amplifiers 14 are input to scalers 16 connected to the respective amplifiers 14. The scaler 16 counts a pulse signal, which is a radiation detection signal, in response to an event exceeding a predetermined threshold among the input electric signals.

The scaler 1 for each of the radiation measuring units 2 and 4
The radiation count rate output from 6 is input to the arithmetic circuit 6. In the present apparatus, the arithmetic circuit 6 includes the radiation measuring unit 2,
A process for correcting the radiation count-down caused by the dead time of No. 4 is performed. That is, the arithmetic circuit 6 has a function as a count rate correction calculation unit, and can calculate the dead correction count rate in which the countdown due to the dead time is corrected. The corrected count rate is converted into, for example, an appropriate radiation dose unit and displayed on the display unit 8 as a measurement result. One of the features of this device is that the radiation measurement units 2 and 4 have different sensitivities. Specifically, the semiconductor detector 10 has a sensitive area of 10 mm square (hereinafter referred to as 10 mm square), that is, 100 mm ² , while the semiconductor detector 12 has
Has a sensitive area of 3 mm square (hereinafter referred to as 3 mm square), that is, 9 mm ² . Thus, the two semiconductor detectors 10 and 12 basically have a sensitivity ratio corresponding to their area ratio.

Due to this difference in sensitivity, the ratio of the radiation counting rates output from the radiation measuring units 2 and 4 is basically the same as that when the semiconductor detectors 10 and 12 are irradiated with the same density of radiation. Should be equal to the area ratio of the vessels 10,12. However, in general, the ratio of the dead time to the measurement time differs between the radiation measurement unit 2 and the radiation measurement unit 4 due to the difference in the count rate due to the sensitivity, and the ratio of the count rate output from them differs from the area ratio. Not be. Specifically, the ratio of the dead time of the radiation measurement unit 2 with high sensitivity is larger than that of the radiation measurement unit 4 with low sensitivity. Therefore, the ratio (count rate of the radiation measurement unit 2 / count rate of the radiation measurement unit 4) usually becomes 100/100 as the density of radiation increases.
It decreases from 9.

FIG. 2 is a graph for explaining how counting efficiency decreases due to counting down when the radiation density increases. Here, the counting efficiency is the ratio of the number of counted radiations to the radiation incident on the sensitive area of the semiconductor detector. When the counting efficiency is represented by η, it is represented by η = N / N ₀ (7), and from Expression (3), η = 1 / (1 + N ₀ τ) (8)

In the following description, in order to clarify the difference in the sensitive area of the semiconductor detector, the true count rate per 1 mm ² (which corresponds to the radiation density) is represented by n
₀ [cps / mm ² ], the count rate affected by counting down is represented by n [cps / mm ² ], and the sensitive area of the semiconductor detector is represented by S [mm ² ]. Then, the equation (8) becomes as follows: η = 1 / (1 + n ₀ Sτ) (9) FIG. 2 shows a semiconductor detector 10 with S = 100 [mm ² ] (hereinafter referred to as S ₁ ) and a semiconductor detector 10 with S = 9 [mm ² ] (hereinafter S _2).
For the semiconductor detector 12 and put) is plotted by taking the n ₀ a η obtained, the horizontal axis (9) below. Here, the decomposition time τ is set to 1 × 10 ⁻⁵ [sec]. As shown in the figure and easily understood from the equation (9), when the radiation density n ₀ increases, the counting efficiency η increases.
Decreases, and the decrease is caused by the semiconductor detector 1 having a large sensitive area.
The curve 50 corresponding to the radiation measurement unit 2 having 0 is
It becomes remarkable earlier than the curve 52 corresponding to the radiation measurement unit 4. The relationship between the curves 50 and 52 is such that the curve 50 is shifted to the right by an amount corresponding to the area ratio between the semiconductor detector 10 and the semiconductor detector 12 to become the curve 52.

In the case where the radiation density n ₀ is constant or stable, for example, in the case of measuring the intensity of a radiation source having a long half-life, the accuracy is conventionally calculated based on equation (9). Good corrections were made. However, this conventional correction has a problem that the error increases when n ₀ changes within the measurement time as described above.

The arithmetic circuit 6 of the present apparatus uses the counting rates from a plurality of semiconductor detectors having different sensitivities to perform correction processing in which the accuracy of the count-down correction is improved. Hereinafter, this correction processing in the present apparatus will be described.

The arithmetic circuit 6 calculates the count rate N output from each of the radiation measuring units 2 and 4 to each semiconductor detector 1.
Divide by the sensitive area S of 0 and 12 to obtain n. Hereinafter, n corresponding to the count rate of the radiation measurement unit ₂ is represented by n ₁ , and n corresponding to the count rate of the radiation measurement unit 4 is represented by n ₂ . It should be noted here that n ₁ and n ₂ are average count rates in a certain measurement time. That is, in order to show the difference from the conventional correction processing for the above problem, that is, the effect of the present apparatus, the following description is based on the assumption that the counting rate changes during the measurement time. Of course, as a special case, the correction processing of the present apparatus is effective even when the count rate is constant over the measurement time.

As described above, the conventional correction has a problem that when the counting rate changes during the measurement time, the error increases due to the non-linear characteristic of the counting efficiency as shown in FIG. . The present apparatus performs two measurements which are affected by the above-described nonlinearity, a count rate N ₁ (or n ₁ ) obtained from the radiation measurement unit 2 and a count rate N ₂ (or n ₂ ) obtained from the radiation measurement unit 4. The value is used to mitigate the effects of each other's nonlinearity. That is, the principles of the present apparatus, since each measurements were affected by the common count rate change, comparison of N ₁ and N _2, or based on a comparison of n ₁ and n _2, each measurement The effect of the nonlinearity on the value can be partially canceled.
Here, the comparison of the measurement values obtained from the two radiation measurement units should be handled mathematically in the form of the difference or ratio between the two, since each measurement value is affected by the change in the counting rate. Can be.

Specific processing contents will be described. The first method is a ratio r between n ₁ and n ₂ defined by the following equation (10).
Is used to determine the insensitive correction count rate n ₀ based on

R = n ₁ / n ₂ (10) Assuming that r is approximated by a theoretical value r ₀ obtained from the equation (3) and expressed by the following equation (11), n ₀ is obtained.

R ₀ = (1 + n ₀ S ₂ τ) / (1 + n ₀ S ₁ τ) (11) That is, by solving r = r ₀ (12), the measured values n ₁ , n _From the ratio r based on ₂ , it is possible to obtain a count rate n ₀ without counting down. Incidentally, the following equation is obtained by solving the equation (12).

N ₀ = (1−r) / τ (rS ₁ −S ₂ ) (13) The second method is basically the same as the first method, except that the ratio is N _The difference is that it is defined based on ₁ and N ₂ . That is, in this case, the ratio R between N ₁ and N ₂ defined by the following equation (14) is used.

R = N ₁ / N ₂ (14) Here, when R = (S ₁ / S ₂ ) r (15) is substituted into the expression (13), the following expression (16) is obtained. An expression format using R of the insensitive correction count rate n ₀ is obtained.

N ₀ = (S ₁ −RS ₂ ) / τS ₁ S ₂ (R−1) (16) The third method is also basically the same as the above method, The difference is that the ratio n ₀ is obtained from an equation including the difference between N ₁ and N _{2 and} the difference between n ₁ and n ₂ . In this case, n
0 is expressed by the following equation (17).

N ₀ = (n ₂ −n ₁ ) / τ (n ₁ S ₁ −n ₂ S ₂ ) = (n ₂ −n ₁ ) / τ (N ₁ −N ₂ ) (17) as described above, in the arithmetic circuit 6, the N ₁ and N ₂ ratio /
The count rate n _{0 in} which the dead time has been corrected is obtained based on the comparison of the count rates from the two radiation measurement units, such as the difference or the ratio / difference between n ₁ and n ₂ . Hereinafter, n ₀ obtained by this correction will be referred to as n _COR to distinguish it from the true value of n ₀ .

Next, an example of correction processing of the present apparatus will be described. Here, in order to show the effect on the conventional problem to be solved, it is necessary to deal with the case where the radiation density changes during the measurement time. For simplicity, the measurement time is the radiation density n ₀
= To the period t _A of n _0A, it shall become from two of period t _B of the radiation density n ₀ = n _0B. In this case, n ₀ is represented by an average value during the measurement time (t _A + t _B ). Hereinafter, the n ₀
Is expressed as <n ₀ >. That is, _{<n 0> = (n 0A} t A + n 0B t B) / (t A + t B) ......... (18). On the other hand, n _COR represented by the equations (13), (16), and (17) indicates that the measured values of N ₁ , N _2, etc. already include temporal changes during the measurement time as described above. So
There is no need to perform averaging again.

FIG. 3 is a graph showing a correction result by the present apparatus. Here, by fixing t _A and t the time ratio t _B / t _A of _B, and n _0A, it employs the n _0B a variable corresponding to the horizontal axis the change of the true value <n _0>. The vertical axis is
This is the correction rate θ defined by the following equation.

Θ = n _COR / <n ₀ > (19) In this figure, t _B / t _A = 1 and n _0A = 1.0 × 10 ⁴
[Cps / mm ² ], τ = 1 × 10 ⁻⁵ [sec]. A curve 60 is a graph of θ by the present apparatus represented by the equation (19). FIG. 2 also shows, for comparison, a correction rate θ when the conventional correction using the equation (2) is performed on the respective count rates of the radiation measurement units 2 and 4. Specifically, a curve 62 is a result of the conventional correction using only the count rates N ₁ and n ₁ from the radiation measurement unit 2, and θ = n ₁ / {(1−N ₁ τ) <n ₀ >}. ... (20) are plotted. Curve 64
Is the result of the conventional correction using only the count rates N ₂ and n ₂ from the radiation measurement unit 4, and θ = n ₂ / {(1−N ₂ τ) <n ₀ >} (21) The result calculated by is plotted.

It is desirable that the correction rate θ is basically close to 1. Both θ obtained by the present apparatus and θ obtained by the conventional correction become substantially 1 when n _0B is close to n _0A , indicating that good correction is performed. Note that the range of n _{0B to} n _{0A is} a range in which the conventional correction processing is effective. Than n _0B is n _0B = n _0A
Θ gradually decreases from θ = 1 when moving away from θ, and θ closer to 1 is obtained, indicating that more preferable correction is performed. For example, in the present apparatus, n _0B = 8.0 × 10 ²
In the range of ~ 2.0 × 10 ⁴ [cps / mm ² ], θ
= 1.0 (± 6%), but the same correction accuracy can be obtained by using the conventional curve 62 with n _0B = 6.0 × 10 ^{3 to} 1.7.
× 10 ⁴ [cps / mm ² ], and in the conventional curve 64, n
_0B = 4.0 × 10 ^{3 to} 2.0 × 10 ⁴ [cps / mm ² ]
It can be obtained only in a much narrower range than this device.

For example, the range in which the accuracy of ± 6% can be obtained is
In this device, the ratio between n _0B and n _0A is within a range of 10 times or more. At normal measurement intervals, it is considered sufficient to be able to cope with such a temporal change in radiation density, that is, a dynamic range.

[0043] Further, the conventional theta, when n _0B leaves the n _0B = n _0A, while decreasing, in this apparatus, n _0B <~
In the range of 1.0 × 10 ³ [cps / mm ² ], the characteristic is that θ increases from 1. This is because conventional devices,
This apparatus is the same in the sense that θ deviates from 1 and the correction accuracy deteriorates. However, the characteristics of the present apparatus in this range are different from the conventional apparatus in that n _COR , that is, n ₀ obtained by the correction is evaluated to be larger than the true value, and the radiation control is led to the safe side. It can be said that it is a feature.

FIG. 4 is another graph showing a correction result by the present apparatus. Here, the ratio t _B / t _A is changed while n _0A and n _0B are fixed. That is, the ratio t _B / t _A is adopted as a variable corresponding to the change of the true value <n ₀ > on the horizontal axis. The vertical axis is the same as in FIG. In this figure, n _0A = 1.0 × 10 ⁴ [cps / mm ² ], n _0B = 1.
0 × 10 ³ [cps / mm ² ] and τ = 1 × 10 ⁻⁵ [sec]. Curve 70, with respect to _{t B / t A (18)} , (19)
It is a plot of θ calculated using the equation. Further, FIG. 4 also shows a correction rate θ by the conventional correction for comparison, similarly to FIG. Specifically, the curve 72 is θ obtained by the conventional correction using only the count rates N ₁ and n ₁ from the radiation measurement unit 2, and the curve 74 is the count rates N ₂ and n ₂ from the radiation measurement unit 4. Θ based on conventional correction using only Note that the value of θ at the ratio t _B / t _A = 1 in FIG. 4 corresponds to the value at n _0B = 1.0 × 10 ³ [cps / mm ² ] in FIG.

In each of the curves 70 to 74, as the ratio t _B / t _A is closer to 0, θ is closer to 1 and is better. This is because t _B / t _A is 0
, The constant radiation density (n
₀ = t _A ). However, as the ratio t _B / t _A increases and the average effect of different radiation densities cannot be ignored, θ due to each correction is at least n _0B = 1.0 × 10 ³ [cp shown in FIG.
s / mm ² ]. Then, as the ratio t _B / t _A further increases and approaches ∽, the condition approaches a constant radiation density (constant at n ₀ = t _B ) again, and each θ approaches 1 again.

As described above, the good correction rate of the present apparatus shown in FIG. 3 does not hold only at the ratio t _B / t _A = 1, but holds at any ratio t _B / t _A. is there.

Further, for example, a decrease in the correction factor θ due to the conventional correction can be ignored only in a limited narrow range of the ratio t _B / t _A. That is, in most of the remaining cases, the correction rate is greatly reduced. Therefore, for example, when a burst of radiation, that is, a very strong radiation is generated for a short time tε, and the remaining time has a low radiation density,
<N ₀ > is evaluated only low and has a problem in safety management.
If this is to be accurately captured by a conventional correction method, the measurement time must be sufficiently reduced to about tε. On the other hand, in the present apparatus, the correction rate θ is about 1 or more and the radiation dose is not underestimated, regardless of the duration of such burst radiation. It is safe.

The arithmetic circuit 6 of the present apparatus performs the above-described correction processing, and displays the result on the display unit 8. Alternatively, it may be input to a recording device (not shown) and recorded.

Although the above-described apparatus has only two radiation measuring units, the present invention also includes a configuration having three or more radiation measuring units having mutually different sensitivities. For example, in such a configuration, a range of <n ₀ > in which a good correction rate θ can be obtained, which is different for each combination of the radiation measurement units, is switched and selected according to the measured count rate, and used. Good counting correction can be performed in a wider range.

[0050]

As described above, according to the radiation detector of the present invention, a plurality of radiation measuring units having different sensitivities are provided, and the counting rate correction operation unit calculates the ratio of the radiation counting rate from each radiation measuring unit. A comparison is made in the form of a difference, and a dead correction counting rate in which the counting down of radiation caused by the dead time is corrected is obtained. As a result, the effect of counting down included in each radiation counting rate is
The effect is obtained that cancellation is performed and the accuracy of the radiation counting rate is improved, or underestimation is avoided.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a gamma-ray survey meter according to an embodiment of the present invention.

FIG. 2 is a graph illustrating a state of a decrease in counting efficiency due to counting down when the radiation density increases.

FIG. 3 is a graph showing a correction rate θ by the present apparatus;
The intensity of one of the two intensities of the time-averaged radiation is displayed on the horizontal axis.

FIG. 4 is a graph showing a correction rate θ by the present apparatus;
The time ratio of radiation of two intensities is displayed on the horizontal axis.

[Explanation of symbols]

2,4 radiation measuring unit, 6 arithmetic circuit, 8 display unit, 1
0,12 semiconductor detector, 14 amplifier, 16 scaler.

Claims (3)

[Claims] 1. A radiation detecting apparatus for measuring a radiation counting rate, comprising: a plurality of radiation measuring units for detecting radiation with mutually different sensitivities and outputting radiation counting rates, respectively; and radiation caused by dead time of the radiation measuring unit. And a count rate correction operation unit for calculating a dead correction count rate that is a radiation count rate corrected for counting down, wherein the count rate correction operation unit compares the radiation count rates from the radiation measurement units. Determining the insensitive correction count rate by using the radiation detection apparatus. 2. The radiation detection apparatus according to claim 1, wherein the plurality of radiation measurement units have different sensitivities due to different sizes of sensitive regions for detecting radiation. Detection device. 3. The radiation detection apparatus according to claim 1, wherein the count rate correction operation unit obtains a ratio between the radiation count rates output from the plurality of radiation measurement units, and calculates a ratio of the radiation count rates. Calculating the insensitive correction count rate on the basis of: