369 research outputs found
Development of semiconductor detectors for fast neutron radiography
A high-energy neutron detector has been developed using a semiconductor diode fabricated from bulk gallium arsenide wafers with a polyethylene neutron converter layer. Typical thickness of the diode layer is 250 to 300 μm with bias voltages of 30 to 150 volts. Converter thicknesses up to 2030 μm have been tested. GaAs neutron detectors offer many advantages over existing detectors including positional information, directional dependence, gamma discrimination, radiation hardness, and spectral tailoring. Polyethylene-coated detectors have been shown to detect 14 MeV neutrons directly from a D-T neutron generator without interference from gamma rays or scattered neutrons. An array of small diode detectors can be assembled to perform fast neutron radiography with direct digital readout and real-time display of the image produced. In addition, because the detectors are insensitive to gamma rays and low energy neutrons, highly radioactive samples (such as spent nuclear fuel or transuranic waste drums) could be radiographed. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87673/2/1118_1.pd
Listening to Children and Young People’s (CYP) Experience and Perceptions During the Period of COVID-19 and Their Advice for Teachers and Schools
This research project aimed to elicit the views of children and young people (CYP) about their experience of COVID-19, and their advice to teachers and schools. The views of fourteen CYP aged between 9 and 15 years of age from within and around London were ascertained through individual semi-structured interviews and analysed through thematic analysis. There were a variety of responses from CYP, including the following: a deep appreciation for their teachers and their support throughout the pandemic; stories of positive personal growth and spending more time with their family. However, their inability to see friends and the challenges of learning from home had a considerable impact on some CYP who would have liked home learning to have been more personalised, interactive and varied and for there to have been a greater awareness of workload. A list of issues for consideration and a checklist based upon the CYP’s views have been compiled, for the use of schools and teachers. Given the small sample, the timing of the study and the fact that the pandemic is ongoing, some suggestions for further research are indicated
Theoretical aspects of the CEBAF 89-009 experiment on inclusive scattering of 4.05 GeV electrons from nuclei
We compare recent CEBAF data on inclusive electron scattering on nuclei with
predictions, based on a relation between structure functions (SF) of a nucleus,
a nucleon and a nucleus of point-nucleons. The latter contains nuclear
dynamics, e.g. binary collision contributions in addition to the asymptotic
limit. The agreement with the data is good, except in low-intensity regions.
Computed ternary collsion contributions appear too small for an explanation. We
perform scaling analyses in Gurvitz's scaling variable and found that for
, ratios of scaling functions for pairs of nuclei differ by less
than 15-20% from 1. Scaling functions for are, for increasing ,
shown to approach a plateau from above. We observe only weak -dependence
in FSI, which in the relevant kinematic region is ascribed to the diffractive
nature of the NN amplitudes appearing in FSI. This renders it difficult to
separate asymptotic from FSI parts and seriously hampers the extraction of
from scaling analyses in a model-independnent fashion.Comment: 11 p. Latex file, 2 ps fig
Final state effects on superfluid He in the deep inelastic regime
A study of Final State Effects (FSE) on the dynamic structure function of
superfluid He in the Gersch--Rodriguez formalism is presented. The main
ingredients needed in the calculation are the momentum distribution and the
semidiagonal two--body density matrix. The influence of these ground state
quantities on the FSE is analyzed. A variational form of is used, even
though simpler forms turn out to give accurate results if properly chosen.
Comparison to the experimental response at high momentum transfer is performed.
The predicted response is quite sensitive to slight variations on the value of
the condensate fraction, the best agreement with experiment being obtained with
. Sum rules of the FSE broadening function are also derived and
commented. Finally, it is shown that Gersch--Rodriguez theory produces results
as accurate as those coming from other more recent FSE theories.Comment: 20 pages, RevTex 3.0, 11 figures available upon request, to be appear
in Phys. Rev.
Relativistic approaches to structure functions of nuclei
We employ a propagator technique to derive a new relativistic 1/\qq
expansion of the structure function of a nucleus, composed of point-nucleons.
We exploit non-relativistic features of low-momentum nucleons in the target and
only treat relativistically the nucleon after absorption of a high-momentum
virtual photon. The new series permits a 3-dimensional reduction of each term
and a formal summation of all Final State Interaction terms. We then show that
a relativistic structure function can be obtained from its non-relativistic
analog by a mere change of a scaling variable and an addition of an energy
shift. We compare the obtained result with an ad hoc generalized
Gersch-Rodriguez-Smith theory, previously used in computations of nuclear
structure functions.Comment: Comparison with data is included, to be published in PRC, Feb. 200
Beyond the binary collision approximation for the large- response of liquid He
We discuss corrections to the linear response of a many-body system beyond
the binary collision approximation. We first derive for smooth pair
interactions an exact expression of the response , considerably
simplifying existing forms and present also the generalization for interactions
with a strong, short-range repulsion. We then apply the latter to the case of
liquid He. We display the numerical influence of the correction
around the quasi-elastic peak and in the low-intensity wings of the response,
far from that peak. Finally we resolve an apparent contradiction in previous
discussions around the fourth order cumulant expansion coefficient. Our results
prove that the large- response of liquid He can be accurately understood
on the basis of a dynamical theory.Comment: 19 p. Figs. available on reques
Description of recent large- neutron inclusive scattering data from liquid He
We report dynamical calculations for large- structure functions of liquid
He at =1.6 and 2.3 K and compare those with recent MARI data. We extend
those calculations far beyond the experimental range q\le 29\Ain in order to
study the approach of the response to its asymptotic limit for a system with
interactions having a strong short-range repulsion. We find only small
deviations from theoretical behavior, valid for smooth . We repeat an
extraction by Glyde et al of cumulant coefficients from data. We argue that
fits determine the single atom momentum distribution, but express doubt as to
the extraction of meaningful Final State Interaction parameters.Comment: 37 pages, 13 postscript fig
Bose-Einstein condensation in the presence of a uniform field and a point-like impurity
The behavior of an ideal -dimensional boson gas in the presence of a
uniform gravitational field is analyzed. It is explicitly shown that,
contrarily to an old standing folklore, the three-dimensional gas does not
undergo Bose-Einstein condensation at finite temperature. On the other hand,
Bose-Einstein condensation occurs at for if there is a
point-like impurity at the bottom of the vessel containing the gas.Comment: 14 pages, REVTEX. Revised version, accepted for publication in Phys.
Rev.
Description of inclusive scattering of 4.045 GeV electrons from D
We exploit a relationship between the Structure Functions of nucleons, the
physical deuteron and of a deuteron, composed of point-nucleons to compute
angular distributions of inclusive cross sections of 4.05 GeV electrons. We
report general agreement with data and interpret the remaining discrepancies.
We discuss the potential of the data for information on neutron structure
functions and the static form factor .Comment: 9 pages,1 Fig., PS fil
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