• PDF / 277,628 Bytes
• 6 Pages / 414.72 x 648 pts Page_size
• 6 Downloads / 235 Views

DOWNLOAD

REPORT

---

*MSI Photogenics Division, 455 North University, Provo, Utah 84601 "**BrighamYoung University, Department of Physics & Astronomy, Provo, Utah 84602

Abtract We have tested a single crystal of Ce-activated lanthanum beryllate BEL(Ce) as a potential gamma detector material. The density (6.1 g.cmn3 ) and decay time (50 ns) are competitive with other recently developed materials. The scintillation efficiency is 57- to -95% that of BGO. For an excitation wavelength of 340 nm, the emission spectrum is a broad peak centered at 450 nm. The H2 annealed sample is transparent for wavelengths greater than 400 nm. We are continuing a program to improve the scintillation efficiency by varying the crystal growth conditions. The crystal was prepared by M. Long and E.W. O'Dell of AlliedSignal, Inc., using the Czochralski technique. Lanthanum Beryllate as a Gamma Detector Material

There is currently an intense, world-wide search for improved high-density gamma-sensitive scintillators. This research interest is of recent origin and follows several decades of relative inactivity during which few new materials were introduced. The performance characteristics of a scintillating material determine the ultimate capabilities of any system of which it is a part. For many applications, the performance characteristics of existing materials such as Bismuth Germanate (BGO) and Sodium Iodide are no longer entirely satisfactory. Heavy crystal scintillators with properties superior to BGO and Nal will also have numerous commercial applications, including Positron Emission Tomography and as a gamma detector in geotechnical exploration. Other projects, such as the electromagnetic calorimeters used in high energy physics would also benefit from improved heavy crystal scintillators. Most of the recent work in high-density gamma-sensitive scintillators has centered around high-melting-point oxidic compounds or rare-earth fluorides. The new materials are often superior in one or more characteristics but none fully satisfy 137 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society

the requirements of high energy physics, medical diagnostics, environmental hazard characterization or hydrocarbon exploration. Our staff have actively participated in this search for a high-density material. Like other investigators, we decided that the rare earths would be a fruitful field for investigation. The rare earths have high atomic numbers and several of them have optical properties which permit the formation of colorless crystals, including yttrium, lanthanum, gadolinium, ytterbium, and lutetium. An example of the interest in the use of lanthanide-based materials as scintillators has been the decade-long investigation of the rare earth silicates, activated by cerium. This investigation has been pursued by scientists at MSI, Hitachi, Schlumberger, NV Philips, various universities such as California Institute of Technology and U.C. Berkeley, and government laboratories. Of this group, yttrium silicate (YSO) was discovered first and demonstrated that