14 research outputs found
Quantum Monte Carlo Calculations of Pion Scattering from Li
We show that the neutron and proton transition densities predicted by recent
quantum Monte Carlo calculations for A=6,7 nuclei are consistent with pion
scattering from 6Li and 7Li at energies near the Delta resonance. This has
provided a microscopic understanding of the enhancement factors for quadrople
excitations, which were needed to describe pion inelastic scattering within the
nuclear shell model of Cohen and Kurath.Comment: 10 pages, REVTeX, 3 postscript figures; added calculation of elastic
and inelastic pion scattering from 6Li at multiple energie
Probing the isovector transition strength of the low-lying nuclear excitations induced by inverse kinematics proton scattering
A compact approach based on the folding model is suggested for the
determination of the isoscalar and isovector transition strengths of the
low-lying () excitations induced by inelastic proton
scattering measured with exotic beams. Our analysis of the recently measured
inelastic O+p scattering data at and 43 MeV/nucleon
has given for the first time an accurate estimate of the isoscalar
and isovector deformation parameters (which cannot be determined from
the (p,p') data alone by standard methods) for 2 and excited
states in O. Quite strong isovector mixing was found in the 2
inelastic O+p scattering channel, where the strength of the isovector
form factor (prototype of the Lane potential) corresponds to a
value almost 3 times larger than and a ratio of nuclear transition
matrix elements .Comment: 5 pages, 3 figure
Demonstration of a solid deuterium source of ultra-cold neutrons
Ultra-cold neutrons (UCN), neutrons with energies low enough to be confined
by the Fermi potential in material bottles, are playing an increasing role in
measurements of fundamental properties of the neutron. The ability to
manipulate UCN with material guides and bottles, magnetic fields, and gravity
can lead to experiments with lower systematic errors than have been obtained in
experiments with cold neutron beams. The UCN densities provided by existing
reactor sources limit these experiments. The promise of much higher densities
from solid deuterium sources has led to proposed facilities coupled to both
reactor and spallation neutron sources. In this paper we report on the
performance of a prototype spallation neutron-driven solid deuterium source.
This source produced bottled UCN densities of 145 +/-7 UCN/cm3, about three
times greater than the largest bottled UCN densities previously reported. These
results indicate that a production UCN source with substantially higher
densities should be possible
EXCITATION OF GIANT RESONANCES IN PION INELASTIC SCATTERING
On présente les résultats obtenus récemment par diffusion inélastique de pions à l'énergie de la résonance, sur la région des résonances géantes des noyaux. Les nouveaux résultats incluent l'observation de candidats pour la résonance dipolaire avec spin-flip dans 12C et 28Si et l'observation de grandes asymétries des sections efficaces π+, π- pour la région du continuum de 208Pb.We present some recently obtained data for resonance energy inelastic pion scattering to the giant resonance region of nuclei. New results include the observation of candidates for spin-dipole resonances in 12C and 28Si, and the observation of large π+, π- cross section asymmetries for the continuum region in 208Pb
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Spin excitations in pion inelastic scattering
The data on spin excitations observed in pion inelastic scattering are reviewed. A predominant feature of this process is the selectivity with which high-spin unnatural-parity states are excited. Constant-q excitation functions have proven valuable in identifying unnatural-parity states because of the unique signature of ..delta..S = 1 transitions. It has recently been shown that angular distributions measured for transitions to natural-parity states are quite different for ..delta..S = 0 and ..delta..S = 1 transitions. Pion scattering should continue to prove useful in studying the spin structure of nuclear transitions because of the sensitivity of both excitation functions and angular distributions to the spin transferred to the nucleus. In particular, pion scattering measurements may be helpful in searches for spin-mode giant resonances. In addition to the ability to distinguish transitions dominated by ..delta..S = 1, comparisons of ..pi../sup +/ and ..pi../sup -/ scattering can be used to determine the relative contributions of neutrons and protons to inelastic transitions. In each N not equal to Z nucleus studied there have been large ..pi../sup +//..pi../sup -/, asymmetries observed for some transitions to stretched states. This results in information that is not obtainable from 180/sup 0/ electron scattering
SPIN FLIP STRENGTH AT HIGH EXCITATION ENERGY IN THE 90Zr([MATH]) 90Zr REACTION
Des mesures de la section efficace, du pouvoir d'analyse, et de la probabilité du renversement du spin sont en accord avec M1 pour le pic à 9,0 MeV dans la réaction 90 Zr(p,p')90Zr à 319 MeV, mais elles ne sont pas définitives. Des mesures de S nn montrent une section efficace d'excitation du spin qui est importante de 8 à 25 MeV.Measurements of the cross section, analyzing power, and spin-flip probability are consistent with an M1 assignment for the 9.0 MeV peak in the 90Zr(p,p')90Zr reaction at 319 MeV, but they are not definitive. The spin-Clip measurements reveal a large spin-excitation cross section from 8 to 25 MeV excitation
Status of the UCN experiment
International audienceThe neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics beyond the standard model. Measurements of neutron lifetime and β-decay correlation coefficients with precisions of 0.02% and 0.1%, respectively, would allow for stringent constraints on new physics. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime, τn = 877.7s (0.7s)stat (+0.4/−0.2s)sys. We discuss the recent result from UCNτ, the status of ongoing data collection and analysis, and the path toward a 0.25 s measurement of the neutron lifetime with UCNτ