204 research outputs found
Cold Crystal Reflector Filter Concept
In this paper the theoretical concept of a cold crystal reflector filter will
be presented. The aim of this concept is to balance the shortcoming of the
traditional cold polycrystalline reflector filter, which lies in the
significant reduction of the neutron flux right above (in energy space) or
right below (wavelength space) the first Bragg edge
The scientific contributions of George Washington Carver
2 unnumbered pages, 60 pages"During the twenty-two years from 1921 to January 5, 1943, George Washington Carver achieved both national and interÂnational fame. Prominent among the words often used to describe him is the expression ’’great scientist". Biographers and reÂporters active in this two-decade period compiled long lists of Carver’s scientific contributions. The purpose of this report is to evaluate these scientific contributions. For this report Dr. Carver’s career is divided into two parts। the first started in 1895, when he went to Tuskegee Institute at the request of Booker T. Washington, and lasted until the death of Booker T. Washington late in 1915. The second division of Carver’s career can itself be considered in two phases: the shorter somewhat obscure part dating from 1916 to about 1921, and the longer portion from 1921 until his death on January 5, 1943. It was during this last portion of his life after he was al ready at least fifty-seven years of age that Dr. Carver became famous."--Introduction.Department of Interior. National Park Service
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
A hemorrhagic factor in moldy lespedeza hay
Digitized 2007 AES.Includes bibliographical references (page 11)
A next-generation inverse-geometry spallation-driven ultracold neutron source
The physics model of a next-generation spallation-driven high-current
ultracold neutron (UCN) source capable of delivering an extracted UCN rate of
around an-order-of-magnitude higher than the strongest proposed sources, and
around three-orders-of-magnitude higher than existing sources, is presented.
This UCN-current-optimized source would dramatically improve cutting-edge UCN
measurements that are currently statistically limited. A novel "Inverse
Geometry" design is used with 40 L of superfluid He (He-II), which acts as
a converter of cold neutrons (CNs) to UCNs, cooled with state-of-the-art
sub-cooled cryogenic technology to 1.6 K. Our design is optimized for a
100 W maximum heat load constraint on the He-II and its vessel. In our
geometry, the spallation target is wrapped symmetrically around the UCN
converter to permit raster scanning the proton beam over a relatively large
volume of tungsten spallation target to reduce the demand on the cooling
requirements, which makes it reasonable to assume that water edge-cooling only
is sufficient. Our design is refined in several steps to reach
s under our other restriction of 1 MW maximum
available proton beam power. We then study effects of the He-II scattering
kernel as well as reductions in due to pressurization to reach
s. Finally, we provide a design for the UCN
extraction system that takes into account the required He-II heat transport
properties and implementation of a He-II containment foil that allows UCN
transmission. We estimate a total useful UCN current from our source of
s from a 18 cm diameter guide 5 m from the source.
Under a conservative "no return" approximation, this rate can produce an
extracted density of cm in 1000~L external experimental
volumes with a Ni (335 neV) cut-off potential.Comment: Submitted to Journal of Applied Physic
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