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RIKEN Accel Próg. Rep. 24 (1990)

111-4. Radiation Chemistry and Radiation Biology

1. High-Density Excitation by Heavy lons: Track-Depth Resolved Luminescence of N-ions Injected-Helium Gas and Liquid

K. Kimura, J. Wada, and M. Arai

lons of few MeV/amu show characteristic radiation effects such as charge exchange, wake field, and convoy electrons. Furthermore, in their tracks, electronic excited States are contained at an extremely high density. Our studies aim to find characteristic phenomena caused by above effects and elucidate them. For these purposes, space- and time-resolved luminescence measurements were done.

A space-resolved or track-depth resolved luminescence were measured using a following eąuip-ment named a tack scope. The track scope was composed of a ąuartz imaging fiber and a position detective photon-counter. One end of the fiber was mounted in a cryostat and thereby temperaturę and pressure of sample helium were adjusted. The image projected from the other end, namely, luminescence intensities along the path of ion tracks, was digitized by a position-detective photon-counter. (See Ref. 1.) Also, depth-resolved luminescence spectra were measured by the change of a section of the fuli image which enters into a monochromator through a monochromator-slit.

Figurę 1 shows helium-density dependent specific luminescence, dL/dx, as a function of track-

WAVELENGTH/A

Fig. 2. Depth-resolved and density-dependent luminescence spectra.

second peak was observed at the Iow energy side.

The positions of the first peaks were invariant with variation in the helium density. These peaking were explained by the effect of excitation density. On the other hand, the positions of the second ones varied with variation in the helium density and excitation density, but they appeared at a given ionic velocity with variation of helium density as shown in Fig. 3. The second peaking may be attributable to charge exchanges or direct excitations.

I

Fig. 1. Specific luminescence, dL/dx, vs. the depth of N-ion tracks and its helium density dependence. AU the curves are illustrated in equiheight.

Fig. 3. Luminescence efficienty, dL/dE, vs. ionic velocity and its helium density dependence. Ali the curves are illustrated in eguiheight.

References

1) K. Kimura: Nuci. lustrum. Methods B, in press.

depth. Luminescence spectra were changed scarcely except for their intensities; peaks were assigned to be due to the d-b, D-B, H-C, and J-C transitions between excimer States (Fig. 2). The most important finding is a splitting of Bragg-like curve of dUdE vs. excitation density. Namely, the first peak positioned at the high energy side of the maximum stopping power and in addition to it the