Recent Articles

Energy levels of ${}^{249}{Cm}$ from measurements of thermal neutron capture gamma rays

R. W. Hoff, W. F. Davidson, D. D. Warner, H. G. Börner, and T. von Egidy

Phys. Rev. C 25, 2232 (1982) - Published 1 May, 1982

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The excited levels of ${}^{249}{Cm}$ have been determined by use of neutron-capture gamma-ray spectroscopy. Gamma-ray measurements were made with curved-crystal spectrometers of focal lengths 5.8 and 24 m and a pair spectrometer. These experimental data represent the first measurement of gamma transitions depopulating the levels of ${}^{249}{Cm}$ . We present evidence for the population of 23 levels in ${}^{249}{Cm}$ up to 1300-keV excitation. The following new configuration assignments were made (listed with the corresponding bandhead energies): ${\frac{5}{2}}^{+} [622]$ , 529.58 keV; ${\frac{3}{2}}^{-} [752]$ , 772.74 keV; $½^{-}$ [501], 917.49 keV. Comparison of the experimentally determined level structure with theoretical calculations shows best agreement with calculations by Soloviev's group where a Woods-Saxon potential form was used and quasiparticle-phonon coupling was included. The neutron binding energy was determined to be 4713.7 ± 0.3 keV.

NUCLEAR REACTIONS ${}^{248}{Cm}$ ( $n$ , $γ$ ), $E = thermal$ ; measured $E_{γ}$ , $I_{γ}$ , ${}^{249}{Cm}$ deduced levels, $J$ , $π$ , Nilsson assignments.

Electroexcitation of giant multipole resonances in ${}^{148}{Sm}$ and ${}^{152}{Sm}$

B. S. Dolbilkin, S. Ohsawa, Y. Torizuka, T. Saito, Y. Mizuno, and K. Saito

Phys. Rev. C 25, 2255 (1982) - Published 1 May, 1982

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The electron scattering cross sections from the enriched ${}^{148}{Sm}$ (96.5%) and ${}^{152}{Sm}$ (99.2%) isotopes have been measured between 5 and 33 MeV excitation energies for incident energies in the range of between 150 and 215 MeV and scattering angles of 30°, 35°, and 40°. The giant resonances at $E_{x} = 14.8 (78 A^{- \frac{1}{3}}), 11.6 (61 A^{- \frac{1}{3}}), 15.5 (82 A^{- \frac{1}{3}}), and 24 (129 A^{- \frac{1}{3}})$ MeV for ${}^{148}{Sm}$ were classified according to their momentum transfer dependence. The $K$ splittings of the giant $E 1 (T = 1)$ and $E 2 (T = 0, 1)$ resonances for deformed ${}^{152}{Sm}$ were observed in agreement with a vibrating potential model. The splittings between the $K = 0^{+} and 2^{+}$ components for the isoscalar and isovector quadrupole resonances are ∼2 MeV and ∼5 MeV, respectively. The fitted parameters classified as the giant monopole resonance are the same for spherical ${}^{148}{Sm}$ and for deformed ${}^{152}{Sm}$ . The difference between the isoscalar giant resonance parameters for resonance energies and width found from hadron scattering and those for electron scattering is discussed for the rare-earth region.

NUCLEAR REACTIONS ${}^{148, 152}{Sm}$ ( $e$ , $e^{'}$ ), enriched targets, $E_{0} = 150 to 215$ MeV, $θ = 30 °, 35 °, 40 °$ , $q = 0.38 - 0.64$ ${fm}^{- 1}$ . Measured $\frac{d^{2} σ}{d Ω d E_{x}}$ up to 33 MeV in excitation energy; deduced multipolarity, excitation energy, width, sum rule exhaustion of giant resonances.

$Cu (γ, p) X$ reaction at $E_{γ} = 150 and 300$ MeV

R. A. Schumacher, G. S. Adams, D. R. Ingham, J. L. Matthews, W. W. Sapp, R. S. Turley, R. O. Owens, and B. L. Roberts

Phys. Rev. C 25, 2269 (1982) - Published 1 May, 1982

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Inclusive photoproton cross sections for the reaction $Cu (γ, p) X$ have been measured for a photon energy of 300 MeV at proton angles 45°, 90°, and 135°, and for 150 MeV at 45°. The data are compared with an intranuclear-cascade calculation and with Ni( $π^{\pm}$ , $p$ ) data. The angular distribution is analyzed to obtain an estimate of the number of nucleons involved in the interaction.

NUCLEAR REACTIONS $Cu (γ, p) X$ , $E = 150$ MeV, $θ = 45 °$ , $E = 300$ MeV, $θ = 45 °, 90 °, 135 °$ ; measured $σ (E_{p}, θ)$ ; intranuclear cascade analysis.

Phenomenological and microscopic optical model analyses of the interaction of low-energy nucleons with ${}^{93}{Nb}$

Ch. Lagrange and A. Lejeune

Phys. Rev. C 25, 2278 (1982) - Published 1 May, 1982

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The phenomenological optical model is parametrized in the energy range 10 keV—50 MeV so as to obtain a good agreement with all the available nucleon data. These include neutron and proton strength functions and elastic scattering data, as well as the neutron total cross sections and ( $p$ , $n$ ) isobaric analog state quasielastic scattering data. Comparison is made with the microscopic model of Jeukenne, Lejeune, and Mahaux including the new parametrization for nucleon energies less or near 10 MeV. From the analyses of sub-Coulomb proton experimental data the fundamental importance of the absorptive Coulomb correction term appears. The volume integral of this term is calculated and its energy dependence is exhibited.

NUCLEAR REACTIONS Microscopic and phenomenological optical model calculations of nucleon strength functions, $A = 93, 92$ shell effect, ${}^{93}{Nb}$ ( $n$ , $n$ ), $E_{n} = 7.0, 8.05, 11.0$ MeV, ${}^{93}{Nb}$ ( $p$ , $p$ ), $E_{p} = 22.2$ MeV, ${}^{93}{Nb}$ ( $p$ , $n$ ) ${}^{93}{Zr}$ , $E_{p} = 18.7, 49.4$ MeV.

Excitation of low lying natural parity levels in ${}^{208}{Pb}$ by inelastic electron scattering

J. Heisenberg, J. Lichtenstadt, C. N. Papanicolas, and J. S. McCarthy

Phys. Rev. C 25, 2292 (1982) - Published 1 May, 1982

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High resolution electron scattering measurements on ${}^{208}{Pb}$ have been performed at 90° and 160°, which allow the spatial reconstruction of transition charge densities and for the first time, transition current densities. The measurement covering the momentum transfer range of $0.5 < q < 2.6$ ${fm}^{- 1}$ is supplemented by high momentum transfer data from Saclay, extending the data for some of the states up to a momentum transfer of 3.4 ${fm}^{- 1}$ . We report on the first three $J^{π} = 5^{-}$ states and the first $J^{π} = 7^{-}$ state. Transition charge densities have been also extracted for the lowest $J^{π} = 2^{+}, 4^{+}, 6^{+}, and 8^{+}$ states. The densities are compared to a number of theoretical calculations. Transverse electric currents are shown for the $5^{-}$ states that indicate a quenching of the magnetization current similar to observations from other states but the absence of quenching in the convection current contribution.

NUCLEAR REACTIONS ${}^{208}{Pb}$ ( $e$ , $e^{'}$ ) measured cross sections at 90° and 160°, $0.5 \leq q \leq 2.6$ ${fm}^{- 1}$ . Low lying $J^{π} = 2^{+}, 4^{+}, 6^{+}, 8^{+}, 5^{-}, 7^{-}$ states analyzed. Transition charge densities and current densities extracted in DWBA.

Decay scheme and transition probabilities of ${}^{85}{Rb}$

T. F. Fazzini, P. R. Maurenzig, G. Poggi, and N. Taccetti

Phys. Rev. C 25, 2309 (1982) - Published 1 May, 1982

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The decay scheme of ${}^{85}{Rb}$ up to 2.4 MeV excitation energy was investigated by the ${}^{84}{Kr}$ $(p, γ)$ reaction and Coulomb excitation with alpha particles. Singles and $γ - γ$ coincidence spectra were recorded. Doppler shift attenuation measurements in gas were performed using the same gas as stopper medium. Lifetimes or lifetime limits were determined for 20 levels by Coulomb excitation and the Doppler shift attenuation method. An existing ambiguity referring to the lifetime of the second excited level has been removed.

NUCLEAR REACTIONS ${}^{84}{Kr}$ ( $p, γ$ ,) Coulomb excitation by alpha bombardment. $E_{p} = 1.85 - 2.87$ MeV. $E_{α} = 3$ MeV. Natural Kr gas target; $p = 0.1 - 106 \times 10^{5}$ Pa. Doppler shift attenuation in gas. Measured: level energies, branching ratios, decay scheme, lifetimes.

Magnetic electron scattering and valence nucleon radial wave functions

S. K. Platchkov, J. B. Bellicard, J. M. Cavedon, B. Frois, D. Goutte, M. Huet, P. Leconte, Phan Xuan-Ho, P. K. A. de Witt Huberts, L. Lapikás, and I. Sick

Phys. Rev. C 25, 2318 (1982) - Published 1 May, 1982

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Cross sections have been measured for elastic electron scattering from the magnetization distributions of ${}^{49}{Ti}$ , ${}^{51}V$ , ${}^{59}{Co}$ , ${}^{87}{Sr}$ , ${}^{93}{Nb}$ , and ${}^{208}{Bi}$ . Particular emphasis has been placed on the multipole distribution of the highest order possible, which dominates the magnetic form factor at momentum transfer values $q$ between 1.7 and 3.0 ${fm}^{- 1}$ . The data for the $1 f_{\frac{7}{2}}$ shell nuclei ${}^{49}{Ti}$ , ${}^{51}V$ and for the $1 g_{\frac{9}{2}}$ shell nuclei ${}^{87}{Sr}$ , ${}^{93}{Nb}$ are interpreted in terms of occupation probability and radial extension of the odd proton or neutron wave function. An accuracy of 1% is obtained for the valence orbit rms radii for both protons and neutrons. Corrections due to two-body magnetization currents and core polarization effects are investigated and found to be small. A detailed comparison of the experimental results with different types of density-dependent Hartree-Fock calculations is made in both momentum space and configuration space. It is found that the best available theory predicts the rms valence radii to within 2%. Comparisons are made between the present results and information on radial wave functions obtained from isotone shifts, proton scattering, and transfer reactions.

NUCLEAR REACTIONS ${}^{49}{Ti}$ , ${}^{51}V$ , ${}^{59}{Co}$ , ${}^{87}{Sr}$ , ${}^{93}{Nb}$ , ${}^{209}{Bi}$ $(e, e)$ ; $E_{0} = 175 - 325$ MeV, $θ = 155 °$ ; $E_{0} = 500$ MeV, $θ = 39 - 73 °$ ; measured $σ (E_{0}, θ)$ ; deduced magnetization distribution parameters, rms radii of neutron and proton $1 f_{\frac{7}{2}}$ and $1 g_{\frac{9}{2}}$ orbits.

${}^{181}{Ta}$ ( $p$ , $t$ ) ${}^{179}{Ta}$ reaction: Evidence for particle-core coupling

E. Warde, R. Seltz, D. Magnac, and H. L. Sharma

Phys. Rev. C 25, 2353 (1982) - Published 1 May, 1982

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The differential cross sections of tritons emitted in the ${}^{181}{Ta}$ ( $p$ , $t$ ) ${}^{179}{Ta}$ reaction have been measured at a bombarding energy of 19 MeV. The energy resolution was better than 15 keV. Thirty-eight levels in ${}^{179}{Ta}$ were observed. A distorted wave program for two nucleon transfer was used to identify levels obtained with $L = 0$ transfer. A comparison with the corresponding $L = 0$ transfers in the ${}^{180}{Hf}$ ( $p$ , $t$ ) ${}^{178}{Hf}$ reaction shows evidence for quasiparticle-core coupling in ${\frac{7}{2}}^{+}$ states of ${}^{179}{Ta}$ .

NUCLEAR REACTIONS ${}^{181}{Ta}$ ( $p$ , $t$ ) ${}^{179}{Ta}$ , $E = 19$ MeV; measured $σ (θ)$ . DWBA analysis, deduced spins; quasiparticle-phonon interaction proposed.

Light particle emission in ${}^{16}O$ -induced reactions at 140, 215, and 310 MeV

T. C. Awes, S. Saini, G. Poggi, C. K. Gelbke, D. Cha, R. Legrain, and G. D. Westfall

Phys. Rev. C 25, 2361 (1982) - Published 1 May, 1982

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Double differential cross sections have been measured for energetic $p$ , $d$ , $t$ , and $α$ particles emitted in ${}^{16}O$ -induced reactions on targets of A1, Zr, and Au at incident energies of 140, 215, and 310 MeV. The energy and angular distributions are well described by isotropic emission from a moving thermal source. The extracted temperature and velocity parameters are found to vary systematically with the incident energy per nucleon above the Coulomb barrier. The observed trends cannot be explained by compound nucleus emission but instead suggest emission from a source which consists of comparable contributions from target and projectile. Alternatively, the proton energy spectra are compared with a precompound model and with a simple knockout model. The $d$ , $t$ , and $α$ -particle cross sections are also described in terms of a generalized coalescence relation which takes into account Coulomb repulsion from the target nucleus.

NUCLEAR REACTIONS ${}^{27}{Al}$ ( ${}^{16}O$ , $x$ ), $E = 140, 215, and 310$ MeV; ${}^{90}{Zr}$ ( ${}^{16}O$ , $x$ ), $E = 215 and 310$ MeV; ${}^{197}{Au}$ ( ${}^{16}O$ , $x$ ), $E = 140, 215, and 310$ MeV; $x = p, d, t, and α$ . Measured $σ (E_{x}, θ_{x})$ . Analysis in terms of moving source, precompound, knockout, and coalescence models.

Optical model and coupled-channels analysis of ${}^{7}{Li}$ + ${}^{28}{Si}$ and ${}^{7}{Li}$ + ${}^{40}{Ca}$ scattering

John S. Eck, T. R. Ophel, P. D. Clark, J. Nurzynski, and D. C. Weisser

Phys. Rev. C 25, 2391 (1982) - Published 1 May, 1982

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Angular distributions for elastic scattering and for excitation of the 1.78 MeV state in ${}^{28}{Si}$ and for elastic scattering and excitation of the 3.73 and 3.90 states in ${}^{40}{Ca}$ by ${}^{7}{Li}$ scattering at a bombarding energy of 45 MeV have been measured and analyzed. Double folding model calculations using a realistic effective nucleon-nucleon interaction similar to that performed for ${}^{9}{Be}$ + ${}^{28}{Si}$ and ${}^{9}{Be}$ + ${}^{40}{Ca}$ scattering have been carried out for the elastic angular distributions and the real potential must be renormalized to yield agreement with the measured cross sections. Coupled channels calculations using a Woods-Saxon potential were performed in an effort to describe the inelastic angular distributions. The extracted deformation parameters are in reasonable agreement with those obtained from light and heavier ion scattering from the same target nuclei. The effect of strong excitation of the 0.48 MeV state in ${}^{7}{Li}$ and of mutual excitation of target and projectile is considered in a qualitative manner.

NUCLEAR REACTIONS ${}^{28}{Si}$ ( ${}^{7}{Li}$ , ${}^{7}{Li}$ ) ${}^{28}{Si}$ , ${}^{28}{Si}$ ( ${}^{7}{Li}$ , ${}^{7}{Li}$ *) ${}^{28}{Si}$ * $Q = - 0.48, - 1.78, and - 2.26$ MeV, $E ({}^{7}{Li}) = 45$ MeV; ${}^{40}{Ca}$ ( ${}^{7}{Li}$ , ${}^{7}{Li}$ ) ${}^{40}{Ca}$ , ${}^{40}{Ca}$ ( ${}^{7}{Li}$ , ${}^{7}{Li}$ *) ${}^{40}{Ca}$ * $Q = - 0.48, - 3.73, and - 3.90$ MeV, $E ({}^{7}{Li}) = 45$ MeV; measured $σ (θ)$ , $θ_{lab} = 10 - 70 °$ ;; performed optical model calculations using Woods-Saxon potential and double folding procedure, deduced optical model parameters; performed coupled-channels calculations, deduced deformation parameters.

Particle production, chemical equilibrium, and the quasiergodic hypothesis in high energy collisions

T. R. Halemane and A. Z. Mekjian

Phys. Rev. C 25, 2398 (1982) - Published 1 May, 1982

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Starting from kinetic theory, it is shown that particles heavier than the pion are not produced in chemical equilibrium. A new theory based on the degree of the reaction is then formulated. Pion induced reactions, following pion production from individual nucleon-nucleon collisions give the main mechanism for the production of strange particles, such as $K^{+}$ 's. "Subthreshold" production is a natural consequence of the theory.

NUCLEAR REACTIONS Heavy ion collisions at high energies; particle production; incomplete chemical equilibrium; pion induced reactions and strange particle production; subthreshold production.

Energy dependence of ${}^{9}{Be}$ + ${}^{12}C$ cross sections: Resonances or fluctuations

M. Hugi, J. Lang, R. Müller, J. Sromicki, E. Ungricht, K. Bodek, L. Jarczyk, B. Kamys, A. Strzałkowski, and H. Witała

Phys. Rev. C 25, 2403 (1982) - Published 1 May, 1982

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266 excitation curves for the emission of protons, deuterons, tritons, α particles, and ${}^{8}{Be}$ and ${}^{9}{Be}$ ions have been measured in the system ${}^{9}{Be}$ + ${}^{12}C$ . Data were taken in 107 keV steps in the energy range from 5.9 to 15.4 MeV (c.m.) at several angles between 5° and 175° (lab). The results were analyzed on the basis of the statistical reaction model and various statistical methods for localizing possible correlated structures were used. The fluctuations are shown to be in agreement with the predictions of the statistical model and no marked correlations between different channels were found.

NUCLEAR REACTIONS ${}^{12}C$ ( ${}^{9}{Be}$ , $x$ ), $x = p, d, t, α, {}^{8}{Be}, and {}^{9}{Be}$ ; measured $σ (E_{x}, θ_{x})$ , $E_{c . m .} = 5.9 - 15.4$ MeV. Statistical analysis of excitation curves; unsuccessful search for resonances.

Charged particle emission from ${}^{194}{Hg}$ compound nuclei: Energy and spin dependence of fission-evaporation competition

M. Rajagopalan, D. Logan, Jane W. Ball, Morton Kaplan, Hugues Delagrange, M. F. Rivet, John M. Alexander, Louis C. Vaz, and M. S. Zisman

Phys. Rev. C 25, 2417 (1982) - Published 1 May, 1982

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Twelve reactions have been studied that produce the compound system ${}^{194}{Hg}$ * at excitation energies of 57 - 195 MeV and with $l_{crit}$ values of $25 - 142 ℏ$ . Beams of ${}^{12}C$ , ${}^{19}F$ , ${}^{20}{Ne}$ , and ${}^{40}{Ar}$ ions in conjunction with appropriate targets have been used to measure cross sections for evaporative H/He, fission, and evaporation residues. These results confirm that most ${}^{1}H$ and ${}^{4}{He}$ is evaporated prior to fission or instead of fission and very little if any from the fission fragments. The probability of H/He evaporation increases dramatically with excitation energy. The evaporation residue cross sections ( $\frac{σ_{ER}}{π λ^{2}}$ ) indicate fission survival for entrance channel $l$ up to $27 - 39 ℏ$ . Fission survival becomes stronger and corresponding fission competition becomes weaker for excitation ≥ 100 MeV; a connection with charged particle emission is suggested. The dimensionless cross section for evaporation residue ( $\frac{σ_{ER}}{π λ^{2}}$ ) depends on both the entrance channel and on energy, indicating that nonequilibrium mechanisms must play an important role, even for $l ≲ 40$ . Heretofore evaporation residue production has been usually thought to arise from lower partial waves while direct reactions have been thought to dominate only for the higher partial waves.

NUCLEAR REACTIONS ${}^{12}C$ + ${}^{182}W$ ; ${}^{20}{Ne}$ + ${}^{174}{Yb}$ ; ${}^{40}{Ar}$ + ${}^{154}{Sm}$ ; ${}^{19}F$ + ${}^{175}{Lu}$ ; reactions forming ${}^{194}{Hg}$ * at excitation energies 57, 80, 100, 142, 195 MeV. Measured cross sections for fission and evaporation residues, evaporative H and He including some energy spectra. Discuss relationship to statistical evaporation model.

Energy equilibration in composite nuclei at high energy and spin: Correlations between evaporative ${}^{1}H$ , ${}^{4}{He}$ , and fission

M. F. Rivet, D. Logan, John M. Alexander, D Guerreau, E. Duek, M. S. Zisman, and Morton Kaplan

Phys. Rev. C 25, 2430 (1982) - Published 1 May, 1982

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Correlations have been studied between evaporative H/He emission and fissionlike products for the reactions 333 MeV ${}^{40}{Ar}$ + ${}^{116}{Sn}$ , ${}^{154}{Sm}$ , and ${}^{197}{Au}$ . Fission products were detected at 60° and 320° in coincidence with H and He at 120° in plane and 27° and 60° out of plane. The coincidence energy spectra of H and He are not consistent with evaporation from the moving fragments. An analysis has been made with the assumption of complete energy equilibration in the particle emission (i.e., evaporation) prior to scission. The rather large data set is essentially consistent with this assumption. From the spectral shapes one can deduce level density parameters and barriers to evaporation. Values inferred for the Fermi gas level density parameters are similar to those inferred from experiments at much lower energies. Values deduced for the emission barriers are much smaller than those from systematics of fusion barriers. The observed cross sections for fission and ${}^{1}H$ and ${}^{4}{He}$ evaporation are not easily reconciled with statistical model calculations. In particular, the proton evaporation seems to compete more favorably with fission and ${}^{4}{He}$ evaporation than implied by phase space considerations alone.

NUCLEAR REACTIONS ${}^{116}{Sn}$ , ${}^{154}{Sm}$ , ${}^{197}{Au}$ ( ${}^{40}{Ar}$ ; H/He, fission), $E = 333$ MeV, measured energy and angular correlations of evaporative H/He in coincidence with fission. Values deduced for emission barriers, temperatures and $J_{rms}$ for the emitter. Comparisons made to evaporation calculations.

Nucleon transfer contribution to the absorptive potential in heavy-ion scattering

Fl. Stancu and D. M. Brink

Phys. Rev. C 25, 2450 (1982) - Published 1 May, 1982

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We propose a simple model for estimating the nucleon transfer contribution to the imaginary part of the nucleus-nucleus optical potential. Using the proximity method we calculate the transfer probability per unit time in terms of the flux of nucleons between two slabs. Pauli blocking and barrier penetration effects are taken into account. We compare our results with phenomenological potentials at the strong absorption radius.

NUCLEAR REACTIONS Imaginary part of the heavy ion optical potential. Nucleon transfer contribution. Barrier penetration, Pauli blocking, and relative motion effects.

Gamma-ray studies of the ${}^{16}O$ + ${}^{20}{Ne}$ system

M. A. Xapsos, P. A. DeYoung, L. J. Satkowiak, and J. J. Kolata

Phys. Rev. C 25, 2457 (1982) - Published 1 May, 1982

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Excitation functions for the yields of eight residual nuclides from the ${}^{16}O$ + ${}^{20}{Ne}$ reaction have been measured over the range $E_{c . m .} = 15 - 29$ MeV using $γ$ -ray techniques. Weak oscillatory structure in the fusion-evaporation yield is observed, with maxima near $E_{c . m .} = 20, 22, and 23$ MeV. Two strong anomalies in the inelastic scattering and $α$ -transfer channels have been located at $E_{c . m .} = 19.9 and 25.4$ MeV. These structures have properties similar to those of characteristic resonances in other light systems. The $E_{c . m .} = 19.9$ MeV resonance occurs at the same ${}^{36}{Ar}$ excitation energy as a similar resonance previously observed in the ${}^{12}C$ + ${}^{24}{Mg}$ reaction yields.

NUCLEAR REACTIONS ${}^{20}{Ne}$ ( ${}^{16}O$ , $x$ ); $E_{c . m .} = 15 - 29$ MeV; measured excitation functions for the production of $A = 20 - 34$ reaction products; observed structure at $E_{c . m .} = 19.9, 22.0, 22.8, and 25.4$ MeV; deduced critical angular momentum for fusion.

Correlations between the alpha particles and ejectiles in the reaction ${}^{93}{Nb}$ + ${}^{14}N$ at $E_{lab} = 208$ MeV

T. Fukuda, M. Ishihara, M. Tanaka, I. Miura, H. Ogata, and H. Kamitsubo

Phys. Rev. C 25, 2464 (1982) - Published 1 May, 1982

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The correlations between alpha particles and various ejectiles were investigated in the reaction ${}^{93}{Nb}$ + ${}^{14}N$ at $E_{lab} = 208$ MeV. The ejectiles were measured at a fixed angle $θ_{1} = + 22 °$ , which was slightly more backward than the grazing angle, and the alpha particles were measured at various angles $θ_{2}$ in and out of the reaction plane. The experimental results were analyzed in terms of various aspects of the correlations such as the energy and angular correlations, the projected energy spectra, and differential multiplicities. An analysis based on the three body kinematics was also made to study the features associated with the sequential ejectile breakup process. It was found that two processes contribute to the coincident alpha particles. The first process was ascribed to the sequential breakup of the excited ejectiles and was found to be dominant in the angular region of $θ_{2}$ close to the ejectile detector. The coincidence cross section of the sequential breakup component can be approximately factorized as a product of the singles cross section of excited ejectiles before breakup and the excitation spectrum of the ejectiles. The other process, ascribed to a nonsequential mechanism, was dominant for the alpha particles detected on the opposite side of the ejectile detector with respect to the beam direction. This process is characterized by the following properties: (i) The energy spectra of the coincident alpha particles have shapes which are almost identical to those of the singles spectra taken at the same angles. (ii) The same is true to a lesser extent for the ejectile spectra except for the higher-energy region. (iii) In this angular region of $θ_{2}$ the differential coincidence cross section can be approximately expressed in the factorization form, $\frac{d^{4} σ}{d Ω_{1} d Ω_{2} d E_{1} d E_{2}} = K \cdot (\frac{d^{2} σ}{d Ω_{1} d E_{1}}) (\frac{d^{2} σ}{d Ω_{2} d E_{2}})$ . The relative contribution of the two processes was found to be roughly comparable.

NUCLEAR REACTIONS ${}^{93}{Nb}$ ( ${}^{14}N$ , $HI α$ ), $E = 208$ MeV; measured two-dimensional HI- $α$ coincident energy and angular correlations; deduced reaction mechanisms.

Macroscopic nucleon-nucleon correlations caused by the bounce-off process in energetic collisions of heavy nuclei

László P. Csernai, Walter Greiner, Horst Stöcker, Isao Tanihata, Shoji Nagamiya, and Jörn Knoll

Phys. Rev. C 25, 2482 (1982) - Published 1 May, 1982

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Two-particle correlation data are presented for the reaction Ar (800 MeV/ nucleon) + Pb. The experimental results are analyzed in the nuclear fluid dynamical and in a linear cascade model. We demonstrate that the collective hydrodynamical correlations dominate the measured two-particle correlation function for the heavy system studied. We discuss the transition from the early stages of the reaction which are governed by few nucleon correlations, to the later stages with their macroscopic flow which can only be reached using heavy colliding systems. The sensitivity of the correlation data on the underlying compressional dissipative processes is analyzed.

NUCLEAR REACTIONS Ar + Pb (800 MeV/nucleon) relativistic heavy-ion reactions, two-proton correlations.

Coherent collective flow versus independent two-nucleon collisions in central high-energy heavy-ion collisions

J. R. Nix, D. Strottman, Y. Yariv, and Z. Fraenkel

Phys. Rev. C 25, 2491 (1982) - Published 1 May, 1982

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For central collisions in the reaction ${}^{20}{Ne}$ + ${}^{238}U$ at a laboratory bombarding energy per nucleon of 393 MeV, we calculate the cross section $\frac{d^{2} σ}{dE d Ω}$ for outgoing charged particles by means of a relativistic intranuclear cascade, conventional relativistic nuclear fluid dynamics, and relativistic nuclear two-fluid dynamics. The results of the three calculations are compared with recent high-multiplicity-selected central-collision experimental data of Stock et al., including contributions from protons, deuterons, and tritons. The intranuclear cascade reproduces most features of the experimental data except the observed sidewards peaking in the angular distributions at low outgoing energy, predicting instead angular distributions that are forward peaked at all outgoing energies, to within statistical errors. Conventional nuclear fluid dynamics fails to reproduce the experimental data in two important respects: (1) The predicted energy spectra in forward directions decrease too rapidly with increasing outgoing energy and (2) the predicted angular distributions are too narrow and peak at increasingly larger angles with increasing outgoing energy, opposite to the experimental trend. Nuclear two-fluid dynamics predicts sidewards peaking for central collisions at intermediate outgoing energy that is in approximate agreement with experimental results, although the calculated peak is somewhat sharper than the experimental peak. With qualifications arising from the possible importance of contributions from large impact parameters, heavy composite particles, Coulomb effects, and thermal folding, we conclude that in central high-energy heavy-ion collisions the target and projectile interpenetrate substantially but that some degree of coherent collective flow is involved.

NUCLEAR REACTIONS ${}^{20}{Ne}$ + ${}^{238}U$ , $\frac{E_{bom}}{20} = 393$ MeV. Calculated $\frac{d^{2} σ}{dE d Ω}$ for outgoing charged particles in central collisions and compared with experimental data. Relativistic intranuclear cascade, relativistic nuclear fluid dynamics, relativistic nuclear two-fluid dynamics, nuclear equation of state.

Analyzing powers in heavy ion scattering with identical cores

Shigeo Ohkubo

Phys. Rev. C 25, 2498 (1982) - Published 1 May, 1982

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The effect of a parity-dependent central potential and a spin-orbit potential on the angular distributions of analyzing powers and cross sections in heavy ion scattering is investigated. The cross section data of ${}^{13}C$ + ${}^{12}C$ , ${}^{15}N$ + ${}^{16}O$ , and ${}^{19}F$ + ${}^{18}O$ scattering are analyzed and it is predicted that a characteristic oscillation appears in the angular distributions of analyzing powers, especially at back angles, for heavy ion scattering with identical cores.

NUCLEAR REACTIONS Spin-orbit potential and analyzing-power angular distributions in heavy ion scattering, parity dependent potential model analysis of ${}^{13}C$ + ${}^{12}C$ , ${}^{15}N$ + ${}^{16}O$ , and ${}^{19}F$ + ${}^{18}O$ scattering.

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Energy levels of ${}^{249}{Cm}$ from measurements of thermal neutron capture gamma rays

Electroexcitation of giant multipole resonances in ${}^{148}{Sm}$ and ${}^{152}{Sm}$

$Cu (γ, p) X$ reaction at $E_{γ} = 150 and 300$ MeV

Phenomenological and microscopic optical model analyses of the interaction of low-energy nucleons with ${}^{93}{Nb}$

Excitation of low lying natural parity levels in ${}^{208}{Pb}$ by inelastic electron scattering

Decay scheme and transition probabilities of ${}^{85}{Rb}$

Magnetic electron scattering and valence nucleon radial wave functions

${}^{181}{Ta}$ ( $p$ , $t$ ) ${}^{179}{Ta}$ reaction: Evidence for particle-core coupling

Light particle emission in ${}^{16}O$ -induced reactions at 140, 215, and 310 MeV

Optical model and coupled-channels analysis of ${}^{7}{Li}$ + ${}^{28}{Si}$ and ${}^{7}{Li}$ + ${}^{40}{Ca}$ scattering

Particle production, chemical equilibrium, and the quasiergodic hypothesis in high energy collisions

Energy dependence of ${}^{9}{Be}$ + ${}^{12}C$ cross sections: Resonances or fluctuations

Charged particle emission from ${}^{194}{Hg}$ compound nuclei: Energy and spin dependence of fission-evaporation competition

Energy equilibration in composite nuclei at high energy and spin: Correlations between evaporative ${}^{1}H$ , ${}^{4}{He}$ , and fission

Nucleon transfer contribution to the absorptive potential in heavy-ion scattering

Gamma-ray studies of the ${}^{16}O$ + ${}^{20}{Ne}$ system

Correlations between the alpha particles and ejectiles in the reaction ${}^{93}{Nb}$ + ${}^{14}N$ at $E_{lab} = 208$ MeV

Macroscopic nucleon-nucleon correlations caused by the bounce-off process in energetic collisions of heavy nuclei

Coherent collective flow versus independent two-nucleon collisions in central high-energy heavy-ion collisions

Analyzing powers in heavy ion scattering with identical cores

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