Flux Density Distributions in and around a Man Sized Phantom Irradiated with Thermal Neutrons

Using a broad beam of thermal neutrons from the graphite column of a nuclear reactor, the presence of the phantom is shown experimentally to produce a disturbance of flux density levels over distances as large as 70 to 100 cm from its surface. From the experimentally determined flux density levels inside the phantom, the level of flux density equivalent to 2·5 mrem hr −1 is derived as 915 n cm −2 sec −1 when gonads and red bone-marrow are considered to be the critical organs. This is greater than the recommended level of 670 n cm −2 sec −1 , which may, therefore, be needlessly restrictive. The significance of the results for the calibration of instruments and dosemeters is discussed briefly.