Recent Articles

Survey of the ( ${}^{3}{He}$ , $t$ ) reaction: Excitation of the isobaric analog of the giant dipole resonance

S. L. Tabor, C. C. Chang, M. T. Collins, G. J. Wagner, J. R. Wu, D. W. Halderson, and F. Petrovich

Phys. Rev. C 25, 1253 (1982) - Published 1 March, 1982

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The ( ${}^{3}{He}$ , $t$ ) reaction at 130 and 170 MeV has been investigated on targets of ${}^{12}C$ , ${}^{16}O$ , ${}^{27}{Al}$ , ${}^{28}{Si}$ , ${}^{40}{Ca}$ , ${}^{46}{Ti}$ , and ${}^{90}{Zr}$ . Data for the ( ${}^{3}{He}$ , ${}^{3}{He}$ ′) reaction were measured simultaneously for reference purposes. Structure is observed in the spectra from the ( ${}^{3}{He}$ , ${}^{3}{He}$ ′) and ( ${}^{3}{He}$ , $t$ ) reactions at the expected positions of the giant quadrupole resonance and the isobaric analog of the giant dipole resonance, respectively. An angular distribution was measured for the suspected giant dipole resonance structure in the ${}^{40}{Ca}$ ( ${}^{3}{He}$ , $t$ ) ${}^{40}{Sc}$ reaction at 130 MeV. The data are reasonably described by a collective model calculation based on the Goldhaber-Teller model for the giant dipole resonance. Several other strong peaks at excitation energies below the giant dipole resonance are observed in the ( ${}^{3}{He}$ , $t$ ) spectra. Most notable of these are the ones at the expected positions for analogs of well known $1^{+}$ states and $1 ℏ ω$ stretched states in the targets.

NUCLEAR REACTIONS ${}^{12}C$ , ${}^{16}O$ , ${}^{27}{Al}$ , ${}^{28}{Si}$ , ${}^{46}{Ti}$ , ${}^{90}{Zr}$ ( ${}^{3}{He}$ , $t$ ) and ( ${}^{3}{He}$ , ${}^{3}{He}$ ′) $E = 130, 170$ MeV; measured $\frac{d σ}{d Ω}$ ( $E$ , $θ$ ); giant resonances; stretched states.

Excitation of the giant resonance region in silicon by inelastic scattering of 115 MeV protons

S. Kailas, P. P. Singh, A. D. Bacher, C. C. Foster, D. L. Friesel, P. Schwandt, and J. Wiggins

Phys. Rev. C 25, 1263 (1982) - Published 1 March, 1982

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Differential cross sections for the excitation of the giant resonance region in silicon have been measured over the angular range 10° to 34° by inelastic scattering of 115 MeV protons. The giant resonance exhibits fine structure which is similar to that observed in ( $α$ , $α^{'}$ ) and low-energy ( $p$ , $p^{'}$ ) data. The angular distribution for the giant resonance has been analyzed in terms of the distorted-wave Born approximation and 19-26% of the energy weighted sum rule strength for $L = 2$ has been identified. It is also found that the angular distribution for the excitation of the giant resonance region cannot be explained by assuming only the presence of giant quadrupole resonance.

NUCLEAR REACTIONS Si( $p$ , $p^{'}$ ), $E = 115$ MeV; measured $σ (θ)$ for giant-resonance excitations and the low lying levels. Calculated energy-weighted sum rule strengths.

Surprisal analysis of inclusive reactions

Tatsuo Tsukamoto and Yoshiyuki Kawazoe

Phys. Rev. C 25, 1272 (1982) - Published 1 March, 1982

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Surprisal analysis is applied to inclusive nuclear reactions of ( $e$ , $e^{'}$ ), ( $α$ , $α^{'}$ ), and (Li,Li'). By introducing constraints on the excitation energy and its square root, excellent fits to the experimental data are obtained. It is suggested that a substantial part of the so-called quasielastic (quasifree) scattering cross sections is due to more complex processes.

NUCLEAR REACTIONS Surprisal analysis. Inclusive nuclear reactions. Estimation of exciton numbers.

Excitation of ${}^{81}{As}$ by the ${}^{82}{Se}$ ( $t$ , $α$ ) reaction

S. Mordechai, S. Lafrance, and H. T. Fortune

Phys. Rev. C 25, 1276 (1982) - Published 1 March, 1982

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The level structure of ${}^{81}{As}$ is probed for the first time and many new states have been identified. Angular distributions were measured and compared with distorted-wave Born approximation calculations, in order to extract $L$ values and spectroscopic factors. Most of the expected strength for pickup from the $2 p$ and $1 f_{\frac{5}{2}}$ orbitals is observed. The level structure of ${}^{81}{As}$ is fairly similar to that of ${}^{79}{As}$ but differs significantly from that of lighter As isotopes.

NUCLEAR REACTIONS ${}^{82}{Se}$ ( $t$ , $α$ ) ${}^{81}{As}$ , $E = 18$ MeV; measured $σ (E_{α}, θ)$ . ${}^{81}{As}$ deduced levels, $L$ , $π$ , ( $J$ ), spectroscopic factors. DWBA analysis. Enriched target.

Electric dipole transitions from neutron capture in ${}^{173}{Yb}$ resonances

O. Shahal, S. Raman, G. G. Slaughter, C. Coceva, and M. Stefanon

Phys. Rev. C 25, 1283 (1982) - Published 1 March, 1982

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Primary neutron capture $γ$ rays have been studied from 49 neutron resonances in ${}^{173}{Yb}$ in the 10-530 eV energy range. These resonances are assigned $J = 2$ and $J = 3$ on the basis of the intensity ratios of suitable pairs of low-energy $γ$ rays. The measured intensities of the high-energy primary $γ$ rays have been converted to partial radiation widths. These widths have been subjected to a correlation analysis against reduced neutron widths, with the result that convincing evidence was not found for previously reported nonstatistical behavior in this nucleus. The ratio of the average population of a particular low-lying level from $J = 3$ resonances to its population from $J = 2$ resonances was found to be in satisfactory agreement with a cascade model. Resonances in the 10-200 eV range were noted to exhibit an enhancement of $E 1$ transition probabilities to $K = 2$ final states as compared to $K = 0$ states. A level scheme for ${}^{174}{Yb}$ was constructed, and the neutron separation energy for this nucleus was deduced as 7464.5±1.0 keV.

NUCLEAR REACTIONS ${}^{173}{Yb}$ ( $n$ , $γ$ ), $E = 0.01 - 0.86$ keV; measured $E_{γ}$ , $I_{γ}$ . ${}^{174}{Yb}$ deduced resonances, $J$ , deduced levels, partial radiation widths, correlations, neutron separation energy. Enriched target, Ge(Li) detector.

Variation of the matter densities of nuclei from ${}^{40}{Ca}$ to ${}^{68}{Zn}$

C. N. Papanicolas, W. Q. Summer, J. S. Blair, and A. M. Bernstein

Phys. Rev. C 25, 1296 (1982) - Published 1 March, 1982

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Analysis is made of elastic scattering of 42 MeV $α$ particles from 19 nuclei from ${}^{40}{Ca}$ to ${}^{68}{Zn}$ in terms of a folding model, allowing determination of matter densities in the nuclear surface region relative to that of ${}^{40}{Ca}$ . Specifically, values are deduced for the radii at which the matter density equals 0.016 nucleon/ ${fm}^{3}$ as well as matter rms radii. The relative sizes vary more slowly than $A^{\frac{1}{3}}$ between ${}^{40}{Ca}$ and ${}^{54}{Fe}$ and more rapidly than $A^{\frac{1}{3}}$ between ${}^{54}{Fe}$ and ${}^{68}{Zn}$ . The overall trend gives an increase with $A^{\frac{1}{3}}$ but with a bowing effect. The near equality of proton and matter rms radii indicates that the neutron-proton radii are approximately equal to within the errors of the present analysis. The results are in reasonable agreement with those obtained with other hadronic probes and with calculated Hartree-Fock-Bogoliubov densities.

NUCLEAR REACTIONS ${}^{40, 42, 44, 48}{Ca}$ , ${}^{46, 48, 50}{Ti}$ , ${}^{52}{Cr}$ , ${}^{54, 56}{Fe}$ , ${}^{58, 60, 62, 64}{Ni}$ , ${}^{63, 65}{Cu}$ , ${}^{64, 66, 68}{Zn}$ ; ( $α$ , $α$ ) 42 MeV; microscopic optical model analysis; deduced matter rms radii; comparison with other results.

Deexcitation of fragments produced in deeply inelastic collisions of 100 MeV ${}^{16}O$ with ${}^{27}{Al}$

G. R. Young, K. A. Van Bibber, A. J. Lazzarini, S. G. Steadman, and F. Videbæk

Phys. Rev. C 25, 1304 (1982) - Published 1 March, 1982

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A study has been made of the $γ$ -ray deexcitation following deeply inelastic collisions between 100 MeV ${}^{16}O$ and ${}^{27}{Al}$ . An experimental apparatus including a gas proportional particle telescope, a Ge(Li) detector, and three NaI(T1) detectors was used. All possible particle- $γ$ and particle-multiple- $γ$ coincidences for projectilelike fragments with $Z \geq 3$ were recorded. Yields and anisotropies of several discrete transitions were measured, as well as the mean and width of the gross multiplicity distribution as a function of detected $Z$ and reaction inelasticity. Estimates of average $γ$ -ray transition energy, average energy carried by $γ$ -ray deexcitation, and the degree of side feeding in observed $γ$ cascades were made. Observed anisotropies are consistent with considerable fragment spin alignment being present. Values of mean $γ$ -ray multiplicity never exceed simple sticking model predictions; particle emission effects are seen to be important. The summed radiative strength of observed discrete line transitions is found to be less than unity, sometimes considerably so, for most deeply inelastic collisions. A short discussion is given of insights obtained on the entry state distribution for $γ$ -ray emission and of the results of statistical model calculations of the relative yields of observed final states.

NUCLEAR REACTIONS ${}^{27}{Al}$ ( ${}^{16}O$ , $X γ)$ , $E = 100$ MeV; measured $X - γ$ coinc, Ge(Li) detector; measured $X - γ - γ$ multiplicity, Ge(Li), NaI detectors; deduced decay product yields, alignment, radiative strengths, $γ$ multiplicity mean and width.

High-spin states in neutron-deficient nuclei near $A = 80$

L. V. Theisen, S. L. Tabor, L. R. Medsker, G. Neuschaefer, L. H. Fry, Jr., and J. S. Clements

Phys. Rev. C 25, 1325 (1982) - Published 1 March, 1982

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In-beam $γ$ -ray spectroscopy with the reactions ${}^{54}{Fe}$ + ${}^{28}{Si}$ and ${}^{56}{Fe}$ + ${}^{28}{Si}$ at beam energies from 80 to 99 MeV were used to study high-spin states in neutron-deficient nuclei in the mass $A \sim 80$ region. Measurements of $γ$ -ray energies, intensities, angular distributions, excitation functions, and $γ - γ$ coincidences were used to assign new levels in ${}^{79}{Rb}$ and ${}^{80}{Sr}$ . For the first time, high-spin states in ${}^{81}{Sr}$ have been observed.

NUCLEAR REACTIONS ${}^{56}{Fe}$ ( ${}^{28}{Si}$ , $xpyn γ$ ) and ${}^{54}{Fe}$ ( ${}^{28}{Si}$ , $xpyn γ$ ) $E_{lab} = 80 - 99$ MeV; measured $E_{γ}$ , $I_{γ}$ , $γ - γ$ coincidences, $σ (E_{γ}, E)$ , and $σ (E_{γ}, θ)$ ; ${}^{79}{Rb}$ , ${}^{80}{Sr}$ , and ${}^{81}{Sr}$ deduced levels, $J^{π}$ . Enriched targets.

Fusion cross section behavior for ${}^{12}C$ + ${}^{24}{Mg}$ and ${}^{12}C$ + ${}^{26}{Mg}$

K. Daneshvar, D. G. Kovar, S. J. Krieger, and K. T. R. Davies

Phys. Rev. C 25, 1342 (1982) - Published 1 March, 1982

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Total fusion cross section excitation functions for the ${}^{12}C$ + ${}^{24}{Mg}$ and ${}^{12}C$ + ${}^{26}{Mg}$ systems have been measured in the energy range $20 \leq E_{lab} < 60$ MeV by detection of the evaporation residues. The excitation function for ${}^{12}C$ + ${}^{24}{Mg}$ is found to show evidence of oscillatory structures with peak to valley difference of ∼5-10% while that for ${}^{12}C$ + ${}^{26}{Mg}$ is relatively smooth. The maximum fusion cross sectin for ${}^{12}C$ + ${}^{24}{Mg}$ is observed to be ∼1180 mb compared to ∼1280 mb for ${}^{12}C$ + ${}^{26}{Mg}$ . The cross sections for ${}^{12}C$ + ${}^{26}{Mg}$ show evidence of a change in behavior at a bombarding energy significantly below the energy at which the cross section saturates. The results are discussed in the context of previous measurements and predictions of macroscopic and microscopic fusion models.

NUCLEAR REACTIONS Fusion measurement, $σ_{fus} (E)$ : ${}^{12}C$ + ${}^{24}{Mg}$ , $20 \leq E_{lab} \leq 63$ MeV; ${}^{12}C$ + ${}^{26}{Mg}$ , $20 \leq E_{lab} \leq 56$ MeV; measured $σ_{elastic} (θ)$ , $σ_{fusion} (θ)$ at $E_{lab} = 20, 24, 30, 41, 48, 56, and 60$ MeV for ${}^{12}C$ + ${}^{24}{Mg}$ , and at 20, 30, 42, and 56 MeV for ${}^{12}C$ + ${}^{26}{Mg}$ .

Multiplicity of $K$ x rays and collective structure in the transitional nuclei with $A ≃ 200$

H. J. Karwowski, S. E. Vigdor, W. W. Jacobs, S. Kailas, P. P. Singh, F. Soga, T. G. Throwe, T. E. Ward, D. L. Wark, and J. Wiggins

Phys. Rev. C 25, 1355 (1982) - Published 1 March, 1982

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The multiplicity $〈 M_{K} 〉$ of prompt $K$ x rays emitted in ( ${}^{6, 7}{Li}$ , $xn$ ) reactions has been measured for twelve targets in the mass range $180 \leq A \leq 209$ , at bombarding energies between 55 and 124 MeV. From the high multiplicities of x rays ( $1 ≲ 〈 M_{K} 〉 ≲ 3$ ) characteristic of the observed evaporation residues, we infer that highly converting, low-energy M1 transitions constitute a substantial portion of the $γ$ -decay cascades (especially at moderately high spin, ( $12 ≲ I ≲ 20$ ) in a large number of nuclides in the transitional region between the shell closure at $N = 126$ and the strongly deformed rare earths. The unexpectedly simple systematic variation of the $〈 M_{K} 〉$ measurements with neutron number within this mass region suggests that the converting transitions occur predominantly among members of as yet unknown, mildly deformed, high- $K$ , deformation-aligned rotational bands. From the measured values of $〈 M_{K} 〉$ and the singles $K$ x ray yields we extract absolute total cross sections for the (Li, $xn$ ) reactions. Expected statistical features of the x-ray multiplicity distributions and associated limits on the applicability of the present technique for evaporation-residue cross section determination are discussed.

NUCLEAR REACTIONS: ${}^{180}{Hf}$ , ${}^{181}{Ta}$ , ${}^{186}W$ , ${}^{185, 187}{Re}$ , ${}^{194, 198}{Pt}$ , ${}^{197}{Au}$ , ${}^{203, 205}{Tl}$ , ${}^{208}{Pb}$ , ${}^{209}{Bi}$ ( ${}^{6, 7}{Li}$ , $xn$ ), $E_{Li} = 55 - 124$ MeV; enriched targets; measured x-ray—x-ray and x-ray $γ$ -ray coincidence yields; deduced $K$ x-ray multiplicity and total (Li, $xn$ ) cross sections. Origin of x rays accompanying nuclear reactions, multipolarity of converting $γ$ transitions, structure properties of transitional nuclei.

High-spin states in ${}^{83}{Br}$ and ${}^{85}{Rb}$

K. O. Zell, J. W. Peters, W. Gast, H. W. Schuh, and P. von Brentano

Phys. Rev. C 25, 1379 (1982) - Published 1 March, 1982

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High spin states in ${}^{83}{Br}$ and in ${}^{85}{Rb}$ were studied via the reactions ${}^{82}{Se}$ ( ${}^{6}{Li}$ , $α n γ$ ) ${}^{83}{Br}$ , ${}^{82}{Se}$ ( ${}^{7}{Li}$ , $α 2 n γ$ ) ${}^{83}{Br}$ , ${}^{82}{Se}$ ( ${}^{6}{Li}$ , $3 n γ$ ) ${}^{83}{Rb}$ , and ${}^{82}{Se}$ ( ${}^{7}{Li}$ , $4 n γ$ ) ${}^{85}{Rb}$ at beam energies of 25 to 36 MeV. In-beam $γ$ techniques were used to collect the data. Level schemes were constructed and spin and parity assignments were deduced. Thirty four $γ$ rays could be placed in two level schemes. Three new levels with spins up to $\frac{17}{2}$ , $\frac{19}{2} ℏ$ could be established for ${}^{83}{Br}$ and thirteen for ${}^{85}{Rb}$ with spins up to $\frac{29}{2} ℏ$ . Strongly populated yrast bands were found in both nuclei.

NUCLEAR REACTIONS ${}^{82}{Se}$ ( ${}^{7}{Li}$ , $α 2 n γ$ ) ${}^{83}{Br}$ , ${}^{82}{Se}$ ( ${}^{7}{Li}$ , $4 n γ$ ) ${}^{85}{Rb}$ , ${}^{82}{Se}$ ( ${}^{6}{Li}$ , $α n γ$ ) ${}^{83}{Br}$ , ${}^{82}{Se}$ ( ${}^{6}{Li}$ , $3 n γ$ ) ${}^{85}{Rb}$ ; measured $E_{γ}$ , $I_{γ}$ , $I_{γ} (θ)$ , $σ (E, E_{γ})$ , $γ γ$ coin.; deduced levels, $J$ , $π$ . Enriched target, Ge(Li) detectors.

${}^{24}{Mg}$ ( ${}^{12}C$ , $α$ ) ${}^{32}S$ reaction from ${E_{12}}_{C} = 24 - 36$ MeV

K. Daneshvar, W. K. Wells, D. P. Bybell, L. Mulligan, and D. P. Balamuth

Phys. Rev. C 25, 1388 (1982) - Published 1 March, 1982

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The ${}^{24}{Mg}$ ( ${}^{12}C$ , $α_{0, 1}$ ) ${}^{32}S$ reaction has been investigated in the energy range $E_{lab} = 24 - 36$ MeV. Excitation curves taken at forward (0°) and backward (173°) angles show striking dissimilarities in both the $α_{0}$ and $α_{1}$ channels. Complete angular distributions in the $α_{0}$ channel taken at selected energies do not resemble the square of a single Legendre polynomial over the full angular range. It is concluded that previous spin assignments to suggested isolated resonances using this reaction cannot be substantiated.

NUCLEAR REACTIONS ${}^{24}{Mg}$ ( ${}^{12}C$ , $α$ ) ${}^{32}S$ , $E_{lab} = 24 - 36$ MeV, measured $σ (E, \bar{ϑ}) = 0 °$ , $\bar{ϑ} = 173 °$ , $σ (ϑ)$ at selected energies.

High spin states in the doubly odd ${}^{72}{Br}$ nucleus

G. Garcia Bermudez, C. Baktash, A. J. Kreiner, and M. A. J. Mariscotti

Phys. Rev. C 25, 1396 (1982) - Published 1 March, 1982

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States of ${}^{72}{Br}$ were studied through the ${}^{58}{Ni}$ ( ${}^{16}O$ , $np$ ) reaction at $E = 40 to 55$ MeV. From the excitation function, $γ$ -ray angular distribution, $γ - γ$ coincidence and decay measurements, $γ$ rays depopulating states with probable spin values ranging up to $I = (9)$ were found. An isomeric state of $T_{\frac{1}{2}} = 10.3 \pm 0.6$ sec, and $I^{π} = (1^{-})$ at 101.0 keV excitation energy was found. The observation of certain similarities with a recently reported band in ${}^{74}{Br}$ suggests that the collective features seen in heavier Br isotopes may persist in ${}^{72}{Br}$ .

NUCLEAR REACTIONS ${}^{58}{Ni}$ ( ${}^{16}O$ , $np$ ) ${}^{72}{Br}$ , $E = 40 - 55$ MeV. Measured $E_{γ}$ , $I_{γ}$ , $I_{γ} (t)$ , $I_{γ} (θ)$ , $γ - γ (t)$ . ${}^{72}{Br}$ deduced levels, $I^{π}$ . Enriched Ni target. Ge(Li) detectors.

Multistep compound processes in heavy-ion-induced reactions

R. Bonetti, L. Colli Milazzo, M. Melanotte, and M. S. Hussein

Phys. Rev. C 25, 1406 (1982) - Published 1 March, 1982

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We suggest the possible contribution of multistep compound processes to light heavyion reactions at above-barrier energies. The presence of several correlation widths that characterize the fluctuation in energy of the excitation functions for different incidentoutgoing channel combinations is indicated and demonstrated explicitly for the system ${}^{12}C$ ( ${}^{15}N$ , $α$ ) at $E_{c . m .} = 9.51 - 17.33$ MeV. The importance of multistep compound processes to heavy-ion fusion studies is pointed out.

NUCLEAR REACTIONS Multistep compound processes in heavy ion reactions discussed.

${}^{10}B$ + ${}^{17}O$ fusion cross sections

Y. -D. Chan, D. E. DiGregorio, J. L. C. Ford, Jr., J. Gomez del Campo, M. E. Oritz, and D. Shapira

Phys. Rev. C 25, 1410 (1982) - Published 1 March, 1982

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The fusion cross section for ${}^{10}B$ + ${}^{17}O$ has been measured at four excitation energies in ${}^{27}{Al}$ of $E^{*} = 48.4, 55.1, 66.9, and 74.4$ MeV in order to study possible compound nucleus limitation effects on fusion for light heavy-ion systems at intermediate excitation energies. Comparing this data with other measurements for different entrance channels populating the same compound nucleus it is found that for $E^{*} \leq 60$ MeV all fusion bands in the $E^{*} - J$ plane of ${}^{27}{Al}$ appear to be parallel and displaced by the corresponding differences in separation energies, and that for $E^{*} > 60$ MeV the bands tend to converge indicating a possible compound nucleus limitation effect. The data are compared with existing models for entrance channel and statistical yrast line limitations.

NUCLEAR REACTIONS ${}^{17}O$ + ${}^{10}B$ , $E ({}^{17}O) = 54, 72, 104, and 124$ MeV; measured $\frac{d^{2} σ}{d Ω dE}$ for reaction products from $Z = 3 to 12$ . Extracted $σ_{fusion}$ .

Gamma-ray studies of ${}^{12}C$ + ${}^{20}{Ne}$ reactions

P. A. DeYoung, J. J. Kolata, R. C. Luhn, R. E. Malmin, and S. N. Tripathi

Phys. Rev. C 25, 1420 (1982) - Published 1 March, 1982

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Excitation functions for the yields of ten residual nuclides from the ${}^{12}C$ + ${}^{20}{Ne}$ reaction have been measured over the range $E_{c . m .} = 11 - 33$ MeV in steps of 150 keV, using $γ$ -ray techniques. The magnitude and energy dependence of the excitation functions for most partial yields, as well as for the total fusion yield, closely resemble those from the ${}^{16}O$ + ${}^{16}O$ system when compared at the same compound-nuclear excitation energy. The total fusion yield exhibits strong anomalies at $E_{c . m .} = 22.7 and 24.1$ MeV, while the ${}^{20}{Ne}$ inelastic scattering yield exhibits a strong uncorrelated structure at $E_{c . m .} = 21.1$ MeV. In addition weaker structure is seen at $E_{c . m .} = 13.6, 16.6, 18.6, and 26.3$ MeV in the total fusion yield. The 24.1 MeV resonance corresponds to a characteristic structure in the ${}^{16}O$ + ${}^{16}O$ reaction yields. Both structures appear at the same ${}^{32}S$ excitation energy and are found to be correlated with the transition to a regime of limited fusion.

NUCLEAR REACTIONS ${}^{20}{Ne}$ ( ${}^{12}C$ , $x$ ); $E_{c . m .} = 11 - 33$ MeV; measured excitation functions for production of $A = 20 - 30$ reaction products; observed structure at $E_{c . m .} = (13.6), 16.6, 18.6, 21.1, 22.7, 24.1, and 26.3$ MeV; deduced critical angular momentum for fusion.

Preequilibrium emission of particles in time-dependent Hartree-Fock calculations of ${}^{16}O$ + ${}^{93}{Nb}$ collisions

A. K. Dhar, M. Prakash, K. T. R. Davies, J. P. Bondorf, B. S. Nilsson, and S. Shlomo

Phys. Rev. C 25, 1432 (1982) - Published 1 March, 1982

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Prompt emission of nucleons is observed in time-dependent Hartree-Fock calculations of ${}^{16}O$ + ${}^{93}{Nb}$ collisions. These nucleons are emitted in the forward direction in about 2×10 ${}^{- 22}s$ after the contact of the ions, with a mean velocity somewhat less than the beam velocity. At $E (lab) = 204$ MeV, the estimated total nucleon cross section is ∼230 mb. For central collisions a lower energy threshold of 130 MeV is established. Force dependence of the results is studied in detail.

NUCLEAR REACTIONS ${}^{16}O$ ( ${}^{93}{Nb}$ , $x$ ) in time-dependent Hartree-Fock approximation. Energy and angular momentum dependence and effect of nuclear interaction on preequilibrium emission of particles.

Fusion, direct, and total reaction cross sections of the ${}^{10}B$ + ${}^{14}N$ system up to ${E_{14}}_{N} = 180$ MeV

M. E. Ortiz, J. Gomez del Campo, Y. D. Chan, D. E. DiGregorio, J. L. C. Ford, D. Shapira, R. G. Stokstad, J. P. F. Sellschop, R. L. Parks, and D. Weiser

Phys. Rev. C 25, 1436 (1982) - Published 1 March, 1982

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The fusion cross section of the ${}^{10}B$ + ${}^{14}N$ system has been measured at five energies covering the range ${E_{14}}_{N} = 86 - 180$ MeV. Angular distributions of fusion and direct reaction components for products from $Z = 3$ to $Z = 11$ have been determined. Hauser-Feshbach calculations of the $Z$ distributions, energies and angular distributions of the evaporation residues are presented and compared to the data. The fusion cross section decreases slowly with increasing energy and reaches a maximum angular momentum of about $21 \pm 1 ℏ$ . The fusion cross section is discussed in terms of entrance channel models and compound nucleus formation and is compared to that of the ${}^{12}C$ + ${}^{12}C$ system. The experimental total reaction cross sections are in good agreement with optical model calculations with parameters deduced from elastic scattering.

NUCLEAR REACTIONS ${}^{14}N$ + ${}^{10}B$ , ${E_{14}}_{N} = 86 to 180$ MeV, measured $\frac{d^{2} σ}{d Ω dE}$ for reaction products from $Z = 3 to 11$ . Extracted $σ_{fusion}$ , $σ_{direct}$ , and $σ_{total}$ .

Measurement and statistical analyses of fission and fusion excitation functions for ${}^{35}{Cl}$ on ${}^{62}{Ni}$ , ${}^{116}{Sn}$ , and ${}^{141}\Pr$ up to $E_{lab} = 215$ MeV

B. Sikora, W. Scobel, M. Beckerman, J. Bisplinghoff, and M. Blann

Phys. Rev. C 25, 1446 (1982) - Published 1 March, 1982

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Evaporation residue and fission-like cross sections are reported for the bombardment of ${}^{62}{Ni}$ , ${}^{116}{Sn}$ , and ${}^{141}\Pr$ targets with 200 and 215 MeV ${}^{35}{Cl}$ ions. These data plus data previously reported at lower energies have been analyzed by a Hauser-Feshbach statistical code with Bohr-Wheeler model fission competition. The rotating liquid drop model was used to evaluate effective fission barriers. Barrier reductions of 35-45% of the rotating liquid drop model values were required over an angular momentum range for which fission was measured, in agreement with earlier analyses. The sensitivity of results of results to the sharp cutoff assumption was tested and found to be unimportant over the energy ranges covered in this work.

NUCLEAR REACTIONS Measured $σ_{E R, f}$ ${}^{35}{Cl}$ + ${}^{62}{Ni}$ , ${}^{116}{Sn}$ , ${}^{141}\Pr$ $E_{lab} = 200, 215$ MeV. Deduced statistical fission parameters.

Dynamics of nuclear fluid. VIII. Time-dependent Hartree-Fock approximation from a classical point of view

Cheuk-Yin Wong

Phys. Rev. C 25, 1460 (1982) - Published 1 March, 1982

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In order to facilitate the comparison of the time-dependent Hartree-Fock approximation with other classical theories and to help guide our intuition in understanding the underlying physics, we study the time-dependent Hartree-Fock approximation from a classical viewpoint. We show that the time-dependent Hartree-Fock approximation is approximately equivalent to a purely classical pseudoparticle simulation. In this simulation, a collection of pseudoparticles is introduced to discretize the phase space of spatial and momentum coordinates. The dynamics is completely determined by following the pseudoparticle trajectories which are the same as the trajectories of real particles moving in the self-consistent field. As an application of the concept of the pseudoparticle simulation, we study the origin of the nonfusion events in nearly-head-on heavy-ion collisions as obtained in the time-dependent Hartree-Fock approximation. It is argued that for these nearly-head-on collisions, the emergence of the most energetic pseudonucleons of one nucleus outside the far surface of the other nucleus initiates a coherent flow-through motion because of self-consistency and leads to the breakup of the composite system. Based on this picture, we obtain quantitative estimates of the threshold energies and the low- $l$ fusion window which agree quite well with the time-dependent Hartree-Fock results.

NUCLEAR REACTIONS Time-dependent Hartree-Fock approximation. Vlasov equation. Pseudoparticle simulation. Low- $l$ fusion window in heavy-ion collisions.

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Survey of the ( ${}^{3}{He}$ , $t$ ) reaction: Excitation of the isobaric analog of the giant dipole resonance

Excitation of the giant resonance region in silicon by inelastic scattering of 115 MeV protons

Surprisal analysis of inclusive reactions

Excitation of ${}^{81}{As}$ by the ${}^{82}{Se}$ ( $t$ , $α$ ) reaction

Electric dipole transitions from neutron capture in ${}^{173}{Yb}$ resonances

Variation of the matter densities of nuclei from ${}^{40}{Ca}$ to ${}^{68}{Zn}$

Deexcitation of fragments produced in deeply inelastic collisions of 100 MeV ${}^{16}O$ with ${}^{27}{Al}$

High-spin states in neutron-deficient nuclei near $A = 80$

Fusion cross section behavior for ${}^{12}C$ + ${}^{24}{Mg}$ and ${}^{12}C$ + ${}^{26}{Mg}$

Multiplicity of $K$ x rays and collective structure in the transitional nuclei with $A ≃ 200$

High-spin states in ${}^{83}{Br}$ and ${}^{85}{Rb}$

${}^{24}{Mg}$ ( ${}^{12}C$ , $α$ ) ${}^{32}S$ reaction from ${E_{12}}_{C} = 24 - 36$ MeV

High spin states in the doubly odd ${}^{72}{Br}$ nucleus

Multistep compound processes in heavy-ion-induced reactions

${}^{10}B$ + ${}^{17}O$ fusion cross sections

Gamma-ray studies of ${}^{12}C$ + ${}^{20}{Ne}$ reactions

Preequilibrium emission of particles in time-dependent Hartree-Fock calculations of ${}^{16}O$ + ${}^{93}{Nb}$ collisions

Fusion, direct, and total reaction cross sections of the ${}^{10}B$ + ${}^{14}N$ system up to ${E_{14}}_{N} = 180$ MeV

Measurement and statistical analyses of fission and fusion excitation functions for ${}^{35}{Cl}$ on ${}^{62}{Ni}$ , ${}^{116}{Sn}$ , and ${}^{141}\Pr$ up to $E_{lab} = 215$ MeV

Dynamics of nuclear fluid. VIII. Time-dependent Hartree-Fock approximation from a classical point of view

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