| Popis: |
Despite considerable work in the field of radiation effects of the 10B(n,α)7Li reaction, the mechanisms of radiation damage to cells and biomolecules are not well understood. More knowledge of the generalities of comparative radiation effects of the other types of radiations, especially those relating to the 14N(n,p)14C reaction is needed. Irradiation by thermal neutrons of 10B-containing biological materials inevitably involves exposure to radiations other than α- and Li-particles, namely those derived from the nuclear reactions l4N(n,p)l4C, H(n,γ)D, etc. Although 10B has a larger cross-section for thermal neutron absorption (about 2000-fold larger than that, for example, of 14N), the smaller abundance and lower accumulation of this nuclide in the usual biological samples make the additional contribution of other nuclear reactions to the total radiation effect inevitable. The initial purpose of this study is to quantitate the contribution of 14N(n,p)14C reaction to the total radiation effect when l0B-containing biological materials are irradiated with thermal neutrons. The Tc-pneumatic irradiation facility (Tc-Pn) attached to KUR has a high thermal neutron flux (4x1011 n cm-2 sec-1) as well as a high mixed γ-ray dose (2x103 Gy hr-1). Hence it is useful for the analysis of the effect of 14N(n,p)14C reactions on biomolecules, such as amino acids, nucleotides, proteins and nucleic acids. The contribution of the 14N(n,p)14C reaction depends on the N-concentration of the samples. Our preliminary calculation for irradiation at the Tc-Pn indicated that when N-concentration is less than 10-2M, most of the radiation damage would arise via mixed γ-rays. But the contribution of the 14N(n,p)14C reaction comprises about 0.8 and 7.4% of total absorption dose when N-concentration of irradiated materials is 10-1M and 10° M, respectively. It reaches nearly 50% when dry materials such as amino acids and proteins are irradiated at the Tc-Pn. In this investigation, an attempt was made to clarify the mechanism of the thermal neutron 14N(n,p) 14C reaction on cells and bio-molecules by examining the inactivation of various enzymes in dry state. |
