Search

The effect of the isovector imaginary optical potential has been studied experimentally by using the particle-evaporation technique for the $^{11}\mathrm{B}+^{48}\mathrm{Ca}$ reaction with a 21.8 MeV $^{11}\mathrm{B}$ beam. Spectra of neutron, proton, and $\ensuremath{\alpha}$ particles emitted from the neutron-rich compound nucleus $^{59}\mathrm{Mn}$ have been measured and analyzed with traditional optical model potentials with their original parametrizations as well as with adjusted isovector imaginary components. It is shown that the isovector component of the imaginary potential is indispensable in the reproduction of proton and $\ensuremath{\alpha}$-particle yields from this reaction and even needs to be enhanced compared with the suggestions of the original model parametrizations. This can lead to important consequences for astrophysical reaction-rate calculations.

Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from $\beta$-stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus $^{60}$Zn. We have determined the nuclear level density of $^{60}$Zn using neutron evaporation spectra from $^{58}$Ni($^3$He, n) measured at the Edwards Accelerator Laboratory. We compare our results to a number of theoretical predictions, including phenomenological, microscopic, and shell model based approaches. Notably, we find the $^{60}$Zn level density is somewhat lower than expected for excitation energies populated in the $^{59}$Cu(p,$\gamma$)$^{60}$Zn reaction under rp-process conditions. This includes a level density plateau from roughly 5-6 MeV excitation energy, which is counter to the usual expectation of exponential growth and all theoretical predictions that we explore. A determination of the spin-distribution at the relevant excitation energies in $^{60}$Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate for the $^{59}$Cu(p,$\gamma$)$^{60}$Zn reaction rate at X-ray burst temperatures., Comment: 10 pages, 8 figures

Background: Spectroscopic factors, overlaps, and isospin symmetry are often used in conjunction with single-particle wave functions for the phenomenological analysis of nuclear structure and reactions. Many differing prescriptions for connecting these quantities to physically relevant asymptotic normalization constants or widths are available in the literature, but their relationship and degree of validity are not always clear. Purpose: This paper derives relationships among the above quantities of interest using well-defined methodology and starting assumptions. Method: $R$-matrix theory is used as the primary tool to interoperate between the quantities of interest to this work. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated. Results: Relationships among the quantities of interest are derived. Example applications of these methods to mirror levels in nucleon+${}^{12}{\rm C}$, nucleon+${}^{16}{\rm O}$, and nucleon+${}^{26}{\rm Al}$ are presented. A new approach to multi-level mirror symmetry is derived and applied to the first three $2^+$ states of ${}^{18}{\rm O}$ and ${}^{18}{\rm Ne}$. Conclusions: The relationship between the quantities of interest is clarified and certain procedures are recommended. It is found that the asymptotic normalization constant of the second $2^+$ state in ${}^{18}{\rm Ne}$ deduced from the mirror state in ${}^{18}{\rm O}$ is significantly larger than found in previous work. This finding has the effect of increasing the ${}^{17}{\rm F}(p,\gamma){}^{18}{\rm Ne}$ reaction rate in novae., Comment: 27 pages, 10 figures

We evaluated polyvinyl toluene (PVT) scintillators fabricated with different emitting dopants and scintillator optical configurations for fast neutron imaging. A neutron imaging apparatus was constructed to study scintillators under MeV neutron exposure. PVT with 2% Xylyl Flrpic emitter was identified as the brightest. The addition of a black backing to the scintillator, compared with a specular reflector film backing, improved the resolution of the neutron image obtained with the PVT scintillator by about 2 ×. It is concluded that a PVT imaging screen with 2% Xylyl Flrpic, configured with a black backing, provides the best quality fast neutron image of the scintillators tested.

Journal of physics / G 49(1), 010502 (2022). doi:10.1088/1361-6471/ac2827, Published by IOP Publ., Bristol

Understanding the effects of high energy proton radiation is essential in planning for the next generation of X-ray space telescopes. We report on the results of an experiment in which an X-ray hybrid CMOS detector was incrementally irradiated with 8 MeV protons up to a total absorbed dose of approximately 3 krad(Si) (4.5 x 109 protons/cm2). The effect of the damage caused by the high energy protons is then analyzed in the context of several detector characteristics, including read noise, dark current, and energy resolution.

The performance of the maximum likelihood expectation maximization method for unfolding neutron energy spectra using deuterated liquid scintillator is evaluated for future utilization with rare isotope beams. High-resolution neutron energy spectra as well as the detector response matrix were measured at the Edwards Accelerator Laboratory at Ohio University. Maximum-likelihood expectation maximization (MLEM) unfolded neutron spectra are compared with spectra from neutron time-of-flight. The effects of the MLEM stopping criteria and spectrum statistics are also investigated.

The Versatile Array of Neutron Detectors at Low Energy (VANDLE) is a new, highly efficient plastic-scintillator array constructed for decay and transfer reaction experimental setups that require neutron detection. The versatile and modular design allows for customizable experimental setups including beta-delayed neutron spectroscopy and (d,n) transfer reactions in normal and inverse kinematics. The neutron energy and prompt-photon discrimination is determined through the time of flight technique. Fully digital data acquisition electronics and integrated triggering logic enables some VANDLE modules to achieve an intrinsic efficiency over 70% for 300-keV neutrons, measured through two different methods. A custom Geant4 simulation models aspects of the detector array and the experimental setups to determine efficiency and detector response. A low detection threshold, due to the trigger logic and digitizing data acquisition, allowed us to measure the light-yield response curve from elastically scattered carbon nuclei inside the scintillating plastic from incident neutrons with kinetic energies below 2 MeV.

Fast neutron imaging is a powerful tool to investigate elemental/isotopic compositions of objects, supporting both scientific studies as well as cargo scanning. Current neutron imaging systems are faced with challenges associated with timing, detection efficiency, and/or spatial resolution. Here, we report on the use of a semiconducting lithium indium diselenide neutron sensor coupled to a Timepix ASIC for fast neutron imaging. Using a 15 cm thick copper knife edge, the spatial resolution of the neutron imager was found to be 1.55 mm for 9 MeV neutrons. The experimental detection efficiency at 9 MeV was in general agreement with calculations.

We report on the results of an experiment to determine the effects of radiation damage caused by high-energy protons on an x-ray hybrid CMOS detector. This detector was utilized in a previous proton radiation experiment, which delivered a total dose to a selected region of ∼3 krad (Si). With updated hardware and experimental procedures, we further irradiated the detector with 7-MeV protons, delivering an additional 1.5 krad (Si) (2.78 × 109 protons / cm2 10 MeV equivalent) with increased uniformity to an overlapping region. The effects of this radiation on several important detector characteristics were analyzed after delivering doses of 0.5 and 1.0 krad. After 16 h of annealing at room temperature, detector performance was found to be unchanged in both cases.

Cross sections of one- and two-neutron removal reactions of 24O, leading to the 23O(½+) ground state and to bound final states of 22O, have been measured at the National Superconducting Cyclotron Laboratory. The experiment was conducted using the S800 spectrograph and a 24O beam energy of 92.3 MeV/u. The measured 23O ground state and 22O inclusive cross section values, of 74(11) mb and 146(33) mb, respectively, are in good agreement with calculations using eikonal reaction dynamics and shell-model nuclear structure overlaps. The widths at half maximum of the associated parallel momentum distributions of these cross sections, deduced from Gaussian fits, are 115(13) MeV/c for 23O and 309(36) MeV/c for 22O in the projectile rest frame. The data and calculations strongly support the shell-model description of 24O as a spherical, doubly-magic structure.

Full calculations of six-nucleon reactions with a three-body final state have been elusive and a long-standing issue. We present neutron spectra from the T(t,2n)α (TT) reaction measured in inertial confinement fusion experiments at the OMEGA laser facility at ion temperatures from 4 to 18 keV, corresponding to center-of-mass energies (E_{c.m.}) from 16 to 50 keV. A clear difference in the shape of the TT-neutron spectrum is observed between the two E_{c.m.}, with the ^{5}He ground state resonant peak at 8.6 MeV being significantly stronger at the higher than at the lower energy. The data provide the first conclusive evidence of a variant TT-neutron spectrum in this E_{c.m.} range. In contrast to earlier available data, this indicates a reaction mechanism that must involve resonances and/or higher angular momenta than L=0. This finding provides an important experimental constraint on theoretical efforts that explore this and complementary six-nucleon systems, such as the solar ^{3}He(^{3}He,2p)α reaction.

The 12C(n, 2n)11C cross section was measured from just below threshold to 26.5 MeV using the Pelletron accelerator at Ohio University. Monoenergetic neutrons, produced via the 3H(d,n)4He reaction, were allowed to strike targets of polyethylene and graphite. Activation of both targets was measured by counting positron annihilations resulting from the β+ decay of 11C. Annihilation gamma rays were detected, both in coincidence and singly, using back-to-back NaI detectors. The incident neutron flux was determined indirectly via 1H(n,p) protons elastically scattered from the polyethylene target. Previous measurements fall into upper and lower bands; the results of the present measurement are consistent with the upper band.

We report on the initial results of an experiment to determine the effects of proton radiation damage on an X-ray hybrid CMOS detector (HCD). The device was irradiated at the Edwards Accelerator Lab at Ohio University with 8 MeV protons, up to a total absorbed dose of 3 krad(Si) (4.5 $\times$ 10$^9$ protons/cm$^2$). The effects of this radiation on read noise, dark current, gain, and energy resolution are then analyzed. This exposure is the first of several which will be used for characterizing detector performance at absorbed dose levels that are relevant for imaging devices operating in a deep-space environment.

The Edwards Accelerator Laboratory at Ohio University is the hub for a vibrant program in low energy nuclear physics. Research performed with the lab's 4.5MV tandem accelerator spans a variety of topics, including nuclear astrophysics, nuclear structure, nuclear energy, homeland security, and materials science. The Edwards Lab hosts a variety of capabilities, including unique features such as the beam swinger with neutron time-of-flight tunnel and the integrated condensed matter physics facility, enabling experiments to be performed with low-to-medium mass stable ion beams using charged-particle, gamma, and neutron spectroscopy. This article provides an overview of the current and near-future research program in low energy nuclear physics at Ohio University, including a brief discussion of the present and planned technical capabilities., To appear in Physics Procedia issue on the The 24th International Conference on the Application of Accelerators in Research and Industry - CAARI 2016. This article corresponds to abstract #125

The 3 H(d , γ )5 He reaction has been measured using a 500-keV pulsed deuteron beam incident on a stopping titanium tritide target at Ohio University’s Edwards Accelerator Laboratory. The time-of-flight (TOF) technique has been used to distinguish the γ -rays from neutrons detected in the bismuth germinate (BGO) γ -ray detector. A stilbene scintillator and an NE-213 scintillator have been used to detect the neutrons from the 3 H(d , n )4 He reaction using both the pulse-shape discrimination and TOF techniques. A newly-designed target holder with a silicon surface barrier detector to simultaneously measure α -particles to normalize the neutron count was incorporated for subsequent measurements. The γ -rays have been measured at laboratory angles of 0°, 45°, 90°, and 135°. Information about the γ -ray energy distribution for the unbound ground state and first excited state of 5 He can be obtained experimentally by comparing the BGO data to Monte Carlo simulations. The 3 H(d , γ )/3 H(d , n ) branching ratio has also been determined.

Here, the proton spectrum from the 57Fe(α,p) reaction has been measured and analyzed with the Hauser-Feshbach model of nuclear reactions. Different input level density models have been tested. It was found that the best description is achieved with either Fermi-gas or constant temperature model functions obtained by fitting them to neutron resonance spacing and to discrete levels and using the spin cutoff parameter with much weaker excitation energy dependence than it is predicted by the Fermi-gas model.

Some applications of few-nucleon physics to Big Bang Nucleosynthesis, solar neutrinos, and neutron stars have been reviewed. The future in all of these areas is very exciting as improved measurements of the light element abundances, solar neutrino fluxes, and neutron star properties are planned. On the nuclear physics side new theoretical calculations and measurements will improve our understanding of the underlying physics. Together these effors will lead to a greater understanding of both our Universe and few-nucleon dynamics.

Double differential cross sections of neutrons from $d\phantom{\rule{0.16em}{0ex}}+{\phantom{\rule{0.16em}{0ex}}}^{63,65}$Cu reactions have been measured at deuteron energies of 6 and 7.5 MeV. The cross sections measured at backward angles have been compared to theoretical calculations in the framework of the statistical Hauser-Feshbach model. Three different level density models were tested: the Fermi-gas model, the Gilbert-Cameron model, and the microscopic approach through the Hartree-Fock-Bogoliubov method (HFBM). The calculations using the Gilbert-Cameron model are in best agreement with our experimental data. Level densities of the residual nuclei ${}^{64}$Zn and ${}^{66}$Zn have been obtained from statistical neutron evaporation spectra. The angle-integrated cross sections have been analyzed with the exciton model of nuclear reaction.

A compact polarimeter has been constructed and calibrated to measure the polarization of 13–16 MeV protons, such as those emitted from the 3He(d,p)4He reaction near the Ed=430 keV resonance. The polarimeter uses p-4He elastic scattering as an analyzer. It consists of a 4He gas cell pressurized to 2.76 MPa and a left–right pair of CsI detectors collimated at 65° to maximize the figure of merit for the device. The effective analyzing power and efficiency of the polarimeter have been measured as a function of energy using a collimated polarized proton beam. These measured values are in good agreement with a Monte Carlo computer simulation that forms the basis for the calibration curve for the device. Preliminary results from the 3He(d,p)4He reaction with polarized deuterons confirm that the proton polarimeter can be used to determine polarization transfer coefficients near the low-energy resonance.

A proton polarimeter has been designed and calibrated over the energy range of 250 ⩽ Ep ⩽ 460 keV. The 6(Li(p→, 3He)4 reaction was chosen due to its relatively large analyzing power and cross section in this energy range. The absolute calibration of the polarimeter has been established by accelerating the beam to 6 MeV and determining the polarization independently using 4He(p→, p) scattering. In addition, angular distributions of the analyzing power were measured for Ep = 255, 321 and 456 keV. The existing data on the analyzing power of the 6Li(p→, 3He)4He reaction below Ep = 1 MeV is summarized.

Angular distributions of the analyzing powers iT{sub 11}, T{sub 20}, and T{sub 22} for {sup 1}H({rvec d},{gamma}){sup 3}He at 40{le}E{sub c.m.}{le}110 keV and the angular distribution of the analyzing power A{sub y} for {sup 2}H({rvec p},{gamma}){sup 3}He at 70{le}E{sub c.m.}{le}210 keV have been measured for the first time. In addition, absolute differential cross sections for proton-deuteron capture have been determined for E{sub c.m.}= 75, 108, 133, and 173 keV. Thick ice or heavy ice targets and two large-volume, high-purity Ge {gamma}-ray detectors were used. Results are in general agreement with an exact three-body calculation utilizing a realistic nucleon-nucleon potential. The vector-polarization observables are found to be especially sensitive to meson-exchange-current effects. The extracted S(0) value for proton-deuteron capture is {approximately}25{percent} lower than that presently used in astrophysical calculations. An expression for the thermonuclear reaction rate below 10 GK is given. {copyright} {ital 1997} {ital The American Physical Society}

We have studied the energy dependence of the reaction mechanism of the T(t,2n)4 He reaction at stellar energies and of its charge symmetric analog reaction 3 He(3 He,2p)4 He at energies up 10 MeV. We find that the reaction mechanism changes dramatically over this energy range in part due to the interference of the two identical fermions in the three-body final state.

The D+D reactions are well known and widely used for a variety of purposes, mainly because of the use of the D(d, n)3He reaction as a mono-energetic neutron source. The least studied of the D+D reactions is the D(d, n)pD reaction known as the deuteron breakup reaction, which produces a continuum of neutrons at energies below the monoenergetic peak. The neutron energy distribution as a function of angle for the cross section, d2σdΩdE${{{d^2}\sigma } \over {d\Omega dE}}$, of the D(d,n)pD reaction has been measured using a 6.94-MeV pulsed deuteron beam incident upon a D2 gas target. The time-of-flight technique was used to determine the energy of the neutrons detected in an array of two lithium glass scintillators and one NE-213 scintillator. The breakup cross section was determined as low as 225-keV neutron energy in the lithium glass detectors.

A good understanding of the level structure of ${}^{19}\mathrm{Ne}$ around the proton threshold is critical to estimating the destruction of long-lived ${}^{18}\mathrm{F}$ in novae. Here we report the properties of levels in ${}^{19}\mathrm{Ne}$ in the excitation energy range of 6.9 $\ensuremath{\leqslant}$ ${E}_{x}$ $\ensuremath{\leqslant}$ 8.4 MeV studied via the proton-transfer ${}^{18}\mathrm{F}(d,n){\mathrm{Ne}}^{*}$ reaction at the Holifield Radioactive Ion Beam Facility. The populated ${}^{19}\mathrm{Ne}$ levels decay by breakup into $p+{}^{18}\mathrm{F}$ and $\ensuremath{\alpha}+{}^{15}\mathrm{O}$ particles. The results presented in this manuscript are those of levels that are simultaneously observed from the breakup into both channels. An $s$-wave state is observed at 1468 keV above the proton threshold, which is a potential candidate for a predicted broad ${J}^{\ensuremath{\pi}}$ $=$ 1/2${}^{+}$ state. The proton and $\ensuremath{\alpha}$ partial widths are deduced to be ${\ensuremath{\Gamma}}_{p}$ $=$ 228 $\ifmmode\pm\else\textpm\fi{}$ 50 keV and ${\ensuremath{\Gamma}}_{\ensuremath{\alpha}}$ $=$ 130 $\ifmmode\pm\else\textpm\fi{}$ 30 keV for this state.

Spectra of outgoing neutrons and protons from the $^{6}\mathrm{Li}$ $+$ $^{55}\mathrm{Mn}$ reaction and protons from the $\ensuremath{\alpha}$ $+$ $^{57}\mathrm{Fe}$ reaction have been measured with beams of 15-MeV $^{6}\mathrm{Li}$ ions and 30-MeV $\ensuremath{\alpha}$ particles. These reactions proceed through the same $^{61}\mathrm{Ni}$ nucleus at the same excitation energy, thus allowing the difference in reaction mechanisms to be studied. It is shown that spectra from the first reaction measured at backward angles are due to emission from a traditional compound nucleus reaction, in which the intermediate nucleus has reached statistical equilibrium; the spectra from the second reaction contain a significant fraction of pre-equilibrium emission at all angles. Level density parameters of the residual nucleus $^{60}\mathrm{Co}$ have been obtained from the first reaction. Both emission spectra and angular distributions have been measured for the second reaction. It was found that the pre-equilibrium component exhibits a forward-peaked angular distribution, as expected, but with a steeper slope than predicted and with an unusual slight rise at angles above ${120}^{\ifmmode^\circ\else\textdegree\fi{}}$. The backward-angle rise is explained qualitatively by the dominance of the multistep compound mechanism at backward angles.

This report presents a summary of research projects in the area of low energy nuclear reactions and structure, carried out between 1 January 2003 and 31 December 2005 and supported by U.S. DOE grant number DE-FG03-03NA00074. Cross sections measured with high resolution have been subjected to an Ericson theory analysis to infer information about the nuclear level density. Other measurements were made of the spectral shape of particles produced in evaporation processes; these also yield level density information. A major project was the development of a new Hauser-Feshbach code for analyzing such spectra. Other measurements produced information on the spectra of gamma rays emitted in reactions on heavy nuclei and gave a means of refining our understanding of gamma-ray strength functions. Finally,reactions on light nuclei were studied and subjected to an R-matrix analysis. Cross sections fora network of nuclear reactions proceedingthrough a given compound nucleus shouldgreatly constrain the family of allowed parameters. Modifications to the formalism andcomputer code are also discussed.

We review some aspects of R‐matrix theory and its application to the semi‐empirical analysis of nuclear reactions. Important applications for nuclear astrophysics and recent results for the 12C(α,γ)16O reaction are emphasized.

We discuss nuclear reactions which could play a role in Big Bang Nucleosynthesis (BBN). Most of these reactions involve lithium and beryllium isotopes and the rates for some of these have not previously been included in BBN calculations. Few of these reactions are well studied in the laboratory. We also discuss novel effects in these reactions, including thermal population of nuclear target states, resonant enhancement, and non-thermal neutron reaction products. We perform sensitivity studies which show that even given considerable nuclear physics uncertainties, most of these nuclear reactions have minimal leverage on the standard BBN abundance yields of 6Li and 7Li. Although a few have the potential to alter the yields significantly, we argue that this is unlikely., Comment: 13 pages, 6 figures

The reactions of {sup 6}Li on {sup 58}Fe and {sup 7}Li on {sup 57}Fe have been studied at 15 MeV beam energy. These two reactions produce the same compound nucleus, {sup 64}Cu. The charged particle spectra were measured at backward angles. The data obtained have been compared with Hauser-Feshbach model calculations. The level density parameters of {sup 63}Ni and {sup 60}Co have been obtained from the particle evaporation spectra. We also find contributions from the break up of the lithium projectiles to the low energy region of the {alpha} spectra.

Neutron and proton evaporation spectra from the {sup 6}Li+{sup 55}Mn and d+{sup 59}Co reactions have been analyzed with the Hauser-Feshbach approach using different input models for nuclear level densities of {sup 60}Ni and {sup 60}Co nuclei. It has been found that models with a Fermi-gas like temperature dependence fail to reproduce particle spectra from both reactions simultaneously. We obtained the surprising result that the only way to describe our data is to assume the independence of the nuclear temperature on the excitation energy up to about the 20 MeV energy range.

The energy spectra of neutrons, protons, and \ensuremath{\alpha}-particles have been measured from the $d+$$^{59}\mathrm{Co}$ and $^{3}\mathrm{He}+^{58}\mathrm{Fe}$ reactions leading to the same compound nucleus, $^{61}\mathrm{Ni}$. The experimental cross sections have been compared to Hauser-Feshbach model calculations using different input level density models. None of them have been found to agree with experiment. It manifests the serious problem with available level density parametrizations especially those based on neutron resonance spacings and density of discrete levels. New level densities and corresponding Fermi-gas parameters have been obtained for reaction product nuclei such as $^{60}\mathrm{Ni}$, $^{60}\mathrm{Co}$, and $^{57}\mathrm{Fe}$.

The multipolarity of the low-energy (< 3 MeV) γ−strength function has been experimentally studied with the 55 Mn(p,2γ) 56 Fe reaction at 1.65 MeV proton beam energy. The spectrum of two-step γ−cascades populating the ground state of 56 Fe has been measured and compared with calculations assuming that E1 or M1 multipolarities dominate in the low-energy region. It was found that experimental data points are reproduced only if the assumption on dominance of the M1 multipolarity is used.

We present new accurate measurements of the differential cross section $\ensuremath{\sigma}(\ensuremath{\theta})$ and the proton analyzing power ${A}_{y}$ for proton-$^{3}\mathrm{He}$ elastic scattering at various energies. A supersonic gas-jet target has been employed to obtain these low-energy cross-section measurements. The $\ensuremath{\sigma}(\ensuremath{\theta})$ distributions have been measured at ${E}_{p}=0.99$, 1.59, 2.24, 3.11, and 4.02 MeV. Full angular distributions of ${A}_{y}$ have been measured at ${E}_{p}=1.60$, 2.25, 3.13, and 4.05 MeV. This set of high-precision data is compared to four-body variational calculations employing realistic nucleon-nucleon ($\mathit{NN}$) and three-nucleon ($3N$) interactions. For the unpolarized cross section, the agreement between the theoretical calculation and data is good when a $3N$ potential is used. The comparison between the calculated and measured proton analyzing powers reveals discrepancies of approximately 50% at the maximum of each distribution. This is analogous to the existing ``${A}_{y}$ puzzle'' known for the past 20 years in nucleon-deuteron elastic scattering.

The $^{55}\mathrm{Mn}$$(d,n)^{56}\mathrm{Fe}$ differential cross section is measured at ${E}_{d}=7$ MeV. The $^{56}\mathrm{Fe}$ level density obtained from neutron evaporation spectra is compared to the level density extracted from the $^{57}\mathrm{Fe}$$(^{3}\mathrm{He}$, $\ensuremath{\alpha}\ensuremath{\gamma})^{56}\mathrm{Fe}$ reaction by the Oslo-type technique. Good agreement is found between the level densities determined by the two methods. With the level density function obtained from the neutron evaporation spectra, the $^{56}\mathrm{Fe}$ \ensuremath{\gamma}-strength function is also determined from the first-generation \ensuremath{\gamma} matrix of the Oslo experiment. The good agreement between the past and present results for the \ensuremath{\gamma}-strength function supports the validity of both methods and is consistent with the low-energy enhancement of the \ensuremath{\gamma} strength below $~4$ MeV that was first discovered by the Oslo method in iron and molybdenum isotopes.

The 19F nucleus has been studied extensively. However, there have been no comprehensive experimental studies of 18F+n single-particle components in 19F, and no measure of neutron vacancies in the 18F ground state, as such experiments require a (radioactive) 18F target or beam. We have used the 2H(18F,p)19F reaction to selectively populate states in 19F that are of 18F+n character. The 108.5-MeV radioactive 18F+9 beam was provided by the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Proton-recoil coincidence data were taken for both -decaying and particle-stable final states. Angular distributions and spectroscopic factors were measured for nine proton groups, corresponding to 13 states in 19F. The results are compared to shell model calculations.

The degree to which the (p,gamma) and (p,alpha) reactions destroy 18F at temperatures 1-4x10^8 K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide 18F, a target of gamma-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the 18F+p threshold (E_x=6.411 MeV in 19Ne). To gain further information about these resonances, we have used a radioactive 18F beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in 19F via the inverse d(18F,p)19F neutron transfer reaction. Neutron spectroscopic factors were measured for states in 19F in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in 19Ne were calculated using a Woods-Saxon potential. The results imply significantly lower 18F(p,gamma)19Ne and 18F(p,alpha)15O reaction rates than reported previously, thereby increasing the prospect of observing the 511-keV annihilation radiation associated with the decay of 18F in the ashes ejected from novae.

Nuclear physics has a long and productive history of application to astrophysics which continues today. Advances in the accuracy and breadth of astrophysical data and theory drive the need for better experimental and theoretical understanding of the underlying nuclear physics. This paper will review some of the scenarios where nuclear physics plays an important role, including Big Bang Nucleosynthesis, neutrino production by our sun, nucleosynthesis in novae, the creation of elements heavier than iron, and neutron stars. Big-bang nucleosynthesis is concerned with the formation of elements with A, To be published in the Proceedings of 19th Lake Louise Winter Institute (15-21 February 2004). 9 pages, 3 figures

Knowledge of the gamma-ray branching ratios of the 7.12-MeV state of 16O is important for the extrapolation of the 12C(a,g)16O cross section to astrophysical energies. Ground state transitions provide most of the 12C(a,g)16O total cross section while cascade transitions have contributions of the order of 10-20%. Determining the 7.12-MeV branching ratio will result in a better extrapolation of the cascade and E2 ground state cross section to low energies. We report here on measurements on the branching ratio of the 7.12-MeV level in 16O., 4 pages, 5 figures. Contribution to the Eigth International Symposium on Nuclei in the Cosmos

Angular distributions of sigma(theta), A_y, iT_11, T_20, T_21, and T_22 have been measured for d-p scattering at E_c.m.=667 keV. This set of high-precision data is compared to variational calculations with the nucleon-nucleon potential alone and also to calculations including a three-nucleon (3N) potential. Agreement with cross-section and tensor analyzing power data is excellent when a 3N potential is used. However, a comparison between the vector analyzing powers reveals differences of approximately 40% in the maxima of the angular distributions which is larger than reported at higher energies for both p-d and n-d scattering. Single-energy phase-shift analyses were performed on this data set and a similar data set at E_c.m.=431.3 keV. The role of the different phase-shift parameters in fitting these data is discussed., Comment: 18 pages, 6 figures

We present measurements of differential cross sections and the analyzing powers A_y, iT11, T20, T21, and T22 at E_c.m.=431.3 keV. In addition, an excitation function of iT11(theta_c.m.=87.8 degrees) for 431.3, 13 pages, 11 figures

Tensor analyzing powers for {sup 2}H(d(vector sign),d){sup 2}H elastic scattering were measured at deuteron energies of 3.0, 4.75, and 6.0 MeV. The measured values are below 0.02 and increase with increasing energy. The data were compared to the results of an R-matrix parametrization and microscopic four-body calculations. The calculations indicate that the nucleon-nucleon p waves have a strong effect on the observables. (c) 2000 The American Physical Society.

A new measurement of the p-d differential cross section at Ep= 1 MeV has been performed. These new data and older data sets at energies below the deuteron breakup are compared to calculations using the two-nucleon Argonne v18 and the three-nucleon Urbana IX potentials. A quantitative estimate of the capability of these interactions to describe the data is given in terms of a chi^2 analysis. The chi^2 per datum drastically improves when the three-nucleon interaction is included in the Hamiltonian., Comment: 13 pages, 5 figures, to be published in Phys. Rev. C

Scientists at the National Ignition Facility plan to generate fusion energy and study fusion in nuclear weapons. But the starlike conditions that NIF creates will also enable them to study astrophysically important nuclear reactions.

We present measurements of the analyzing powers Ay and iT11 for proton-deuteron scattering at Ecm=432 keV. Calculations using a realistic nucleon-nucleon potential (Argonne V18) are found to underpredict both analyzing powers by 40. The inclusion of the Urbana three-nucleon interaction does not significantly modify the calculated analyzing powers. Due to its short range, it is difficult for this three-nucleon interaction to affect Ay and iT11 at this low energy. The origin of the discrepancy remains an open question., 12 pages, Revtex, one figure, to be published in Phys. Lett. B

The three-nucleon system is studied at energies a few hundred keV above the N-d threshold. Measurements of the tensor analyzing powers $T_{20}$ and $T_{21}$ for p-d elastic scattering at $E_{c.m.}=432$ keV are presented together with the corresponding theoretical predictions. The calculations are extended to very low energies since they are useful for extracting the p-d scattering lengths from the experimental data. The interaction considered here is the Argonne V18 potential plus the Urbana three-nucleon potential. The calculation of the asymptotic D- to S-state ratio for $^3$H and $^3$He, for which recent experimental results are available, is also presented., Comment: Latex, 11 pages, 2 figures, to be published in Phy.Lett.B

A leading order determination of the gluon density in the proton has been performed in the fractional momentum range $1.9 \cdot 10^{-3} < x_{g/p} < 0.18$ by measuring multi-jet events from boson-gluon fusion in deep-inelastic scattering with the H1 detector at the electron-proton collider HERA. This direct determination of the gluon density was performed in a kinematic region previously not accessible. The data show a considerable increase of the gluon density with decreasing fractional momenta of the gluons., 19 pages, latex, 5 figures appended as uuencoded file

The cross sections for the charged current processes ${e^{-}p}\rightarrow{\nu_e+hadrons}$ and, for the first time, ${e^{+}p}\rightarrow{\overline{\nu}_e+hadrons}$ are measured at HERA for transverse momenta larger than 25 GeV., Comment: 21 pages, latex, 10 figures appended as uuencoded file

Events with no hadronic energy flow in a large interval of pseudo-rapidity in the proton direction are observed in photon-proton interactions at an average centre of mass energy 〈√sγp〉 of 200 GeV These events are interpreted as photon diffractive dissociation. Evidence for hard scattering in photon diffractive dissociation is demonstrated using inclusive single particle spectra, thrust as a function of transverse energy, and the observation of jet production. The data can be described by a Monte Carlo calculation including hard photon-pomeron scattering.

Photon-proton ($\gamma p$) interactions with~$Q^25$~GeV$^2$ are studied at the high energy electron-proton collider HERA. The transverse energy flow and relative rates of large rapidity gap events are compared in the two event samples. The observed similarity between $\gamma p$ and $\gamma^* p$ interactions can be understood in a picture where the photon develops as a hadronic object. The transverse energy density measured in the central region of the collision, at $\eta^*=0$ in the $\gamma^* p$ centre of mass frame, is compared with data from hadron-hadron interactions as function of the CMS energy of the collision., Comment: 15 pages, latex, 4 figures appended as uuencoded file