TRIAC Progress Report - KEK

difference spectra, more specifically a clear one-to-one correspondence between
decaying position of 8 Li and energy difference of two coincidently measured α-particles.
For example, looking at the time evolution of the counts of coincident events with zero
energy difference in the energy difference spectra should be a good measure of the time
when 8 Li is across the middle of the sample, because the zero energy difference means
that the path lengths experienced by two coincident α-particles are identical. We can
conclude that the sensitivity against the diffusion of 10 -12 cm 2 /s could be easily achieved
by the coincident measurement of two α-particles with the geometry assumed in the
simulation.
Fig. 3-34 (a) Simulated concentration profiles of 8 Li implanted into LiCoO2 with a thickness of
50nm with an energy of 1keV and their evolution by diffusion simulated at 1, 2, 3 and 4 seconds
after implantation with a diffusion coefficient of 10 -12 cm 2 /s. (b) Spectra of energy difference of
α-particles coincidently emitted at angles of 5 o relative to the surface of the sample. They are
respectively simulated in the same time sequence as done in Fig. 3-34 (a).
The proposal of KJ02 has met difficulties in the fabrication of the samples with an
appropriate thickness and surface roughness, especially for the coincidence
measurements of two α-particles where the sample is required to have a form of a
self-support foil with a thickness of about 100 nm. After all considerations, the proposal
has been modified to confirm the feasibility with a reduced sensitivity (e.g. 10 -10 ~10 -11
cm 2 /s), as a simple extension of the previously developed method, by focusing the
time-evolution of the energy spectra of α-particles emitted with a large angle from
β-decaying 8 Li implanted with an energy of about 10 keV. An experimental set-up was
newly fabricated and is ready for an experiment to be carried out soon.
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