JPS6063484A - Radioactivity measuring method - Google Patents

Abstract

PURPOSE:To measure radioactivity efficiently by reducing the volume of an active carbon, a silver alumina, or the like, which is used normally as an adsorber of iodine, with press or the like. CONSTITUTION:The active carbon to which radioactivity is stuck is taken out from a cartridge, and about 10% KC flock or the like is added as a binder, and this active carbon is put in a press frame 3. A press body is operated to apply a proper force with a press mandrel 2, and the volume of the active carbon is reduced. The active carbon is taken out from the press frame once and is put in it again and is pressed again. In the second press, a high collapsing strength is attained because the active carbon is pulverized and the binder is distributed uniformly. The sample subjected to volume reduction by compression is wrapped with a polyethylene bag or the like for the purpose of preventing pollution, and thereafter, the sample is set in a well of a well-type Gl semiconductor detector provided in a shielding body 10 and is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a radioactivity measurement method, and more particularly to a radioactivity measurement method suitable for measuring trace amounts of radioactivity in bamboo.

[Background of the invention]

Activated carbon is used in the iodine removal filters installed in current nuclear power plants.

It is mandatory to extract a portion of this activated carbon (KI-impregnated BC-727) once a year and check its performance. In the test, the sample is packed into a cartridge of a certain thickness, stacked in a certain number of stages, and after aeration of radioactive iodine-131, the radioactivity adsorbed in each stage is measured.
This is a method to evaluate the adsorption performance of activated carbon. Typically, the cartridge used for testing is 4QInm in diameter and 10mm thick.
, the number of stages is 10. At this time, for iodine-131,
A detection limit of 1.0 x 10-'' μci was requested by the customer.

The conventional lower limit of detection is about lXl0-'μci, -
This required extremely high performance. A well-type Qt semiconductor detector has been developed as a measuring device with the best performance and has been used in recent years. The well type Qt semiconductor detector currently on the market has an effective body ijk of 120 cc and a well diameter of 14
．． 7φInm, depth 50mm.

The volume is 7 cc, and the counting efficiency when a sample is placed in the well is 25%. With the current technology, it is difficult to create a single crystal with a larger Qt, and no well-type Gt semi-dedicated detector larger than this is commercially available. In addition, due to the characteristics of the Gt semi-dedicated detector, increasing the diameter of the power door is a negative factor because the thickness of the GL as a detector becomes thinner and the counting efficiency for the photoelectric peak decreases significantly. Become.

Such a well-type Gt semiconductor detector and well-type N, I (
T4) As a result of measuring for 200,000 seconds using a 4,000-channel wave height analyzer after taking anti-coincidence with the detector and providing sufficient shielding, the bank ground was 1.
The count was 180 per channel. You g131
Since the half IIk width of the GL semiconductor detector is 2.3 kLV, 11 channels are necessary for the peak channels.

If the counting efficiency is t-25%, the detection limit is lX10-7
μci, and the target can be achieved by using a 7CC sample.

However, the cartridge currently in use has a diameter of 4Qm.
m, thickness 10rnm, volume 12cc,
In order to measure the entire amount, it is necessary to inhale twice. If the measurement time is divided into two times, the bank ground will also be doubled, so in order to achieve the target lower limit of detection, the measurement time must be quadrupled,
The total time is 8 times and 1,600,000 seconds are required. Iodine-
The half-life of 131 is 700,000 seconds, and it would be necessary to measure twice that amount, which is practically impossible.

For these reasons, conventional activated carbon performance tests have shown that 1.0
A detection limit of X10-7 μci was not achieved.

[Purpose of the invention]

An object of the present invention is to provide a method for measuring radioactivity that can improve the above-mentioned problems and efficiently measure radioactivity using a simple method.

[Summary of the invention]

The present invention focuses on the fact that activated carbon, silver alumina, etc., which are normally used as adsorbents for iodine, can be reduced in volume by pressing, etc., and has made it possible to measure efficiency ↓<<radioactivity.

[Embodiments of the invention]

An embodiment of the radioactivity measuring method using the present invention will be described below with reference to the drawings. In this method, KIlli≦adherent activated carbon (B
This is an example of a method for measuring the total amount of radioactivity attached to C-727). In Figure 1, 1 is the K I-impregnated carbon of the sample for measurement, 2 is the press bodyguard, 3 is the press frame, 4 is the press body, 5 is the press lower frame, and 6 is the press V press 1111g working device. show. In Fig. 2, 1 is the K I-impregnated carbon of the measurement sample that has been pressed, 7 is a well-type Qt semiconductor tester, and 8
9 is a liquid nitrogen container, and 9 is a well type N for anti-coincidence.
, I(Tt) detector, 10 is lead? A shield body 11 made of iron, octopus plate, etc. is a multiple wave height analyzer, and 12 is a data processing minicomputer.

The activated carbon sample with radioactivity is compressed in 40 steps to reduce its volume, placed in the well of a 7-well type Qt semiconductor detector, and measured with low counting efficiency.

In other words, in Figure 1, activated carbon to which radioactivity is attached is removed from the cartridge, and K C is used as a binder.
Add about 10% of flock, etc., and place it in the press mold frame in step 3. After that, the press body is operated and an appropriate force of about 100 kg/crn2 is applied using the 2nd bush/spindle to reduce the volume. The results are shown in Table 1. First 14c
Activated carbon from the sample (L, 7cc in the first press)
Reduce the volume to In this state, it is possible to take it out of the mold frame 3 and measure it with the well type GT half-humiliated body detector shown in 7, but the pressure strength is very weak at about 5 kg/cm.
1. Because there is a risk of damage during the installation and removal stages of the GA semiconductor detector and contamination of the detector, the product is removed from the press V-shaped frame and put back in for a second press. After the second press, the volume is 6,
5CC, the pressure strength is 2glcg/cm2, and it is possible to measure inside the well of a well-type C1 semiconductor detector by preventing contamination with a plastic bag or the like. In the first press, the granular activated carbon is only broken and powdered, so the binder is not evenly distributed and no pressing strength can be obtained. In the second press, the activated carbon is pulverized and the binder is evenly distributed, resulting in high pressing strength. After the compressed volume was reduced, the sample was wrapped in a plastic bag to prevent contamination, and then placed in the well of a 7-well type Gt semiconductor detector installed in a 10-hole container. , measured.

The energy resolution of the well-type Gt semiconductor detector is 2 in half width.
．． 3 ktV, anti-coincidence with well type N, I (T/) detector, maximum energy 2000 kL V with 4000 channels of pulse height analyzer.

In other words, 0.5 per channel! As V, the following results were obtained using activated carbon, which does not contain radioactivity. When measured for 200,000 seconds, the average count of iodine-131°3 was 180 per channel around 51c LV. Well 1g 1JGt When a sample is placed in the well of a half-centred body detector, the divisor efficiency is 25chi.

C, -60 1332 ktV r, half width 2.3 k tV Gt detector at 19/14 ite 36 s
When measuring iodine-131, which emits ktV gamma rays, 11 channels are required as a peak, so the lower limit of detection at this time is as follows.

N=NcXe where N: Total count value (count) in the engineering V corresponding to the target photoelectric peak of nuclear Germany when planning a sample that does not contain radioactivity. Nc: Sample that does not contain radioactivity. 20000
The count value per channel (counts/channel) JFl s at the energy corresponding to the photoelectric peak of the target and the nuclear decay l divided by 0 seconds.

C: Number of channels in which the gamma rays of iodine-131 will be distributed = 11 From this, N = 180 x 11 = 1980 counts.

Let σ be the standard deviation of σ=7i'r−44. If s 3σ is the lower limit of detection, L = 3 0 = 133.5 The detection limit radioactivity at this time is 1 = A'3.7X10'Xε・I where A: Radioactivity (μci) T: Measurement time ( seconds) 200,000 seconds ε: Iodine-131 gamma ray emission rate (-) 0.82 β: Counting efficiency of well-type Qt semiconductor detector (-) 0.25 A = 8.8 x 10""μci, target 1.0X
10-8 μC1 can be achieved.

If this total Ij'llll is measured, the detection lower limit will be as follows if the measurement is carried out twice without entering the well of the well IMGt detector at once.

H, G N = 1980 count difference in 200000 second measurement σ2/i'r = 44. As mentioned above, if the lower limit of detection is s 3σ, then 8.8 × 10−
'μci. Since the measurement is performed twice, the new detection limit is F22A=2X8.8X10-'=1.76X10-
'μci. Therefore, the target lower limit of detection I
In order to achieve 0-7 μci, it is necessary to reduce the lower limit of detection to 1/2 by rounding the - measurements, and therefore it is necessary to quadruple the measurement time. In other words, one sample has 8000
When measured for 00 seconds, N = 180X4X11-7920 The standard deviation σ is σ = l group 2 tf penalty = 89 If 3σ is the detection limit, L = 3σ = 267 counts The detection minimum radioactivity at this time is A = 4.4 X 10-8μci When the two samples are added together, F:2A:8.8X10-'μci.

Total? l111 time is 4 times longer than one measurement x 2 pieces = 8
Therefore, to achieve the detection limit of LXIO-7μci, 200000 seconds x 8 times = 1600000 seconds = 444
Time = 18 days of measurement would be required, which would be laughably close to impossible.

Reducing the volume by pressing, etc. in this way is an unconventional operation that takes about 30 minutes for each sample, making it possible to perform measurements in 1/8 of the counting time, which is below the lower limit of conventional detection. It is now possible to detect even samples that were

〔Effect of the invention〕

According to the present invention, there are cases where it is possible to measure even a trace amount of radioactivity, which was difficult to do with the conventional 6111 method. This allows release sources that were previously unknown (e.g. valves, tanks, etc.)
By clarifying this and taking countermeasures against it, it becomes possible to effectively reduce the series emitted radioactivity at low cost. In addition, radioactivity measurement in ventilation and air conditioning systems (NVAC), which has traditionally been limited to m++, has become more effective, and can be used to reduce employee exposure.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of sample volume reduction by 172 machine.
Figure 2 shows a well-type Gt semiconductor detector and a well-type N, 1Tt)
It is a diagram showing a radioactivity measuring device N using a detector.

Claims (1)

[Claims] 1. When measuring the total amount of radioactivity adsorbed on an adsorbent using a well-type radioactivity detector, the volume of the adsorbent is reduced by pressing, and this is reduced by the well-type radioactivity detector. put it in the well,
A radioactivity measurement method characterized by measuring radioactivity. 2. In the radioactivity measurement method according to claim 1, the radioactivity measurement is characterized in that when the volume is reduced by pressing, a binder is added, and the operation is carried out in two separate steps: crushing and molding. Method. 3. The method for measuring radioactivity according to claim 1, wherein the adsorbent is impregnated carbon, silver alumina, silver zeolite, or silver silica gel. 4. The radioactivity measuring method according to claim 3, wherein the well-type radioactivity measuring device is a well mGt semiconductor detector.