Publications (90)176.05 Total impact

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ABSTRACT: The inclusive and exclusive reactions have been studied with a beam energy of 171 MeV and scattering angles for the reaction θ=0° and 3°. The studies focused on the separation of the isovector spindipole resonance (IVSGDR) into its components by measuring tensoranalysing powers and observing the direct neutron decay to the lowlying protonhole states in 11B. Merging the information obtained from both measurements resulted in the firsttime verification of modelindependent predictions of tensoranalysing powers at extreme forward angles and the experimental decomposition of the IVSGDR into its Jπ components. The experimental results are in reasonable agreement with theoretical estimates based on shellmodel calculations.  [Show abstract] [Hide abstract]
ABSTRACT: Without Abstract  [Show abstract] [Hide abstract]
ABSTRACT: Neutron inner hole responses in 115Sn and 119Sn nuclei have been studied via the (d⃗,t) reaction at Ed=200MeV using a polarized beam with both vector and tensor components. Onestep pickup observables corresponding to the overlapping 1g9/2, 1f5/2, and 1f7/2 responses were analyzed between 3° and 15° via a least square fit procedure up to EX=21.5MeV and 20 MeV in 115Sn and 119Sn, respectively. The relative enhancement of transitions with high total angular momentum j and the strongly characteristic angular distributions of j=l1/2 versus j+=l+1/2 vector and tensor analyzing powers allow the extraction for the first time of 1f5/2 and 1f7/2 strength distributions and of new 1g9/2 strength in addition to its previously known main component. The standard DWBA analysis is complemented by a refined analysis taking into account the form factor dependence on excitation energy due to the hole coupling with surface vibrations calculated in the framework of the quasiparticlephonon coupling model (QPMFF). Residual nucleus spectra were measured, mainly in 115Sn, up to EX∼45MeV where the underlying background of multistep reactions is dominant and can be calibrated. The background of multistep pickup cross section is calculated for the first time in the forward angle region, assuming a dominant role of collective excitations in inelastic steps. Coupled channel calculations for twostep pickup observables involving low multipole collective excitations are performed for comparison. Integrated strengths deduced in the present work are compared with previous data on the 1g9/2 structure and tail, and with the very limited previous information existing on the 1f strengths. The 1g9/2, 1f5/2, and 1f7/2 QPMFF and standard strength distributions are compared with available theoretical predictions. In particular, we find that the 1f5/2 and 1f7/2 strength distributions are not well reproduced by the QPM model. The QPMFF spreading widths are found much narrower than the standard ones, but nevertheless much wider than predicted by theoretical calculations. 
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ABSTRACT: The study of the 208Pb(d→,t)207Pb reaction at Ed = 200 MeV has been extended up to typically Ex = 40 MeV in 207Pb using a polarized beam with both vector and tensor components. Twostep pickup reactions involving low multipolarity collective transitions have been evaluated for the first time via systematic coupled channel calculations, allowing a new approach of the background determination. The (d→,t) observables corresponding to the overlapping 1h11/2, 1g7/2, and 1g9/2 inner hole responses have been analyzed up to Ex = 25 MeV via a least squares fit procedure. Necessary input values were deduced for hole states of interest from finite range distorted wave (DWBA) calculations. The optical parameters and the range function were those successfully used in a previous survey of valence state observables. The highest j transitions are enhanced in the reaction and analyzing powers exhibit strongly characteristic features for j = l1/2 versus j+ = l+1/2 states. We have calculated for the first time the separation energy dependence of nlj transition observables, taking into account the form factor modifications induced by the hole coupling with surface vibrations. The calculations have been performed in the framework of the quasiparticlephonon model (QPM). This analysis (QPMFF) predicts a large variation of differential cross sections with excitation energy of the hole fragments, while angular distribution shapes remain quite stable. The strength distributions resulting of the QPMFF analysis and of a standard analysis using DWBA observables calculated at the centroid energies are systematically compared. As a general rule, the QPMFF analysis increases the strength concentration toward lower excitation energy. The corresponding 1h11/2, 1g7/2, and the tentative 1g9/2 strength distributions are compared and discussed with the available theoretical calculations. In particular, the narrower spreading widths deduced via the QPMFF analysis are quite well predicted by the calculation of spectral functions in a modified mean field. The 1i13/2 and 1h9/2 valence strength distributions are revisited along this new approach and found to be in fair agreement with the fragmentation predicted by the QPM, which is not the case of inner hole strength distributions.  [Show abstract] [Hide abstract]
ABSTRACT: The study of the 208Pb(d⃗,t)207Pb reaction at Ed=200MeV has been extended up to typically Ex=40MeV in 207Pb using a polarized beam with both vector and tensor components. Twostep pickup reactions involving low multipolarity collective transitions have been evaluated for the first time via systematic coupled channel calculations, allowing a new approach of the background determination. The (d⃗,t) observables corresponding to the overlapping 1h11/2, 1g7/2, and 1g9/2 inner hole responses have been analyzed up to Ex=25MeV via a least squares fit procedure. Necessary input values were deduced for hole states of interest from finite range distorted wave (DWBA) calculations. The optical parameters and the range function were those successfully used in a previous survey of valence state observables. The highest j transitions are enhanced in the reaction and analyzing powers exhibit strongly characteristic features for j=l1/2 versus j+=l+1/2 states. We have calculated for the first time the separation energy dependence of nlj transition observables, taking into account the form factor modifications induced by the hole coupling with surface vibrations. The calculations have been performed in the framework of the quasiparticlephonon model (QPM). This analysis (QPMFF) predicts a large variation of differential cross sections with excitation energy of the hole fragments, while angular distribution shapes remain quite stable. The strength distributions resulting of the QPMFF analysis and of a standard analysis using DWBA observables calculated at the centroid energies are systematically compared. As a general rule, the QPMFF analysis increases the strength concentration toward lower excitation energy. The corresponding 1h11/2, 1g7/2, and the tentative 1g9/2 strength distributions are compared and discussed with the available theoretical calculations. In particular, the narrower spreading widths deduced via the QPMFF analysis are quite well predicted by the calculation of spectral functions in a modified mean field. The 1i13/2 and 1h9/2 valence strength distributions are revisited along this new approach and found to be in fair agreement with the fragmentation predicted by the QPM, which is not the case of inner hole strength distributions.  [Show abstract] [Hide abstract]
ABSTRACT: The 154Sm(d>,t) reaction at high energy resolution (n,gamma), average resonance capture (ARC), and coincidence measurements were performed to study the deformed nucleus 153Sm. Strength distributions from (d>,t) and completeness for Ipi=12 and 32 states up to 1500 keV from ARC provide one of the first detailed tests of the interacting boson fermion model (IBFM) in a deformed nucleus in a multiorbit environment. For negative parity states the model accounts for the large number of low spin (12, 32) states much better than the Nilsson model since the eveneven core in the IBFM calculations automatically includes excited vibrational states. The IBFM calculations also predict (d,t) spectroscopic factors better than the Nilsson model with pairing and Coriolis mixing. Neither the IBFM nor the Nilsson approach can explain the low lying positive parity states. The IBFM calculations show that for certain combinations of parameters, the monopole term in the bosonfermion Hamiltonian has more than a scaling effect: it can attenuate the Coriolis mixing (energy staggering). Finally suggested improvements in the treatment of pairing in the IBFM are made. 
Article: Lowlying states of 56Fe
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ABSTRACT: Lowlying states at Ex=4.48.6 MeV of excitation energy in 56Fe have been studied by means of inelastic deuteron scattering at Ed=56 MeV. The spin, parity, and isoscalar matrix element of detected levels have been deduced by comparing the measured cross sections with coupledchannel calculations using collective form factors. The present data for higher excitation energies have been analyzed by combining with previous data at lower excitation energies. The lowenergy octupole strength in 56Fe is found to be mostly located in the excitation energy range of Ex=4.48.6 MeV. The strength is weakly fragmented, and the 31 level exhausts the major part of the octupole energyweightedsumrule value. A similar behavior is observed for the quadrupole strength in 56Fe, which is mostly located below Ex=4.4 MeV. This is in contrast with the behavior of the 3 and 2+ states in 54Fe, which are heavily fragmented despite the weaker quadrupole deformation. The hexadecapole strength is strongly fragmented both in 56Fe and in 54Fe. The strength distributions for the transitions with multipolarities λ=2, 3, and 4 in 54,56Fe have been compared with random phase approximation calculations. The theoretical calculations show that the closure of the νf7/2 shell is responsible for the observed fragmentation of the 2+ and 3 strengths in 54Fe, and that the collectivity of the 2+1 and 31 levels of 56Fe is restored by the presence of two neutrons outside the νf7/2 shell.  [Show abstract] [Hide abstract]
ABSTRACT: Single particle strength distributions have been investigated in the deformed nucleus 153Sm via high resolution (p,d) and (d→,t) reactions. About 170 levels were observed below 2.2 MeV excitation energy; for most of them the ℓtransfer value could be assigned. Distorted Wave calculations have been performed.The strength distributions have been described within the IBFM model.  [Show abstract] [Hide abstract]
ABSTRACT: Excited states in the 153Sm nucleus have been investigated via the (p,d) reaction performed with a good resolution. About 170 levels were observed below 2.2 MeV excitation energy; for most of them the ℓtransfer value could be assigned. Distorted wave calculations have been performed and discussed. The 153Sm is already rather deformed, and can be described in terms of the Nilsson model. Levels below 0.5 MeV were identified as members of rotational bands based on the Nilsson orbitals. The strength distributions have been described within the Quasiparticle Phonon Model. 
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ABSTRACT: Lowlying states in 56Fe, up to an excitation energy of about 4 MeV, have been investigated by means of inelastic proton and deuteron scattering experiments at Ep=65 and 400 MeV and at Ed=56 MeV, respectively. Measured cross sections and analyzing powers have been compared with coupledchannels calculations using collective form factors; calculations in both the Schrödinger and Dirac formalisms have been carried out for the proton data. For each probe, the matrix elements have been deduced for transitions from the ground state and from the 2+1 state to six quadrupole (2+) states to one octupole (31) and two hexadecapole (4+1 and 4+2) states. The obtained matrix elements and the previous values from gamma decay or electron inelastic scattering have been used to evaluate the isospin character of the transitions. To discuss the quadrupole mixedsymmetry states in 56Fe, the deduced neutron (Mn) and proton (Mp) components of the matrix elements, or equivalently the isoscalar (Ms) and isovector (Mv) parts, have been compared with theoretical calculations based on the neutronproton interacting boson model and on the shell model evaluated in a full fp configuration space.  [Show abstract] [Hide abstract]
ABSTRACT: Excited states in 140, 142, 144, 146Nd nuclei, up to an excitation energy of about 5 MeV, were investigated by (p,t) experiments performed with a good energy resolution. These data, together with proton and deuteron scattering data from a previous experiment, are compared with QuasiParticle Phonon Model evaluations, in which the competition between particlehole and particleparticle residual interactions is considered. The B(Eλ) distributions are satisfactorily reproduced. The 146, 148Nd(p,t) reaction data are well accounted for, while difficulties are found in reproducing those for 142, 144Nd(p,t). Limitations and improvements of the model are discussed.  [Show abstract] [Hide abstract]
ABSTRACT: Using the Munich Q3D spectrograph the 154Sm(d,t), (d,t), (p,d), and (3He,4He) 153Sm reactions have been measured at beam energies between 23 and 32 MeV: The high resolution of up to 4 keV FWHM especially in (p,d) is essential to achieve reliable energy calibration. All levels reported in the Nuclear Data Sheets [1] with the exception of high spin states (J ≥ 13/2) are observed and at higher excitation energy (Ex > 1MeV) many new levels could be identified. The analysis in the framework of the Nilsson model uses CCBA to include inelastic transfer amplitudes.  [Show abstract] [Hide abstract]
ABSTRACT: A cross section enhancement, persisting to high momentum transfer, has been observed around 1ħω in excitation energy in spectra from inelastic proton, alpha and electron scattering on 90Zr, 116Sn, 196Pt and 208Pb. Data are presented for (p,p') at 201 MeV, (α, α') at 120 MeV and analyzed together with existing data obtained with 133.8 MeV polarized (,p') on 116Sn and electronscattering data on 116Sn and 196Pt. Two different interpretations of the observed enhancement are discussed: that of the incoherent sum of all 1ħω cross section and alternatively the sum over the isoscalar normal modes of all multipolarities. 
Article: Experimental survey of the (d
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ABSTRACT: Differential cross sections, vector and tensor analyzing powers of the (d→,t) reaction on 120Sn, 116Sn, 90Zr, 58Ni, 16O, and 12C have been measured at 200 MeV bombarding energy. Deuteron elastic scattering measurements have been performed on 116Sn and 208Pb at the same energy. These data have been analyzed together with previous ones on 58Ni and 16O to get best fit optical parameters describing deuteron elastic scattering. The (d→,t) experimental survey bears on 28 transitions populating well known valence levels, including previous data in 207Pb and 27Si. The vector and tensor analyzing powers exhibit striking similarities for transitions measured in different nuclei. The angular distributions are found to strongly depend on the number of nodes in the neutron form factor and on the coupling of spin and angular momentum j=l1/2 versus j+=l+1/2. The j effect is especially pronounced, for both analyzing powers for n=1 transitions. The slopes of the differential cross sections in different nuclei depend mainly on the number of nodes. Exact finite range calculations including S and D components have been performed, using two sets of deuteron parameters together with a deep triton potential. Both analyses reproduce rather well the differential cross sections and currently adopted spectroscopic factors. The conventional analyses with deuteron parameters fitting elastic scattering data reproduce rather well analyzing powers of n>1 transitions (with l=0,1,2), but disagree with the data for n=1 transitions (except for j+Ayy values). Good or qualitative agreement is achieved for all transitions with the second deuteron potential, characterized by larger spin orbit terms and an additional imaginary tensor term. This allows using the reaction as a spectroscopic tool.  [Show abstract] [Hide abstract]
ABSTRACT: Highresolution inelasticscattering measurements on 112Cd with polarized deuterons (20 MeV) and polarized protons (16 and 65 MeV) provide complete spectroscopic information. Transition moments are obtained from the angular distributions of the cross section and analyzing power in a coupledchannel reaction analysis. The results are compared with interacting boson model predictions aiming to describe intruder states, quadrupolehexadecapole and quadrupoleoctupole excitations.  [Show abstract] [Hide abstract]
ABSTRACT: High resolution inelastic scattering measurements with 20 MeV polarized deuterons and results of recent Coulomb excitation studies of Hasselgren et al. on 110Pd are compared with predictions from new IBA calculations, where configuration mixing or QQ interaction between like bosons was included to describe intruder states and triaxial features, respectively. The spectroscopic properties of the four lowenergy collective bands are well described.
Publication Stats
1k  Citations  
176.05  Total Impact Points  
Top Journals
 Physical Review C (28)
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 Il Nuovo Cimento (6)
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Institutions

19572007

INFN  Istituto Nazionale di Fisica Nucleare
 Laboratori Nazionali di Legnaro LNL
Frascati, Latium, Italy


19672002

University of Milan
 Department of Physics
Milano, Lombardy, Italy


1988

VU University Amsterdam
 Department of Physics and Astronomy
Amsterdamo, North Holland, Netherlands


19631965

Fondazione IRCCS Istituto Nazionale dei Tumori di Milano
Milano, Lombardy, Italy
