A 5 MeV betatron for calibration of radiation detectors

The design and fabrication of a 5 MeV betatron developed for calibration of radiation detectors at the Bhabha Atomic Research Centre, Bombay, is described. The magnet has been fabricated from 14 mil silicon steel laminations and weighs 225 kg. The field index is 0.75 and the radius of the equilibrium orbit is 5.6 cm. The betatron operates from 230 volts 50 cycles mains and requires about 2 KW of power. The electrons are injected from a heated thoriated tungsten filament by means of a high voltage (8KV) negative pulse. The pulse has approximately half sine wave shape having rise time of 1 μsec and duration 8 μsec. The electrons are accelerated to 5 MeV and produce X-rays on striing an internal tungsten target. The shifting of the electron orbit towards the target is effected by the saturation of the central core. The X-rays are emitted in the forward direction in a cone. The angle between the half intensity directions is 15 deg. The radiation output from the machine is equivalent to 50 mc of radium. (author)