Gamow-Teller beta decay of 105Sn

The β-decay of ¹⁰⁵Sn was re-investigated at the ISOL facility of GSI Darmstadt by using a total absorption spectrometer. The experimental results include the half-life and β-delayed proton branching ratio of 32.7(5)s and 1.1(4) ^. 10^-4, respectively, and the contribution of electron capture to the ¹⁰⁵Sn decay of 0.420(35). The Gamow-Teller strength distribution peaking at 3.6MeV was measured, yielding a summed Gamow-Teller strength of 3.0(4). The latter data are discussed in comparison with shell-model predictions based on an empirical interaction.     

The new beta-delayed proton precursors103Sn and105Sn

Using⁵⁸Ni+⁵⁰Cr and⁵⁸Ni+⁵⁴Fe reactions and on-line mass separation, the new isotopes¹⁰³Sn and¹⁰⁵Sn with half-lives of 7±3 s and 31±6 s, respectively, were identified via their beta-delayed proton decays. The relative yields and the possibility of reaching¹⁰¹Sn are discussed.     

Shears band with a large dynamic moment of inertia in 197Bi

High-spin states in ¹⁹⁷Bi were studied with the AFRODITE γ-ray array at iThemba LABS using the ¹⁸¹Ta( ²²Ne, 6n) reaction at a beam energy of 125 MeV. A new shears band was found and linked to the low-lying states in ¹⁹⁷Bi. Its dynamic moment of inertia, , is considerably larger than the of the shears bands in the neighbouring Pb isotopes. This is probably a result of the involvement of an additional high-K h_9/2 proton orbital.     

Structural evolution of the intruder band in 118Sn

Excited states of the positive-parity intruder band in~(118) Sn have been studied via the ~(116)Cd(~7Li,lp4n) reaction at ~7Li energy of 48 MeV using techniques of in-beam γ-ray spectroscopy.This intruder band has been observed up to 7187 keV with spin (16~+). The structural evolution of this intruder band with increasing angular momentum has been discussed in terms of the aligned angular momentum and the ratio of the E-Gamma Over Spin (E-GOS) curve.     

Pseudo-spin band in the odd-odd nucleus 172Lu

High-spin states in the odd-odd nucleus ¹⁷²Lu have been populated in a ¹⁷⁰Er(⁷Li, 5n) reaction and the emitted -radiation was detected with the GASP array. Two sequences of a new identical band have been observed with the transition energies in the favoured and unfavoured sequences being identical within keV at low spins and keV at high spins over the whole observed spin range. Aninterpretation as a pseudo-spin singlet band of configuration is proposed. It represents the best example of a pseudo-spin singlet band in normal deformed nuclei known until now.Received: 19 February 2003, Revised: 27 March 2003, Published online: 12 August 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.70.+q      

Magic nucleus 132Sn and its one-neutron-hole neighbor 131Sn

Prompt and delayed gamma-ray cascades in doubly magic 132Sn and its neighbor 131Sn have been studied at Gammasphere using a 248Cm fission source. Isotopic assignments of unknown gamma rays were based on coincidences with known transitions in A = 112-116 Pd fission partners. The yrast level spectra of both tin nuclei are interpreted using empirical nucleon-nucleon interactions from the 132Sn and 208Pb regions. Results include identification of the (nuf(7/2)h(-1)(11/2))9(+) aligned state in 132Sn and of extensive (nuf(7/2)h(-2)(11/2)), (nuf(7/2)d(-1)(3/2)h(-1)(11/2)) and (nuh(-1)(11/2)x3(-)) multiplets in 131Sn. The previously reported beta(-) decay of an unusual 131In high-spin isomer to levels in 131Sn is also elucidated.     

Four quasi-particle band in the odd-odd158TM nucleus

The¹²⁵Te (³⁷CI,4n) reaction has been used to study the high spin states of¹⁵⁸Tm by means of in beam gamma ray spectroscopy using Compton suppressed germanium detectors of the “Château de Cristal” facility. Besides the Yrast band, the rotational character of which is clearly established up to the 23^? level only, a new rotational band developed up to spin 33⁺ is also observed. It is interpreted as a 4QP band.     

Identification of band structures in the 137La nucleus

High-spin states of ¹³⁷La have been investigated with the reaction ¹³⁰Te(¹¹B, 4n) at a beam energy of 50MeV. The level scheme of ¹³⁷La has been expanded with spin up to 33/2ℏ. Several new bands have been found in this nucleus. A band crossing in the band based on the 17/2^- level has been observed at a rotational frequency of ℏω ∼ 0.48MeV. From systematic comparison, this band crossing probably originates from the alignment of protons. One of the bands with strong M1 transitions is proposed as a collective oblate band ( γ ∼ -60^°).     

Collective structures and smooth band termination in109Sn

Six rotational bands up to energies E _x =24.7 MeV and spinsj ^π=(79/2^?) have been identified in¹⁰⁹Sn using the GAMMASPHEREγ-detector array. Four of the bands show smoothly decreasing dynamic moments of inertia at rotational frequencies?ω>0.6 MeV. The bands arise at medium spins from a coupling of a valence d_5/2, g_7/2 or h_11/2 neutron to the deformed 2p2h proton excitation of the Z=50 core¹⁰⁸Sn. At very high?ω these bands show the typical behaviour of smoothly terminating bands, i.e. a gradual alignment of the angular momenta of the valence particles and holes corresponding to a transition from high collectivity to noncollective states.     

Collective structures and smooth band termination in 109Sn

Six rotational bands up to energies E _x = 24.7 MeV and spins J^π=(79/2^?) have been identified in ¹⁰⁹Sn using the GAMMASPHERE γ-detector array. Four of the bands show smoothly decreasing dynamic moments of inertia at rotational frequencies ?ω > 0.6 MeV. The bands arise at medium spins from a coupling of a valence d_5/2, g_7/2 or h_11/2 neutron to the deformed 2p2h proton excitation of the Z=50 core ¹⁰⁸Sn. At very high ?ω these bands show the typical behaviour of smoothly terminating bands, i.e. a gradual alignment of the angular momenta of the valence particles and holes corresponding to a transition from high collectivity to noncollective states.     

Structural evolution of the intruder band in ~(118)Sn

Excited states of the positive-parity intruder band in ¹¹⁸Sn have been studied via the ¹¹⁶Cd(⁷Li, 1p4n) reaction at ⁷Li energy of 48 MeV using techniques of in-beam γ-ray spectroscopy. This intruder band has been observed up to 7187 keV with spin (16⁺). The structural evolution of this intruder band with increasing angular momentum has been discussed in terms of the aligned angular momentum and the ratio of the E-Gamma Over Spin (E-GOS) curve.     

Observation of band structures in the odd-odd nucleus126La

The odd-odd nucleus¹²⁶La has been studied in the reactions¹¹¹Cd(¹⁹F,4n) and⁹³Nb(³⁷Cl,p3n). Three band structures have been identified, two of them having both signature members and ΔI=1 character. These are proposed, respectively, to have πh_11/2 ? νh_11/2 and πh_11/2 ? νg_7/2 configurations and tentative 4⁺ and 3^? band heads.     

Ultraviolet band edge photorefractivity in LiNbO3:Sn crystals

The ultraviolet (UV) band edge photorefractivity of Sn-doped LiNbO(3) (LN:Sn) at 325 nm has been investigated. A sharp decrease of beam distortion, which is accompanied by a significant increase in the photoconductivity, is observed in LN:Sn crystals with Sn-doping concentrations at or above 2.0 mol%. The diffraction efficiency, the holographic recording sensitivity and response rate, and the two-wave coupling gain coefficient are greatly enhanced when the Sn-doping concentration reaches 2.0 mol% or more. Unlike LiNbO(3) doped with Hf in which the UV gratings can be erased easily by a red beam, the UV gratings in LN:Sn can withstand long-term red beam illumination. Electrons are determined to be the dominant light-induced charge carriers responsible for the UV band edge photorefraction. The observed enhancement on the UV band edge photorefractivity is found to be associated with the showup of an absorption band around 325 nm in LN:Sn crystals with Sn-doping concentrations at or above 2.0 mol%.     

Shears bands in the Pb region

The properties of the M1 bands in the Pb region are reviewed. They can be explained by ‘magnetic rotation’ which is a new concept in nuclear excitations. Spin and excitation energy along the bands are increased by the shears effect, a step-by-step alignment of large proton-particle and large neutron-hole spins into the direction of the total angular momentum. First evidence is presented for band termination connected with the closing of the shears.     

The doubly closed shell nucleus 13250Sn82

The structure of excited states in ¹³²Sn, fed in the β-decay of ¹³²In, has been investigated. Absolute intensities were deduced from γ-singles measurements. From multi-spectrum analysis of γ-lines the half-life of ¹³²In was determined to be 186 ± 22 ms. A level scheme based on γγ and βγ coincidences is presented. The conversion electron spectrum has been studied and internal conversion coefficients deduced for two low-energy transitions. The total decay energy of ¹³²In was determined, from γ-gated β-spectra, to be Q_β = 13.6 ± 0.4 MeV. A lower limit of 6.968 MeV for the neutron separation energy in ¹³²Sn was deduced from the β-delayed neutron spectrum. The experimental results on the level structure of the doubly closed shell nucleus ¹³²Sn show that the shell model is applicable even far from the valley of stability.     

Excited states in the doubly closed shell nucleus 50 132 Sn82

New excited states in the nucleus¹³²Sn have been identified fromγγ coincidence measurements. Strong beta feeding to a state at 7,210 keV was established. This level is interpreted as a 6^? state formed after aπg ₉ ^2/?1 →vg ₇ ^2/?1 GTβ ^? transition from the 7^? ground state of¹³²In. The deexcitation of the 7,210 keV state passes through a 4,351 keV state, providing support for a 3^? assignment of this level.     

Observation of a rotational band in the odd-Z transfermium nucleus 101251Md

A rotational band has been unambiguously observed in an odd-proton transfermium nucleus for the first time. An in-beam gamma-ray spectroscopic study of 101/251Md has been performed using the gamma-ray array JUROGAM combined with the gas-filled separator RITU and the focal plane device GREAT. The experimental results, compared to Hartree-Fock-Bogolyubov calculations, lead to the interpretation that the rotational band is built on the [521]1/2(-) Nilsson state.     

Shears bands in 112In

A new level scheme of 112In have been established up to 6.8 MeV in excitation energy and to a tentative spin of (21+) through the reaction 110Pd(7Li,5n)112In at a beam energy of 50 MeV. In-beam measurements involving γ-γ coincidences and directional correlation of oriented states were performed. M1 bands consisting of/△I = 1 dipole transitions have been observed. Possible quasiparticle configurations suggest that these bands are similar to the shears bands observed in Pb nuclei.     

E2 transition probabilities in the decoupled band of the 129La nucleus

Lifetimes of the yrast levels with spins I ^π = 23/2^? to 39/2^? in ¹²⁹La produced via the ¹²⁰Sn(¹⁴N, 5n) reaction at a beam energy of 77MeV have been measured by the Doppler shift attenuation method. The properties of the studied levels belonging to the πh_11/2 band were compared with the theoretical predictions obtained in the framework of the core quasi-particle coupling model. It is suggested that the rigid-rotor model used to describe the cores is too simplified as the even-even nuclei from the A ～ 130 region are susceptible to shape deformation. Reasonable agreement was obtained with the phenomenological cores based on the experimental data of ¹²⁸Ba.