RESISTANCE OF LEAD TUNGSTATE AND CERIUM FLUORIDE TO LOW RATE GAMMA IRRADIATION OR FAST NEUTRONS EXPOSURE
We present here the results of recent low dose rate gamma irradiation of lead tungstate and cerium fluoride long crystals, and, for lead tungstate only, fast neutron exposure. For the low rate tests, recovery processes are taking place during irradiation and, compared to the usual high rate tests, only a very low damage is noticed, if any. No saturation effect is observed in these previously irradiated samples. For the neutron tests, a very small variation with fluence is not excluded, after a fast saturation at low fluence. The samples tested here are very resistant.
Radiation-Induced Optical Absorption in PbWO4:La Scintillation Crystals
The radiation resistance of scintillation lead tungstate crystals (PbWO4) activated with lanthanum ions is investigated as part of an international project. The transmission spectra of various sections of standard PbWO4:La crystals before and after irradiation of the crystals with doses 10, 102, 103, 2·104 rad with dose rate 0.24 R/sec and doses 2·104, 105, 106, and 107 rad with dose rate 97 R/sec from a 60Co source are measured in the wavelength range 400–700 nm. The change in the radiation resistance of a crystal along the growth axis is analyzed on the basis of the data obtained. The nature of the γ-induced absorption is discussed. The effect of irradiation with fast neutrons up to fluence 1012–1014 cm–2 on the radiation resistance of these crystals is studied. The contribution of γ rays and neutrons to the radiation-induced absorption is estimated.
Electron dose-rate conversion factors for external exposure of the skin from uniformly deposited activity on the body surface.
Dose-rate conversion factors have been calculated for external exposure of the skin from electrons emitted by sources that are deposited uniformly on the body surface. The dose-rate factors are obtained from electron scaled point kernels developed by Berger (Be71; Be73; Be74). The dose-rate factors are calculated at depths of 4, 8, and 40 mg cm-2 below the body surface as recommended by Whitton (Wh73), and at a depth of 7 mg cm-2 as recommended in ICRP Publication 26 (ICRP77). The dependence of the dose-rate factors at selected depths on the energy of the emitted electrons is displayed. The dose-rate factors for selected radionuclides of potential importance in radiological assessments are tabulated.