Excitation of 3−1, 5−1 and 7−1 states in Te isotopes A = 120, 122; 124, 126, 128 WITH (p,t) reactions

The reactions ^ATe(p, t)^A?2Te have been studied with even-A targets using 51.9 MeV protons. Three or more strongly excited triton peaks were observed in the spectra of the ^A-2Te nuclei at energies of ≈ 2–3 MeV excitation. Angular distributions are analyzed using DWBA theory. The lowest octupole (3^?₁) states of five Te isotopes are strongly excited. The lowest 3^? state in ¹²⁰Te is established at 2.09 ±0.02 MeV. The systematics of excitation energies and cross sections for the lowest 5^? and 7^? states are interpreted by a quasiparticle model.     

Rotational and vibrational states in 115Te

High-spin states of the ¹¹⁵Te were studied by in-beam spectroscopy with the ⁸⁹Y (²⁹Si, p2n) fusion-evaporation reaction at a beam energy of 108 MeV. γ?γ coincidence and γ?γ angular correlation analyses were employed for determining the level scheme of ¹¹⁵Te. We have identified two vibrational-like bands built on the νh_11/2 and νg_7/2 quasiparticle states and the noncollective oblate states from the full alignment of quasiparticle configurations. In addition, a regular ΔI = 2 sequence with positive-parity was found for the first time in odd-A Te nuclei. This sequence is interpreted as a deformed structure resulting from three-quasiparticle alignment having the [π(g_7/2, h _11/2) ? ν(h _11/2)] configuration. Calculations of total Routhian surfaces and cranked shell model were performed and were used for assigning quasiparticle configurations to the states in ¹¹⁵Te.     

Decay of126m Sb and the energy levels of126Te

The decay characteristics of 19 min^126m Sb have been studied using Ge(Li) and scintillation spectrometers. The sources of^126m Sb were obtained by the (n, p) reaction on enriched¹²⁶Te. The gamma rays of energies 414.4±0.3, 666.7±0.5 and 696.1±0.5 keV were found decaying with a half-life of 19 min. The study of beta spectra employing an anthracene crystal yielded two beta groups with end-point energies of 1.9±0.15 and 2.5±0.15 MeV. The results of singles and coincidence measurements have been incorporated into a decay scheme with excited states of¹²⁶Te at 666.7, 1,362.8 and 1,777.2 keV.     

Yrast excitations in A = 126–131 Te nuclei from deep inelastic 130Te+64Ni reactions

Thick target γγ coincidence measurements for the system ¹³⁰Te + 275 MeV ⁶⁴Ni have been performed using the GASP Ge detector array at Legnaro. For the isotopic assignments of previously unknown γ-ray cascades, prompt γγ coincidences observed between Te and Ni partner products were of vital importance. The results yield much new information about excited states of moderate spins in A = 126–131 tellurium nuclei, especially about yrast excitations of the little studied odd-A isotopes ¹²⁷Te, ¹²⁹Te, and ¹³¹Te. Level systematics of tellurium nuclei are presented, and both single-particle and collective aspects of the level spectra are discussed.     

High-spin states in123Te

The¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of⁸He. In addition to the known excited state of⁸He at E _x =3.6MeV, withJ ^π=2⁺, three additional states were found at excitation energies of 4.54(25)MeV, 6.03(10)MeV and 7.16(4)MeV.     

Study of the Gamow-Teller resonance in 90Nb and 208Bi

An approach is proposed for studying the spreading properties of the Gamow-Teller resonance (GTR) in heavy nuclei including the coupling to 2p2h configurations and the ground-state correlations beyond RPA. The GTR is generated by a proton p-neutron h (πp-νh) phonon within the renormalized RPA. The second-order configuration mixing beyond RPA is realized by constructing two-phonon configurations, in which one of two intermediate phonon states is a πp-νh phonon. The numerical calculations are performed in the parent nuclei ⁹⁰Zr and ²⁰⁸Pb making use of M3Y nucleon-nucleon interaction and the single-particle wave functions obtained in the standard harmonic oscillator potential. The single-particle energies around the Fermi surface are substituted with the empirical values or those given by a Woods-Saxon potential. The results obtained provide a reasonable account for recent experimental findings on the GTR in these nuclei. The extension of the present approach to highly excited (hot) nuclei is also provided. The GTR is found to be stable against temperatures up to T = 6 MeV.     

On the nature of the isomeric 6+ state in the heavy doubly-even Te isotopes

The isomeric 6⁺ state in the heavy doubly-even Te isotopes has been studied in the two-proton cluster core coupling model. The lifetime is calculated and compared to the experimental data. Reduced quadrupole transition probabilities for transitions between the first excited 2⁺ state and the ground state are discussed.     

Levels in124Te populated in the decay of124Sb

The levels in¹²⁴Te have been investigated by studying the gamma rays emitted following the decay of 60d¹²⁴Sb. Gamma-gamma coincidence spectra have been taken with gates set at 603, 646, 709, 714 and 723 keV gamma rays by using 105 cm³ Ge(Li)-110 cm³ HPGe coincidence system. 69 gamma rays have been observed and nine of them are reported for the first time. Four new levels in¹²⁴Te at 2512, 2550.2, 2808 and 2814.5 keV are proposed. Levels reported in literatures at 2412 and 2733 keV are excluded from the level scheme of¹²⁴Te based on the present study. The experimentally determined energy spectrum of low-lying positive parity states, B(E2) ratios and electric quadrupole moment of the first excited state are compared with the IBM-1 predictions.     

On the decay of compound nuclei following alpha-particle and12C induced reactions

Multiple coincidence rates have been measured using a detector system consisting of a Ge(Li) spectrometer and eight NaI(Tl) or eight liquid scintillators. Reactions induced byα-particles with energies of 51–55 MeV and 118 MeV¹²C ions are studied. The data are analysed to give the first and second central moments of the distribution of the number ofγ-rays feeding individual levels in the final nuclei. When these numbers are compared to spin distributions calculated with the statistical model code GROGI the relative importance of dipole and quadrupole deexcitation modes can be ascertained. In particular, in the¹²²Te(α, 4n)¹²²Xe reaction theγ-decay prior to the entry into the ground band is well described as a statistical process proceeding to 50% by dipole and 50% by quadrupole radiation. In the¹⁶⁶Er(α,4n)¹⁶⁶Yb and¹⁹²Os(α,4n)¹⁹²Pt reactions the relative amount of quadrupole radiation is larger and it seems that the dipole and quadrupole decay takes place via separate cascades. In the¹⁶⁴Dy(¹²C, 7-8n) reactions the average multiplicity is independent of spin, suggesting that the nucleus forgets the spin of the entry state before the process enters into the ground band. In the¹⁷⁶Yb(¹²C, 8n)¹⁸⁰Os reaction, finally, the nucleus definitely retains memory of the entry state during the decay. In this last case the multiplicity measurement is combined with aγ-ray singles measurement to give an average excitation energy prior to theα-decay and the average moment of inertia characterising the decay of the high-spin states.     

In-beam gamma-ray spectroscopy of 116Te

High-spin states of the even-even ¹¹⁶Te were studied by in-beam g-ray spectroscopy using the ¹⁰³Rh (¹⁶O, p2n) fusion-evaporation reaction at a beam energy of 80 MeV. γ-γ coincidence and γ-γ angular correlation analyses were employed for determining the level scheme of ¹¹⁶Te. Levels up to I^π = 27^? and several new states were established. We identified two rotational bands with negative parity, one of which was newly established in the present work. We suggest that such two bands be associated with two proton [(g_7/2) ? (h_11/2)] and two neutron [(d_5/2) ? (h_11/2)] configurations, respectively.     

First observation of low lying states in the doubly odd nucleus132Pr from beta decay of132Nd

Excited states of ¹⁰⁸ Te were populated in the ⁵⁴ Fe + ⁵⁸ Ni (270 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. Gamma rays belonging to the neutron deficient nucleus ¹⁰⁸ Te were identified for the first time. On the basis of γγ-coincidence and angular correlation relations a level scheme was constructed with tentative spin and parity assignments. The structure of the nucleus is discussed in the framework of systematics of heavier Te nuclei.     

Magnetic field effect on state energies and transition frequency of a strong-coupling polaron in an anisotropic quantum dot

By employing a variational method of the Pekar-type, which has different variational parameters in the x–y plane and the z-direction, we study the ground and the first excited state energies and transition frequency between the ground and the first excited states of a strong-coupling polaron in an anisotropic quantum dot (AQD) under an applied magnetic field along the z-direction. The effects of the magnetic field and the electron–phonon coupling strength are taken into account. It is found that the ground and the first excited state energies and the transition frequency are increasing functions of the external applied magnetic field. The ground state and the first excited state energies are decreasing functions, whereas transition frequency is an increasing function of the electron–phonon coupling strength. We find two ways of tuning the state energies and the transition frequency: by adjusting (1) the magnetic field and (2) the electron–phonon coupling strength.     

Coupling effects of resonant and discretized non-resonant continuum states in4He +6Li scattering at 10 MeV/A

Alpha- particle scattering from the resonant (3 ₁ ⁺ ) and non-resonant continuum states of⁶Li is studied at incident energy 10 MeV/A. Theα+d breakup continuum part within the excitation energyE _ex=1.475–2.475 MeV is discretized in two energy bins. Unlike the results at higher incident energies, here the coupled-channel calculations show significant breakup continuum coupling effects on the elastic and inelastic scattering. It is shown that even when the continuum-continuum coupling effects are strong, the experimental data of the ground state and the resonant as well as discretized non-resonant continuum states impose stringent constraint on the coupling strengths of the non-resonant continuum states.     

Spins and parities of hole states in25Na and25Mg

Angular distributions of differential cross sections and vector analyzing powers were measured forl=0, 1 and 2 transitions induced by the \(^{26} Mg\left( {\overrightarrow d ,\tau } \right)^{25} Na\) reaction at 52 MeV. The following spins and parities of final states in²⁵Na were deduced:J ^π =1/2⁺ (1.069 MeV), 3/2⁺ (2.202 MeV), 5/2⁺ (2.914 MeV), 1/2^? (3.995 MeV) and 3/2^? (5.190, 5.690, 6.549 and 7.603 MeV). The DWBA analysis of proton and neutron pick-up spectra obtained from a parallel measurement of the²⁶Mg(d, τ)²⁵Na and²⁶Mg(d, t)²⁵Mg reactions allows the identification ofT=3/2 analog states in²⁵Mg. Interpretation in terms of the Nilsson model of energies and spectroscopic factors of the first 1/2^? and 3/2^? hole states observed in proton pick-up reactions from even 1d _5/2- shell nuclei indicates a close correspondence of the final state deformations with those of the first excited 2⁺ states in the target nuclei.     

Identification of a 3.2μs isomer in76Rb

Fusion evaporation reactions were investigated to search for short lived isomeric states of nuclei near the proton drip line. Gamma spectra were measured, both singles and in delayed coincidence with evaporation residues implanted into a silicon detector after a velocity separation. A short lived activity was measured in the⁴⁰Ca+⁴⁰Ca →⁸⁰Zr^* reaction at excitation energies between 55 and 79 MeV. A half-life of 3.20 (10) μs was determined from delayed coincidences between evaporation residues and gamma rays. AtE ^*=55 MeV the cross section is 9 mb. The activity was assigned to an isomeric state in⁷⁶Rb by investigation of excitation functions. The isomer decays by emission of four gamma rays with energies of 70.55(5), 101.30(4), 145.11 (5), and 246.32(10) keV. A first level scheme is proposed assigning to the isomeric state an energy of 316.94(7) keV above the ground state. The isomer decaying into the low spin 1^(?) ground state band is explained from systematics as a band head of a high spin (4⁺) (πg_9/2,νg_9/2) structure. A high hindrance factor of 3×10⁶ forE1 radiation compared to a single particle transition is due possibly to a change of the core particle structure in the transition.     

The low-energy level structure and the electromagnetic properties of191Ir and193Ir

TheM 1 andE 2 reduced transition probabilities in¹⁹¹Ir and¹⁹⁹Ir have been calculated on the weak particle-core coupling model. The static moments of the ground state and the first three low-lying excited states have been computed. The theoretical values are in good agreement with the experimental results, in particular, the existing discrepancy between the theoretical and the experimental value for the magnetic moment of the first excited 5/2⁺ state, in both these nuclei, has been removed. The predicted sign of the quadrupole moment of the 2⁺ state in the neighbouring even-even nuclei is consistent with the results reported for Platinum nuclei. The level structure of both these nuclei has been calculated assuming the particle-core interaction to be dipole-dipole and quadrupole-quadrupole type.     

Shell model and octupole states in148Gd from in-beam experiments

Through (α, 4n) and (τ, 3n) reactions the high-spin states in the two-neutron nucleus¹⁴⁸Gd were populated up toI ^π=21? at 7.2 MeV, including numerous states above the yrast line. The¹⁴⁸Gd energy spectrum is interpreted in terms of the spherical shell model. Identification of the (νf _7/2 i _{1 3/2})_10? state gives the νi _13/2 single particle energy free of octupole admixtures as 2.1(1) MeV. Eight high-spin states between 1.2 and 3.7 MeV were identified as the couplings of the two valence-particles to the¹⁴⁶Gd octupole phonon, and three above-lying levels are assigned as double-octupole excitations including a 12⁺ state which decays by anE3-E3 stretched cascade. All these octupole levels can be quantitatively predicted from the one-particle x phonon spectrum of¹⁴⁷Gd. The high-spin states above 3 MeV are four-quasiparticle excitations ofπ ⁺¹ π ^?1 ν ² andπ ² ν ² type and their energies are in good accord with shell model estimates.     

Noncollective oblate states in 113Te

High-spin states of 113Te were studied by in-beam spectroscopy using the 88Sr (28Si, 3n) fusion-evaporation reaction at a beam energy of 120 MeV. 7-7, charged particle-7-7 coincidences, and 7-7 angular correlation analyses were employed for determining the level scheme of 113Te. The levels based on the 11/2 - state in 113Te were identified for the first time. The present result of the level scheme of 113Te was in accord with the systematics of those in the heavier isotopes, namely 115Te and 117Te. A particularly favoured 37/2+ state was observed and suggested to be the fully aligned noncollective oblate 7r[(g9/2)2]6+ <8)^[(^5/2) <8s> (h 11/2)2]25/2+ configuration.     

Mössbauer study of amorphous and crystalline tellurium

Comparison of the ¹²⁵Te Mössbauer spectra in amorphous and crystalline Te films indicates that in the amorphous phase the quadrupole splitting is slightly greater and the recoil-free fraction about one-third as great as in the crystalline phase. These changes are interpreted as indicating a decrease in the length of the covalent bond between the nearest neighbor Te atoms in the amorphous state, and furthermore that dangling bonds at the ends of the Te chains are responsible for a change in the density of phonon states in the system.