[en] An initial study has been performed of the feasibility of employing an axial array of gamma detectors located outside the pressure vessel to monitor the coolant in a PWR. A one-dimensional transport analysis model is developed for the LOFT research reactor and for a mock-PWR geometry. The gamma detector response to coolant voiding in the core and downcomer has been determined for both geometries. The effects of various conditions (for example, time after shutdown, materials in the transport path, and the relative void fraction in different water regions) on the detector response are studied. The calculational results have been validated by a favorable comparison with LOFT experimental data. Within the limitations and approximations considered in the analysis, the results indicate that the gamma-ray detection scheme is able to unambiguously respond to changes in the coolant inventory within any vessel water region

[en] New results for the neutron-deuteron analyzing power A_y(θ) at E_n=1.2 and 1.9 MeV and their comparison to proton-deuteron data reveal a sizeable and unexpected difference which increases with decreasing center-of-mass energy. This finding calls for the theoretical treatment of a subtle electromagnetic effect presently not incorporated in rigorous three-nucleon scattering calculations, before it is justified to invoke charge-dependent three-nucleon forces and/or other new physics

[en] Long wavelength neutrons (λ>1 A) in a cold neutron beam provide a valuable probe to study the strong and weak nuclear forces in hadronic systems, where the description is complicated by the quark structure of the particles. As a consequence of parity-violation (PV) arising from the weak interaction, the low-energy neutron transverse spin-polarization vector rotates as the neutrons transverse a medium. The magnitude of the PV spin-rotation observable in the n-α system provides important new data to determine the strength of the neutron-nucleus weak interaction. Measurement of the spin-rotation in the bare neutron-proton system with a parahydrogen target, will provide important constraints on the weak nucleon-nucleon (NN) interaction including the neutral current contribution, and will increase our understanding of the strong NN interaction. This paper will review the recent spin-rotation measurement in a liquid helium target, and the proposed measurement in a parahydrogen target

[en] Wiescher, Goerres, and Thielemann suggested that a ''missing'' J^π=3⁺ level in ¹⁸Ne should occur at E_x∼4.33 MeV, only ∼410 keV above the ¹⁷F+p threshold. They noted that this level would provide an s-wave resonance in the ¹⁷F(p,γ) reaction, greatly increasing its thermonuclear reaction rate. This, in turn, would have a pronounced effect on the production of ¹⁷O and ¹⁸O in explosive stellar environments. We have searched for this level using the ¹⁶O(³He,n) reaction. High-resolution time-of-flight spectra show that the 3⁺ level occurs at E_x=4.561±0.009 MeV, ∼230 keV higher than suggested. The astrophysical consequences of this result are discussed

[en] We report relative measurements of the n(vector sign)-d(vector sign) longitudinal spin-dependent total cross-section difference (Δσ_L)_d, at E_n(lab) = 5.0, 6.88, and 9.0 MeV. The deuteron target was polarized via dynamic nuclear polarization at 250 mK in a 2.5-T external magnetic field. The target polarization was monitored by nuclear magnetic resonance and was calibrated by a (Δσ_L)_d measurement at E_n(lab) = 1.18 MeV. The polarized neutron beams were produced through the ³H(p(vector sign),n(vector sign))³He and ²H(d(vector sign),n(vector sign))³He reactions. The neutron polarizations were determined either by direct measurement or from known or calculated polarization-transfer coefficients. The results for (Δσ_L)_d show agreement with theoretical calculations based on nucleon-nucleon potential models but are not of sufficient precision to distinguish the presence or absence of three-nucleon force contributions to the cross sections

[en] A liquid helium target system was designed and built to perform a precision measurement of the parity-violating neutron spin rotation in helium due to the nucleon-nucleon weak interaction. The measurement employed a beam of low energy neutrons that passed through a crossed neutron polarizer-analyzer pair with the liquid helium target system located between them. Changes between the target states generated differences in the beam transmission through the polarizer-analyzer pair. The amount of parity-violating spin rotation was determined from the measured beam transmission asymmetries. The expected parity-violating spin rotation of order 10^-6rad placed severe constraints on the target design. In particular, isolation of the parity-odd component of the spin rotation from a much larger background rotation caused by magnetic fields required that a nonmagnetic cryostat and target system be supported inside the magnetic shielding, while allowing nonmagnetic motion of liquid helium between separated target chambers. This paper provides a detailed description of the design, function, and performance of the liquid helium target system.

[en] We used the ¹⁶O(³He,n)¹⁸Ne, ¹²C(¹²C,⁶He)¹⁸Ne, and ²⁰Ne(p,t)¹⁸Ne reactions to study ¹⁸Ne states up to an excitation energy of 10 MeV, with emphasis on levels corresponding to ¹⁴O(α,p)¹⁷F and ¹⁷F(p,γ)¹⁸Ne resonances that could strongly affect these reaction rates in hot stellar environments. Excitation energies, widths, absolute cross sections, and angular distributions were measured. We found previously unidentified states at E_x=6.15±0.01 MeV, 7.12±0.02 MeV, 7.35±0.02 MeV, 7.62±0.02 MeV, 8.30±0.02 MeV, (8.45±0.03 MeV), 8.55±0.03 MeV, 8.94±0.02 MeV, and 9.58±0.02 MeV. We combined level width, cross section, and angular distribution data to infer J^π values for a number of the new levels as well as for the previously known 5.1-MeV doublet. Using information from our experiments, we recalculated the ¹⁴O(α,p)¹⁷F reaction rate, which constitutes a possible path out of the hot CNO cycle into the rp process and could play an important role in transforming nuclei involved in the hot CNO cycle into heavier nuclei with Z≥10. copyright 1996 The American Physical Society

[en] We present an improved measurement of the oscillation between the first two neutrino families based on a 766.3 ton-year exposure of KamLAND to reactor anti-neutrinos. KamLAND observes 258 events with nue-bar energies above 3.4MeV compared to 365.2 events expected in the absence of neutrino oscillation. The confidence level for reactor nue-bar disappearance is now 99.995%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at the 99.9% confidence level but agrees with the distortion expected from nue-bar oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives a best-fit point at ΔMSq=8.3 x 10^-5eV² and tan²θ=0.41. A global analysis of data from KamLAND and solar neutrino experiments yields ΔMSq=8.2^+0.6_-0.5 x 10^-5eV² and tan²θ =0.40^+0.09_-0_.07, the most precise determination to date

[en] Measurements of parity-violating neutron spin rotation can provide insight into the poorly understood nucleon-nucleon weak interaction. Because the expected rotation angle per unit length is small (10^-7 rad/m), several properties of the polarized cold neutron beam phase space and the neutron optical elements of the polarimeter must be measured to quantify possible systematic effects. This paper presents (1) an analysis of a class of possible systematic uncertainties in neutron spin rotation measurements associated with the neutron polarimetry, and (2) measurements of the relevant neutron beam properties (intensity distribution, energy spectrum, and the product of the neutron beam polarization and the analyzing power as a function of the beam phase space properties) on the NG-6 cold neutron beam-line at the National Institute of Standards and Technology Center for Neutron Research. We conclude that the phase space nonuniformities of the polarimeter in this beam are small enough that a parity-violating neutron spin rotation measurement in n-⁴He with systematic uncertainties at the 10^-7 rad/m level is possible.

[en] KamLAND has been used to measure the flux of barν_e's from distant nuclear reactors. In an exposure of 162 ton·yr (145.1 days) the ratio of the number of observed inverse Β-decay events to the expected number of events without disappearance is 0:611 ± 0:085(stat) ± 0:041(syst) for barν_e energies > 3.4 MeV. The deficit of events is inconsistent with the expected rate for standard barν_e propagation at the 99.95% confidence level. In the context of two-flavor neutrino oscillations with CPT invariance, these results exclude all oscillation solutions but the 'Large Mixing Angle' solution to the solar neutrino problem using reactor barν_e sources