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The absolute intensities of transitions in the 2 ν 3 vibrational band of 12 C 16 O 18 O at 4639.5 cm -1 have been measured in natural isotopic abundance; the spectra were obtained with 0.012 cm -1 resolution using the McMath Fourier transform spectrometer of the National Solar Observatory located at Kitt Peak National Observatory. About 70 transitions have been fitted with an rms deviation of approximately 1.5% to obtain the rotationless band strength of S 0 vib =1.442×10 -23 cm molecule -1 at 296 K along with a small first-order Herman–Wallis parameter of A 1 =3.5×10 -5 ; higher order Herman–Wallis parameters could not be determined. The measured line positions, obtained using the CO 2 gas samples in the range of 45–65 Torr at room temperature, confirm the current HITRAN tabulated values. The internal precision of our intensity measurements is very high, and the uncertainty due to possible systematic errors is judged to be less than ±3%.

The effects of isospin-symmetry breaking on the observables for parity-violating electron scattering are investigated within the framework of the nuclear shell model for 12C, 16O, and 28Si. Contributions due to mixing with low-lying states as well as admixtures of 1p-1h configurations (via the radial wave functions) are accounted for. It is found that isospin-mixing can be important, and the consequences regarding precision tests of the standard model are addressed., Comment: 12 pages, 2 postscript figures, RevTex. Submitted to Phys. Rev. Lett

The ${}^{16}O ({}^{3}He,d) {}^{17}F$ reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of ${}^{17}F$. The coefficients provide the normalization for the tails of the overlap functions for ${}^{17}F \to{}^{16}O + p$ and allow us to calculate the S-factors for ${}^{16}O (p,\gamma){}^{17}F$ at astrophysical energies. The calculated S-factors are compared to measurements and found to be in very good agreement. This provides the first test of this indirect method to determine astrophysical direct capture rates using transfer reactions. In addition, our results yield S(0) for capture to the ground and first excited states in $^{17}F$, without the uncertainty associated with extrapolation from higher energies., Comment: 6 pages, 2 figures

The degrees of nuclear spin polarization of 8,12B, 9C, 12N, 13O, 20,21F, 23Mg, 27Si and 39Ca produced in the high energy 12,13C, 16O, 22Ne, 24Mg, 28Si and 40Ca ions on Be collisions have been measured systematically, for the technical developments of the nuclear moment studies as well as the hyperfine interaction studies by means of β-NMR technique. The fragment momentum dependences were well reproduced by the simple kinematical model. Incident energy dependence and the mass dependence as well as the reaction angle dependences were qualitatively explained by the mixing of the near and far side collisions.

Nodulating (T202) and non-nodulating (T201) soybean isolines were hydroponically cultivated, then nitrate labeled with 13N or 15N, was added to the culture solution in order to investigate the nitrate absorption and transport in soybean. The accumulation pattern of the absorbed 13N in the first trifoliate was observed by positron emitting tracer imaging system (PETIS) as well as bioimaging analyzer system (BAS) . The 15N abundance of each part was determined by emission sjectrometrv.Real time changes in two dimensional image of the radioactivity could be monitored by PETIS, besides the distribution 13N in whole plant could be observed by BAS. However quantitative data were hardly obtained by the 13N analysis. Stable isotope 15N is more reliable in the quantitative analysis in each part. Combing the data obtained by 15N and 13N tracer experiments, the absorption and translocation of N in plant should be more clearly figured out.

We have measured the charge changing cross sections from 10 individual beams of isotopes from 8 different nuclei between Be and Ni which were accelerated to energies from 400-650 MeV nucleon-1 at the SATURNE Accelerator in France in 1993 and 1994. These nuclei interacted in a 1.52 g cm-2 thick liquid hydrogen target and the fragments were observed. This is the first use of a pure hydrogen target to measure cross sections that has a thickness approximating the amount of hydrogen traversed by cosmic rays in our Galaxy. Several of the beam charges such as 9Be,11B,15N, and 22Ne have not had their fragmentation cross sections measured previously. The cross sections from the 12C,14N,16O,20Ne,56Fe, and 58Ni beams are compared with earlier measurements by our group using a CH2 - C target subtraction technique to determine the hydrogen cross sections. The overall agreement between the new measurements and the earlier measurements using CH2 - C subtraction is excellent with a systematic consistency between measurements of 3%-5%. Using these new cross sections the predictions of both the B/C and Z = (21-23)/Fe ratios at ~1 GeV nucleon-1 now agree with HEAO measurements to ~1%-2%, thus obviating the need for truncation of the exponential path length distribution path length distribution that is expected from uniform propagation models. Also, these new charge changing cross sections along with the isotopic cross sections reported in paper two of this series, define the production of cosmic-ray beryllium and boron nuclei in the galaxy and also the secondary isotopes 10Be,13C,14N,15N,18O, and all of the Fe secondary isotopes to a level of precision of 3%-5% or better. These cross sections are important for determining the abundance of these rare isotopes and others in the cosmic-ray sources as well as tracing the detailed propagation history of cosmic rays in the Galaxy. These measurements also provide high precision cross sections for the study of the nuclear physics of the interaction process.

Simultaneous 17 O/ 16 O and 18 O/ 16 O measurements of atmospheric carbon monoxide (CO) and two of its major sources are presented. CO was collected in situ at ground level in La Jolla, CA, Pasadena, CA and White Mountain, CA, altitude 3.8 km. Samples were also taken directly from engine exhaust and during a local wild brushfire. Results indicate that atmospheric carbon monoxide has a significant mass independent component, which increases as carbon monoxide concentrations decrease. The origin of the observed mass independent fractionation is discussed. CO samples from engine exhaust and brushfires are clearly mass dependent, but with a wide variation in 18 O values from different engines.

Measurements of the 16O and 18O distribution functions in the solar wind at low to average solar wind speeds from the MASS instrument on the Wind spacecraft are reported. The 16O/18O density ratio is 450 ± 130, a value consistent with terrestrial, solar photospheric, solar energetic particle, and galactic cosmic ray 16O/18O isotopic ratios. This study constitutes the first reported spacecraft measurement of the isotope 18O in the core solar wind and may represent the best determination of the solar 16O/18O density ratio to date.

The capture cross section of the reaction ${}^{16}\mathrm{O}(p,\ensuremath{\gamma}{)}^{17}\mathrm{F}$ was measured in the energy range from ${E}_{\mathrm{c}.\mathrm{m}.}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}200--3750\mathrm{keV}$ using the windowless gas target facility Rhinoceros. The low-energy $S$ factor that is dominated by the transition to the $1/{2}^{+}$ first excited state in ${}^{17}\mathrm{F}$ increases strikingly with decreasing energy. This behavior is explained by the halo properties of this $1/{2}^{+}$ state within the framework of the direct capture model.

Exclusive and inclusive ({nu}{sub {mu}},{mu}{sup {minus}}), ({nu}{sub e},e{sup {minus}}) cross sections and {mu}{sup {minus}}-capture rates are calculated for {sup 12}C and {sup 16}O using the consistent random phase approximation (RPA) and pairing model. After a pairing correction is introduced to the RPA results, the flux-averaged theoretical ({nu}{sub {mu}},{mu}{sup {minus}}), ({nu}{sub e},e{sup {minus}}) cross sections and {mu}{sup {minus}}-capture rates in {sup 12}C are in good agreement with experiment. Predictions of ({nu}{sub {mu}},{mu}{sup {minus}}) and ({nu}{sub e},e{sup {minus}}) cross sections in {sup 16}O are also presented. {copyright} {ital 1997} {ital The American Physical Society}

Cross sections for single $(1p)$ and multinucleon ${(2p,}^{4}$He, and ${p}^{4}$He) transfer reactions have been measured in ${}^{19}$F, ${}^{16}$O, ${}^{12}$C+${}^{232}$Th systems at beam energies around the Coulomb barrier. Angular distributions and energy spectra of the projectilelike particles exhibit characteristics of direct transfer reactions. The ratio of the transfer to total reaction (transfer+fusion-fission) cross section is observed to be significantly smaller for the ${}^{12}$C projectile, as compared to that for ${}^{19}$F and ${}^{16}$O projectiles. All the systems show large transfer cross sections relative to the total reaction cross section at subbarrier energies. The angular distribution data were analyzed in terms of transfer probabilities to derive the slope parameter $(\ensuremath{\alpha})$ for the stripping of $1p$ and $2p$ in the case of ${}^{16}$O and ${}^{12}$C projectiles and for $1p$, ${}^{4}$He and correlated (${p}^{4}$He) stripping in the case of ${}^{19}$F projectile, for comparison with the semiclassical calculations. It is observed that the semiclassical picture is valid for $1p$ transfer at energies near the Coulomb barrier, whereas for correlated $2p$, ${}^{4}$He, and (${p}^{4}$He) multinucleon transfers, the experimental values of $\ensuremath{\alpha}$ are anomalously small as compared to the semiclassical calculations even at subbarrier energies. At the above-barrier energies, the slope anomaly can be explained after inclusion of the nuclear effects in semiclassical calculations.

Angle averaged cross sections for the mutual excitation of the ${0}_{2}^{+},$ 6.05 MeV excited state of ${}^{16}\mathrm{O}$ have been measured over the center of mass energy region 30.0--43.5 MeV in steps of 200--400 keV. The excitation function is dominated by three wide structures centered at center of mass energies 33.0, 37.0, and 40.5 MeV. A spin assignment for an angular distribution measurement at 37.0 indicates the dominant spins of this exit channel are smaller than the spins that dominate the resonances observed in the single excitation to the ${0}_{2}^{+},$ 6.05 MeV excited state of ${}^{16}\mathrm{O}$ at comparable center of mass energies. This result is consistent with preliminary coupled channel calculations.

The angular distribution of differential cross sections for \ensuremath{\alpha} and ${}^{3}\mathrm{He}$ projectiles elastically scattered from ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ are calculated at the energy range from 25 to 217 MeV. The double folding model with an energy-target density dependent Jeukenne, Lejeune, and Mahaux effective nucleon-nucleon interaction is used to obtain both real and imaginary parts of the central optical potential. The dependence of the potential on densities of projectile and target nuclei in a factorized form is considered. Good fits to the experimental data are obtained. Nuclear rainbow scattering is also observed and discussed.

The effects of the real potential on the absorption of lighter heavy ions are discussed. The effects are illustrated with ''effective potentials'' reproducing the elastic scattering phase shifts in ...

Experimental data on strongly energy-damped yields from the {sup 28}Si+{sup 16}O reaction at E{sub c.m.}=39.1 and 50.5 MeV are analyzed in the context of fission from the {sup 44}Ti compound system. Several features of this system, including the presence of resonantlike structures in the elastic- and inelastic-scattering excitation functions, the observation of large cross sections for strongly damped yields, and the recognition that there are relatively few channels open for reactions involving the near-grazing partial waves, have been taken to infer a deep-inelastic as opposed to fission origin of the strongly damped yields. We test this claim by comparing the predictions of the transition-state model for fission to the experimental results. The statistical model is found to adequately describe the experimental results at the higher energy. The fully energy-damped {ital inelastic} yields at 39.1 MeV, however, are found to be far in excess of expectations based on the fission model. This result is in sharp contrast to what has been observed in the nearby {sup 224}Mg+{sup 16}O system. {copyright} {ital 1997} {ital The American Physical Society}

Nuclear rainbows, which appear in the elastic scattering angular distributions for certain combinations of lighter heavy ions like ${}^{12}$C${+}^{12}$C and ${}^{16}$O${+}^{16}$O, uniquely determine the major features of the optical potentials for these systems. These features are conveniently summarized by the central depth of the real part of the potential, $V(r=0)\ensuremath{\sim}100\ensuremath{-}300$ MeV, and by the ratio of imaginary to real parts of the potential, $W(r)/V(r)$, found to be $\ensuremath{\ll}1$ for both small and large $r$ (internal and far-tail transparency), but $\ensuremath{\approx}1$ in the surface region. The resulting maximum in $W/V$, which is found over the entire energy range 6 MeV $\ensuremath{\lesssim}{E}_{L}/A\ensuremath{\lesssim}100$ MeV, appears to correlate with the peripheral reactions that occur in this energy range. At higher energies the data available indicate that the far-surface region is no longer transparent. Rather, $W\ensuremath{\approx}V$ there, suggesting the dominance of nuclear knockout reactions in the far tail. The knockout mode of inelasticity is the one described by the double-Glauber approximation, and $W(r)\ensuremath{\approx}V(r)$ agrees with the Glauber prediction in the high-energy range. This suggests that the double-Glauber prediction begins to be accurate in the low-density tail of the ${A}_{1}{+A}_{2}$ interaction around ${E}_{L}/A\ensuremath{\approx}100$ MeV and that its failure for the higher-density interior may provide a means of investigating the density dependence of Pauli blocking on $\mathrm{NN}$ scattering in the nuclear medium. By way of contrast, systems like ${}^{20}$Ne${+}^{12}$C and ${}^{14}$N${+}^{12}$C, which do not exhibit rainbows, have distinctly more absorptive potentials and do not follow the above systematics. This suggests that the imaginary part of the optical potential reflects the shell structure of the target and/or projectile in important ways, and so will not be easy to calculate from an infinite-matter many-body approach.

Accreted helium layers on white dwarfs have been highlighted for many decades as a possible site for a detonation triggered by a thermonuclear runaway. In this paper, we find the minimum helium layer thickness that will sustain a steady laterally propagating detonation and show that it depends on the density and composition of the helium layer, specifically C12 and O16. Detonations in these thin helium layers have speeds slower than the Chapman-Jouget (CJ) speed from complete helium burning, v_cj=1.5e9 cm/s. Though gravitationally unbound, the ashes still have unburned helium (~ 80% in the thinnest cases) and only reach up to heavy elements such as Ca40, Ti44, Cr48, and Fe52. It is rare for these thin shells to generate large amounts of Ni56. We also find a new set of solutions that can propagate in even thinner helium layers when O16 is present at a minimum mass fraction of ~0.07. Driven by energy release from alpha captures on O16 and subsequent elements, these slow detonations only create ashes up to Si28 in the outer detonated He shell. We close by discussing how the unbound helium burning ashes may create faint and fast ".Ia" supernovae as well as events with virtually no radioactivity, and speculate on how the slower helium detonation velocities impact the off-center ignition of a carbon detonation that could cause a Type Ia supernova in the double detonation scenario., Comment: 21 pages, 33 figures. Accepted to ApJ - 08/19/2013

We report the results of a sensitive search for the minor isotopologues of water, H2-17O and H2-18O, toward the carbon-rich AGB star IRC+10216 (a.k.a. CW Leonis) using the HIFI instrument on the Herschel Space Observatory. This search was motivated by the fact that any detection of isotopic enhancement in the H2-17O and H2-18O abundances would have strongly implicated CO photodissociation as the source of the atomic oxygen needed to produce water in a carbon-rich circumstellar envelope. Our observations place an upper limit of 1/470 on the H2-17O/H2-16O abundance ratio. Given the isotopic 17O/16O ratio of 1/840 inferred previously for the photosphere of IRC+10216, this result places an upper limit of a factor 1.8 on the extent of any isotope-selective enhancement of H2-17O in the circumstellar material, and provides an important constraint on any model that invokes CO photodissociation as the source of O for H2O production. In the context of the clumpy photodissociation model proposed previously for the origin of water in IRC+10216, our limit implies that 12C-16O (not 13C-16O or SiO) must be the dominant source of 16O for H2O production, and that the effects of self-shielding can only have reduced the 12C-16O photodissociation rate by at most a factor ~ 2., Comment: 14 pages, 4 figures, accepted for publication in ApJ Letters

Traditionally, the method used for measuring the isotope ratios is the Isotope Ratio Mass Spectrometers (IRMS). A new method has been used to determine the isotopic abundances, the Cavity Ring-Down Spectroscopy (CRDS). It consists of a technique of direct absorption, of high sensitivity, which is based on measuring the absorption ratio, as a function of time, of the light confined in a high finesse optical cavity, instead of the magnitude of light beam absorption. The values of 18O/16O and D/H ratios are determined with respect to international standards VSMOW, GISP and SLAP from the International Atomic Energy Agency (IAEA). In this work, the IRMS and CRDS techniques are compared, verifying that the CRDS technique is promising and has some advantages compared to IRMS. It uses a smaller amount of sample, the isotope measurements are made simultaneously from the steam, reducing the analysis time. It also shows good reproducibility and accuracy, and it does not require a preliminary sample preparation.

The 13C(?, n)16O reaction is the neutron source for the main component of the s-process, responsible for the production of most of the nuclei in the mass range 90 A 208. This reaction takes place inside the helium-burning shell of asymptotic giant branch stars, at temperatures 108?K, corresponding to an energy interval where the 13C(?, n)16O reaction is effective in the range of 140-230?keV. In this regime, the astrophysical S(E)-factor is dominated by the ?3?keV sub-threshold resonance due to the 6.356?MeV level in 17O, giving rise to a steep increase in the S-factor. Its contribution is still controversial as extrapolations, e.g., through the R-matrix and indirect techniques such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of three or more precisely at astrophysical energies. To provide a more accurate S-factor at these energies, we have applied the Trojan horse method (THM) to the 13C(6Li, n 16O)d quasi-free reaction. The ANC for the 6.356?MeV level has been deduced through the THM as well as the n-partial width, allowing us to attain unprecedented accuracy for the 13C(?, n)16O astrophysical factor. A larger ANC for the 6.356?MeV level is measured with respect to the ones in the literature, ?fm?1, yet in agreement with the preliminary result given in our preceding letter, indicating an increase of the 13C(?, n)16O reaction rate below about 8 ? 107?K if compared with the recommended values. At ~108?K, our reaction rate agrees with most of the results in the literature and the accuracy is greatly enhanced thanks to this innovative approach.

The 12C(αγ)16O reaction rate is considered one of the most important unknown parameters in the physics of structure and evolution of massive stars. While extensive experimental campaigns have been performed trying to improve the quality of the measurements, the rate still holds very large uncertainties. Here we discuss a new experimantal scheme to measure the cross section of this reaction with a bubble chamber and a bremsstrahlung beam. The main advantage of the technique is a gain in the luminosity of several orders of magnitude when compared to other ongoing experiments.

The iterative perturbative inversion method is extended to determine explicitly energy and parity dependent potentials from {ital S} matrices specified at a series of discrete energies. The energy dependence is inserted only in the potential magnitude, although enhanced {open_quote}{open_quote}energy bite{close_quote}{close_quote} techniques allow this approximation to be tested. With a linear energy dependence in both real and imaginary components, {ital S}-matrix data for {ital p}+{alpha} scattering is fitted with a single potential for a wide range of energies above the inelastic threshold. The imaginary potential is shown to be parity dependent. The real potential is consistent, in both the potential shape and the parity and energy dependence, with potentials established for subthreshold energies. The method is also applied to resonating group model (RGM) phase shifts for {ital n}+{sup 16}O and {ital p}+{alpha} scattering to give energy and parity dependent potentials in both cases. For {ital p}+{alpha}, a close correspondence is obtained between the RGM and the empirical potentials in both the energy and parity dependence up to about 65 MeV. For {ital n}+{sup 16}O, potentials are determined for positive and negative energies. {copyright} {ital 1996 The American Physical Society.}

A geometrical mapping of the semimicroscopic algebraic cluster model is given. The geometrical variables are the relative radius vector and the quadrupole deformation parameters. The last ones correspond to absolute \ensuremath{\beta} and \ensuremath{\gamma} values, while the orientation of the deformed nucleus in the laboratory can be changed. We show that the position of the minimum of the nuclear molecular potential is determined by the minimal number of \ensuremath{\pi} bosons describing the relative motion. The minimal number of \ensuremath{\pi} bosons is determined by the implementation of the Pauli principle. Applications to simple systems ${(}^{16}$O+\ensuremath{\alpha} and $^{12}\mathrm{C}$+\ensuremath{\alpha}) are presented. \textcopyright{} 1996 The American Physical Society.

Nuclear transparencies for the fundamental process {gamma}{ital n}{r_arrow}{pi}{sup {minus}}{ital p} on {sup 4}He and {sup 16}O have been calculated using nucleon configurations obtained from realistic ground-state wave functions by the Monte Carlo method. Comparisons between nuclear transparency results using nucleon configurations and the correlated Glauber approximation are made in the case of ({ital e},{ital e}{sup {prime}}{ital p}) on {sup 4}He and {sup 16}O. Furthermore, nuclear transparencies for the {gamma}{ital n}{r_arrow}{pi}{sup {minus}}{ital p} and ({ital e},{ital e}{sup {prime}}{ital p}) processes have been calculated including a color transparency effect. {copyright} {ital 1996 The American Physical Society.}

The excitation function of the $^{12}\mathrm{C}$(\ensuremath{\alpha},\ensuremath{\gamma}${)}^{16}$O reaction and the angular distribution of its \ensuremath{\gamma} rays were measured at nine center-of-mass energies ranging from E=1.37 to 2.98 MeV. These measurements allowed the separation of the E1 and E2 contributions and their extrapolation to the region of astrophysical interest. The analysis of all the available E1 cross sections with the K-matrix method and with a three-level R-matrix method yields a consistent prediction of 79\ifmmode\pm\else\textpm\fi{}16 keV b for the E1 S factor at 300 keV. The E2 contribution at the same energy is 36\ifmmode\pm\else\textpm\fi{}6 keV b from a cluster model analysis of the present data. The best estimate of the total S factor at 300 keV is 120 keV b, and it is unlikely that it will fall outside the range of 80--160 keV b. \textcopyright{} 1996 The American Physical Society.

We used the $^{16}\mathrm{O}$${(}^{3}$He,n${)}^{18}$Ne, $^{12}\mathrm{C}$${(}^{12}$C${,}^{6}$He${)}^{18}$Ne, and $^{20}\mathrm{Ne}$(p,t${)}^{18}$Ne reactions to study $^{18}\mathrm{Ne}$ states up to an excitation energy of 10 MeV, with emphasis on levels corresponding to $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F and $^{17}\mathrm{F}$(p,\ensuremath{\gamma}${)}^{18}$Ne 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 ${\mathit{E}}_{\mathit{x}}$=6.15\ifmmode\pm\else\textpm\fi{}0.01 MeV, 7.12\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.35\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.62\ifmmode\pm\else\textpm\fi{}0.02 MeV, 8.30\ifmmode\pm\else\textpm\fi{}0.02 MeV, (8.45\ifmmode\pm\else\textpm\fi{}0.03 MeV), 8.55\ifmmode\pm\else\textpm\fi{}0.03 MeV, 8.94\ifmmode\pm\else\textpm\fi{}0.02 MeV, and 9.58\ifmmode\pm\else\textpm\fi{}0.02 MeV. We combined level width, cross section, and angular distribution data to infer ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ 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 $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F 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\ensuremath{\ge}10. \textcopyright{} 1996 The American Physical Society.

A procedure for the calculation of the two-body spectral function of a finite nucleus is presented. This spectral function is used to calculate the longitudinal part of the $^{16}\mathrm{O}$(e,${\mathit{e}}^{\ensuremath{'}}$pp) cross section assuming plane waves for the outgoing nucleons. Short-range correlation effects are included in the pair-removal amplitudes by adding corresponding defect wave functions that are obtained from the solution of the Bethe-Goldstone equation in the finite nucleus. The associated G matrix is used as the effective interaction in a large but finite model space to calculate the pair-removal amplitudes in a random-phase approach. The resulting spectral functions exhibit clear differences between different realistic interactions in the momentum range 2--5 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ for the initial proton momenta. \textcopyright{} 1996 The American Physical Society.

The neutron rich nuclei {sup 61,63}Co have been studied using the reactions {sup 16}O({sup 48}Ca,{ital p}2{ital n}){sup 61}Co and {sup 18}O({sup 48}Ca,{ital p}2{ital n}){sup 63}Co at a bombarding energy of 110 MeV. Discrete {gamma} rays from the channels of interest were investigated using prescaled {gamma} singles, charged-particle{endash}{gamma}, neutron{endash}charged-particle{endash}{gamma}, and charged-particle{endash}{gamma}{endash}{gamma} coincidence techniques. Decay schemes, with level spins deduced from two-point angular distribution data, are presented together with some approximate information on apparent state lifetimes. The experimental results are compared with previous light ion data for these systems and with theoretical shell model predictions. These data represent the first study of medium to high spin states in these nuclei. {copyright} {ital 1996 The American Physical Society.}

Because a knowledge of the 12C/16O ratio is crucial to the understanding of the later evolution of massive stars, new R- and K-matrix fits have been completed using the available angular distribution data from radiative α capture and elastic α scattering on 12C. Estimates of the total 12C(α,γ)16O rate at stellar energies are reported. In contrast with previous work, the analyses generally involve R- and K-matrix fits directly to the primary data, i.e., the energy- and angle-dependent differential yields, with all relevant partial waves fitted simultaneously (referred to here as surface fits). It is shown that, while the E1 part of the reaction is well constrained by a recent experiment on the β-delayed α-particle decay of 16N, only upper limits can be placed on the E2 ground state cross section factor which we take conservatively as SE2(300)

Reaction cross sections for deuterons have been measured for {sup 9}Be, {sup 12}C, {sup 16}O, {sup 28}Si, {sup 40,48}Ca, {sup 58,60}Ni, {sup 112,116,120,124}Sn, and {sup 208}Pb at 37.9, 65.5, and 97.4 MeV. {copyright} {ital 1996 The American Physical Society.}

The binary decay into strongly damped fragments and the quasielastic reactions of the $^{28}\mathrm{Si}$+ $^{16}\mathrm{O}$ system were measured at ${E}_{\mathrm{lab}}=107.5 \mathrm{and} 139.0$ MeV in the angular range of $30\ifmmode^\circ\else\textdegree\fi{}l~{\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}l~150\ifmmode^\circ\else\textdegree\fi{}$ using kinematic coincidence. The loss in the binary decay cross section due to light particle evaporation by the highly excited fragments was evaluated. The $Q$-value-integrated angular distributions of the primary decay exhibit the $\frac{1}{{sin\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}}$ behavior at backward angles, indicating a long lifetime. Mass distributions and the $^{16}\mathrm{O}$/$^{12}\mathrm{C}$ ratio suggest a noncompound process for the reaction mechanism. Coupled-channels calculations, including a great number of channels populated in the reactions, yield good agreement with the experimental angular distributions.

Measurements from the MASS instrument on the WIND spacecraft from late Dec. 94 through Aug. 95 are reported for 20Ne, 16O, and 4He. The average 4He/20Ne density ratio is 566±87 with considerable variability. The average 16O/20Ne density ratio is 8.0±0.6 and is independent, within experimental uncertainty, of solar wind speed. The 20Ne/4He and 16O/4He temperature ratios at the lowest solar wind speeds are consistent with unity, increasing with increasing speed to values exceeding that expected from mass proportionality. 20Ne, 16O, and 4He distribution functions exhibit high energy tails which are well-fit by a kappa function.

The Krell–Ericson transformation provides a local potential that is exactly equivalent to the nonlocal Kisslinger-type potential. The associated scattering wave functions are related by a Perey factor. We examine the properties of examples of these local potentials, based upon low-order multiple scattering theory, at energies ranging from 20 to 291 MeV. The radial shapes of the potentials may display considerable structure in the nuclear surface. The general characteristics of the local real potentials reproduce the five features identified by Friedman from his model-independent analysis of pion scattering data. The Perey factors show a simple, mostly monotonic, behavior.

Spectroscopic factors for one-nucleon knock-out from $^{16}\mathrm{O}$ are calculated for states with low excitation energy in $^{15}\mathrm{N}$ with the Bonn-C potential. A method is proposed to deal with both short- and long-range correlations consistently. For this purpose a Green's function formalism is used and the self-energy in the Dyson equation is approximated as the sum of an energy-dependent Hartree-Fock (HF) term and dispersion and correlation terms of higher order in the G-matrix interaction. This G matrix is obtained by solving the Bethe-Goldstone equation with a Pauli operator which excludes just the model space treated in the subsequent calculation of the self-energy. The energy dependence of the HF energies induces an additional reduction of the spectroscopic factors for quasiparticle states close to the Fermi level by about 10%. Experimental data may signal the need of some further improvement in the treatment of intermediate- and long-range correlations. \textcopyright{} 1996 The American Physical Society.

We suggest that photons with energies between 5 and 10 MeV, generated by the ( ν,ν′pγ) and ( ν,ν′nγ) reactions on 16O, constitute a signal which allows a unique identification of supernova νμ and ντ neutrinos in water Cerenkov detectors. We calculate the yield of such γ events and estimate that a few hundred of them would be detected in Superkamiokande for a supernova at 10 kpc distance.

This experiment has measured cross sections, analyzing powers, and the spin observables P, ${\mathit{D}}_{\mathit{ss}}^{\ensuremath{'}}$, ${\mathit{D}}_{\mathit{sl}}^{\ensuremath{'}}$, ${\mathit{D}}_{\mathit{nn}}^{\ensuremath{'}}$, ${\mathit{D}}_{\mathit{ll}}^{\ensuremath{'}}$, ${\mathit{D}}_{\mathit{ls}}^{\ensuremath{'}}$ for the reaction $^{16}\mathrm{O}$(p,${\mathit{p}}^{\ensuremath{'}}$) at 350 MeV populating three ${4}^{\mathrm{\ensuremath{-}}}$ states. These ``stretched'' states, at excitation energies of 17.79 MeV, 19.80 MeV (both mainly T=0), and 18.98 MeV (mainly T=1), have well known nuclear structure and are used as a nuclear filter to examine the tensor and spin-orbit components of the effective nucleon-nucleus interaction at 350 MeV. A complete set of spin observables was obtained at an angle of 22\ifmmode^\circ\else\textdegree\fi{} in the laboratory frame, whereas the ${\mathit{D}}_{\mathit{ss}}^{\ensuremath{'}}$ and ${\mathit{D}}_{\mathit{sl}}^{\ensuremath{'}}$ observables were measured at laboratory angles of 17, 22, 27, and 32 degrees. The data are compared with distorted-wave impulse approximation calculations from several theoretical models. \textcopyright{} 1996 The American Physical Society.

A study of the $^{12}\mathrm{C}$${(}^{24}$Mg${,}^{16}$O $^{16}\mathrm{O}$${)}^{4}$He reaction has revealed $^{16}\mathrm{O}$ + $^{16}\mathrm{O}$ breakup from states in $^{32}\mathrm{S}$ in the excitation region ranging from 32 to 38 MeV. The spins of the states near 33, 35, and 38 MeV of excitation, obtained from angular correlations, are measured to be (${10}^{+}$ or ${12}^{+}$), (${12}^{+}$ or ${14}^{+}$), and (${14}^{+}$ or ${16}^{+}$), respectively. These may be interpreted as arising from a highly deformed band in $^{32}\mathrm{S}$. \textcopyright{} 1996 The American Physical Society.

Tellurobismuthite (${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$) has been analyzed for Xe isotopes to determine the half-life for double-\ensuremath{\beta} decay of $^{130}\mathrm{Te}$. Excess $^{130}\mathrm{Xe}$ amounts to (6.18\ifmmode\pm\else\textpm\fi{}0.18)\ifmmode\times\else\texttimes\fi{}${10}^{7}$ atom/g with 47.8 wt. % Te, or (1.24\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}${10}^{13}$ for the parent/daughter ratio $^{130}\mathrm{Te}$${/}^{130}$Xe. With (9.3\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}${10}^{7}$ yr for the Xe retention age of Te mineral, this provides (7.9\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}${10}^{20}$ yr for the absolute half-life of $^{130}\mathrm{Te}$ double-\ensuremath{\beta} decay. With this and a literature ratio ${\mathit{T}}_{1/2}$(130)/${\mathit{T}}_{1/2}$(128) of (3.52\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$, we have (2.2\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{24}$ yr for the absolute half-life of $^{128}\mathrm{Te}$ double-\ensuremath{\beta} decay. \textcopyright{} 1996 The American Physical Society.

A comprehensive vibronic assignment of the 3Πu states in the energy region approaching the first ionization threshold of O2 is presented for the first time. Measurements of seventeen 3Πu←X 3Σ−g bands in the 85 800–93 000 cm−1 region of the ground‐state photoabsorption spectra of 16O2 and 18O2 at 79 K are reported, including six bands in the spectrum of 18O2 for the first time. Irregularities in vibrational spacings and in the extent of broadening by predissociation are shown to result from Rydberg‐valence interactions. The observed transitions have been assigned, using semiempirical modeling of the 3Πu Rydberg‐valence interactions based on the coupled‐channel Schrodinger equations technique, to two vibrational progressions with upper states which we call F 3Πu and F′ 3Πu. The F and F′ states are formed from the avoided crossings of the npσu (n=3–5) Rydberg potential‐energy curves by the lowest repulsive 3Πu valence potential‐energy curve.

We present calculations for {sup 8}Be-{sup 8}Be cluster states in {sup 16}O based on our recent schematic coupled-channels model. We justify some of the approximations made in the schematic model in this paper. The present calculations broadly support our assumptions about the states in {sup 16}O which formed the basis of our previous calculations in {sup 24}Mg. {copyright} {ital 1996 The American Physical Society.}

The stopping powers for 0.32–0.43 MeV/A 16O ions in Al, Cu and Ag foils have been measured with the elastic recoil detection (ERD) method. The results are compared with the calculated values of SRIM2000 and previous experimental data.

The fission fragment angular distributions were measured at energies above the fusion barrier, for the systems {sup 11}B and {sup 19}F + {sup 238}U. An analysis of the present data along with those already available for the systems {sup 6,7}Li, {sup 12}C, and {sup 16}O + {sup 238}U was made in terms of the saddle-point statistical model. While the anisotropies were ``normal`` for {sup 6,7}Li, {sup 11}B, {sup 12}C+{sup 238}U systems, the ones for {sup 16}O and {sup 19}F+{sup 238}U systems were found to be ``anomalous.`` The entrance channel mass asymmetry dependence of the anisotropies as observed here is consistent with the expectations of preequilibrium fission dynamics. This result emphasizes the importance of preequilibrium fission in heavy-ion induced fusion-fission reactions.

Proton momentum distributions of the {sup 12}C, {sup 16}O, {sup 40}Ca, {sup 56}Fe, and {sup 208}Pb nuclei are calculated by a model using the natural orbital representation and the experimental data for the momentum distribution of the {sup 4}He nucleus. The model allows realistic momentum distributions to be obtained using only hole-state natural orbitals (or mean-field single-particle wave functions as a good approximation to them). To demonstrate the model two different sets of wave functions were employed and the predictions were compared with the available empirical data and other theoretical results.

Natural abundance 17O NMR data for six classes of N-acyl compounds RCONX are reported: acylazide, acylisocyanate, acylisothiocyanate, diacyldiimide, 1-acylimidazole and N,N′-carbonyldiimidazole. Compared with the normal amide group, they all show strong deshielding (Δδ ≈ 70–130 ppm), which is attributed to diminished resonance of the CO group with the weaker electron donor NX. The high shielding of isocyanate oxygen is attributed to symmetry-based anisotropy effects.

We present a completely microscopic approach for obtaining the preformation factors and the decay widths of [alpha], [sup 12]Ca, and [sup 16]O cluster decays. We start from realistic sing0[sub [minus]0.09][sup +0.13] [mu]b. The new isotope [sup 114]Ba represents the heaviest [ital N]=[ital Z]+2 nucleus known to date. With [Delta][ital E]-[ital E] telescopes we measured the total ([beta]-decay) half-life to be [ital T][sub [beta]]=0.43[sub [minus]0.15][sup +0.30] s and the partial [alpha]-decay half-life to be [ital T][sub [alpha]][ge]1.2[times]10[sup 2] s (1 MeV[le][ital E][sub [alpha]][le]4 MeV) for [sup 114]Ba. With track detectors we found a half-life for spontaneous [sup 12]C emission [ital T][sub [ital C]][ge]1.1[times]10[sup 3] s based on three carbon events.

The reaction {sup 12}C({sup 16}O,7{alpha}) has been studied over the center-of-mass energy range from 37.7 MeV to 51.4 MeV, in a search for evidence for a 7-{alpha} chain state in {sup 28}Si. The yields of the {sup 12}C(0{sub 2}{sup +})-{sup 12}C(0{sub 2}{sup +})-{alpha} and {sup 12}C(0{sub 2}{sup +})-{sup 8}Be-{sup 8}Be final states agree broadly with previous measurements but contain no structure, indicating that a {sup 28}Si chain state is probably not being observed. The yields for the inelastic scattering reaction {sup 12}C+{sup 16}O decaying to other excited states in {sup 12}C and {sup 16}O have also been studied. They also contain no gross structure.

Ion-implanted silicon detectors were irradiated with 18-150 MeV /sup 16/O, 20 MeV /sup 40/Ar, and 53 MeV /sup 110/Xe. A linear increase of the leakage current was observed as a function of the particle fluence up to 2.2/spl times/10/sup 8/ cm/sup -2/. Extracted damage factors are proportional to the averaged nuclear stopping power over five orders of magnitude covering heavy ions studied in the present work and also protons of 25-800 MeV energies. >

The population of excited states in {sup 24}Mg and {sup 28}Si has been investigated through the reactions {sup 12}C({sup 16}O,{sup 12}C{sup 12}C){alpha} and {sup 16}O({sup 16}O,{sup 12}C{sup 16}O){alpha}, at beam energies of 80.5 and 99 MeV. The heavy-ion fragments from the breakup of the {sup 24}Mg and {sup 28}Si nuclei were detected in coincidence, permitting a study of both the reaction kinematics and the spins of the fissioning states. These measurements indicate a series of states in {sup 24}Mg between 25 and 32 MeV with spins ranging from {ital J}=10 to 14 {h_bar}. Evidence was also found for the breakup of {sup 28}Si into {sup 12}C + {sup 16}O from states between 27 and 29 MeV.

Measurements of the reaction {sup 16}O({gamma},{ital n}), made with tagged photons at {ital E}{sub {gamma}}{similar_to}58 MeV, are presented. Neutron energy determination was by time of flight, giving a resolution of {similar_to}2 MeV which enabled the ground-state excitation in {sup 15}O to be resolved from states at 5.2 and 6.2 MeV. Differential cross sections were measured in the angular range 30{degree}--110{degree} and are compared with the predictions of a microscopic, self-consistent Hartree-Fock, random phase approximation model of ({gamma},{ital N}) reactions. The implications for the theoretical description are discussed, notably the dependence of the ({gamma},{ital n}) cross section on meson exchange currents and final-state rescattering.