115In as a probe for the characterization of therapy bremsstrahlung beams and the detection of photoneutrons

Variation of the photoactivation rate across radiation fields of three different bremsstrahlung beams of two medical accelerators has been measured, making use of the photonuclear reactions in natural indium probes: 115In(y,y')115mIn and 115In(y,n)114mIn. The third nuclear reaction, 115In(n,y)116mIn, was used to detect the presence of neutrons in the photon beam and to estimate the spatial distribution of thermal and fast neutrons in the patient plane as a function of collimator opening.