Search

Parity violation has been studied recently for neutron resonances in {sup 117}Sn. The neutron resonance spectroscopy is essential for the analysis of the parity violation data. We have measured neutron resonances in {sup 117}Sn for neutron energies from 1 to 1500 eV using the time-of-flight method and the (n,{gamma}) reaction. The sample was enriched to 87.6{percent} {sup 117}Sn. Neutron scattering and radiative widths were determined, and orbital angular momentum assignments were made with a Bayesian analysis. The {ital s}-wave and {ital p}-wave strength functions and average level spacings were determined. {copyright} {ital 1999} {ital The American Physical Society}

A new search has been performed for parity violation in the compound nuclear states of ${}^{94}\mathrm{Nb}$ by measuring the helicity dependence of the neutron total cross section. Transmission measurements on a thick niobium target were performed by the time-of-flight method at the Manuel Lujan Neutron Scattering Center with a longitudinally polarized neutron beam in the energy range 32 to 1000 eV. A total of 18 p-wave resonances in ${}^{93}\mathrm{Nb}$ were studied with none exhibiting a statistically significant parity-violating longitudinal asymmetry. An upper limit of $1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ eV (95% confidence level) was obtained for the weak spreading width ${\ensuremath{\Gamma}}_{w}$ in ${}^{93}\mathrm{Nb}.$

Parity nonconservation (PNC) was studied in {ital p}-wave resonances in Ag by measuring the helicity dependence of the neutron total cross section. Transmission measurements on natural Ag were performed in the energy range 32 to 422 eV with the time-of-flight method at the Manuel Lujan Neutron Scattering Center at Los Alamos National Laboratory. A total of 15 {ital p}-wave neutron resonances were studied in {sup 107}Ag and nine {ital p}-wave resonances in {sup 109}Ag. Statistically significant asymmetries were observed for eight resonances in {sup 107}Ag and for four resonances in {sup 109}Ag. An analysis treating the PNC matrix elements as random variables yields a weak spreading width of {Gamma}{sub w}=(2.67{sub {minus}1.21}{sup +2.65}){times}10{sup {minus}7} eV for {sup 107}Ag and {Gamma}{sub w}=(1.30{sub {minus}0.74}{sup +2.49}){times}10{sup {minus}7} eV for {sup 109}Ag. thinsp {copyright} {ital 1999} {ital The American Physical Society}

Parity nonconserving asymmetries have been measured in $p$-wave resonances of ${}^{106}\mathrm{Pd}$ and ${}^{108}\mathrm{Pd}$. The data analysis requires knowledge of the neutron resonance parameters. Transmission and capture $\ensuremath{\gamma}$-ray yields were measured for ${E}_{n}=20$--2000 eV with the time-of-flight method at the Los Alamos Neutron Science Center (LANSCE). A total of 28 resonances in ${}^{106}\mathrm{Pd}$ and 32 resonances in ${}^{108}\mathrm{Pd}$ were studied. The resonance parameters for ${}^{106}\mathrm{Pd}$ are new for all except one resonance. In ${}^{108}\mathrm{Pd}$ six new resonances were observed and the precision improved for many of the resonance parameters. A Bayesian analysis was used to assign orbital angular momentum for the resonances studied.

We report the results of a high-resolution study of neutron resonances below 500 eV in {sup 166}Ho. We find nine previously unreported weak resonances at energies 24.79, 75.08, 119.98, 187.94, 210.86, 227.87, 235.94, 248.60, and 264.98 eV. Bayesian probability analysis of the widths indicates they are formed primarily by {ital s}-wave capture and are therefore negative-parity resonances. If they have measurable {ital d}-wave neutron widths, they are candidates for the fivefold correlation test of time reversal. {copyright} {ital 1996 The American Physical Society.}

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 large parity nonconserving longitudinal analyzing power was discovered in polarized-neutron transmission through Xe. An analyzing power of 4.3\ifmmode\pm\else\textpm\fi{}0.2% was observed in a $p$-wave resonance at ${E}_{n}=3.2$ eV. The measurement was performed with a liquid Xe target of natural isotopic abundance that was placed in the polarized epithermal neutron beam, flight path 2, at the Manuel Lujan Neutron Science Center. This apparatus was constructed by the TRIPLE Collaboration, and has been used for studies of parity symmetry in compound nuclear resonances. Part of the motivation of the experiment was to discover a nucleus appropriate for a sensitive test of time-reversal invariance in polarized-neutron transmission. The large analyzing power of the observed resonance may make it possible to design a test of time reversal invariance using a polarized-Xe target.

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.

Calculations of polarized neutron-polarized [sup 3]He scattering are presented for the transverse and longitudinal total cross-section differences [Delta][sigma][sub [ital T]] and [Delta][sigma][sub [ital L]] in the energy range [ital E][sub [ital n]]=0.1 to 10 MeV. Predictions made from phase-shift analyses, [ital R]-matrix analysis, and a multichannel resonating group-model calculation are compared. The predictions are in qualitative agreement and show that polarized neutron-polarized [sup 3]He scattering is sensitive to the level structure of [sup 4]He in the excitation energy range 20--30 MeV.

The neutron total cross section for natural indium was measured for ${\mathit{E}}_{\mathit{n}}$=25--500 eV with the time-of-flight method at the Los Alamos Neutron Scattering Center. The neutron capture reaction was studied on a highly enriched sample (99.99%) of $^{115}\mathrm{In}$. A total of 47 previously unreported resonances were observed. The combination of the two measurements allowed assignment of the new resonances to $^{113}\mathrm{In}$ or $^{115}\mathrm{In}$. Resonance parameters were extracted for all of the neutron resonances observed.

The parity-nonconserving longitudinal asymmetry [ital P] has been measured in nonresonant regions in [sup 232]Th for neutron energies in the range 6--86 eV. The measured value of [ital P][sub nonres]=(9.8[plus minus]21.7)[times]10[sup [minus]6] is consistent with statistical descriptions of parity violation.

The parity nonconserving longitudinal analyzing power [ital P] was measured for the [ital E][sub [ital n]]=0.88 eV neutron resonance in [sup 81]Br. The value of [ital P]=+1.77[plus minus]0.33 %; the sign is determined relative to the 0.73-eV resonance in [sup 139]La.

Parity nonconservation (PNC) was studied for 16 p-wave resonances in $^{238}\mathrm{U}$ by measuring the helicity dependence of the total cross section for epithermal neutrons scattered from $^{238}\mathrm{U}$. A statistical analysis yields a root-mean-square PNC matrix element M=0.${56}_{\mathrm{\ensuremath{-}}0.20}^{+0.41}$ meV, which corresponds to a spreading width of ${\mathrm{\ensuremath{\Gamma}}}^{\mathrm{PV}}$=0.9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ eV. Under plausible assumptions this gives a value of 4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ for \ensuremath{\Vert}${\mathrm{\ensuremath{\alpha}}}_{\mathit{p}}$\ensuremath{\Vert}, the ratio of strengths of the P-odd and P-even effective nucleon-nucleon interactions.

Parity nonconservation was studied for seventeen states in {sup 239}U by measuring the helicity dependence of the total cross section for epithermal neutrons scattered from {sup 238}U. The root-mean-squared parity-violating matrix element for the mixing of {ital p}-wave and {ital s}-wave states was determined to be {ital M}=0.58{sub {minus}0.25}{sup +0.50} meV. This corresponds to a parity-violating spreading width of {Gamma}{sup PV}=1.0{times}10{sup {minus}7} eV. Under plausible assumptions this gives a value of 4{times}10{sup {minus}7} for {vert bar}{alpha}{sub {ital P}}{vert bar}, the ratio of strengths of the {ital P}-odd and {ital P}-even effective nucleon-nucleon interactions.

Weak levels in the compound nucleus {sup 114}Cd were located by neutron time-of-flight spectroscopy techniques. Neutron capture measurements were performed with both a natural cadmium target and a highly enriched {sup 113}Cd target. A total of 22 new resonances were located in the neutron energy interval 20-500 eV and were assumed to be {ital p}-wave. Resonance parameters, {ital E}{sub 0} and {ital g}{Gamma}{sub {ital n}}, are given for the newly identified levels. The {ital p}-wave strength function was determined to be 10{sup 4}{ital S}{sub 1}=2.8{plus minus}0.8 and the average level spacing {l angle}{ital D}{sub 1}{r angle}=14 eV. Comparison of the reduced widths with a Porter-Thomas distribution is consistent with having missed 15% of the {ital p}-wave levels.

Spin-spin cross sections were measured for 7.5-MeV polarized neutrons incident on cryogenically polarized $^{93}\mathrm{Nb}$. Measurements were made with spin orientations transverse and longitudinal to the beam direction, yielding ${\mathrm{\ensuremath{\sigma}}}_{\mathit{T}}^{\mathit{s}\mathit{s}}$=-5.2\ifmmode\pm\else\textpm\fi{}5.3 mb and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{L}}^{\mathit{s}\mathit{s}}$=-2.2\ifmmode\pm\else\textpm\fi{}6.9 mb, respectively. The results are consistent with recent valence-nucleon folding model calculations. The tensor spin-spin potential is found to be small, ${\mathit{V}}_{12}$=-67\ifmmode\pm\else\textpm\fi{}190 keV. Volume integrals of spin-spin potentials are derived from depolarization and transmission experiments on $^{13}\mathrm{C}$, $^{15}\mathrm{N}$, $^{27}\mathrm{Al}$, and $^{93}\mathrm{Nb}$. The results for the central spin-spin potential are shown to be consistent with the folding model predictions.

Parity nonconservation has been studied in the transmission of longitudinally polarized epithermal neutrons incident upon a {sup 139}La target. Previous experiments have demonstrated the existence of a large value of the longitudinal asymmetry in the 0.734-eV {ital p}-wave resonance of the compound nucleus {sup 140}La, but report conflicting values for the measured asymmetry. We report the results of an experiment at the Los Alamos Neutron Scattering Center (LANSCE) which measured the asymmetry by two independent methods. One of these methods utilizes a conventional polarizer and a single lanthanum target. The other method uses an unpolarized beam with two lanthanum targets, and therefore does not require a separate measurement of the beam polarization. The asymmetry values determined from these two methods (0.1015{plus minus}0.0045 and 0.0955{plus minus}0.0035, respectively) are compared to previously measured values. Measurement of the asymmetry of the 0.734-eV resonance in {sup 139}La provides a highly accurate method of determining the polarization of an epithermal neutron beam.

Two-dimensional pulse height and time-of-flight (TOF) spectra were measured at the IBR-30 pulsed neutron source to make the isotopic identification of the parity-violating {ital p}-wave resonance at {ital E}{sub 0}=3.2 eV recently observed in Xe. Analysis of the TOF spectra corresponding to the characteristic low-energy gamma-rays established the {sup 131}Xe isotope as the origin of the 3.2-eV resonance. This new finding poses a challenge for the development of a polarized solid {sup 131}Xe target for a test of time-reversal invariance with neutrons. {copyright} {ital 1996 The American Physical Society.}

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

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

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

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

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

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

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

A polarized neutron beam has been used to measure the angular distribution of the analyzing power for the /sup 3/He(n,..gamma..)/sup 4/He reaction at E/sub n/(E/sub x/) = 9.0 (27.3) MeV. The angular distribution of the cross section, obtained with an unpolarized beam, is combined with these data to obtain the b/sub k/ coefficients. These coefficients are compared to the results of a previous measurement performed for the /sup 3/H(p,..gamma..)/sup 4/He reaction, and to the results of a recent continuum shell model calculation.

The angular distributions of cross sections and of analyzing powers for the /sup 5/9Co(p,..gamma../sub 0/) /sup 6/0Ni reaction have been measured throughout the giant dipole resonance region of /sup 6/0Ni. In addition, the 90/sup 0/ yield curve has been measured for E/sub p/ from 5.8 to 16.5 MeV. The data are analyzed to deduce the amplitudes and phases of the T matrix elements involved. Comparison of the results is made to both the dynamic collective model calculation of Ligensa and Greiner and to a direct-semidirect model calculation. The direct-semidirect calculation indicates that the reaction proceeds predominantly via the radiative capture of d/sub 5/2/ protons. Isospin splitting is also discussed.

Angular distributions for the /sup 12/C(n,..gamma../sub 0/)/sup 13/C reaction have been measured with neutrons corresponding to excitation energies of 16.0, 19.2, 20.1, 20.8, and 21.8 MeV. Legendre polynomial coefficients have been determined to second order (a/sub 3/ is small). Polarized neutron measurements were obtained at excitation energies of 16.0, 18.6, 19.2, 20.1, 21.0, 21.8, and 22.3 MeV. A structure seen in the coefficient of the Legendre polynomial P/sub 2/ for the /sup 12/C(p, ..gamma../sub 0/)/sup 13/N reaction is also seen in the present data. A secondary doorway state at 20.5 MeV with an apparent width of 0.5 MeV is suggested by previously measured /sup 11/B(d,..gamma../sub 0/)/sup 13/C data. The presence of this state provides an explanation for the energy dependence of the cross section, the a/sub 2/ coefficient, and the analyzing power coefficient b/sub 2/ in the /sup 12/C(n,..gamma../sub 0/)/sup 13/C data. The same model is also able to describe the energy dependence of the cross section and the a/sub 2/ coefficient observed in the /sup 12/C(p,..gamma../sub 0/)/sup 13/N reaction in the region of 16 to 22 MeV.

The 90/sup 0/ cross section yield curve for the /sup 13/C(n,..gamma../sub 0/) /sup 14/C reaction has been measured from E/sub n/(E/sub x/) = 5.6(13.4) to 17.0(24.0) MeV. Angular distributions of cross section and analyzing power were measured at seven energies spanning this excitation region. In addition, the fore-aft asymmetry and 90/sup 0/ analyzing power were measured as a function of energy from E/sub n/ = 7.75 to 17.0 MeV. The data were compared to direct-semidirect model calculations which included the isovector dipole and isoscalar electric quadrupole transitions. These comparisons indicate the presence of two narrow M1 resonances at E/sub x/ = 16.5 and 17.5 MeV and that sigma(E2) is less than 2% of the total capture cross section in the energy region of this experiment.

The 90/sup 0/ yield curve for the /sup 2/H(p,..gamma..) /sup 3/He reaction has been studied over the excitation region in /sup 3/He of approximately 7 to 15 MeV. Both polarized and unpolarized proton beams were used to measure the angular distributions of cross section and analyzing power at E/sub x/ = 8.83, 9.83, and 10.83 MeV. If only the four non-spin-flip E1 and E2 T-matrix elements are considered, their amplitudes and relative phases can be extracted. The E2 cross section obtained from this analysis is found to be (12 +- 5) % of the total cross section. The detailed balanced differential (theta/sub lab/ = 90/sup 0/) and total cross sections at E/sub x/ = 10.83 MeV are found to be (117 +- 11) ..mu..b/sr and (1.07 +- 0.11) mb, respectively; the quoted errors represent the total uncertainties in the cross sections obtained in this experiment. The results are also compared with recent E1 and E2 calculations.

The $g$ factor of the 738 keV second excited state in $^{43}\mathrm{K}$ has been measured using a perturbed angular correlation technique. A value for the half-life was also obtained. The level was populated via the $^{40}\mathrm{Ar}(\ensuremath{\alpha},p)^{43}\mathrm{K}$ reaction at 15 MeV with a pulsed beam. The spin precession was measured in an external magnetic field of \ensuremath{\sim} 3.8 and 5.4 kOe. The measured $g$ factor is + 1.28 \ifmmode\pm\else\textpm\fi{} 0.04, which is consistent with the reported spin of ${7/2}^{\ensuremath{-}}$. A comparison of the $g$ factor with other ${7/2}^{\ensuremath{-}}$ states in the odd potassium isotopes, and the ground state moments of the odd scandium isotopes reveal the state to be predominantly single particle in nature.

We have performed two independent measurements of the $^{11}\mathrm{B}(p, {\ensuremath{\gamma}}_{0})^{12}\mathrm{C}$ reaction over the energy range of ${E}_{p}=5\ensuremath{-}14$ MeV. The two measurements are in good agreement with each other and indicate that the previously accepted results are in error. The new values for the ${\ensuremath{\gamma}}_{0}$ cross section reported here resolve several outstanding conflicts. Their implications are discussed.NUCLEAR REACTIONS $^{11}\mathrm{B}(p, {\ensuremath{\gamma}}_{0})^{12}\mathrm{C}$, $5\ensuremath{\le}{E}_{p}\ensuremath{\le}14$ MeV; measured ${E}_{\ensuremath{\gamma}}$, absolute cross sections for $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$ (90\ifmmode^\circ\else\textdegree\fi{}, ${E}_{{\ensuremath{\gamma}}_{0}}$), $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$ (90\ifmmode^\circ\else\textdegree\fi{}, ${E}_{{\ensuremath{\gamma}}_{1}}$).

Angular distributions of cross section were measured for the $^{2}\mathrm{H}(\mathrm{p}, \ensuremath{\gamma})^{3}\mathrm{He}$ reaction at ${E}_{x}=9.83, 10.83, 12.78, 15.47, \mathrm{and} 16.12$ MeV and of analyzing power at ${E}_{x}=10.83 \mathrm{and} 16.12$ MeV. The data were fitted by expansions of Legendre and, where appropriate, associated Legendre polynomials. The coefficients of those fits are reported. The data at ${E}_{x}=10.83 \mathrm{and} 16.12$ MeV were also analyzed under simplifying assumptions to extract the $s=\frac{1}{2}(E1)$, $s=\frac{1}{2}(E2)$, and $s=\frac{3}{2}(E1)$ transition matrix elements, where $s$ represents the incident channel spin. The results indicate that the data are consistent with a 2(3)% $E2$ and a 3(5)% $s=\frac{3}{2}(E1)$ admixture at ${E}_{x}=10.83(16.12)$ MeV. These results are discussed in light of other recent experiments and calculations.

The 90/sup 0/ yield curves for the /sup 13/C(p,..gamma../sub 0/)/sup 14/N and /sup 13/C(p,..gamma../sub 1/)/sup 14/N reactions have been measured in 200 keV steps for E/sub p/=6.25 to 13.6 MeV and in 100 keV steps for E/sub p/=13.6 to 17.0 MeV. In addition, 50 keV step data were obtained for E/sub p/ of 12.6 to 14.55 MeV. Angular distributions of both the cross section and the analyzing power were also obtained for these two reactions at twelve energies which span the giant dipole energy region. The cross section was measured at nine angles between 30/sup 0/ and 154/sup 0/ while the analyzing power was measured at seven angles between 42/sup 0/ and 142/sup 0/. These data were used to obtain the complex E1 and E2 transition matrix elements in the case of /sup 13/C(p,..gamma../sub 1/)/sup 14/N. The results are compared to a direct-semidirect calculation. It is found that there is little justification in introducing E2 amplitudes other than a pure direct E2 term.

A comparison is made between the yield curves of the measured /sup 52/Cr(..cap alpha..,..gamma../sub 0/) and /sup 55/Mn(p,..gamma../sub 0/) reactions in the giant dipole resonance region of /sup 56/Fe (E/subx/=14.0 to 21.5 MeV) to determine if the gross differences can be interpreted as being due to isospin effects. Above 18 MeV the yield of (..gamma..,..cap alpha../sub 0/), determined by the principle of detailed balance, is observed to drop below the value obtained when the energy dependence of the transmission coefficients is removed. This leads to the conclusion that while the diminished yield in the (..gamma..,..cap alpha../sub 0/) channel may be due to the failure to populate the isospin forbidden T/sub greater-than/ states, other effects cannot be ruled out. (AIP)

We have measured the cross sections and the analyzing powers for the $^{14}\mathrm{C}(\stackrel{\ensuremath{\rightarrow}}{p}, \ensuremath{\gamma})^{15}\mathrm{N}$ reaction for proton energies from 4.0 to 16.2 MeV. The corresponding range in excitation energies, 13.94 to 25.33 MeV, covers the region of the giant dipole resonance in $^{15}\mathrm{N}$. The five-angle angular distributions measured with unpolarized and with polarized beams at eight energies over this region were analyzed to determine the magnitudes and relative phases of the transition matrix elements. The analysis included $E1$, $M1$, and $E2$ transitions. The observed $E1$ strength exhausts only about 6% of the classical dipole sum rule. The dominant $E1$ strength is compared to a shell-model calculation which includes 3p-3h excitations. A fairly uniform distribution of $E2$ strength is observed which exhausts about 7% of the total energy-weighted sum rule. Although large uncertainties on this result could allow the existence of a giant $E2$ resonance, the most probable values indicate that no appreciable concentration of $E2$ strength is observed.

Cross sections have been measured for the ($\ensuremath{\alpha}$,${\ensuremath{\alpha}}^{\ensuremath{'}}$) reaction leading to the first excited (${2}^{+}$) state for targets of $^{52}\mathrm{Cr}$, $^{54}\mathrm{Fe}$, $^{58}\mathrm{Fe}$, and $^{60}\mathrm{Ni}$. Data were obtained at several angles as a function of ${E}_{\ensuremath{\alpha}}$ in the region of 8 to 18 MeV. These energies cover the region of the isoscalar giant quadrupole resonance of the composite nuclei-$^{56}\mathrm{Fe}$, $^{58}\mathrm{Ni}$, $^{60}\mathrm{Ni}$, and $^{64}\mathrm{Zn}$. It has recently been reported that the giant quadrupole resonance of $^{58}\mathrm{Ni}$, $^{60}\mathrm{Ni}$, and $^{62}\mathrm{Ni}$ decays primarily by $\ensuremath{\alpha}$ emission. Although the present data exhibit a giant resonancelike energy dependence, a coupled channels calculation indicates that several ${J}^{\ensuremath{\pi}}$ values can be expected to contribute to a resonancelike envelope in this reaction at the energies of the giant quadrupole resonance in these nuclei.NUCLEAR REACTIONS $^{52}\mathrm{Cr}$, $^{54,58}\mathrm{Fe}$, $^{60}\mathrm{Ni}$($\ensuremath{\alpha}$,${\ensuremath{\alpha}}_{1}$), ${E}_{\ensuremath{\alpha}}\ensuremath{\cong}8 \mathrm{to} 14\ensuremath{-}19$ MeV; measured $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}};\ensuremath{\theta})$. Targets \ensuremath{\sim}500 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ foils. Results examined for evidence of GQR and compared to coupled-channels calculation.

The mean lifetimes of levels in $^{59}\mathrm{Cu}$ below 3.6 MeV have been investigated with the Doppler-shift attenuation method and the $^{58}\mathrm{Ni}(^{3}\mathrm{He},d)^{59}\mathrm{Cu}$ reaction at 11.6 MeV. Scattered particles were detected in two $E\ensuremath{-}\ensuremath{\Delta}E$ telescopes at \ifmmode\pm\else\textpm\fi{} 55\ifmmode^\circ\else\textdegree\fi{} with respect to the beam axis, in coincidence with $\ensuremath{\gamma}$ rays observed at 90\ifmmode^\circ\else\textdegree\fi{} in a 50-${\mathrm{cm}}^{3}$ Ge(Li) detector. New levels were observed at 3114 and 3615 keV. Mean lifetimes are reported for the following levels (energy in keV, lifetime in fs): 491 (830 \ifmmode\pm\else\textpm\fi{} 300), 914 (g 1600), 1399 (570 \ifmmode\pm\else\textpm\fi{}240), 2266 (310 \ifmmode\pm\else\textpm\fi{} 140), 2324 (36 \ifmmode\pm\else\textpm\fi{}5), 3043 (1150 \ifmmode\pm\else\textpm\fi{} 500), 3114 (20 \ifmmode\pm\else\textpm\fi{} 11), 3130 (10 \ifmmode\pm\else\textpm\fi{} 4), 3551 ( 15), 3580 (2400 \ifmmode\pm\else\textpm\fi{} 1400), and 3615 ( 35). The experimental results are compared with the predictions of a core-particle coupling calculation.

The yield curve for proton capture on /sup 7/Li, leading to the region of the isospin-mixed pair of states at E/sub x/ = 16.63 and 16.92 MeV in /sup 8/Be, has been measured as a function of bombarding energy from 4 to 30 MeV. A direct capture model provides a good description of the data.

The cross sections of $^{15}\mathrm{N}$($\ensuremath{\gamma}$,${d}_{0}$)$^{13}\mathrm{C}$ and $^{13}\mathrm{C}$($d$,${\ensuremath{\gamma}}_{0}$)$^{15}\mathrm{N}$ have been measured. A resonance was observed at ${E}_{x}\ensuremath{\simeq}21.9$ MeV in the ($\ensuremath{\gamma}$,${d}_{0}$) channel. Vector polarized deuterons were used to measure the angular distribution of gamma rays at this resonance and the results were analyzed assuming the two $S=\frac{1}{2}$ $E1$ transition matrix elements are dominant.NUCLEAR REACTIONS $^{15}\mathrm{N}$($\ensuremath{\gamma}$,${d}_{0}$)$^{13}\mathrm{C}$, $^{13}\mathrm{C}$($d$,${\ensuremath{\gamma}}_{0}$)$^{15}\mathrm{N}$; measured $\ensuremath{\sigma}(\ensuremath{\theta})$, $A(\ensuremath{\theta})$ and $\ensuremath{\sigma}(\mathrm{tot})$. Deduced $E1$ $T$-matrix elements and phases at ${E}_{x}\ensuremath{\approx}21.9$ MeV.

The vector analyzing powers have been measured for the /sup 1/H(d,..gamma..) /sup 3/He and the /sup 2/H(p,..gamma..) /sup 3/He reactions at E/sub x/ = 6 MeV. The results indicate the presence of channel spin (3/2) capture strength. An M1 strength amounting to between 1 and 8% of the cross section is able to explain the observations if a significant s = (3/2) component is included.

The angular distributions of cross sections and analyzing powers have been measured for the /sup 58/Fe(p, ..gamma../sub 0/)/sup 59/Co reactions throughout the giant dipole resonance regions of /sup 55/,/sup 57/,/sup 59/Co. In addition, the 90degree yield curve has been measured for the /sup 58/Fe(p, ..gamma../sub 0/)/sup 59/Co reaction for E/subp/ from 5.0 to 16.0 MeV in 100 keV steps. The data are analyzed to deduce the amplitudes and phases of the T matrix elements involved. The preferred solution indicates that the major change occurring in crossing the giant dipole resonance occurs in the relative phase between the d/sub 5///sub 2/ and g/sub 9///sub 2/ amplitudes. The implications of these results are discussed vis a vis the isospin splitting of the giant dipole resonance. (AIP)

A recently reported measurement of the photoneutron cross section for $^{4}\mathrm{He}$ indicates a value of about 1.0 mb for ${E}_{x}$ of \ensuremath{\sim}23 to \ensuremath{\sim}33 MeV. This result, when combined with the previously reported ($\ensuremath{\gamma},p$) cross section in this energy region, implies a ($\ensuremath{\gamma},p$)-to-($\ensuremath{\gamma},n$) cross section ratio of 1.6 to 1.9 in the 26 to 29 MeV region of $^{4}\mathrm{He}$. We have used the inverse reaction $^{3}\mathrm{He}(n,\ensuremath{\gamma})^{4}\mathrm{He}$ to measure the photoneutron cross section for $^{4}\mathrm{He}$. Our detailed balanced results confirm the recently reported measurements.

The 90/sup 0/ yield curves for the /sup 30/Si( p,..gamma../sub 0/)/sup 31/P and /sup 30/Si( p,..gamma../sub 1/)/sup 31/P reactions have been measured for E/sub p/=5.0 to 28.0 MeV. Angular distributions of cross section and analyzing power were obtained at twelve energies between E/sub p/=6.36 and 14.45 MeV. The cross sections were measured at nine angles between 30/sup 0/ and 154/sup 0/, the analyzing power at seven angles between 42/sup 0/ and 142/sup 0/. For the case of ( p,..gamma../sub 0/) the complex T-matrix elements were extracted, assuming that the angular distributions are governed by coherent E1 and E2 processes. Two sigma(E2) yield curves are obtained, one of which exhausts 9--12% of the ..delta..T=0 E2 energy weighted sum rule while the other exhausts 21--31%. The results are compared to direct-semidirect model calculations which suggest that the larger E2 cross sections are the physical solutions.

Angular distributions of cross sections and analyzing powers were measured for the /sup 3/H(p-arrow-right,..gamma..)/sup 4/He reaction at incident proton energies of 2.0, 5.0, and 9.0 MeV. The 90/sup 0/ analyzing power was measured at 11 energies between 0.8 and 9.0 MeV. A transition matrix element analysis indicated that the inclusion of M1 strength gave better fits and eliminated the anomalously large /sup 3/D/sub 2/ (E2) strength reported in earlier work. An E1-plus-E2 direct capture calculation was performed. It is shown that this calculation can be brought into agreement with the data if an M1 strength comparable to that found in the T-matrix element analysis (0.5--1.0% of the total capture cross section) is added.

The mean lifetime of the 2.94-MeV level in $^{33}\mathrm{S}$ has been measured by the recoil distance method using the $^{30}\mathrm{Si}(\ensuremath{\alpha},n)^{33}\mathrm{S}$ reaction. The lifetime was found to be 40.5\ifmmode\pm\else\textpm\fi{}2.0 psec.