ABSTRACT
Boron (B) is one of the least abundant chemical elements: boron content in the earth’s crust is no more than about 0.005 wt% and in the ocean water even lesser (Kuznetsov 1988). However, the role of boron in the formation of various molecular and solid-state structures is incommensurably great. The explanation of the diversity of materials containing boron atoms reduces to its electronic structure in isolated state. The conguration of valence electrons peculiar to the free B atom is 2s22p. In atomic structures, it becomes an energetically unstable conguration tending to more stable ones-at rst 2s22p2 and then 2s22p3. Thus, boron atom is a strongly distinct acceptor and all boron structures are electron decient. It is the main reason why boron crystalline modications as well as amorphous boron exhibit clustered structures. They are considered to be stabilized by intrinsic point defects and/or certain impurities in high concentrations compensating electron deciency inherent in ideal structures (Jemmis and Prasad 2006). For instance, a unit cell of β-rhombohedral boron, which is believed to be the ground-state modication, consists of 105 atomic sites. But in real crystals containing both partially occupied regular sites and interstitials, there are ∼106.5 boron
3.1 Introduction ............................................................................................................................ 43 3.2 B-n Interaction ....................................................................................................................... 45 3.3 Neutron Analysis of Boron-Containing Materials ................................................................. 47 3.4 Neutron Radiation Treatment of Boron-Rich Materials ......................................................... 49 3.5 Semiconductor Devices Utilizing B-n Interaction ................................................................. 51 3.6 Boron-Based Materials in Nuclear Technologies ................................................................... 53 3.7 Boron-Based Neutron Shielding Materials ............................................................................. 56
3.7.1 Neutron Sources and Their Biological Effects ........................................................... 57 3.7.2 Maximal Concentration of 10B Atoms in Boron-Rich Materials................................ 59 3.7.3 Neutron Shielding by Boron-Containing Materials ................................................... 62
3.8 Boron Neutron Capture Therapy ............................................................................................64 3.8.1 Boron Delivery Agents ...............................................................................................65 3.8.2 Determination of 10B Levels .......................................................................................68 3.8.3 Boron Neutron Capture Synovectomy ........................................................................ 70
3.9 Conclusions ............................................................................................................................. 70 References ........................................................................................................................................ 70
atoms per cell. An almost regular icosahedron B12 with boron atoms at its vertices serves as a main structural unit of this crystal. Because of electron deciency and extremely high concentration of intrinsic point defects, at moderate temperatures, undoped β-rhombohedral boron is a p-type semiconductor revealing the specic mechanism of hopping conduction (Chkhartishvili 1989). On the other hand, the large unit cell contains interstitial voids of different types, which are able to accommodate high concentrations of metal atoms without noticeable distortions in the host lattice. Consequently, doping makes it possible to form the series of β-rhombohedral boron-based alloys with tunable electronic properties.
