Paul W. Levy

A study on the properties of lead tungstate crystals

Abstract This report summarizes the results of a study on the properties of five large and five small size lead tungstate (PbWO 4 ) crystals. Data are presented on the longitudinal optical transmittance and light attenuation length, light yield and response uniformity, emission spectra and decay time. The radiation resistance of large crystals and possible curing with optical bleaching are discussed. The result of an in depth materials study, including trace impurities analysis, are also presented. The general conclusion from this investigation is that further research and development is needed to develop fast, radiation-hard PbWO 4 crystals for the CMS experiment at the CERN LHC.

Thermoluminescence of LiF TLD‐100: Glow‐curve kinetics

The thermoluminescence kinetics have been determined for the 13 glow peaks contained in the glow curves obtained from LiF TLD‐100 after exposure to 60Co irradiations. The glow curves were constructed from measurements made with recently developed equipment for recording emission spectra at closely spaced temperature intervals. In addition, the recorded data has been subjected to all corrections needed to make it suitable for reliable kinetic analysis. The recorded emission spectra can be described by a single Gaussian‐shaped band whose width and peak‐energy parameters vary erratically with temperature or, alternatively, by resolving the observed spectra into three Gaussian‐shaped bands whose parameters vary with temperatures in accord with theoretical expressions relating the emission‐spectra peak energy and full width at half‐maximum to the sample temperature. The kinetics and kinetic parameters were independently determined for the two most intense resolved emission bands. All peaks are described by first‐order kinetics and the independently determined parameters are in very good agreement. The glow curves for the least intense component are also described by the same kinetics and parameters. Inasmuch as the single‐band emission is a superposition of the three components, the same kinetics and parameters apply to the glow curve constructed from unresolved spectra. The identification number, nominal peak temperature in °C (for a heating rate of 10.3 °C/min), the activation energy E (eV), and preexponential factor s (sec−1) for the 13 peaks are as follows: (1) 1.62, 1.04, and 1014; (2) 94, 1.07, and 1013; (3a) 112, 0.987, and 1011; (3) 137, 1.05, and 1011; (4) 170, 1.54, and 4×1015; (5) 190, 2.20, and 1022; (5a) 210, 1.61, and 1015; (6) 235, 1.70, and 1015; (7) 260, 1.79, and 1015; (8) 285, 1.96, and 5×1015; (9) 315, 2.10, and 1016; (10) 345, 2.19, and 1016; (11) 370, 2.27, and 1016. The unusual value of s=1022 for the 190 °C peak, previously reported by other authors, was obtained during this study. However, it appears that this value can be obtained from relatively simple mechanisms and one of these is described.The thermoluminescence kinetics have been determined for the 13 glow peaks contained in the glow curves obtained from LiF TLD‐100 after exposure to 60Co irradiations. The glow curves were constructed from measurements made with recently developed equipment for recording emission spectra at closely spaced temperature intervals. In addition, the recorded data has been subjected to all corrections needed to make it suitable for reliable kinetic analysis. The recorded emission spectra can be described by a single Gaussian‐shaped band whose width and peak‐energy parameters vary erratically with temperature or, alternatively, by resolving the observed spectra into three Gaussian‐shaped bands whose parameters vary with temperatures in accord with theoretical expressions relating the emission‐spectra peak energy and full width at half‐maximum to the sample temperature. The kinetics and kinetic parameters were independently determined for the two most intense resolved emission bands. All peaks are described by fir...

Readout techniques and radiation damage of undoped cesium iodide

Several readout techniques for undoped CsI have been studied which utilize the fast scintillation component for speed and the high photon yield for good energy resolution. Quantum yields have been measured for samples up to 30 cm in length using photomultiplier tubes, wavelength shifters, and silicon photodiodes. A study has also been made of the scintillation properties of undoped CsI. It is found that the light output and decay time of the 310-nm fast component increases and the emission spectrum shifts to longer wavelengths at lower temperatures. The effects on the optical transmission and scintillation light output due to radiation damage from /sup 60/Co gamma rays have been measured for doses up to approximately 10/sup 6/ rad. It is found that the radiation resistance of undoped CsI is substantially higher than has been reported for thallium-doped CsI. >

Reactor and gamma-ray induced coloring of corning fused silica∗

Abstract When crystalline quartz, fused silica and many other substances are subject to reactor or gamma-ray radiations the samples develop optical absorption bands in the region 0.2–1 μ. Usually, there are many broad bands which overlap and resolution of the observed spectrum into the component bands is difficult. Coming fused silica is colored less than all of the materials studied and the observed spectrum can be resolved into its components by properly utilizing the variations in the relative absorption of the different bands created by changing the irradiation conditions. The most intense band is near 5.75 eV (218 mμ) and there is a smaller one at 5.05 eV (242 mμ) when the sample is irradiated in the reactor at 70°C. The 5.05 eV band has, relative to the 5.75 eV band, low intensity when the reactor irradiation is at 170°C but is much stronger when the irradiation is at liquid nitrogen temperature. Also, the peak of the 5.75 eV band shifts slightly with irradiation temperature. The band at 5.05 eV, which can be separated from the other bands without assuming a shape for it, is well fitted by a Gaussian curve and we have assumed that all other bands are similarly shaped. When a sample originally colored in the reactor is subsequently subjected to gammarays, additional absorption bands appear and their intensity is proportional to both the reactor and gamma-ray exposures. In all, new bands at approximately 5.5 (223 mμ), 4.5 (278 mμ), 2.0 (625 mμ) and one near 6.1 (200 mμ) eV, are present with indications of four others.

Effects of 60Co gamma-ray irradiation on the optical properties of natural and synthetic quartz from 85 to 300 K

Abstract Optical absorption and luminescence measurements have been made between 85 and 300 K on natural and synthetic quartz during and after 60Co gamma-ray irradiation. Absorption vs. dose curves can be resolved into the sum of a saturating exponential and a linear component. At 85 K the slope of the linear component is small, while at 300 K the linear term dominates the growth curves. The coloring induced by irradiation at 85 K decreased in a complex manner during anneal at a linear rate to 300 K. During this annealing process multiple-peak thermoluminescent (TL) glow curves were observed and recorded. The TL emission spectra are described accurately by single Gaussian-shaped bands, whereas the gamma-ray induced luminescence is comprised of several poorly resolved bands. All recorded TL glow curves are characterized by a set of four first order glow peaks between 150 and 220 K. The temperature dependence of radioluminescence intensity is described by a classical model in which a temperature-independent...

Radiation damage in undoped CsI and CsI (Tl)

Radiation damage has been studied in undoped CsI and CsI(Tl)-crystals using /sup 60/Co gamma radiation for doses up to approximately 4.2*10/sup 6/. Samples from various manufacturers were measured ranging in size from 2.54-cm-long cylinders to a 30-cm-long block. Measurements were made on the change in optical transmission and scintillation light output as a function of dose. Although some samples showed a small change in transmission, a significant change in light output was observed for all samples. Recovery from damage was also studied as a function of time and exposure to UV light. A short-lived phosphorescence was observed in undoped CsI, similar to the phosphorescence seen in CsI(Tl).<<ETX>>

Slow component suppression and radiation damage in doped BaF/sub 2/ crystals

The scintillation and radiation damage properties of barium fluoride crystals doped with various rare earths have been studied in an attempt to develop a fast, radiation hard scintillating crystal with a suppressed slow component for use at high counting rates. The light output of doped BaF/sub 2/ samples was measured with a solar blind (CsTe) photomultiplier tube and compared with a standard bialkali phototube. For dopants showing strong slow component suppression, measurements were also made at elevated temperatures and indicate that additional suppression can be achieved by heating. Radiation damage was studied by measuring the light transmission before, during and after irradiation with /sup 60/Co gamma rays for doses greater than 10/sup 6/ rad. The results show that several dopants suppress the slow component, but only one, namely lanthanum, preserves the radiation hardness of undoped BaF/sub 2/. >

Thermoluminescence of LiF TLD‐100: Emission‐spectra measurements

The thermoluminescence of LiF TLD‐100 dosimeter crystals has been studied using recently developed equipment for determining simultaneously the emission intensity and the emission spectrum as a function of sample temperature. Measurements were made on numerous samples exposed to 60Co irradiations at room temperature and at exposures varying from 500 to 3×107 R. Spectra were obtained at 1.38 and 5.5 °C intervals over the temperature range 20–350 °C. Below 105 R the thermoluminescent emission can be described by a single Gaussian‐shaped band whose peak energy and full width vary irregularly with temperature and not in accord with the well‐known expressions, given in the text, relating the emission‐spectra peak energy and full width at half‐maximum to the sample temperature. However, the emission is accurately described by three Gaussian‐shaped bands whose approximate peak energies and full widths are 3.01, 0.90; 2.90, 0.72; and 2.71, 0.96 eV. The peak energies and full widths of these three bands vary with ...

Overview Of Nuclear Radiation Damage Processes: Phenomenological Features Of Radiation Damage In Crystals And Glasses

The principle radiation damage effects occurring in optical materials, particularly those produced by energetic particles and gamma rays, are described phenomenologically. Included is a description of the basic processes whereby radiation interacts with non-metals. Emphasized are: 1) ionization induced electron and hole formation and migration processes and, 2) the displacement and ionization damage effects that are responsible for atoms being displaced from their normal lattice positions. In nonmetals, the principal radiation damage effect produced by these processes is the creation of color centers. In turn, it is shown that the radiation induced color center formation, as well as the changes that occurs after an irradiation is terminated, are described by a particularly simple theory. Radiation damage in transparent crystals and glasses is illustrated by measurements made with unique equipment fn making optical measurements during and after irradiation. One arrangement utilizes a 60 Co gamma-ray source and the other a 3.0 MeV electron accelerator. The illustrations include: 1) Measurements on F-center formation during irradiation--and the changes that occur after irradiation--on LiF, NaC1, and KC1 synthetic crystals. 2) Studies on the radiation induced F-center and Na metal colloid formation occurring in natural rock salt (NaCl) from potential radioactive waste repository sites. 3) The growth during irradiation and decay after irradiation of color centers in glasses irradiated at different temperatures. Lastly, the radioluminescence emitted during irradiation, as well as the absorption spectrum changes and the thermoluminescence emission that is observed when irradiated samples are heated, is illustrated by studies on natural quartz.

Radiation damage studies on non-metals utilizing measurements made during irradiation

Abstract To investigate radiation effects in non-metals, particularly radiation-induced color center formation, two facilities were constructed at Brookhaven National Laboratory for making optical absorption, luminescence, and other measurements during irradiation. In one facility the radiation is provided by a 60Co gamma-ray source. In the second facility samples are irradiated with 0.5–3.0 MeV electrons from an accelerator. Both facilities have large “walk-in” irradiation chambers. Optical measurements are made with a 13-m-long optical relay system that functions as a double-beam spectrophotometer, light-collecting system, etc. All equipment sensitive to radiation is located outside the irradiation chamber. A large variety of measurements can be made, e.g. simultaneous optical absorption and (radio)luminescence measurements can be made from approximately 210–1000 nm on samples before, during, and after irradiation. Usually separate 250 point absorption spectra and luminescence spectra are recorded simultaneously as often as every 2 min. However, more detailed spectra can be recorded conveniently. At a fixed wavelength measurements have been made every 1.4 ms; much faster measurements are possible. Samples can be measured during irradiation at temperatures between liquid helium temperatures and 900 °C. Measurements have been made on a large variety of crystals and glasses including alkali halides, quartz, fused silica, optical component glasses and minerals—especially natural rock salt. Numerous examples are given in the text. These examples, and other measurements, are the basis for a number of conclusions: the radiation-induced absorption in non-metals measured during irradiation differs from that measured after the irradiation is terminated, with only one or two possible exceptions. In most samples the absorption decays after irradiation. In certain samples some absorption bands decay and others increase. A few bands increase immediately after irradiation and then decrease. In a few cases, e.g. synthetic NaCl at room temperature, the resumption of radiation after an interruption initiates a complex sequence of F-center absorption band changes. Curves of absorption band intensity vs irradiation time measured during irradiation at a constant dose rate can usually be described precisely by simple functions, e.g. one, two, or three saturating exponential components plus a linear component. Similarly, some, but not all, changes occurring after irradiation can be described precisely by decaying exponential components and increasing saturating exponential components. Many samples emit copious radioluminescence during irradiation. Often, e.g. in quartz, the luminescence is strongly temperature dependent. Also, the radiation-induced absorption is usually strongly temperature dependent; most often the dependence on temperature is complex. In synthetic NaCl crystals and natural rock salt, irradiations in the temperature range 100–250°C produce F, V and other centers at low doses but, in addition, Na metal colloid bands at higher doses. Below 150°C the radiation-induced color center and colloid particle bands in natural and synthetic rock salt change little after irradiation. However, at higher temperatures the decay occurring after irradiation increases with increasing irradiation temperature. Based on measurements made during irradiation at the high dose rate of 120 Mrad h−1, the colloid growth rate is low at 120°C, increases to a maximum at 150–170°C, and decreases with increasing temperature to a low rate at 250–300°C. If the colloid growth temperature dependence were determined from measurements made a few hours after irradiation an entirely different, and misleading, temperature dependence would appear to occur. This example, as well as numerous other examples of the type sketched above, illustrates a general conclusion resulting from these studies. Namely, in almost all non-metals, to determine the levels of radiation damage present during irradiation and, more importantly, to determine the kinetics of radiation-induced processes, it is necessary to make measurements during irradiation.