Q- and Z-dependence of angular momentum transfer in deeply inelastic collisions of 86Kr with 209Bi

The dependence of the in-plane and out-of-plane angular correlations of fragments from fissioning heavy products on the kinetic energy and Z of the light reaction partner have been measured. From the dependence of the angular correlations on Q-value and hence energy loss, together with existing data from which the total angle-integrated cross section as a function of energy loss can be extracted, we have determined the dependence of the angular momentum transferred to the heavy product on the initial orbital angular momentum or impact parameter. The resulting dependence is qualitatively consistent with the sticking limit for a reaction intermediate of touching deformed fragments. More specific nuclear models generally underestimate the angular momentum transfer, although the one-body proximity-friction model accounts for the major fraction of the angular momentum transfer. A recent model incorporating both one-body proximity friction and collective excitations accounts quite well for the observed angular momentum transfer. The Z-dependendence of the anisotropy shows the importance of angular momentum fractionation for the less probable events, where the Z of the fissioning system is appreciably less than that of the target. The transferred angular momentum is shown to be fairly strongly aligned along the perpendicular to the reaction plane, with alignment values of 0.6 to 0.8. The component of angular momentum not along the perpendicular to the reaction plane is found to be primarily oriented perpendicular rather than parallel to the recoil direction. The absolute fission probabilities are found to be qualitatively consistent with J-dependent calculations using the J-values deduced from the angular correlations.     

Measurements of evaporation residues and fission for 40Ar + 110Pd

Fusion cross sections for the reaction ⁴⁰Ar + ¹¹⁰Pd have been measured in the bombarding energy range 164–262 MeV. Evaporation residues and fission fragments have been detected by ΔE-E telescopes. We compare the fusion cross sections to various theoretical models with special attention to the high-energy data. An analysis is also given for entrance-channel spin zones for evaporation residues and fission.     

Energy loss and nucleon exchange in the reaction of 86Kr with 166Er

Projectile-like products from the reaction ⁸⁶Kr on ¹⁶⁶Er at 8.18 MeV/amu have been measured using a large-area position-sensitive ionization chamber. The observed element distributions for a given energy loss are found to be asymmetric. An analysis of the data in terms of the residual kinetic energy above the Coulomb barrier, however, yields symmetric and Gaussian-shaped element distributions. At large energy losses, the centroids of these Gaussian distributions exhibit a drift towards symmetric mass splits. The correlation between the variance of the element distribution σ_z² and the number of exchanged nucleons N_ex is discussed. The exchange mechanism, as described by a simple one-body dissipation model, can account for a large portion of the measured energy loss.     

Determination of angular momenta in the incomplete-fusion channels of the reactions Ta+22Ne and Ir+12C

By using the γ-ray-multiplicity technique, experiments were carried out to determine the input angular momenta lⁱⁿ corresponding to the heavy-ion induced incomplete-fusion reactions involving the emission of fast charged particles. The α-particle and Li-nuclei emission channels were investigated in the reaction ¹⁸¹Ta + ²²Ne at the average Ne-ion energy of 155 MeV and for the α-particle emission channel in the reaction ^natIr+¹²C at E = 100 MeV. The separation of the reaction channels was carried out using an X-ray spectrometer. The angular distributions of the fission fragments were measured in the reaction ¹⁸¹Ta(²²Ne, αf). The data obtained indicate that input angular momenta are equal to about 60 ? and 50 ? for the channels of Li emission and α-emission, respectively, being practically independent of the particle energy. For the α-emission channel the lⁱⁿ values are the same for both reactions within experimental errors. The lifetime of the system of interacting target and projectile nuclei, prior to the emission of an α-particle, has been estimated to be equal to 10^?20s.     

States in 89Sr excited by the 86Kr(α, n)89Sr reaction

The reaction ⁸⁶Kr(α, n) with E_α = 12?16 MeV was used to populate excited states in ⁸⁹Sr. The de-excitation of these states was studied by in-beam γ-ray spectroscopy. DSA lifetime measurements were performed using a solid gas target. A number of new high-spin states was found, and lifetimes of ten states were obtained. Some of the states are discussed within the framework of a particle-anharmonic vibrator model.     

Evidence for critical angular momenta in the formation of 26Al via the 14N + 12C channel

States in ²⁰Ne have been studied through the ¹²C(¹⁴N, ⁶Li)²⁰Ne reaction. Excitation functions have been measured from 20 MeV to 60 MeV in steps of 5 MeV at different angles for ²⁰Ne states up to 10 MeV excitation energy. States of ²⁴Mg have been also populated using the ¹²C(¹⁴N, d)²⁴Mg reaction; excitation functions of ²⁴Mg states up to 9 MeV excitation energies as well as angular distributions at 35 MeV bombarding energy have been obtained. Comparisons of data with Hauser-Feshbach calculations show clearly that the compound nucleus mechanism is the main process for both ¹²C(¹⁴N, ⁶Li)²⁰Ne and ¹²C(¹⁴N, d)²⁴Mg reactions. Strong evidence has been provided for inhibition of the ²⁶Al compound nucleus formation for angular momenta higher than critical values. The location of the yrast line in the ²⁶Al nucleus is discussed.     

A study of the 84Kr(α, 2nγ)86Sr reaction

Decay properties of levels of ⁸⁶Sr populated by the 28 MeV ⁸⁴Kr(α, 2nγ) reaction have been studied by in-beam γ-ray spectroscopy. The observation of several new levels with $\text{J ≧ 6}$ allows a detailed comparison of the 2p-2n structures of ⁸⁶Sr with those of neighboring N = 48 nuclei. The results are discussed in terms of the weak-coupling model.     

In-beam study of 80Kr; Quasiparticle excitations in nuclei around mass 80

The excited states in ⁸⁰Kr have been studied in the reactions ⁷⁷Se(α, n), ⁷⁸Se(α, 2n), ⁸⁰Se(α, 4n) and ⁶⁵Cu(¹⁸O, p2n) by using in-beam γ-ray spectroscopy. In addition to γγ-coincidences, excitation functions and angular distributions, linear polarization of γ-rays and conversion electrons were also measured. All together, 32 levels have been identified up to spin 14 at an excitation energy of 6.7 MeV in ⁸⁰Kr. For 21 of these levels the mean lifetime could be determined by Doppler shift methods and by the pulsed-beam γ-timing method. The B(E2) values of 30–60 W.u., derived for many transitions, indicate strong collectivity and the existence of several band structures is suggested. Above 2.5 MeV 2-quasiparticle (qp) excitations become important. The excitation energies of ⁸⁰Kr and its neighbours ^{77, 78, 79}Kr, ⁷⁷Br and ⁸¹Rb have been analysed in terms of the cranked shell model. In ^78,80Kr two-proton excitations have been found to be responsible for the observed band crossing. Quasiparticle excitations strongly influence the pairing and stabilize the deformation. The anomalies in the negative-parity bands of ⁸¹Rb and ⁷⁷Br are interpreted as a crossing of a 3qp and a 1qp band and the relatively low frequency of the crossing point is ascribed to the blocking effect.     

Deep inelastic collisions in the interaction of 280 MeV 40Ar with 58Ni

Masses and charges of all the nuclei with 5 ≦ Z ≦ 20 produced in the reaction ⁴⁰Ar + ⁵⁸Ni have been identified using combined ΔE · E and time-of-flight techniques. Energy spectra, angular distributions and cross sections have been measured. The formation of an intermediate composite system, in which charge equilibrium is achieved, is discussed. Also, the transition between the quasi-elastic and the deep inelastic process is studied. The angular distribution behaviour is shown to be related to the interaction time. The total cross section of the deep inelastic process has been found to be 700 mb and is compared to the evaporation residue cross section.     

Reactions of 40Ar with 159Tb, 142Nd and 144Sm; New α-activities from 189Bi, 173Pt and 177Au

Reactions of ⁴⁰Ar ions with targets of ¹⁵⁹Tb, ¹⁴²Nd, and ¹⁴⁴Sm have been studied at energies below 300 MeV with a helium gas-jet system. Excitation functions for (Ar, xn) reactions, where x = 5–10, were obtained for the radioactive products that decay by α-emission. Based on the characteristics of these excitation functions and on the systematics of α-decay, evidence is presented for the existence of the nuclides ¹⁸⁹Bi with α-particle energy E_α = 6.67±0.01 MeV and half-life < 1.5 sec, and ¹⁷³Pt with E_α = 6.19±0.01 MeV; and for the emission from ¹⁷⁷Au of an α-particle with E_α = 6.15±0.01 MeV.     

Average g-factors for high-spin states in 78Kr

Inverse reactions of ^{63, 65}Cu beams on ^{18, 16}O targets have been used to populate states of ⁷⁸Kr by fusion-evaporation reactions. The excited nuclei recoiled at high velocity v/c ≈ 7 % through a polarized iron (⁵⁴Fe) layer and were stopped in a copper layer. During the period in iron, 0.05–0.65 ps, the nuclei were subjected to the intense transient magnetic field (initially ～ 3500 T). The resulting precession of the high-spin nuclear states populated during this time was determined by measuring the time integral rotation angle of the discrete γ-ray transitions at low spin.The average g-factor at low spin 2 ≦ J ≦ 8 compared to that at higher spin 8 ≦ J ≦ 12 in ⁷⁸Kr was found to be identical within the experimental uncertainties of ～ 15 %. This result implies that either there are no rotational alignment effects at the backbend in ⁷⁸Kr or more plausibly, proton (g ≈ 1) and neutron (g ≈ 0) aligned bands are equally competitive and both populated in the reaction. It is then likely that the resulting g-factor represents an average over many populated proton and neutron aligned bands.     

Photonuclear reactions in medium weight nuclei 51V, 55Mn and Cu

New results on the photospallation of the medium weight nuclei ⁵¹V, ⁵⁵Mn and Cu at maximum bremsstrahlung energy between 2 and 5 GeV are presented. The yields of residual nuclei were measured by the activation method using a Ge(Li) detector. The results are analyzed with the empirical Rudstam formula and compared with data obtained in lower energy photon and proton induced reactions.     

Model independent Jπ assignments in 38Ar from γ-ray experiments in heavy-ion induced reactions

High-spin states of ³⁸Ar and ³⁵Cl have been investigated with the ²⁴Mg(¹⁶O, 2pγ)³⁸Ar and ²⁴Mg(¹⁶O, pαγ)³⁵Cl reactions at beam energies of 38 and 45 MeV. The experiments consisted of γ-γ coincidence, angular distribution and linear polarization measurements. A high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer and a three-Ge(Li) Compton polarimeter were used. The analysis of the data, without assumptions about the reaction mechanism for the formation of the levels under study, is discussed. Unambiguous spin-parity assignments of J^π = 6⁺, 8⁺, and limitations of (5, 6, 7) and (7, 8⁺, 9) for the ³⁸Ar levels at E_x = 6408.3±0.2, 7609.3±0.3, 8012.9±0.3 and 10173.8±0.4 keV, respectively, are obtained. They are compared with results of shell-model calculations. Mixing ratios and spin-alignment attenuation factors for several transitions and levels in ³⁸Ar and ³⁵Cl are reported.     

Recoil-distance lifetime measurements of levels in 36Ar and 36Cl

Lifetimes of levels in ³⁶Ar and ³⁶Cl populated in the ²H(³⁵Cl, n) and ²H(³⁵Cl, p) reactions, respectively, were measured with the recoil distance method. Gamma rays were detected in coincidence with a neutron detector to study the ³⁶Ar levels and in singles to study the ³⁶Cl levels. Mean lifetimes τ_m = 125 ± 20, 19.6 ± 3.1 and 4.1 ± 0.9 ps were obtained from decay curves for the ³⁶Ar levels at 5171, 4974 and 4178 keV, respectively and τ_m = 23 ± 2, 10.4 ± 0.5, 2.95 ± 0.14 and 4.9 ± 1.0 ps for ³⁶Cl levels at 788, 1165, 1951 and 2810 keV, respectively. Shell-model calculations, with a model space comprising selected 5h-1p configurations and with an effective charge of 0.5e, are compared to the transition rates for the low-lying negative parity states in ³⁶Ar.     

Levels in 74Se, 78, 80Kr and 84Sr and systematics of quasi-γ bands

Quasi-band structures in ⁷⁴Se, ^{78, 80}Kr and ⁸⁴Sr have been investigated using (p, 2nγ) reactions. The members of the quasi-γ band have been observed up to 5⁺ in ⁷⁴Se, ^{78, 80}Kr and up to 3⁺ in⁸⁴Sr. The analyses of the energy systematics of the quasi-γ bands studied in this mass region as well as in other regions make clear the evolution of the quasi-γ band to the γ-band in well-deformed nuclei. In addition to these positive-parity bands, negative-parity levels were observed in ⁷⁴Se, ⁸⁰Kr and ⁸⁴Sr.     

Transfer reactions induced by 16O on 29, 30Si

Angular distributions for one- and two-nucleon transfer reactions induced by ¹⁶O on ^{29, 30}Si and for the elastic scattering of ¹⁶O on ^{28, 29, 30}Si have been measured at 73.5 MeV bombarding energy. The results are analyzed with the DWBA code BRUNHILD that includes recoil effects. Spectroscopic factors extracted for all observed transitions in one-nucleon transfer reactions agree well with those derived from light panicle reactions. The effects of recoil on the Spectroscopic factors for transitions to final states with different spins are discussed. The transitions from smooth to oscillating angular distributions are examined. It is found that the shape of the angular distributions depends on both the matching conditions of the reaction and the localization of the S-matrix amplitudes in L-spacef.     

Transfer reactions induced by 12C ON 18O and 26Mg AT 46 MeV

It is argued that a recent claim that there is an error of a factor of two in the Law- Campbell theory of K-electron shake-off in β^? decay is wrong.     

Deuteron induced pickup reactions on 41Ca

The ⁴¹Ca(d, t)⁴⁰Ca and ⁴¹Ca(d, τ)⁴⁰K reactions have been investigated at a bombarding energy of 40 MeV. A distorted-wave analysis of the measured angular distributions and a sum-rule analysis of the resulting spectroscopic factors has enabled the identification of members of various particle-hole multiplets. Values obtained for the matrix elements of the $\text{1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}{}^{\mathrm{?}}\text{1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$ effective interaction are in poor agreement with values obtained from other nuclei, but are reasonably well reproduced by calculations with a simple force.     

Search for intermediate structure in 36Ar via the 24Mg(12C, α)32S reaction

The ²⁴Mg(¹²C,α)³²S reaction was investigated in the energy range E_c.m. = 11.9–19.4 MeV by measuring excitation functions of the α₀ and α₁ groups. Angular distributions (θ_c.m. = 12–97°) were also measured at a number of energies. The excitation functions were subjected to a statistical analysis by means of evaluating correlation and deviation functions; no statistically significant anomalies were found. The α₀ angular distributions display fairly high angular-momentum selectivity as pairs of Legendre polynomials provide acceptable fits to most of them: however, only one, at E_c.m. = 18.1 MeV, is strongly dominated by a single partial wave, l = 11. Excitation functions as well as angular distributions of both α₀ and α₁ cross sections were found to be in good qualitative agreement with Hauser-Feshbach calculations throughout the energy range studied. Thus, the analysis of the data shows that intermediate resonant structures, if present, are weak and interfere strongly with the statistical compound-nucleus background, which effectively prevents their clear observation and identification in the present study.     

Fusion and neutron-transfer cross sections for 13C + 10B and 13C + 11B reactions at subbarrier energies

The cross sections for the ¹⁰B(¹³C, ¹²C)¹¹B neutron-transfer reaction, leading to the ¹¹B 4.45 and 6.74 MeV and ¹²C 4.44 MeV excited states, and for ¹³C + ¹⁰B fusion have been measured by the characteristic and total γ-ray yield methods, respectively, over the energy (c.m.) interval 2.4–5.8 MeV. For ¹³C + ¹¹B, with no transfer reactions present, the fusion cross sections have been measured between E_c.m. = 2.3 and 6.4 MeV. The fusion cross sections for ¹³C + ¹⁰B and ¹³C + ¹¹B are found to be almost equal and slightly enhanced with respect to those for ¹²C + ¹⁰B and ¹²C + ¹¹B.