Radiation Damage and Activation from Proton Irradiation of Advanced Scintillators

We present results from a proton accelerator beam test to measure radiation damage and activation in advanced scintillator materials. Samples of LaBr3:Ce and LaCl3:Ce were exposed to protons from 40-250 MeV at the Proton Irradiation Facility of the Paul Scherrer Institute in Switzerland. Twelve energy bands were used to simulate the spectrum of the South Atlantic Anomaly (SAA), with different samples exposed to the equivalent of 4 months, 1 year, and 5 years of SAA passage. No significant decrease in light output was found due to radiation damage, indicating that these new scintillator materials are radiation tolerant. High-resolution spectra of the samples were obtained before and after irradiation with a Germanium spectrometer to study activation. We present a detailed analysis of these spectra and a discussion of the suitability of these scintillator materials for detectors in future space missions

Slow epidemic extinction in populations with heterogeneous infection rates

We explore how heterogeneity in the intensity of interactions between people affects epidemic spreading. For that, we study the susceptible-infected-susceptible model on a complex network, where a link connecting individuals $i$ and $j$ is endowed with an infection rate $\beta_{ij} = \lambda w_{ij}$ proportional to the intensity of their contact $w_{ij}$, with a distribution $P(w_{ij})$ taken from face-to-face experiments analyzed in Cattuto $et\;al.$ (PLoS ONE 5, e11596, 2010). We find an extremely slow decay of the fraction of infected individuals, for a wide range of the control parameter $\lambda$. Using a distribution of width $a$ we identify two large regions in the $a-\lambda$ space with anomalous behaviors, which are reminiscent of rare region effects (Griffiths phases) found in models with quenched disorder. We show that the slow approach to extinction is caused by isolated small groups of highly interacting individuals, which keep epidemic alive for very long times. A mean-field approximation and a percolation approach capture with very good accuracy the absorbing-active transition line for weak (small $a$) and strong (large $a$) disorder, respectively

GRAPE - A Balloon-Borne Gamma-Ray Polarimeter Experiment

This paper reviews the development status of GRAPE (the Gamma-Ray Polarimeter Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X-rays in the 50-300 keV energy range. We are particularly interested in X-rays that are emitted from solar flares and gamma-ray bursts (GRBs), although GRAPE could also be employed in the study of other astrophysical sources. Accurately measuring the polarization of the emitted radiation will lead to a better understating of both emission mechanisms and source geometries. The GRAPE design consists of an array of plastic scintillators surrounding a central high-Z crystal scintillator. The azimuthal distribution of photon scatters from the plastic array into the central calorimeter provides a measure of the polarization fraction and polarization angle of the incident radiation. The design of the detector provides sensitivity over a large field-of-view (>pi steradian). The design facilitates the fabrication of large area arrays with minimal deadspace. This paper presents the latest design concept and the most recent results from laboratory tests of a GRAPE science model.Comment: 6 pages; paper presented at the FRASCATI Workshop 2005 on Multifrequency Behaviour of High Energy Cosmic Sources; submitted to Chinese Journal of Astronomy and Astrophysic

Large-area submillimeter resolution CdZnTe strip detector for astronomy

We report the first performance measurements of a sub-millimeter CdZnTe strip detector developed as a prototype for space-borne astronomical instruments. Strip detector arrays can be used to provide two-dimensional position resolution with fewer electronic channels than pixellated arrays. Arrays of this type and other candidate technologies are under investigation for the position-sensitive backplane detector for a coded-aperture telescope operating in the range of 30 - 300 keV. The prototype is a 1.4 mm thick, 64 multiplied by 64 stripe CdZnTe array of 0.375 mm pitch in both dimensions, approximately one square inch of sensitive area. Pulse height spectra in both single and orthogonal stripe coincidence mode were recorded at several energies. The results are compared to slab- and pixel-geometry detector spectra. The room-temperature energy resolution is less than 10 keV (FWHM) for 122 keV photons with a peak-to-valley ratio greater than 5:1. The response to photons with energies up to 662 keV appears to be considerably improved relative to that of previously reported slab and pixel detectors. We also show that strip detectors can yield spatial and energy resolutions similar to those of pixellated arrays with the same dimensions. Electrostatic effects on the pulse heights, read-out circuit complexity, and issues related to design of space borne instruments are also discussed

Progress in the study of CdZnTe strip detectors

We report new performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector under study as a prototype imaging spectrometer for astronomical x-ray and gamma-ray observations. The prototype is 1.5 mm thick with 375 micron strip pitch in both the x and y dimensions. Previously reported work included demonstrations of half-pitch spatial resolution (approximately 190 microns) and good energy resolution and spectral uniformity. Strip detector efficiency measurements have also been presented. A model that includes the photon interaction, carrier transport and the electronics was developed that qualitatively reproduced the measurements. The new studies include measurements of the CdZnTe transport properties for this prototype in an effort to resolve quantitative discrepancies between the measurements and the simulations. Measurements of charge signals produced by laser pulses and (alpha) -rays are used to determine these transport properties. These are then used in the model to predict gamma-ray efficiencies that are compared with the data. The imaging performance of the detector is studied by scanned laser and gamma beam spot measurements. The results support the model\u27s prediction of nearly linear sharing of the charge for interactions occurring in the region between electrodes. The potential for strip detectors with spatial resolution much finer than the strip pitch is demonstrated. A new design scheme for strip detectors is shortly discussed

Development of an orthogonal-stripe CdZnTe gamma radiation imaging spectrometer

We report performance measurements of a sub-millimeter resolution CdZnTe strip detector developed as a prototype for astronomical instruments operating with good efficiency in the 30-300 keV photon energy range. The prototype is a 1.4 mm thick, 64×64 contact stripe CdZnTe array of 0.375 mm pitch in both dimensions. Pulse height spectra were recorded in orthogonal-stripe coincidence mode which demonstrate room-temperature energy resolution \u3c10 keV (FWHM) for 122 keV photons with a peak-to-valley ratio \u3e5:1. Good response is also demonstrated at higher energies using a coplanar grid readout configuration. Spatial resolution capabilities finer than the stripe pitch are demonstrated. We present the image of a 133Ba source viewed through a collimator slit produced by a 4×4 stripe detector segment. Charge signals from electron and hole collecting contacts are also discussed

Performance of CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

We report & gamma;-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for & gamma;-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64×64 orthogonal stripeCdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8×8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (~0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals, and the photon detection efficiency. We also present a technique for determining the location of the event in the third dimension (depth). We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results with the data. The data indicate that the cathode signal-as well as the anode signal-arises more strongly from the conduction electrons rather than the holes

CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

We report γ-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for γ-ray measurements in the range of 20-600 keV. The prototype is a 1.5 mm thick, 64×64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8×8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (~0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals. We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results with the data. The data indicate that cathode signal-as well as the anode signal-arises more strongly from the conduction electrons rather than the holes

The Discovery of Cepheids and a New Distance to NGC 2841 Using the Hubble Space Telescope

We report on the discovery of Cepheids in the spiral galaxy NGC 2841, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. NGC 2841 was observed over 12 epochs using the F555W filter, and over 5 epochs using the F814W filter. Photometry was performed using the DAOPHOT/ALLFRAME package. We discovered a total of 29 variables, including 18 high-quality Cepheids with periods ranging from 15 to 40 days. Period-luminosity relations in the V and I bands, based on the high-quality Cepheids, yield an extinction-corrected distance modulus of 30.74 +/- 0.23 mag, which corresponds to a distance of 14.1 +/- 1.5 Mpc. Our distance is based on an assumed LMC distance modulus of 18.50 +/- 0.10 mag (D = 50+/- 2.5 kpc) and a metallicity dependence of the Cepheid P-L relation of gamma (VI) = -0.2 +/- 0.2 mag/dex.Comment: 31 preprint pages including 10 figures. Accepted for publication in ApJ. High-resolution version available from http://cfa-www.harvard.edu/~lmacri/n2841.p

Administration of protein hydrolysates from anchovy (Engraulis encrasicolus) waste for twelve weeks decreases metabolic dysfunction‐associated fatty liver disease severity in ApoE–/–mice

Metabolic dysfunction‐associated fatty liver disease (MAFLD) includes several diseases, ranging from simple steatosis to steatohepatitis, fibrosis and cirrhosis. Fish‐rich diets are considered helpful in the prevention of MAFLD, and the enzymatic hydrolysis of fish waste has been explored as a means of obtaining high‐value protein hydrolysates, which have been proven to exert beneficial bioactivities including anti‐obesity and hypocholesterol effects. This study aimed to assess the effect of the administration of protein hydrolysates from anchovy waste (APH) for 12 weeks on attenuated high‐fat diet‐induced MAFLD in apolipoprotein E‐knockout mice (ApoE–/–). Thirty ApoE–/– mice were divided into two groups (n = 15/group) and fed a high‐fat diet (HFD), with and without the addition of 10% (w/w) APH. After 12 weeks, serum and hepatic lipid profiles, hepatic enzyme activities, liver histology and immunohistochemistry were analyzed to assess hepatic steatosis, inflammation and fibrosis. Twelve‐weeks on a 10% (w/w) APH diet reduces total cholesterol and triglyceride serum levels, hepatic enzyme activity and hepatic triacylglycerol content (p < 0.0001), and results in a reduction in hepatic fat accumulation and macrophage recruitment (p < 0.0001). The results suggest that a 10% APH diet has an anti‐obesity effect, with an improvement in lipid metabolism, hepatic steatosis and liver injury as a result of a high‐fat diet. Protein hydrolysates from fish waste may represent an efficient nutritional strategy in several diseases, and their use as nutraceuticals is worthy of future investigation