JPS6157584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the radioactivity intensity of a liquid sample containing a high concentration of radioactive substances.

BACKGROUND ART Methods and apparatuses for determining the radioactive substance concentration by measuring the radioactivity intensity of a liquid sample containing a radioactive substance are conventionally known. This known technique is primarily concerned with the measurement of low concentrations of radioactivity, in which the detector is
Measurements are made in the radioactivity intensity area without counting losses. Expressing this in terms of radioactive substance concentration, if a sample contains about 1 microcury of radioactive substance per milliliter of solution, it is possible to measure several milliliters of the sample by applying it directly to the detector.

However, if the concentration exceeds this level, the detector may start to lose counts, and at even higher concentrations, a suffocation phenomenon may occur, and the count value per unit time (counting rate) may decrease.

In the case of such a high concentration, the amount of sample can be reduced, but when the amount decreases beyond a certain point, it becomes difficult to handle the sample. For example, in order to quantify impurities in the fuel (including americium-241), 1 gram of the fuel is dissolved in acid, the impurities are separated using an ion exchange resin column, and the resulting impurity effluent is
Suppose it is milliliter. Considering the case where americium-241, one of the impurities, is determined by measuring the gamma radioactivity intensity of this solution, it is assumed that the original fuel contains 1% americium-241.
When containing 241, this solution has 650 microcuries per milliliter, and the sample volume is required to be several microliters.

Packing such a small amount of sample into a container in a reproducible shape and measuring it requires a container with a sophisticated structure, which also makes it difficult to handle the liquid. Furthermore, as the structure becomes more sophisticated, it is expected that cleaning after measurement will become more difficult.

Therefore, in general, the sample is diluted to lower its concentration, but the detection efficiency is reduced by moving the sample away from the detector.

The disadvantage of the former is that the dilution operation increases the risk of radioactive contamination to the surrounding area and increases the amount of radioactive waste, while the disadvantage of the latter is that the space containing the detector and sample becomes larger, reducing the background. The large size of the holding body increases the weight, making it expensive and inconvenient to handle.

In addition, a sample tube that matches the radioactivity concentration in the liquid sample is selected from multiple tubes with different cross-sectional areas based on the signal from the radiation detector for monitoring the total radioactivity level, and the selected sample tube is filled with the liquid sample to determine the radioactivity. Devices that determine the concentration are also known, but even with this device, if the radiation detector for monitoring the total radioactivity level of a highly concentrated sample becomes suffocated, the counted value will drop incorrectly, resulting in an incorrect sample tube being used. This method has the disadvantage of causing a suffocation phenomenon in the detector used to determine the radioactivity concentration and determining the wrong concentration.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an apparatus that is capable of measuring the radioactivity of a trace amount of a highly concentrated sample using a method with good reproducibility and that can be easily cleaned after measurement.

A further object of the present invention is to provide an apparatus that can confirm the dangers associated with measuring high concentrations of radioactivity, that is, whether the detector is miscounting or not, and whether or not the patient is suffocating. .

Furthermore, it is an object of the present invention to improve measurement accuracy by easily and immediately switching to a known sample before or after measuring an unknown sample, and by calibrating the detection section of the detector and the attached counting section. The aim is to provide a device that can enhance

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

FIG. 1 is a schematic sectional view shown to facilitate understanding of the present invention. Reference numeral 1 denotes a scintillation counter for line detection, and a thin tube 3 made of Teflon (trade name), a fluorine resin, is placed in its effective sensitivity space in close proximity to a scintillator 2 at its tip. A sample solution is allowed to flow into the thin tube 3 via a pump. Around the scintillator 2, there is a shielding body 4 for shielding gamma rays from sources other than the thin tubes 3.
is located.

The effective diameter of the scintillator is 25.4 mm, with an inner diameter of 0.5
mm, and a thin tube with an outer diameter of 1 mm is placed so as to pass through its center. (See Figure 2) In this case, the amount of solution contributing to the measurement is approximately 5 μm since the diameter is 0.5 m and the length is 25.4 mm, which is a suitable amount for the determination of americium in the nuclear fuel.

When cleaning after measurement, the thin tube material Teflon (trade name) has water-repellent properties, so most of the solution in the drain can be removed just by blowing air, but it is important to flush the cleaning water. If it is, it will be thoroughly cleaned. Another feature of this device is that it can be easily cleaned after measurement. Note that the transmittance of americium-241 gamma rays (energy 60 Kev) through a thin tube with a wall thickness of 0.25 mm is over 99% and does not affect measurements.

FIG. 3 shows a first embodiment of the invention. The thin tube 3 made of fluorine resin is folded back in the middle, and two tubes of equal length, an outward path and a return path, are arranged in parallel in the effective sensitivity space above the scintillator 2. With this device, it is possible to make measurements while checking whether the detector is suffocating or not. If the detection unit and its attached counting unit become suffocated, the counting rate will decrease as the radioactivity intensity increases, so a sample with a very high concentration may be interpreted as having a low concentration. In this device, the pump for sending liquid to the thin tube is stopped, and the operation is set at a time lag.The pump first sends the liquid to the thin tube 3, and before it reaches the return path, the pump is stopped and the sample solution is only sent to the outward path. Fill it and measure the radioactivity. Next, the pump is operated again, and radioactivity is measured with the sample solution filling the forward and return paths.

If the two measured values are compared and the latter is higher than the former, it can be determined that the detector is not causing a suffocation phenomenon. Furthermore, according to this device, it is possible to check the degree of miscounting, and to check the measurable concentration range and
Can be expanded twice. In other words, it can be seen that if the latter measured value is twice as large as the former measured value, counting errors can be ignored. The upper limit of measurable concentration can be doubled if the latter measurement value is normally used, and if counting errors cannot be ignored, the former measurement value is used. Although it may not be exactly doubled due to variations in the inner diameter of the outward and return paths of the thin tube, it is sufficient to accurately determine the magnification by measuring a low-concentration sample in advance. Note that if the number of reciprocations is increased instead of just one reciprocation, the measurable concentration range can be further expanded, but the number of reciprocations is limited by the effective area of the detection section.

FIG. 4 shows a second embodiment of the invention. tubule 3
The sample solution flowing through the tube is switched to the capillary tube 3' or the capillary tube 3'' with a time difference by the switching valves 5 and 6,
Each capillary tube 3', 3'' is filled with a sample solution and passed through the effective sensitivity space above the scintillator 2. First, the sample solution is poured into the capillary tube 3' and the radioactivity is measured.
Next, if the switching valves 5 and 6 are switched so that the sample solution flows into the capillary tube 3'', the sample solution in the capillary tube 3' stays as it is, so the sample solution staying in both the capillary tube 3' and the capillary tube 3'' is removed. Radioactivity can be measured, and by comparing both measured values and looking at the difference, the same effect as in the case of Fig. 3 can be obtained. Also, first, the sample solution is poured into the capillary tube 3, and then the three-way switching valves 5 and 6 are switched so that the sample solution flows into the capillary tube 3'', so the sample solution in the capillary tube 3' is in a sealed form, so that there is no concentration change due to evaporation. It can be used as a comparison sample for calibrating the detection unit and attached counting unit.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view to facilitate understanding of the present invention, FIG. 2 is a schematic diagram showing the arrangement of a scintillator and a thin tube, and FIG. 3 is a schematic diagram showing the first embodiment of the present invention. FIG. 4 is a schematic diagram showing a second embodiment of the present invention. 1... scintillation counter, 2... scintillator, 3, 3', 3''... tubule, 4... shinohei body,
5, 6...Three-way switching valve.

Claims (1)

[Claims] 1. A radioactivity detector, at least two thin tubes provided in parallel within the effective sensitivity space of the radioactivity detector, and at least one of the thin tubes filled with a sample solution. a time-difference filling means capable of filling another capillary with the sample solution after detecting radioactivity with the radioactivity detector; A radioactivity measuring device comprising means for comparing a measured value obtained by detecting the radioactivity of the at least one tube with a measured value obtained by detecting the radioactivity of the at least one thin tube. 2. The radioactivity measuring device according to claim 1, characterized in that the thin tube is made of fluororesin. 3. The time difference filling means is used to transport a sample solution into a narrow tube provided with a folded tube on the outward path, and is stopped before the sample solution reaches the return path to measure the radioactivity.
2. The radioactivity measuring device according to claim 1, further comprising means for filling the sample solution in the forward and backward paths. 4 Using the time difference filling means, measure the radioactivity by feeding the sample solution into at least one of the capillaries provided with a switching valve at both ends, and then filling the other capillaries with the sample solution. 2. The radioactivity measurement apparatus according to claim 1, further comprising means for switching said switching valve to fill said sample solution in said thin tube at a time lag.