Full Energy Absorption Research Articles

The light yield nonproportionality component of scintillator energy resolution

The scintillator energy resolution component which is due to light yield nonproportionality has been characterized for NaI(Tl) and LSO. Results are based on a discrete convolution of measured electron response data and the electron energy distribution resulting from full-energy absorption events. The behavior of this energy resolution component as a function of energy is observed to be strongly dependent on the shape of the electron response. Furthermore, in some energy regions, the light yield nonproportionality component is observed to be larger than the resolution predicted by assuming Poisson photoelectron statistics. Characterization of this energy resolution component will facilitate deconvolution of other components from the total energy resolution.

Measurement of absolute light yield and determination of a lower limit for the light attenuation length for YAP:Ce crystal

In small animal PET applications, the YAP:Ce scintillator has given some promising results. Because of its somewhat lower efficiency with respect to other PET crystals at 511 keV the depth of the crystal is a crucial parameter. Past measurements of the light attenuation length for YAP:Ce scintillator have given rather different results with values as low as 3 cm. We have studied the pulse height spectra of full energy absorption events as a function of the interaction distance from the photomultiplier window for five match like 2/spl times/2/spl times/30 mm/sup 3/ YAP:Ce crystals. Each crystal was covered on the four long sides and on one of the square section sides with a 5 /spl mu/m reflective layer. The crystals were the middle row of a bundle of 5 by 5 such crystals. By using a transport model for light within the crystals, for this crystal configuration, we obtained a lower limit of 6.8/spl plusmn/0.3 cm on the average 'bulk' (not including the losses from reflection) light attenuation length. This lower limit is significantly higher than the attenuation length measured by other authors. From these measurements and calculations, we have also determined the average absolute light yield for the five crystals to be 24000/spl plusmn/1400 photons/MeV.

Full-energy absorption of x-ray energies near the Xe L- and K-photoionization thresholds in xenon gas detectors: Simulation and experimental results

Distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range, which includes the xenon L- and K-absorption edges, were simulated in xenon gas detectors with the Monte Carlo technique. These simulated full-energy absorption distributions are calculated as frequency plots of the number of primary electrons produced per incident x-ray photon. The simulation includes the absorption of x-rays and the de-excitation of the residual xenon ions, followed by the development of the primary electron cloud. The discontinuities observed in the Fano factor, w-value, energy linearity and energy resolution reflect the discontinuities of the Xe photoionization cross-section at the photoabsorption edges. The simulation results are compared with experimental values measured with a gas proportional scintillation counter, and with recent data from other authors. The discontinuities in energy linearity produce an ambiguity in determining the x-ray energy in certain narrow ranges containing the edges. However, our simulation results permit a detailed analysis of observations in these regions. At the K-edge, the discontinuities in the calculated Fano factor and energy resolution were found to depend on the extent to which the K-fluorescence produced by the xenon atoms is allowed to escape. A discussion of the asymmetry of the calculated full-energy absorption peaks is made in terms of the distinction between the different decay branches initiated by photoionization of the Xe atoms, and K-fluorescence escape is found to influence strongly the skewness of the calculated distributions.

The response of xenon X-ray detectors to full-energy absorption and fluorescence-escape events: measurement and modelling

We have observed that the pulse-height distributions of X-ray events that deposit essentially the same amount of energy in a xenon gas detector will vary according to the deexcitation pathways available to the photoionized atoms. A xenon gas proportional scintillation counter was used to compare the pulse-height distributions of events in which fluorescence X-rays from xenon escape detection. Experimental results are presented and the behaviour for different types of events is clarified using Monte Carlo simulation. The results indicate that particular care must be taken when using escape peaks for energy calibration of xenon gas detectors.

A Comprehensive Model for Predicting Semiconductor Detector Performance

A Monte-Carlo computational model has been developed to simulate the photon and electron spectral response in semiconductor detectors. Source photons from 10 eV to 1 GeV are three-dimensionally absorbed in detectors of almost arbitrary shape. One-dimensional charge collection in an arbitrary electric field profile includes trapping and electronics system effects. HgI2, CdTe, and Ge spectra, as well as full energy peak and absorption efficiency calculations, are made into the MeV range.

The Effect of Residual Elements on the Response of Selected Pressure-Vessel Steels and Weldments to Irradiation at 550°F

The effect of variable content of residual elements on the sensitivity of pressure-vessel steels to embrittlement from irradiation at 550°F was examined. Results indicate that phosphorus and copper can contribute significantly to the 550°F-irradiation embrittlement sensitivity of Type A302-B steel. The results also show that vanadium may have a slight adverse effect and that sulfur is neutral, although the latter serves to decrease the full shear energy absorption level of the steel. Nitrogen variations from ∼ 0.008 to 0.015% in aluminum-deoxidized steel have no significant effect, while the addition of aluminum to Ni-Cr-Mo steel with a given nitrogen content may slightly promote irradiation embrittlement. The program results demonstrate that apparent insensitivity to 55°F-irradiation embrittlement can be consistently achieved with laboratory heats of a nominal A302-B steel composition by maintaining the total residual element contents at a low level.Investigations of radiation-embrittlement sensitivity o...

An internal conversion coefficient spectrometer utilizing semi-conductor detectors

A description is given a device that has been designed for the measurement on internal conversion coefficients by simultaneous observation of electron and gamma spectra with lithium-drifted silicon and germanium detectors, respectively. Calibration of the device was made by use of several well-known internal conversion coefficients (Hg 203, Au 198, Cs 137, Bi 207, Cd 109 sources). Dependence of the efficiency of the germanium detector for full-energy absorption of gamma-rays has been determined. Application of the method to the determination of conversion coefficients of the 191-keV transition from Pt 197 decay and of the 346-keV transition from Pt 197m decay is described. The following results are obtained: Pt 197: 191 keV transition, ϵκ = 0.69 ± 0.07, K/ L = 5.2 ± 0.6. Pt 197m: 346 keV transition, ϵκ = 3.9 ± 0.4, K/ L = 1.8 ± 0.2.