EPR and UV investigation of sucrose irradiated with nitrogen ions and gamma-rays

Abstract

Sucrose irradiated with N-ions and gamma-rays is investigated by EPR and UV spectroscopy. Irradiation doses are in the range of 20–380 Gy and linear energy transfer (LET) for N-ions of 90, 125 and 160 keV μ m - 1 . All EPR spectra recorded in irradiated solid samples are identical, suggesting that generated free radicals are not sensitive to the radiation quality. The EPR response of free radicals linearly depends on the absorbed dose but when generated by N-ions it is always lower than that obtained by irradiation with the same absorbed dose from gamma-rays. Water solutions of irradiated sucrose exhibit UV absorption at 267 nm due to the product of free radicals recombination, which spectrum remains independent on the radiation quality. The intensity of this band however depends on the absorbed dose and for equal doses it is higher for samples irradiated with N-ions than with gamma-rays. For different high LET-radiations with N-ions and low-LET radiation from gamma rays is found an excellent linearity between the EPR signal intensity and the UV absorbance of the obtained water solution. The relation between EPR and UV response of N-ions irradiated samples is reciprocal as well as between them and gamma-irradiated samples suggesting different impact of the high-energy photons and heavy particles on the solid state. For low LET photon radiation with moderate dose rate the probability for a successful hitting of two neighboring molecules is low. Therefore, only a small part of low LET radiation-induced free radicals may be expected to recombine giving an UV detectable product. In opposite, because of the dense ionizations and heaviness of N-ions almost all molecules in the core of the track are ionized yielding mainly products of the recombined free radicals. In the outer part of the track delta particles, which are more like low LET radiation electrons, stands for ionizations and produces a small number of free radicals situated far from each other. Therefore, we can expect higher EPR response of sugar irradiated with a certain dose of gamma-rays than of heavy particles. Just the opposite behavior should be expected for the UV absorption, which should be higher in the irradiation with heavy particles than with gamma-rays. The reported observations suggest that a sucrose/UV/EPR dosimetric system seems to be very promising for dose determinations from both gamma and heavy particle radiation and indicate a method for simultaneous determination of absorbed dose and LET. It also seems to be a new way for calibration of EPR dosimeters irradiated with N-ions via UV spectrometry.