Lithium-Drifted p-i-n Junction Detectors

Lithium-ion-drifted diodes were prepared by diffusion of lithium into silicon in vacuo at 350-400°C, followed by electric-field-drift in a silicone oil bath at 150 °C. Extension of the sensitive region toward the p-type surface was interrupted and observed intermittently by means of alpha particles incident upon this surface at three energies in the range of 6 to 9 Mev. Ion-drift was then continued until the plot of pulse height vs energy for these alpha particles showed a negligible (<50 kev) energy intercept for distances of drift up to 4 mm from the lithium-diffused surface. The response to protons at energies from 4.5 to 10 Mev was linear to within ±0.3%. The resolution width (FWHM) for protons at the higher energy, for deuterons at 20 Mev and for alpha particles at 40 Mev was limited by beam energy spread in the Argonne 60-in. cyclotron. At room temperature, resolution widths down to 20 kev were observed for electrons at energies of 500 kev and 1 Mev, and that for gamma rays was 9 kev at 661 kev. Resolution widths down to 12-13 kev were observed for electrons at 1 Mev when the detectors were cooled to liquid nitrogen temperature.