Detectors bismuth germanate

Bismuth germanate detectors have even better efficiency than sodium iodide detectors but their energy resolution is poor. Therefore, this type of detector material is used for special purposes but not for spectrometry. 

When it reaches its full capability, TASCC will accelerate all ions between lithium and uranium to energies up to 50 MeV/u and 10 MeV/u, respectively, It will feed some major pieces of apparatus the Q3D magnetic spectrometer, the isotope separator, a growing array of gas and solid-state detectors housed in a 1.5 m diameter scattering chamber, and the 8ir" Y-ray spectrometer [AND 84], All are currently operational except the 8ir spectrometer, which is being built by a consortium of Canadian universities and AECL Chalk River, with completion scheduled for late 1986. It will comprise two subsystems i) a spin spectrometer of 72 bismuth germanate (BGO) detectors, and ii) an array of 20 Compton-suppressed hyperpure (HP) Ge detectors. 

A redundant medical PET scanner, a CTI ECAT931/08, was acquired. This comprises 128 detector blocks (Figure 2a), each consisting of four photomultiplier tubes viewing a 30 mm thick crystal of bismuth germanate scintillator approximately 49 x 56 mm2 in area, which is cut into an array of 8 x 4 elements (each approximately 5.6 x 12.9 mm2,... 

The detection efficiency of a detector is another important property in PET technology. Since it is desirable to have shorter scan times and low tracer activity for administration, the detector must detect as many of the emitted photons as possible. The 511-keV photons interact with detector material by either photoelectric absorption or Compton scattering, as discussed in Chap. 1. Thus, the photons are attenuated (absorbed and scattered) by these two processes in the detector, and the fraction of incident 7 rays that are attenuated is determined by the linear attenuation coefficient (/x) given in Chap. 1 and gives the detection efficiency. At 511 keV, /x = 0.92 cm-1 for bismuth germanate (BGO), 0.87 cur1 for lutetium oxyorthosilicate (LSO), and 0.34 cm-1 for Nal(Tl) (Melcher, 2000). Consequently, to have similar detection efficiency, Nal(Tl) detectors must be more than twice as thick as BGO and LSO detectors. 

The mean life, or lifetime, of an excited activator state is very short - of the order of 0.1 p.s. This direct emission is termed luminescence. The short decay time means that very short detector pulses are possible. (Figure 10.2 shows schematically the shape of the light pulse.) In most cases, only one excited state is significantly populated but in others a more complex decay is evident. For example, the decay of the luminescence from bismuth germanate is characterized by two components of 60 ns and 300 ns lifetimes. 

BGO Bismuth Germanate, Bi(Ge04)3. A material used in a scintillation detector whose advantages are high density and high efficiency. 

Cho ZH and Earukhi S (1977) New bismuth germanate crystal — a potential detector for the positron camera application./oMrwa/ of Nuclear Medicine 18 840-844. 

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