JPS6073386A - Survey meter for low energy radioactive nuclide - Google Patents

Abstract

PURPOSE:To enable the detection of low energy radioactive rays, by mounting a radiation incident part comprising a material pervious to low energy radioactive rays without absorbing the same and a scintillator having a shape pervious to high energy radioactive rays and absorbing low energy radioactive rays. CONSTITUTION:A scintillator part 1 is constituted of an incident window 3 formed of a bellirium thin plate pervious to low energy radioactive rays but not absorbing the same and a scintillator 4 which is arranged so as to allow the flat surface thereof to butt against that of the window plate 3 and has a shape with a relatively thin thickness for allowing incident radioactive rays to be incident at right angles in the thickness direction thereof and is pervious to high energy radioactive rays but absorbs low energy radioactive rays. In this case, a scintillation phenomenon corresponding to low energy radioactive rays through an optial window 5 is measured and low energy radioactive rays can be detected even in the presence of high energy radioactive rays.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a survey meter for detecting and measuring low-energy radionuclides such as ``51'' and their energies.

1251 is widely used in large quantities in the medical field, particularly in the diagnostic field, as a tracer for accurately and quickly determining 81g of trace substances in living organisms.

Manufacturing for this purpose is also actively carried out.

Regarding the problem of radiation damage of 125■, the energy of the electron capture (EC) is about 35
Because of its low EV, there are few problems with external exposure, but it has the most serious impact on internal exposure, along with 1311 of the nuclides used as tracers in the medical field. This is because once 1251 is ingested into the body, it is selectively accumulated in the thyroid gland, and about 30% of the amount at the time of intake is deposited, and this thyroid gland has a maximum allowable load of 1 μCj.
(3,7X 10' l+q) or less, the more susceptible to radiation damage, and it is said to be a cause of thyroid cancer.

+25 On the other hand, workers who handle ■ are ingested through the respiratory tract by inhaling air contaminated with 125■, and through the esophagus by smoking, eating and drinking with contaminated hands, and are ingested into the body without knowing 5■. It is expected that
It has been discovered that many people have accumulated ``μC'' files that actually handle 1251, and similar reports have been made from the UK and other countries, so there are increasing calls for the establishment of safety measures regarding +51. There is.

Therefore, when we closely examined the environmental pollution caused by the use of 12'1, we found that 125I is responsible for the 125I staining of the air, which is the cause of ingestion through the respiratory tract. (1) Separation during chemical reaction operations (2) After the reaction Happens (:l)? & from the body or solid radioactive isotope waste (71), from surface contamination of debris in the vicinity, and the direct cause of ingestion through the esophagus is from the hands and fingers (71).
5 ■ Contamination, this is because: (1) 1251 permeates through protective gloves and rubber gloves (2) 125I contamination on protective clothing and surfaces in the laboratory
Furthermore, the amount of thyroid accumulation in the thyroid gland was estimated by taking into account the human respiratory rate and residence time in the laboratory, and the actual measured air concentrations in rooms where 125I was used over the past five years. As a result, it was found that the effect of ingestion through the respiratory tract was small, and that the effect of ingestion of light meals was greater.

Therefore, as mentioned above, in order to avoid internal exposure to 125I, which poses a serious danger to the human body,
It is necessary to quickly and accurately clarify the state of contamination caused by contamination, and to take decontamination and other strict measures.For this purpose, a survey meter that can detect the state of contamination and confirm decontamination is essential. However, there are no survey meters in Japan or overseas that can detect and measure the energy level of low-energy radionuclides such as 151, and this is because current survey meters cannot detect and measure low-energy radionuclides such as 12J. This is because R1 is not set up so that detection and measurement can be performed.

That is, the survey meters currently in practical use for general use mainly include (A) electric [111 box survey meter] (f3) Geiger Mueller survey meter (C) scintillation survey meter. The international and legal density limit is txto μCi/cJ, and decontamination is required to be 1X10 μCi/cJ, which corresponds to this 171O, and the maximum allowable thyroid loading time for 125■ is 1μ("j However, the ion chamber survey meter in (A) is originally for measuring air dose and cannot be used for surface contamination measurement due to poor sensitivity, and the Geiger-Mueller survey meter in (])) (hereinafter referred to as 1) The IF factor effect for 125 irises of (:tl-baymeter) is 0.1% based on the distance of 51 books, that is, it is only 2.2 force for 1 × 10 μC1 (371) q). per minute (hereinafter referred to as Cpnl), which is virtually impossible to detect considering the background GOcpm.Furthermore, the inventors of the present invention have developed a gas flow type for H2C using a GM sampler. I tried this as an improved product, but this also had a counting efficiency of 1%.
While the background is only 22 cpm, the background rises to 150 cpm, making measurement not only difficult, but also requiring a gas cylinder, which poses a problem for mobile use.
All I learned was that it was unsuitable for detection of 5■.

On the other hand, the remaining method is (C) scintillation survey meter (hereinafter referred to as SnL survey meter).
However, this is highly energy dependent, and the current product uses a 1 inch diameter and 1 inch thick Na1 (TQ) scintillator.
10 because it uses a scintillator and stainless steel window.
0 has the characteristic of being able to detect only gamma rays and X-rays with energies higher than EV, and 1251, which has about 35 keys, cannot be detected by EC.

In view of the above-mentioned drawbacks of the prior art, the present invention has been made with the aim of providing a survey meter that can detect and measure surface contamination caused by low-energy radiation and its energy. In the survey meter, the survey meter is composed of a detection section consisting of an optical means for detecting the scintillation phenomenon and converting it into an electrical signal, and an 81 measuring section for processing the electrical signal outputted from the optical means and displaying it in relation to the intensity of radiation. The scintillator is formed in a shape that allows high-energy radiation to pass therethrough, while low-energy radiation is absorbed, and faces a radiation incident portion made of a material that transmits low-energy radiation without absorbing it. This is characterized in that low-energy radiation can be detected and measured even in the presence of high-energy radiation.

That is, although the survey meter using the scintillator radiation light conversion method has pressure points as described above, the inventors of the present invention focused on the fact that it has the highest sensitivity to gamma rays and X-rays, and maximized this feature. As a result of repeated prototyping and experiments, we found that it is possible to develop a low-energy survey meter by making use of the By devising the positional relationship with the radiation entrance part, it was possible to detect and measure low-energy radiation such as 1251, and this invention was completed by learning that this was possible even under high-energy radiation. This is what I did.

Next, an example of the present invention will be explained with reference to the drawings.

(3) is a scintillation section consisting of a casing 2, an entrance window 3 which is a radiation entrance section housed in the casing in order, a scintillator 4 made of Na I (TQ), and an optical window 5 made of Pyresogs. The following configuration is adopted so that scintillation phenomenon can be selectively and highly efficiently caused by low-energy radiation such as 125 cm even in the presence of high-energy radiation.

That is, the entrance window 3 is made of a material that has excellent radiation transparency and has the property of transmitting not only high-energy radiation but also low-energy radiation without absorbing it. By using a thin plate of as the entrance window 3, in addition to mechanical strength and light-shielding properties, the radiation of 30 K e
It also ensures transparency for low-energy radiation, allowing 99.6% of radiation of 40% and 40 ev to pass through.

By using the entrance window 3 with such characteristics, even low-energy radiation from 1251 etc. can reach the scintillator 4, but with this alone, the diameter and thickness are limited as shown in Figure 3. For example, in a 1-inch x 1-inch scintillator S, high-energy radiation is emitted in the direction (h, ) of the incident window of the scintillator S and in the side direction (h2).
) and causes one scintillation phenomenon, while low energy radiation (Q) causes 100% scintillation phenomenon at a shallow area of +11p. This means that in the case of high-energy radiation n-1 radiation, scintillation phenomenon occurs due to high absorption rate, and in the end, 12
Low-energy radiation such as 51 becomes unmeasurable in the presence of high-energy radiation.

Therefore, regarding the scintillator 4, we examined the shape etc.
By adding 1 and making it relatively thin, the amount of radiation incident from the side is reduced, while high-energy jN of the radiation transmitted through the entrance window 3 is transmitted, suppressing the scintillation phenomenon and reducing the energy. The scintillator 4 is made to face the entrance window 3 in the thickness direction by using a scintillator that absorbs a low amount of light so as to cause an almost complete scintillation phenomenon.
In an example of the present invention shown in FIG. As a result, the radiation incident from the 41g surface is approximately 1713, and all the radiation passing through the entrance window 3 hits the scintillator 4 at right angles to the thickness direction, resulting in a high-energy radiation, for example, 1
Mcν absorbs and emits only 39%, but low-energy radiation, for example, 30 to 98 ev,
．． 2%, 40 and EV absorb nearly 100%.

Comparing this using radionuclides that are actually often used in medical fields, the results are as follows, and it can be seen that only low-energy radionuclides such as 1251 can be absorbed with sufficient selectivity.

Nuclide Energy (Kev) Absorption rate (%) Half-life (hour) I2J 35.5 99.4 60 (days) 28
98.2 Ga 93 72.7 78 185 21.3 394 8.1 ””I'c 140 45.2 6 ”' TL 135 52 73 167 38 Iso 1--bu notebook 1982 edition (Iso 1--bu association ms) Note that in order to further reduce the radiation incident on the scintillator 4 from the side, it goes without saying that the scintillator 4 may be surrounded by a radiation shielding material.

Reference numeral 6 denotes a photomultiply as an optical means, and the photomultiplier 6 absorbs the scintillation phenomenon caused by absorption of radiation by the scintillator 4 of the scintillation section 1 into the optical window 5.
In order to optically detect the signal and convert it into an electric signal through the scintillation section 1, the measuring end is placed in contact with the rear of the scintillation section 1 (on the side of the optical window 5). Configure the measurement section.

7 is a shield case of hooks 1 to 6 that surround the sides of the measuring section, and 8 is a photo-maru box 1 to 6. 9 is the socket 1~
The cable connected to IO is an outer cylinder, and the cable 9 is pulled out from the rear end of the outer cylinder 10, and a cap member 11 is fitted therein. The detection section A is constructed by fitting the cap 13 onto the other end of the outer cylinder lO through the backing 12 to the mount 1. It consists of an a1 measurement section B that accommodates an appropriate electric circuit for processing the electrical signal output by the circle 6 and displaying it as the intensity of radiation.

In the above embodiment, the detection section and the measurement section 13 are separate bodies, and the cable 9 is used to connect them.
This design takes into account the convenience of operation when detecting surface contamination on floors, etc. In addition to this configuration, it has a length that is approximately equal to the detection part Δ when contracted, and can be extended to an appropriate length. It is possible to further improve the operability of the survey meter of the present invention by attaching the operating rod J4, which can be tilted freely relative to the detection part A, to the bracket 15 arranged on the side surface of the outer cylinder 10 to the detection part by means of a pivot R16L. can.

Therefore, in order to measure the surface staining of floors etc. using the survey meter of the present invention, afil+! After activating part 1B,
After bringing the tip of the detection section (scintillation phenomenon side) close to the desired site, it is sufficient to directly read the numerical values etc. displayed on the display means provided in the 81 measurement section B. In this way,
The survey meter of the present invention used for
J&! ? The scintillator is made of a material that allows even low-energy radiation to pass through, and the scintillator is designed to allow high-energy radiation to pass through while absorbing low-energy radiation. Because we have paid special attention to the thickness, etc., the background is lowered due to the reduction of gamma rays incident from the side, and the related directivity is improved. Even in the presence of high-energy radiation, the It is possible to selectively detect surface contamination by radioactive nuclides of equal low energy.

When the 81 number efficiency of the survey meter of the present invention was actually inserted at a distance of 5 mm using a standard radiation source of 125 summer, it showed a high value of 24%.
It has been confirmed that it is 240 times more sensitive than the M Sasurimeter, and has a short half-life, so it is less dangerous.
+111. It has now become possible to selectively and sensitively detect contamination of people, clothing, and facility surfaces by 1251 in a nuclear medicine facility where 1251 is used for many cases of c, 67 Ga.

Furthermore, the survey meter of the present invention has been designed with consideration to operability so that it can be easily and quickly measured when contamination is assumed. If B is made into a separate body and the cables 9 are used to connect them, it is possible to attach a telescopic operation rod 14 to the detection section, for example, to monitor while standing on the floor, and to connect the detection section 11. Since B can be used by placing it on a desk so that the value of the meter can be easily read, this is combined with the fact that it is small and light in appearance.
It is significantly easier to operate than conventional large floor monitors, etc.
``Gamu'' - shiiteru.

Furthermore, 1ildl! Regarding part 1 13, a storage hole 17 is bored that corresponds to the contour from the side to the detection part so that the detection part A can be stored therein, and a take-up reel 8 for the cable 9 is provided. Of course you can.

The present invention is as follows, and the present invention is applicable to the floor of a facility.

Experiment bench and tool 1~. Surface contamination by 1251 of equipment, etc. is more than t, it i (during and after the 15° experiment, the surface of people, protective clothing, and protective gear should be contaminated with 10μCj/c).
With the order of ♂ (σ), we can take prompt safety measures and reduce the risk of thyroid dysfunction due to transesophageal ingestion.
5I accumulation can be completely prevented.

In addition, the number of disposable plastic test tubes used in +51's clinical tests exceeds several million each year, and as a new treatment measure, a group of plastic test tubes that will be centrally incinerated once the strength has weakened to ]/1.000 has been introduced. However, according to the survey meter of the present invention, the 12% remaining in the test tube, which was previously impossible.
It is possible to check for 5I contamination, and the contribution in this area is extremely large.

Therefore, the present invention is extremely excellent as a survey meter for low energy radionuclides.

[Brief explanation of drawings]

Fig. 1 is a side view with a part of an example of the present invention in cross section;
The figure is a side view with a part of the scintillator body used in the present invention in cross section, Figure 3 is a conceptual diagram showing the difference in scintillation phenomenon depending on the intensity of radiation energy, and Figure 4 is a perspective view of one example of the present invention. It is a diagram. ■...Scintillation section, 2 Casing, 3.Incidence window, 4 Scintillator, 5 Optical window, 6 Photomal, 1
0・Outer cylinder, 14 Old operation, A...Detection section, B Measurement section Fig. 2 Fig. 3

Claims (1)

[Claims] ■ A detection unit comprising a suitable scintillator and an optical means for detecting the scintillation phenomenon and converting it into an electric signal, and processing the electric signal outputted from the optical means and correlating it with the intensity of radiation. il'i! In a survey meter consisting of an IQ section, the scintillator is formed in a shape that allows high-energy radiation to pass through and low-energy radiation to be absorbed, and is made of a raw material that transmits low-energy radiation without absorbing it. 1. A survey meter for low-energy radionuclides, characterized in that it can detect and measure low-energy radiation even in the presence of high-energy radiation by facing the radiation incidence part. 2. The detection part has a telescopic operating rod that can be folded down and down.
A survey meter according to claim 1.