GB2150743A

GB2150743A - A proportional counter

Info

Publication number: GB2150743A
Application number: GB08426297A
Authority: GB
Inventors: Hans Kiefer; Lothar Leidner; Ismael Sadri
Original assignee: Kernforschungszentrum Karlsruhe GmbH
Current assignee: Forschungszentrum Karlsruhe GmbH
Priority date: 1983-10-22
Filing date: 1984-10-17
Publication date: 1985-07-03
Also published as: DE3338454A1; FR2553897A1; GB2150743B; FR2553897B1; GB8426297D0

Abstract

A large area proportional counter having a low inherent capacitance for detecting alpha and beta radiation or gamma radiation utilising a counter tube gas, in which a gas regenerating device (2) is connected to a chamber (9) defined in the counter tube (1) and which contains the gas. The gas is nitrogen and is capable of being passed through the gas regenerating device (2). <IMAGE>

Description

SPECIFICATION A proportional counter The present invention relates to a large area proportional counter having a low inherent capacitance and which can be used for detect ing alpha and beta radiation or gamma radiation utilising a countering gas.

Conventional large area proportional counters may operate either with gas flowing in a conduit or as tightly sealed counting tubes filled with gas. A counter having a gas flow is, however, disadvantageous because it necessitates a permanent gas supply. This, in many cases, is expensive to provide. In the case of a tightly sealed counter tube filled with gas, the leakage rate and chemical annihilation radiation determine the service-life of the counter tube. The gas multiplication effect of a proportional counter is considerably dependent on the purity of the gas. To ensure low leakage rates and, hence, a long service-life, a counter tube filled with gas requires windows of such a thickness that alpha radiation is stopped thereby and cannot be measured.

The invention seeks to provide a large area proportional counter which is generally of the above-mentioned type but the operation of which is more independent of the gas.

From the point of view of availability, air would be an ideal counter tube gas. However, natural ambient air cannot be utilised. This is because oxygen has unfavourable electrochemical properties which preclude oxygen concentrations of the level contained in atmospheric air from being utilised. Mixtures of nitrogen and oxygen containing a concentration of up to 2% O2 are, however, suitable for use as the gas. This is because the gas amplification remains constant up to this concentration and such gas is, to all intents and purposes, similar to that of pure nitrogen.

According to the present invention, there is provided a large area proportional counter including a counter tube for detecting alpha and beta radiation or gamma radiation utilising a counter tube gas and having a low inherent capacitance, wherein the counter tube defines a chamber containing the counter tube gas, a gas regenerating device is connected to the chamber, the counter tube gas is nitrogen and the counter tube gas is capable of being passed through the gas regenerating device.

Preferably, the gas regenerating device includes a molecular sieve or filter and an oxygen absorber, the filter removing oxygen impurities from the counter tube.

Desirably a ventilator, fan or pump is disposed in a circuit for the counter tube gas, which circuit connects the chamber to the molecular filter and to the absorber.

Accordingly, in the device according to the present invention, nitrogen is used as the gas in a tightly sealed counter tube. The gas purifying device attached thereto, which has gas circulating therethrough, ensures that the composition of the gas remains constant over long periods of time. This, in turn, ensures a long service-life for the detector.

Because of the low gas-amplification factor of nitrogen, an electronics system which has as favourable a signal-to-noise ratio as possible should be employed. In the arrangement according to the present invention, low-noise, charge-sensitive preliminary amplifiers and low-capacitance detectors are preferably usad.

The invention will be described further, by way of example, with reference to the accompanying drawing, the single Figure of which shows a schematic view of a proportional counter in accordance with the present invention.

In the Figure, there is shown a gas regenerating device 2, in the form of a cartridge, which is connected to the bottom end of a large area proportional counter 1. The counter 1 includes a chamber 9.

In the cartridge 2, an O2 absorber 5 is disposed between two molecular filters 4 which are provided with grids 3 at their respective ends. The cartridge may be screwconnected into a block 6 which has a recess formed therein for accommodating a fan 7.

The fan 7 is disposed beneath the lower grid 3. A conduit 8 leads from the recess in the block 6 into the chamber 9 of the large area proportional counter 1, so that gas can be pumped round the system.

The gas purifying cartridge 2 removes oxygen and atmospheric moisture from the gas.

Any impurities which enter from externally, primarily O2 and moisture, are thus eliminated. However, any nitrogen which may possibly diffuse into the system is desirable for replenishment of the gas.

The device of the present invention therefore comprises a combination of certain features.

These are a conventional, gas-tight large area proportional counter having a low inherent capacitance and high amplification, a gas purifying cartridge and means for causing circulation of the gas. Thus, a preferred embodiment of the device of the present invention may have the following characteristics: 235 mV/106 ion pairs, amplification factor 550; a molecular filter (3 A or 4 ) for the removal of water vapour, a catalyzer (such as R3-11 made by BASF) reduced, for adsorbing oxygen; and a tightly sealed pump, a fan incorporated in the gas purifying cartridge or a temperature gradient.

1. A large area proportional counter including a counter tube for detecting alpha and beta radiation or gamma radiation utilising a counter tube gas and having a low inherent

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A proportional counter The present invention relates to a large area proportional counter having a low inherent capacitance and which can be used for detect ing alpha and beta radiation or gamma radiation utilising a countering gas. Conventional large area proportional counters may operate either with gas flowing in a conduit or as tightly sealed counting tubes filled with gas. A counter having a gas flow is, however, disadvantageous because it necessitates a permanent gas supply. This, in many cases, is expensive to provide. In the case of a tightly sealed counter tube filled with gas, the leakage rate and chemical annihilation radiation determine the service-life of the counter tube. The gas multiplication effect of a proportional counter is considerably dependent on the purity of the gas. To ensure low leakage rates and, hence, a long service-life, a counter tube filled with gas requires windows of such a thickness that alpha radiation is stopped thereby and cannot be measured. The invention seeks to provide a large area proportional counter which is generally of the above-mentioned type but the operation of which is more independent of the gas. From the point of view of availability, air would be an ideal counter tube gas. However, natural ambient air cannot be utilised. This is because oxygen has unfavourable electrochemical properties which preclude oxygen concentrations of the level contained in atmospheric air from being utilised. Mixtures of nitrogen and oxygen containing a concentration of up to 2% O2 are, however, suitable for use as the gas. This is because the gas amplification remains constant up to this concentration and such gas is, to all intents and purposes, similar to that of pure nitrogen. According to the present invention, there is provided a large area proportional counter including a counter tube for detecting alpha and beta radiation or gamma radiation utilising a counter tube gas and having a low inherent capacitance, wherein the counter tube defines a chamber containing the counter tube gas, a gas regenerating device is connected to the chamber, the counter tube gas is nitrogen and the counter tube gas is capable of being passed through the gas regenerating device. Preferably, the gas regenerating device includes a molecular sieve or filter and an oxygen absorber, the filter removing oxygen impurities from the counter tube. Desirably a ventilator, fan or pump is disposed in a circuit for the counter tube gas, which circuit connects the chamber to the molecular filter and to the absorber. Accordingly, in the device according to the present invention, nitrogen is used as the gas in a tightly sealed counter tube. The gas purifying device attached thereto, which has gas circulating therethrough, ensures that the composition of the gas remains constant over long periods of time. This, in turn, ensures a long service-life for the detector. Because of the low gas-amplification factor of nitrogen, an electronics system which has as favourable a signal-to-noise ratio as possible should be employed. In the arrangement according to the present invention, low-noise, charge-sensitive preliminary amplifiers and low-capacitance detectors are preferably usad. The invention will be described further, by way of example, with reference to the accompanying drawing, the single Figure of which shows a schematic view of a proportional counter in accordance with the present invention. In the Figure, there is shown a gas regenerating device 2, in the form of a cartridge, which is connected to the bottom end of a large area proportional counter 1. The counter 1 includes a chamber 9. In the cartridge 2, an O2 absorber 5 is disposed between two molecular filters 4 which are provided with grids 3 at their respective ends. The cartridge may be screwconnected into a block 6 which has a recess formed therein for accommodating a fan 7. The fan 7 is disposed beneath the lower grid 3. A conduit 8 leads from the recess in the block 6 into the chamber 9 of the large area proportional counter 1, so that gas can be pumped round the system. The gas purifying cartridge 2 removes oxygen and atmospheric moisture from the gas. Any impurities which enter from externally, primarily O2 and moisture, are thus eliminated. However, any nitrogen which may possibly diffuse into the system is desirable for replenishment of the gas. The device of the present invention therefore comprises a combination of certain features. These are a conventional, gas-tight large area proportional counter having a low inherent capacitance and high amplification, a gas purifying cartridge and means for causing circulation of the gas. Thus, a preferred embodiment of the device of the present invention may have the following characteristics: 235 mV/106 ion pairs, amplification factor 550; a molecular filter (3 A or 4 ) for the removal of water vapour, a catalyzer (such as R3-11 made by BASF) reduced, for adsorbing oxygen; and a tightly sealed pump, a fan incorporated in the gas purifying cartridge or a temperature gradient. CLAIMS

1. A large area proportional counter including a counter tube for detecting alpha and beta radiation or gamma radiation utilising a counter tube gas and having a low inherent capacitance, wherein the counter tube defines a chamber containing the counter tube gas a gas regenerating device is connected to the chamber, the counter tube gas is nitrogen and the counter tube gas is capable of being passed through the gas regenerating device.

2. A large area porportional counter as claimed in claim 1, in which the gas regenerating device includes a molecular sieve or filter and an oxygen absorber, the filter removing oxygen impurities from the couter tube.

3. A large area proportional counter as claimed in claim 1 or 2, in which a ventilator, fan or pump is disposed in a circuit for the counter tube gas, which circuit connects the chamber to the molecular filter and to the absorber.

4. A large area proportional counter as claimed in claim 1 constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.