Super-allowed α decay above doubly-magic <Superscript>100</Superscript>Sn and properties of <Superscript>104</Superscript>Te = <Superscript>100</Superscript>Sn ⊗ α

α-decay half-lives for ^{104, 105, 106}Te and ^{108, 109, 110}Xe close above the doubly-magic ¹⁰⁰Sn are calculated from systematic double-folding potentials. The derived α preformation factors are compared to results for ^{212, 213, 214}Po and ^{216, 217, 218}Rn above the doubly-magic ²⁰⁸Pb. α-decay energies of Q _α = 5.42±0.07MeV and 4.65±0.15MeV are predicted for ¹⁰⁴Te and ¹⁰⁸Xe; the corresponding half-lives are T _1/2 ≈ 5ns for ¹⁰⁴Te and of the order of 60μs for ¹⁰⁸Xe. Additionally, the properties of rotational bands in ¹⁰⁴Te are analyzed, and the first excited 2⁺ state in ¹⁰⁴Te is predicted at E _x = 650±40keV; it decays preferentially by γ emission with a reduced transition strength of 10 Weisskopf units to the ground state of ¹⁰⁴Te and with a minor branch by α emission to the ground state of ¹⁰⁰Sn.     

Mössbauer study of the formation of impurity-vacancy complexes in copper

The formation of impurity-vacancy complexes has been studied with ion-implanted radioactive¹¹⁹Xe and its decay products, which populate the¹¹⁹Sn Mössbauer state via the decay chain¹¹⁹Xe→¹¹⁹I→¹¹⁹Te→¹¹⁹Sb→¹¹⁹Sn. The results of these implantations arecompared to those from earlier¹¹⁹In or Sbimplantations.     

Identification of the 109Xe and 105Te α-decay chain

The α-decay chain ¹⁰⁹Xe → ¹⁰⁵Te → ¹⁰¹Sn was identified at the Holifield Radioactive Ion Beam Facility. Advances in digital electronics have made possible the identification of both alpha emitters in the same experiment despite the disparate half-lives of 13 ±2 ms and 620 ±70 ns for ¹⁰⁹Xe and ¹⁰⁵Te, respectively. Two α-decay transitions were observed from ¹⁰⁹Xe with Q_α values of 4067 ±10 and 4217 ±8 keV. One transition between the ground states of ¹⁰⁵Te and ¹⁰¹Sn was observed with a Q_α value of 4889 ±6 keV. Using the measured half-lives, branching ratios, and Q_α values the reduced α-decay widths, δ², were determined. Comparison of the δ² value for ¹⁰⁵Te with ²¹³Po indicates a “superallowed" character in the α emission of ¹⁰⁵Te.     

Decay properties of the new proton-rich nucleus104Sn: Mass determinations beyond the proton drip line

The new proton-rich nucleus¹⁰⁴Sn was produced in a⁵⁰Cr(⁵⁸Ni, 2p2n)¹⁰⁴Sn reaction. Its half-life was measured to be 21±1s. From a newly established partial decay scheme, aQ _EC value of 4,000 _?300 ⁺⁶⁵⁰ keV was estimated. The resulting mass excess value for¹⁰⁴Sn, combined with decay energies for α and proton emission, leads to mass excess values for the nuclei¹⁰⁸Te,¹⁰⁹I,¹¹²Xe, and¹¹³Cs. These mass values are compared to predictions of mass formulae.     

Searching critical-point nuclei in Te- and Xe-isotopic chains using sextic oscillator potential

We have identified the nuclei in the Te- and Xe-isotopic chains lying close to the critical point, through which the shape phase transition occurs, by using the sextic oscillator potential formalism. It has been found that ¹¹⁰Te, ¹²⁴Te, and ¹²⁴Xe isotopes are the most promising candidates for the critical-point nuclei slightly above the Z = 50 proton shell closure.     

New in-beam data on125Xe and reinterpretation of negative-parity levels in odd-A neutron deficient Xe isotopes

In-beam data have been obtained on¹²⁵Xe produced in the¹²⁴Te(α, 3n) reaction and have led to new experimental results on theh _11/2 band structure in contradiction with earlier works. From these results, the negative-parity levels known in the odd-A ^123–133Xe isotopes are reinterpreted in the frame of the triaxial rotor model.     

Nuclear-structure aspects of the neutrinoless ββ -decays

In this article, we analyze some nuclear-structure aspects of the 0ν double-beta decay nuclear matrix elements (NME). We give results for the decays of ⁴⁸Ca , ⁷⁶Ge , ⁸²Se , ¹²⁴Sn , ¹²⁸Te , ¹³⁰Te , and ¹³⁶Xe , using improved effective interactions and valence spaces. We examine the dependence of the NMEs on the effective interaction and the valence space, and analyze the effects of the short-range correlations and the finite size of the nucleon. Finally, we study the influence of the deformation on the values of the NMEs.     

Infra red photodetachment threshold measurements: Li− and P−

Using gaseous sources of I₂ and HI containing the radioactive isotopes¹²⁴I and¹²⁶I effective cross sections for nuclear resonance scattering from the first 2⁺ states of¹²⁴Te and¹²⁶Te were measured. Information is obtained about the charging of the nonradioactive molecular partner afterEC decay, the interaction of highly charged ions with neutral molecules, and the slowing down of atoms in a Xe buffer gas. Indications of an iodine complex being stable in the gaseous phase are found.     

Nuclear resonance fluorescence in124Te and126Te: Vacancy cascades in molecules

Using gaseous sources of I₂ and HI containing the radioactive isotopes¹²⁴I and¹²⁶I effective cross sections for nuclear resonance scattering from the first 2⁺ states of¹²⁴Te and¹²⁶Te were measured. Information is obtained about the charging of the nonradioactive molecular partner afterEC decay, the interaction of highly charged ions with neutral molecules, and the slowing down of atoms in a Xe buffer gas. Indications of an iodine complex being stable in the gaseous phase are found.     

Properties of N=84, even-even nuclei populated in the spontaneous fission of 248Cm

Excited states in the neutron-rich, N=84 nuclei ¹³⁴Sn, ¹³⁶Te and ¹³⁸Xe, populated in the spontaneous fission of ²⁴⁸Cm, were studied to medium spins using the EUROGAM2 array. OXBASH code calculations support the experimental identification of maximum aligned configurations in these isotopes. Empirical shell model calculations agree with the proposed excitation energy of the neutron h_9/2 excitation in the ¹³²Sn region. A discrepancy between the observed and calculated excitation energy of the I^π= 12⁺ level in ¹³⁶Te indicates possible admixtures of collective excitations in this nucleus. Clear signs of collective excitations are observed in ¹³⁸Xe. Received: 10 November 1999 / Revised version: 22 December 1999     

Isospin splitting of nucleon effective mass and symmetry energy in isotopic nuclear reactions

Within an isospin and momentum dependent transport model, the dynamics of isospin particles(nucleons and light clusters) in Fermi-energy heavy-ion collisions are investigated for constraining the isospin splitting of nucleon effective mass and the symmetry energy at subsaturation densities. The impacts of the isoscalar and isovector parts of the momentum dependent interaction on the emissions of isospin particles are explored, i.e., the mass splittings of m_n~*=m_p~* and m_n~* m_p~*(m_n~* m_p~*). The single and double neutron to proton ratios of free nucleons and light particles are thoroughly investigated in the isotopic nuclear reactions of ~(112)Sn+~(112)Sn and ~(124)Sn+~(124)Sn at incident energies of 50 and 120 MeV/nucleon, respectively. It is found that both the effective mass splitting and symmetry energy impact the kinetic energy spectra of the single ratios, in particular at the high energy tail(larger than 20 Me V). The isospin splitting of nucleon effective mass slightly impacts the double ratio spectra at the energy of 50 MeV/nucleon. A soft symmetry energy with stiffness coefficient of γ_s =0.5 is constrained from the experimental data with the Fermi-energy heavy-ion collisions.     

Measurements of 110Xe and 106Te decay half-lives

The -decays of ¹¹⁰Xe and ¹⁰⁶Te were studied at the GSI on-line mass separator. By using the grow-in and decay of the activity, observed in pulsed-beam measurement, the half-life of ¹¹⁰Xe was found to be T_1/2 = 105⁺³⁵_-25ms. The lifetime of ¹⁰⁶Te was determined to be T_1/2 = 70⁺²⁰_-10s by measuring the time between two successive ¹¹⁰Xe ^{106} Te ^{102} Sn -decays. The newly determined half-lives were used to calculate reduced -decay widths for ¹⁰⁶Te and ¹¹⁰Xe. Universal systematics of reduced widths are proposed to search for the evidence of enhancement of the formation amplitude in the emitters above ¹⁰⁰Sn.     

Structure of 136Te and the problem of mass of 134Te

Neutron-rich, N=84 nuclei from the ₁₃₂Sn region, populated in spontaneous fission of ₂₄₈Cm, have been studied with EUROGAM 2. Excited states and their spins and parities in the ₁₃₆Te nucleus were established up to 17ħ. OXBASH code calculations support the experimental identification of maximum aligned configurations in ₁₃₆Te. Empirical shell model calculations for the I_π= 14₊ level in ₁₃₆Te indicate that the adopted mass of the ₁₃₄Te nucleus should be lowered by 200(80) keV. Received: 3 August 1998     

Experimental beta-decay energies of several neutron-rich nuclides with mass number 131≦A≦146

With sources obtained from the on-line mass separator LOHENGRIN the beta-decay energies of¹³¹Sn,¹³⁴Sb,^135,136Te,^143,146Ba and¹⁴⁶La have been determined from measuredβ-endpoint energies. The experimental values are compared with the predictions of several mass formulae.     

Isospin effect in peripheral heavy-ion collisions at Fermi energies

The isospin effect in peripheral heavy-ion collisions was thoroughly investigated within the framework of the Lanzhou quantum molecular dynamics (LQMD) transport model. A coalescence approach was used to recognize the primary fragments formed in nucleus-nucleus collisions. The secondary decay process of these fragments was described using the statistical code GEMINI. The production mechanism and isospin effect of the projectile-like and target-like fragments were analyzed using the combined approach. It was found that the isospin migration from the high-isospin density to the low-density matter occurred in the neutron-rich nuclear reactions, i.e., ⁴⁸Ca+²⁰⁸Pb, ⁸⁶Kr+⁴⁸Ca/²⁰⁸Pb/¹²⁴Sn, ¹³⁶Xe+²⁰⁸Pb, ¹²⁴Sn+¹²⁴Sn, and ¹³⁶Xe+¹³⁶Xe. A hard symmetry energy was available for creating the neutron-rich fragments, particularly in the medium-mass region. The isospin effect of the neutron-to-proton (n/p) ratio of the complex fragments was reduced when the secondary decay process was included. However, a soft symmetry energy enhanced the n/p ratio of the light particles, particularly at kinetic energies greater than 15 MeV/nucleon.     

Precision atomic mass spectrometry with applications to fundamental constants, neutrino physics, and physical chemistry

We present a summary of precision atomic mass measurements of stable isotopes carried out at Florida State University. These include the alkalis ⁶Li, ²³Na, ^39,41K, ^85,87Rb, ¹³³Cs; the rare gas isotopes ^84,86Kr and ^{129,130,132,136}Xe; ^17,18O, ¹⁹F, ²⁸Si, ³¹P, ³²S; and various isotope pairs of importance to neutrino physics, namely ^74,76Se/^74,76Ge, ¹³⁰Xe/¹³⁰Te, and ¹¹⁵In/¹¹⁵Sn. We also summarize our Penning trap measurements of the dipole moments of PH^?+? and HCO^?+?.     

Life-times of the 4 1 + -states in134Te and136Xe

The half-lives of the first excited 4⁺-levels in theN=82 isotones ₅₂ ¹³⁴ Te and ₅₄ ¹³⁶ Xe have been determined tot _1/2=(1.50±0.13) ns andt _1/2=(1.32±0.10) ns, respectively, through the measurement of delayedγ,γ-coincidences. The value for¹³⁴Te is in agreement with the assumption that the low lying levels of this nucleus are based mainly on theg ₇ ^{2 /2} proton configuration. In¹³⁶Xe the half-life is unexpectedly small which indicates a more strongly admixed structure of the levels involved in this case.     

Evidence for particle-core coupling in the Te nucleus

The high-spin states of ¹²⁵Te have been investigated using the ¹²⁴Sn (α, 3nγ) reaction and the in-beam technique. Besides low-spin levels observed in the radioactive decay, the high-spin positive- and negative-parity bands have been established. As a possible explanation of the nature of the excited states in ¹²⁵Te the idea of the odd-neutron(hole)-core coupling is discussed.     

Formation of close-to-target products in reactions induced by <Superscript>12</Superscript>C ions on tin isotopes at the energy of 2.2 GeV per nucleon

Cross sections for charge-exchange reactions induced by the interaction between ¹²C ions of energy E_{¹² C} = 2.2E_{^{12} C} = 2.2 GeV per nucleon and tin targets enriched in the isotopes ^118,120,124Sn were measured by the induced-activity method. The cross sections for products whose charge numbers were in excess of the target charge number (Sb and Te) were determined. The shape of the isotope distribution of Sb products was indicative of the evaporative character of neutron emission in the formation of final-state products. The dependence of cross sections for charge-exchange reactions on the nucleonic composition of the target was considered. The contribution of electromagnetic excitation to the cross section for the reaction ¹²⁴Sn(¹²C, x)¹²⁴Sn was estimated.     

E2 transition andQ_{J^ + } systematics of even mass tellurium nucleisystematics of even mass tellurium nuclei

The yrast spectra withJ _max ^π = 6⁺,B(E2) transition probabilities and $Q_{J^ + } $ values are calculated for even-even tellurium isotopes by carrying out Hartree-Fock-Bogoliubov (HFB) anstaz employing a pairing-plus-quadrupole-quadrupole effective interaction operating in a reasonably large valence space outside the¹⁰⁰Sn core. Our calculations reproduce qualitatively the observed parabolic systematics of the low-lying yrast states as a function of mass number for tellurium isotopes. The results onB(E2) transition probabilities predict a dip in the isotopes^114,118,124Te which might be construed to imply different structures for^114,118,124Te as compared to their neighbours. Besides this, our results also reveal that both the HFB technique as well as the quadrupole-quadrupole-plus-pairing model of the two body interaction are fairly reliable in this mass region.