Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Patent
1979-09-26
1984-01-17
Smith, Alfred E.
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
G01T 118
Patent
active
044265816
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an arrangement for measuring the radioactivity concentrations of a gas, with a measuring chamber for receiving the gas and a beta-ray measuring device which measures the activity concentrations and whose detector is arranged in the measuring chamber.
Arrangements of this type are usually used for measuring the activity concentrations of isotopes of noble gases. Since the detection sensitivity deteriorates when the basic load of the detector increases due to external radiation, the measuring chamber is set up at locations with low external radiation, for example, in special spaces next to the exhaust stack of a nuclear power plant.
It would be conceivable to shield the measuring chamber by a housing of shielding material to such an extent that the measuring chamber could be set up at locations with high basic load. However, such an arrangement could only be operated as a stationary system because the weight would not allow moveable, i.e. portable embodiments.
It is the object of the invention to specify an arrangement for measuring the radioactivity concentration of a gas which has a high detection sensitivity even in the case of a high basic load due to external radiation, but whose weight is so low that the arrangement can be used as a moveable system.
In an arrangement of the above-explained type, this object is met by arranging the measuring chamber in a pressure-type housing of shielding material, particularly lead, and by connecting the measuring chamber to a compressor which increases the gas pressure in the measuring chamber. In this manner, the volume of the measuring chamber can be reduced by such an extent that the weight of the shielding housing required for a high basic load remains low.
To compensate for the external radiation, the measuring device is preferably provided with a second detector which is shielded from the measuring chamber. By means of the second detector, the share of the external radiation in the measuring result of the first detector can be eliminated. Those embodiments have been found advantageous in which the first and second detectors are arranged on opposite locations of the first measuring chamber.
In a preferred embodiment, the compressor is connected to an aerosol filter arranged in a second measuring chamber. For measuring the aerosol activity concentration, a third detector of the measuring device is arranged in the second measuring chamber. This embodiment facilitates the assessment of the incorporation dose. The incorporation dose is caused by the intake of radioactive gases and aerosols through the respiratory tract.
The total weight of the arrangement stays within the limits to be required of a portable measuring device when the two measuring chambers are arranged in a common housing and are merely separated from each other by a shielding dividing wall. The volume of the second measuring chamber is generally much smaller than the volume of the first measuring chamber, so that the outer housing walls of the second measuring chamber in connection with the shielding dividing wall ensure the shielding of the first measuring chamber.
The second detector is advantageously also utilized for the compensation of the basic load of the third detector. The second detector is preferably arranged in the region of the shielding dividing wall between the first and the third detectors.
Especially high detection sensitivities can be obtained with the use of a detector which compensates for the external radiation (second detector) when the outer shape of the housing and the wall thickness of the housing walls and the shielding dividing wall are chosen in such a way that the thickness of the shielding material is about the same for the three detectors independently from the direction of incidence of the external radiation. Last but not least, the background compensation is improved by the fact that all the detectors are of the same type.
In order to keep the volume of the first measuring chamber as small as possible and, thus, the weight of the shielding hou
REFERENCES:
patent: 3531639 (1970-09-01), Baum et al.
patent: 4092541 (1978-05-01), Neidl
Levins et al., ".beta.-Scintillation Monitor for Krypton-85 at High Presss", Nuc. Ins. & Methods 146, No. 3, (1977), pp. 517-525.
Kreiner Hans-Jurg
Seif Rudolf
Zimmer Wilhelm
Gesellschaft fur Strahlen-und Umweltforschung mbH
Howell Janice A.
Munchener Apparatebau Fur Elektronische Gerate Kimmel GmbH & Co.
Smith Alfred E.
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