DNA 1240H-2 energy spectrum of the radioactive sources; (2) specification of the major ship characteristics, particularly the shielding configuration for the point considered and the nature of the shielding materials; (3) development of methods for computing the interaction of the radiations with the ship. Basically, the method presented of calculating ship-shielding factore for the transit dose (from a volume radioactive source surrounding the ship) is a point-by-point calculation. The radioactive source region is considered to be made up of an aggregate of point iatropic sources. The dose rate from each source is calculated at a given location by commiting the radiation attenuation along the entire path length, and the total dose rate is found by summing over all sources. All the energies in each source spectrum as well as all the sources mst be sumed. In practice, the summation process is replaced, to whatever extent poss- ible, vy integration. The theoretical development of ship-shielding calculations is based on ean idealized concept of the interaction of radiations with e ship. The expression of the shielding factor for the transit dose was developed from the expression of dose rate due to a point source. For a point isotropic source emitting 1 photon/second of energy Ey (Mev/photon), the exposure dose rate d, (r/hr) at a distance x (cm) from that source ina homogeneous medium can be expressed by: dy = K Hy, Ey By ed® r/hr Luscx (17-13) vhere k = a factor to convert Mev absorbed in a cm or gm of the medium per second to r/pr. 3 If up te in units of em,» k = 5.086 x 10° r/hr per Mev/cm>-eec If 4A is in units of cm°/em, k = 6.6 x 10-9 r/nr per Mev/gm-sec Hai «= the energy-absorption coefficient for air corresponding to the quantum energy E, By = the infinite-medium dose buildup factor® Ky = the linear total absorption coefficient for the medium. Then the exposure dose rate d (r/hr) at the same distance x (cm) from a point isotropic source emitting ny (photone/sec) quanta of energy E, (Mev/photon) in a homogeneous medium can be expressed as the eum of the exposure dose rates due to all the emitted energies: *This buildup factor is defined as the ratio of the dose from both unscattered and scattered radiation to the dose from unscattered radiations only. 17-56 ee ee eee: