111 research outputs found
Change in Percentage of Families Offered Coverage at Work, 1998-2005
Uses data from the National Health Interview Survey to measure changes between 1998 and 2005 in the percentage of families with working adults that have at least one offer of health insurance through an employer
In-Beam Background Suppression Shield
The long (3ms) proton pulse of the European Spallation Source (ESS) gives
rise to unique and potentially high backgrounds for the instrument suite. In
such a source an instrument capabilities will be limited by it's Signal to
Noise (S/N) ratio. The instruments with a direct view of the moderator, which
do not use a bender to help mitigate the fast neutron background, are the most
challenging. For these beam lines we propose the innovative shielding of
placing blocks of material directly into the guide system, which allow a
minimum attenuation of the cold and thermal fluxes relative to the background
suppression. This shielding configuration has been worked into a beam line
model using Geant4. We study particularly the advantages of single crystal
sapphire and silicon blocks .Comment: 12 pages, 8 figures, proceeding of NDS 2015, 4th International
Workshop on Neutron Delivery Systems, 28 -30 September 2015, ILL Grenoble,
Franc
Measurements and Monte-Carlo simulations of the particle self-shielding effect of B4C grains in neutron shielding concrete
A combined measurement and Monte-Carlo simulation study was carried out in
order to characterize the particle self-shielding effect of B4C grains in
neutron shielding concrete. Several batches of a specialized neutron shielding
concrete, with varying B4C grain sizes, were exposed to a 2 {\AA} neutron beam
at the R2D2 test beamline at the Institute for Energy Technology located in
Kjeller, Norway. The direct and scattered neutrons were detected with a neutron
detector placed behind the concrete blocks and the results were compared to
Geant4 simulations. The particle self-shielding effect was included in the
Geant4 simulations by calculating effective neutron cross-sections during the
Monte-Carlo simulation process. It is shown that this method well reproduces
the measured results. Our results show that shielding calculations for
low-energy neutrons using such materials would lead to an underestimate of the
shielding required for a certain design scenario if the particle self-shielding
effect is not included in the calculations.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0
license http://creativecommons.org/licenses/by-nc-nd/4.0
Impact of crystallite size on the performance of a beryllium reflector
Beryllium reflectors are used at spallation neutron sources in order to
enhance the low-energy flux of neutrons emanating from the surface of a cold
and thermal moderator. The design of such a moderator/reflector system is
typically carried out using detailed Monte-Carlo simulations, where the
beryllium reflector is assumed to behave as a poly-crystalline material. In
reality, however, inhomogeneities in the beryllium could lead to discrepancies
between the performance of the actual system when compared to the modeled
system. The dependence of the total cross section in particular on crystallite
size, in the Bragg scattering region, could influence the reflector
performance, and if such effect is significant, it should be taken into account
in the design of the moderator/reflector system. In this paper, we report on
the preliminary results of using cross-section libraries, which include
corrections for the crystallite size effect, in spallation source neutronics
calculations.Comment: ICANS-XXII
Simulating neutron transport in long beamlines at a spallation neutron source using Geant4
The transport of neutrons in long beamlines at spallation neutron sources
presents a unique challenge for Monte-Carlo transport calculations. This is due
to the need to accurately model the deep-penetration of high-energy neutrons
through meters of thick dense shields close to the source and at the same time
to model the transport of low-energy neutrons across distances up to around 150
m in length. Typically, such types of calculations may be carried out with
MCNP-based codes or alternatively PHITS. However, in recent years there has
been an increased interest in the suitability of Geant4 for such types of
calculations. Therefore, we have implemented supermirror physics, a neutron
chopper module and the duct-source variance reduction technique for low-energy
neutron transport from the PHITS Monte-Carlo code into Geant4. In the current
work, we present a series of benchmarks of these extensions with the PHITS
software, which demonstrates the suitability of Geant4 for simulating long
neutron beamlines at a spallation neutron source, such as the European
Spallation Source, currently under construction in Lund, Sweden.Comment: ICANS-XXII
Racial/Ethnic Disparities in Access to Care among Children: How Does Medicaid Do in Closing the Gaps?
While Medicaid and the Children\u27s Health Insurance Program (CHIP) have become increasingly important sources of health coverage for low-income children in all racial and ethnic groups, the program plays an especially large role for children of color, who are more likely than white children to be low-income. In 2007, Medicaid and CHIP covered nearly one in five white children, but roughly two in five African American and Hispanic children.
As policymakers engaged in health reform consider the merits of public and private approaches to expanding coverage, this report provides an assessment of Medicaid\u27s relative impact on racial and ethnic disparities in access. The analysis compared health care access for white, African American and Hispanic children who were privately insured, uninsured, or enrolled in Medicaid or CHIP.
Key findings include: Racial and ethnic disparities in access to care were no more likely among children enrolled in Medicaid than among privately insured children. Insurance coverage – both private and Medicaid – often improved access for children in each racial and ethnic group, but generally did not significantly narrow racial and ethnic disparities in their access to health care.
This report analyzes data for more than 15,000 children from the 2003 and 2004 Medical Expenditure Panel Survey, a nationally representative household survey conducted by the Agency for Healthcare Research and Quality
Development of High Intensity Neutron Source at the European Spallation Source
The European Spallation Source being constructed in Lund, Sweden will provide
the user community with a neutron source of unprecedented brightness. By 2025,
a suite of 15 instruments will be served by a high-brightness moderator system
placed above the spallation target. The ESS infrastructure, consisting of the
proton linac, the target station, and the instrument halls, allows for
implementation of a second source below the spallation target. We propose to
develop a second neutron source with a high-intensity moderator able to (1)
deliver a larger total cold neutron flux, (2) provide high intensities at
longer wavelengths in the spectral regions of Cold (4-10 \AA ), Very Cold
(10-40 \AA ), and Ultra Cold (several 100 \AA ) neutrons, as opposed to Thermal
and Cold neutrons delivered by the top moderator. Offering both unprecedented
brilliance, flux, and spectral range in a single facility, this upgrade will
make ESS the most versatile neutron source in the world and will further
strengthen the leadership of Europe in neutron science. The new source will
boost several areas of condensed matter research such as imaging and spin-echo,
and will provide outstanding opportunities in fundamental physics
investigations of the laws of nature at a precision unattainable anywhere else.
At the heart of the proposed system is a volumetric liquid deuterium moderator.
Based on proven technology, its performance will be optimized in a detailed
engineering study. This moderator will be complemented by secondary sources to
provide intense beams of Very- and Ultra-Cold Neutrons.Comment: 12 pages, 4 figures, proceeding of the 23rd meeting of the
International Collaboration on Advanced Neutron Sources (ICANS XXIII) 13th -
18th October 2019 in Chattanooga, Tennesse
Overcoming High Energy Backgrounds at Pulsed Spallation Sources
Instrument backgrounds at neutron scattering facilities directly affect the
quality and the efficiency of the scientific measurements that users perform.
Part of the background at pulsed spallation neutron sources is caused by, and
time-correlated with, the emission of high energy particles when the proton
beam strikes the spallation target. This prompt pulse ultimately produces a
signal, which can be highly problematic for a subset of instruments and
measurements due to the time-correlated properties, and different to that from
reactor sources. Measurements of this background have been made at both SNS
(ORNL, Oak Ridge, TN, USA) and SINQ (PSI, Villigen, Switzerland). The
background levels were generally found to be low compared to natural
background. However, very low intensities of high-energy particles have been
found to be detrimental to instrument performance in some conditions. Given
that instrument performance is typically characterised by S/N, improvements in
backgrounds can both improve instrument performance whilst at the same time
delivering significant cost savings. A systematic holistic approach is
suggested in this contribution to increase the effectiveness of this.
Instrument performance should subsequently benefit.Comment: 12 pages, 8 figures. Proceedings of ICANS XXI (International
Collaboration on Advanced Neutron Sources), Mito, Japan. 201
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