H. A. Roth

Charged particle production in peripheral reactions induced by 118 MeV 12C ions on 118Sn

Abstract The multiplicities of γ -cascades observed in coincidence with fast charged ejectiles from 118 Sn + 118 MeV 12 C collisions are measured. The analysis gives evidence for a peripheral nature of these reactions and supports the sum-rule model for incomplete (and complete) fusion.

Identification of theN=79147Er nucleus throughγ-recoil coincidences

Abstracthe so far unknown nucleus147Er has been identified by means of γ- recoil and γ — γ coincidences through the reaction92Mo(58Ni,2pn) at a bombarding energy of 260 MeV. The level scheme has been obtained up to 5.0 MeV of excitation energy and shows collective excitations built on the h11/2 intruder orbital.

In-beam γ-ray spectroscopy on56Ni

Yrast levels in the doubly-magic nucleus56Ni have been studied by in-beam gg-spectroscopy with the reaction54Fe(α, 2n)56Ni. A cascade of five γ -transitions is established. A shell model calculation of 2p2h, T=0 states, using empirical matrix elements, suggests the assignments 8+ and 10+ for the two highest levels.

Cross sections for 18O+9Be induced reactions at sub-coulomb energies

Abstract Cross sections for reactions induced by 18 O on 9 Be have been measured in the energy range E c . m . = 1.8 MeV to 6.7 MeV. The yields of characteristic γ-rays were observed with a Ge(Li) detector and absolute cross sections were deduced for formation of 19 O, 21, 22, 23 Ne, 24, 25 Na and 25 Mg. The 9 Be( 18 O, 19 O) 8 Be transfer cross section was found to dominate over the total fusion cross section below E c . m . = 4.5 MeV. The energy dependence of the measured transfer cross section agrees well with what is expected for a reaction of optimum Q -value at low incident energies.

Structure of As-68 studied via the C-12(Ni-58, pn) reaction

Excited states of As-68 nucleus were populated through the C-12(Ni-58,pn) reaction and investigated by in-beam gamma-spectroscopic methods. The NORDBALL detector array equipped with charged particle and neutron detectors was used to detect the evaporated particles and gamma-rays. The level scheme of As-68 was constructed on the basis of gamma gamma-coincidence relations up to 6 MeV excitation energy and J(pi) = (15(+)). The structure of the nucleus is discussed in the framework of the interacting boson-fermion-fermion model. The states below 2.3 MeV are described as members of proton-neutron-phonon multiplets

A New Type of Band Crossing at Large Deformation

A detailed study of the positive parity yrast and yrare rotational bands in Rb-77 is presented. Using the reaction Ca-40(Ca-40,3p) and the EUROGAM I spectrometer, gamma gamma gamma coincidences enabled us to follow both bands over a large spin range and to measure many E2 strengths. The moments of inertia and transition quadrupole moments indicate that a more deformed band (epsilon(2) approximate to 0.38) is crossed by a less deformed one (epsilon(2) approximate to 0.29), Since the yrare band starts at the extremely low spin value of I = 9/2, the conventional band crossing mechanism of two aligning high-j quasiparticles is excluded. The frequency-dependent equilibrium shapes were calculated with Nilsson-Strutinsky type calculations using a diabatic tracing of configurations near the neutron Fermi level, This is the first observation of such a band crossing. (Less)

In-beam study of 102Sn

Excited states in 102Sn have been identified for the first time, in an in-beam γ-ray spectroscopic experiment. Two γ-ray transitions with energies 1472 and 497 keV following the decay of the seniority 6+ isomer with t1/2 = 1.0(5) μs were unambiguously assigned to 102Sn. Due to the very low cross section of about 2 μb for producing 102Sn in the reaction 50Cr(58Ni,1α2n), a highly selective detector setup utilizing NORDBALL ancillary detectors and a recoil catcher device was used. High γ-ray detection efficiency was achieved with two EUROBALL Ge cluster detectors.

Non-equilibrium neutron emission in α-induced reactions on124Sn

Neutron time-of-flight spectra were measured in coincidence withγ-rays characteristic for thexn (x=2, 3, 4, 5) fusion-like products in reactions of 35–57 MeVα-particles with124Sn. Additional information was obtained from excitation function andγ-multiplicity measurements. The neutron energy spectra for a specificx n channel at high bombarding energies clearly show the presence of nonequilibrium neutron emission. The spectra are parameterized in terms of emission from a slow equilibrated and a fast moving source. The fast moving source has a velocity close to the beam velocity indicating a close relationship between the movement of the projectile and the neutron emission.

Interpretation of the residue mass distribution from 12C + 64Zn collisions at E(12C) = 118 MeV

The distribution of residual nuclei from 12C + 64Zn collisions at E(12C) = 118 MeV has been investigated by charged particle and γ-ray spectroscopy and is compared to predictions from evaporation codes (CASCADE, JULIAN-PACE). A satisfactory agreement is generally found for the distribution of residual nuclei and the γ-ray multiplicity values. The computer codes, however, strongly underestimate the α- and 2α-emission channels compared to channels involving nucleon evaporation only. Reaction channels involving heavy ejectiles are relatively weak and are accounted for by including non-fusion processes in the calculations.

Angular Momentum Transfer in Reactions Induced by 14N Ions on 154Sm

The angular momentum input in reactions induced by 151 MeV 14N ions on 154Sm has been investigated by measuring the gamma-ray multiplicity in coincidence with emitted charged particles. The average multiplicity of gamma-ray cascades following the emission of protons, deuterons and tritons in reactions leading to 158Er amounts to 17.5 which is far below the value 31, earlier reported for a bombarding energy of 167 MeV. Predictions by Wilczynskis sum-rule model for complete and incomplete fusion reactions combined with statistical evaporation of particles are in good agreement with the present results.