J&a .H NlilMl zyxwvutsrqp B EISEVIER Nuclear Instruments and Methods in Physics Research B 134 (1998) 202-208 Beam Interections with Materials & Atoms Repair by radiation itself or not? A study of threonine irradiated by keV ion zyxwvutsrqponmlkjihgfedcbaZY Structure Rewurch Center. USTC. H+ei. Anhui ’ Insiirute zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Plmmu Pllysics. Acudemiu Sinicu. Hffti, 230026. People’s Republic of’ Chincr Anhui 230031. People’s Rephlic of Chinu Received 9 April 1997: received in revised form 23 July 1997 zyxwvutsrqponmlkjihgfedcbaZYXWVU Abstract A saddle type dose-survival rate curve of threonine was confirmed in low energy ion irradiation. Mass spectrometry has been used as an analytical tool in determining the species and quantities of volatile reaction products generated during the decomposition of threonine by fast atom bombardment. The radiation chemistry was related to the radiation physics of fundamental interaction between the projectile and target molecule. The nuclear collision process was pro- posed as the main reason of the particular dose effects curve, based on the analysis of the interaction process between the projectile and target molecule. A new repair model was assumed. 0 1998 Elsevier Science B.V. Ke~ords: Low energy ion; Irradiation; Nuclear collision; Dose effects; Threonine 1. Introduction Now low energy ion irradiation biology is being developed vigorously and some achievements of the mechanism researches have been obtained [lL 31. By studies, it was found that the biological ef- fects of the low energy ion irradiation have some characteristics that are different from those of X-. y-rays or high energy particle radiation. The spe- cialists in breeding conclude that the low energy ion irradiation has high mutation rate and wide mutation type. In aspect of dose effect, the survival rate of the organism radiated by X-, y-rays or high *Corresponding author. Tel.: 86 551 360 2807: fax: 86 551 360 2803: e-mail: huangwd@email.sc.ustc.edu.cn. energy particle usually follows the exponential de- creasing law. But the dose effect curves of the sur- vival rates of the organisms irradiated by the low energy N’ ions used to have the shape of saddle type that the survival rate decreased at the first dose range, but then increased along with dose and finally decreased again [4-61. Based on the study of low energy irradiated tyrosine [7], it was assumed that the particularity of the survival rate’s dose effect about the low energy ion irradiation is relative to the mass deposition effects. The experi- mental data of ultra-violet absorption dose of ion implantation of tyrosine were well fitted with the model of this assumption [8]. A new molecular model for the low energy ion irradiation which as- sumed that the mass deposit effects can produce molecules to repair the damage of DNA in organ- 0168-583X/98/$19.00 0 1998 Elsevier Science B.V. All rights reserj PIISO168-583X(98)00484-9 ied