Methods For A Systematic, Comprehensive Search for Fast, Heavy Scintillator Materials
- PDF / 630,131 Bytes
- 11 Pages / 414.72 x 648 pts Page_size
- 79 Downloads / 170 Views
Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, CA 94720. ABSTRACT Over the years a number of scintillator materials have been developed for a wide variety of nuclear detection applications in industry, high energy physics, and medical instrumentation. To expand the list of useful scintillators, we are pursuing the following systematic, comprehensive search: (1) select materials with good gamma-ray interaction properties from the 200,000 data set NIST crystal diffraction file, (2) synthesize samples (doped and undoped) in powdered or single crystal form, (3) test the samples using sub-nanosecond pulsed x-rays to measure important scintillation properties such as rise times, decay times, emission wavelengths, -,-d light output, (4) prepare large, high quality crystals of the most promising candidates, and (5) test the crystals as gamma-ray detectors in representative configurations. An important parallel effort is the computation of electronic energy levels of activators and the band structure of intrinsic and host crystals to aid in the materials selection process. DESIRED SCINTILLATOR PROPERTIES Scintillator materials are widely used for the detection of ionizing radiation in a variety of applications including high energy physics, astrophysics, geophysical exploration, medical imaging, security inspection, and industry. As different applications place very different priorities on density, atomic number, light output, decay time, emission wavelength, mechanical and chemical stability, radiation hardness, optical quality, and cost, it is unlikely that a single material will be found that is ideal for all applications. In this paper we shall be interested mainly in
scintillator materials for detecting 511 keV gamma rays in positron emission tomography. Here stopping power and light yield are of prime importance. This is in contrast, for example, to materials needed for electromagnetic calorimetry in high energy physics experiments where light yield is of lesser importance but radiation hardness is a prime consideration. High Stopping Power For the detection of gamma rays with good spatial resolution, it is necessary to have a material with both a high density and an element with a high atomic number. Photoelectric absorption of the incident gamma is strongly preferred because the photon energy is deposited at a single position whereas Compton interactions lead to several spatially separated energy depositions. Figure 1 illustrates how the photofraction E= ap/(ap + ac) for 511 keV photons depends on atomic number (up and ac are the cross sections for photoelectric absorption and Compton scattering). The photoelectric attenuation length P is defined as the attenuation length/photoelectric fraction in cm for 511 keV photons. The probability of photoelectric absorption of 511 keV photons on the first *Work supported in part by the U.S. Department of Energy contract DE-AC03-76SF00098, and in part by Public Health Service Grants Nos. P01 25840, R01 CA48002, and R01 NS29655.
39 Mat. Res. Soc. Symp. Proc. Vol. 3
Data Loading...
