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Abstract:: The 137I nucleus, populated in the spontaneous fission of 248Cm has been studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. Medium-spin yrast excitations in 137I were observed for the first time. The experimental level scheme is compared to the shell model calculation with modified Kuo-Herling interaction. The theoretical predictions differ significantly from the experimental results, indicating that the excitation pattern in 137I deviates significantly from the shell model scheme.

Coulomb breakup of neutron-rich nuclei around mass A∼ 20 has been studied experimentally using secondary beams (∼ 500–600 MeV/u) of unstable nuclei produced at GSI. The spectroscopic factor deduced for the neutron occupying s1/2level in 15C ground state is consistent with the earlier reported value. The data analysis for Coulomb breakup of 17C shows that most of the cross section yields the 16C core in its excited state. For 17–22O, the low-lying E1 strength amounts up to about 12% of the energy weighted dipole sum rule strength depending on neutron excess. The cluster sum rule limit with 16O as a core is almost exhausted for 17,18O, while for more neutron rich isotopes the strength with respect to that limit decreases.

Abstract:: Neutron-rich, 88-94Kr nuclei, populated in spontaneous fission of 248Cm, have been studied with EUROGAM 2, by measuring prompt γ-rays. Many new excited states in even-even Kr isotopes have been identified. For the first time spins and parities were determined experimentally in these nuclei. Our results indicate that the quadrupole deformation of Kr isotopes will appear only above N = 58, as observed in Sr and Zr nuclei. The newly found 3- level at 1506.4 keV in 90Kr suggests the exsistence of a new region of increased octupole correlations, probably associated with the ν(d 5/2 h 11/2) pair of Δl = Δj = 3 orbitals.

Abstract:: Excited states in the neutron-rich, N=84 nuclei 134Sn, 136Te and 138Xe, populated in the spontaneous fission of 248Cm, were studied to medium spins using the EUROGAM2 array. OXBASH code calculations support the experimental identification of maximum aligned configurations in these isotopes. Empirical shell model calculations agree with the proposed excitation energy of the neutron h9/2 excitation in the 132Sn region. A discrepancy between the observed and calculated excitation energy of the Iπ= 12+ level in 136Te indicates possible admixtures of collective excitations in this nucleus. Clear signs of collective excitations are observed in 138Xe.

G-factors of excited states in 154Dy were measured up to high spins by a recoil-distance transient field technique. The results can be explained by i32neutron alignment at the first band-crossing and confirm the alignment of protons in the spin 30 region.

Excitation of the two-phonon isovector giant dipole resonance was observed in 208Pb projectiles incident on different target nuclei (C, Sn, Ho, Pb, U) at high energy (640 A·MeV). Evidence is found for a two-step electromagnetic excitation mechanism. An enhancement of 1.33(16) for the excitation cross section is observed relative to the harmonic approximation. Neutron- and γ-decay probabilities are derived as well.

We investigate the beam energy dependence of neutron and proton squeeze-out in collisions of197Au+197Au atE/A=400—800 MeV. The azimuthal anisotropy that describes the enhanced emission of mid-rapidity neutrons perpendicular to the reaction plane rises strongly with the transverse momentum of the neutrons. This dependence of the azimuthal anisotropy follows a universal curve — independent of beam energy — if the neutron momenta are measured in fractions of the projectile momentum per mass unit. Analogously, the kinetic energy spectra of mid-rapidity neutrons exhibit a universal behaviour as a function of the kinetic energy of the projectile.

Aγ-γ coincidence technique has been developed forg-factor measurements of short-lived nuclear states. The method involvesγ-detection in 4π geometry as well as transient magnetic fields and the recoil-distance technique. A first experiment was performed for the isotope160Yb produced in the reaction64Ni(100Mo, 4n) at 430 MeV beam energy. The valueg=− 0.23(31) of the 14+ yrast state, which is compatible with zero, establishes thevi13/2 quasiparticle structure to be responsible for the first backbend. A meang-factor for low spin states around the 4+ state,g=+0.48(26) was also derived as well as lifetimes for yrast states up toIπ=8+.

A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of 178Hf in the Kπn = 16+isomeric state has been performed at 4.77 MeV/u 208Pb beam energy. The first excited Iπ= 17+state has been observed at an excitation energy of 357.4 ± 0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment of Q0= 8.2 ± 1.1 b has been derived from the experimental data within the rigid rotor model.

A search for octupole deformation in neutron-rich Xe isotopes has been conducted through prompt gamma-ray spectroscopy of secondary fragments produced in the spontaneous fission of$^{248}$ Cm. The spectrometer consisted of the Eurogam 1 array and a set of 5 LEPS detectors. Level schemes were constructed for Xe isotopes with mass number ranging from 140 to 144 and excited states for$^{143,144}$ Xe nuclei were observed for the first time. None of the level schemes exhibit an alternating parity quasimolecular band, a feature usually expected in nuclei in which octupole correlation effects are strong enough to produce stable octupole deformation. For several isotopes, structures observed in the level schemes are consistent with an octupole softness of the nuclei.

A search for octupole deformation in neutron-rich Xe isotopes has been conducted through prompt gammaray spectroscopy of secondary fragments produced in the spontaneous fission of248Cm. The spectrometer consisted of the Eurogam 1 array and a set of 5 LEPS detectors. Level schemes were constructed for Xe isotopes with mass number ranging from 140 to 144 and excited states for143,144Xe nuclei were observed for the first time. None of the level schemes exhibit an alternating parity quasimolecular band, a feature usually expected in nuclei in which octupole correlation effects are strong enough to produce stable octupole deformation. For several isotopes, structures observed in the level schemes are consistent with an octupole softness of the nuclei.

Nucleon transfer accompanied by Coulomb excitation was studied in the system206Pb+232Th atELab=6.4 MeV/u. Particle-particle-gamma coincidence techniques were used to identify excited states of reaction products populated through inelastic scattering and nucleon transfer reactions. The mean excitation energy was measured by means of a?-ray energy and multiplicity filter consisting of 6 NaI detectors. Large cross sections for one-neutron and two-neutron pick-up from232Th are observed. The impact-parameter dependence of the neutron transfer is analyzed in terms of semiclassical barrier penetration models. Using realistic neutron potentials with a diffuse surface, the experimental data are in accordance with the assumption of a “cold” transfer to states near the yrast line.

Prompt γ radiation following spontaneous fission has been measured using the EUROGAM 2 array. Using these data and newly developed analysis techniques a number of subjects were studied, which are briefly discussed. One of these subjects, shape transition in A≈100 Sr and Zr nuclei is discussed in more detail. Quadrupole moments were determined for rotational bands in the N=58,59,60,62 and 64 Sr and Zr isotopes. Deformation parameters, which increase from β2≈ 0.1 at N=56 to β2≈ 0.4 at N=64, suggest that in strontium and zirconium isotopes shape change happens gradually between N=56 and N=62 and is probably due to an occupancy of three or more deformation-driving orbitals of h11/2parentage.

A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of178Hf in the Kπ= 16+isomeric state has been performed at 4.77 MeV/u208Pb beam energy. The first excited Iπ= 17+state has been observed at an excitation energy of 357.4±0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment ofQ0=8.2±1.1 b has been derived from the experimental data within the rigid rotor model.

Abstract: Excited levels in 141Xe, populated in spontaneous fission of 248Cm, were studied by means of prompt γ-ray spectroscopy, using the EUROGAMM2 array. Level scheme of 141Xe obtained in this work shows patterns characteristic of simplex symmetry with s = +i and s = −i bands present but low value of D 0 moment indicates that octupole correlations in Xe isotopes are systematically lower than in Ba nuclei.

Excited levels in ¹³⁹Cs, populated in spontaneous fission of ²⁴⁸Cm, have been studied by means of prompt gamma spectroscopy, using the EUROGAMM 2 array. New level scheme of ¹³⁹Cs, different from the one proposed recently, has been established. To confirm the new scheme, additional study of ¹³⁹Cs has been performed, where -rays following -decay of ¹³⁹Xe to ¹³⁹Cs have been measured at the mass separator OSIRIS.

Abstract:: Excited levels in 133Sn and 134Sb, populated in spontaneous fission of 248Cm, were studied by means of prompt-γ spectroscopy, using the EUROGAM 2 multidetector array. The neutron i 13/2 single-particle energy has been determined for the first time in the 132Sn region. The energy of the h 9/2 neutron level, proposed previously, has been confirmed.

Abstract:: Neutron-rich, N=84 nuclei from the 132Sn region, populated in spontaneous fission of 248Cm, have been studied with EUROGAM 2. Excited states and their spins and parities in the 136Te nucleus were established up to 17ħ. OXBASH code calculations support the experimental identification of maximum aligned configurations in 136Te. Empirical shell model calculations for the Iπ= 14+ level in 136Te indicate that the adopted mass of the 134Te nucleus should be lowered by 200(80) keV.

By analysis of fission product γ-rays measured at Eurogam II using a 248Cm source, the (vf7/2)2multiplet in the N= 84 nucleus 134Sn has been identified up to a 6+isomeric state at 1246 keV. The B(E2; 6+→4+) is determined to be 36±7 e2fm4corresponding to a vf7/2E2 effective charge of 1.02±0.10.10 e.

High-spin structures in the neutron-rich nuclei138Xe and139Xe have been investigated by observing prompt ? -rays from the spontaneous fission of248Cm with the Eurogam spectrometer. The partial level schemes were constructed on the basis of double-, triple- and quadruple-? coincidences. The ground state band in138Xe has been extended up to 5 MeV excitation energy. The structure of the newly observed medium-spin states in139Xe is similar to the one of heavier N=85 isotones where vf72/3, vh9/2f72/2 and vf72/3 ? 3- multiplets have been observed.

Abstract:: By analysis of fission product γ-ray data measured at Eurogam II using a 248Cm source, yrast levels up to about 2 MeV in the N=84 three-particle nucleus 135Sb have been identified. These levels are interpreted as π g7/2ν f7/22 and π g7/2ν f7/2h9/2 states with the help of shell model calculations using empirical nucleon-nucleon interactions.

Prompt γ-ray cascades in neutron-rich nuclei around doubly-magic 132Sn have been studied using a 248Cm fission source. Yrast states located in the N= 82 isotones 134Te and 135I are interpreted as valence proton and neutron particle-hole core excitations with the help of shell model calculations employing empirical nucleon-nucleon interactions from both 132Sn and 208Pb regions.