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Using time-of-flight techniques, we have measured neutron emission spectra from 6- and 10-MeV incident neutron energies on 10B and 11B for laboratory angles between 20 and 145 deg using the unique ...

Single-event upsets (SEUs) were measured in thermal neutron-irradiated microcontrollers with 65- and 130-nm-node static random-access memories (SRAMs). The suspected upset mechanism is charge deposition from the energetic byproducts of 10B thermal neutron capture. Although elemental analysis confirmed that both microcontrollers contain 10B, only the 65-nm node microcontroller exhibited a strong response to thermal neutrons. Monte Carlo simulations were performed to investigate the effects of 11B enrichment on thermal neutron-induced SEUs in a 65-nm SRAM node when boron is present in the p -type well, p -type source and drain, or tungsten plug. Simulations indicate that the byproducts of 10B(n, $\alpha $ ) 7Li reactions are capable of generating sufficient charge to upset a 65-nm SRAM. The highest amount of charge deposition from 10B(n, $\alpha $ ) 7Li reaction byproducts occurs when natural boron is used to dope the p -type source and drain regions. Simulations also show that the SEU cross section is nonnegligible when 11B-enriched boron is used for doping.

A detector efficiency model based on energy extraction from neutrons is described and used to compare ^4He detectors with liquid scintillators (EJ301/NE-213). Detector efficiency can be divided into three regimes: single neutron scattering, multiple neutron scattering, and a transition regime in-between. For an average fission neutron of 2 MeV, the amount of ^4He needed would be about 1/4 of the amount of the mass of EJ301/NE-213 in the single-scattering regime. For about 50% neutron energy extraction (1 MeV out of 2 MeV), the two types of detectors (^4He in the transition regime, EJ301 still in the single-scattering regime) have comparable mass, but ^4He detectors can be much larger depending on the number density. A six-tube 11-bar-pressure ^4He detector prototype is built and tested. Individual electrical pulses from the detector are recorded using a 12-bit digitizer. Differences in pulse rise time and amplitudes, due to different energy loss of neutrons and gamma rays, are used for neutron/gamma separation. Several energy spectra are also obtained and analyzed.

Much of the absolute differential cross-section data for elastic scattering by 3He depends on an experiment at the Los Alamos National Laboratory (LANL), published in 1974. Since that time, computer techniques have been developed that can make more accurate corrections for, e.g., sample-size effects. Since complete documentation of the LANL experiment is available, modern analysis techniques were applied to improve these data, based on simulations using the Los Alamos Monte Carlo neutron transport code MCNPX. Of a total of 29 published differential cross-section distributions, 15 published in 1982 from another laboratory depend on the LANL data but were not corrected for sample-size effects and therefore provide only relative yield functions. The present study simulates these latter data using MCNPX to obtain self-attenuation correction factors for the scattered neutrons. An energy-dependent analysis shows that at neutron energies between 5 and 14 MeV, these latter corrected data are in good agree...

The Los Alamos Neutron Science Center, or LANSCE, uses the first truly high-current medium-energy proton linear accelerator, which operated originally at a beam power of 1 MW for medium-energy nuclear physics. Today LANSCE continues operation as one of the most versatile accelerator-based user facilities in the world. During eight months of annual operation, scientists from around the world work at LANSCE to execute an extraordinarily broad program of defense and civilian research. Several areas operate simultaneously. The Lujan Neutron Scattering Center (Lujan Center) is a moderated spallation source (meV to keV), the Weapons Neutron Research Facility (WNR) is a bare spallation neutron source (keV to 800 MeV), and a new ultra-cold neutron source will be operational in 2005. These sources give LANSCE the ability to produce and use neutrons with energies that range over 14 orders of magnitude. LANSCE also supplies beam to WNR and two other areas for applications requiring protons. In a proton radiography (pRad) area, a sequence of narrow proton pulses is transmitted through shocked materials and imaged to study dynamic properties. In 2005, LANSCE began operating a facility that uses 100-MeV protons to produce medical radioisotopes. To sustain a vigorous program beyond this decade, LANSCE has embarked on a project to refurbish key elements of the facility and to plan capabilities beyond those that presently exist.

The Accelerator Production of Tritium Target/Blanket (T/B) system is comprised of an assembly of tritium-producing modules supported by safety, heat removal, shielding, and retargeting systems. The T/B assembly produces tritium using a high-energy proton beam, a tungsten/lead spallation neutron source and {sup 3}He gas as the tritium-producing feedstock. The supporting heat removal systems remove the heat deposited by the proton beam during both normal and off-normal conditions. The shielding protects workers from ionizing radiation, and the retargeting systems remove and replace components that have reached their end of life. All systems reside within the T/B building, which is located at the end of a linear accelerator. For the nominal production mode, protons are accelerated to an energy of 1030 MeV at a current of 100 mA and are directed onto the T/B assembly. The protons are expanded to a 0.19- x 1.9-m beam spot before striking a centrally located tungsten neutron source. A surrounding lead blanket produces additional neutrons from scattered high-energy particles. A total of 27 neutrons are produced per incident proton. Tritium is produced by neutron capture in {sup 3}He gas that is contained in aluminum tubes throughout the blanket. The {sup 3}He/tritium mixture is removed on amore » semi-continuous basis for purification in an adjacent Tritium Separation Facility. Systems and components are designed with safety as a primary consideration to minimize risk to the workers and the public. Materials and component designs were chosen based on the experiences of operating spallation neutron sources that have been designed and built for the neutron science community. An extensive engineering development and demonstration program provides detailed information for the completion of the design.« less

Double differential cross sections and analyzing powers over the quasielastic region have been measured using the ({ital {rvec p}},{ital n}) reaction on {sup 12}C and {sup nat}Pb. The data were obtained at proton energies of 495 and 795 MeV and cover momentum transfers from 1.0--2.1 fm{sup {minus}1} at 495 MeV data and from 0.0--3.5 fm{sup {minus}1} at 795 MeV. The cross section data are compared to results from a nonrelativistic reaction model that includes contributions from two-step scattering. The analyzing power measurements are compared to a recent relativistic plane-waves model.

Neutron-induced fission of $^{236}\mathrm{U}$ has been measured at the Los Alamos Neutron Scattering Center with a white neutron source using a fast parallel plate ionization chamber at a flight path of \ensuremath{\sim}56 m. In the resonance and the intermediate resonance region, very little of the previously reported structure was detected. Only five resonance structures were observed. Additionally, the width of the 5.45 eV resonance is approximately 100 times smaller than previously reported. An explanation for the discrepancies between old data and data reported here is discussed. New fission widths for resonances from 5.45 eV to 10.4 keV are reported. The new data are in agreement with theoretical estimates.

The construction of a neutron flux monitor that can measure absolute neutron intensities in the neutron energy range from below 1 MeV to over 500 MeV is described. The detector consists of an ionization chamber with several thin deposits of fissionable material. The ionization chamber is thin enough that it does not significantly affect the neutron beam and may be left in the neutron flight path during experimental measurements to continuously monitor the beam flux. The use of this monitor at the continuous-energy spallation neutron source at the WNR target area at LAMPF is described.

We describe a new approach for commercial nuclear energy production without a long-term high-level waste stream and for transmutation of both fission product and higher actinide commercial nuclear waste using a thermal flux of accelerator-produced neutrons in the 1016 n/cm2s range. Continuous neutron fluxes at this intensity, which is approximately 100 times larger than is typically available in a large scale thermal reactor, appear practical, owing to recent advances in proton linear accelerator technology and to the spallation target-moderator design presented here. This large flux of thermal neutrons makes possible a waste inventory in the transmutation system which is smaller by about a factor of 100 than competing concepts. The accelerator allows the system to operate well below criticality so that the possibility for a criticality accident is eliminated. No control rods are required. The successful implementation of this new method for energy generation and waste transmutation would eliminate the need for nuclear waste storage on a geologic time scale. The production of nuclear energy from 232Th or 238U is used to illustrate the general principles of commercial nuclear energy, production without long-term high-level waste. There appears to be sufficient thorium to meet the world's energy needs for many millenia.

Cross sections have been measured for the reaction $^{64}\mathrm{Ni}$(n,p${)}^{64}$Co at laboratory angles between 0\ifmmode^\circ\else\textdegree\fi{} and 10\ifmmode^\circ\else\textdegree\fi{} for incident neutron energies from 90 to 240 MeV. The ground-state cross sections together with the ${\mathrm{\ensuremath{\beta}}}^{\mathrm{\ensuremath{-}}}$ decay ft value for the transition $^{64}\mathrm{Co}$(g.s.)${\ensuremath{\rightarrow}}^{64}$Ni(g.s.) are used to normalize the q=0 differential cross section in units of mb/sr per unit Gamow-Teller (GT) strength. This is the first absolute measurement of the A(n,p) unit cross section for a nucleus in the (fp) shell, and it may be used to calibrate the GT strength measured in other (n,p) reactions of similar mass nuclei. Since the (${\mathit{e}}^{\mathrm{\ensuremath{-}}}$,${\ensuremath{\nu}}_{\mathit{e}}$) channel involves the same nuclear matrix element as the (n,p) channel, knowledge of GT strength in these nuclei is important for supernova modeling codes which depend on knowledge of ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ capture rates of (fp)-shell nuclei to determine parameters of stellar core collapse.

Compact electron spectrometers have been designed and fabricated using permanent magnets. The design allows a very broad range of electron momenta (1 to 25 MeV/c) with resolutions dual to the greater of either 1% or 0.1 MeV/c. Two types of magnet material have been employed (SmCo and NdFe) to build two models of the spectrometer. Measurements of the spectrometer characteristics are compared to design calculations.

Two neutron sources used for nuclear physics research at Los Alamos National Laboratory are described. Both are driven by the 800-MeV proton beam from the Los Alamos Meson Physics Facility. The Los...

The Los Alamos Neutron Science Center, or LANSCE, is an accelerator‐based national user facility for research in basic and applied science. At present LANSCE has two experimental areas primarily using neutrons generated by 800‐MeV protons striking tungsten target systems. A third area uses the proton beam for radiography. This paper describes the three LANSCE experimental areas, gives highlights of the past operating period, and discusses plans for the future.

The Accelerator Production of Tritium (APT) concept proposes the production of tritium by means of an accelerator and target system. The Los Alamos APT design incorporates a high‐energy, high‐current proton accelerator, a tungsten neutron source, a lead neutron multiplier, and a moderating blanket that contains 3He for the production of tritium. This innovative system makes use of existing spallation neutron source technology, and proven design concepts. Inherent safety and environmental features include low decay heat, the absence of fissile or fertile material, no criticality concerns, no potential for overpower transients, and the fact that no high level waste is produced.

Pulsed-beam time-of-flight techniques are used in a transmission measurement with a continuous spectrum of neutrons to determine neutron total cross sections with good precision up to 600 MeV. Neutrons are produced by spallation of the 800 MeV proton beam from the Los Alamos Meson Physics Facility accelerator incident on a thick, heavily shielded tungsten target at the Weapons Neutron Research facility at Los Alamos National Laboratory. Transmission measurements were completed for fifteen elements with 9\ensuremath{\le}A\ensuremath{\le}209 and three isotopically enriched samples of $^{40}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, and $^{208}\mathrm{Pb}$. Principal features of the experiment are the intensity and time structure of the neutron source, tight collimation of the neutron beam line, good geometry, rapid cycling of the samples, stable electronics, and a small, fast neutron detector. Errors due to counting statistics were generally less than 1% for each of several hundred energy bins for each target. The measurements represent steps in the development of a neutron-nucleus optical potential at intermediate energy and important input for the clarification of isovector effects in the nucleon-nucleus interaction. The data also provide insight into the long-standing discussion of mean free paths of the nucleon in the nucleus.

Cross sections from 0{degree} to 10{degree} (lab) have been measured for ground-state Gamow-Teller transitions for the reactions {sup 6}Li({ital n},{ital p}){sup 6}He, {sup 12}C({ital n},{ital p}){sup 12}B and {sup 13}C({ital n},{ital p}){sup 13}B from 60 to 260 MeV. The 90-m station at the Weapons Neutron Research facility at Los Alamos National Laboratory was used to obtain these data. Unit cross sections ({sigma}) have been obtained and are compared with existing ({ital n},{ital p}) and ({ital p},{ital n}) data. The volume integrals ({ital J}{sub {sigma}{tau}}) for the spin-flip isospin-flip part of the effective nucleon-nucleon interaction have also been obtained and are compared with theoretical predictions.

There is renewed interest in using accelerator driven neutron sources to address the problem of high level long-lived nuclear waste. Several laboratories have developed systems that may have a significant impact on the future use of nuclear power, adding options for dealing with long-lived actinide wastes and fission products, and for power production. This paper describes a new Los Alamos concept using thermal neutrons and examines the nuclear data requirements.

Recent developments in experimental facilities have enabled new techniques for measurements of neutron interactions above 30 MeV. Foremost is the development of both monoenergetic and continuous neutron sources using accelerators in the medium energy region between 100 and 800 MeV. Measurements of the reaction products have been advanced by the continuous improvement in detector systems, electronics and computers. Corresponding developments in particle transport codes and in the theory of nuclear reactions at these energies have allowed more precise design of neutron sources, experimental shielding and detector response. As a result of these improvements, many new measurements are possible and the data base in this energy range is expanding quickly.

Neutron-induced fission cross section ratios from 0.5 to 400 MeV for samples of 233,234,236U relative to 235U have been measured at the WNR neutron Source at Los Alamos. The fission reaction rate was determined using a fast parallel plate ionization chamber at a 20-m flight path. Cross sections over most of the energy range were also extracted using the neutron fluence determined with three different proton telescope arrangements. Those data provided the shape of the 235U(n,f) cross section relative to the hydrogen scattering cross section. That shape was then normalized to the very accurately known value for 235U(n,f) at 14.1 MeV which will allow us to obtain cross section section values from the ratio data and our values for 235U(n,f).

To improve the accuracy of the {sup 235}U(n,f) cross section, measurements have been made of this standard cross section at the target 4 facility at Los Alamos National Laboratory (LANL). The data were obtained at the 20-meter flight path of that facility. The fission reaction rate was determined with a fast parallel plate ionization chamber and the neutron fluence was measured with an annular proton recoil telescope. The measurements provide the shape of the {sup 235}U(n,f) cross section relative to the hydrogen scattering cross section for neutron energies from about 3 to 30 MeV neutron energy. The data have been normalized to the very accurately known value near 14 MeV. The results are in good agreement with the ENDF/B-VI evaluation up to about 15 MeV neutron energy. Above this energy differences as large as 5% are observed.

New measurements of neutron total cross sections have been performed as a function of neutron energy up to 600 MeV using the WNR facility at Los Alamos National Laboratory. Transmission measurements were performed for eighteen target nuclei with 9 < A < 209 including isotopically enriched samples of 40Ca, 90Zr and 208Pb. While the goal of the experiment was to measure total cross sections above 100 MeV in small energy bins and with 1% statistical accuracy, much of the data at lower energy is significantly better than that. Rapid fluctuations In the cross sections of light nuclei below 20 MeV provide information on nuclear level density at high excitation energy. The overall dependence of the cross section on neutron energy can be interpreted in terms of optical models ranging in complexity from simple Ramsauer pictures to Dirac phenomenology. Preliminary results of some of these calculations will be presented.

An important process occuring in presupernova stars is e- capture on free protons and nuclei.1,2 As e- capture and the charge exchange reaction (n,p) between same initial and final states are both To → To + 1 transitions involving the same nuclear matrix element, the (n,p) reaction can be used to provide the input required to calculate e- capture rates. Specifically, the e- capture rate λ if for a nucleus going from an initial state i to a final state f is proportional to the Gamow-Teller strength Bif(GT)3: $${\lambda ^{if}}\alpha {B^{if}}\left( {GT} \right)$$ Where Bif(GT) is given by4 $${B^{if}}\left( {GT} \right) = \frac{1}{{2{J_i} + 1}}{\left| { } \right|^2}$$ .

We have measured the polarization of protons from the /sup 9/Be(/sup 3/He,p)/sup 11/B reaction between 35 and 50/sup 0/ at an incident bombarding energy of 13.6 MeV to check claims of time-reversal noninvariance. We find complete disagreement with other polarization measurements for the same energy and angular range, but our results are in agreement with earlier measurements of the analyzing power in the inverse reaction initiated with polarized protons. Consequently we maintain that this reaction and its inverse exhibit no evidence for a violation of time-reversal invariance.

The total $^{7}\mathrm{Be}$(n,p${)}^{7}$Li cross section has been measured from 25 meV to 13.5 keV. These energies correspond to temperatures of T=2.9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ to 0.16 GK. For thermal neutrons the cross sections to the ground state (${p}_{0}$) and the first excited state (${\mathit{p}}_{1}$) of $^{7}\mathrm{BLi}$ are 38 400\ifmmode\pm\else\textpm\fi{}800 b and 420\ifmmode\pm\else\textpm\fi{}120 b, respectively. This result for the total $^{7}\mathrm{Be}$(n,p${)}^{7}$Li thermal cross section is about 25% lower, and is approximately a factor of 10 more precise than previous published measurements. For energies above 100 eV, a significant departure from a 1/v shape for the total cross section is observed. The data were analyzed using a single-level approximation, and were also analyzed together with other data using multilevel-multichannel R-matrix theory. Results are presented for the properties of the ${2}^{\mathrm{\ensuremath{-}}}$ threshold state and for a possible nearby ${2}^{\mathrm{\ensuremath{-}}}$ state. The astrophysical reaction rate, ${N}_{A}$〈\ensuremath{\sigma}v〉, was calculated from the measured cross sections for the combined ${p}_{0}$ and ${p}_{1}$ transitions. The resulting reaction rate is approximately 60--80 % of the rate currently in use. This reduction in the $^{7}\mathrm{Be}$(n,p${)}^{7}$Li reaction rate could result in a calculated increase in the production of $^{7}\mathrm{Li}$ during the big bang by as much as 20%.

A method is described in which 805 MHz acceleration cavities in the LAMPF linac are used to form a nearly isochronous beam of particles for use in high-resolution neutron time-of-flight spectroscopy at energies less than 800 MeV.

Differential cross sections are reported for elastic and inelastic scattering of neutrons from beryllium. Source neutrons were provided by the D(d,n)3 He reaction at energies from 7 to 15 MeV in 1-...

Measurements have been made of the branching ratio for the reactions $^{3}\mathrm{H}$(d,\ensuremath{\gamma}${)}^{5}$He${/}^{3}$H(d,n) $^{4}\mathrm{He}$ for several incident deuteron energy ranges between 0 and 0.72 MeV. A stopping length tritium gas target bombarded by a pulsed deuteron beam was used to obtain a high reaction rate as well as provide neutron-gamma ray separation by time of flight. The branching ratio was determined to be 5.6\ifmmode\pm\else\textpm\fi{}0.6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ integrated over the resonance from 0 to 275 keV.

Angular distributions have been measured for the (p, n) reaction on targets of Li, C, C, and N at 800 MeV with an energy resolution of 2.7 MeV allowing observation of discrete nuclear levels. As is the case at lower energies, this reaction is very selective, emphasizing Gamow-Teller (GT) and Fermi transitions. Absolute cross sections of pure GT transitions are reproduced by impulse approximation calculations. The ratio |Jστ|2/|Jτ|2 was extracted from C and N measurements at 800 MeV and from a C measurement at 31

Zero-degree (p,n) cross sections, measured with approximately 1-MeV energy resolution at ${E}_{p}$=492 MeV, are reported for $^{7}\mathrm{Li}$, $^{11}\mathrm{B}$, and $^{12}$,13,14C. Measurements for $^{11}\mathrm{B}$(p,n) and $^{13}\mathrm{C}$(p,n) were also obtained at 590 MeV. The cross sections for Gamow-Teller and Fermi type transitions are used to estimate the strengths of the isovector spin-dependent (${J}_{\ensuremath{\sigma}\ensuremath{\tau}}$) and spin-independent (${J}_{\ensuremath{\tau}}$) terms of the effective interaction. The measured zero-degree cross sections for the $^{14}\mathrm{C}$(p,n${)}^{14}$N transitions to the 2.31 MeV isobaric analog state and the 3.95-MeV ${J}^{\ensuremath{\pi}}$${=1}^{+}$ state are compared with calculated values. Values for the unit cross-section ratio ${R}^{2}$=\ensuremath{\sigma}${^}_{\mathrm{GT}}$/\ensuremath{\sigma}${^}_{F}$ =(${J}_{\ensuremath{\sigma}\ensuremath{\tau}}$/${J}_{\ensuremath{\tau}}$${)}^{2}$ (${N}_{\ensuremath{\sigma}\ensuremath{\tau}}$/${N}_{\ensuremath{\tau}}$) obtained from the present data are compared with results for other energies.

We have determined the absolute efficiency of an NE-213 scintillator for neutrons with energies from 0.5 to 800 MeV. The detector was 5.1 cm in diameter and 2.5 cm deep. The efficiencies were obtained for detector thresholds of 0.011, 0.48, 1.12, and 4.48 MeVee. Our results are compared to predictions of the STANTON computer code.

A fast-neutron time-of-flight spectrometer has been constructed for the purpose of measuring neutron differential cross sections of interest to the controlled thermonuclear reactor (CTR) program. T...

The $\mathrm{np}$ total cross section has been measured from 40 to 770 MeV with good statistical precision and better than 1% energy resolution. No evidence is seen for narrow resonances with areas greater than 5 mb MeV or for the $I=0$, $^{1}F_{3}$ state reported by other authors. From 200 to 700 MeV the present results are as much as 6% lower than previous data.

A phenomenological optical model analysis of neutron 208 Pb data from 2 to 250 MeV has been performed. The energy dependence of the real potential strength was found to be linear up to about 60 MeV and logarithmic above that energy. The strength of the real isovector potential, determined from a comparison with proton- 208 Pb results, was found to have a negligible energy dependence below about 50 MeV.

Data for the analyzing power ${A}_{y}(\ensuremath{\theta})$ for $n\ensuremath{-}p$ scattering at 16.9 MeV have been measured for the range from 50 to 145\ifmmode^\circ\else\textdegree\fi{} (c.m.). Eleven values are reported to an accuracy of about \ifmmode\pm\else\textpm\fi{}0.002, the highest overall precision ever obtained in any fast-neutron polarization experiment. Predictions based on phase-shift sets obtained from global analyses of nucleon-nucleon scattering disagree significantly with the new data. The data are sufficiently precise to show a dependence on the $f$-wave spin-orbit phase parameter.

The polarization of neutrons from the reaction /sup 2/H(d, n)/sup 3/He has been measured for a deuteron energy E/subd/ = 2.44 MeV at emission angles of 45degree and 55degree (lab). The polarization values are discussed in relation both to previously reported discrepant data and to measured differences between p/suby/ and A/suby/ in the reaction /sup 3/H(p, n)/sup 3/He. (AIP)

A description of the experimental setup used at the WNR facility to study the interaction of polarized neutrons with polarized samples is given. Planned measurements of the magnetic moments of compound nuclear resonances are discussed.

Measurements have been made of the neutron polarization from the \(D(\vec t,\vec n){}^4He\) reaction with polarized tritons1) incident. The neutron polarization was measured by means of a liquid helium neutron polarimeter2). The bulk of the data ware taken at a reaction angle of 0°. These results are shown in fig. 1, along with the predictions furnished by D. C. Dodder and G. M. Hale from their R-matrix analysis of the 5-nucleon system. The lack of agreement is surprising in view of the past successes of their parameterization. In fig. 2 an angular distribution of ky y′(θ) at 10.5 MeV is presented, again together with the Dodder-Hale prediction. Here there is at least qualitative agreement with the shape of the curve.

It has been recognized for a number of years that certain spin-isospin components of the nucleon-nucleus effective interaction can be inferred from (p,n) reactions to states of known nuclear structure. For L = 0, S = 0 and L = 0, S = 1 transitions, the 0-degree (p,n) cross section can be related respectively to Fermi and Gamow-Teller beta decay matrix elements1. If these transitions occur in the same nucleus, the ratio of isovector spin-flip to non-spin-flip effective interactions can be measured without regard for absolute normalization. The best reaction to measure this is 14C(p,n) which goes by a pure Gamow-Teller transition to the 1+ state at 3.95 MeV in 14N, and Fermi transition to the 2.31 MeV 0+ state. This work extends the ratio measurements made at lower energies (ref. 1, 2, 3) to 492 and 590 MeV.

Scattering from 4He has been the most widely employed method for accurately measuring the polarization of nucleon beams. Below 18 MeV the analyzing power for the 4He(n,n)4He interaction is probably known to within about ± 0.03 at the forward angle minimum as well as at the backward angle maximum. This information has been obtained through energy-dependent phase-shift analyses of the available data which have gradually grown in quantity and quality. At higher energies, due to the complexity of the phase-shift analyses and the difficulty of the measurements, the understanding of the 4He(n,n)4He interaction is not as advanced. In order to provide additional information on the five-nucleon system and to calibrate the analyzing power near 119°(lab), measurements were made of Ay(θ) for neutron energies En from 20 to 30 MeV using neutron beams whose polarization values had been determined without any reliance on neutron polarization analyzers. Such neutron beams were obtained by utilizing the properties of the zero degree longitudinal polarization transfer coefficient K z z′ of the T( \(\overrightarrow d ,\overrightarrow n \) )3He reaction as described in the contribution of Lisowski et al.1) Neutrons emitted at 0° from the T + d reaction initiated by a 75% longitudinally polarized deuteron beam were incident on a liquid 4He scintillator. Measurements of Ay(θ) were obtained for θ = 60° and 70° (lab) for En = 20.9 MeV and for 119° (lab) at five energies between 20 and 30 MeV, by detecting the scattered neutrons in coincidence with the 4He recoils. To perform the Ay(θ) determination the neutron-polarization axis was rotated to a transverse orientation by means of a transverse magnetic field between the tritium target and the 4He scatterer. The deuteron beam polarization was determined to within ± 0.01 by the quench-ratio method and Azz values were obtained from previous measurements.1)

In a contribution to the Third Polarization Symposium, Ohlsen, Keaton, and GaTl1) reported that certain properties of the spin structure of the \( T{\left( {\vec d,\vec n} \right)^4}He \) reaction permitted a calculation of the longitudinal neutron polarization from the zero-degree analyzing power Azz(0°) and the deuteron beam polarization.

The angular distribution of neutral hydrogen following electron detachment from H/sup -/ has been measured for H/sup -/ on nitrogen and hydrogen gas, both for neutral atoms left in the 2S state, and for all neutrals independent of the state of excitation. The results are essentially in agreement with calculations based on the Born approximation, although there is some disagreement in detail.

High resolution measurements of neutron induced charged particle reactions on 23Na have been performed. A NaI(T1) detector served as both target and detector, with pulse shape discrimination being applied for the separation of protons and alpha-particles from each other and from events involving gamma-ray detection. The neutron energy was measured by time-of-flight, using an 80 m flight path at the Los Alamos National Laboratory WNR facility.