This is called fick's law of diffusion, derived long ago for the description of gases. it applies if obsorption is small compared with scattering. in terms of the flux =nv and the diffusion coefficient d=au/3, this may be written compactly as j=-df' where ' is the slope of the neutron flux. o tocid m notonlo o 1odmun ogo ar mool loun ania () 4.8 summary chemical and nuclear reactions have similarities in the form of equations and in the requirements on conservation of particles and charge. the bombardment of nuclei by charged particles or neutrons pro- duces new nuclei and particles. final energies are found from mass differences and final speeds from conservation of momentum. the cross section for interaction of neutrons with nuclei is a measure of the chance of collision. reaction rates depend mutually on neutron flows and macroscopic cross section. as a particle stream passes through a medium, the uncollided particle intensity is reduced exponen- tially. neutron absorption cross sections vary greatly with target isotope and with neutron energy, whereas scattering cross sections are relatively constant. neutrons are slowed readily by collisions with light nuclei and migrate from their point of origin. on reaching thermal energy, they continue to dis- perse, with the net flow dependent on the spatial variation of flux. noilbs peoubrou. clope b 1sdmun in01 in 4.9 exercises fulo nb sinno 4.1 the energy of formation of water from its constituent gases is said to be 54.5 kcal/mole. verify that this corresponds to 2.4 ev per molecule of h20. 4.2 complete the following nuclear reaction equations: seton o noisnoade or calula alde gnlwoilo 2 mo (a) dn+14n0+ h (b) h+be-0+dn (e) dn+b0+he edmu aat 4.3 using the accurate atomic masses from table a.5, find the minimum amount of energy an a particle must have to cause the transmutation of nitrogen-14 to oxygen-17. 4.4 find the energy release in the reaction li(n, a)h 4.5 a slow neutron is caught by the nucleus of a hydrogen atom and the final products are a deuterium atom and a y-ray (see example 4.1). the energy released is 2.22 mev. if the y-ray is assumed to have almost all of this energy, what is its effective mass in kg? what is the speed of the "h particle in m/s, using equality of momenta on separation? what is the recoil energy of h in mev? how otrdoes this compare with the total energy released? was the assumption about the y-ray reasonable? 4.6 calculate the speeds and energies of the individual o particles in the 'li(p, 2a) reaction of equation (4.3), assuming that they separate along the line of the 2 mev proton motion