Thick-target yield of γ-rays emitted in the reactions14N(p,p′γ1)14N and15N(p,αγ1)12C were measured as a function of bombarding energy in order to select the conditions favoring the employment of these reactions
in nitrogen isotopic analysis. The applicability of these reactions in the determination of relative as well as absolute nitrogen
isotopic abundances was demonstrated at 4.3 MeV bombarding energy.
The radioactive content of alfalfa and rye grass was measured in five consecutive harvests covering a period of one and a half years after the contamination of a field caused by the Chernobyl fallout. The measured long-lived isotopes were106Ru,134Cs and137Cs. In the first four harvests alfalfa contained significantly less radioactivity than rye grass, while in the last harvest both plants contained comparable levels of radioactivity. The results from the first harvest, demonstrating the radioactivity obtained in the direct fallout, indicate that the fraction of total initial deposition retained on rye grass is by 55% and 70% greater than alfalfa for Cs and Ru isotopes, respectively. The second, third and fourth harvests demonstrate values of plant to soil concentration ratios /CR/ considerably larger than those observed in the fifth harvest. Only the CR values obtained in the last harvest overlap with commensurate values previously reported in the literature.
Consecutive short bombardment of thick biological specimens with proton beams demonstrated that the yield from oxygen decreases
with increasing amounts of total deposited beam; those from carbon and sulfur appear not to be affected, while significant
yield increases are observed with respect to the γ-ray yields of all the other investigated isotopic nuclear reactions. The
yield alterations were investigated in freeze-dried plant and animal specimens as well as in targets prepared by air drying
at several temperatures. Only in ashed specimens do the γ-ray yields remain constant as a function of increasing amounts of
deposited beam. The yield alterations induced by the beam on non-ashed biological specimens depend on (I) the total dissipated
beam charge, (II) energy of the beam, (III) chemical element, (IV) origin of the biological specimen, and (V) method of preparation
of the target. The underlying mechanism and implications of the yield alterations in the elemental analysis of non-ashed biological
specimens are investigated and discussed.
Authors:A. Xenoulis, F. Trouposkiadis, and C. Douka
A simple target-moving system, in which the movement of the target is achieved by externally moving the whole miniature scattering chamber, was developed and tested as a means for suppressing -ray yield increase induced by proton beams in biological specimens. Although there is a limit in the total beam charge which may be safely deposited on a moving biological target, the duration of the safe bombardment is sufficiently prolonged by the motion to allow the accumulation of meaningful statistics.
Authors:A. Xenoulis, C. Douka, T. Paradellis, and A. Katsanos
The applicability of the14N(p,p’ γ1)14N nuclear reaction in the determination of the absolute abundance of14N, with a 2% uncertainty, was demonstrated at 4.3 MeV bombarding energy. The fact that almost all of the thick target γ-ray
yield resulted from a resonance at Ep=4.0 MeV allowed to consider the necessary stopping-power corrections only at the energy
of that resonance. Alternatively, the method was used to obtain the stopping power of 4.0 MeV protons in complex biological