JPS60172155A - Bf3 proportional counter tube - Google Patents

Abstract

PURPOSE:To obtain a proportional counter tube having high neutron detection sensitivity and small temperature dependence by installing at least one unit counter tube along a unit counter tube charged with BF3 gas at given pressure and electrically connecting the anodes of the unit counter tubes together and their cathodes together. CONSTITUTION:A unit proportional counter tube is constituted of an anode 1a, a cathode 2a and insulating supports 11a and 13a. Another unit proportional counter tube is constituted of an anode 1b, a cathode 2b and insulating supports 11b and 13b. These unit proportional counter tubes are charged with BF3 gas at 350Torr or below. When d.c. high voltage is applied from the outside to the electric conductor 10 and the airtight case 7 of a BF3 proportional counter tube charged with BF3 at 350Torr or below and the BF3 proportional counter tube is placed in a field of neutrons, the number of pulse signals taken outside the counter tube equals the sum of the numbers of pulse signals from the two unit counter tubes. Therefore the total neutron detection sensitivity equals the sum of the neutron detection sensitivities of the two unit counter tubes. However, since the detection characteristics of the two unit counter tubes have equal temperature dependence, the temperature dependence of the total detection characteristic is equal to that of the detection characteristics of the two unit counter tubes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a BP'a proportional counter for detecting neutrons.

[Prior art]

Conventionally, there was a BF3 proportional counter tube of this type, as shown in the partially cutaway front view of Figure A1 to show the inside. In the figure, (1) is a linear anode, (2) is a cylindrical cathode that is electrically insulated from the anode (1) and kept coaxial with the anode (1), and (3a) (3t+) are The end plate is hermetically sealed to the cathode, (4) is an exhaust and gas filling pipe whose one end is hermetically sealed to the end plate (3a), and (5) is the shade between (2) and the end plate (3a) ( 3b) A pipe (4) in a container consisting of
(6) is a connector for drawing out electrical signals attached to the end plate (3b).Next, we will briefly discuss the operation. When a neutron enters the BF3 proportional counter tube, the BF3 gas contained in the tube is
Reacts with B to produce high-energy α particles and L1 nuclei. These high-energy charged particles ionize BF3 gas molecules as they pass through the BF3 gas, producing electrons and BPa cations. -This is called -order ionization. Since a DC voltage is applied between the negative and positive poles, the generated electrons and cations are collected at the anode and cathode, respectively. When electrons are collected at the anode, the electric field near the anode is strong, so when the electrons receive strong acceleration and collide with the BF3 gas molecules, they ionize the gas molecules and create new electrons.
Generates ion pairs. Further, the newly generated electrons also ionize the BF3 gas molecules, so that when the electrons are collected at the anode, they become a much larger charge than the initially generated primary '\a' separation charge. This is called gas amplification, and the ratio of the charge finally collected on the electrode to the primary charge is called the gas amplification factor.Normally, this charge is counted in pulses to measure neutrons.

Now, it has been found that when the BF3 proportional counter is used in a place where the environmental temperature changes, the neutron detection characteristics also change. According to our experiments, we found that as the temperature rises, the gas amplification factor decreases, that is, the wave height of the signal pulse becomes smaller. In pulse counting,
This means that changes in temperature introduce errors in neutron measurements. The sealed BF3 gas pressure is 55 in Figures 2 and 3.
Experimental results in the case of 0 torr are shown. Wow, the anode diameter at this time is 25 μm and the cathode diameter is 2L8 mm. FIG. 2 is a characteristic diagram showing the temperature dependence of the gas amplification factor, in which the value of the gas amplification factor at room temperature is assumed to be 1, the vertical axis represents the change in the gas amplification factor, and the horizontal axis represents the temperature. FIG. 3 is a characteristic diagram showing the temperature dependence of the wave height discrimination characteristic, in which the vertical axis represents the counting rate and the horizontal axis represents the relative wave height discrimination level. Woman, the applied voltage at this time is 1.8kv. Furthermore, the broken line represents the wave height discrimination characteristics at room temperature, the dashed line represents the wave height discrimination characteristics at 160°C, and the solid line represents the wave height discrimination characteristics at 200°C.

In this way, the neutron detection characteristics of the BF3 proportional counter are considerably dependent on temperature, and there are problems when using it at high temperatures or in places where the environmental temperature changes. Through various experiments conducted to develop the BF3 proportional counter, the temperature dependence of the BF3 proportional counter characteristics
It was found that the F3 gas pressure is low when the gas pressure is low.The results are shown in the characteristic diagram showing the temperature dependence of the gas amplification factor in Figure 4.In the graph, the vertical axis represents the value of the gas amplification factor at room temperature.
The horizontal axis represents the temperature and the change in the gas amplification factor when This experiment was conducted with the anode and cathode diameters the same as in the case shown in Figure 2, and the filled gas pressure was 250 torr.As can be seen from the figure, when the filled gas pressure was set to 250 tOrr, almost no temperature dependence was observed, and it is not practical. It can be seen that there is no problem.

Figure 5 is a characteristic diagram showing how the amount of temperature change in the gas amplification factor changes depending on the sealed BF3 gas pressure, and the vertical axis is 1.
It is the ratio of the gas amplification factor value at 50° C. to the gas amplification factor value at room temperature, and the cherry axis is the sealed BF3 gas pressure. When the filled gas pressure is below 350 tOrr, the temperature change is small;
It can be seen that when tOrr is exceeded, the temperature change becomes much larger. This tendency also holds true for the ratio of the gas amplification factor at 200° C. to the amplification factor at room temperature. If the force F3 gas pressure is reduced too much, the neutron detection sensitivity characteristics will deteriorate, so it is desirable to set it to 1'50 torr or more.

Note that the applied voltage at this time is BF3 gas pressure of 150 torr.
250tOrr, 350tOrr, 450to
LllcV in order from those of rr and 550 torr.
, 1.3kv, 1.5kv, L6kv and 1. 'lkv. The reason why the applied voltages are different is because the comparison was made at approximately the same gas amplification factor value.

However, the neutron detection sensitivity of the unit length along the axis of the BF and proportional counter tube is proportional to the inserted BF3 gas pressure, so if the sealed BF3 gas pressure is lowered to eliminate temperature dependence, the neutron detection sensitivity decreases. Resulting in.

Therefore, simply lower the gas pressure and increase the diameter of the counter tube.
Measures to increase neutron detection sensitivity are undesirable because they deteriorate other detection characteristics. That is, since the time it takes for electrons generated by -order ionization to reach the gas amplification region is greatly reduced, the width of the signal pulse becomes wider and the upper limit of the measurable count rate becomes lower.

[Summary of the Invention] This invention was developed in order to eliminate the above-mentioned drawbacks, and includes a linear anode and a linear anode, which is provided coaxially with the frame and electrically insulated from the anode. The space formed by the linear anode and the cylindrical cathode is 350 to
By placing one or more unit meters or tubes along a unit counter filled with BF3 gas of rr or less, and electrically connecting the anodes and cathodes of each unit counter, the kW is generated. The present invention aims to provide a BF3 proportional counter in which the neutron detection sensitivity does not decrease and the temperature dependence of the six detections is small enough to cause no practical problems.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 6th
In the cross-sectional view of the figure, (7) is a cylindrical case, (3a)
(3b) is an end plate hermetically sealed to both ends of the case (7);
(9) is an insulated terminal for signal extraction that is hermetically sealed to the end plate (3b), and an electric conductor 0Q passes through the inside thereof while maintaining airtightness. (4) is a nozzle for exhaust and gas filling that is hermetically sealed to the end plate (3a), and (5) is a nozzle for exhaust and gas filling that is hermetically sealed to the end plate (3a).
), an airtight container consisting of end plates (3a), (3b) and an insulated terminal (9) is filled with BF3 gas as much as the pipe (4), (2a) and (2b) are installed in the airtight container. cylindrical cathodes, (la) and (lb) are cathodes (
2a) and (21:1), a linear anode electrically insulated from each other and installed coaxially, (lla) (13a)
and (11b) and (13b) are insulating supports that electrically insulate and support the cathode and anode (1a) and (2a) and (1b) and (2b), respectively, and the insulating supports (13a) (13
b) Shoulder the through hole. (8a) and (8b) are the lead wires that electrically connect the anodes (1a) and (1b) to the electrical conductor Q□, respectively, and (12&) and (ub) are the leads that hermetically seal the cathodes (2a) and (2b), respectively. This is a lead wire that connects to the container. Each unit counter has an anode (la
), shade 1 (2a) and insulating support (lla) (13
a), an anode (1b), a cathode (2b) and an insulating support (
llb) (1:Th), and since this unit counter tube is not airtight to the outside, the pipe is
tOrr or less, in this case 250 torr filled B
The F3 gas is also filled inside at the same pressure.

Further, the cathode inner diameter and the anode wire outer diameter of the two unit counter tubes are mutually different.

Next, the operation will be explained. When a high DC voltage is applied from the outside to the electric conductor θQ and the airtight container, the same voltage is applied between the cathode and anode of the two unit counter tubes, so the two unit counter tubes operate in the same way. When placed in a neutron field, the number of pulse signals taken out to the outside is equal to the sum of the number of pulse signals from the two unit counters, so the overall neutron detection sensitivity is the neutron detection sensitivity of the two unit counters. The sum of Totoru. However, the temperature dependence of the detection characteristics as a whole is
Since the temperature dependencies of the detection characteristics of the two unit counter tubes are equal, the temperature dependencies are equal. In order to keep the neutron sensitivity constant per unit length in the axial direction of the BF3 proportional counter, if you try to configure it with one set of unit counters, you will have to increase the pressure of the BFs gas to be filled. Gas pressure is 3
When the temperature exceeds 50 torr, the temperature dependence of the detection characteristics of the BF3 proportional counter becomes quite large, which becomes a problem.
If it is composed of two sets of unit counters, the BFs to be filled
Since the gas pressure of the gas is only half that in the case of one set, the temperature dependence of the detection characteristics can be made much smaller. Note that even if the gas pressure is the same as in the case of two sets of unit counters and the cathode diameter is increased with one set of unit counters, the neutron detection sensitivity can be maintained high, but in this case, as described above, This results in deterioration of the detection characteristics itself.

In the above embodiment, two sets of unit counters that are not airtight to the outside are incorporated into one airtight container, but the above effect will be even greater if there are three or more sets of unit counters. . In addition, the same effect can be obtained by making the unit counter tube installed inside the container airtight and inserting BF3 gas into the tube independently. If it is necessary to electrically insulate the container and the unit counter, two insulated terminals for signal extraction may be installed on the container, one for the anode and the other for the cathode. . Additionally, cables and connectors may be attached to the container wall for signal extraction.

〔Effect of the invention〕

As described above, the present invention has a linear anode and a cylindrical cathode provided coaxially with the anode and electrically insulated from the anode, the linear anode and the cylindrical cathode. One or more unit counters are placed along the space formed by the unit counter filled with BF3 gas of 350 torr or less, and the anodes and cathodes of each unit counter are electrically connected. %#: By doing so, it is possible to obtain a BF3 proportional counter having a high neutron detection sensitivity and a temperature dependence of detection characteristics so small as to pose no practical problem.

[Brief explanation of drawings]

Figure 1 is a front view of a conventional BF3 proportional counter with a part cut away to show the inside, Figure 2 is an EF, gas charging lateral pressure is 550 to
Figure 3 is a characteristic diagram showing the temperature change in the gas amplification factor of the BF3 proportional counter of RR with reference to room temperature; Figure 4 shows B with BF3 gas filling lateral pressure of 250 torr.
Figure 5 is a characteristic diagram showing the temperature change in the gas amplification factor of the F3 proportional counter tube with reference to room temperature. FIG. 1 is a sectional view showing a BF3 proportional counter according to an embodiment of the present invention. (1), (1a), (lb)... Anode, (2
) l (2a) l (2b) ... cathode, (3a),
(3b)...End plate, (4)...Pipe, (5)-
BF3 gas, (6)...connector, (7)--case, (8a), (8b)...lead wire, (9)...
・Insulated terminal, αq...electric conductor, (Ila'),
(llb), (13a), (13b)...
Insulating support, (12a). (12b)... Lead wire In the figures, the same reference numerals indicate the same or equivalent parts 0 Agent Masuo Oiwa Figure 1 Figure 2 Temperature acclimatization valve 11 Top Figure 4 Temperature tube 5 Fig.Sa/60 25θ 35θ dfO revision θ Enclosed eFi direction Matashiri (Mu1)

Claims (1)

[Claims] The space formed by the linear anode and the cylindrical cathode is filled with BIF3 gas of 350 torr or less. A BP'3 proportional counter tube is refined by placing one or more unit counter tubes along a unit counter filled with the same amount of water, and electrically connecting the anodes and cathodes of each unit counter tube.