Recent Articles

Effects of entrance channel and compound nucleus in the fusion cross sections for ${}^{28}$ Si $+^{28}$ Si, ${}^{16}$ O $+^{40}$ Ca, ${}^{32}$ S $+^{30}$ Si, and ${}^{12}$ C $+^{50}$ Cr

Y. Nagashima, J. Schimizu, T. Nakagawa, Y. Fukuchi, W. Yokota, K. Furuno, M. Yamanouchi, S. M. Lee, N. X. Dai, T. Mikumo, and T. Motobayashi

Phys. Rev. C 33, 176 (1986) - Published 1 January, 1986

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In order to study the physics responsible for a limitation in angular momentum in heavy-ion fusion reactions, fusion cross sections for the reactions ${}^{28}$ Si $+^{28}$ Si, ${}^{16}$ O $+^{40}$ Ca, ${}^{32}$ S $+^{30}$ Si, and ${}^{12}$ C $+^{50}$ Cr have been measured at several incident energies covering lower and higher energy regions by detecting the yields of the fusion-evaporation residues. The limiting angular momenta for fusion are extracted from the measured fusion cross sections and compared with calculations based upon several models. Through the systematic study of different entrance channels forming the same compound nucleus, a strong entrance channel effect has been observed for very asymmetric systems. Our conclusion is that the entrance channel is significant in limiting the fusion cross section in the higher energy region.

Few-nucleon transfer in quasi-elastic collisions at 20 MeV/nucleon

H. Utsunomiya, E. C. Deci, R. A. Blue, L. H. Harwood, R. M. Ronningen, K. Siwek-Wilczynska, J. Wilczynski, and D. J. Morrissey

Phys. Rev. C 33, 185 (1986) - Published 1 January, 1986

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We report measurements of the isotopic distributions of targetlike fragments in coincidence with nitrogen, carbon, and boron isotopes from the reaction of 20 MeV/nucleon ${}^{14}N$ with ${}^{165}{Ho}$ and ${}^{164}{Dy}$ . The binary nature of the reaction was studied by observing particle-γ-ray coincidences; projectilelike fragments were identified near the classical grazing angle with a telescope consisting of silicon surface barrier detectors, and the targetlike fragments were identified by observing their discrete deexcitation γ rays in either of two high purity germanium detectors. The following reactions were studied: ${}^{164}{Dy}$ $(^{14}$ N,χxn), ${}^{164}{Dy}$ $(^{14}$ N,χαxn), ${}^{165}N$ ,Cxn), ${}^{165}{Ho}$ $(^{14}$ N,Cαxn), where χ=nitrogen or boron isotopes. The inclusive energy spectra of the projectilelike fragments are reasonably described by either the extended Serber or the Friedman model of projectile breakup. Such interpretations of the reaction mechanism were further tested by comparing the targetlike fragment isotopic distributions to those expected from transfer of the unobserved breakup fragment to the target followed by statistical decay. The agreement of the predicted targetlike fragment isotopic distributions with the present data is remarkably good.

Phenomenological consequences of a hypothetical light neutral particle in heavy ion collisions

J. Reinhardt, A. Schäfer, B. Müller, and W. Greiner

Phys. Rev. C 33, 194 (1986) - Published 1 January, 1986

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We discuss the possibility that the line structure observed in the spectrum of the positrons produced in heavy ion collisions is due to the decay of a new neutral elementary particle. We argue that this can be ruled out unless one is willing to accept fine tuning of parameters, or to assume the dominance of nonlinear effects.

Low energy $π^{+}$ inelastic scattering from nuclei to the continuum

K. A. Aniol, D. T. Chiang, K. G. R. Doss, I. Halpern, M. Khandaker, D. W. Storm, D. R. Tieger, P. D. Barnes, B. Bassalleck, N. J. Colella, S. A. Dytman, R. A. Eisenstein, R. Grace, C. Maher, D. Marlow, P. Pile, R. Rieder, F. Takeutchi, W. R. Wharton, J. F. Amann, and J. Julien

Phys. Rev. C 33, 208 (1986) - Published 1 January, 1986

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Differential cross sections $d^{2}$ σ/dΩ dE have been measured with a germanium telescope for the ( $π^{+}$ , $π^{+ ’}$ ) reaction on C, Ca, Sn, and Pb at incident energies of 67, 85, and 100 MeV. The yields at backward angles along with available information on total reaction cross sections are interpreted in terms of a simple classical model in which it is assumed that free-space pion nucleon interaction parameters prevail inside the nucleus. Among the experimental findings which can be accounted for in terms of the model (to within 10–15 %) are the measured pion reaction cross sections and their dependence on target mass, the energy and mass dependences of the differential scattering cross section at backward angles, and the ratio of normal to charge exchange scattering cross sections. The model appears to overestimate the ratios $π^{-}$ to $π^{+}$ reaction and scattering cross sections but there appear to be some inconsistencies in the available data.

Energy dependence of ${}^{24}{(p \to}$ ,d) cross section and analyzing-power measurements from 50 to 150 MeV

D. W. Miller, J. D. Brown, D. L. Friesel, W. W. Jacobs, W. P. Jones, H. Nann, P. Pichardo, J. Q. Yang, P. W. F. Alons, and J. J. Kraushaar

Phys. Rev. C 33, 22 (1986) - Published 1 January, 1986

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Detector telescope measurements of cross sections and analyzing powers for the ${}^{24}{(p \to}$ ,d) reaction to states of ${}^{23}{Mg}$ up to 4.36 MeV in excitation are reported for bombarding energies of 49.2 and 150.3 MeV. Taken together with earlier spectrometer measurements at 94.8 MeV at the same laboratory, a smooth energy dependence of the results for transitions leading to ${1 / 2}^{+}$ , ${1 / 2}^{-}$ , ${(3 / 2)}^{-}$ , ${(3 / 2)}^{+}$ , ${(5 / 2)}^{+}$ , and ${(7 / 2)}^{+}$ states is obtained. Exact finite-range, adiabatic, distorted-wave analyses give reasonable fits in most cases to the cross-section angular distributions using an rms radius prescription for the bound-state geometry, and the energy-dependent set of proton optical potentials employed by Hatanaka extrapolated to higher energies; however, the calculated analyzing powers often differ in magnitude and shape from experiment. With the exception of the $l_{n}$ =0 transitions, spectroscopic factors derived from this particular comparison exhibit only a relatively small energy dependence.

Theoretical antideuteron-nucleus absorptive cross sections

W. W. Buck, J. W. Norbury, L. W. Townsend, and J. W. Wilson

Phys. Rev. C 33, 234 (1986) - Published 1 January, 1986

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Antideuteron-nucleus absorptive cross sections for intermediate to high energies are calculated using an ion-ion optical model. Good agreement with experiment (within 15 percent) is obtained in this same model for p¯-nucleus cross sections at laboratory energies up to 15 GeV. We describe a technique for estimating antinucleus-nucleus cross sections from NN¯ data and suggest that further cosmic ray studies to search for antideuterons and other antinuclei be undertaken.

Spin-rotation parameter Q for 800 MeV proton elastic scattering from ${}^{16}O$ , ${}^{40}{Ca}$ , and ${}^{208}{Pb}$

R. W. Fergerson, M. L. Barlett, G. W. Hoffmann, J. A. Marshall, E. C. Milner, G. Pauletta, L. Ray, J. F. Amann, K. W. Jones, J. B. McClelland, M. Gazzaly, and G. J. Igo

Phys. Rev. C 33, 239 (1986) - Published 1 January, 1986

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The spin-rotation parameter Q(theta) was measured for 800 MeV p→ $+^{16}$ O, ${}^{40}{Ca}$ , and ${}^{208}{Pb}$ elastic scattering for 2°≤ ${theta}_{lab \leq 21 °}$ . Microscopic ‘‘relativistic’’ (Dirac equation dynamics) and ‘‘nonrelativistic’’ (Schrödinger equation dynamics) optical model predictions are compared with the data. Slight preference for the relativistic impulse approximation approach is observed, but a marked mass dependence of the quality of the fit is evident. Other calculations are presented which suggest that inclusion of nuclear two-body correlation effects in the relativistic impulse approximation model might lead to better agreement with experiment.

Medium energy probes and the interacting boson model of nuclei

J. N. Ginocchio, T. Otsuka, R. D. Amado, and D. A. Sparrow

Phys. Rev. C 33, 247 (1986) - Published 1 January, 1986

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The Glauber approximation for medium energy scattering of hadronic projectiles from nuclei is combined with the interacting boson model of nuclei to produce a transition matrix for elastic and inelastic scattering in algebraic form which includes coupling to all the intermediate states. We present closed form analytic expressions for the transition matrix elements for the three dynamical symmetries of the interacting boson model. We show the effect of channel coupling on the elastic and inelastic differential cross sections for proton scattering on nuclei which behave like a spherical quadrupole vibrator, a γ-unstable rotor, and both prolate and oblate axially symmetric rotors.

Problem of backward proton production

Y. Haneishi and T. Fujita

Phys. Rev. C 33, 260 (1986) - Published 1 January, 1986

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The problem of backward proton production in proton-nucleus collisions at intermediate energies is discussed. We develop a model which is based on the correlated two-nucleon-cluster picture. Feynman diagrams including intermediate Δ-resonance states are evaluated. The model is applied first to the deuteron target (p+d→p+X) at intermediate energies. This presents a good test for the elementary process in our model. Our calculation reproduces well the observed energy spectra of backward protons. Then the model is applied to heavier nuclear targets. There we employ the Fermi momentum distribution which is deduced from other sources of information. This contains high momentum components that play a crucial role in reproducing the high energy part of the backward proton spectra. The model describes remarkably well a wide range of the single particle energy spectra as well as the angular distributions of the backscattered proton. As a further test of the model, we calculate the coincidence spectra of the backward- and the forward-going protons at 800 MeV. The calculation reproduces well the shape (particularly two mountains in the contour plot) of the coincidence experiment which has recently been done by Miake et al. The present analysis strongly supports the existence of the high momentum components in the nuclear Fermi motion. This seems to be rather universal from light to heavy nuclei, and may reflect a new length scale inside the nucleus.

Estimate of the pionic contribution to very forward electron scattering from ${}^{3}{He}$ by surprisal analysis

Yoshiyuki Kawazoe and Tatsuo Tsukamoto

Phys. Rev. C 33, 275 (1986) - Published 1 January, 1986

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Surprisal analysis is applied to the very forward electron scattering data on ${}^{3}{He}$ , for which the three-body theory fails to explain the excitation function. This discrepancy is often attributed to higher momentum components in the wave function of ${}^{3}{He}$ . An explicit expression for the final state densities including the nucleon and pion degrees of freedom is proposed. The present surprisal analysis succeeds in reproducing the experimental data without calling upon higher momentum components and suggests that even in the so-called quasielastic scattering region, not only nucleons but also a considerable number of pions are emitted in electron scattering.

Pion single charge exchange angular distributions at $T_{π}$ =48 MeV

M. J. Leitch, H. W. Baer, J. D. Bowman, M. D. Cooper, E. Piasetzky, U. Sennhauser, H. J. Ziock, F. Irom, P. B. Siegel, and M. A. Moinester

Phys. Rev. C 33, 278 (1986) - Published 1 January, 1986

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Angular distributions for pion single charge exchange to the isobaric analog state were measured for ${}^{39}K$ and ${}^{48}{Ca}$ at $T_{π}$ =48 MeV. The cross sections on ${}^{39}K$ and ${}^{48}{Ca}$ exhibit a less deep minimum at zero degrees than was seen previously on ${}^{15}N$ . The large-angle ${}^{39}K$ cross sections are roughly equal to those for ${}^{15}N$ , while the 0° to 60° ${}^{48}{Ca}$ cross sections are approximately four times larger. The extrapolated zero-degree center-of-mass cross sections are 2.7±1.0 μb/sr for ${}^{15}N$ , 12±5 μb/sr for ${}^{39}K$ , and 110±25 μb/sr for ${}^{48}{Ca}$ , and the angle-integrated cross section for ${}^{39}K$ is 557±65 μb. The large back-angle cross sections for ${}^{39}K$ are attributed to strong quadrupole contributions to the isobaric analog state transition.

Relativistic treatment of p¯-atom shifts and widths

D. A. Sparrow

Phys. Rev. C 33, 287 (1986) - Published 1 January, 1986

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The relativistic approach to p¯-nucleus interactions is extended to p¯-atom interactions. Both the relativistic impulse approximation and Dirac phenomenology are used to obtain low energy p¯-nucleus potentials. The impulse approximation is qualitatively successful at describing the p¯-atom data. For ${}^{12}C$ , potentials fit to the 46.8 MeV data yield the experimental shifts and widths well within the assigned errors.

Photoactivation of isomeric levels in ${}^{113}{In}$ and ${}^{87}{Sr}$

M. Krmar, A. Ljubiić, B. A. Logan, and M. Bistrović

Phys. Rev. C 33, 293 (1986) - Published 1 January, 1986

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A ${}^{60}{Co}$ source has been used to photoactivate the 392 keV ( $T_{1 / 2}$ ∼99.5 min) isomeric level of ${}^{113}{In}$ and the 388 keV ( $T_{1 / 2}$ ∼2.8 h) isomeric level of ${}^{87}{Sr}$ . As observed in investigations of ${}^{115}{In}$ and ${}^{111}{Cd}$ , nonresonant processes were found to make significant contributions to the excitation of isomeric levels.

Shell-model calculation of ${}^{99}{Tc}$ beta decay in astrophysical environments

K. Takahashi, G. J. Mathews, and S. D. Bloom

Phys. Rev. C 33, 296 (1986) - Published 1 January, 1986

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Using the shell-model Lanczos method, we calculate the Gamow-Teller matrix elements for beta transitions of astrophysical interest from excited states of ${}^{99}{Tc}$ ${((7 / 2)}^{+}$ ,141 keV; ${(5 / 2)}^{+}$ ,181 keV) to the ground and excited states of ${}^{99}{Ru}$ . The level schemes of low-lying positive-parity states in these nuclei and in the analogous isotonic nuclei ${}^{97}-^{97}$ Mo are reproduced fairly well within a model space consisting of low-seniority excitations in the 1g2d shell, which are mixed via the Kallio-Kolltveit effective interaction. The calculations lead to a ${}^{99}{Tc}$ half-life of ∼20 yr at a stellar temperature of 3× $10^{8}$ K typical for the s process with a ${}^{22}{(α}$ ,n $)^{25}$ Mg neutron source. Referring to recent studies of thermal-pulse s-process models, we stress that a substantial amount of ${}^{99}{Tc}$ can survive the s process in spite of its enormously enhanced decay rate. The factual observation of ${}^{99}{Tc}$ at the surface of certain stars, therefore, does not necessarily contradict an s-process scenario with ${}^{22}{Ne}$ as a neutron source.

R-matrix analysis of the $β^{\mp}$ -delayed alpha spectra from the decay of ${}^{8}{Li}$ and ${}^{8}B$

E. K. Warburton

Phys. Rev. C 33, 303 (1986) - Published 1 January, 1986

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The general question of the analysis of beta-delayed particle emission is discussed. It is emphasized that neither an integrated Fermi function nor a beta branching ratio is, in general, rigorously defined for beta decay to a specific level (resonance). As an example, spectra of breakup α particles observed following ${}^{8}{Li}$ ( $β^{-}$ $)^{8}$ Be and ${}^{8}B$ ( $β^{+}$ $)^{8}$ Be are analyzed by the many-level one-channel approximation of R-matrix theory. In addition, the L=2 α-α elastic scattering phase shifts are analyzed up to $E_{α}$ =34 MeV. It is found that satisfactory fits are obtained without introducing intruder states below 26-MeV excitation. Gamow-Teller matrix elements are extracted for decay to the 3.0-MeV first-excited state of ${}^{8}{Be}$ and for the doublet near 16 MeV. The width and location of the ${}^{8}{Be}$ 3.0-MeV state are also obtained. The results are compared to shell-model predictions.

Proton stripping to $6^{-}$ stretched states of ${}^{26}{Al}$

R. J. Peterson, B. L. Clausen, J. J. Kraushaar, H. Nann, W. W. Jacobs, R. A. Lindgren, and M. A. Plum

Phys. Rev. C 33, 31 (1986) - Published 1 January, 1986

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The (α,t) stripping reaction on ${}^{25}{Mg}$ was used to measure the $f_{7 / 2}$ proton spectroscopic factors for the $4^{-}$ ;T=0 (5.39 MeV), $6^{-}$ ;0 (6.89 and 7.53 MeV), and $6^{-}$ ;1 (9.26, 11.97, 12.40, and 12.55 MeV) states of ${}^{26}{Al}$ . The T=1 levels were identified with the aid of their analogs known in ${}^{26}{Mg}$ by inelastic electron scattering. Only 31% of the single particle strength is found for the two $6^{-}$ ;0 levels and only 59% is found for five $6^{-}$ ;1 levels. The lowest $6^{-}$ ;1 state has more than twice the spectroscopic factor of any of the others. Further $6^{-}$ candidate states are also examined.

Thermostatic properties of nuclear matter at low temperature in a saturating chiral field theory

Safayet Karim Chowdhury and Sasabindu Sarkar

Phys. Rev. C 33, 314 (1986) - Published 1 January, 1986

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Properties and behavior of nuclear matter at finite temperature are studied in the saturating chiral field theory of Boguta. Fermi integrations occurring in the expressions for scaler density and vector density are carried out in the low temperature approximation and the field equation, to find the effective nucleon mass $M^{*}$ , is derived as a quartic equation in the scaler meson field σ with input parameter η= $K_{F}$ / $M^{*}$ . Quantities of physical interest ɛ, P, and S are expressed in closed form.

Shape transition in Os and Pt isotopes

A. Ansari

Phys. Rev. C 33, 321 (1986) - Published 1 January, 1986

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Ground state structure of the A=186–196 Os-Pt region is investigated through a self-consistent Hartree-Fock-Bogoliubov calculation employing a pairing plus quadrupole plus hexadecapole model interaction Hamiltonian. The influence of the hexadecapole degrees of freedom on the triaxiality is especially examined. A gradual prolate to oblate shape transition is found in Pt isotopes but such a change is almost abrupt in Os at A≊194. This difference in behavior of the Os and Pt isotopes is obtained only if all the hexadecapole degrees of freedom, instead of merely an axial $Y_{40}$ component, are treated fully self-consistently.

Interacting boson model with surface delta interaction between nucleons: Structure and interaction of bosons

C. H. Druce and S. A. Moszkowski

Phys. Rev. C 33, 330 (1986) - Published 1 January, 1986

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The surface delta interaction is used as an effective nucleon-nucleon interaction to investigate the structure and interaction of the bosons in the interacting boson model. We have obtained analytical expressions for the coefficients of a multipole expansion of the neutron-boson-proton-boson interaction for the case of degenerate orbits. A connection is made between these coefficients and the parameters of the interaction boson model Hamiltonian. A link between the latter parameters and the single boson energies is suggested.

Skyrme-force parametrization: Least-squares fit to nuclear ground-state properties

J. Friedrich and P.-G. Reinhard

Phys. Rev. C 33, 335 (1986) - Published 1 January, 1986

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We investigate systematically the possibilities and the limits of the Skyrme force for reproducing nuclear ground-state properties in a spherical Hartree-Fock calculation. This investigation is performed by means of least-squares fits of the force parameters to the measured binding energy, diffraction radius, and surface width of eight selected nuclei. Particular emphasis is put on the density dependence of the interaction, which turns out to be determined mainly by the surface width. The least-squares fitting procedure yields the best-fit parameters together with uncertainties on them, and it also allows one to estimate the uncertainties of an extrapolation to other fields, e.g., nuclear matter properties. We also study the contribution of random-phase-approximation correlations to the ground-state properties and their influence on the parameters of the effective interaction. Here, we also compare to giant dipole resonance energies.

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Effects of entrance channel and compound nucleus in the fusion cross sections for ${}^{28}$ Si $+^{28}$ Si, ${}^{16}$ O $+^{40}$ Ca, ${}^{32}$ S $+^{30}$ Si, and ${}^{12}$ C $+^{50}$ Cr

Few-nucleon transfer in quasi-elastic collisions at 20 MeV/nucleon

Phenomenological consequences of a hypothetical light neutral particle in heavy ion collisions

Low energy $π^{+}$ inelastic scattering from nuclei to the continuum

Energy dependence of ${}^{24}{(p \to}$ ,d) cross section and analyzing-power measurements from 50 to 150 MeV

Theoretical antideuteron-nucleus absorptive cross sections

Spin-rotation parameter Q for 800 MeV proton elastic scattering from ${}^{16}O$ , ${}^{40}{Ca}$ , and ${}^{208}{Pb}$

Medium energy probes and the interacting boson model of nuclei

Problem of backward proton production

Estimate of the pionic contribution to very forward electron scattering from ${}^{3}{He}$ by surprisal analysis

Pion single charge exchange angular distributions at $T_{π}$ =48 MeV

Relativistic treatment of p¯-atom shifts and widths

Photoactivation of isomeric levels in ${}^{113}{In}$ and ${}^{87}{Sr}$

Shell-model calculation of ${}^{99}{Tc}$ beta decay in astrophysical environments

R-matrix analysis of the $β^{\mp}$ -delayed alpha spectra from the decay of ${}^{8}{Li}$ and ${}^{8}B$

Proton stripping to $6^{-}$ stretched states of ${}^{26}{Al}$

Thermostatic properties of nuclear matter at low temperature in a saturating chiral field theory

Shape transition in Os and Pt isotopes

Interacting boson model with surface delta interaction between nucleons: Structure and interaction of bosons

Skyrme-force parametrization: Least-squares fit to nuclear ground-state properties

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