Fabrication of radiation detector using PbI/sub 2/ crystal

Abstract

Radiation detectors have been fabricated from lead iodide (PbIJ crystals grown by two methods: zone melting and Bridgman methods. In response characteristics of the detector fabricated from crystals grown by the zone melting method, a photopeak for y-rays from an v"Am source (59.5 kev) has been clearly observed with applied detector bias of 500 V at room temperature. The hole drift mobility is estimated to be about 5.5 cm2/Vs from measurement of pulse rise time for 5.48 MeV a-rays from "Am. By comparing the detector bias versus saturated peak position of the PbI, detector with that of the W e detector, the average energy for producing electronhole pairs is estimated to be about 8.4 eV for the PbI, crystal.A radiation detector fabricated from PbI, crystals grown by the Bridgman method, however, exhibited no response for y-rays.

Electronic and optical properties of lead iodide

“…Our calculations show that there is a very small anisotropy in the optical properties of PbI 2 . This is in contrast to what our previous calculations on HgI 2 ͑Ref. 21͒ have shown.…”

“…For PbI 2 we obtain E g (0)ϭ2.485 eV, Sϭ3.60, and ͗ប͘ϭ13.1 meV. It is worth to mention that this notation is adopted from the vibronic model of Huang and Rhys.…”

“…It is a wide-band-gap semiconductor (E g Ͼ2 eV͒ with high environmental stability efficiency. [1][2][3][4] The performance of the detector cannot be fully understood unless its electronic and optical properties are determined. Recently, its band-gap energy and thermal properties were determined by photoacoustic spectroscopy.…”

Improved growth of PbI2 single crystals

“…Zhu et al [3] have obtained PbI 2 single crystal with resistivity of the order of magnitude of 10 10 O cm using the VBM. The resistivity of grown crystal by Shoji et al [4] through 60-pass ZM is also of the order of magnitude of 10 10 O cm, and Oliveira et al [5] have not yet obtained high-resistivity PbI 2 single crystal using purified 500-pass raw materials by VBM. However, the resistivity of PbI 2 crystal grown in an ampoule filled with argon at 1.5 atm by TMZM is up to 10 12 O cm [6].…”

“…However, the resistivity of PbI 2 crystal grown in an ampoule filled with argon at 1.5 atm by TMZM is up to 10 12 O cm [6]. For many years, in order to get a high quality of PbI 2 single crystal and enhance the resistivity of the crystal, studies on different growth methods of PbI 2 single crystal were performed [1][2][3][4][5][6]. Many difficult problems were encountered, such as decomposition of the PbI 2 melt during the crystal growth process, deposition of segregated Pb, and I 2 evaporation, and they are still not solved.…”