Evaluation of production samples of the scintillators LaBr3:Ce and LaCl3:Ce

We report on the evaluation of the performance of two recently developed scintillator materials, LaCl{sub 3}:Ce and LaBr{sub 3}:Ce, at the task of gamma ray spectroscopy. Their performance is compared to a standard scintillator used for gamma ray spectroscopy--a 25 mm diameter 25 mm tall cylinder of NaI:Tl. We measure the pulse height, energy resolution, and full-energy efficiency of production LaBr{sub 3}:Ce and LaCl{sub 3}:Ce scintillation crystals of different sizes and geometries for a variety of gamma-ray energies. Using production rather than specially selected crystals will establish whether immediate large-scale use is feasible. The crystal is excited by gamma rays from one of six isotopic sources ({sup 125}I, {sup 241}Am, {sup 57}Co, {sup 22}Na, {sup 137}Cs, and {sup 60}Co) placed 15 cm away from the scintillator. Our measurements show that both LaCl{sub 3} and LaBr{sub 3} outperform NaI:Tl in almost all cases. They outperform NaI:Tl at all energies for the photopeak fraction and counting rate measurements, and for energy resolution at higher energies (above 200 keV for LaCl{sub 3} and 75 keV for LaBr{sub 3}). The performance of production crystals is excellent and these scintillators should be considered for immediate use in systems where stopping power and energy resolution are crucial

ELECTRON AVALANCHE IN LIQUID XENON

We present detailed measurements of the electron avalanche process in liquid Xenon. The measurements were made by using liquid-Xe-filled proportional chambers with anode diameters of 2.9, 3.5, and 5.0 {approx} to detect 279-keV y rays and measure the photopeak pulse height as a function of applied voltage. The use of uniform pulses of electrons enabled us to discriminate against secondary Townsend processes. We present a table of the first Townsend coefficient a as a function of electric field E; a typical value is {alpha} = (4.5 {+-} 0.3) x 10{sup 4} cm{sup -1} at E = 2 x 10{sup 6} V/cm. The electron avalanche occurs in liquid Xe at electric fields 26 times smaller than would be predicted using measurements made in gaseous Xe and E/{rho} density scaling

INITIAL IMAGES FROM A 24-WIRE LIQUID XENON Y -CAMERA.

A prototype liquid xenon {gamma}-camera has been constructed and preliminary results obtained. The sensitive volume is 7 c x 7 cm in area and 1.5 cm thick. Orthogonal coordinates for each interacting {gamma}-ray are provided by 24 anode wires 5 {micro} in diameter spaced 2.8 mm apart and 24 cathode strips

Scintillation of tantalate compounds

A screening of 63 metal-tantalate-oxides was conducted in search of heavy scintillator materials operating at ambient temperature. While tantalates are known to have slow scintillation decay times, the high atomic number of tantalum (73) provides good stopping power for gamma rays. Screened samples were synthesized by solid state reactions. Scintillation properties of these materials were evaluated by X-ray diffraction, X-ray excited luminescence and pulsed X-ray luminescence. Of the 63 synthesized tantalates examined only 12 had luminosity values greater than 1000 ph/MeV at room temperature. From these, ScTaO4, YTa3O9, and Zn3Ta2O8 have greater than 40% of their emission in the first μs. The brightest and fastest compound of those tested was Zn3Ta2O8 with an estimated luminosity of 26,000 ph/MeV and a main decay time of 600 ns from its crystalline powder. Further attention is given to Zn3Ta2O8 and Mg4Ta2O9 scintillation properties, demonstrating their potential for scintillation applications

Temperature dependence of CsI(Tl) gamma-ray excited scintillation characteristics

The gamma-ray excited, temperature dependent scintillation characteristics of CsI(Tl) are reported over the temperature range of -100 to + 50[deg]C. The modified Bollinger-Thomas and shaped square wave methods were used to measure the rise and decay times. Emission spectra were measured using a monochromator and corrected for monochromator and photocathode spectral efficiencies. The shaped square wave method was also used to determine the scintillation yield as was a current mode method. The thermoluminescence emissions of CsI(Tl) were measured using the same current mode method. At room temperature, CsI(Tl) was found to have two primary decay components with decay time constants of [tau]1 = 679+/-10 ns (63.7%) and [tau]2 = 3.34+/-0.14 [mu]s (36.1%), and to have emission bands at about 400 and 560 nm. The [tau]1 luminescent state was observed to be populated by an exponential process with a resulting rise time constant of 19.6+/-1.9 ns at room temperature. An ultra-fast decay component with a 1 and [tau]2 were determined to be 2.22+/-0.33 [mu]s and 18.0+/-2.59 [mu]s, respectively, while the 400 nm emission band was not observed below -50[deg]C. At +50[deg]C the decay constants were found to be 628 ns (70.5%) and 2.63 [mu]s (29.3%) and both emission bands were present. The scintillation yield of CsI(Tl) was observed to be only slightly temperature dependent between -30 and +50[deg]C, peaking at about -30[deg]C (about 6% above the room temperature yield) and monotonically decreasing above and below this temperature. Four different commercially available CsI(Tl) crystals were used. Minimal variations in the measured scintillation characteristics were observed among these four crystals. Thermoluminescence emissions were observed to have peak yields at -90, -65, -40, +20, and possibly -55[deg]C. The relative magnitudes and number of thermoluminescence peaks were found to vary from crystal to crystal.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30984/1/0000659.pd

PARTICLE DETECTORS BASED ON NOBLE LIQUIDS

In order to build a thin particle detector with 10 micron spatial resolution and automatic readout, the avalanche of ionization electrons in high electric fields in liquid argon and liquid xenon has been studied. We present a scheme using an array of points that could be used to make a reliable liquid argon filled detector. The avalanche pulses in liquid xenon have a rise time more than three orders of magnitude faster than that in liquid argon, suggesting that the positive charge carriers are holes, and making possible a detector with a time resolution of better than 100 nanoseconds. A direct observation of hole conduction is described