JPH04320987A - Radioactive contamination detector - Google Patents

Abstract

PURPOSE:To obtain a radioactive contamination detector capable of shortening measurement time and improving drastically a processing ability. CONSTITUTION:A radioactive detector is provided with a radiation detector 1, a contamination counter means 11 to count the pulse signal output from the radiation detector 1 in a set time, a contamination judgment means 14 which compares the count obtained with the contamination counter means 11 and a contamination regulation level to judge contamination. It also has a background counter means 12 to obtain the background by always counting the signal output from the radiation detector 1 in standby and an optimum count time setting means 13 which takes in the latest background level from the background counter means 12 immediately before the measurement initiation, calculates the shortest count time based on the background level and set the calculated count time in the contamination counter means 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive contamination detection apparatus for measuring articles, the body surface of workers, other solids, liquids, gases, etc. in nuclear facilities and the like.

0002

[Prior Art] Figure 3 shows an example of the configuration of a conventional radioactive contamination monitor.
Shown below.

[0003] This radioactive contamination monitor detects radiation emitted from a measurement object with a radiation detector 1, inputs the detected pulse signal to a data processing device 2, and counts the pulse signals to determine contamination. According to the contamination determination result, a signal is output to the contamination presence control processing section 3 or the contamination non-control processing section 4 to perform processing such as an alarm. FIG. 4 shows the operation of the radioactive contamination monitor configured as described above.

In such a device, prior to actual measurement, the counting time T' is inputted to the data processing device 12 from the counting time setting device 5.
is set, and the management level is set from the management level setting device 6. The data processing device 2 counts the background until the measurement target is set. Counting start detection means 7
When a counting start timing signal is input from , pulse signals are counted for a preset counting time T'. NET to subtract the background count value from that count value.
A computation is performed, and the computed value is compared with the contamination control level to determine contamination. When the calculated value exceeds the contamination control level, a signal is output to the contamination control processing section 3, and an alarm or the like is output. Further, when the calculated value is below the contamination control level, a signal is output to the contamination non-control processing section 4, and, for example, a process for carrying out the article to be measured is performed.

By the way, as shown in FIG. 5, the actual radiation detection values are distributed with a predetermined statistical error around the average value at the counting time T'. The data processing device 2 is set to determine that there is contamination when the statistical error exceeds the contamination control level. However, the statistical error increases in proportion to the square root of the number of detected radiation n (number of pulses), so even if the radiation dose of the measurement target does not increase, if the background rises, the statistical error will increase up to the shaded area in Figure 5. It grows and exceeds pollution control levels.

Therefore, in conventional radioactive contamination monitors, the counting time T' is set based on the assumption that there is an upper limit on the background in the measurement environment, so that the statistical error does not exceed the contamination control level even if the background reaches the upper limit. was set to a sufficiently long time.

For this reason, even if the background is sufficiently lower than the expected value, the measurement does not end until a preset counting time has elapsed, resulting in a large loss of measurement time.

[0008]

Therefore, the conventional radioactive contamination monitor has a problem in that the measurement time is large and the measurement time becomes longer than necessary, resulting in a decrease in processing capacity.

The present invention has been made in view of the above-mentioned circumstances, and is based on the method of sequentially determining the shortest counting time within a range where the detectable radioactivity level does not exceed the contamination control level by following background fluctuations. It is an object of the present invention to provide a radioactive contamination detection device that can be set automatically, shortens measurement time, and improves throughput.

0010

[Means for Solving the Problems] In order to achieve the above objects, the present invention provides a radiation detector that outputs a pulse signal according to the amount of incident radiation, and a radiation detector that starts measurement relative to a measurement target. A contamination counting means for counting pulse signals outputted from the contamination counting means in a set counting time, and a contamination determining means for determining contamination by comparing the count value obtained by the contamination counting means with a contamination control level. In the radioactive contamination detection apparatus, a background counting means constantly counts pulse signals outputted from the radiation detector in a standby state with no object to be measured to obtain a current background level; Immediately before starting, the latest background level is taken in from the background counting means, the shortest counting time is calculated based on the background level, and the calculated counting time is set in the contamination counting means. The configuration includes time setting means.

[0011]

According to the present invention, in the standby state, the background level is always updated to the latest value by the background counting means. Then, when the measurement target is set and the measurement is about to start, the latest background level is taken into the optimal counting time setting means, and the radiation level that can be detected by the radiation detector is within a range that does not exceed the contamination control level. The minimum counting time is determined depending on the background level. This counting time is calculated, for example, using the following formula. T=[4nb −4(A−α)/aK]/[{2(A−
α)/aK}2 −4nb/Tb]

[0012] Note that the counting time T is the latest background level nb
, the background counting time is Tb, the contamination control level is A, the arbitrary margin of 0 or more of the contamination control level A is α, the detection efficiency of the radiation detector is a, and the reliability of the count value is K.
It is said that

[0013] Then, this calculated counting time is set in the contamination counting means, and counting starts at the same time as the measurement starts, and counting ends when the newly set counting time has elapsed. A judgment is made.

[0014]

[Embodiment] An embodiment of the present invention will be described below.

FIG. 1 shows functional blocks of a radioactive contamination monitor according to one embodiment. Note that parts having the same functions as those of the monitor shown in FIG. 3 are given the same reference numerals, and detailed explanations will be omitted.

In this embodiment, a data processing device 10 that receives pulse signals from a radiation detector 1 and performs contamination determination includes a contamination counting means 11, a background counting means 12, an optimum counting time calculating means 13, It is configured to include a contamination determining means 14.

The contamination counting means 11 is connected to the counting start detection means 7.
When a measurement start timing signal is input from , the pulse signal from the radiation detector 1 is counted in the counting time T set by the optimum counting time calculating means 13 and the counted value is output to the contamination determining means 14 .

The background counting means 12 counts the pulse signals output from the radiation detector 1 in a state where no object to be measured is set, and detects a background count value.

The optimum counting time calculation means 13 receives a measurement preparation signal from the measurement object setting detection means 15 which detects that the measurement object is ready for measurement relative to the radiation detector 1. When the measurement preparation signal is input, the optimum counting time calculating means 13 takes in the latest background level from the background counting means 12, and calculates the optimum counting time T by executing the following formula. T=[4nb-4(A-α)/aK]
/[{2(A-α)/aK}2-4nb
/Tb ] …(1)

[0020] Note that nb is the latest background level (cps), and Tb is nb
Background counting time (sec) when calculating
A is the contamination control level (Bq/cm2), α is an arbitrary margin of 0 or more of the contamination control level A, and a is the detection efficiency (Bq/cm2) indicating the ratio at which the radiation detector detects the radiation emitted from the measurement target. /cps), and K indicates the reliability (usually 3).

The contamination determination means 14 calculates the background level n from the count value NG inputted from the contamination counting means 11.
A NET operation is performed to subtract b, and the result of this operation is compared with the contamination control level to determine contamination. Here, the principle of calculating the optimal counting time T will be explained.

[0022] Generally, when radiation is counted, statistical errors are included, and this statistical error is the minimum detectable level. When the system is configured to match this detectable minimum level with the pollution control level, the following relational expression holds true. Contamination control level A = detection efficiency a x statistical error
A=a・(K/2)[K/T+{(K/T)2
+4nb (1
/T+1/Tb)}1/2]...(2) When the above equation (2) is solved for T, the equation is obtained by removing the margin α from the equation (1). The operation of this embodiment configured as above will be explained with reference to FIG. 2.

In the standby state where there is no object to be measured, the background is measured. Then, when the measurement target is set and the measurement preparation signal is input, the optimum counting time T is calculated by equation (1) and set in the contamination counting means 11. Next, when a measurement start timing signal is input from the counting start detection means 7, counting is performed for the set counting time T. At this time, the counting time T is the time during which the detectable radiation level of the apparatus is adjusted to the minimum value within a range that does not exceed the contamination control level with respect to the background level immediately before that.

The contamination determining means 14 executes a NET operation to subtract the background level nb from the count value NG, and compares this calculated value with the contamination control level. As a result of this comparison, if the calculated value exceeds the contamination control level, a signal is output to the contamination control processing section 3 to output an alarm or the like. Further, when the calculated value is below the contamination control level, a signal is output to the contamination non-control processing section 4, and, for example, a process for carrying out the article to be measured is performed.

As described above, according to this embodiment, the optimum counting time T for matching the minimum detectable level with the contamination control level is calculated according to the background level using the above equation (1), and the counting time is Since counting is performed at T, it accurately follows background fluctuations and is always adjusted to the shortest counting time, significantly reducing counting time and significantly improving measurement processing capacity compared to conventional methods. can.

In addition, since it accurately follows background fluctuations, even if the background level increases more than expected, it will ensure that the detectable radioactivity level does not exceed the contamination control level. Since radiation can be prevented and normal radiation management can be performed at all times, the reliability of the device can be improved.

In the above embodiment, the counting time T is calculated using equation (1), but the present invention is not limited to calculation using equation (1). Other calculation methods may be used as long as the calculation can determine the optimal counting time T that matches the level.

[0028]

[Effects of the Invention] As detailed above, according to the present invention, the shortest counting time within the range where the detectable radioactivity level does not exceed the contamination control level is sequentially determined by following background fluctuations. It is possible to provide a radioactive contamination detection device that can be configured, shortened measurement time, and greatly improved processing capacity.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram of a radioactive contamination monitor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of the radioactive contamination monitor according to one embodiment.

FIG. 3 is a functional block diagram of a conventional radioactive contamination monitor.

FIG. 4 is an explanatory diagram of the operation of a conventional radioactive contamination monitor.

FIG. 5 is a diagram for explaining the principle of setting the counting time.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...Radiation detector, 10...Data processing device, 11...Contamination counting means, 12...Background counting means, 13...Optimum counting time calculation means, 14...Contamination determination means.

Claims (2)

[Claims] 1. A radiation detector that outputs a pulse signal according to the amount of incident radiation, and a pulse signal output from the radiation detector that starts measurement relative to a measurement target, and is counted at a set counting time. A radioactive contamination detection device is equipped with a contamination counting means for measuring contamination, and a contamination determining means for determining contamination by comparing the count value obtained by the contamination counting means with a contamination control level. a background counting means that constantly counts pulse signals output from the radiation detector in a standby state to obtain the current background level; and immediately before starting the measurement, the latest background level is calculated from the background counting means. and an optimum counting time setting means for calculating the shortest counting time based on the background level and setting the calculated counting time in the contamination counting means. Contamination detection equipment. 2. The optimum counting time setting means sets the latest background level as nb, the background counting time as Tb, the contamination control level as A, an arbitrary margin of 0 or more for the contamination control level A as α, and radiation detection. Let the detection efficiency of the device be a, the reliability of the count value be K, and the counting time T be
T=[4nb −4(A−α)/aK]/[{2(A−
2. The radioactive contamination detection apparatus according to claim 1, wherein the radioactive contamination detection apparatus is calculated by the following calculation.