Study of X-ray Radiation Damage in Silicon Sensors

The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully coherent, high brilliance X-ray pulses per second each with a duration below 100 fs. This will allow the recording of diffraction patterns of single complex molecules and the study of ultra-fast processes. Silicon pixel sensors will be used to record the diffraction images. In 3 years of operation the sensors will be exposed to doses of up to 1 GGy of 12 keV X-rays. At this X-ray energy no bulk damage in silicon is expected. However fixed oxide charges in the insulating layer covering the silicon and interface traps at the Si-SiO2 interface will be introduced by the irradiation and build up over time. We have investigated the microscopic defects in test structures and the macroscopic electrical properties of segmented detectors as a function of the X-ray dose. From the test structures we determine the oxide charge density and the densities of interface traps as a function of dose. We find that both saturate (and even decrease) for doses between 10 and 100 MGy. For segmented sensors the defects introduced by the X-rays increase the full depletion voltage, the surface leakage current and the inter-pixel capacitance. We observe that an electron accumulation layer forms at the Si-SiO2 interface. Its width increases with dose and decreases with applied bias voltage. Using TCAD simulations with the dose dependent parameters obtained from the test structures, we are able to reproduce the observed results. This allows us to optimize the sensor design for the XFEL requirements

Design, development and evaluation of Stanford/Ames EVA prehensors

Space Station operations and maintenance are expected to make unprecedented demands on astronaut EVA. With Space Station expected to operate with an 8 to 10 psi atmosphere (4 psi for Shuttle operations), the effectivness of pressurized gloves is called into doubt at the same time that EVA activity levels are to be increased. To address the need for more frequent and complex EVA missions and also to extend the dexterity, duration, and safety of EVA astronauts, NASA Ames and Stanford University have an ongoing cooperative agreement to explore and compare alternatives. This is the final Stanford/Ames report on manually powered Prehensors, each of which consists of a shroud forming a pressure enclosure around the astronaut's hand, and a linkage system to transfer the motions and forces of the hand to mechanical digits attached to the shroud. All prehensors are intended for attachment to a standard wrist coupling, as found on the AX-5 hard suit prototype, so that realistic tests can be performed under normal and reduced gravity as simulated by water flotation

Neutron irradiation effect on SiPMs up to Φneq\Phi_{neq} = 5 ×\times 1014^{14} cm−2^{-2}

Silicon Photo-Multipliers (SiPM) are becoming the photo-detector of choice for increasingly more particle detection applications, from fundamental physics to medical and societal applications. One major consideration for their use at high-luminosity colliders is the radiation damage induced by hadrons, which leads to a dramatic increase of the dark count rate. KETEK SiPMs have been exposed to various fluences of reactor neutrons up to $\Phi_{neq}$ = 5$\times$10$^{14}$ cm$^{-2}$ (1 MeV equivalent neutrons). Results from the I-V, and C-V measurements for temperatures between $-$30$^\circ$C and $+$30$^\circ$C are presented. We propose a new method to quantify the effect of radiation damage on the SiPM performance. Using the measured dark current the single pixel occupation probability as a function of temperature and excess voltage is determined. From the pixel occupation probability the operating conditions for given requirements can be optimized. The method is qualitatively verified using current measurements with the SiPM illuminated by blue LED light

Inequality in mortality decreased among the young while increasing for older adults, 1990–2010

Many recent studies point to increasing inequality in mortality in the U.S. over the past twenty years. These studies often use mortality rates in middle and old age. Here we study inequality in mortality for all age groups in 1990, 2000, and 2010. Our analysis is based on groups of counties ranked by their poverty levels. Consistent with previous studies, we find increasing inequality in mortality at older ages. For children and young adults below age 20, however, we find strong mortality improvements that are most pronounced in poorer counties, implying a strong decrease in mortality inequality. These younger cohorts will form the future adult U.S. population, so this research suggests that inequality in old age mortality is likely to decline in future

Design, development and evaluation of Stanford/Ames Extra-Vehicular Activity (EVA) prehensors

A summary is given of progress to date on work proposed in 1983 and continued in 1985, including design iterations on three different types of manually powered prehensors, construction of functional mockups of each and culminating in detailed drawings and specifications for suit-compatible sealed units for testing under realistic conditions

Study of continuum nuclear structure of 12C via (p,p'X) at intermediate energies

The inclusive 12C(p,p') and exclusive 12C(p,p'X) reactions have been studied with a beam energy of 156 MeV and for X = p and alpha. The study focuses on the (p,p'X) reaction mechanism and on the structure of 12C just above the particle-emission threshold, 14 < E_x < 28 MeV. Cross sections were simultaneously measured for all three reactions. The exclusive data were analyzed by making multiple-peak fits of the spectra and by Legendre-polynomial fits of the angular correlations. Multiple-peak fits were also made of the inclusive spectra. The resultant cross sections were compared to theoretical calculations. An analysis of the results shows that this region of E_x consists predominantly of resonant excitations, in contradiction to the findings of previous analyses.Comment: 12 pages, 4 figures, elsart style files, submitted to Physics Letters