tailieunhanh - Material Science_ Vol 2 of 2 - US DOE (1993) WW part 13

Tham khảo tài liệu 'material science_ vol 2 of 2 - us doe (1993) ww part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Plant Materials DOE-HDBK-1017 2-93 EFFECT DUE TO NEUTRON CAPTURE EFFECT DUE TO NEUTRON CAPTURE Neutron radiation affects material because of neutrons being captured. This chapter discusses the effects that the neutrons being captured have on the material. EO DESCRIBE how the emission of radiation can cause dislocation of the atom emitting the radiation. EO STATE the two effects on a crystalline structure resulting from the capture of a neutron. EO 1. 22 STATE how thermal neutrons can produce atomic displacements. Effect D ue to N eutron C apture The effects of neutrons on materials arise largely from the transfer of kinetic energy to atomic nuclei in one way or another. Thus highly energetic recoil nuclei may be indirectly produced by the absorption of a neutron and the subsequent emission of a Y As previously discussed if the energy of the recoil nucleus is sufficient to permit it to be displaced from its normal or equilibrium position in the crystal lattice of a solid physical changes of an essentially permanent nature will be observed. The effects of fast neutrons in disrupting or damaging the crystal lattice by displacement of atoms are discussed in the two previous chapters Atomic Displacement Due to Irradiation and Thermal and Displacement Spikes Due to Irradiation. This damage is commonly referred to as radiation damage. The absorption or capture of lower energy thermal neutrons can produce two effects. a. introduction of an impurity atom this is used in the electronics industry to uniformly dope semiconductors due to the transmutation of the absorbing nucleus b. atomic displacement caused by recoil atoms or knock-ons As noted the introduction of an impurity atom was discussed previously and atomic displacement is the result of n p and n a reactions and n Y reactions followed by radioactive decay. Thermal neutrons cannot produce atomic displacements directly but they can do so indirectly as the result of radioactive capture n Y and other neutron .