Germanium Lithium-Drifted Detectors

Chassery et al. [97] studied the 87Sr/86Br composition in marine sediments, observing excellent agreement between results obtained by ICP-MS and thermal ionisation mass spectrometry. Low level a-spectrometry with lithium drifted germanium detectors has been used to determine 90strontium in seawater [59]. 

Lithium-Drifted Germanium Detectors. Two kinds of planar Ge(Li) diodes were fabricated in our Laboratory for the spectrometer (I). The chief consideration was maximum cross section with a resolution of less than 3 k.e.v. at 60Co FWHM (full width half maximum). The available single-crystal germanium material dictated the shape of the detector. The first detector was fabricated from a 15-cm. long Sylvania ingot with a trapezoidal cross section its finished dimensions were 6 cm. X 3 cm. X 1 cm. Our second detector was fabricated from circular Hoboken stock (NPC Metal and Chemical Co., Los Angeles) its finished dimensions were 2.8 cm. diameter X 1.2 cm. thick. 

Table III gives the conditions, data and reactions for the long irradiations of iridium, osmium and ruthenium. Samples and standards were irradiated in the University of London Reactor under a maximum thermal neutron flux of 1.4 x 10 n cm" s". The samples were counted using a lithium drifted germanium detector (Ortec Inc) linked to a computer based gamma ray spectrometer (Nuclear Data Inc. 6620 Multichannel Analyser). A general Neutron Activation Package written in FORTRAN IV was employed to run a peak search and calculate PGM concentrations in the plant samples. The irradiation of platinum is a special case and details are given in Table IV. Various nuclides emit y-rays of similar energy, and in INAA these become a serious interference in the determination of platinum in biological samples.

The Tm parent used for the 66-74-keV resonance does not populate the 75-89-keV level, and the shorter-lived Lu parent must be used [185]. This has a very complex decay, and a lithium-drifted germanium detector is required to detect the y-ray with sufficient discrimination. The Tm(a, 2n) Lu reaction provides a convenient route so that cubic... 

The neutron activation analysis was carried out at Livermore s 3-megawatt reactor. High resolution lithium-drifted germanium detectors were used to count the samples. Details of the irradiation and counting sequence can be found in an earlier paper (6). 

The lithium-drifted germanium detector, denoted Ge(Li), is similar in construction to the Si(Li) detector. However, a striking difference is found in the very high lithium mobility in the germanium detector at room temperature. A Ge(Li) detector will be destroyed if it is allowed to warm up from the normal 77 K operating temperature. The Si(Li) detector and preamplifier, on the other hand, usually can withstand a warm-up, providing the detector bias voltage is turned off. 

Lithium drifted germanium detectors were in use during the first years of semiconductor detectors application for gamma-ray spectrometry. They showed good resolution and efficiency but had to be kept at the temperature of liquid nitrogen all the time. 

Semiconductor transducers have assumed major importance as detectors of X-radiation. These devices are sometimes called lithium-drifted silicon detectors, Si(Li), or lithium-drifted germanium detectors, Ge(Li). 

Lithium-drifted germanium detectors are available in many configurations and sizes. Prices for these devices are relative to the size. One of the disadvantages of these detectors is the necessity for low temperatures. Permanent damage may result if such a detector is warmed to room temperature. 

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