Evaluation of wavelength shifters for spectral separation of barium fluoride emissions

Application of the barium fluoride (BaF2) scintillator for characterization of intense radiation fields has been pursued since the fast component was discovered in the early 1980's. Unfortunately, ~ 80% of the scintillator emissions have a slow ~ 600 ns decay time constant. The long decay time hampers the use of BaF2 at high count rates because the slow emissions appear as an afterglow which has an intensity that varies with the interaction rate in the crystal. The temporal separation of BaF2 emissions by spectral separation using wavelength shifting techniques has been explored in this work. Of the wavelength shifting techniques that were examined, the solvent excitation technique showed the greatest potential, but was insufficient by itself to suppress the slow emissions to the desired degree. All the wavelength shifting techniques yield an enhanced ratio of fast to slow photons, but a decreased fast photoelectron yield.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31384/1/0000297.pd

Evaluation of p-terphenyl and 2,2" dimethyl-p-terphenyl as wavelength shifters for barium fluoride

p-Terphenyl (PTP) and 2,2" dimethyl-p-terphenyl (DMT) have been investigated for use as wavelength shifters (WLSs) for barium fluoride (BaF2) scintillation emission. These two organic fluors are attractive due to their high quantum efficiency, fast fluorescence decay time, and emissions above the wavelength cut-off of borosilicate glass. Measurements of these WLSs dissolved in cyclohexane are presented. Coincidence time spectra and fluorescence decay spectra measured with BaF2 as the pump source, are shown. The fluorescence decay time and the ratio of fast to slow intensities were determined from the fluorescence decay spectrum. The increase in signal resulting from using a WLS between the borosilicate end-window photomultiplier tube and the BaF2 crystal is measured. The motivation behind this work is the development of a gamma-ray spectrometer suitable for high count rate applications. We are also investigating the possibility of separating the fast and slow emissions of BaF2 using optical techniques. PTP and DMT both can spectrally separate BaFe2 emissions to a marginal extent.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30880/1/0000545.pd

Charge calibration of CsI(Tl)/photodiode spectroscopy systems

A charge calibration method for spectroscopy systems that use inorganic scintillators, photodiodes, and charge-sensitive preamplifiers is presented. The shaped square wave (SSW) method accounts for ballistic deficit when long decay time constants are present. The SSW method is demonstrated for CsI(T1) and compared to other calibration methods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30115/1/0000491.pd

AST: An Automated Sequence-Sampling Method for Improving the Taxonomic Diversity of Gene Phylogenetic Trees

A challenge in phylogenetic inference of gene trees is how to properly sample a large pool of homologous sequences to derive a good representative subset of sequences. Such a need arises in various applications, e.g. when (1) accuracy-oriented phylogenetic reconstruction methods may not be able to deal with a large pool of sequences due to their high demand in computing resources; (2) applications analyzing a collection of gene trees may prefer to use trees with fewer operational taxonomic units (OTUs), for instance for the detection of horizontal gene transfer events by identifying phylogenetic conflicts; and (3) the pool of available sequences is biased towards extensively studied species. In the past, the creation of subsamples often relied on manual selection. Here we present an Automated sequence-Sampling method for improving the Taxonomic diversity of gene phylogenetic trees, AST, to obtain representative sequences that maximize the taxonomic diversity of the sampled sequences. To demonstrate the effectiveness of AST, we have tested it to solve four problems, namely, inference of the evolutionary histories of the small ribosomal subunit protein S5 of E. coli, 16 S ribosomal RNAs and glycosyl-transferase gene family 8, and a study of ancient horizontal gene transfers from bacteria to plants. Our results show that the resolution of our computational results is almost as good as that of manual inference by domain experts, hence making the tool generally useful to phylogenetic studies by non-phylogeny specialists. The program is available at http://csbl.bmb.uga.edu/~zhouchan/AST.php

Gamma-ray spectral imaging using a single-shutter radiation camera

As part of a program to develop mobile robots for reactor environments, we are developing a radiation-imaging camera capable of operating in medium-intensity (Z scintillator. The raster-scanning camera uses a lead-shielded bismuth germanate (BGO) scintillator (1.25 cm x 1.25 cm right-circular cylinder) coupled to a photomultiplier tube (PMT) operated in pulse mode. Measurements yielded an angular resolution of 2.5[deg] and energy resolution of 12.9% at 662 keV. The camera motion is totally automated and controlled by stepping motors connected to a remote computer. Several 2D images of radioactive sources have been acquired in fields of up to 400 mR/h and energies up to 2.75 MeV. Some of the images demonstrate the ability of the camera to image a polychromatic field.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28266/1/0000011.pd

One-year observation on the population structure of Diopatra neapolitana Delle Chiaje (Polychaeta : Onuphidae) in Izmir Bay (Aegean Sea, eastern Mediterranean)

WOS: 000234482700014The present paper deals with the morphology and population structure of Diopatra neapolitana collected in Izmir Bay between July 1997 and June 1998. The density of the species in the area ranged from 42 ind(.)m(-2) (November 1997) to 198 ind(.)m(-2) (March 1998), the biomass from 84 g(.)m(-2) (November) to 408 g(.)m(-2) (March). The coelom contained gametes in all months, except for January, indicating that it has a very long reproductive period in the area. The relationships among the biometrical measurements taken on specimens of Diopatra neapolitana from Izmir Bay were assessed by using regression and correlation analysis. A re-description of the species is provided