The NPL Protection-level Secondary Standard X- and Gamma-ray Dose Rate Meter
- 1 August 1977
- journal article
- research article
- Published by Wolters Kluwer Health in Health Physics
- Vol. 33 (2) , 131-137
- https://doi.org/10.1097/00004032-197708000-00002
Abstract
An instrument is described which provides the means of calibrating instruments used for monitoring X- and gamma-rays (over the range 10 kV to 2 MV) for protection purposes. The chamber utilizes a thin walled spherical conducting rubber balloon as its outer electrode, of diameter about 190 mm and thickness approx 0.3 mm. To inflate it to a nicely firm shape requires an excess pressure of about 0.4% only. A radioactive check source [a 4-mCi (1.5 × 108 Bq) encapsulated bead of 241Am] is integral with the chamber. The source is stowed at the base of the hollow stem of the collecting electrode and is released into the centre of the inverted chamber using an externally positioned magnet. Ionization current is measured by means of a current to voltage transducer with variable negative feed-back for range changing. The instrument is scaled in absorbed dose rate to air on nine ranges from 1 mrad/hr (10 μGy/h)(f.s.d.) to rad/hr (100 mGy/h).Keywords
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