Recent Articles

Isovector M1 collective excitations in light nuclei

L. Chaves and A. Poves

Phys. Rev. C 34, 1137 (1986) - Published 1 September, 1986

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We calculate the M1 strength functions of ${}^{20}{Ne}$ and ${}^{36}{Ar}$ using the wave functions obtained in a full sd-shell configuration-mixing calculation. Our results strongly suggest that the $1^{+}$ T=1 state of ${}^{20}{Ne}$ at 11.24 MeV is the counterpart in light nuclei of the recently discovered ‘‘twisting mode’’ in heavy nuclei.

Comment on ‘‘Triad of three-particle Lippmann-Schwinger equations’’

F. S. Levin and W. Sandhas

Phys. Rev. C 34, 1140 (1986) - Published 1 September, 1986

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All existing derivations of the triad of Lippmann-Schwinger equations have been rejected by Benoist-Gueutal as lacking in mathematical rigor, leading her to conclude that the question of the validity of the triad is still to be settled. We settle this question by deriving the triad directly from the mathematically rigorous set of Faddeev wave function equations, using one of the ‘‘rejected’’ proofs. This analysis also yields a new derivation of the relation between the Faddeev components and the full scattering state.

Comment on ‘‘Triad of three-particle Lippmann-Schwinger equations’’

E. Gerjuoy

Phys. Rev. C 34, 1143 (1986) - Published 1 September, 1986

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It is argued that despite Benoist-Gueutal’s criticisms, the inhomogeneous and homogeneous Lippmann-Schwinger equations describing two-body collisions in three-particle systems are valid. In particular, it is shown that the integrals which occur in Gerjuoy’s derivation of those equations can be meaningfully defined.

Erratum: Few channel models of nuclear reactions: Proton and deuteron elastic scattering expansions

R. Kozack and F. S. Levin

Phys. Rev. C 34, 1149 (1986) - Published 1 September, 1986

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Doubly decoupled structures in ${}^{182}$ ,184Ir

A. J. Kreiner, P. Thieberger, and E. K. Warburton

Phys. Rev. C 34, 1150(R) (1986) - Published 1 September, 1986

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A search for structures in which both valence neutron and proton occupy predominantly Ω=(1/2) orbits, called doubly decoupled, has been successfully conducted in ${}^{182}$ ,184Ir. These evaporation residues were populated through the ${}^{172}$ ,174Yb $(^{14}$ N,4n) fusion reactions and studied using γ-ray spectroscopy techniques.

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Identification of the first excited state in the N=Z nucleus ${}_{32}^{64}{Ge}_{32}$

S. S. L. Ooi, R. F. Davie, D. Sinclair, C. J. Lister, B. J. Varley, and H. G. Price

Phys. Rev. C 34, 1153(R) (1986) - Published 1 September, 1986

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Gamma-rays from ${}^{64}{Ge}$ have been investigated using the reaction ${}^{12}C$ $(^{54}$ Fe,2nγ $)^{64}$ Ge at 150 MeV beam energy. The first excited state was found to be 901.6±0.5 keV. The observation of pure neutron evaporation from a very neutron deficient compound nucleus is potentially important for the prospect of observing heavier exotic self-conjugate systems.

Microscopic theory of the sup3H+α system with the multichannel resonating-group method

T. Kaneko, M. Shirata, H. Kanada, and Y. C. Tang

Phys. Rev. C 34, 771 (1986) - Published 1 September, 1986

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The effects of specific distortion in the ${}^{3}$ H+α system are examined, within the framework of the multiconfiguration resonating-group method, by including a large number of pseudo-inelastic cluster configurations involving pseudo-states of both ${}^{3}H$ and α clusters. In this investigation, the variational stability conditions for both ${}^{3}H$ and α clusters are well satisfied. The result shows that the effects of distortion are important to explain the main characteristics of the ${}^{3}$ H+α system, and that the dependence of the distortion effect on the choice of the nucleon-nucleon potential is rather weak. In addition, it is found that the distortion effect of the α cluster is enhanced when the triton-cluster distortion is properly considered.

Potential model calculation of proton-proton bremsstrahlung using the Paris potential

R. L. Workman and Harold W. Fearing

Phys. Rev. C 34, 780 (1986) - Published 1 September, 1986

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Cross sections and analyzing powers are calculated for proton-proton bremsstrahlung (ppγ) using the Paris and extended Reid soft-core potentials. One pion exchange contributions have been added for partial waves with J≥6. Relativistic spin corrections, certain other relativistic corrections, and some Coulomb corrections have also been added. The calculation utilizes fully relativistic kinematics and is performed in the center of mass frame in order to put to zero the leading contribution of the double scattering terms. This is the first ppγ calculation to use one of the modern theoretically based nucleon-nucleon potentials. The results of this calculation are compared with experimental data, as well as older potential model and soft-photon approximation calculations. The off-shell behaviors of the Paris and extended Reid potentials are also investigated. We find that the analyzing powers are sensitive to details of the calculation. Asymmetry data are expected from a new TRIUMF ppγ experiment which will provide the first opportunity for a detailed comparison of such data with a modern potential model calculation.

Structure of ${}^{96}{Ru}$

E. Adamides, J. Sinatkas, L. D. Skouras, A. C. Xenoulis, E. N. Gazis, C. T. Papadopoulos, and R. Vlastou

Phys. Rev. C 34, 791 (1986) - Published 1 September, 1986

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The level structure and the decay properties of levels in ${}^{96}{Ru}$ up to 3.3 MeV of excitation have been investigated via singles directional-correlation and Doppler-shift measurements following the ${}^{96}{Ru}$ (p,p’γ) reaction at 7.0 MeV proton energy. The level and decay scheme of ${}^{96}{Ru}$ was supplemented and clarified on the basis of γγ-coincidence measurements. The directional correlations for many transitions provided (i) reliable branching ratios, (ii) $J^{π}$ assignments, and (iii) multipole mixing ratios δ(E2/M1) from analysis of the correlations via the compound statistical theory for nuclear reactions. In many cases the measured cross sections helped for a more precise assignment of $J^{π}$ values. Lifetimes for four states and limits to three additional states were obtained by the Doppler-shift attenuation method from singles spectra, taken in the presence of standards, at eight angles between 0° and 110° to the beam direction. For several transitions in ${}^{96}{Ru}$ values or limits of B(E1), B(E2), and B(M1) were obtained. The levels of ${}^{96}{Ru}$ and their decay properties were calculated in the shell-model framework and are compared with the corresponding experimental quantities.

Neutron total cross section of ${}^{40}{Ca}$ and cross section difference of ${}^{44}{Ca}$

H. S. Camarda, T. W. Phillips, and R. M. White

Phys. Rev. C 34, 810 (1986) - Published 1 September, 1986

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We have used a 100-MeV electron linac and neutron time-of-flight facility to measure the neutron total cross section of ${}^{40}{Ca}$ and the cross section difference of ${}^{44}$ Ca $-^{40}$ Ca for incident neutron energies of 6–60 MeV. Optical model calculations of ${}^{40}{Ca}$ $σ_{T}$ have been made and compared to the data. Modifications of a global set of optical model parameters necessary to fit the ${}^{44}$ Ca $-^{40}$ Ca difference data are discussed. Using these parameters we calculated Δ=〈 $r^{2}$ $〉_{44}^{1 / 2}$ -〈 $r^{2}$ 〉 ${}_{40}^{1 / 2}$ for the real part of the potential and found a value of 0.16±0.05 fm. The value of Δ is sensitive to the difference in the matter distribution of the ${}^{44}{Ca}$ and ${}^{40}{Ca}$ nuclei and our result is consistent with the same quantity determined from low energy alpha particle scattering.

Analyzing powers for ${}^{207}{Pb}$ (t→,p $)^{209}$ Pb at 17 MeV as evidence for multistep contributions

W. W. Daehnick, Ronald E. Brown, E. R. Flynn, R. A. Hardekopf, and J. C. Peng

Phys. Rev. C 34, 815 (1986) - Published 1 September, 1986

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Analyzing powers and differential cross sections for ${}^{207}{Pb}$ (t→,p $)^{209}$ Pb have been studied at 17 MeV in order to identify the effects of second-order (t→,p) transfer mechanisms. Angular distributions for transitions to seven single-particle states in ${}^{209}{Pb}$ and to the first pairing vibration state in ${}^{209}{Pb}$ were measured for the angular range 6?(de≤theta≤70°. The observed L dependence of the differential cross sections is adequately reproduced by one-step finite-range distorted-wave Born approximation calculations, but the absolute magnitude of these transitions is underpredicted by factors ranging from 1.25 to 2.5.

The analyzing powers for the transitions to the seven well-known single-particle states are significantly different from each other and do not follow one-step distorted-wave Born approximation predictions or any other simple dependence on the transferred angular momentum L. The observed analyzing powers for the L=5 transfers to the ${(9 / 2)}^{+}$ ground state and the ${(11 / 2)}^{+}$ state at 0.778 MeV differ even in sign. It is found that the inclusion of two-step second-order distorted-wave Born approximation channels, which treat the dominant single-neutron stripping channels as intermediate states, can yield qualitatively correct analyzing powers. In agreement with experiment, two-step calculations predict analyzing powers which depend strongly on the spins ( $j_{1}$ , $j_{2}$ ) of the transferred neutrons.

However, quantitatively satisfactory results have only been obtained if an ‘‘adiabatic’’ scattering potential for the intermediate projectile is used. The adiabatic potential, obtained as the sum of a proton and a neutron potential, gives a considerably deeper absorptive part than the empirical deuteron optical model potential. This representation of the intermediate scattering state is supported by a recent two-nucleon transfer model by Austern and Kawai. The inclusion of sequential stripping channels also gives a needed enhancement of the absolute cross sections, although zero-range calculations do not always give quantitatively correct enhancements.

Differential cross sections and analyzing powers for neutron elastic scattering from ${}^{89}Y$ between 8 and 17 MeV

G. M. Honoré, R. S. Pedroni, C. R. Howell, H. G. Pfützner, R. C. Byrd, G. Tungate, and R. L. Walter

Phys. Rev. C 34, 825 (1986) - Published 1 September, 1986

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Differential cross sections and analyzing powers for neutron elastic scattering from ${}^{89}Y$ have been measured at energies from 8 to 17 MeV using a neutron time-of-flight facility. The data have been analyzed with the spherical optical model and excellent representations are achieved at all energies with the derived optical potential parameters, which were constrained to vary linearly with energy. Comparisons have been made to two previously reported global spherical optical models as well.

Parities of bound dipole states in ${}^{40}{Ar}$

H. Wickert, K. Ackermann, K. Bangert, U. E. P. Berg, C. Bläsing, W. Naatz, A. Ruckelshausen, S. Schennach, and R. Stock

Phys. Rev. C 34, 835 (1986) - Published 1 September, 1986

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Nuclear resonance fluorescence experiments with linearly polarized bremsstrahlung were performed to determine parities of strong dipole transitions in ${}^{40}{Ar}$ . A total of 14 transitions—ten of them previously unknown—in the energy range from 4.7 to 10.2 MeV could be identified. From this experiment it is evident that the main dipole strength to bound states is due to E1 excitations. An upper limit of B(M1)↑<0.5 $μ_{N^{2}}$ was found for individual magnetic dipole excitations in ${}^{40}{Ar}$ in the energy region below neutron threshold.

Spherical optical model potential for the Re/Os stellar nucleosynthesis chronometer from s-wave neutrons on ${}^{186}$ ,187,188Os

R. R. Winters, R. F. Carlton, J. A. Harvey, and N. W. Hill

Phys. Rev. C 34, 840 (1986) - Published 1 September, 1986

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This paper reports resonance parameters and spherical optical model potentials obtained from the analyses of neutron transmission measurements for ${}^{186}$ ,188Os over the incident neutron energy range 27–1000 eV and for ${}^{187}{Os}$ over the range 27–140 eV. Multilevel R-matrix analyses of 77 s-wave resonances yielded sets of resonance parameters ( $E_{λ}$ , $Γ_{n)}$ and the associated external (background) R functions. The statistical properties of the resonance parameters, mean-level spacings, and strength functions are reported. The external R functions and strength functions were used to determine spherical optical model potential well depths, which in the case of ${}^{187}{Os}$ we find to be strongly dependent on the spin of the compound nucleus. These optical model well depths can be used to estimate the capture cross section of the first excited state in ${}^{187}$ Os+n. Since this state is highly populated at stellar temperatures, the ratio of excited to ground-state capture cross sections is an important parameter in using the s-process model of stellar nucleosynthesis to determine what fraction of the abundance of ${}^{187}{Os}$ should be ascribed to the radiogenic decay of ${}^{187}{Re}$ . That fraction determines, in part, the estimate of the duration Δ of stellar nucleosynthesis to be derived from ${}^{187}{Re}$ beta decay. A determination of Δ for the Re/Os chronometer based on our data leads to an age of the universe of (17±3)× $10^{9}$ yr.

Effect of ${}^{8}{Be}$ decay on nuclear temperature measurements

C. Bloch, W. Benenson, E. Kashy, D. J. Morrissey, R. A. Blue, R. M. Ronningen, and H. Utsunomiya

Phys. Rev. C 34, 850 (1986) - Published 1 September, 1986

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We have investigated the effect of ${}^{8}{Be}$ decay on nuclear temperature measurements in the ${}^{14}$ N+Ag reaction at E/A=35 MeV. We have determined what percentage of the apparent ${}^{7}{Li}$ spectrum is due to the identification of the coincident alpha particles from ${}^{8}{Be}$ decay as ${}^{7}{Li}$ . This information, coupled with previously published temperature measurements, produces agreement between temperatures obtained from ${}^{7}{Li}$ excited state populations and those obtained from ${}^{7}{Be}$ excited state populations. Additionally, we measured the production of the excited states of ${}^{7}{Li}$ and ${}^{7}{Be}$ nuclei emitted from the same reaction at beam energies of E/A=20 MeV and E/A=25 MeV. The temperatures extracted from these excited state populations are consistent with one another when corrected for the ${}^{8}{Be}$ contamination of the ${}^{7}{Li}$ spectra.

Light particle emission in ${}^{16}{induced}$ reactions on ${}^{12}C$ , ${}^{27}{Al}$ , and ${}^{197}{Au}$ at E/A=25 MeV

C. B. Chitwood, D. J. Fields, C. K. Gelbke, D. R. Klesch, W. G. Lynch, M. B. Tsang, T. C. Awes, R. L. Ferguson, F. E. Obenshain, F. Plasil, R. L. Robinson, and G. R. Young

Phys. Rev. C 34, 858 (1986) - Published 1 September, 1986

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Single- and two-particle inclusive cross sections of light particles (p,d,t) were measured for ${}^{16}{induced}$ reactions on ${}^{12}C$ , ${}^{27}{Al}$ , and ${}^{197}{Au}$ at E/A=25 MeV. The energy and angular distributions indicate that these particles originate from violently interacting subsets of the projectile-target system. For reactions on ${}^{197}{Au}$ , the two-particle correlations at large relative momenta indicate an ordered motion in the entrance channel reaction plane which is superimposed on the random velocities of the constituents of these subsets. For reactions on ${}^{12}C$ , the two-particle correlations appear to be dominated by momentum and energy conservation.

pn to d and αpn to αd emission ratios in heavy-ion-induced reactions

E. N. Gazis, C. T. Papadopoulos, R. Vlastou, and A. C. Xenoulis

Phys. Rev. C 34, 872 (1986) - Published 1 September, 1986

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The competition between pn and d as well as between αpn and αd evaporation leading to the production of the same residual nuclei has been measured for nine and five heavy-ion-induced nuclear reactions, respectively, each at several bombarding energies. The deduced $σ_{pn / σ_{d}}$ ratios have been found to be in very good agreement with the predictions of a previously extracted empirical equation. The ratios $σ_{α pn / σ_{α d}}$ do not seem to depend on either the interacting system or the maximum excitation energy available to the residual nucleus.

Clues to the shapes of very hot nuclei: Calculated patterns for evaporative emission from deformed nuclei

N. N. Ajitanand, G. La Rana, R. Lacey, David J. Moses, Louis C. Vaz, G. F. Peaslee, D. M. de Castro Rizzo, Morton Kaplan, and John M. Alexander

Phys. Rev. C 34, 877 (1986) - Published 1 September, 1986

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Evaporation-like emission of light particles (n, H, He, . . .) has been observed for many nuclear reactions that populate composite nuclei with temperatures of up to ≊5 MeV and spins as high as ≊150ħ. The measured average energies for the light charged particles are often significantly lower than calculations for evaporation from spherical nuclei. Detailed calculations have not been reported for the role of deformation in evaporative emission patterns, and thus the interpretation of such data has been severely limited. In this paper we describe a method for making evaporation calculations for deformed nuclei, and we present results for several systems with temperatures of 2–5 MeV. The trends of the calculated results are compared to those for spherical emitters in order to get a feeling for those effects peculiar to the deformations. The patterns of calculated spectra and angular distributions encourage the notion that such studies can give valuable clues to the shapes of these very hot nuclei.

Anomalous behavior of singly charged relativistic secondary particles produced in collisions of ${}^{16}O$ ions with emulsion nuclei at ∼2A GeV

Barbara Judek

Phys. Rev. C 34, 890 (1986) - Published 1 September, 1986

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Reaction mean free paths in emulsions, of the secondary particles from ${}^{16}O$ collisions, show normal behavior for the particles produced with P sintheta<200 MeV/c (theta is the lab emission angle and P the incident momentum per nucleon). For 200≤P sintheta<400 MeV/c, the particles exhibit shorter mean free paths for the first few cm from their origin than at larger distances. Conventional explanations of this result are rejected at 99.5% confidence level. The data are consistent with the presence of an ∼6% anomalous component with a mean free path of 1.8 cm. Primary deuteron mean free path at 2.1A GeV, measured for comparison, is 20.7±2.6 cm.

Geometric interpretation of the adiabatic model for heavy-ion fusion

M. A. Nagarajan, A. B. Balantekin, and N. Takigawa

Phys. Rev. C 34, 894 (1986) - Published 1 September, 1986

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The relation between the finite basis adiabatic model and the classical adiabatic model (corresponding to a complete set of degenerate states) is elucidated when the internal system is rotational or vibrational. It is shown that the finite basis results can be obtained from the classical model results using the Gaussian quadrature to evaluate the former and Hermite quadrature for the latter.

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Isovector M1 collective excitations in light nuclei

Comment on ‘‘Triad of three-particle Lippmann-Schwinger equations’’

Comment on ‘‘Triad of three-particle Lippmann-Schwinger equations’’

Erratum: Few channel models of nuclear reactions: Proton and deuteron elastic scattering expansions

Doubly decoupled structures in ${}^{182}$ ,184Ir

Identification of the first excited state in the N=Z nucleus ${}_{32}^{64}{Ge}_{32}$

Microscopic theory of the sup3H+α system with the multichannel resonating-group method

Potential model calculation of proton-proton bremsstrahlung using the Paris potential

Structure of ${}^{96}{Ru}$

Neutron total cross section of ${}^{40}{Ca}$ and cross section difference of ${}^{44}{Ca}$

Analyzing powers for ${}^{207}{Pb}$ (t→,p $)^{209}$ Pb at 17 MeV as evidence for multistep contributions

Differential cross sections and analyzing powers for neutron elastic scattering from ${}^{89}Y$ between 8 and 17 MeV

Parities of bound dipole states in ${}^{40}{Ar}$

Spherical optical model potential for the Re/Os stellar nucleosynthesis chronometer from s-wave neutrons on ${}^{186}$ ,187,188Os

Effect of ${}^{8}{Be}$ decay on nuclear temperature measurements

Light particle emission in ${}^{16}{induced}$ reactions on ${}^{12}C$ , ${}^{27}{Al}$ , and ${}^{197}{Au}$ at E/A=25 MeV

pn to d and αpn to αd emission ratios in heavy-ion-induced reactions

Clues to the shapes of very hot nuclei: Calculated patterns for evaporative emission from deformed nuclei

Anomalous behavior of singly charged relativistic secondary particles produced in collisions of ${}^{16}O$ ions with emulsion nuclei at ∼2A GeV

Geometric interpretation of the adiabatic model for heavy-ion fusion

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