W. Schauer

Two-phonon J = 1 states in even-mass Te isotopes with A = 122–130☆

Abstract Excited states of the nuclei 122,126,130 Te were populated via the (γ, γ′) reaction at endpoint energies of the bremsstrahlung between 4.5 and 5.5 MeV. Gamma rays were detected with a EUROBALL CLUSTER detector and a single HPGe detector. In all investigated nuclei two or three prominent dipole transitions were identified at E γ ≈ 3 MeV. The corresponding low-lying J = 1 states are interpreted as two-phonon excitations. Quasiparticle-phonon-model calculations predict at about 3 MeV one 1 − state arising from the coupling of the first quadrupole and the first octupole phonon, and one 1 + state arising from the coupling of the first and the second quadrupole phonon, where the latter has isovector character. Such an excitation mode can be considered as an analogue of the scissors mode in vibrational nuclei. The calculated transition strengths are compatible with experimental ones within a factor of about 1.5.

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

Abstract Levels in 125 Te were investigated in the range up to 3.3 MeV excitation energy by the (n,γ), (d,p) and ( 3 He,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.

Study of 121Te with the reaction

Abstract The structure of the 121 Te nucleus has been studied with the 122 Te ( 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 121 Te. The level scheme up to about 1.5 MeV excitation is reasonably well accounted for. Possible indications of states with “intruder” character are discussed.

Nuclear levels in 187W

Abstract Levels in 187W have been studied up to 2.2 MeV with the (d, p) and (n, γ) reactions. The (d, p) studies were performed at deuteron energies of 24 and 28 MeV and at two angles of 30° and 50° by using the high resolution Q3D spectrograph in Munich. Primary and secondary γ-rays and γ-γ coincidences were studied with Ge detectors. The combination of these results with the previously known ones allows us to extend the existing level scheme and refine some of its structure assignments. Most of the low-lying states have been classified in terms of the Nilsson model with the extension of some vibrational degrees of freedom. The possibility for the coexistence of triaxial or oblate shapes in 187W is observed in the form of anti-aligned states with a bandhead of 9 2 − at 364 keV. The polarization effects towards the triaxial shape produced by the odd neutron in specific Nilsson orbitals have been studied. The calculated polarization energies for some γ-driving orbitals are comparable with the prolate-oblate energy difference which indicates the possibility of the stabilization of triaxial or oblate shapes in these states.

The nuclear structure of 126Te studied with (d,p), (d,3He) and (d,d′) reactions☆

Abstract At the Munich Tandem Accelerator the reactions 125 Te(d, p) 126 Te, 126 Te(d, d′) 126 Te and 127 I(d, 3 He) 126 Te were measured with deuteron energies between 24 and 28 MeV up to excitation energies of about 3.2 MeV. Using γ-lines from previous (n,γ), (n,n′γ) and (γ,γ′) experiments, a level scheme of 126 Te up to above 3 MeV was established. The results are compared with quasiparticle-phonon model calculations.

A position sensitive cathode strip detector with single strip readout

Abstract The detector presented is a special kind of MWPC combined with a scintillator and is used for nuclear spectroscopy at the Munich Q3D magnetic spectrograph. It allows both identification and position determination of the incident particles. The position is derived from the charge distribution influenced on a few neighboring cathode strips which are read out individually. During data acquisition the position is calculated with the center of gravity method. This reduces the dead time per event to about 60 μs but causes a systematic error. This is eliminated later in a replay, which calculates the position by fitting the charge distribution. With this method the position precision is better than 0.1 mm.

Nuclear structure studies of 123Te with (n,γ) and (d,p) reactions

Abstract 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 122Te with charged particle reactions

Abstract The reactions 122 Te(d,d′) 122 Te, 123 Te(d,t) 122 Te, 123 Te( 3 He, 4 He) 122 Te, and 121 Sb( 3 He,d) 122 Te were measured with the Q3D magnetic spectrograph of the Munich Tandem Accelerator. The level scheme of 122 Te was extended up to about 4 MeV using also previous results and new 122 Te(γ,γ′) 122 Te data. The level scheme is compared with IBA and QPM calculations. An intruder band is proposed with the 0 + band head at 1746 keV.

Nuclear structure of 183W studied in (n, γ), (n, n′γ) and (d, p) reactions

Abstract The nucleus 183 W was studied with ( n , γ), ( n , γγ) and ( n , n ′ γ ) reactions at the Nuclear Research Center Reactor in Riga and with the ( d , p ) reaction measured with the Q3D spectrograph at the Munich Tandem Accelerator. The 183 W γ-transition data from the ( n , γ) reaction were obtained in the energy range from 90 to 6200 keV and from the ( n , n ′ γ ) reaction in the energy range from 40 to 2080 keV. The new data allowed to obtain much more accurately the energies and depopulation of excited levels, and to extend the level scheme up to about 1.7 MeV. The one-quasiparticle states below 1.6 MeV were interpreted as belonging to the Nilsson configurations 1 2 − [510] , 1 2 − [501] , 1 2 − [521] , 3 2 − [512] , 3 2 − [501] , 3 2 − [521] , 3 2 + [642] , 3 2 + [651] , 5 2 + [642] , 5 2 − [512] , 7 2 − [503] , 7 2 − [514] , 9 2 − [505] , 9 2 + [624] , 11 2 + [615] and to the βγ-vibrational band. Structure calculations in terms of the quasiparticle-phonon and quasiparticle-rotation-vibration models were performed.

SINGLE PARTICLE EXCITATIONS IN 129BA FROM A (D, T) REACTION STUDY

Abstract The 130Ba( d , t) 129Ba reaction was studied with 25 MeV deuterons and excellent energy resolution. About 50 excited states have been observed up to Ex = 2.0 MeV and for 42 of them transferred l values and/or Jπ values were assigned on the basis of the measured angular distributions and asymmetries. The level scheme of 129Ba, the neutron pickup strength distribution and the known electromagnetic decay scheme are compared with results of calculations with the interacting boson-fermion model. These simple multi-shell IBFM-1 calculations describe well the main features of the experimental data.