203 TABLE 69. Neutron energy Total damage (1) (2) MeV Calc. area/ . 6.2 7.2 8.2 9.2 10.1 11.1 12.1 14.1 Fast Neutron Errect on Postposep TLD-700 l | | 33.5 | 98.6 114.5 | 139.7 | 185.4 228.4 211.9 199.1 244.0 (6) | | (7). | ove | Precalib. area/ \Postcalib, area/ mg X Rad 87 42.5 38 64.4 AF 80.9 89.9 111.2 .38 45 46 84.7 (5) (3)72)} Obs.“areal mg 59.4 (3) Irreversible damage mg ™ Rad 9.0 w.4 | | 8.0 8.0 49 15.5 | 12.4 37 10.8 | 7.7 pears necessary to attribute the irreversible and re- versible damage to the same mechanism, the differ- ences in these factors being due only to the annealing process, At the neutron energies present in this ex- periment, 6 to 14 MeV,the deformation of the crystal by collision processes appears to be the mechanism for the damage. CONCLUSIONS The effect of fast neutrons on the gamma ray re- 10.5 10.7 11.3 10.0 | | (8) a) | | | 7.1 7.8 7.1 8.3 Reversible 0.89 0.64 0.78 0.62 0.73 0.52 0.78 0.69 | : 0.73 0.63 0.84 0.48 0.68 0.54 0.71 0.54 should not be used in the presence of fast neutrons to monitor gamma radiation. Wewish to thank Prof. Herman Cember, Civil Engineering Department, Northwestern University, for his encouragement and cooperation. One of us (K.E.) carried out this work under a fellowship from the U.S. Public Health Services. REFERENCES sponse of 7LiF has been investigated. The dosimeters 1. Kastner, J., Oltman, B. G., Tedeschi, P., and Beggs, J. N Health Phis, 13, 918 (1967). 2, Kastner, J., Ramesh, Hukkoo, Oltman B.G., and Dayal, Y. is reversible with the annealing procedure employed. The results from this experiment indicate that "LiF 3. Lauritsen T., and Ajsenberg-Selove, F. Energy Levels of Light Nuclei. To be published. J’ were found to suffer a marked damage, part of which Radiat. Res. 82, 625 (1967). . ULTRASONIC EXCITATION OF THERMOLUMINESCENTLITHIUM FLUORIDE* Jacob Kastner, R. H. Selner, C. M. Paden, and B. G. Oltman Ultrasonic excitation of luminescence has been proposed to eliminate the black-body radiation background noise inevitably associated with thermoluminescent dosimeter readout. Studies have been carried out with single LiF crys- tals bonded directly to piezoelectric transducers. The transducers were driven with a continuous radiofrequency generator over a range of frequencies from 4 to 10 megacycles/sec (MHz}. * Abstract of paper published in Health Phys. 16, 803 (1969). Glow peaks were observed at 10 MHz. After observing a rise in the transducer-LiF temperature, we duplicated the temperature ramp with our normal thermoluminescent readout apparatus. The recorded glow peaks were identical with the luminescence pro- duced by the ultrasonic excitation, verifying the latter’s essentially thermal character and thus eliminat- ing the hope that ultrasonics might provide real advantages as a readout technique.