Interacting Boson Fermion Model Research Articles

Shape phase transition in odd nuclei in a multi-jmodel: TheUB(6)⊗UF(12)case

The phase transition in odd nuclei when the underlying even-even core nuclei experience a transition from spherical to deformed {gamma}-unstable shapes is investigated. The odd particle is assumed to be moving in the three single-particle orbitals j=1/2,3/2, and 5/2 . At the critical point in the phase transition, an analytic solution to the corresponding Bohr Hamiltonian, called E(5/12), is worked out. Energy spectra and electromagnetic transitions and moments are presented. The same problem is also attacked in the framework of the interacting boson-fermion model (IBFM). Two different Hamiltonians are used. The first one is constructed ad hoc so as to mimic the situation in the E(5/12) model. The second one leads to the occurrence of the O{sup B}(6xU{sup F}(12) symmetry when the boson part approaches the O(6) condition. The entire transition line is studied with this Hamiltonian and, in particular, the critical point. Both IBFM calculations at the critical point are consistent with the E(5/12) results.

Lifetime measurements inNb93from photon and inelastic neutron scattering

The low-spin structure of $^{93}\mathrm{Nb}$ has been studied using the $^{93}\mathrm{Nb}$$(\ensuremath{\gamma},{\ensuremath{\gamma}}^{'})$, $^{93}\mathrm{Nb}$$(n,{n}^{'}\ensuremath{\gamma})$ and $^{94}\mathrm{Zr}$$(p,2n\ensuremath{\gamma}\ensuremath{\gamma})$$^{93}\mathrm{Nb}$ reactions. Lifetimes were determined from both $^{93}\mathrm{Nb}$$(\ensuremath{\gamma},{\ensuremath{\gamma}}^{'})$ and $^{93}\mathrm{Nb}$$(n,{n}^{'}\ensuremath{\gamma})$ measurements. Branching ratios were measured, and multipolarities and spin assignments were determined from the $^{94}\mathrm{Zr}$$(p,2n\ensuremath{\gamma}\ensuremath{\gamma})$$^{93}\mathrm{Nb}$ angular correlation experiment. From $M1$ and $E2$ strengths, the ${J}^{\ensuremath{\pi}}=9/{2}^{+}$ and $7/{2}^{+}$ states at 1297.1 keV and 1483.6 keV, respectively, are proposed as members of the quintet of mixed-symmetry states associated with the $\ensuremath{\pi}1{g}_{9/2}\ensuremath{\bigotimes}({2}_{1,\mathrm{MS}}^{+}$,$^{92}\mathrm{Zr}$) configuration. The large $B(M1)$ values determined in $^{93}\mathrm{Nb}$ cannot be explained within the weak coupling limit of the interacting boson fermion model.

Positive parity low spin states of odd-mass tellurium isotopes

In this work, we analyse the positive parity of states of odd-mass nucleus within the framework of interacting boson fermion model. The result of an IBFM-1 multilevel calculation with the lg 9/2, 2d 5/2, 2d 3/2, 3s 1/2 and one level, 1h 11/2 with negative parity, single particle orbits is reported for the positive parity states of the odd mass nucleus 123–125Te. Also, an IBM-1 calculation is presented for the low-lying states in the even–even 124–126Te core nucleus. The energy levels and B (E2) transition probabilities were calculated and compared with the experimental data. It was found that the calculated positive parity low spin state energy spectra of the odd-mass 123–125Te isotopes agree quite well with the experimental data.

Phase transitions in the interacting boson fermion model: The γ-unstable case

The phase transition around the critical point in the evolution from spherical to deformed \ensuremath{\gamma}-unstable shapes is investigated in odd nuclei within the interacting boson fermion model. We consider the particular case of an odd $j=3/2$ particle coupled to an even-even boson core that undergoes a transition from spherical U(5) to \ensuremath{\gamma}-unstable O(6) situation. The particular choice of the $j=3/2$ orbital preserves in the odd case the condition of \ensuremath{\gamma}-instability of the system. As a consequence, energy spectrum and electromagnetic transitions, in correspondence of the critical point, display behaviors qualitatively similar to those of the even core. The results are also in qualitative agreement with the recently proposed E(5/4) model, although few differences are present, due to the different nature of the two schemes.

Energy Level Statistics of SO(5) Limit of Super-symmetry U(6/4) inInteracting Boson–Fermion Model**The project supported by National NaturalScience Foundation of China under Grant Nos. 10265001 and 10347115and Key Scientific Research Fund of Inner Mongolian Educational Bureauunder Grant No. NJ04116

We study the energy level statistics of the SO(5) limit ofsuper-symmetry U(6/4) in odd-A nucleus using the interacting boson–fermionmodel. The nearest neighbor spacing distribution (NSD) and the spectralrigidity (Δ3) are investigated, and the factors that affect theproperties of level statistics are also discussed. The results show thatthe boson number N is a dominant factor. If N is small, both theinteraction strengths of subgroups SOB(5) andSOBF(5) and the spin play important rolesin the energy level statistics, however, along with the increase of N, thestatistics distribution would tend to be in Poisson form.

Precision electron-gamma spectroscopic measurements in 75As

The decay of 75Se to levels of 75As has been studied using an HPGe detector for gamma-ray and a mini-orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 18 gamma rays and 16 conversion electron lines reported for the first time. New results also include E2 multipolarity assignment for the 81 keV transition, M1 assignment to three newly observed transitions and M1 + E2 for the 617 keV transition. A revised 75As level scheme is constructed using the Ritz combination principle through the computer code GTOL. While confirming the existence of 10 well-established levels, two levels at 587 and 859 keV are newly placed into the decay scheme of 75Se. The interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly placed 586.8 keV 1/2- and 859.9 keV 1/2+ levels are studied in the light of the Interacting Boson-Fermion Model.

Nuclear structure of 127Te studied with [formula omitted] and [formula omitted] reactions and interpreted with IBFM and QPM

The nuclear structure of 127Te has been investigated with the Te 126 ( n , γ γ ) Te 127 reaction using thermal neutrons and with the Te 126 ( d → , p ) Te 127 reaction at E d = 20 MeV . About 190 levels were identified in a region to 4.1 MeV excitation energy, in most cases including spin, parity and γ-decay. The γ-decay scheme after neutron capture is essentially complete containing about 100% of the population of the 11 / 2 − isomer and of the ground state. The thermal neutron capture cross section and isomer production of the 11 / 2 − state at 88.3 keV were determined to be 0.44(6) b and 0.069(10) b, respectively. The neutron binding energy was determined to be 6287.6(1) keV. A significant number of the ( d , p ) angular distributions of cross section and asymmetry are anomalous with respect to the distorted-wave Born-approximation calculations and could be accounted for by inelastic multi-step mechanisms. The observed strong correlation of the ( d , p ) and primary ( n , γ ) strengths gives evidence for the direct neutron capture process which is mainly responsible for the primary population of 16 levels. The experimental level scheme is compared with predictions of the interacting boson–fermion model and of the quasiparticle phonon model.

Shape phase transitions in odd-mass nuclei using a supersymmetric approach

The concept of supersymmetry and phase transitions are brought together through a study of the consistent-$Q$ Hamiltonian of the interacting Boson-Fermion model, constructed with a vibrational one-body term and a quadrupole-quadrupole interaction, and which is applicable to odd-$A$ nuclei with dominant $j=\frac{1}{2}$, $\frac{3}{2}$, and $\frac{5}{2}$ single-particle orbits. A conservation condition for the pseudo-orbital angular momentum is discussed.

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.

Microscopic derivation of interacting boson-fermion model Hamiltonian and its application to singly magic nuclei

The interacting boson-fermion model (IBFM) Hamiltonian is derived microscopically based on the generalized seniority scheme starting from the shell-model interaction. Employing many nondegenerate levels and identical nucleon systems, systematic studies of singly magic nuclei are given in comparison with experiments. The resulting energy spectra in the IBFM are found to be in good agreement with those of the shell model and the $\mathrm{SD}$ pair plus one-particle model.

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.

Electromagnetic properties of low-excitation states in 191Ir and 193Ir and supersymmetry schemes

The electromagnetic properties of low-excitation states in 191Ir and 193Ir have been studied following Coulomb excitation. Gyromagnetic ratios were measured by the transient-field technique and level lifetimes were measured by the Doppler-shift recoil distance method. Multipolarity mixing ratios were determined from measured particle– γ angular correlations. The present lifetime and g-factor results extend the data available for comparison with theory and help discriminate between disparate experimental values reported previously in the literature. We compare the experimental data with particle-triaxial-rotor model calculations and with the predictions of the U(6/4) and U(6/20) supersymmetry models based on the interacting-boson–fermion model.

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.

Nuclear structure studies of 125Te with (n,γ), (d,p) and ( 3He,α) reactions

Levels in 125Te were investigated in the range up to 3.3 MeV excitation energy by the (n,γ), (d,p) and ( 3He,α) reactions. Over 160 levels and about 360 γ-transitions were established, most for the first time. The states below 2.3 MeV with the most complete spectroscopic information were interpreted in terms of the interacting boson-fermion model (IBFM). Unitary treatment of both positive- and negative-parity states is achieved with the same model parameter close to the intermediate case between O(6) and U(5) limits. Excitation energies, electromagnetic transition rates, γ-branchings and spectroscopic factors are discussed in connection with the possible structures. A family of low-spin negative-parity states has been identified and understood by the IBFM proving their antialigned origin.

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 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.

Interacting Boson-Fermion Description of Odd-Odd Nuclei

I present an algebraic model and the relevant computing code for the analysis of low-energy spectra and electromagnetic properties of nuclei with an odd number of neutrons and/or protons within the framework of the Interacting Boson–Fermion Model (IBFM), taking explicitly into account the isospin degree of freedom. Some results for odd–mass and doubly–odd nuclei in the shape-transitional region around A ≈ 100 will be shown and compared with the experimental data.

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.