Search

Detailed information about nuclear level densities is obtained by direct counting of individual resonances. A collection of individual resonances with the same spin and parity follows the predictions of the Gaussian Orthogonal Ensemble (GOE) version of Random Matrix Theory (RMT). RMT predictions are used to determine the corrections due to the imperfections in the measurement. We derived a general expression for the probability distribution for imperfect eigenvalue sequences. The missing level correction for the number of levels is obtained by two methods, the newly developed eigenvalue (or spacing) analysis and the more traditional reduced width analysis. Proton resonances in three nuclei are analyzed using the two methods. Improved values for the level densities are obtained, and the parity dependence of level density is considered.

In order to resolve long‐standing discrepancies in indirect measurements of the neutron‐neutron scattering length ann and contribute to solving the problem of the charge symmetry of the nuclear force, the collaboration DIANNA (Direct Investigation of ann Association) plans to measure the neutron‐neutron scattering cross section σnn. The key issue of our approach is the use of the through‐channel in the Russia reactor YAGUAR with a peak neutron flux of 1018 /cm2/s. The proposed experimental setup is described. Results of calculations are presented to connect σnn with the nn‐collision detector count rate and the neutron flux density in the reactor channel. Measurements of the thermal neutron fields inside polyethylene converters show excellent prospects for the realization of the direct nn‐experiment.

An experimental primary γ‐ray spectrum per excitation‐energy bin (P(Ex, Eγ) matrix) in a light‐ion reaction is obtained for 56,57Fe isotopes using a subtraction method. By factorizing the P(Ex, Eγ) matrix according to the Axel‐Brink hypothesis the nuclear level density and the radiative strength function (RSF) in 56,57Fe are extracted simultaneously. A step structure is observed in the level density for both isotopes, and is interpreted as the breaking of Cooper pairs. The RSFs for 56,57Fe reveal an anomalous enhancement at low γ‐ray energies.

Average nuclear level densities close to the nuclear binding energy in 56Fe and 57Fe are extracted from primary γ‐ray spectra. A step structure is observed in the level density for both isotopes, and is interpreted as breaking of Cooper pairs. Thermal properties of 56Fe are studied within the statistical canonical ensemble. The experimental heat capacity in 56Fe is compared with the theoretical heat capacity calculated within the shell model Monte Carlo approach.

Parity violation in p-wave neutron resonances of the palladium isotopes 104, 105, 106, and 108 has been measured by transmission of a longitudinally polarized neutron beam through a natural palladium target. The measurements were performed at the pulsed spallation neutron source of Los Alamos Neutron Science Center. The rms weak interaction matrix elements and the corresponding spreading widths were determined for ${}^{104}\mathrm{Pd},$ ${}^{105}\mathrm{Pd},$ and ${}^{106}\mathrm{Pd}.$

We have measured neutron resonances in the palladium isotopes 104, 105, and 110 for neutron energies from 1 to 2100 eV. Many new p-wave resonances have been observed. Their neutron widths and, in several cases, the radiative widths were measured. The average level spacings and the s-wave and p-wave neutron strength functions were determined. The time-of-flight method was used for both neutron total cross section measurements and total $(n,\ensuremath{\gamma})$ reaction yield measurements at the pulsed spallation neutron source of Los Alamos Neutron Science Center. Well established resonance spectroscopy for these isotopes is essential for the analysis of parity violation data that were recently measured in palladium.

Parity violating effects in the nucleus are normally very small, but in certain compound nuclear resonances such effects are enhanced to several percent, as in the 0.734 eV p-wave resonance in 139 La. We have used this enhanced parity violation to measure the depolarization of neutrons traversing a thick single crystal of ferromagnetic holmium. The depolarization was dependent on the relative orientation of the neutron polarization and the holmium c crystalline axis. The effect was explained in terms of neutron precession in an array of highly correlated domains magnetized in the c axis direction. The results show the high degree of correlation of magnetic domains in the single crystal and demonstrate the usefulness of epithermal neutrons in measuring magnetic properties of thick crystals. The use of other parity violating resonances should allow polarization analysis of neutrons over a range of neutron energies.

Bunakov and Weidenmuller suggested that large enhancement of time reversal invariance violation may be observed near two interfering resonances via a test of detailed balance. In our (p, α) resonance data on 23Na, 27Al, 31P, 35Cl, and 39K, there are 33 pairs of adjacent resonances which have the same spin and parity. The difference in the differential cross sections for the (p, α0) and (α, p0) reactions was calculated for these resonance pairs using experimental values for the partial widths. The collision matrix elements were obtained for a Hamiltonian H = H0 + iH', following the approach of Moldauer. The differences show striking dependence on energy and angle and on the particular pair of resonances, with the relative sensitivity of the detailed balance test varying by many orders of magnitude. These preliminary results indicate that this class of experiments may be more sensitive than previous detailed balance tests.

Polarized neutron transmission experiments show remarkable sensitivity to the presence of small symmetry violating forces in nuclear interactions. Parity-nonconserving (PNC) analyzing powers of a percent or more have been measured on p-wave neutron resonances in nuclei ranging from 81Br to 238U. A brief summary is given of the study of PNC effects in neutron resonances. Details of ongoing polarized neutron transmission experiments are discussed and some sample data presented. Several development projects are currently under way, which taken together should improve the sensitivity of these experiments by a factor of ∼ 20. Similar large PNC effects can be observed in (n, γ) resonances with much smaller samples. A design for a near 4π gamma ray detector to be constructed of CsI(pure) is described.

Parity nonconservation (PNC) was studied in p-wave neutron resonances of {sup 103}Rh in the neutron energy range 30 to 490 eV. The helicity dependence of the neutron total cross section of rhodium was determined by capture measurements with the time-of-flight method at the Manuel Lujan Neutron Scattering Center at the Los Alamos National Laboratory. A total of 32 p-wave resonances were studied and statistically significant longitudinal asymmetries were observed for resonances at E{sub n}=44.5, 110.8, 321.6, and 432.9 eV. A statistical analysis treating the PNC matrix elements as random variables yields a weak spreading width {Gamma}{sub w}=(1.42{sub {minus}0.59}{sup +1.21}){times}10{sup {minus}7}heV. {copyright} {ital 1999} {ital The American Physical Society}

Parity violation in p-wave neutron resonances of ${}^{121}\mathrm{Sb},$ ${}^{123}\mathrm{Sb},$ and ${}^{127}\mathrm{I}$ has been measured by transmission of a longitudinally polarized neutron beam through natural antimony and iodine targets. The measurements were performed at the pulsed spallation neutron source of the Los Alamos Neutron Science Center. Five statistically significant parity violation effects were observed in ${}^{121}\mathrm{Sb},$ one effect in ${}^{123}\mathrm{Sb},$ and seven effects in ${}^{127}\mathrm{I}.$ The weak interaction rms matrix elements and the corresponding spreading widths were determined.

The morphology, size distributions, spatial distributions, and quantitative chemical compositions of co-polymer polyol-reinforcing particles in a polyurethane have been investigatedwith scanning transmission X-ray microscopy (STXM). A detailed discussion of microscope operating procedures is presented and ways to avoid potential artifacts are discussed. Images at selected photon energies in the C 1s, N 1s and O 1s regions allow unambiguous identification of styrene–acrylonitrile-based (SAN) copolymer and polyisocyanate polyaddition product-based (PIPA) reinforcing particles down to particle sizes at the limit of the spatial resolution (50 nm). Quantitative analysis of the chemical composition of individual reinforcing particles is achieved by fitting C 1s spectra to linear combinations of reference spectra. Regression analyses of sequences of images recorded through the chemically sensitive ranges of the C 1s, N 1s andO 1s spectra are usedto generate quantitative compositional maps, which provid e a fast andeffective means of investigating compositional distributions over a large number of reinforcing particles. The size distribution of all particles determined by STXM is shown to be similar to that determined by TEM. The size distributions of each type of reinforcing particle, which differ considerably, were obtained by analysis of STXM images at chemically selective energies. # 2001 Elsevier Science B.V. All rights reserved.

The quantum numbers of over 100 states in 30P have been determined from the ground state to 8 MeV. Previous measurements had provided complete spectroscopy in 26Al. For these N=Z=odd nuclei, states of isospin T=0 and T=1 coexist at all energies. These spectra provide a unique opportunity to test the effect of symmetry breaking (of the approximate symmetry isospin) on the level statistics and on the transition strength distributions. The level statistics are strongly affected by the small symmetry breaking and the transition strength distributions differ from the Porter-Thomas distribution.

Level statistics and reduced transition probability distributions have been analyzed over the region E{sub x}=0--8014keV in {sup 30}P and compared to previous results from {sup 26}Al. The level statistics in {sup 30}P show clear evidence of broken isospin symmetry and are very similar to those from {sup 26}Al. Transition distributions in the two nuclides are different, but both suggest that the broken symmetry also affects the transitions.

The {sup 29}Si(p,{gamma}){sup 30}P reaction was studied for 32 resonances in the energy range E{sub p}=1.0-2.5 MeV. Angular distributions were measured for 230 primary and secondary transitions. Results from the analysis of these data were combined with previous measurements of the {sup 29}Si(p,p{sub 0}){sup 29}Si and {sup 29}Si(p,{gamma}){sup 30}P reactions to determine the spin J, parity {pi}, and isospin T of many levels. Remaining ambiguities were eliminated by comparison with the spectrum of the parent nucleus {sup 30}Si and with the calculated shell-model spectrum. J, {pi}, and T have been assigned for 103 states up to an excitation energy of 8.0 MeV. (c) 2000 The American Physical Society.

The parity-violating longitudinal asymmetry of the neutron scattering cross section has been measured for thorium in the off-resonance energy intervals from 30 to 300 eV. The observed result of $(0.5\ifmmode\pm\else\textpm\fi{}1.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ is compared with theoretical predictions.

The analysis of parity nonconservation (PNC) measurements performed on {sup 232}Th by the TRIPLE Collaboration has been extended to include the neutron energy range of 250 to 1900 eV. Below 250 eV all ten statistically significant parity violations have the same sign. However, at higher energies PNC effects of both signs were observed in the transmission of longitudinally polarized neutrons through a thick thorium target. Although the limited experimental energy resolution precluded analysis in terms of the longitudinal asymmetry, parity violations were observed and the cross section differences for positive and negative neutron helicities were obtained. For comparison, a similar analysis was performed on the data below 250 eV, for which longitudinal asymmetries were obtained previously. For energies below 250 eV, the p-wave neutron strength functions for the J=1/2 and J=3/2 states were extracted: S{sub 1/2}{sup 1}=(1.68{+-}0.61)x10{sup -4} and S{sub 3/2}{sup 1}=(0.75{+-}0.18)x10{sup -4}. The data provide constraints on the properties of local doorway states proposed to explain the PNC sign effect in thorium. (c) 2000 The American Physical Society.

The TRIPLE Collaboration has performed measurements of the helicity dependence of the neutron resonance cross section for many nuclides. More than 70 statistically significant parity violations have been observed. Generic enhancements amplify the signal for symmetry breaking and the stochastic properties of the compound nucleus permit the strength of the symmetry-breaking interaction to be determined without knowledge of the wave functions of individual states. The measurements are concentrated in the regions of the 3p and 4p maxima of the neutron strength function-near A=110 and A=230. The results to date are summarized.

Odd-odd nuclides in the sd-shell have states of different isospin coexisting even near the ground state. Because isospin is not a perfect symmetry, this coexistence provides an opportunity to examine directly the effects of a broken symmetry on the statistical properties of a quantum system. We present results for the nuclides 26Al and 30P, for which the level schemes are relatively complete.

Parity nonconservation (PNC) has been studied in the neutron {ital p}-wave resonances of {sup 106}Pd and {sup 108}Pd in the energy range of 20 to 2000 eV. Longitudinal asymmetries in {ital p}-wave capture cross sections are measured using longitudinally polarized neutrons incident on {approximately}20-g metal-powder targets at LANSCE. A CsI {gamma}-ray detector array measures capture cross section asymmetries as a function of neutron energy which is determined by the neutron time-of-flight method. A total of 21 {ital p}-wave resonances in {sup 106}Pd and 21 {ital p}-wave resonances in {sup 108}Pd were studied. One statistically significant PNC effect was observed in {sup 106}Pd, and no effects were observed in {sup 108}Pd. For {sup 106}Pd a weak spreading width of {Gamma}{sub w}=34{sub {minus}28}{sup +47}{times}10{sup {minus}7} eV was obtained. For {sup 108}Pd an upper limit on the weak spreading width of {Gamma}{sub w}{lt}12{times}10{sup {minus}7} eV was determined at the 68{percent} confidence level. {copyright} {ital 1999} {ital The American Physical Society}

Eight multicatheterized wethers (35.9 +/- .8 kg BW) were used in a replicated 4 x 4 Latin square design to measure N retention and net uptake and release of plasma metabolites across the portal-drained viscera (PDV), hepatic (HEP), and total splanchnic (TS) tissues in response to changes in supplemental N source. Treatments selected to provide different amounts of undegradable intake protein (UIP) were urea, soybean meal (SBM), poultry by-product meal (PBM), and bloodmeal:corn gluten meal (BMCGM; 50:50 CP basis). Diets (urea, SBM, PBM, and BMCGM) contained 12.9, 13.8, 13.6, and 13.2% CP, respectively. Periods were 10 d, with total feces and urine collected on d 7 to 10 and blood sampled on d 10. Wethers were fed at 2% of BW in 12 daily portions. Nitrogen retention was 2.2, 3.3, 4.1, and 4.4 g/d for urea, SBM, PBM, and BMCGM, respectively. Urea had less (P < .01) N retention than SBM, PBM, and BMCGM; SBM had less N retention (P < .01) than PBM and BMCGM. Arterial, portal, and hepatic plasma flows were greater (P < .09) for SBM than for PBM and BMCGM (21 vs 16, 17; 84 vs 72, 72; 105 vs 87, 88 L/h). Portal plasma flow was greater (P < .10) for urea than for SBM, PBM, and BMCGM (85 vs 84, 72, 72 L/h). Portal-drained viscera and TS alpha-amino N (AAN) fluxes were less (P < .05) for PBM than for BMCGM (20.5 vs 26.6 and 7.2 vs 15.1 mmol/h), but TS AAN flux was less (P < .05) for urea than for SBM, PBM, and BMCGM (6.9 vs 16.9, 7.2, 15.1 mmol/h). Portal-drained viscera flux and HEP removal of NH3 N were greater (P < .001) for SBM than for PBM and BMCGM (27.7 vs 19.4, 20.6; -28.1 vs -20.0, -21.4 mmol/h). Gut use was less (P = .07) and HEP and TS fluxes of urea N were greater (P < .01) for SBM than for PBM and BMCGM (-4.92 vs -8.32, -7.93; 25.87 vs 16.54, 20.00; 20.95 vs 8.22, 12.07 mmol/h). These data suggest that PBM and BMCGM improved efficiency of N use compared with urea and SBM by reducing urinary N loss.

Neutron resonances in {sup 103}Rh have been measured for neutron energies from 30 to 2000 eV using the time-of-flight method and the (n,{gamma}) reaction. The rhodium resonance spectroscopy is essential for the analysis of parity violation measurements recently performed on neutron resonances in {sup 103}Rh. Neutron scattering and radiative widths were determined, and orbital angular momentum assignments made with a Bayesian analysis. The s-wave and p-wave strength functions and average level spacings were determined. {copyright} {ital 1999} {ital The American Physical Society}

In order to extend our knowledge of the weak spreading width to the nuclear mass 30 region, parity-violation measurements have begun at the Triangle Universities Nuclear Laboratory using the 31P(p,α0)28Si reaction. Longitudinally polarized protons are scattered from 31P nuclei at several MeV, and a large solid angle silicon-strip detector detects the alpha particles at backward angles. By rapidly reversing the spin direction of the protons, we measure the helicity dependence of the alpha yield. A discussion of the working system and preliminary results are given.

We conducted three studies with steers to evaluate poultry by-product meal (PBM) as a supplemental N source for ruminants. An in situ study compared the solubility, degradation rate, and ruminal escape of PBM N with blood meal (BM), corn gluten meal (CGM), and soybean meal (SBM) N. Additionally, an 84-d growth study (n = 95, 228+/-5 kg BW) and a digestion trial (6 x 6 Latin square) were conducted. The basal diet for the growth and digestion studies consisted of 49% corn silage, 36% cottonseed hulls, and 15% supplement (DM basis). Sources of supplemental N (% of total supplemental N) were 100% SBM and 0, 25, 50, 75, and 100% PBM, with urea used to balance for N. In situ ruminal escape N (25.2, 55.3, 86.7, and 98.9% for SBM, PBM, CGM, and BM, respectively) was greater (P.05) for PBM than for SBM; however, a greater (P.05) proportion of BM and CGM N escaped ruminal degradation compared with PBM. Dry matter intake, ADG and gain/ feed increased linearly (P.003) as PBM increased; however, no differences (P.48) were observed in these variables for 100% PBM compared with 100% SBM. Duodenal N flow and small intestinal N disappearance increased linearly (P.05) as PBM increased in the diet. Bacterial N flow to the small intestine was not affected (P.19) by treatment; however, 100% SBM decreased (P.04) bacterial CP synthesis (g bacterial N/kg OM disappearance from the stomach) compared with 0 and 100% PBM. In vivo ruminal escape N of PBM and SBM was 40.6 and 13.7%, respectively. Ruminal NH3 N decreased linearly (P.001) as PBM increased. These data suggest that PBM can replace SBM as a source of supplemental N for steer calves that consume a diet based on corn silage and cottonseed hulls.

Parity nonconservation was studied for 23 p-wave resonances in 113Cd up to En = 500 eV at the LANSCE pulsed neutron source using a longitudinally polarized neutron beam and the time-of-flight method. The helicity dependence of the total neutron capture cross section was measured with an enriched 113Cd target and with a target of natural cadmium. Parity violating effects were observed for several resonances in 113Cd and 111Cd. A root-mean-square value of the parity nonconserving matrix element MJ=1 = 2.9+1.3-0.9 meV was obtained for the spin J=1 levels in the compound nucleus 114Cd. This result from the 3p-peak region of the neutron strength function is compared with the parity violation results for nuclei from the 4p-peak region.

Parity nonconservation (PNC) was measured for 24 p-wave resonances from 8 to 300 eV in 232Th by measuring the helicity dependence of the total neutron cross section for epithermal neutrons with an improved experimental system. Ten resonances show statistically significant parity violation. For these ten resonances the analyzing powers are all positive, thus confirming the previously observed sign correlation. The data are fit to the sum of two terms, a constant asymmetry and a fluctuating asymmetry. With this ansatz the root-mean-square PNC matrix element M=1.12 meV, which corresponds to a weak spreading widthΓw=4.7×10-7 eV. For the neighboring nuclide 238U there is no constant offset, suggesting that the sign correlation is specific to 232Th. Disciplines Atomic, Molecular and Optical Physics | Physics Authors Sharon L. Stephenson, J D. Bowman, Bret E. Crawford, P P J. Delheij, C M. Frankle, M IInuma, J N. Knudsen, L Y. Lowie, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, H Postma, N R. Roberson, S J. Seestrom, E I. Sharapov, Y-F Yen, and V W. Yuan This article is available at The Cupola: Scholarship at Gettysburg College: http://cupola.gettysburg.edu/physfac/20 Parity nonconservation in neutron resonances in Th S. L. Stephenson,* J. D. Bowman, B. E. Crawford, P. P. J. Delheij, C. M. Frankle, M. Iinuma, J. N. Knudson, L. Y. Lowie, A. Masaike, Y. Matsuda, G. E. Mitchell, S. I. Penttila, H. Postma, N. R. Roberson, S. J. Seestrom, E. I. Sharapov, Y.-F. Yen, and V. W. Yuan North Carolina State University, Raleigh, North Carolina 27695-8202 and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708-0308 Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Duke University, Durham, North Carolina 27708 and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708-0308 TRIUMF, Vancouver, British Columbia, Canada V6T 2A3 Department of Physics, Kyoto University, Kyoto 606-8502, Japan University of Technology, Delft, 2600 GA, The Netherlands Joint Institute for Nuclear Research, 141980 Dubna, Russia ~Received 6 April 1998! Parity nonconservation ~PNC! was measured for 24 p-wave resonances from 8 to 300 eV in Th by measuring the helicity dependence of the total neutron cross section for epithermal neutrons with an improved experimental system. Ten resonances show statistically significant parity violation. For these ten resonances the analyzing powers are all positive, thus confirming the previously observed sign correlation. The data are fit to the sum of two terms, a constant asymmetry and a fluctuating asymmetry. With this ansatz the root-meansquare PNC matrix element M51.12 meV, which corresponds to a weak spreading width Gw54.7310 27 eV. For the neighboring nuclide U there is no constant offset, suggesting that the sign correlation is specific to Th. @S0556-2813~98!03608-5# PACS number~s!: 25.40.Ny, 24.80.1y, 11.30.Er, 27.90.1b

I describe a new generation of experiments studying the weak interaction between nucleons. Measurements of the effect of this interaction are few in number and the significance of the observed effects are generally small. It is well known that the weak interaction violates parity. This was first experimentally established by C. S. Wu through measurement of an asymmetry of electrons emitted in the beta-decay of polarized 60Co. The measured asymmetry was large because beta decay is a weak interaction process. For a process in which the strong interaction can contribute, we expect much smaller asymmetries, or order 10-7.

Safflower and coconut oil were compared as protective carriers of dietary vitamin A supplemented to abomasally cannulated sheep. Vitamin A, 240,000 I.U., was predissolved in 11.7 g of safflower or coconut oil and bolused directly into the rumen of mature wethers along with 4 g of chromic oxide. The vitamin A was pre-dissolved in 0, 11.7, 23.4 or 35.0 g of coconut oil in experiment 2. Determination of carrier oil protectiveness of solubilized dietary vitamin A was based on recoveries of vitamin A supplement and chromic oxide in abomasal digesta 24 h post dosage. Vitamin A recoveries were significantly higher (P0.05) when dissolved in coconut oil (55.6%) compared to safflower oil (35.5%). Recoveries of vitamin A in abomasal digesta increased linearly (P0.01) with the amount of carrier coconut oil in experiment 2. Results of these experiments support the potential use of coconut oil as a protective carrier of ruminal labile vitamin A.

A high efficiency γ-ray detection system based on a 12′′×12′′ NaI(Tl) bore hole detector has been used to measure the strength of low-energy narrow resonances in proton-induced capture reactions. The strengths of the Ep=324 keV and the Ep=416 keV resonances in 29Si(p,γ)30P and of the Ep=620 keV resonance in 30Si(p,γ)31P have been measured. The applicability of these resonances for high resolution depth profiling in materials analysis is discussed.

The fluctuation properties of quantum systems now are used as a signature of quantum chaos. The analyses require data of extremely high quality. The 29Si(p,γ) reaction is being used to establish a complete level scheme of 30P to study chaos and isospin breaking in this nuclide. Determination of the angular momentum J, the parity π, and the isospin T from resonance capture data is considered. Special emphasis is placed on the capture angular distributions and on a geometric description of these angular distributions.

Recent parity non-conservation (PNC) measurements in nuclei use the compound nucleus as a laboratory for the study of symmetry breaking, with the symmetry breaking matrix elements treated as random variables. We plan to measure parity-violating longitudinal analyzing powers Az in (p,α) scattering on resonances in A∼30 nuclei. Since the resonances are often narrow, the proton beam energy must be carefully controlled. In addition, since the effects are expected to be small (Az

Parity violation has been observed in a number of previously unreported neutron resonances in silver. Analysis of these parity violation data requires improved neutron resonance spectroscopy. The neutron total cross section for natural silver was measured for E{sub n}=10{endash}800 eV with the time-of-flight method at the Los Alamos Neutron Scattering Center. The neutron capture reaction was studied with both a natural silver target and a highly enriched sample (98.29{percent}) of {sup 107}Ag. A total of 38 previously unreported resonances were observed. The combination of the two measurements allowed assignment of the newly observed resonances to {sup 107}Ag or to {sup 109}Ag. Resonance parameters were determined for almost all of the neutron resonances observed. {copyright} {ital 1997} {ital The American Physical Society}

Spectra of γ-rays following the neutron capture at isolated resonances of stable Gd nuclei were measured with the DANCE detector. The objectives were to obtain new information on the photon strength of 153,155−159Gd with emphasis on the role of the M1 scissors-mode vibration. An analysis of the data obtained clearly indicates that the scissors mode is built not only on the ground state, but also on all excited levels of the nuclei studied. Our approach allows estimating the summed scissors-mode strength even for odd product nuclei for which conventional nuclear resonance fluorescence measurements yield only limited information. Our data indicate that for 157,159Gd the strength is significantly higher compared to 156,158Gd.

Parity nonconservation (PNC) measurements utilizing charged-particle resonance reactions are proposed. PNC observables have been calculated for over 300 resonance pairs (with the same angular momentum and opposite parity) in five {ital s}-{ital d} shell nuclei. Detailed numerical results are presented for the longitudinal analyzing powers in the {sup 31}P({ital p}{searrow},{alpha}{sub 0}) reaction. There is strong dependence on energy, angle, and resonance parameters. A figure of merit that includes both the relative enhancement of the parity violation and the cross section is used to identify the most promising resonances for study. A proposed detector design and experimental procedure are described. These measurements should provide information on the weak spreading width (the effective nucleon-nucleus weak interaction) in light nuclei. {copyright} {ital 1996 The American Physical Society.}

The analysis used to determine the rms parity violating matrix element M from the longitudinal asymmetries measured by the TRIPLE Collaboration is described. The likelihood method is used to analyze the limited number of experimental data points available for each target nuclide. Much spectroscopic information is required to determine M, including resonance parameters (spins, neutron widths, resonance energies) of the s- and p-wave resonances which mix to cause the parity violation, and (for targets with I\ensuremath{\ne}0) p-wave neutron partial decay amplitudes. We have developed statistical techniques to determine M in situations where incomplete spectroscopic information is available. Methods are described that can be applied when different amounts of partial spectroscopic information are available. The use of the methods is illustrated by examples. \textcopyright{} 1996 The American Physical Society.

Measurements have been performed on the helicity dependence of the neutron resonance cross section for many nuclei by our TRIPLE Collaboration. A large number of parity violations are observed. Generic enhancements amplify the signal for symmetry breaking and the stochastic properties of the compound nucleus permit the strength of the symmetry-breaking interaction to be determined without knowledge of the wave functions of individual states. A total of 15 nuclei have been analyzed with this statistical approach. The results are summarized.

Eight crossbred wethers (51 +/- 2 kg BW), surgically fitted with abomasal cannulas, were used to determine the extent and time course of cysteamine (CSH)-induced depletion of somatostatin (SRIF) in abomasal tissue and associated changes in plasma metabolites, insulin, and growth hormone (GH). Cysteamine was administered as a single i.v. bolus (50 mg.kg BW-1 x 10 min-1) on d 0. Abomasal biopsies were obtained on d -7, -3, 0, 1, 3, and 10. On d 0, additional biopsies were taken at 2, 4, and 8 h after CSH administration. Jugular blood samples were collected over 8 h at 15-min intervals on d -2, 0, and 1. Cysteamine administration decreased (P < .05) tissue SRIF on d 0 (2, 4, and 8 h), 1, and 3; maximal depletion (42 to 55% of Pre-treatment; Pre-trt) occurred during the initial 24 h, returning to Pre-trt by d 10. Gel chromatography of pooled -7 d abomasal tissue extracts showed five peaks of SRIF immunoreactivity; the predominate peak eluted in the same position as synthetic SRIF-14. Plasma glucose, lactate, and NEFA concentrations increased (P = .001) after CSH administration and reached peak at 2 h after treatment and declined to Pre-trt concentrations by 24 h. Insulin increased (P = .001) to a maximum at h 4 and returned to Pre-trt by 24 h. Mean and baseline GH were higher (P < .07) on day of CSH administration, and pulse amplitude was lower (P < .10) on d 0 and 1. These data show that CSH rapidly reduces SRIF in abomasal tissue in a reversible manner; suggesting that CSH-treated sheep may provide a SRIF-deficient model for studying the physiological role of SRIF in ruminants.

The parity and time‐reversal symmetries can be studied in neutron‐nucleus interactions. Parity non‐conserving asymmetries have been observed for many p‐wave resonances in a compound nucleus and measurements were performed on several nuclei in the mass region of A∼100 and A∼230. The statistical model of the compound nucleus provides a theoretical basis for extracting mean‐squared matrix elements from the experimental asymmetry data, and for interpreting the mean‐squared matrix elements. The constraints on the weak meson‐exchange couplings calculated from the compound‐nucleus asymmetry data agree qualitatively with the results from few‐body and light‐nuclei experiments. The tests of time‐reversal invariance in various experiments using thermal, epithermal, and MeV neutrons are being developed.

The potential role of charged particle resonance reactions in the study of parity nonconservation (PNC) in the nucleus is examined in light of recent statistical interpretations of PNC measurements in neutron resonances. Several PNC observables have been calculated using experimental resonance parameters for five s-d shell nuclei. Longitudinal analyzing powers in (p\ensuremath{\rightarrow},${\mathrm{\ensuremath{\alpha}}}_{0}$) reactions show strong dependence on energy, angle, and resonance parameters. Measurements of analyzing powers at the ${10}^{\mathrm{\ensuremath{-}}4}$ level should provide new information on parity vaiolation in the nucleon-nucleus interaction.

We describe how the scanning transmission x-ray microscope at Brookhaven National Laboratory can be used to investigate the bulk characteristics of polymeric materials with chemical sensitivity at a spatial resolution of about 50 nm. We present examples ranging from unoriented multiphase polymers to highly oriented Kevlar fibers. In the case of oriented samples, a dichroism technique is used to determine the orientation of specific chemical bonds. Extension of the technique to investigate surfaces of thick samples is discussed.

Direct comparisons between the surface and bulk of diverse materials can be made by simultaneous electron yield (5 nm depth sensitivity) and fluorescence yield (200 nm) ultra soft x-ray absorption spectroscopy measurements utilizing a rapid sample interchange apparatus. For example the orientations of functional groups have been characterized at and near the surface of a series of model polymeric materials highlighting the chemical and molecular sensitivity of ultra soft x-ray absorption spectroscopy. In addition we discuss a bulk sensitive use of fluorescence yield to non destructively study a buried metal polymer interface. A second bulk sensitive example is the use of fluorescence yield oxygen K near edge x-ray spectroscopy as a method to determine the hole state density of high Tc materials.

In this paper we illustrate the use of Ultra Soft X-ray Absorption Spectroscopy (USXAS) for the characterization of polymeric materials by highlighting three novel applications of the technique. The surface sensitivity of electron yield (3 nm) and the bulk information available from fluorescence yield USXAS (200 nm) provide unique information on the chemistry of polymer surfaces and interfaces. USXAS is sensitive to both concentration and orientation of functional groups in polymers. The systems highlighted here include the characterization of flame treated model acrylic automotive coatings, ultra-low surface energy crosslinked fluorocarbon films, and spin cast polystyrene films. The chemical and surface sensitivity of the technique are emphasized by the ability of USXAS to detect an increase in the trigonally coordinated carbon at the surface after treatment with a reducing flame. The sensitivity to functional group orientation at the surface is demonstrated by the characterization of the crosslinked flurocarbon polymer films. The results show that the pendant fluoroalkyl moieties of these polymers are strongly oriented perpendicular to the film surface. Spin coated polystyrene films were characterized as a functionv of molecular weight, film thickness and casting solvent. The pendant phenyl groups were found to be preferentially oriented towards the normal to the surface plane, independent of casting solvent, molecular weight, and film thickness

Previous research at this station adapted a maximal dose response (MDR) method of evaluating vitamin A status and utilization for use in beef cattle. This method was used in two experiments. In this first experiment, forty-eight crossbred steers (average weight, 284 kg) were fed diets supplemented with salt, monensin or both, and injected with vitamin E, zinc or selenium. Steers receiving monensin had higher (38.5 micrograms/dl, monensin; 31.0 micrograms/dl, controls) initial plasma concentrations of vitamin A (P = .14). However, monensin did not affect post-dosing (MDR) vitamin A concentrations. None of the other dietary treatments or injections affected either pre- or post-dosing concentrations of vitamin A in the plasma. In a second experiment 23 lactating multiparous beef cows (average weight, 500 kg) grazing either fungal endophyte-infected or endophyte-free tall fescue were used to assess possible influences of infected fescue upon vitamin A metabolism. Fungal endophyte infection did not affect either pre- (44.9 micrograms/dl, end-noninf.; 47.7 micrograms/dl, end-inf.) or post-dosing (57.2 micrograms/dl, end-noninf.; 59.3 micrograms/dl, end-inf.) vitamin A concentrations.