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B. Million

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Papers by B. Million

Spectroscopy of neutron-rich Co nuclei populated in the 70 Zn+ 238 U reaction

Journal of Physics: Conference Series, 2012

Neutron-rich Co isotopes from N = 34 to 40 were studied through multinucleon transfer by bombardi... more Neutron-rich Co isotopes from N = 34 to 40 were studied through multinucleon transfer by bombarding a 238 U target with a 460 MeV 70 Zn beam at LNL. Gamma-recoil coincidences were recorded identifying the ions by a high-acceptance magnetic spectrometer (PRISMA) and detecting the gamma radiation by an array of HPGe clover detectors (CLARA). The results are discussed in comparison with the predictions of large-scale shell-model calculations.

The High Energy Photons From Very Symmetric Reactions: The Giant Dipole Resonance In 179Au Nucleus

AIP Conference Proceedings, 2003

High‐energy γ rays emitted in the symmetric reaction 90Zr + 89Y have been measured at the Argonne... more High‐energy γ rays emitted in the symmetric reaction 90Zr + 89Y have been measured at the Argonne National Laboratory using the LEPPEX array coupled to the Fragment Mass Analyzer (FMA). The high‐energy γ‐ray spectra emitted by the giant dipole resonance built on excited states and associated with the evaporation of 0, 1 and 2 nucleons have been measured. The statistical model analysis indicates that the radiative‐fusion process, namely the 0 particle emission channel, can be well described as a compound nucleus decay channel. In addition, the analysis of the high‐energy γ‐ray spectra associated with the different evaporation channels provides the first evidence that shell effects still play a role in determining the nuclear shapes of 179Au in the temperature interval 0.5–1 MeV.

Population Of Neutron Rich Nuclei Around [sup 48]Ca With Deep Inelastic Collisions

AIP Conference Proceedings, 2009

Compound And Rotational Damping In Warm Nuclei

AIP Conference Proceedings, 2005

The gamma-decay from excited nuclei is used to study the interplay between rotational motion and ... more The gamma-decay from excited nuclei is used to study the interplay between rotational motion and compound nucleus formation in deformed nuclei. A new analysis technique is presented which allows for the first time to directly measure the rotational and compound damping widths Gammarot and Gammamu from gamma-coincidence spectra. The method is first tested on simulated spectra and then applied to

Conservation of the K-quantum number in warm nuclei

Nuclear Physics A, 2005

The selection rules on the K-quantum number in rapidly rotating warm nuclei are investigated anal... more The selection rules on the K-quantum number in rapidly rotating warm nuclei are investigated analyzing quasi-continuum spectra feeding into low-K and high-K bands in 163 Er. The data are compared to simulated spectra obtained using the band mixing model predictions including the residual interaction and a term representing the effect of the Kquantum number on the rotational energy. K-selection rules are found to be obeyed by the decay along excited unresolved rotational bands of heat energy up to around 1.2 MeV and angular momentum 30h ≤ I ≤ 40h. In contrast, the results corresponding to higher heat energy of 1.2 to 2.5 MeV indicate that the selection rules are only partially satisfied.

The giant dipole resonance in superdeformed nuclei and the feeding of superdeformed bands

Nuclear Physics A, 2001

Effect of E1 decay in the population of superdeformed structures

Spectra of the yrast and excited superdeformed bands, forming the E2 quasi-continuum, are measure... more Spectra of the yrast and excited superdeformed bands, forming the E2 quasi-continuum, are measured with the EUROBALL array for the nucleus 143 Eu, in coincidence with high-energy γ-rays (E γ > 3 MeV). It is found that the intensity population of the superdeformed states is enhanced by a factor of ≈ 1.6 when a coincidence with a γ-ray with energy > 6 MeV is required, in reasonable agreement with the increase of the line shape of the Giant Dipole Resonance built on a superdeformed configuration. This result shows that when an high energy E1 γ-ray is involved in the decay it is more likely connected with a SD rather than a ND nucleus. In addition, the analysis of the rotational quasi-continuum suggests the presence of a superdeformed component. The data are also compared and found consistent with simulation calculations of the relative intensities of the SD states, including the E1 decay of superdeformed nature.

Excited Superdeformed Band in 143 Eu

European Physical Journal A, 1999

A new superdeformed band has been discovered in a EUROBALL experiment and assigned to 143Eu. It h... more A new superdeformed band has been discovered in a EUROBALL experiment and assigned to 143Eu. It has a maximum intensity of 35% of the 143Eu yrast superdeformed band and the transition energies of the two bands are very similar. Based on comparison with cranked shell model calculations the new band is tentatively assigned the high-N intruder configuration &#6362&#5770 and the

$Research paper thumbnail of GDR Feeding of the Highly-deformed band in $^{42} $ Ca$

GDR Feeding of the Highly-deformed band in $^{42} $ Ca

Arxiv preprint nucl-ex/ …, 2004

The γ-ray spectra from the decay of the GDR in the compound nucleus reaction 18 O+ 28 Si at bomba... more The γ-ray spectra from the decay of the GDR in the compound nucleus reaction 18 O+ 28 Si at bombarding energy of 105 MeV have been measured in an experiment using the EUROBALL IV and HECTOR arrays. The obtained experimental GDR strength function is highly fragmented, with a low energy (≈10 MeV) component, indicating a presence of a large deformation and Coriolis effects. In addition, the preferential feeding of the highly-deformed band in 42 Ca by this GDR low energy component is observed.

Radiative fusion from very symmetric reactions: the giant dipole resonance in the 179Au nucleus

Physics Letters B, 2003

The spectra of high-energy γ rays emitted by the Giant Dipole Resonance (GDR) built on moderately... more The spectra of high-energy γ rays emitted by the Giant Dipole Resonance (GDR) built on moderately excited states associated with the evaporation of 0, 1 and 2 nucleons were measured in the 90 Zr + 89 Y symmetric fusion reaction. The radiative fusion data suggest statistical emission from the compound nucleus. In addition, the analysis of the high-energy γ-ray spectra associated with the different evaporation channels at the present temperature of 0.7 MeV and spin range 15-20h show a fairly narrow width of 5.0 ± 0.35 MeV. This value is smaller than what would be expected in a nucleus where shell effects do not play a role.

Lifetime measurements of the rotational quasi-continuum transitions in 163 Tm

Physics Letters B, 1997

The lifetime of the unresolved transitions forming the rotational quasi-continuum spectra has bee... more The lifetime of the unresolved transitions forming the rotational quasi-continuum spectra has been measured in 163 Tm using the Doppler shift attenuation technique. Spectra associated to different values of the coincidence folds, angular anisotropies and the dynamical moment of inertia were also obtained from the present experiment. The Doppler shift has been measured for discrete transitions, for the ridge structures in E = E spectra and for the rotational E2 bump in one g 1 g 2 dimensional spectra. The data were compared to the theory using a simulation model which makes use of microscopically calculated levels and transition probabilities. Above 1300 keV the results indicate collectivity with lifetime faster than y14 Ž. 10 s, while at lower E the results are well described by predictions with B E2 s 400 WU.

The T=2 mirrors 36Ca and 36S: A test for isospin symmetry of shell gaps at the driplines

Physics Letters B, 2007

The first excited 2 + state of 36 Ca has been identified by its γ-decay, exploiting the two-step ... more The first excited 2 + state of 36 Ca has been identified by its γ-decay, exploiting the two-step fragmentation technique at the FRS-RISING setup at GSI. This is the heaviest T z = −2 nucleus in the Segré chart in which a γ-decay of an excited state has been observed. A stable beam of 40 Ca at 420A MeV impinged on a primary 9 Be target. Out of the secondary beam of fragmentation products, 37 Ca was separated by the FRS and struck on a second 9 Be target at the final focus of the FRS. The energy for the 2 + 1 decay of 36 Ca was determined to be 3015(16) keV, which is 276 keV lower than in its T = 2 mirror 36 S. This mirror energy difference (MED) is discussed in the framework of shell model calculations using a 16 O core, the sd shell isospin symmetric interaction USD and experimental single-particle energies from 17 O and 17 F. The results show that the MED within the sd shell provide a sensitive test for the evolution of the N, Z = 14, 16 subshell gaps towards the driplines. Especially the N , Z = 16 gap is determined by Thomas-Ehrman shift in the A = 17, T = 1/2 isospin doublet, while Coulomb effects are found to have marginal influence.

Phase-space selection of the GDR gamma ray emission from hot 162Yb nuclei

Physics Letters B, 1992

The angular distribution of the high energy gamma rays emitted in the decay of the giant dipole r... more The angular distribution of the high energy gamma rays emitted in the decay of the giant dipole resonance built on excited states, in mainly ~62yb, has been measured using a differential technique to enhance decays originating from the highest region of nuclear temperatures. A simple formalism to analyze such data is presented. Such experiments provide information on the shapes and orientation distribution of atomic nuclei at finite temperature.

Evidence for different time scales controlling thermal fluctuations in hot nuclei

Physical Review Letters, 1992

ABSTRACT

Giant Dipole Resonance in the Hot and ThermalizedCe132Nucleus: Damping of Collective Modes at Finite Temperature

Physical Review Letters, 2006

The decay of the giant dipole resonance (GDR) in the 132 Ce compound nucleus with temperature up ... more The decay of the giant dipole resonance (GDR) in the 132 Ce compound nucleus with temperature up to 4 MeV has been measured, using the reaction 64 Ni 68 Zn at E beam 300, 400, and 500 MeV. The and charged particles measured in coincidence with recoils are consistent with a fully equilibrated compound nucleus emission. The GDR width, obtained with the statistical model analysis, is found to increase almost linearly with temperature. This increase is rather well reproduced within a model including thermal shape fluctuations and the lifetime of the compound nucleus.

Increase in Width of the Giant Dipole Resonance in Hot Nuclei: Shape Change or Collisional Damping?

Physical Review Letters, 1995

The strength function and the angular distribution of the high energy y rays emitted by the giant... more The strength function and the angular distribution of the high energy y rays emitted by the giant dipole resonance (GDR) in hot rotating 'O9"OSn nuclei have been measured at temperature T = 1.8 MeV and at four values of the angular momentum I. The GDR width is =2 times larger than at T = 0 and increases by =20% as I goes from 40 to 54h. The a2(E~) increases by a factor of =2. Based on these two facts and on the comparison with theory we conclude that large deformations driven by I and combined with shape and orientation fluctuations are responsible for the measured increases. Collisional damping is constant and practically equal to the T = 0 case.

Rotation and shape changes in Tb151 and Pb196: Probes of nuclear structure and tunneling process in warm nuclei. I. Experimental analysis

Physical Review C, 2009

The γ decay associated with the warm rotation of the superdeformed nuclei 151 Tb and 196 Pb has b... more The γ decay associated with the warm rotation of the superdeformed nuclei 151 Tb and 196 Pb has been measured with the Euroball IV array. Several experimental quantities are presented, putting strong constraints on the decay dynamics in the superdeformed well. The data are successfully reproduced using a Monte Carlo simulation of the γ decay based on microscopically calculated energy levels, E2 decay probabilities, collective mass parameters, and potential energy barriers between the wells associated with normal and super deformation. This allows one to test the basic ingredients of the physical process, such as the strength of the two-body residual interaction and the potential barriers as a function of spin and excitation energy. We also show that the data probe the E1 strength function, indicating an enhancement around 1-2 MeV γ rays, which might be related to octupole vibrations.

Selective studies of the excited rotational bands in the superdeformed nucleus Tb151

Physical Review C, 2007

The experimental study of the unresolved rotational bands, forming ridge structures in gamma-gamm... more The experimental study of the unresolved rotational bands, forming ridge structures in gamma-gamma spectra, has been performed on the superdeformed nucleus Tb151. gamma transitions from the reaction Al27, at 155 MeV, on Te130 were measured with EUROBALL IV in high fold coincidence. The analysis of the intensities and count fluctuations of the ridge structures shows the existence of &ap;30 discrete rotational bands of superdeformed nature, half of which is in direct coincidence with the superdeformed yrast band. A comparison with band mixing model predictions and with a previous work on the superdeformed nucleus Eu143 is presented.

The GDR in Hg and Eu nuclei from selected decay chains

Nuclear Physics A, 1999

ABSTRACT

Angular momentum dependence of the GDR width in Sn nuclei at fixed excitation energy

Nuclear Physics A, 1997

High-energy ~,-rays from the decay of the giant-dipole resonance (GDR) in the hot l~Sn compound n... more High-energy ~,-rays from the decay of the giant-dipole resonance (GDR) in the hot l~Sn compound nucleus and its daughters were measured in coincidence with heavy recoiling evaporation residues. The compound nucleus was formed at excitation energy E* = 80 MeV using the reaction 56Ni+4STi at a bombarding energy of 260 MeV. The analysis yields the GDR width for two different intervals of angular momentum (J) = 24 and 36h. The present data, combined with previous data at higher angular momentum permit a study of the angular momentum dependence of the GDR width for 10 ~< J ~< 60h at approximately fixed temperature. The width of the GDR is found to be roughly constant for J < 35h, increasing rapidly for higher angular momenta. The data are found to be in good agreement with theoretical calculations within an adiabatic model describing thermal fluctuations of the nuclear shape. The model also reproduces the much weaker angular momentum dependence of the GDR width in the heavier nucleus t76W.