Recent Articles

Polarization transfer in ( $\vec{d}$ , $\vec{n}$ ) reactions on light nuclei at $θ = 0 °$

P. W. Lisowski, R. C. Byrd, G. Mack, W. Tornow, R. L. Walter, T. B. Clegg, and F. D. Santos

Phys. Rev. C 24, 1852 (1981) - Published 1 November, 1981

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Transverse vector polarization transfer coefficients $K_{y}^{y^{'}}$ have been measured at a reaction angle of 0° for the processes ${}^{12}C$ ( $d$ , $n$ ) ${}^{13}N$ , ${}^{14}N$ ( $d$ , $n$ ) ${}^{15}O$ , ${}^{16}O$ ( $d$ , $n$ ) ${}^{17}F$ , and ${}^{28}{Si}$ ( $d$ , $n$ ) ${}^{29}P$ . The deuteron beam energy ranged from about 5 to 15 MeV for most cases. For the ${}^{12}C$ ( $d$ , $n$ ) ${}^{13}N$ reaction an excitation function of the differential cross section at 0° also was obtained from 6 to 14 MeV for the ground state and first excited state transitions. The polarization transfer coefficients were all positive and typically just slightly lower than the value of $\frac{2}{3}$ . This indicates that the contribution from spin transfer $s = \frac{3}{2}$ is small at 0°. Theoretical predictions of $K_{y}^{y^{'}}$ (0°) using the distorted-wave Born approximation agree with the data to within about 10%.

NUCLEAR REACTIONS ${}^{12}C$ , ${}^{14}N$ , ${}^{16}O$ , ${}^{28}{Si}$ ( $\vec{d}$ , $\vec{n}$ ), $E = 5 - 15$ MeV; measured polarization transfer $K_{y}^{y^{'}}$ (0°). ${}^{12}C$ ( $d$ , $n$ ), $E = 6 - 14$ MeV; measured $σ (0 °)$ . Comparison of $K_{y}^{y^{'}}$ (0°) to DWBA.

Structure of ${}^{18}{Ne}$

A. V. Nero, E. G. Adelberger, and F. S. Dietrich

Phys. Rev. C 24, 1864 (1981) - Published 1 November, 1981

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We have studied ${}^{18}{Ne}$ states up to 9 MeV excitation energy via the ${}^{16}O$ ( ${}^{3}{He}$ , $n$ ) ${}^{18}{Ne}$ and ${}^{20}{Ne}$ ( $p$ , $t$ ) ${}^{18}{Ne}$ reactions. Excitation energies, widths, absolute cross sections, and angular distributions were measured. Distorted-wave Born approximation calculations were performed for comparison with the ( ${}^{3}{He}$ , $n$ ) angular distributions and the ( $p$ , $t$ ) data were compared with previous calculations. Members of the 4.5-MeV doublet were found to have excitation energies of 4.518 ± 0.008 and 4.590 ± 0.008 MeV with spin and parity $1^{-}$ and $0^{+}$ , respectively. The 5.1-MeV group was resolved into a doublet with 5.090 ± 0.008 and 5.144 ± 0.008 MeV excitation energies. Several previously unidentified states were found at excitation energies greater than 5 MeV, including a state at 7.062 ± 0.012 MeV that is strongly populated via ( ${}^{3}{He}$ , $n$ ), but not observed in ( $p$ , $t$ ). We calculated two-particle Coulomb energy shifts for model mass-18 $T = 1$ states and found that the difference between the excitation energy of the 4.59-MeV $0^{+}$ state and the analogous state at 5.34 MeV in ${}^{18}0$ gives strong evidence for the predominantly ${s_{\frac{1}{2}}}^{2}$ character of the state.

NUCLEAR REACTIONS, NUCLEAR STRUCTURE ${}^{16}O$ ( ${}^{3}{He}$ , $n$ ) ${}^{18}{Ne}$ , $E = 10 - 22$ MeV; measured $σ (E_{n}, θ)$ . ${}^{20}{Ne}$ ( $p$ , $t$ ) ${}^{18}{Ne}$ , $E = 41.8$ MeV; measured $σ (E_{t}, θ)$ . Gas targets. DWBA analysis. Deduced ${}^{18}{Ne}$ levels, J, $π$ . Calculated Coulomb shifts for model mass 18 $T = 1$ states.

Influence of the statistical distribution of level parameters on compound nuclear cross sections for strongly overlapping resonances

H. M. Hofmann, T. Mertelmeier, and Hans A. Weidenmüller

Phys. Rev. C 24, 1884 (1981) - Published 1 November, 1981

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We examine numerically the influence of the distribution of the poles and residues of the $K$ matrix on the elastic enhancement factor $W$ in the Hauser-Feshbach formula. For a distribution of pole parameters consistent with the results of random matrix theory, our results strongly suggest a value of $W = 2.0$ , in the limit of strongly overlapping resonances.

NUCLEAR REACTIONS Influence of statistical distribution of level parameters on compound nucleus reaction cross section for strong absorption.

${}^{20}{Ne}$ ( $α$ , ${}^{12}C$ ) ${}^{12}C$ reaction

Charles A. Davis

Phys. Rev. C 24, 1891 (1981) - Published 1 November, 1981

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Cross sections at up to 15 angles and in 10 keV steps between $13.4 < E_{α} < 20.8$ MeV for both ${}^{20}{Ne}$ ( $α$ , ${}^{12}C$ ) ${}^{12}C$ and ${}^{20}{Ne}$ ( $α$ , $α_{i}$ ) ${}^{20}{Ne}$ are reported. The absolute cross sections indicate (via detailed balance) serious systematic errors in published ${}^{12}C$ ( ${}^{12}C$ , $α$ ) ${}^{20}{Ne}$ cross sections. The data show much resonant structure and, using the ${}^{20}{Ne}$ ( $α$ , ${}^{12}C$ ) ${}^{12}C$ data, $J^{π}$ assignments and extracted resonant parameters for 55 states in ${}^{24}{Mg}$ can be found, only 10 of which had been assigned previously. The systematics of these states seem more consistent with the Friedman-Goebel barrier top resonances than with "quasimolecular" resonances. The alpha scattering data show little correlation with the ${}^{20}{Ne}$ ( $α$ , ${}^{12}C$ ) ${}^{12}C$ channel.

NUCLEAR REACTIONS ${}^{20}{Ne}$ ( $α$ , ${}^{12}C$ ) ${}^{12}C$ ; measured $σ (E, θ)$ at up to 15 angles. ${}^{20}{Ne}$ ( $α$ , $α_{0} α_{1} α_{2} α_{3} α_{4} α_{5} α_{6} α_{10} α_{11} α_{13}$ ) measured $σ (E, θ)$ at one or two angles. $13.4 < E_{α} (MeV) < 20.8$ , $Δ E_{α} = 10$ keV. Deduced ${}^{24}{Mg}$ level parameters $J^{π}$ , $Γ$ , $\frac{{(Γ_{α} Γ_{c})}^{\frac{1}{2}}}{Γ}$ , $E_{r}$ . Ne gas target.

Antisymmetrized Lippmann-Schwinger equations and optical potentials

K. L. Kowalski

Phys. Rev. C 24, 1915 (1981) - Published 1 November, 1981

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A recent study of the effect of the Pauli principle in elastic nuclear scattering uses the prior off-shell extension for the multichannel transition operators to derive antisymmetrized Lippmann-Schwinger equations, while such equations are shown not to exist if the off-shell extension due to Alt, Grassberger, and Sandhas is employed instead. We show that the limitations associated with this second off-shell extension are inconsequential for all physical considerations. New physically constrained antisymmetrized Lippmann-Schwinger equations are found in terms of a simple effective interaction which incorporates all of the effects of the Pauli principle and whose properties are explicit. These equations, which are based on the Alt et al. off-shell extension, are employed to obtain in a direct manner the antisymmetrized generalization of the Feshbach formalism for the two fragment optical potential.

NUCLEAR REACTIONS Pauli principle in nuclear reaction theory. Comparison of different off-shell extensions for transition operators. Antisymmetrized Lippmann-Schwinger equations. Antisymmetrized optical potential.

Statistical properties of complex states of ${}_{30}^{67}{Zn}$

J. B. Garg, V. K. Tikku, J. A. Harvey, R. L. Macklin, and J. Halperin

Phys. Rev. C 24, 1922 (1981) - Published 1 November, 1981

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High resolution neutron total and capture cross section measurements have been made on the separated isotope ${}^{66}{Zn}$ in the energy range from a few keV to about 1 MeV using the neutron time-of-flight technique and the pulsed Oak Ridge Electron Linear Accelerator. The nominal resolution of the measurements was 0.07 ns/m. The total cross section data have been analyzed up to 380 keV using a multilevel $R$ -matrix formalism and the capture data up to 130 keV using a least squares fit program. From these analyses we have obtained the values of the resonance parameters $E_{0}$ , $g Γ_{n}$ , and $Γ_{γ}$ , and values of average quantities: $D_{l = 0} = (4.62 \pm 0.55)$ keV, $D_{l = 1} = (1.17 \pm 0.14)$ keV, $S_{0} = (2.06 \pm 0.36)$ , $S_{1} = (0.66 \pm 0.06)$ , and $S_{2} = (0.50 \pm 0.12)$ in units of $10^{- 4}$ ${eV}^{- 1 / 2}$ . The values of average radiation widths are (0.39 ± 0.06) eV for $s$ -wave resonances and (0.190 ± 0.013) eV for $p$ -wave resonances. The distributions of neutron reduced widths and of level spacings of $s$ - and $p$ -wave resonances show excellent agreement with the Porter-Thomas and Wigner distributions, respectively. The value of the $Δ_{3}$ statistic for the long range correlation of $s$ -wave energy levels is found to be in reasonable agreement with the theoretical prediction of Dyson and Mehta. A value of 0.59 ± 0.10 has been determined for the linear coefficient for the correlation between the neutron reduced widths and the radiation widths of 26 $s$ -wave resonances. This value is highly significant and has a confidence level of 99.7%.

NUCLEAR REACTIONS ${}^{66}{Zn}$ ( $n$ , $n$ ), ${}^{66}{Zn}$ ( $n$ , $γ$ ), $E = few keV to \sim 380 keV$ . Measured total and capture cross sections versus neutron energy, deduced resonance parameters, $E_{0}$ , $J^{π}$ , $g Γ_{n}$ , $Γ_{γ}$ , $S_{0}$ , $S_{1}$ , $S_{2}$ , $D_{0}$ , $D_{1}$ .

Photon scattering studies of the giant dipole resonance in medium weight nuclei

T. J. Bowles, R. J. Holt, H. E. Jackson, R. M. Laszewski, R. D. McKeown, A. M. Nathan, and J. R. Specht

Phys. Rev. C 24, 1940 (1981) - Published 1 November, 1981

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Quasimonochromatic photons have been used to measure elastic and inelastic photon scattering cross sections in the giant dipole resonance region of ${}^{52}{Cr}$ , Fe, ${}^{60}{Ni}$ , ${}^{92}{Mo}$ , and ${}^{96}{Mo}$ in an experiment in which the elastic and inelastic scattering are resolved. The elastic scattering cross sections show clear evidence for isospin splitting of the giant dipole resonance. The inelastic scattering to low-lying vibrational levels, which is a measure of the coupling between the giant dipole resonance and collective surface vibrations, is in qualitative agreement with the predictions of the dynamic collective model. However, when examined in detail, this model does not provide an adequate description of the scattering data.

NUCLEAR REACTIONS ${}^{52}{Cr}$ , Fe, ${}^{60}{Ni}$ , ${}^{92, 96}{Mo}$ ( $γ$ , $γ^{'}$ ), $14 \leq E_{γ} \leq 22$ MeV; measured $E_{γ}$ , $E_{γ^{'}}$ , $\frac{d σ}{d Ω}$ for $γ_{0}$ , $γ_{1}$ . Compared to DCM predictions. Tagged photons.

Electrodisintegration of ${}^{56}{Fe}$ , ${}^{59}{Co}$ , and ${}^{64}{Zn}$

W. R. Dodge, R. G. Leicht, E. Hayward, and E. Wolynec

Phys. Rev. C 24, 1952 (1981) - Published 1 November, 1981

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The ( $e$ , $p$ ) and ( $e$ , $α$ ) cross sections for ${}^{56}{Fe}$ , ${}^{59}{Co}$ , and ${}^{64}{Zn}$ have been measured in the electron energy range 16-100 MeV. They have been analyzed using the distorted-wave Born approximation $E 1$ and $E 2$ virtual photon spectra. The $E 1$ and $E 2$ components in the proton and $α$ channels have been obtained.

NUCLEAR REACTIONS ${}^{56}{Fe}$ ( $e$ , $p$ ), ${}^{56}{Fe}$ ( $e$ , $α$ ), ${}^{59}{Co}$ ( $e$ , $p$ ), ${}^{59}{Co}$ ( $e$ , $α$ ), ${}^{64}{Zn}$ ( $e$ , $p$ ), and ${}^{64}{Zn}$ ( $e$ , $α$ ); measured $σ (E_{0}, E_{x}, 34 °)$ , $σ (E_{0}, E_{x}, 48 °)$ , $σ (E_{0}, E_{x}, 62 °)$ , $σ (E_{0}, E_{x}, 90 °)$ , $σ (E_{0}, E_{x}, 118 °)$ , $σ (E_{0}, E_{x}, 132 °)$ ; obtained $σ (e, p)$ , $σ (e, α)$ ; deduced $σ_{γ, p}^{E 1} (E)$ , $σ_{γ, p}^{E 2} (E)$ , $σ_{γ, α}^{E 1} (E)$ , $σ_{γ, α}^{E 2} (E)$ .

${}^{206}{Pb}$ + $n$ resonances for $E = 600 - 900$ keV: Neutron strength functions

D. J. Horen, J. A. Harvey, and N. W. Hill

Phys. Rev. C 24, 1961 (1981) - Published 1 November, 1981

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Data from high resolution neutron transmission and differential scattering measurements performed on ${}^{206}{Pb}$ have been analyzed for $E = 600 - 900$ keV. Resonance parameters (i.e., $E$ , $l$ , $J$ , and $Γ_{n}$ ) have been deduced for many of the 161 resonances observed. Strength functions and potential phase shifts for $s$ -, $p$ -, and $d$ -wave neutrons for $E_{n} - 0 - 900$ keV are compared with optical model calculations. It is found that the phase contributed by the external $R$ function as well as the integrated neutron strength functions can be reproduced for the $s$ and $d$ waves with a well depth of $V_{0} = 50.4$ MeV for the real potential and $W_{D} = 6.0$ MeV for an imaginary surface potential. Somewhat smaller values ( $V_{0} = 48.7$ MeV and $W_{D} = 2.0$ MeV) are required to reproduce the $p$ -wave data. These values of the real potential are also found to give the experimentally observed binding energies for the $4 s_{\frac{1}{2}}$ , $3 d_{\frac{3}{2}}$ , and $3 d_{\frac{5}{2}}$ single particle levels ( $V_{0} = 50.4$ MeV), and the $3 p_{\frac{1}{2}}$ single particle level ( $V_{0} = 48.7$ MeV). Nuclear level densities for $s$ and $d$ waves are found to be well represented by a constant temperature model. However, the model under estimates the number of $p$ -wave resonances.

NUCLEAR REACTIONS ${}^{206}{Pb}$ ( $n$ ), ( $n$ , $n$ ), $E = 600 - 900$ keV; measured $σ_{T} (E)$ , $σ (E, θ)$ . ${}^{207}{Pb}$ deduced resonance parameters, $J^{π}$ , $Γ_{n}$ , neutron strength functions, optical model parameters for $l = 0, 1, 2$ .

Electroexcitation of giant electric-dipole and electric-quadrupole resonances in ${}^{42}{Ca}$ and ${}^{44}{Ca}$

K. Itoh, Y. M. Shin, T. Saito, and Y. Torizuka

Phys. Rev. C 24, 1969 (1981) - Published 1 November, 1981

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We present the giant electric-dipole and electric-quadrupole cross sections of ${}^{42}{Ca}$ and ${}^{44}{Ca}$ measured by inelastic electron scattering with incident energies between 124 and 250 MeV. Spectra were decomposed into dipole, quadrupole, and other higher multipole components. The giant dipole resonances in both nuclei have a large width of approximately 12 MeV, with at least two gross resonance structures. The quadrupole resonances are distributed in several clusters between 10 and 22 MeV, depleting (61±9)% in ${}^{42}{Ca}$ and (46±7)% in ${}^{44}{Ca}$ of the isoscalar energy-weighted sum rule, respectively. Higher multipole resonances were also found in the same excitation energy region. The observed structure in the dipole and quadrupole resonances are examined in terms of the collective model, and it is suggested that the splitting of the dipole resonance revealed in ${}^{44}{Ca}$ may reflect the effect of nuclear deformation.

NUCLEAR REACTIONS ${}^{42}{Ca}$ ( $e$ , $e^{'}$ ) and ${}^{44}{Ca}$ ( $e$ , $e^{'}$ ), $E = 124 \sim 250$ MeV, $q = 0.4 \sim 1.2$ fm ${}^{- 1}{, e n r i c h e d}$ target, measured $σ (E^{'}, θ)$ up to 35 MeV in excitation energy; deduced electric-dipole, electric-quadrupole, and higher multipole strength in the giant resonance region.

High-spin states in ${}^{56, 58}{Co}$ with the ${}^{58, 60}{Ni}$ ( $d$ , $α$ ) ${}^{56, 58}{Co}$ reaction

H. Nann, A. D. Bacher, W. W. Jacobs, W. P. Jones, and E. J. Stephenson

Phys. Rev. C 24, 1984 (1981) - Published 1 November, 1981

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Angular distributions of the ${}^{58, 60}{Ni}$ ( $d$ , $α$ ) ${}^{56, 58}{Co}$ reaction at 80 MeV bombarding energy have been measured for strongly populated states in ${}^{56, 58}{Co}$ up to an excitation energy of 5.3 MeV. Besides the transitions to the known $7^{+}$ state at 2.283 MeV and $6^{+}$ state at 2.372 MeV in ${}^{56}{Co}$ , states at 3.54(2) and 4.44(3) MeV in ${}^{56}{Co}$ , and at 2.69(2), 2.94(2), 3.78(2), and 4.79(3) MeV in ${}^{58}{Co}$ are strongly excited by characteristic $L = 6$ angular distributions. This limits the $J^{π}$ values for these states to ( $5^{+}$ ), $6^{+}$ , or $7^{+}$ . The experimental angular distributions are compared with distorted-wave Born approximation calculations based on two sets of recent shell model wave functions, calculated in the same configuration space but with different effective residual interactions.

NUCLEAR REACTIONS ${}^{58, 60}{Ni}$ ( $d$ , $α$ ), $E_{d} = 80$ MeV. Measured $σ (θ)$ ; enriched targets. Deduced $L$ transfer. DWBA analysis.

High resolution measurement of proton resonances in ${}^{57}{Co}$

W. A. Watson, III, E. G. Bilpuch, and G. E. Mitchell

Phys. Rev. C 24, 1992 (1981) - Published 1 November, 1981

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Differential cross sections for the reactions ${}^{56}{Fe}$ ( $p$ , $p$ ) and ${}^{56}{Fe}$ ( $p$ , $p^{'}$ ) were measured at 5 angles from $E_{p} = 3.1 to 4.0$ MeV with an overall energy resolution of 425-450 eV, full width at half maximum. Over 340 resonances were observed, half of which were $d$ -wave levels. Angular distributions of deexcitation $γ$ rays were measured for the stronger $l = 2$ resonances and a few $p$ -wave resonances to aid in assigning spins. Excitation functions were analyzed with a multilevel, multichannel $R$ -matrix formalism. Analogs of the fourteenth ( ${\frac{5}{2}}^{-}$ ) and seventeenth through twentieth ( ${\frac{9}{2}}^{+}$ , ${\frac{5}{2}}^{+}$ , ${\frac{3}{2}}^{-}$ , ${\frac{1}{2}}^{-}$ ) excited state of ${}^{57}{Fe}$ were identified. Coulomb energies, fine structure parameters, and spectroscopic factors for these analogs are given. Proton strength functions are presented, and level densities are compared with semiempirical predictions.

NUCLEAR REACTIONS ${}^{56}{Fe}$ ( $p$ , $p$ ), ( $p$ , $p^{'}$ ), $E = 3.1 - 4.0$ MeV, measured $σ (E, θ)$ ; ${}^{56}{Fe}$ ( $p$ , $p^{'} γ$ ), measured $σ (θ)$ . ${}^{57}{Co}$ levels deduced $J^{π}$ , $Γ_{p}$ , $Γ_{p^{'}}$ , proton strength functions, level densities; ${}^{57}{Co}$ IAR deduced fine structure, Coulomb energies, spectroscopic factors. Enriched targets, resolution 425-450 eV.

Inelastic proton scattering to particle-hole states in ${}^{40}{Ca}$ and spin-isospin excitation of pion symmetry states

H. Ejiri, M. Sasao, T. Shibata, H. Ohsumi, Y. Fujita, M. Fujiwara, T. Yamazaki, I. Katayama, S. Morinobu, and H. Ikegami

Phys. Rev. C 24, 2001 (1981) - Published 1 November, 1981

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Inelastic proton scattering to the ${(d \frac{3}{2})}^{- 1} (f \frac{7}{2})$ particle-hole states in ${}^{40}{Ca}$ were studied at the proton energy of 65 MeV by using a high resolution magnetic spectrograph. Angular distributions for both isoscalar mode ( $T = 0$ ) and isovector mode ( $T = 1$ ) excitations were reproduced by a distorted-wave Born approximation code with the microscopic particle-hole configurations. The effective interaction used consists of central, $LS$ , and tensor forces with Yukawa-type radial forms. The isovector spin excitation of the 8.424 MeV state ( $J^{π} = 2^{-}$ , $T = 1$ ) and the isoscalar spin excitation of the 6.751 MeV state ( $J^{π} = 2^{-}$ , $T = 0$ ) were compared to look for speculated precritical effects of pion condensation. The observed angular distributions for both the $2^{-}$ , $T = 1 and 2^{-}$ , $T = 0$ states are similar and smooth as a function of the momentum transfer $q$ . No obvious enhancement around $q \approx 2.5 m_{π} C$ due to the proximity of the pion condensation was found in the pion mode ( $2^{-}$ , $T = 1$ ) excitation. The observed feature is in accord with the smoothly $q$ dependent $LS$ and tensor interactions.

NUCLEAR REACTIONS ${}^{40}{Ca}$ ( $p$ , $p^{'}$ ), $E = 65$ MeV; measured $σ (E_{p^{'}}, θ)$ , resolution ∼ 15 keV, DWBA calculations, deduced nuclear effective interactions and nonexistence of pion opalescence enhancement.

Inclusive neutron production by 337 MeV/nucleon neon ions on carbon, aluminum, copper, and uranium

R. A. Cecil, B. D. Anderson, A. R. Baldwin, R. Madey, W. Schimmerling, J. W. Kast, and D. Ortendahl

Phys. Rev. C 24, 2013 (1981) - Published 1 November, 1981

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We measured inclusive double-differential cross sections at angles of 30, 45, 60, and 90 deg for the production of neutrons above about 12 MeV from 337 MeV/nucleon neon ions bombarding targets of C, Al, Cu, and U. Three different energy regions can be distinguished in the neutron spectra: (1) a low-energy "evaporation" region, (2) a high-energy exponential tail reflecting the internal momentum distribution of the nucleons, and (3) an intermediate energy region reflecting quasifree and preequilibrium processes. The intermediate-energy region becomes less pronounced with increasing angle and is almost nonexistent at 90 deg. This behavior is consistent with the interpretation that the intermediate-energy region consists mainly of scattering processes with a few direct collisions. The intermediate-energy region is relatively flat at the forward angles and merges into an exponential falloff at wide angles. The 30-deg spectrum from the carbon target shows a broad peak around 150 MeV, which we interpret as a signature of quasifree nucleon-nucleon collisions. Although the neutron detection threshold does not permit us to see the evaporation peaks, we do see evidence of the evaporation tails. The evaporation yields apparent in our spectra increase with the mass number of the target. The neutron spectra differ from proton spectra reported for similar targets at 385 and 393 MeV/nucleon. The neutron-to-proton cross section ratios are fit well by an intranuclear-cascade model calculation, but poorly by a "firestreak" model calculation.

NUCLEAR REACTIONS C, Al, Cu, U(Ne, $nX$ ), $E = 337$ MeV/nucleon. Measured double-differential cross sections at $θ_{lab} = 30, 45, 60, and 90$ deg. Deduced total integrated neutron cross sections above 25 MeV. Compared neutron spectra with proton spectra and neutron/proton cross section ratios with the firestreak model.

Alpha-particle emission from the fusion of ${}^{32}S$ with ${}^{27}{Al}$

G. M. Berkowitz, P. Braun-Munzinger, J. W. Harris, C. M. Jachcinski, and J. Barrette

Phys. Rev. C 24, 2030 (1981) - Published 1 November, 1981

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Alpha particles produced in the fusion of ${}^{32}S$ with ${}^{27}{Al}$ at $E_{lab} = 160$ MeV were observed at $θ_{lab} = 15 °, 40 °, 45 °, 75 °, 130 °, and 160 °$ in coincidence with evaporation residues detected at $θ_{lab} = - 5.8 °$ using a time-of-flight spectrometer. The data were compared to a simple Monte Carlo calculation based on the statistical evaporation of light particles from an equilibrated compound nucleus. The total coincidence energy spectra show no evidence of preequilibrium emission of alpha particles.

NUCLEAR REACTIONS ${}^{27}{Al}$ ( ${}^{32}S$ , $x$ ), $x = evaporation residues$ , $E = 160$ MeV, measured coincidences with evaporated $α$ particles, deduced limit on pre-equilibrium $α$ emission.

Higher-order WKB phase shifts for the heavy-ion optical potential

C. K. Chan, P. Suebka, and P. Lu

Phys. Rev. C 24, 2035 (1981) - Published 1 November, 1981

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It is shown that a higher-order correction improves the accuracy of the zeroth order WKB phase for a heavy-ion optical potential. The WKB phase shifts, correct to the first order in $ℏ^{2}$ , agree with those obtained from a quantal optical model code.

NUCLEAR REACTIONS Higher-order WKB calculation ${}^{58}{Ni}$ ( ${}^{18}O$ , ${}^{18}O$ '); $E_{lab} = 60$ MeV; calculated reflection coefficients.

Enhanced fragment emission in the interaction of 18.5 GeV ${}^{12}C$ ions with complex nuclei

G. D. Cole and N. T. Porile

Phys. Rev. C 24, 2038 (1981) - Published 1 November, 1981

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Cross sections for the formation of seven fragments ranging from ${}^{24}{Na}$ to ${}^{52}{Mn}$ in the interaction of 18.5 GeV ${}^{12}C$ ions and 400 GeV protons with Cu, Ag, Gd, Ta, Au, and U have been measured. After correction for the difference in bombarding energy, the results were used to test the factorization hypothesis. Enhanced fragment emission in ${}^{12}C$ reactions was observed for all targets excepting copper. The magnitude of the enhancement and its dependence on target and product $A$ are described. The variation of fragment yields with target $A$ is examined. The neutron excess products obey modified $Qgg$ systematics while the neutron deficient ones do not. The implications of these results for the reaction mechanism are considered.

NUCLEAR REACTIONS Cu, Ag, Gd, Ta, Au, U [ ${}^{12}C$ and $p$ , fragments ( $A = 24 - 52$ )] $T_{{}^{12}C} = 18.5$ GeV, $T p = 400$ GeV. Measured cross sections. Test of factorization, yield systematics. Gross $γ$ -ray assay [Ge (Li)].

Neutron emission in ${}^{12}C$ + ${}^{158}{Gd}$ and ${}^{13}C$ + ${}^{157}{Gd}$ reactions between 8 and 12 MeV/nucleon

A. Gavron, J. R. Beene, R. L. Ferguson, F. E. Obenshain, F. Plasil, G. R. Young, G. A. Petitt, K. Geoffroy Young, M. Jääskeläinen, D. G. Sarantites, and C. F. Maguire

Phys. Rev. C 24, 2048 (1981) - Published 1 November, 1981

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Neutron spectra in coincidence with evaporation residues and with projectilelike fragments emitted in inelastic scattering reactions have been measured at several bombarding energies for ${}^{12}C$ - and ${}^{13}C$ -induced reactions leading to the same compound nucleus ${}^{170}{Yb}$ . In the fusion reactions, a nonequilibrium component was observed in the neutron spectra at all beam energies. This component is forward peaked and is associated with a high temperature. The spectra can be parametrized by assuming the nonequilibrium part to result from a hot region ( $T \sim 4$ MeV) emitting neutrons isotropically and moving with a velocity of approximately 1 cm/ns. This apparent velocity decreases with decreasing beam velocity. Comparisons are made with predictions based on the generalized critical angular momentum model of incomplete fusion of Siwek-Wilczynska et al. No significant difference has been observed between nonequilibrium neutron emission from ${}^{12}C$ - and ${}^{13}C$ -induced reactions. Neutron emission associated with inelastic scattering reactions cannot be described by simple statistical evaporation from two fragments of equal temperature. Effects which may give rise to the observed energy and angular distributions of neutrons in coincidence with inelastic products are discussed.

NUCLEAR REACTIONS ${}^{158}{Gd}$ + ${}^{12}C$ → $A + n$ , ${}^{157}{Gd}$ + ${}^{13}C$ → $A + n$ , $103 \leq E_{lab} \leq 160$ MeV; $A = evaporation residue or projectilelike fragments$ . $A - n$ coin., $13 \leq θ_{n} \leq 141 °$ , $θ_{A} = 18 °, 24 °$ . Neutron multiplicities and energy spectra.

Fusion of ${}^{24}{Mg}$ + ${}^{24}{Mg}$

C. M. Jachcinski, D. G. Kovar, R. R. Betts, C. N. Davids, D. F. Geesaman, C. Olmer, M. Paul, S. J. Sanders, and J. L. Yntema

Phys. Rev. C 24, 2070 (1981) - Published 1 November, 1981

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Total fusion cross sections for ${}^{24}{Mg}$ + ${}^{24}{Mg}$ have been measured in the energy range from $24.7 \leq E_{c . m .} \leq 66.2$ MeV by the detection of evaporation residues, either directly in a $Δ E - E$ telescope, or by measurement of prompt $γ$ -ray activity. The excitation functions for the individual reaction channels, and the total fusion cross section show relatively smooth behavior with no evidence for oscillatory structure of magnitude greater than 5%. The parameters obtained by fitting the data with a $\frac{1}{E_{c . m .}}$ energy dependence are somewhat different from those expected from the systematics of fusion reactions in the high-energy region.

NUCLEAR REACTIONS ${}^{24}{Mg}$ + ${}^{24}{Mg}$ , $E_{c . m .} = 24.7 - 66.2$ MeV measured. $σ_{fusion}$ .

Spectroscopy of excited states in ${}^{102}{Mo}$ and ${}^{106}{Ru}$

J. Koenig, H. Bohn, T. Faestermann, P. Kienle, H. J. Körner, W. A. Mayer, D. Pereira, K. E. Rehm, and H. J. Scheerer

Phys. Rev. C 24, 2076 (1981) - Published 1 November, 1981

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Excited states in the transitional nuclei ${}^{102}{Mo}$ and ${}^{106}{Ru}$ have been populated in ${}^{18}O$ induced two neutron transfer reactions at bombarding energies around 5 MeV/nucleon. The succeeding $γ$ decay was measured employing a particle- $γ$ coincidence technique in which the ejectiles were identified with a quadrupole-three-dipole magnetic spectrograph. This method is especially suited for studying the decay modes of regions with selected excitation energy and spin. A characteristic evolution in the population of known states ( $I^{π} \leq 4^{+}$ ) with changing excitation energy was observed. Previously unknown $γ$ transitions are attributed to the decay of $6^{+}$ and $8^{+}$ yrast states in ${}^{102}{Mo}$ and ${}^{106}{Ru}$ , respectively.

NUCLEAR REACTIONS ${}^{100}{Mo}$ ( ${}^{18}O$ , ${}^{16}O$ ), $E_{lab} ({}^{18}O) = 84$ MeV, $θ_{lab} = 34 °$ ; ${}^{104}{Ru}$ ( ${}^{18}O$ , ${}^{16}O$ ), $E_{lab} ({}^{18}O) = 84 and 100$ MeV, $θ_{lab} = 34 ° and 30 °$ . Measured particle- $γ$ coinc. for selected excitation energy ranges, deduced ${}^{102}{Mo}$ and ${}^{106}{Ru}$ level energies (and spins). Enriched targets.

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Physical Review C

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