Recent Articles

RAPID COMMUNICATION

Pion interferometry analysis for 1.2 GeV/nucleon Ar on KCl

D. Beavis, S. Y. Chu, S. Y. Fung, W. Gorn, D. Keane, R. T. Poe, G. VanDalen, and M. Vient

Phys. Rev. C 28, 2561(R) (1983) - Published 1 December, 1983

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The technique of pion interferometry is used to study the pion source for central collisions of 1.2 GeV/nucleon Ar on KCl. The data are described by a Gaussian source of radius 3.8 ± 0.5 fm, a lifetime of 5.4 ± 1.8 fm/c, and a degree of coherence of 0.74 ± 0.17. The sensitivity of the analysis to the two-particle phase space is discussed. A comparison with previously reported results at 1.5 GeV/nucleon is presented.

NUCLEAR REACTIONS ${}^{40}{Ar}$ (KCl) $E_{lab} = 1.2$ GeV/nucleon, $π^{-} - π^{-}$ correlations, pion interferometry, pion source, Hanbury-Brown Twiss effect, multipion production, streamer chamber.

RAPID COMMUNICATION

Pion single charge exchange on ${}^{14}C$

F. Irom, J. R. Comfort, R. Jeppesen, J. J. Kraushaar, R. A. Ristinen, W. Tew, J. L. Ullmann, H. W. Baer, J. D. Bowman, M. D. Cooper, E. Piasetzky, U. Sennhauser, A. Erell, M. A. Moinester, and E. R. Siciliano

Phys. Rev. C 28, 2565(R) (1983) - Published 1 December, 1983

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Forward-angle differential cross sections for the isobaric-analog state in the ${}^{14}C (π^{+}, π^{0}) {}^{14}N$ reaction were measured at 100, 165, 230, and 295 MeV. The extracted excitation function is found to have a maximum near 200 MeV and its shape resembles that of the free $π N$ cross sections. Impulse-approximation calculations with optical potentials linear in the nuclear density do not reproduce the trends of the data. Systematics of 0° cross sections with $N$ and $Z$ are presented.

RAPID COMMUNICATION

Fragment emission and the lifetime of pre-equilibrium states

David H. Boal

Phys. Rev. C 28, 2568(R) (1983) - Published 1 December, 1983

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The production of nuclear fragments in the 10-30 mass number range is viewed as a nonequilibrium process in which individual nucleons in kinetic equilibrium coalesce to form fragments. A simplified set of rate equations for fragment formation is solved numerically which allows for a determination of the lifetime of the fragment formation epoch by comparison with data. The lifetime so calculated is about 4 × $10^{- 23}$ sec.

RAPID COMMUNICATION

Distribution of $E 1$ spin flip strength in ${}^{12}C$

B. Castel and A. G. M. van Hees

Phys. Rev. C 28, 2571(R) (1983) - Published 1 December, 1983

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A very recent pion inelastic scattering experiment has revealed the existence of strong spin flip $E 1$ resonances in light nuclei. The data are particularly impressive in ${}^{12}C$ where two strong peaks are observed in the vicinity of the giant dipole resonance. We present here the first large scale shell model calculation of such electric spin excitations in ${}^{12}C$ and discuss their admixture and influence on other $S = 0$ states.

NUCLEAR STRUCTURE Spin flip $E 1$ , shell model calculation.

Channel-coupling effects in the resonating-group study of the seven-nucleon system

Y. Fujiwara and Y. C. Tang

Phys. Rev. C 28, 1869 (1983) - Published 1 November, 1983

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A three-channel resonating-group calculation is performed to study the effects of channel coupling on the properties of the ${}^{3}H$ + $α$ system. The channels included are ${}^{3}H$ + $α$ , n+ ${}^{6}{Li}$ , and n+ ${}^{6}{Li}$ * channels, with ${}^{6}{Li}$ and ${}^{6}{Li}$ * described by ${(1 s)}^{4} {(1 p)}^{2}$ harmonic-oscillator functions representing d+ $α$ cluster configurations with relative orbital angular momenta equal to 0 and 2, respectively. By comparing with the ${}^{3}H$ + $α$ single-channel result, it is found that the three-channel calculation improves the $L = 1$ ground state energy by 0.68 MeV and yields additional features such as cusps in the $L = 0 and 2$ phase shifts and a dispersionlike resonance structure in the $L = 1$ phase shift. In addition, it is noted that, in states with larger $L$ values, the n+ ${}^{6}{Li}$ * aligned configurations make particularly important contributions. Characteristics of nucleon-exchange terms have also been briefly investigated; here one finds that, as far as the ${}^{3}H$ + $α$ system is concerned, the important one-exchange and core-exchange contributions are only weakly affected by the presence of other channels.

NUCLEAR REACTIONS ${}^{3}H (α, n) {}^{6}{Li}$ , ${}^{3}H (α, n) {}^{6}{Li}^{*}$ . Effects of channel coupling. Resonating-group method with ${}^{3}H$ + $α$ , n + ${}^{6}{Li}$ , and n + ${}^{6}{Li}$ * channels.

${}^{4}{He} (\vec{d}, p) n {}^{4}{He}$ reaction at 12 and 21 MeV deuteron energy

M. Ishikawa, S. Seki, K. Furuno, Y. Tagishi, M. Sawada, T. Sugiyama, K. Matsuda, T. Murayama, N. X. Dai, J. Sanada, and Y. Koike

Phys. Rev. C 28, 1884 (1983) - Published 1 November, 1983

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The double differential cross section, the vector analyzing power, and the tensor analyzing powers for the ${}^{4}{He} (\vec{d}, p) n {}^{4}{He}$ reaction were measured at 12 and 21 MeV deuteron energy and in steps of 5° between 15° and 75° in the laboratory system. The experimental results are compared with the Faddeev calculations, in which three cases for the treatment of the neutron-proton interaction are tested. As a result, we can demonstrate what interaction is effective on each observable.

NUCLEAR REACTIONS ${}^{4}{He}$ $(\vec{d}, p) n {}^{4}{He}$ , $E_{d} = 12.0, 21.0$ MeV; measured $\frac{d^{2} σ}{d Ω d E_{p}}$ , $i T_{11} (θ)$ , $T_{20} (θ)$ , $T_{21} (θ)$ , $T_{22} (θ)$ . Faddeev calculations.

Emission of alpha particles in statistical multistep compound reactions

R. Bonetti, L. Colli Milazzo, R. Landini, M. Melanotte, A. De Rosa, G. Inglima, E. Perillo, M. Sandoli, and F. Shahin

Phys. Rev. C 28, 1892 (1983) - Published 1 November, 1983

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Excitation functions and angular distributions of alpha particles emitted from the ${}^{27}{Al} ({}^{3}{He}, α)$ and ${}^{27}{Al} (p, α)$ reactions are measured at a composite nucleus excitation energy of about 30 MeV. The experimental results together with the widely varying correlation widths extracted from the fluctuation analysis are successfully interpreted on the basis of the statistical multistep compound emission mechanism. Confirmation is found of the interpretation of each experimental correlation width in terms of a coherent sum of the widths of the relevant stages of the reactions, previously proposed in the case of proton channels. Moreover, the $α$ -spectrum shape and the correlation width values are shown to be consistent with an $α$ preformation picture of the target nuclei considered.

NUCLEAR REACTIONS ${}^{27}{Al} ({}^{3}{He}, α)$ $E = 8.2 - 13$ MeV; ${}^{27}{Al} (p, α)$ , $E = 18.5 - 25.6$ MeV; measured $σ (E; ϑ)$ ; statistical multistep compound emission, calculated $σ (E)$ , $σ (E_{α})$ ; generalized autocorrelation analysis, extracted coherence widths; suggested $α$ preformation.

Optical model description of $α$ + ${}^{16}O$ elastic scattering and alpha-cluster structure in ${}^{20}{Ne}$

F. Michel, J. Albinski, P. Belery, Th. Delbar, Gh. Grégoire, B. Tasiaux, and G. Reidemeister

Phys. Rev. C 28, 1904 (1983) - Published 1 November, 1983

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${}^{16}O (α, α)$ elastic scattering angular distributions have been measured for incident energies 39.3, 49.5, and 69.5 MeV. These data, and previous measurements at 32.2, 104, and 146 MeV, have been subjected to a global optical model analysis. The deduced global potential has two energy-dependent parameters which are found to vary smoothly with energy and it is uniquely determined by the data. Backward angular distributions measured between 40 and 54 MeV are also presented and shown to be nicely reproduced by the model. The sensitivity of the cross sections to the various regions of the real potential has been investigated as a function of energy using the notch test technique. The low energy behavior of the differential cross sections can be understood in terms of the semiclassical decomposition of Brink and Takigawa. A natural extrapolation of the global potential below 30 MeV is shown to reproduce the wide bump observed in the experimental excitation functions around 20 MeV. This bump is shown to be due to an $l = 8$ shape resonance and is interpreted as the $J^{π} = 8^{+}$ member of the $K^{π} = 0_{4}^{+}$ rotational band of ${}^{20}{Ne}$ , in contradiction with the current attribution. Other bound and quasibound states supported by the potential are discussed in the light of orthogonality condition model-type arguments and shown to be consistent with the well-known $K^{π} = 0_{1}^{+} and 0^{-}$ bands, and with the first three states of the $K^{π} = 0_{4}^{+}$ band of ${}^{20}{Ne}$ .

NUCLEAR REACTIONS ${}^{16}O (α, α)$ , measured $σ (θ)$ , $E_{α} = 39.3, 49.5, 69.5$ MeV; global optical model analysis, $E_{α} = 32 - 146$ MeV; semiclassical decomposition of the scattering amplitude; investigation of the compatibility of the potential description with existing low energy data and comparison with cluster models.

Variational estimate of a breakup amplitude

B. G. Giraud and M. A. Nagarajan

Phys. Rev. C 28, 1918 (1983) - Published 1 November, 1983

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Estimates of the correction to the Born amplitude are obtained from a variational principle. A wave packet representation is used to provide an off-shell amplitude in a time-independent theory of collisions. The theory is applied numerically to a breakup reaction p + ${}^{3}H$ → p + n + d.

NUCLEAR REACTIONS Time independent, off-shell amplitude, obtained from variational principle. Wave packet representation generates fragmentation exclusive cross sections.

Deuteron-gamma angular correlations in the reactions ${}^{24, 26}{Mg}$ , ${}^{28, 30}{Si} (d, d_{1} γ)$ at $E_{d} = 10$ MeV

F. Vogler, J. Böttcher, W. Eyrich, A. Hofmann, M. Meyer, and U. Scheib

Phys. Rev. C 28, 1925 (1983) - Published 1 November, 1983

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We measured differential cross sections and $d_{1}$ - $γ$ angular correlations for the scattering of 10 MeV deuterons on ${}^{24}{Mg}$ , ${}^{26}{Mg}$ , ${}^{28}{Si}$ , and ${}^{30}{Si}$ . The data were analyzed in terms of coupled channels in a $0^{+}$ - $2^{+}$ coupling scheme on the basis of a symmetric rigid rotator model and in the framework of the distorted wave Born approximation. The correlation data of ${}^{24, 26}{Mg}$ show a remarkable prolateoblate sensitivity. They can be described also in the distorted wave Born approximation, but only in the prior interaction form. For ${}^{30}{Si}$ multistep processes can be indicated. The results are consistent with a prolate nuclear shape of ${}^{30}{Si}$ .

NUCLEAR REACTIONS ${}^{24, 26}{Mg}$ ${}^{28, 30}{Si} (d, d^{'} γ)$ , $E_{d} = 10$ MeV; measured inplane $d_{1} - γ$ correlations. ${}^{24, 26}{Mg}$ ${}^{28, 30}{Si}$ deduced prolate-oblate nuclear shape, restriction of optical model parameters. Coupled channels and DWBA analyses, enriched targets.

Charge exchange (p,n) reactions to the isobaric analog states of high $Z$ nuclei: $73 \leq Z \leq 92$

L. F. Hansen, S. M. Grimes, C. H. Poppe, and C. Wong

Phys. Rev. C 28, 1934 (1983) - Published 1 November, 1983

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Differential cross sections have been measured for the (p,n) reaction to the isobaric analog states of ${}^{181}{Ta}$ , ${}^{197}{Au}$ , ${}^{209}{Bi}$ , ${}^{232}{Th}$ , and ${}^{238}U$ at an incident energy of 27 MeV. Because of the importance of collective effects in this mass region, coupled-channel calculations have been carried out in the analysis of the data. Optical potentials obtained from the Lane model for the charge exchange reaction have been used in the simultaneous analysis of coupled proton and neutron channels. The sensitivity of the calculations to the different couplings between the levels and to the magnitude of the isovector potentials, $V_{1}$ and $W_{1}$ , is discussed. The good agreement obtained between the measured and calculated (p,n) angular distributions to the analog state confirms the validity of the Lane formalism for high- $Z$ nuclei ( $Z \geq 50$ ). Elastic neutron differential cross sections inferred from the coupled-channel analysis are compared with measurements available in the literature in the energy range 7-8 MeV. The results of these calculations agree with the measured values as well as the results of calculations made using global neutron optical potential parameters optimized to fit neutron data.

NUCLEAR REACTIONS ${}^{181}{Ta}$ , ${}^{197}{Au}$ , ${}^{209}{Bi}$ , ${}^{232}{Th}$ , ${}^{238}U$ (p,n)IAS; $E = 27$ MeV; Measured $σ (θ)$ for ground-state analog transition; deduced (n,n) $σ (θ)$ , $E = 7 - 8$ MeV; coupled-channel analysis.

Isoscalar giant resonances in ${}^{208}{Pb}$ —in particular $2 ℏ ω$ $L = 0, 2, 4, and 6$ excitations—studied in small angle $α$ scattering

H. P. Morsch, P. Decowski, M. Rogge, P. Turek, L. Zemło, S. A. Martin, G. P. A. Berg, W. Hürlimann, J. Meissburger, and J. G. M. Römer

Phys. Rev. C 28, 1947 (1983) - Published 1 November, 1983

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Inelastic excitation of giant resonances has been studied in 172 MeV $α$ scattering from ${}^{208}{Pb}$ at scattering angles of 1.5°-8°. Fine structures in the region of the giant monopole and quadrupole resonances indicate multipolarities also different from $L = 0 and 2$ . The isoscalar $L = 0 and 2$ strengths in the giant resonance region yield (90±20)% and (70±20)% of the corresponding energy weighted sum rule limit. This is consistent with other hadron scattering results, with higher energy electron scattering, and with microscopic random phase approximation results. However, the strength for $L = 2$ excitations is significantly larger than extracted from lower energy electron scattering. Fine structures observed are compared with high resolution (p,p′) and (e,e′) results. At scattering angles 5°-8° new structures have been observed at $E_{x} = 12.5 and 16.0$ MeV consistent with multipolarities $L = 4 and 6$ . Together with the contribution of higher multipolarity extracted at lower excitation energies from the angular distributions of giant monopole and quadrupole excitations, this indicates rather broad distributions of $2 ℏ ω$ $L = 4 and 6$ excitations with centroid energies of 12.2 and 13.7 MeV and widths of 4.5 and 7.8 MeV, respectively. The extracted sum rule strengths for $L = 4 and 6$ are in the order of 30% in each case. In the region of the giant monopole resonance evidence for additional $L = 2$ excitation was found (≤14% energy weighted sum rule strength). The fact that strong contributions of $L > 0$ are obtained solves the problem of a former too large monopole cross section in $α$ scattering which was inconsistent with microscopic descriptions. A recently suggested "antiscaling" mode for the giant monopole resonance, in which the nuclear surface vibrates opposite in phase to the "scaling" mode, can be ruled out by our experimental data. The existence of two odd parity giant resonances at $E_{x} = 18.7$ MeV ( $L = 3$ ) MeV ( $L = 1$ ) with widths of 5.0 and 5.9 MeV, respectively, are confirmed by our small angle scattering experiments. Our description of the dipole compressional mode is in excellent agreement with 200 MeV proton scattering data.

NUCLEAR REACTIONS ${}^{208}{Pb} (α, α^{'})$ ; $E_{α} = 172$ MeV. Small angle scattering, $θ = 1.5 ° - 8 °$ ; measured $σ (θ)$ . Deduced excitation strength distributions for giant resonances of multipolarities $L = 0 - 6$ .

Direct-semidirect model angular distributions for radiative capture or photonuclear reactions involving nonzero target or residual spins

H. R. Weller, R. G. Seyler, and R. Moreh

Phys. Rev. C 28, 1959 (1983) - Published 1 November, 1983

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A recent study of ( $γ$ , $n_{0}$ ) reactions on ${}^{207}{Pb}$ and ${}^{208}{Pb}$ produced a direct-semidirect model calculation of the angular distribution (the $a_{2}$ coefficient) which was vastly different for these two cases. In this paper we offer the formal proof that this is incorrect. It is shown that the angular distribution involving a target with spin is exactly equal to that obtained if the target is treated as spin zero with the residual spin being the single particle total angular momentum in the final state. A corrected calculation for $a_{2}$ is presented for the case of ${}^{208}{Pb} (γ, n_{0}) {}^{207}{Pb}$ and ${}^{207}{Pb} (γ, n_{0}) {}^{206}{Pb}$ .

NUCLEAR REACTIONS Formal derivation of the relationship between the angular distribution for radiative capture involving targets with and without spin for the direct-semidirect model. Errors in the literature are corrected.

Complete fusion of ${}^{74}{Ge}$ + ${}^{74}{Ge}$

M. Beckerman, M. K. Salomaa, J. Wiggins, and R. Rohe

Phys. Rev. C 28, 1963 (1983) - Published 1 November, 1983

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Differential cross sections for evaporation residue formation following complete fusion of ${}^{74}{Ge}$ with 218-305 MeV ${}^{74}{Ge}$ ions were measured with high precision using a velocity selector together with a counter telescope. The resulting excitation function for complete fusion ranged in magnitude from 435 mb near 150 MeV down to 27 μb at 108.5 MeV (c.m.). We observed increases in the subbarrier fusion of ${}^{74}{Ge}$ + ${}^{74}{Ge}$ , compared to ${}^{58, 64}{Ni}$ + ${}^{74}{Ge}$ , consistent with those observed previously in systems where ${}^{74}{Ge}$ replaces either ${}^{58}{Ni}$ or ${}^{64}{Ni}$ as a collision partner. Correlations between variations among fusion excitation functions for the ${}^{58}{Ni}$ + ${}^{58}{Ni}$ to ${}^{74}{Ge}$ + ${}^{74}{Ge}$ systems and the underlying nuclear structure were examined. We discussed nucleon transfer and other dynamic processes which may be responsible for the complex variations and for the overall increases in sub-barrier fusion observed in comparisons to static, barrier penetration calculations.

NUCLEAR REACTIONS Complete fusion, ${}^{74}{Ge}$ + ${}^{74}{Ge}$ $E = 218 - 305$ MeV (lab), measured $σ (E, θ)$ for evaporation residues; discussed fusion dynamics.

Low and intermediate energy nucleus-nucleus elastic scattering and the optical limit of Glauber theory

J. Chauvin, D. Lebrun, A. Lounis, and M. Buenerd

Phys. Rev. C 28, 1970 (1983) - Published 1 November, 1983

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It is shown that a simplified Glauber approach using an experimental nucleon-nucleon forward amplitude and a Gaussian nucleus density reproduces fairly well both nucleus-nucleus reaction cross sections and elastic scattering differential cross sections over a broad energy range.

NUCLEAR REACTIONS ${}^{12}C$ + ${}^{12}C$ elastic scattering, $\frac{E}{A} = 25, 30, and 85$ MeV, optical limit of Glauber theory, reaction cross section.

Breakup fusion of ${}^{7}{Li}$

H. Utsunomiya, S. Kubono, M. H. Tanaka, M. Sugitani, K. Morita, T. Nomura, and Y. Hamajima

Phys. Rev. C 28, 1975 (1983) - Published 1 November, 1983

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A breakup process of ${}^{7}{Li}$ has been studied by performing the following measurements with a 77 MeV ${}^{7}{Li}$ beam; (i) energy and angular distributions of $z = 1 and 2$ particles in the ${}^{159}{Tb}$ + ${}^{7}{Li}$ reaction measured in singles and in coincidence with $γ$ rays from some heavy residual nuclei, (ii) out-of-plane angular distributions of $γ$ rays taken in coincidence with $α$ particles in the ${}^{159}{Tb} ({}^{7}{Li}, α x n) {}^{162 - x}{Dy}$ reaction to deduce the spin alignment involved, and (iii) in-plane and out-of-plane angular distributions of fission fragments measured in coincidence with $z = 1 and 2$ particles emitted in the reaction of ${}^{232}{Th} ({}^{7}{Li}, x f)$ to extract the magnitude and alignment of the transferred angular momenta. The observed energy spectrum of tritons and $α$ particles measured at forward angles exhibits a broad bump centered at a kinetic energy corresponding to the beam velocity, which is characteristic of the breakup mechanism. Roughly a half of the yield at this bump has been shown to originate from a breakup-fusion process, in which one of the breakup fragments is captured by a target nucleus. It is also shown that angular momenta transferred to residual nuclei by breakup fusion are well aligned along the normal to the reaction plane and have the magnitude, on the average, consistent with a direct reaction process occurring at the surface region of projectile and target nuclei.

NUCLEAR REACTIONS ${}^{159}{Tb} ({}^{7}{Li}, x)$ , ( ${}^{7}{Li}$ , $α x n$ ), $E = 77$ MeV; measured $σ (E_{x}, θ_{x})$ , $α - γ$ coin, angular correlations $W (θ_{γ})$ of discrete $γ$ rays; deduced $σ (E_{α})$ in coin with final nuclei; ${}^{232}{Th} ({}^{7}{Li}, x f)$ , $E = 77$ MeV; measured $x - f$ angular correlations; deduced magnitude and alignment of average $J$ . Average $l$ for particle emission.

Spin alignment and phase angles in ${}^{12}C$ + ${}^{12}C$ inelastic scattering

S. J. Willett, S. K. Korotky, R. L. Phillips, D. A. Bromley, and K. A. Erb

Phys. Rev. C 28, 1986 (1983) - Published 1 November, 1983

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The spin alignment $A$ and the relative phase angle $β$ between the $m = + 2 and - 2$ substates populated in ${}^{12}C$ + ${}^{12}C$ ( $2_{1}^{+}$ ) inelastic scattering were measured over a wide range of particle scattering angles ( $53 ° < θ_{c . m .} < 101 °$ ) and interaction energies ( $15 < E_{c . m .} < 33$ MeV). Although the substate population parameters depend rather strongly on reaction angle, the angle-averaged alignment is markedly enhanced at energies where either broad or narrow maxima occur in $σ (E)$ , at least below $E_{c . m .} = 26$ MeV. Above that energy variations in the alignment become damped with respect to both bombarding energy and reaction angle. The relative phase $β (θ)$ is approximately linear in $θ$ at most energies. For energies below $E_{c . m .} = 26$ MeV corresponding to gross structure maxima in the inelastic cross sections, the measured dependence of the phase on reaction angle suggests that the reaction is dominated at these energies by individual entrance and exit channel partial waves $L$ and $L^{'}$ , respectively, and that these are related by $L^{'} = L - 2$ . Thus a strongly aligned configuration can be associated with the maxima. At neighboring energies no evidence for such alignment was found. Calculations with the band-crossing, diffraction, distorted-wave Born approximation, and barrier-top models were compared to the measurements. None provide an adequate representation of the data.

NUCLEAR REACTIONS ${}^{12}C ({}^{12}C, {}^{12}C γ)$ , $E_{lab} = 30 - 65$ MeV, $θ_{c . m .} ({}^{12}C) = 53 ° - 101 °$ . Measured particle- $γ$ angular correlations; deduced magnetic substate alignments, phase angles; compared with model predictions.

Fragment emission in high-energy heavy-ion reactions

László P. Csernai, Horst Stöcker, Pal R. Subramanian, Gerd Buchwald, Gerhard Graebner, Albrect Rosenhauer, Joachim A. Maruhn, and Walter Greiner

Phys. Rev. C 28, 2001 (1983) - Published 1 November, 1983

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We present a theoretical description of nuclear collisions which consists of a three-dimensional fluid-dynamical model, a chemical equilibrium breakup calculation for local light fragment (i.e., p, n, d, t, ${}^{3}{He}$ , and ${}^{4}{He}$ ) production, and a final thermal evaporation of these particles. The light fragment cross sections and some properties of the heavy target residues are calculated for the asymmetric system Ne+U at 400 MeV/N. The results of the model calculations are compared with recent experimental data. Several observable signatures of the collective hydrodynamical processes are consistent with the present data. An event-by-event analysis of the flow patterns of the various clusters is proposed which can yield deeper insight into the collision dynamics.

NUCLEAR REACTIONS Relativistic heavy-ion reactions, hydrodynamic description, nucleon and nuclear cross sections.

Doorways and multistep compound reactions

Sadhan K. Adhikari

Phys. Rev. C 28, 2013 (1983) - Published 1 November, 1983

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The "optical background" representation of Kawai, Kerman, and McVoy for the fluctuation amplitude is written in an alternate form which has certain advantages in formulating the theory of doorway states and of multistep compound reactions. We reconsider the doorway state approach of Feshbach, Kerman, and Lemmer using the present representation of the fluctuation amplitude. Finally, we use the present representation of the fluctuation amplitude for developing a theory of multistep compound reactions following the idea of chaining due to Feshbach, Kerman, and Koonin. The advantages of the present approach are emphasized in both the cases.

NUCLEAR REACTIONS Optical background representation of the fluctuation amplitude, doorways, preequilibrium reactions, multistep compound reactions.

Fission of polonium, osmium, and erbium composite systems

J. van der Plicht, H. C. Britt, M. M. Fowler, Z. Fraenkel, A. Gavron, J. B. Wilhelmy, F. Plasil, T. C. Awes, and G. R. Young

Phys. Rev. C 28, 2022 (1983) - Published 1 November, 1983

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Fission cross section excitation functions were measured from near threshold to ∼10 MeV/nucleon using ${}^{9}{Be}$ , ${}^{12}C$ , ${}^{16, 18}O$ , ${}^{24, 26}{Mg}$ , ${}^{32}S$ , and ${}^{64}{Ni}$ beams. The systems studied included ${}^{210}{Po}$ formed in ${}^{12}C$ and ${}^{18}O$ induced reactions; ${}^{186}{Os}$ formed in ${}^{9}{Be}$ , ${}^{12}C$ , ${}^{16}O$ , and ${}^{26}{Mg}$ reactions; and ${}^{158}{Er}$ formed in ${}^{16}O$ , ${}^{24}{Mg}$ , ${}^{32}S$ , and ${}^{64}{Ni}$ reactions. In addition, the composite systems ${}^{204, 206, 208}{Po}$ formed with ${}^{16}O$ and ${}^{18}O$ projectiles were studied. In the experiment the velocities and emission angles of two coincident fission fragments were measured using position-sensitive multiwire proportional counter stop detectors and a thin (∼200 μg/ ${cm}^{2}$ ) gas "start" detector. The measured fission excitation functions along with previous data from ${}^{4}{He}$ and ${}^{11}B$ bombardments for the ${}^{186}{Os}$ and ${}^{210}{Po}$ systems and recent data on the ${}^{200}{Pb}$ system are compared to statistical model calculations using recent angular momentum dependent fission barriers calculated by Sierk. Comparisons of calculated and measured fission excitation functions show good overall agreement between data and theoretical predictions. These comparisons give good agreement for both a wide range of mass of the composite system and for a wide range of mass asymmetry in the entrance channel. It is concluded that the fission barriers of Sierk give a good description of both the mass and angular momentum dependence of fission barriers in this region.

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Pion interferometry analysis for 1.2 GeV/nucleon Ar on KCl

Pion single charge exchange on ${}^{14}C$

Fragment emission and the lifetime of pre-equilibrium states

Distribution of $E 1$ spin flip strength in ${}^{12}C$

Channel-coupling effects in the resonating-group study of the seven-nucleon system

${}^{4}{He} (\vec{d}, p) n {}^{4}{He}$ reaction at 12 and 21 MeV deuteron energy

Emission of alpha particles in statistical multistep compound reactions

Optical model description of $α$ + ${}^{16}O$ elastic scattering and alpha-cluster structure in ${}^{20}{Ne}$

Variational estimate of a breakup amplitude

Deuteron-gamma angular correlations in the reactions ${}^{24, 26}{Mg}$ , ${}^{28, 30}{Si} (d, d_{1} γ)$ at $E_{d} = 10$ MeV

Charge exchange (p,n) reactions to the isobaric analog states of high $Z$ nuclei: $73 \leq Z \leq 92$

Isoscalar giant resonances in ${}^{208}{Pb}$ —in particular $2 ℏ ω$ $L = 0, 2, 4, and 6$ excitations—studied in small angle $α$ scattering

Direct-semidirect model angular distributions for radiative capture or photonuclear reactions involving nonzero target or residual spins

Complete fusion of ${}^{74}{Ge}$ + ${}^{74}{Ge}$

Low and intermediate energy nucleus-nucleus elastic scattering and the optical limit of Glauber theory

Breakup fusion of ${}^{7}{Li}$

Spin alignment and phase angles in ${}^{12}C$ + ${}^{12}C$ inelastic scattering

Fragment emission in high-energy heavy-ion reactions

Doorways and multistep compound reactions

Fission of polonium, osmium, and erbium composite systems

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