Modifications of the Victoreen model 660-4A ionisation chamber for beta dose measurements

A description is presented of simple modifications of a Victoreen 660-4A ionisation chamber probe, whose normal use is for photon field exposure measurements, to allow measurements of beta radiation fields. One face of the 660-4A detector has been replaced with a thin window and the chamber volume behind the central plate electrode has been eliminated. The latter modification negates the attenuating characteristics of the collecting electrode on low and moderate energy electrons and provides an instrument for assessing beta radiation dose rates from a variety of sources. Response to both point sources and extended beta sources over a wide range of end-point energies have been evaluated with very acceptable results. The modifications are easy to implement and extend the versatility of the instrument. (author)