5,046 research outputs found
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
Neutron irradiation effect on SiPMs up to = 5 10 cm
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 =
510 cm (1 MeV equivalent neutrons). Results from the I-V,
and C-V measurements for temperatures between 30C and 30C
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
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
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
Perceived Risks Associated with Contraceptive Method Use among Men and Women in Ibadan and Kaduna, Nigeria
Research shows that side effects are often the most common reason for contraceptive non-use in Nigeria; however, research to date has not explored the underlying factors that influence risk and benefit perceptions associated with specific contraceptive methods in Nigeria. A qualitative study design using focus group discussions was used to explore social attitudes and beliefs about family planning methods in Ibadan and Kaduna, Nigeria. A total of 26 focus group discussions were held in 2010 with men and women of reproductive age, disaggregated by city, sex, age, marital status, neighborhood socioeconomic status, and—for women only—family planning experience. A discussion guide was used that included specific questions about the perceived risks and benefits associated with the use of six different family planning methods. A thematic content analytic approach guided the analysis. Participants identified a spectrum of risks encompassing perceived threats to health (both real and fictitious) and social concerns, as well as benefits associated with each method. By exploring Nigerian perspectives on the risks and benefits associated with specific family planning methods, programs aiming to increase contraceptive use in Nigeria can be better equipped to highlight recognized benefits, address specific concerns, and work to dispel misperceptions associated with each family planning method
Self-heating Effect in Silicon-Photomultipliers
The main effect of radiation damage in a Silicon-Photolumtiplier (SiPM) is a
dramatic increase in the dark current. The power dissipated, if not properly
cooled, heats the SiPM, whose performance parameters depend on temperature.
Heating studies were performed with a KETEK SiPM, glued on an AlO
substrate, which is either directly connected to the temperature-controlled
chuck of a probe station, or through layers of material with well-known thermal
resistance. The SiPM is illuminated by a LED operated in DC-mode. The SiPM
current is measured and used to determine the steady-state temperature as a
function of power dissipated in the multiplication region of the SiPM and
thermal resistance, as well as the time dependencies for heating and cooling.
This information can be used to correct the parameters determined for
radiation-damaged SiPM for the effects of self-heating. The method can also be
employed for packaged SiPMs with unknown thermal contact to a heat sink. The
results presented in this paper are preliminary
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