Fabrication and application of semi-conductor radiation detectors in high resolution nuclear decay studies.

Factors which determine performance of lithium-drifted semiconductor radiation detectors, particularly lithium-drifted germanium detectors for gamma-ray spectroscopy, are discussed in terms of general semiconductor theory The analysis includes the effects of electronic noise and the statistical effects of radiation-induced ionization and charge collection in semiconductors. The fabrication technique is discussed for obtaining small volume planar Ge(Li) detectors and large volume (totally compensated) Ge(Li) detectors using the lithium-ion drifting process. In the case of detectors of the former type, devices have been fabricated with unusual operating characteristics; excellent resolution has been obtained from such devices at collection fields as low as 15 volts/mm. A new technique for treating the exposed surfaces of Ge(Li) detectors by coating them with a layer of CaFo which both lowers detector leakage current and protects the surface from exposure to the ambient is discussed. An estimate of the Fano factor in germanium has been made using Ge(Li) detectors. The value of F =0.11 +0.05 has been obtained, and this result as well as previous ones is discussed in terms of the charge collection efficiency of Ge(Li) detectors, the interaction of gamma-rays with matter and the radiation-induced ionization process, and recent theoretical predictions for the Fano factor. The calibration and use of Ge(Li) detectors for gamma-ray spectroscopy is discussed. Detectors fabricated in this laboratory have been used as gamma-ray spectrometers in high resolution nuclear decay studies. In the study of the decay of Co and Mn two previously unobserved gamma-rays have been detected at energies of 3119 3 keV and 3SQ8.7 koV; ?? ? these new transitions result in placing of two levels in Fe at energies of 3119.3 keV and 4445.3 keV which have been previously observed only in nuclear reaction studies. The present study, which has included both single Ge(Li) detector measurements and two-parameter coincidence experiments using a Ge(Li) detector and Nal(Tl) detector, has confirmed c-fl the existence of certain other energy levels in Fe and has provided added information on spin and parity assignments to the levels. The nuclear decay study of Ge has yielded new results for the levels in Ga . A gamma-ray of energy 536.9 keV has been detected for the first time resulting in the placement of a new energy level in Ga of this energy. The previously reported gamma-ray of energy 185 ke V has been resolved with Ge(Li) detectors into two transitions of energies 181.9 keV and 189.8 keV. The existence of a gamma-ray of energy 515.0 keV has been postulated; more precise values for the energies of the other gamma -rays from the decay of Ge have been obtained and a revised decayed scheme has been constructed. Aft The decay of Ga has been studied using Ge(Li) detectors and preliminary gamma-ray data obtained.