Interacting Boson Fermion Research Articles

Detailed spectroscopy of 113Cd through transfer reactions

High energy resolution studies of 113Cd have been performed with the ( d , p ) and ( d , t ) reactions, using polarized beams. In both reactions, a large number of levels (about 80) have been observed up to 2.6 MeV excitation energy, for many of them unambiguous spin and parity assignment being made. Together with previous data from other experiments, the level scheme has probably become essentially complete up to this energy. A detailed comparison is made between the experimental levels and calculations performed with the interacting boson–fermion model-1 (IBFM-1) and with the quasiparticle phonon model (QPM), which allows a good understanding of the level scheme up to about 2 MeV excitation. This nucleus is a special case for the QPM, where due to a strong anharmonicity rather complex configurations must be taken into account in order to get a good description even at low excitation energies. The multiplet structures arising from the coupling of the 3 s 1 / 2 , 2 d 3 / 2 , 2 d 5 / 2 , and 1 g 7 / 2 neutron orbitals to the quadrupole one-phonon excitation of the core nucleus 112Cd have been assigned, and the possible identification of 1 / 2 + and 3 / 2 + “intruder” states (based on two particle–two hole excitations of the core) is discussed. The observation of many ℓ = 1 transitions above 2 MeV excitation gives a clue to the way by which the 11 / 2 − isomeric state can be populated in the ( n , γ ) and ( γ , γ ′ ) reactions.

Nuclear structure of 129Te studied with (n, γ), (d, p) and [formula omitted], t) reactions

The nuclear structure of 129Te has been investigated with the 128Te(n, γγ) 129Te reaction using thermal neutrons, with the 128Te(d, p) 129Te reaction at E d=24 MeV and E d=18 MeV, and with the 130Te( d → , t) 129Te reaction at E d=24 MeV. More than 110 levels were identified already below 3 MeV excitation energy, in most cases including spin, parity, and γ decay. The neutron binding energy was determined to be 6082.42(11) keV. The thermal neutron capture cross sections to the ground state and to the 11/2 − isomer were found to be 0.165(20) b and 0.021(3) b, respectively. The mechanism of direct neutron capture was verified to play an important role in the 128Te(n, γ) 129Te reaction. The experimental level scheme is compared with predictions of the Interacting Boson–Fermion Model (IBFM) and of the Quasiparticle Phonon Model (QPM).

Nuclear structure of 131Te studied with ( n, γ) and [formula omitted] reactions

The structure of 131Te has been investigated with the 130Te( n, γγ) 131Te reaction using thermal neutrons and with the 130Te( d, p) 131Te reaction using polarized deuterons with energy E d =18 MeV. About 290 levels were identified in most cases including spin, parity and γ-decay. The γ-decay scheme after neutron capture is essentially complete containing about 100% of the decay of the capture state and about 100% of the population of the 11/2 − isomer and of the ground state. The scheme includes 42 primary transitions with energies between 750 keV and 2500 keV. The experimental level scheme is compared with predictions of the Interacting Boson–Fermion model (IBFM) and of the Quasiparticle Phonon Model (QPM). The isomeric ratio of the 11/2 − isomer at 182.31(5) keV was determined to be 0.054(2). The neutron binding energy is 5929.38(6) keV. The total thermal neutron capture cross section was found to be 186(13) mbarn.

High-spin states in the odd–odd nucleus 80Y

The high-spin states of 80Y have been studied with the reactions 24Mg( 58Ni, pn γ) at 180 MeV and 58Ni( 24Mg, pn γ) at 77 MeV. Gamma-ray transitions in this nucleus have been unambiguously assigned by using the GASP detector array in conjunction with the recoil mass spectrometer CAMEL and the ISIS Silicon detector ball. These transitions have been arranged into several rotational bands extending up to an excitation energy of about 12 MeV and spin 24 ℏ. The bands are discussed within the framework of the interacting boson–fermion–fermion and cranked shell models.

Three-quasiparticle rotational bands in 101Rh: IBFBPM description and signature inversion of the πg9/2 orbital

High- and intermediate-spin level structures of the 101Rh nucleus have been studied using the reaction 70Zn+ 36S at 130 MeV bombarding energy. γ-rays were detected with the EUROGAM II detector array. Three new ΔI=1 rotational bands have been observed in this nucleus. The deduced level scheme is compared with results of calculations using Interacting Boson–Fermion plus Broken Pair Model. The model calculations give a consistent description of the one- and three-quasiparticle states providing fair agreement between the observed and calculated level energies and branching ratios. Experimental Routhians of the new high-spin bands and the πg 9/2 νh 11/2 bands in the neighbouring Rh and Ag nuclei have been found to exhibit signature inversion. This signature inversion can be interpreted qualitatively as the inversion of the two signatures of the proton g 9/2 orbital caused by triaxial nuclear shape with large positive γ parameter.

Low-lying levels and collective bands in doubly-odd 124Cs

The nucleus 124Cs has been studied by in-beam γ- and e −-spectroscopy techniques with the fusion–evaporation reaction 115In( 12C, 3n γ) at 57 MeV. Multipolarities of the main low-energy transitions have been deduced from electron spectra. A level scheme is proposed with firm I π assignments. Low-spin low-lying levels and high-spin states have been investigated. The low-spin levels and two-quasiparticle bands are interpreted by using the interacting boson–fermion–fermion model. The band structures are also discussed in the frame of the cranked-shell model.

Lifetime measurements of high-spin states in101Agand their interpretation in the interacting boson fermion plus broken pair model

Lifetimes of 20 high spin states in Ag-101 in the range between 0.2 and 200 ps have been measuredand interpreted within the boson fermion plus broken pair model.

The nuclear structure and backbending phenomenon for 114-130 Xe isotopes

In view of interacting boson fermion formalism, a microscopic sdIBM-2 +2q.p. model is used to describe the ground-state band, β-band, γ-band and two-quasi-particle band for 114-130Xe isotopes. The theoretical investigations indicate that the backbending is caused by crossing of the two-quasi-proton band and the ground-state band. This result seems to provide a possible way for understanding the backbending phenomenon of 114-130Xe isotopes.

Level structure of100Nb

Levels in the odd-odd nucleus ${}^{100}\mathrm{Nb}$ situated at the edge of a region of especially fast shape transitions have been calculated in the framework of the interacting boson fermion fermion model. Levels observed in decay studies can be interpreted in a spherical basis. Low-lying ${I}^{\ensuremath{\pi}}{=8}^{+}$ and ${10}^{\ensuremath{-}}$ states are predicted. Their relationship with the unplaced levels populated with a $12 \ensuremath{\mu}\mathrm{s}$ delay after fission is discussed.

Nuclear structure studies of [formula omitted]Te with [formula omitted] and [formula omitted] reactions

Levels in 123 Te were investigated in the range up to 3 MeV excitation energy by (n,γ) and (d,p) reactions. Over 120 levels and about 140 γ-transitions were established most of them for the first time. The states below 2 MeV with the most complete spectroscopic information were interpreted in terms of the Interacting Boson–Fermion Model (IBFM). Unified treatment of both positive- and negative-parity states is achieved with constant parameters of the boson-fermion interaction for the whole chain of Te isotopes. Excitation energies, electromagnetic transition rates, γ-branchings and spectroscopic factors are discussed in connection with their possible structure. A family of low-spin negative-parity states has been identified and understood within the IBFM framework, thus proving their antialigned origin.

Study of 121Te with the [formula omitted] reaction

The structure of the 121Te nucleus has been studied with the 122Te ( d , t) reaction at E d =24.0 MeV. About 100 excited states have been observed up to an excitation energy of 2.65 MeV, and for most of them spin and parity values are proposed. A theoretical analysis based on the Interacting Boson–Fermion Model-1 is presented for the whole isotopic chain from 119 Te to 129 Te. The evolution of both positive and negative parity low-lying levels in these nuclei is reasonably well described with an essentially constant boson–fermion interaction. A detailed comparison of the calculations with experimental data is presented for 121Te. The level scheme up to about 1.5 MeV excitation is reasonably well accounted for. Possible indications of states with “intruder” character are discussed.

Study of [formula omitted] Te with the [formula omitted] reaction

The structure of the nucleus 119 Te has been studied with the 120 Te( d,t) reaction at E d=24.0 MeV. Almost 90 excited states have been observed up to an excitation energy of 2.5 MeV, and spin and parity values have been assigned to many of them. The existing experimental data are compared with calculations made on the basis of the Interacting Boson–Fermion Model-1. The large number of low-spin states observed up to about 1.2 MeV is well accounted for, whereas at higher energies the correspondence of calculated states with experimental ones becomes unreliable. The possibility of the occurence of `intruder' states is also discussed.

Lifetimes and collectivity of low-lying states in115Sn

The lifetimes of excited states in ${}^{115}\mathrm{Sn}$ have been measured using the Doppler shift attenuation method in the reaction ${}^{113}\mathrm{Cd}(\ensuremath{\alpha},2n\ensuremath{\gamma})$ at ${E}_{\ensuremath{\alpha}}=27.2 \mathrm{MeV}$. Lifetimes were obtained for 18 states and lifetime limits for 6 states with ${E}_{x}<~4 \mathrm{MeV}$ and $J<~23/2$. The experimentally obtained $B(\ensuremath{\sigma}L)$ values for transitions deexciting positive-parity states are compared with calculations in the framework of the Bardeen-Cooper-Schrieffer quasiparticle model and the interacting boson fermion model, whereas the values for transitions between negative-parity states are discussed qualitatively within a core-particle coupling picture. The value of $B(E2)=3.5(11)$ Weisskopf units (W.u.) for the transition linking the ${19/2}^{\ensuremath{-}}$ state of the intruder $\ensuremath{\nu}{h}_{11/2}\ensuremath{\pi}2p2h$ band to the ${15/2}^{\ensuremath{-}}$ state of the $\ensuremath{\nu}{h}_{11/2}\ensuremath{\bigotimes}{2}_{1}^{+}$ multiplet strongly supports the configuration $\ensuremath{\nu}{h}_{11/2}\ensuremath{\pi}{(g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}^{2})$ ascribed to this band.

Rotational bands in133Nd

The high-spin structure of the nucleus ${}^{133}\mathrm{Nd}$ has been studied with the GASP array using the ${}^{104}\mathrm{Pd}{(}^{32}\mathrm{S},2pn)$ and ${}^{105}\mathrm{Pd}{(}^{32}\mathrm{S},2p2n)$ reactions. The observed levels have been organized into nine rotational bands including the well-known highly deformed band which has been linked to the states at normal deformation. The bands, which have been classified as being built on different Nilsson orbitals, are discussed in the framework of the interacting boson fermion, particle-plus-triaxial rotor, and cranked shell models.

Structure of low and high spin states in 112Sb in interacting boson fermion fermion model

In this paper, properties of the low and the high spin states in 112Sb have been studied in the framework of Interacting Boson Fermion Fermion Model. A surface delta plus spin-spin type of interaction has been taken as the residual interaction between the odd neutron and the odd proton. Energy values, magnetic moments of the ground state and the isomeric 8− state, E2/M1 mixing ratios of some of the low-lying transitions and log ft values for the Gamow-Teller transitions in 112Sb →112Sn and 111Sb →111Sn decay have been calculated and are compared with the experimental results. The band based on the configuration π g-19/2π g27/2⊗ν h11/2 is obtained in this calculation by coupling the proton in the g9/2 and the neutron in the h11/2 orbital to the deformed band of 110Sn. The B(M1)/B(E2) ratios and branching ratios for the transitions in this band have also been calculated and compared with the experimental results.

Transition probabilities and interacting boson-fermion model description of positive parity states in117Sb

The Doppler shift attenuation method was used to determine lifetimes in the picosecond region for excited states of ${}^{117}\mathrm{Sb}$ populated with the $(\ensuremath{\alpha},2n\ensuremath{\gamma})$ reaction at ${E}_{\ensuremath{\alpha}}=27.2\mathrm{MeV}.$ Interacting boson-fermion model calculations explain reasonably well the main features of the positive parity levels known up to about 2.5 MeV excitation. The mixing of the lowest one-quasiparticle ${9/2}^{+}$ state with the intruder $(2p\ensuremath{-}1h)$ ${9/2}^{+}$ state, as well as the quadrupole deformation of the intruder band are also discussed.

Experimental study of the deformed nucleus 153Sm via (d→,t) and average resonance capture as a test case for the multiorbit interacting boson fermion model

The ${}^{154}\mathrm{Sm}(\stackrel{\ensuremath{\rightarrow}}{d},t)$ reaction at high energy resolution $(n,\ensuremath{\gamma}),$ average resonance capture (ARC), and coincidence measurements were performed to study the deformed nucleus ${}^{153}\mathrm{Sm}.$ Strength distributions from $(\stackrel{\ensuremath{\rightarrow}}{d},t)$ and completeness for ${I}^{\ensuremath{\pi}}={\frac{1}{2}}^{\ensuremath{-}}$ and ${\frac{3}{2}}^{\ensuremath{-}}$ 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 (${\frac{1}{2}}^{\ensuremath{-}}$, ${\frac{3}{2}}^{\ensuremath{-}}$) states much better than the Nilsson model since the even-even 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 boson-fermion 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.

Nuclear structure of97Yin the interacting boson fermion plus broken pair model and the nature of the 3.523 MeV high-spin isomer

Nuclear structure of ${}^{97}\mathrm{Y}$ is described in the interacting boson fermion plus broken pair model, including quasiproton and quasiproton-two-quasineutron configurations in the basis states. In particular, the yrast bands and the decay of the ${27/2}^{\ensuremath{-}}$ high-spin isomer are accounted for in this approach.

Nuclear shell model and interacting boson fermion approximation

Abstract The Interacting Boson-Fermion Model (IBFM) hamiltonian is derived starting from the shell-model interaction, by a straightforward extension of the Otsuka, Arima and Iachello mapping procedure to odd-mass systems. Employing a single j -shell model and identical many nucleon systems, systematic studies of spectra giving the comparison in the shell-model, SD pair truncated model and IBFM are carried out: (i) for various proportions of monopole pairing and Q · Q interactions which simulate vibrational-rotational transition; (ii) for a particular combination of these interactions together with the quadrupole pairing interaction, which conserves seniority.

IBFM2 description of odd Xe and Cs isotopes

Excitation energies, branching ratios and E2/M1 mixing ratios of the negative-parity states in 125,127Xe and 125,127,129Cs have been calculated by using the proton-neutron Interacting Boson Fermion Model (IBFM2). A good agreement with the experiment has been obtained. The sensitivity of the calculated observables to changes in model parameters is discussed and the results are compared with those obtained from the IBFM1. We examine a symmetry of the Hamiltonian with respect to the change of sign of the parameters χ π , χ ν and Г. The different behaviours of the odd Xe and Cs isotopes arise from the different position of the proton and neutron Fermi levels. In particular the exchange term of the Hamiltonian in 125,127,129Cs can be neglected.