Search

We report a high-precision determination of the 1 S 0 neutron–neutron scattering length ( a nn ) using the 2 H( π − , nγ ) n reaction. The value obtained in the present work is −18.50± 0.05 (statistical) ± 0.44 (systematic) ± 0.30 (theoretical) fm, which is consistent with the values from previous measurements. Combining our result with previous measurements reduces the total uncertainty in the world average of a nn to ±0.4 fm, matching the accuracy to which the charge-symmetric parameter a pp is determined.

The current status of the three-nucleon analyzing power puzzle is reviewed. Applying tight constraints on the allowed deviations between calculated predictions and accepted values for relevant nucleon-nucleon observables reveals that energy independent correction factors applied to the 3Pj nucleon-nucleon interactions can not solve the puzzle. Furthermore, using the same constraints, charge-independence breaking in the 3Pj nucleon-nucleon interactions can be ruled out as a possible tool to improve the agreement between three-nucleon calculations and data. The study of the energy dependence of the three-nucleon analyzing power puzzle gives clear evidence that the 3Pj nucleon-nucleon interaction obtained from phase-shift analyses and used in potential models are correct above about 25 MeV, i.e., the 3Pj nucleon-nucleon interactions have to be modified only at lower energies in order to solve the three-nucleon analyzing power puzzle, unless new three-nucleon forces can be found that account for the three-nucleon analyzing power puzzle without destroying the beautiful agreement between rigorous three-nucleon calculations and a large body of accurate three-nucleon data.

A beam of nearly monochromatic γ-rays was produced via intracavity Compton backscattering in the OK-4/Duke storage ring FEL. The OK-4 FEL operated in the near-UV range (345–413 nm) with electron energies of 260–550 MeV. The energy of the produced γ-rays varied from 3 to 16 MeV. In the near future we plan to increase the energy of the γ-rays to 50 MeV by increasing the electron energy and reducing FEL wavelength. Results from direct measurements of the γ-ray flux and energy resolution (using a 3 mm diameter lead collimator) (Litvinenko et al., Phys. Rev. Lett. 78 (1997) 4569) are very close to our theoretical predictions. The energy resolution of the γ-rays was ∼1%. In this paper we present a comparison of our measurements with theoretical predictions and our plans for future improvements. We discuss upgrades of our system to attain an energy resolution down to 0.1% and to increase the flux. A brief description of the experimental program utilizing the OK-4/Duke monochromatic γ-ray source is presented.

The neutron-neutron and neutron-proton 1 S 0 scattering lengths a nn and a np , respectively, were determined simultaneously from the neutron-deuteron breakup reaction. Their comparison with the recommended values obtained from “two-body” reactions gives a measure of the importance of three-nucleon force effects in the three-nucleon continuum. In order to check on the result obtained for a nn from the “two-body” π − - d capture reaction, a new measurement was performed at LANL. Preliminary results of the three experiments are given.

We have performed single-energy phase-shift analyses of proton-deuteron elastic scattering data in the proton energy range from 3.5 to 10 MeV. The resulting values for the 2 S 1 2 and 4 P 1 2 , 4 P 3 2 , and 4 P 5 2 phase shifts are important benchmark values for three-nucleon calculations based on nucleon-nucleon potential models (with and without three-nucleon forces) aimed at describing the triton binding energy and at resolving the nucleon-deuteron A y (θ) and i T 11 (θ) puzzles, respectively.

The ${}^{4}{P}_{J}$ waves in nucleon-deuteron scattering were analyzed using proton-deuteron and neutron-deuteron data at ${E}_{N}$=3 MeV. New sets of nucleon-nucleon ${}^{3}{P}_{j}$ phase shifts were obtained that may lead to a better understanding of the long-standing ${A}_{y}(\ensuremath{\theta})$ puzzle in nucleon-deuteron elastic scattering. However, these sets of ${}^{3}{P}_{j}$ phase shifts are quite different from the ones determined from both global phase-shift analyses of nucleon-nucleon data and nucleon-nucleon potential models.

We have constructed a 0.4 mole solid 3 He target, cryogenically polarized at 12 mK in a field of 7 T. The 0.04 atoms/b target reached a polarization of 38% in 35 h. Such a target may be applied to any experiment which is tolerant of the large ambient magnetic field and which produces target heating of less than a microwatt. High energy neutron and photon scattering experiments meet these requirements. The target's figure of merit for neutron transmission measurement exceeds that of polarized gas targets by greater than 35. At the Triangle Universities Nuclear Laboratory we have used the target to measure the total cross section differences Δσ T and Δσ L for incident polarized neutrons of energies 2–8 MeV. The cross section difference is sensitive to the excited state structure of the n- 3 He system. The results have been compared to a recent R-matrix analysis of R = 4 scattering and reaction data, and provide support for the 4 He level scheme derived from that analysis.

The absolute efficiency of an NE213 liquid scintillator of 12.7 cm diameter and 5.08 cm thickness was measured in the neutron energy range 2.5–16 MeV using the 2 H(d, n) 3 He reaction as a source of monoenergetic neutrons. The efficiencies were measured at the time-of-flight facility of Triangle Universities Nuclear Laboratory (TUNL). The experimental data are compared to calculations from the Monte Carlo code NEFF of Physikalisch-Technische Bundesanstalt, Braunschweig, Germany (PTB).

A nearly monochromatic beam of 100% linearly polarized g rays has been produced via Compton backscattering inside a free electron laser optical cavity. The beam of 12.2 MeV g rays was obtained by backscattering 379.4 nm free-electron laser photons from 500 MeV electrons circulating in a storage ring. A detailed description of the g-ray beam and the outlook for future improvements are presented. [S0031-9007(97)03322-X]

The low-lying dipole strength of the open-shell nucleus ${}^{94}$Mo was studied via the nuclear resonance fluorescence technique up to 8.7 MeV excitation energy at the bremsstrahlung facility at the Superconducting Darmstadt Electron Linear Accelerator (S-DALINAC), and with Compton backscattered photons at the High Intensity $\ensuremath{\gamma}$-ray Source (HI$\ensuremath{\gamma}$S) facility. In total, 83 excited states were identified. Exploiting polarized quasi-monoenergetic photons at HI$\ensuremath{\gamma}$S, parity quantum numbers were assigned to 41 states excited by dipole transitions. The electric dipole-strength distribution was determined up to 8.7 MeV and compared to microscopic calculations within the quasiparticle phonon model. Calculations and experimental data are in good agreement for the fragmentation, as well as for the integrated strength. The average decay pattern of the excited states was investigated exploiting the HI$\ensuremath{\gamma}$S measurements at five energy settings. Mean branching ratios to the ground state and first excited ${2}_{1}^{+}$ state were extracted from the measurements with quasi-monoenergetic photons and compared to $\ensuremath{\gamma}$-cascade simulations within the statistical model. The experimentally deduced mean branching ratios exhibit a resonance-like maximum at 6.4 MeV which cannot be reproduced within the statistical model. This indicates a nonstatistical structure in the energy range between 5.5 and 7.5 MeV.

We have carried out photodisintegration cross-section measurements on 86Kr using monoenergetic photon beams ranging from the neutron separation energy, S(n) = 9.86 MeV, to 13 MeV. We combine our experimental 86Kr(γ,n)85Kr cross section with results from our recent 86Kr(γ,γ') measurement below the neutron separation energy to obtain the complete nuclear dipole response of 86Kr. The new experimental information is used to predict the neutron capture cross section of 85Kr, an important branching point nucleus on the abundance flow path during s-process nucleosynthesis. Our new and more precise 85Kr(n,γ)86Kr cross section allows us to produce more precise predictions of the 86Kr abundance from s-process models. In particular, we find that the models of the s process in asymptotic giant branch stars of mass

The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A = 124, 128, 132 and 134 in nuclear resonance fluorescence experiments using the ELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIgS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides.

The electric dipole strength distribution in 130Te has been investigated using the method of Nuclear Resonance Fluorescence. The experiments were performed at the Darmstadt High Intensity Photon Setup using bremsstrahlung as photon source and at the High Intensity ~γ-Ray Source, where quasi-monochromatic and polarized photon beams are provided. Average decay properties of 130Te below the neutron separation energy are determined. Comparing the experimental data to the predictions of the statistical model indicate, that nuclear structure effects play an important role even at sufficiently high excitation energies. Preliminary results will be presented.

We present data characterizing the performance of the first segmented, N-type Ge detector, isotopically enriched to 85% $^{76}$Ge. This detector, based on the Ortec PT6x2 design and referred to as SEGA (Segmented, Enriched Germanium Assembly), was developed as a possible prototype for neutrinoless double beta-decay measurements by the {\sc Majorana} collaboration. We present some of the general characteristics (including bias potential, efficiency, leakage current, and integral cross-talk) for this detector in its temporary cryostat. We also present an analysis of the resolution of the detector, and demonstrate that for all but two segments there is at least one channel that reaches the {\sc Majorana} resolution goal below 4 keV FWHM at 2039 keV, and all channels are below 4.5 keV FWHM.

Comprehensive and high-accuracy n-3He elastic scattering analyzing power Ay(θ) angular distributions were obtained at five incident neutron energies between 1.60 and 5.54 MeV. The data are compared to rigorous four-nucleon calculations using high-precision nucleon-nucleon potential models; three-nucleon force effects are found to be very small. The agreement between data and calculations is fair at the lower energies and becomes less satisfactory with increasing neutron energy. Comparison to p-3He scattering over the same energy range exhibits unexpectedly large isospin effects.

The dipole strength of the $N=50$ nucleus ${}^{86}$Kr was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.9 and 11.2 MeV delivered by the linear accelerator ELBE as well as using quasimonoenergetic and linearly polarized $\ensuremath{\gamma}$ rays of 10 energies within the range from 4.7 to 9.3 MeV delivered by the HI$\ensuremath{\gamma}$S facility. A high-pressure gas target was used. We identified 39 levels up to an excitation energy of 10.1 MeV. Simulations of $\ensuremath{\gamma}$-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from a $(\ensuremath{\gamma},n)$ experiment at HI$\ensuremath{\gamma}$S. The enhanced $E1$ strength found in the range from 6 to 10 MeV is compared with the ones in the $N$ $=$ 50 isotones ${}^{88}$Sr, ${}^{90}$Zr, and ${}^{92}$Mo and with predictions of calculations within the quasiparticle-phonon model.

We present results from the first phase of the KamLAND-Zen double-beta decay experiment, corresponding to an exposure of 89.5 kg yr of Xe136. We obtain a lower limit for the neutrinoless double-beta decay half-life of T0ν1/2>1.9×1025 yr at 90% C.L. The combined results from KamLAND-Zen and EXO-200 give T0ν1/2>3.4×1025 yr at 90% C.L., which corresponds to a Majorana neutrino mass limit of ⟨mββ⟩

The cross section of the reaction ${}^{136}$Xe(n,2n)${}^{135}$Xe to both the ground state and the 526.6 keV isomeric states of ${}^{135}$Xe was measured between 9.0 and 14.9 MeV. These data are important to guide evaluations and theoretical calculations aimed at estimating the importance of neutron-induced background effects in searches for neutrinoless double-\ensuremath{\beta} decay of ${}^{136}$Xe.

The M1 excitations in the nuclide 90Zr have been studied in a photon-scattering experiment with monoenergetic and linearly polarized beams from 7 to 11 MeV. More than 40 J(π)=1+ states have been identified from observed ground-state transitions, revealing the fine structure of the giant M1 resonance with a centroid energy of 9 MeV and a sum strength of 4.17(56) μ(N)(2). The result for the total M1 strength and its fragmentation are discussed in the framework of the three-phonon quasiparticle-phonon model.

The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor ν¯e flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor ν¯e oscillation analysis. The data set also has improved sensitivity for other ν¯e signals, in particular ν¯e’s produced in β-decays from U238 and Th232 within the Earth’s interior, whose energy spectrum overlaps with that of reactor ν¯e’s. Including constraints on θ13 from accelerator and short-baseline reactor neutrino experiments, a combined three-flavor analysis of solar and KamLAND data gives fit values for the oscillation parameters of tan2θ12=0.436+0.029−0.025, Δm221=7.53+0.18−0.18×10−5 eV2, and sin2θ13=0.023+0.002−0.002. Assuming a chondritic Th/U mass ratio, we obtain 116+28−27 ν¯e events from U238 and Th232, corresponding to a geo ν¯e flux of 3.4+0.8−0.8×106 cm−2 s−1 at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo ν¯e rate.

Background: The most significant source of background in direct dark matter searches are neutrons that scatter elastically from nuclei in the detector's sensitive volume. Experimental data for the elastic scattering cross section of neutrons from argon and neon, which are target materials of interest to the dark matter community, were previously unavailable. Purpose: Measure the differential cross section for elastic scattering of neutrons from argon and neon in the energy range relevant to backgrounds from (alpha,n) reactions in direct dark matter searches. Method: Cross-section data were taken at the Triangle Universities Nuclear Laboratory (TUNL) using the neutron time-of-flight technique. These data were fit using the spherical optical model. Results: The differential cross section for elastic scatting of neutrons from neon at 5.0 and 8.0 MeV and argon at 6.0 MeV was measured. Optical-model parameters for the elastic scattering reactions were determined from the best fit to these data. The total elastic scattering cross section for neon was found to differ by 6% at 5.0 MeV and 13% at 8.0 MeV from global optical-model predictions. Compared to a local optical-model for 40Ar, the elastic scattering cross section was found to differ from the data by 8% at 6.0 MeV. Conclusions: These new data are important for improving Monte-Carlo simulations and background estimates for direct dark matter searches and for benchmarking optical models of neutron elastic scattering from these nuclei.

We review published analyses of the final-state-interaction enhancement observed in proton energy distributions obtained from kinematically incomplete neutron-deuteron breakup experiments. We compare the results derived from these analyses for the neutron-neutron scattering length, ann, with our results based on a rigorous treatment of the three-nucleon Faddeev equations in conjunction with the use of realistic nucleon-nucleon potentials. Our values for ann deviate outside the quoted uncertainties from the ones obtained in the previous analyses where simplified nucleon-nucleon interaction models were employed. In contrast to the previous determinations, the present results for ann are in clear disagreement with the values for ann based on π−-deuteron capture experiments. Unless inconsistencies in the experimental neutron-deuteron breakup data at low energies can be resolved and the neutron-deuteron breakup data at low energies can be resolved and the influence of possible three-nucleon-force effects can be reliably determined, we recommend that one not resort to the kinematically incomplete neutron-deuteron breakup reaction as a tool for determining a quantity as important for nuclear and particle physics as is the neutron-neutron scattering length ann.

Cross-section measurements of a collinear configuration, the space-star and the coplanar-star configurations in nd breakup at E n = 13.0 MeV are reported. The present measurements for the collinear configuration are in good agreement with pd and nd data. Our coplanar-star data are consistent with theoretical predictions and resolve the reported problem with this configuration. The previously observed large discrepancy between theory and nd cross-section data for the space-star configuration is confirmed in the present work.

High-accuracy measurements of ${\mathit{A}}_{\mathit{y}}$(\ensuremath{\theta}) data for elastic scattering for n${+}^{209}$Bi have been performed at 6 and 9 MeV. The data are incorporated into a large database of \ensuremath{\sigma}(\ensuremath{\theta}), ${\mathit{A}}_{\mathit{y}}$(\ensuremath{\theta}), and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{T}}$ for n${+}^{209}$Bi covering the energy range 1.0--80 MeV. A complementary database is constructed for n${+}^{208}$Pb and a dispersive optical-model analysis is performed for both scattering systems while constraining many of the parameters to be identical for both systems. A good representation of both databases is obtained with conventional geometry and spin-orbit parameters. The $^{208}\mathrm{Pb}$ model predicts quite well the measured energies of valence single-particle and single-hole bound states. Occupation probabilities and spectroscopic factors for the same bound states are also calculated. Finally, a fully constrained model is presented in which the only differences between the n${+}^{208}$Pb and the n${+}^{209}$Bi systems are the Fermi energy and the isospin dependence in the real volume potential. \textcopyright{} 1996 The American Physical Society.

The theoretical approaches for studying N-d processes using realistic, semi-phenomenological NN potentials have matured considerably during the last few years. Accurate calculations of scattering observables are now feasible. Recently, high-quality measurements of N-d scattering at energies below the deuteron breakup threshold became available. Therefore, a detailed comparison between theory and experimental data can now be performed. In this paper the various sets of experimental data for the N-d differential cross section, and the vector and tensor analyzing powers are examined in a critical way in the incident nucleon energy range from 1 to 3 MeV. In order to identify possible inadequacies of the interaction models adopted, phase-shift analyses were performed and compared to the theoretical parameters.

Measurements of polarized-neutron--polarized${\mathrm{\ensuremath{-}}}^{3}$He scattering are reported. The target consisted of cryogenically polarized solid $^{3}\mathrm{He}$, with thickness 0.04 atom/b and polarization \ensuremath{\sim}0.4. Polarized neutrons were produced via the $^{3}\mathrm{H}$(p\ensuremath{\rightarrow},n\ensuremath{\rightarrow}${)}^{3}$He or $^{2}\mathrm{H}$(d\ensuremath{\rightarrow},n\ensuremath{\rightarrow}${)}^{3}$He polarization-transfer reactions. The longitudinal and transverse total cross-section differences \ensuremath{\Delta}${\mathrm{\ensuremath{\sigma}}}_{\mathit{L}}$ and \ensuremath{\Delta}${\mathrm{\ensuremath{\sigma}}}_{\mathit{T}}$ were measured for incident neutron energies 2--8 MeV. The results are compared to phase-shift predictions based on four different analyses of n${\mathrm{\ensuremath{-}}}^{3}$He scattering. The best agreement is obtained with a recent R-matrix analysis of A=4 scattering and reaction data, lending strong support to the $^{4}\mathrm{He}$ level scheme obtained in that analysis. Discrepancies with other phase-shift parametrizations of n${\mathrm{\ensuremath{-}}}^{3}$He scattering exist, attributable in most instances to one or two particular partial waves. \textcopyright{} 1996 The American Physical Society.

A review of kinematically incomplete {ital n}-{ital d} breakup data and their comparison to rigorous 3{ital N} calculations using realistic nucleon-nucleon interactions revealed unexplained differences of more than 25{percent} in regions where a large number of different three-nucleon configurations contribute to the cross section. {copyright} {ital 1996 The American Physical Society.}

Data for the neutron-neutron final-state-interaction cross section obtained recently in a kinematically complete neutron-deuteron breakup experiment have been reanalyzed using rigorous solutions of the three-nucleon Faddeev equations with realistic nucleon-nucleon interactions. A discrepancy was found with respect to a recent analysis based on the W-matrix approximation to the Paris potential. We also estimate theoretical uncertainties in extracting the neutron-neutron scattering length resulting from the use of different nucleon-nucleon interactions and the possible action of the two-pion-exchange three-nucleon force. We find that there exists a certain production angle for the interacting neutron-neutron pair where the uncertainties become minimal.

The tensor analyzing power {ital A}{sub {ital yy}} in the symmetric constant relative energy geometry for the {ital dp} breakup reaction has been calculated using solutions of the three-nucleon Faddeev equations based on the Argonne AV14, AV18, Bonn-B, Nijm78, Nijm93, NijmI, NijmII, and Paris potentials, as well as the Bonn-B potential in conjunction with the Tucson-Melbourne three-nucleon interaction. The comparison with recent {ital dp} data at {ital E}{sub {ital d}}=94.5 MeV revealed a clear discrepancy in the region where the data exhibit a pronounced structure which is not present in the theoretical results.

The spin-dependent total cross-section difference {Delta}{sigma}{sub {ital T}} has been measured at energies of 7.43, 9.57, and 11.60 MeV for neutrons, polarized transverse to the beam momentum, transmitted through a transversely polarized proton target. In addition, the energy at which {Delta}{sigma}{sub {ital T}} crosses through zero has been determined in the energy range 3.65--6.25 MeV. The measurements were carried out with a polarized TiH{sub 2} target and polarized neutrons from the {sup 3}H(p,n){sup 3}He and {sup 2}H(d,n){sup 3}He reactions. The cross-section differences {Delta}{sigma}{sub {ital T}} are sensitive to the strength of the {sup 3}{ital S}{sub 1}--{sup 3}{ital D}{sub 1} mixing parameter {epsilon}{sub 1}. Phase-shift analyses are used to determine {epsilon}{sub 1} values from the data. The values are in good in agreement with {ital NN} potential models and do not support the low {epsilon}{sub 1} values found in previous studies around 15--20 MeV.

Published n${\mathrm{\ensuremath{-}}}^{209}$Bi elastic differential cross-section, analyzing power, and total cross-section data in the energy range from 1.5 to 14 MeV were analyzed via a phase-shift analysis in order to find out whether these data show similar, unexplained resonance structures as observed recently for n${\mathrm{\ensuremath{-}}}^{208}$Pb scattering. Although the n${\mathrm{\ensuremath{-}}}^{209}$Bi and n${\mathrm{\ensuremath{-}}}^{208}$Pb data are very similar, some of the phase shifts are quite different for the two systems. Only one resonancelike structure was observed for n${\mathrm{\ensuremath{-}}}^{209}$Bi scattering in the excitation energy range from 9 to 18 MeV compared to eleven in the n${\mathrm{\ensuremath{-}}}^{208}$Pb system, implying that n${\mathrm{\ensuremath{-}}}^{209}$Bi data are probably more suitable than the classical n${\mathrm{\ensuremath{-}}}^{208}$Pb system for detailed mean-field analyses approached through dispersion-relation optical models.

The low-lying electromagnetic dipole strength of the odd-proton nuclide 205Tl has been investigated up to the neutron separation energy exploiting the method of nuclear resonance fluorescence. In total, 61 levels of 205Tl have been identified. The measured strength distribution of 205Tl is discussed and compared to those of even–even and even–odd mass nuclei in the same mass region as well as to calculations that have been performed within the quasi-particle phonon model.

Results of our recent kinematically complete cross-section measurements of the space-star and coplanar-star configurations in n-d breakup at 13.0 MeV are reported. The experimental setup and details of the analysis are described. The new data for the space-star configuration are in good agreement with previous n-d data but differ significantly from both “exact” n-d calculations and p-d data. In constrast, the new coplanar-star data are in fair agreement with the calculations but are in gross disagreement with previous n-d data. The implications of these data for three-nucleon forces are discussed.

Low-lying electric and magnetic dipole excitations (E1 and M1) below the neutron separation threshold, particularly the Pygmy Dipole Resonance (PDR), have drawn considerable attention in the last years. So far, mostly moderately heavy nuclei in the mass regions around A = 90 and A = 140 were examined with respect to the PDR. In the present work, the systematics of the PDR have been extended by measuring excitation strengths and parity quantum numbers of J = 1 states in lighter nuclei near A = 50 in order to gather information on the onset of the PDR. The nuclei 50,52,54Cr and 48,50Ti were examined via bremsstrahlung produced at the DArmstadt Superconducting electron Linear Accelerator (S-DALINAC) with photon energies up to 9.7 MeV with the method of nuclear resonance fluorescence. Numerous excited states were observed, many of which for the first time. The parity quantum numbers of these states have been determined at the High Intensity Gamma-ray Source (HIγS) of the Triangle Universities Nuclear Laboratory in Durham, NC, USA. Informations to the methods and the experimental setups will be provided and the results on 54Cr achieved will be discussed with respect to the onset of the PDR.

We describe the construction and operation of a solid 3 He polarized nuclear target which we have used for measurements of the spin dependence of the n- 3 He interaction at MeV energies. The target, which contains 0.4 mole of 3 He was polarized to 38% at 12 mK in a field of 7 T. The target is suitable for nuclear physics measurements which are insensitive to the large magnetic field and produce beam heating of tenths of microwatts. We discuss refinements and paths to improved solid 3 He targets at higher polarizations and lower fields.

A summary of the polarized and aligned nuclear targets which have been constructed and used at the Triangle Universities Nuclear Laboratory is given. Statically polarized targets, typically operating at a temperature of 12 mK and a magnetic field of 7 T, have provided significant nuclear polarization in 1 H, 3 He, 27 Al, 93 Nb and 165 Ho. A rotating, aligned 165 Ho target is also in use. A 3 He melting curve thermometer has been developed for use in statically polarized targets. A dynamically polarized proton target is under construction.

The dipole strength distribution of 130Te was investigated with the method of Nuclear Resonance Fluorescence using continuous-energy bremsstrahlung at the Darmstadt High Intensity Photon Setup and quasi-monoenergetic photons at the High Intensity γ-Ray Source. The average decay properties were determined between 5.50 and 8.15 MeV and compared to simulations within the statistical model.

The central goal of few-nucleon research at the Triangle Universities Nuclear Laboratory (TUNL) is to perform measurements that contribute to advancing ab-initio calculations of nuclear structure and reactions. The program aims include evaluating theoretical treatments of few-nucleon reaction dynamics through strategically comparing theory predictions to data, determining properties of the neutron-neutron interaction that are not accessible in two-nucleon reactions, and searching for evidence of longrange features of three-nucleon interactions, e.g., spin and isospin dependence. This paper will review studies of three- and four-nucleon systems at TUNL conducted using unpolarized and polarized neutron beams. Measurements of neutron-induced reactions performed by groups at TUNL over the last six years are described in comparison with theory predictions. The results are discussed in the context of the program goals stated above. Measurements of vector analyzing powers for elastic scattering in A=3 and A=4 systems, differential cross sections for neutron-deuteron elastic scattering and neutrondeuteron breakup in several final-state configurations are described. The findings from these studies and plans for the coming three years are presented in the context of worldwide activities in this front, in particular, research presented in this session.

The activation technique was used to measure the cross section for the reaction ${}^{40}\mathrm{Ar}(n,\phantom{\rule{-0.16em}{0ex}}p){\phantom{\rule{0.16em}{0ex}}}^{40}\mathrm{Cl}$ in 0.5 MeV energy steps in the neutron energy range between 9 and 15 MeV. These data are important for estimating background contributions in neutrinoless double-beta decay and dark matter searches, as well as in argon-based large neutrino detectors. The data are compared to evaluations and theoretical predictions.

Background: The nucleon-nucleus dispersive optical model (DOM) has been successful in providing good fits to scattering data and in making valuable predictions for bound-state properties in single- and double-closed shell nuclei. However, the generalizability of the DOM remains an ongoing issue.Purpose: We investigate the DOM in the continuum and bound-state regions of the open-shell, self-conjugate nuclei ${}^{28}$Si and ${}^{32}$S. We collect new differential cross section and analyzing power data for elastic scattering at incident neutron energies between 8.0 and 18.9 MeV.Methods: The measurements were conducted using a pulsed deuteron beam, the ${}^{2}$He($d$,$n$)${}^{3}$He source reaction, and time-of-flight techniques. All data were corrected for finite-geometry effects. Phenomenological DOM potentials were tailored to fit the differential and total cross section data, and then extrapolated to the bound-state regions. The DOM bound-state predictions were then compared to experimental data available for single-particle energies, occupation probabilities, root-mean-square radii, and spectroscopic factors.Results: The DOM bound-state predictions are in only fair agreement with experimental data and with USD shell-model predictions. Similar results are found after converting our neutron DOMs into proton DOMs. We investigate the separate effects of the dispersive surface and volume potential components on occupation probability and find that the volume component leads to a uniform depletion of the hole states, while the surface component acts mainly to deplete the valence orbitals. We compare these results to those of a variational multiparticle multihole configuration mixing (mp-mh CM) calculation using the Gogny D1S effective force.Conclusions: We find that the phenomenological DOM, which was originally designed for spherical nuclei, show certain deficiencies when applied to open-shell nuclei and suggest possible avenues of improvement. We also find that the predictions of occupation probability by the DOM using the dispersive surface component are similar to those by the mp-mh CM. This lends support to the interpretation that the surface absorption in the optical model originates from particle-vibration couplings, that is, long-range correlations.

We present limits on Majoron-emitting neutrinoless double-β decay modes based on an exposure of 112.3 days with 125 kg of 136Xe. In particular, a lower limit on the ordinary (spectral index n=1) Majoron-emitting decay half-life of 136Xe is obtained as T1/20νχ0>2.6×1024 yr at 90% C.L., a factor of five more stringent than previous limits. The corresponding upper limit on the effective Majoron-neutrino coupling, using a range of available nuclear matrix calculations, is 〈gee〉

The photodisintegration cross section of ${}^{4}$He into a neutron and helion was measured at incident photon energies of 27.0, 27.5, and 28.0 MeV. A high-pressure ${}^{4}$He-Xe gas scintillator served as target and detector while a pure Xe gas scintillator was used for background measurements. A NaI detector in combination with the standard HI$\ensuremath{\gamma}$S scintillator paddle system was employed for absolute photon-flux determination. Our data are in good agreement with the theoretical prediction of the Trento group and the recent data of Nilsson et al. [Phys. Rev. C 75, 014007 (2007)] but deviate considerably from the high-precision data of Shima et al. [Phys. Rev. C 72, 044004 (2005)].