Solid State Gamma-Ray Irradiation Facility

Introduction

The Solid State Gamma-ray Irradiation Facility (The Brickpile) was designed for basic radiation damage studies on transparent nonmetals. The existing facility was completed in 1965. It was preceded by a prototype with a relatively low level source. In 1991 the ⁶⁰Co source in the facility was upgraded to approximately 20,000 Curies. As of January, 1998 the conveniently obtained dose rates, on samples roughly 8 by 8 inches, range from approximately 10⁴ to 2 x 10⁵ rad/hour. This can be increased to about 10⁶ rad/hr for small samples. By remotely moving the source and its shield the dose rate at a fixed sample position can be changed, even during an irradiation. The "walk-in" irradiation chamber is roughly 14 by 14 feet and is surrounded by a concrete block shield sufficiently thick to permit people to work adjacent to the shield during irradiations.

Personnel

• 0.5 physicist/engineer/technician with experience in radiation effects in transparent nonmetals.
• 2 physicists/visitors working on ongoing projects.

Facility

The principal scientific equipment contained in this facility is a 13 meter long optical relay system that can be configured to operate as a spectrophotometer, a system for measuring luminescence spectra and intensity, etc. Studies completed with this equipment have unequivocally demonstrated that the radiation damage levels in almost all nonmetals is higher during irradiation than after irradiation; in some materials appreciably higher¹. Thus to reliably evaluate the extent of radiation damage in a transparent material to be used in a radiation field it is essential to make measurements during irradiation. Usually measurements are made at room temperature but measurements can be made at temperatures between liquid helium temperature and roughly 1000⁰ C (equipment not available). Figure 1 (taken from ref. 1) shows the irradiation chamber and the equipment used to make measurements during irradiation. With the upgrade of the spectrophotometer system (nearly completed) it will be possible to make simultaneous optical absorption and luminescence emission spectrum measurements on strongly emitting luminescent materials, such as crystals, plastic scintillators and other materials used in particle detectors, during irradiations ranging from the highest to lowest dose rates. At the present time (1/98) optical absorption measurements are restricted to nonluminescent or weakly luminescent materials during irradiation, or strongly luminescent materials after irradiation. This capability makes the facility unique.

In addition to the studies for which it was designed, this gamma-ray irradiation facility has been very useful for a large variety of radiation damage studies. It is particularly useful for making measurements during irradiation on items such as electronic circuit boards, optical lenses, prisms, biological samples, etc. Also, it has been used extensively to irradiate equipment too large to be irradiated in other radiation facilities. Recently the facility has been used to induce polymer crosslinking (Stony Brook) and to predose crystal oscillators used in satellites (FEI).

MATERIALS STUDIED AND PUBLICATIONS

This facility has been used for measurements of radiation induced absorption, radioluminescence,thermoluminescence, etc. of many materials. In the table below is a partial list of materials, particularly scintillating crystals, studied at this facility.

Material	Publications
BaF2	Radiation Damage in BaF2 Crystals, C.L.Woody et.al., IEEE Trans. Nuc. Sci. NS-39 (1992) 515-523. Radiation Damage in Barium Fluoride Detector Materials, Levy et.al., Laser Induced Damage in Optical Materials: 1988, NIST Special Publication 775, U.S. Dept. of commerce, Nat. Inst. of Stds. And tech., Washington, DC, 49-60, 1989. Slow Component Suppression and Radiation Damage in Doped BaF2, C.L. Woody et.al., IEEE trans. Nucl. Sci., NS-36 (1989).
CsI	Radiation Damage in Undoped CsI and CsI(Tl),C.L.Woody et.al., IEEE Trans. Nuc. Sci. NS-39 (1992) 524-531. Readout Techniques and Radiation Damage in Undoped Cesium Iodide. C.L. Woody, et al. IEEE Trans. Nucl. Sci., NS-37, 492-499 (1990).
PbWO4	A Study of the Optical and Radiation Damage Properties of Lead Tungstate Crystals, C.L.Woody et.al., IEEE Trans. Nucl. Sci. NS-43 (1996) 1585-1589. Light Output and Radiation Damage in a Lead Tungstate Crystal, J.Kierstead et.al., Proceedings of the Materials Research Society, Symposium on Scintillator and Phosphor Materials, Vol. 238 (1994) 475-480.
CeF3	Radiation Damage in Undoped and Barium Doped Cerium Fluoride, C.L.Woody et.al., IEEE Trans. Nucl. Sci. NS-41 (1994) 675-680. Further Results on Cerium Fluoride Crystals, Crystal Clear Collaboration, S. Anderson et.al., Nucl. Inst. Meth. A339 (1993) 373-394.>/li
PbF2	A Search for Scintillation in Doped and Orthorhombic Lead Fluoride, D.F.Anderson et.al., Nucl. Inst. Meth. A342 (1994) 473-476. Observation of Fast Scintillation Light in a PbF2:Gd Crystal, C.L.Woody et. Al., IEEE Trans. Nucl. Sci. NS-43 (1996) 1303-1306.
YalO3	Light Output and Radiation Damage in a YalO3:Ce Crystal, J.Kierstead et.al.,Proceedings of the Materials Research Society , Symposium on Scintillator and Phosphor Materials, Vol. 238 (1994) 469-473.
FeS2	Thermoluminescence Kinetics of Pyrite (FeS2), Silverman et.al., BNL-46067
PbCO3	Further Measurements of the Scintillation Properties of Lead Carbonate, Moses et.al.,BNL-46095
Alkalai Halides	Numerous papers in the 70s and 80s.

References

1. P. W. Levy, "Radiation Damage Studies on Nonmetals Utilizing Measurements Made During Irradiation,"
   Defect and Impurity Centers in Ionic Crystals, Part II, P. W. M. Jacobs, ed., J. Phys. Chem. Solids
   (Special Topics Issue) Vol. 52, No. 1, pp 319­349, 1991.

Figure 1. The experimental equipment for making simultaneous optical absorption, radioluminescence and other measurements on samples during 60Co gamma-ray irradiation. As presently operated, measurements can be made at any wavelength between 219 and 1000nm at temperatures between 4K and approx. 900oC. Additional equipment can be installed in the facility, e.g. a stress-strain machine to study the effects of strain applied during irradiation. Also, to study luminescence the phototube is replaced with a scanning spectrophotometer. All control functions and data recording are performed by a computer. A typical radiation-induced color center formation study consists of a cycle of measurements made at selected wavelengths which is repeated at selected intervals. Also, most studies are continued after the irradiation has been abruptly terminated; to study the decay of the coloring, phosphorescence, and other properties of the radiation-induced defects. Note that the equipment used to make measurements at temperatures other than room temperature is not presently available.