The new isotope218U

The new neutron-deficient isotope²¹⁸U was produced in the bombardment of¹⁹⁷Au target with²⁷Al ions and identified using the- correlation method. The -decay energy and the half-life of²¹⁸U were determined to be 8625±25 keV and 1.5 _–0.7 ^+7.3 ms, respectively. Evaporation residues recoiling from the target were separated in-flight from the projectiles and from the products of other nuclear reactions by the electrostatic separator VASSILISSA [1].     

Investigation of the fusion reaction27Al+236U→263105 at excitation energies of 57 MeV and 65 MeV

The neutron-deficient isotopes^257,258105 were produced in the reaction²⁷Al+²³⁶u in 6n and 5n evaporation channels, respectively. The evaporation residues emerging from the target were separated in-flight from the projectiles and from products of different nuclear reactions by the electrostatic separator VASSILISSA [1]. The isotopes were then implanted into position-sensitive silicon detectors and identified using the --correlation method. The measured production cross-section is (5n)=(0.45±0.20)nb atE _P =154 MeV and (6n)=(0.075±0.055) nb atE _P =163 MeV. These cross-sections are compared with data measured for the same isotopes in the more symmetrical reaction⁵⁰Ti+²⁰⁹Bi.     

Non-collective oblate states in121Te

Two new neutron-deficient isotopes,²¹³Pa and²¹⁴Pa were produced in complete fusion reactions of⁵¹V-ions with¹⁷⁰Er targets at (5.2–5.6) AMeV. The assignment was based on delayed evaporation residue - - time and position coincidences. The- decay energies of^213,214Pa were measured to be E=(8236±20) keV and E=(8116±20) keV, respectively. The half-lives of^213,214Pa were determined to be T_1/2=(5.3 _–1.6 ^+4.0 ms and T_1/2=(17 ±3) ms, respectively.This article was processed by the author using the LAT_EX style filecljour2 from Springer-Verlag.     

Proton alignment in the 21/2+ yrast state of89Mo

The magnetic moment of the isomeric 2584 keV 21/2⁺ yrast state in⁸⁹Mo was measured via the time differential perturbed angular distribution method after recoil implantation (IMPAD) into a polarized Ni target. A g-factor of +0.79(4) was extracted, indicating a (g _9/2)² v(g _9/2)^–1 structure of this state. The result is placed in a systematic survey of g-factors in this mass region as well as compared with the prediction of shell model calculations.Communicated by: D. Schwalm     

Cross sections of 102 element isotopes formation in the reactions of22Ne+236U and26Mg+232Th

The production cross sections of the isotopes²⁵²102,²⁵³102, and²⁵⁴102 were measured for the heavy ion fusion reactions of²²Ne+²³⁶U and²⁶Mg+²³²Th by using the kinematic separator VASSILISSA. The obtained excitation functions and the maximum production cross sections are compared with the ones for more asymmetric reactions leading to the same compound nucleus²⁵⁸102. The experimental cross sections and the results of statistical model calculations are compared and discussed.The authors express their gratitude to Prof. Yu. Ts. Oganessian for his great interest and support of this work, to Drs. E.A. Cherepanov, Yu.A. Muzychka and B.I. Pustylnik for the calculations and for the useful discussions.     

New investigation of83Zr and85Zr beta decay

The decay of on-line mass separated⁸³Zr and⁸⁵Zr sources has been studied by singles and coincident X-ray and-ray and conversion electron measurements. The previous level scheme of⁸³Y is confirmed and 5 new levels have been added up to 2.74 MeV excitation. A decay scheme of^85gZr with 40 levels up to 2.66 MeV in⁸⁵Y is deduced. The experimental observation below 2 MeV excitation in⁸⁵Y agrees qualitatively with the predictions of the interacting boson-fermion model.     

Subthreshold pion production from nucleus-nucleus collisions around 100 MeV/nucleon

Several global variables were tested with the aim to determine the impact parameter in nucleus-nucleus collisions producing pions at incident energies around 100 MeV/nucleon. The experimental set-up includes the MEDEA multidetector, part of which is used as a ⁰ spectrometer, and an additional hodoscope of plastic scintillators to cover very forward angles. A statistical model was used to generate bothinclusive and pion-triggered events. Selection ofwell measured events was made through the measured total parallel momentum. Among the different global variables which were tested, the average parallel velocity was seen to give the best correlation with the impact parameter.     

The competition between fusion-fission and deeply inelastic reactions in the medium mass systems

The competition between fusion-fission and deeply inelastic reactions in the Cl + Ni system has been studied by investigating the exit channelQ-value dependence of theZ-distributions of fission-like fragments. TheZ-, kinetic energy- and angular distributions of the fission-like fragments produced in the³⁷Cl +⁶⁴Ni system atE _lab=170, 186 MeV and in the²⁸Si +⁷⁴Ge system atE _lab=176 MeV have been measured by counter telescopes. TheZ-distribution of the³⁷Cl +⁶⁴Ni system was found to be essentially the same as that of the³⁵Cl +⁶²Ni system at the same bombarding energy. It is shown that this result can not be explained by the statistical fusion fission model but is consistent with a deeply inelastic model. A systematic study of the fission-like phenomenon in this mass region indicates that the maximum angular momenta for fusion reactions as well as the minimum angular momenta for DIC can be reproduced by the Bass model in the sliding limit (f=1.0) while the maximum angular momenta for fully energy-damped deeply inelastic reactions are governed by the strong interaction radius as predicted by the successive critical distance fusion model. The significance of these results are discussed.Communicated by V. Metag     

Possible candidates for discrete gamma rays linking superdeformed and yrast states in an odd nucleus:193Pb

The francium isotopes^200–202Fr were produced in the reaction³⁵Cl+¹⁷⁰Yb using bombarding energies of 4.9–5.3 MeV/nucleon. Fusion products were separated in-flight from the primary beam using a gas-filled recoil separator. An alpha line with the alpha particle energy and half-life of (7468±9) keV and (19 ₋₆ ⁺¹³ ) ms, respectively, was assigned to²⁰⁰Fr. Previously reported decay properties of^201,202Fr were confirmed. Communicated by V. Metag     

Reflection asymmetry in the structure and spectroscopy of224Ac

Minor changes in the assignments of gamma rays following the alpha decay of²²⁸Pa in two previous studies make possible a reinterpretation of²²⁴Ac into two alternative level schemes. The resulting level structures arise from the reflection asymmetric configurations π3/2^±(0.0 −0.3)−ν3/2^±(−0.1 0.6), π5/2^±(0.0 −0.2)±ν3/2^±(−0.1 0.6) and π5/2^±(0.0 −0.2)±ν1/2^±(0.2 −0.1 3) which give rise to eitherK=0^± or 1^±,K=4^±,K=2^± andK=3^± parity doublet bands. The bands with appreciable band structure, namelyK=0^± or 1^± andK=3^±, have average parity doublet splittings of 11.0 and 5.8 keV respectively. These are extremely small values and suggest that²²⁴Ac is the most octupole deformed nucleus studied thus far. A method of calculating the parity doublet splitting in odd-odd nuclei is suggested and tested for²²⁴Ac. It seems to work remarkably well. The systematics of the hindrance factors for the bands with extended band structures confirm their interpretations as band structures. Finally, the two alternative level schemes are analyzed in the framework of the axially-symmetric rigid rotor model including the Coriolis interaction.     

Intermittency in the Fisher's droplet model

Intermittent behaviour of fragment multiplicity distributions in the nuclear liquid-gas phase transition is studied in terms of the droplet model of Fisher. The anomalous fractal dimensions are compared with data on heavy ion reactions and classical molecular dynamics simulations. A signature of the transition in the anomalous fractal dimensions is shown.We thank Profs. S. Ayik, M. Di Toro and V. Kondratyev for discussions. One of us (T.K.) acknowledges the support of INFN-LNS.     

Excitation functions for production of heavy residues in the interaction of12C with181Ta

The excitation functions for production of 21 isotopes and isomers of Au, Pt, Ir, Os and Re in the interaction of¹²C with¹⁸¹Ta from 54 to 98 MeV incident energy have been measured by the activation technique. The analysis of these data allows one to estimate the reaction cross-section and the cross-sections for complete fusion of¹²C and the incomplete fusion of⁸Be and fragments with tantalum.     

Dynamical and thermal aspects of relativistic heavy-ion collisions

Within a covariant BUU-approach we simulate heavyion collisions at various bombarding energies from 400 MeV/u to 1 GeV/u. We evaluate locally the energymomentum tensorT ^v (x), and extract pressures, energydensities and temperatures. The connection of these thermodynamical quantities to experimental observables and their sensitivity to the equation of state is discussed. Furthermore, we investigate the question of local equilibration and evaluate the entropy produced in these reactions.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday. Work supported by BMFT and GSI Darmstadt     

Pion production in heavy ion reactions induced by16O and84Kr beams at 60 MeV per nucleon

Low energy ⁺ and ^– production cross sections have been measured in¹⁶O at 65 MeV/u and⁸⁴Kr at 60 MeV/u induced reactions on⁷Li,¹²C,²⁷Al,¹⁰⁸Ag and¹⁹⁷Au. The results are compared with a previous measurement obtained with¹⁶O at 93 MeV/u. Large deviations are observed between light and heavy ion data. At variance with¹⁶O, the ratios ^–/ ⁺ are independent of the target in the Krypton case. A change in the regime of the projectile-target mass scaling of cross-sections is observed with the heaviest projectile.Experiments performed at GANIL facility, F-14032 Caen, France     

Partial charge-changing cross sections for neutron-deficient isotopes from58Ni fragmentation

At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of⁵⁸Ni at 650 MeV/nucleon in a beryllium target. By means of aE—B—TOF measurement, the fragments were identified and their charge-changing probabilities in targets of (CH₂) _n , C, Al, and Pb placed at the exit of the FRS were determined. Whereas a first article dealt with the total charge-changing cross sections, we describe in this second article the element distributions of these secondary fragments, which are found to depend strongly on the isospin of the secondary projectile as well as on the target material. In the case of the lead target, the influence of the electromagnetic dissociation is clearly visible in the one-proton and two-proton removal channels. The preference for the formation of even-Z fragments is much more pronounced for exotic secondary projectiles than for projectiles close to stability. Calculations with a geometrical abrasion-ablation model allow to understand the global features of the experimental data. However, far from stability, the discrepancies between calculations and experimental data increase.On leave of absence from Institute of Experimental Physics, University of Warsaw, PL-00-681 Warszawa, Hoa 69, Poland     

Pion production in nuclear collisions

The production of pions in nuclear collisions is analyzed in terms of a microscopic reaction model, where the free energy of the entrance channel is transferred to the final channel through the coupling of the relative motion to the internal excitation of N^*-resonances. Such a model allows quite naturally for a consistent analysis of the exclusive and the inclusive production of pions. It turns out that the pionic fusion cross section is determined predominantly by the spectroscopic parentage between the initial target projectile combination and the final nucleus, whereas the inclusive part is dominated by the energy dependence of the phase space factor, i.e. by the number of the degrees of freedom which are relevant in a given kinematical situation. This model is applied to the analysis of available experimental data from threshold to the (1232)-region. A consistent analysis of both the inclusive and the exclusive part of the pion spectrum is presented.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

Damping of the high-spin neutron hole orbitals of the207Pb

The neutron strength functions of the high-spin 1g _7/2 and 1h _11/2 hole states of the²⁰⁷Pb have been deduced within the formalism of the hole-core vibrational coupling scheme. The attenuation of the shell-model strengths of these two high-spin hole states have been compared with the distribution of the neutron strength functions of the discrete 1h _9/2 and 1i _13/2 states. The theoretical results have been discussed in the light of the recent experimental findings on the neutron hole orbitals of the²⁰⁷Pb nucleus. Side by the side the implication of the present research works has been reviewed on the basis of the other existing theoretical calculations on the high-spin neutron hole states of the²⁰⁷Pb.     

Admixture of the giant dipole resonance to low lying 1−-states in heavy nuclei

The mass of ¹³ Be has been measured with the reaction ¹³ C(¹⁴ C,¹⁴ O)¹³ Be at E _Lab =337 MeV. A Q-value of Q ₀=–37.02(5) MeV was obtained and the mass excess is M.E.=35.16(5) MeV. If the observed line corresponds to the ground state,¹³ Be is particle unstable with respect to the oneneutron emission by 2.01 MeV. The observed line width of 0.3(2) MeV supports an assignment ofJ =5/2⁺ or 1/2^–, but excludesJ =1/2⁺. An excited state is seen at 3.12(7) MeV; there are indications of a second excited state at 6.5(2) MeV.     

In-beam magnetization measurements of thin Fe foils and simultaneous observation of the transient magnetic field at Pd ions

The well established phenomenon of heavy ion beam induced attenuations of transient magnetic fields (TF) was studied by measuring the in-beam magnetization of bombarded Fe foils employing the magneto-optical Kerr-effect. Whereas the macroscopic magnetization did not show any deterioration, the simultaneously measured TF of recoiling¹⁰⁸Pd(2⁺) ions was found to be substantially attenuated.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday