Ground state correlation effects on the Gamow-Teller strength distribution in 48Ca

We calculate the Gamow-Teller strength distribution in ⁴⁸Ca using an extended second RPA which explicitly includes ground state correlations. The following effects are taken into account: (i) the reduction of the 1p1h matrix elements due to the partial occupation of single-particle orbitals, (ii) the modification of the 1p1h Green function in the presence of ground state correlations and 2p2h correlations in the excited states, (iii) renormalization of the external field and (iv) the pure 2p2h response due to unblocking of the ground state. The first three effects largely cancel in the region of the Gamow-Teller resonance while the last two cancel at higher energies. The resulting strength distribution is therefore quite similar to the one obtained previously in second RPA.     

Level schemes of100Y and100Zr from the beta-decay of mass separated100Sr

The beta-decay of¹⁰⁰Sr and the low-spin isomer in the daughter nucleus¹⁰⁰Y were investigated from sources of¹⁰⁰Sr produced from thermal neutron fission in a high-temperature ion source of the online-separator facility OSTIS installed at the Institut Laue-Langevin (ILL), Grenoble. Gamma-single, gamma-multispectra and gamma-gamma-coincidence measurements were performed resulting in the first level scheme of¹⁰⁰Y as well as a considerably extended scheme of¹⁰⁰Zr. The schemes are placed in level systematics and implications for the appearance of shape coexistence atN=60 are discussed.     

Gamow-Teller strength near the pion threshold

The Gamow-Teller strength at high energy, in the vicinity of the pion mass, is linked to the absorption of p wave pions. It is not subject to Pauli blocking and increases linearly with the nucleon number.     

Missing Gamow-Teller strength in mass 42

The reaction ⁴²Ca(p,n)⁴²Sc at E_p = 160 MeV is used to measure the Gamow-Teller (GT) strength function. Normalization of the dominant peak in the (p,n) spectrum to B(GT) determined from the analogous transition in the beta decay of ⁴²Ti renders the strength function absolute, and the total measured stregth is about half of the minimum value required for a T = 1 nucleus. Shell model calculations are presented which reproduce the shape of the strength function, but overpredict the absolute measured strength by about a factor of two. Evidently the missing strength has been moved out of the region of nucleon particle-hole excitations, and quenching, due possibly to Δ₃₃ coupling, is indicated. Symmetry implications of an observed strong suppression of the T_> component of the GT strength are discussed.     

The Gamow-Teller beta decay of100Cd

Neutron-deficient isotopes of cadmium were produced in thep(600 MeV)+^natSn spallation reaction. The ISOLDE facility provided mass-separated beams of these isotopes. The production yield was 10³ to 10⁴ atoms/s for¹⁰⁰Cd and roughly two orders of magnitude less for⁹⁸Cd. The properties of the¹⁰⁰Cd→¹⁰⁰Ag decay were studied in detail by X-ray,γ-ray and conversion electron spectroscopy. Forty nineγ-transitions were assigned to this decay, and all but five of them were placed in the decay scheme. The half-life was determined to be 49.1±0.5 s. TheQ _EC value of 3890±70 keV was deduced from a comparison of experimental and theoreticalβ ⁺/(EC+β ⁺ probability ratios. Seven 0⁺→1⁺ Gamow-Teller transitions with log ft values between 3.5 and 4.9 were identified. The total (summed) strength is about five times smaller than predicted by the shell model for the transformation of ag _9/2 proton into ag _7/2 neutron. The quenching of the Gamow-Teller strength and other questions of nuclear structure are discussed for the¹⁰⁰Cd decay. The properties of⁹⁸Cd are inferred by extrapolation of^104,102,100Cd data, and some preliminary experimental results on⁹⁸Cd decay are presented.     

Gamow-Teller strength in the β+ decay of104In

Theβ-strength function of¹⁰⁴Cd is studied in theβ ⁺/EC decay of mass-separated¹⁰⁴In. The determination of theβ ⁺ feeding and theβ ⁺/β ⁺EC ratio is the result of the simultaneous measurement of beta and gamma rays in one semiconductor beta-spectrometer. Information on the strength function near theQ _EC value is obtained from the detection of high-energyγ rays. The total observedβ strength amounts up to 10% of the Extreme Single-Particle Shell Model value. A strong enhancement in theβ ⁺/EC feeding to a group of levels around 5.6 MeV shows the influence of the Gamow-Teller Resonance.     

Origin of quenching of Gamow-Teller strength in54Fe

The recent charge exchange (n,p) and (p,n) reaction data on⁵⁴Fe is used to determine the importance of Δ-isobar excitations and RPA-type correlations in the quenching of GT strength.     

On the Fermi and Gamow-Teller strength distributions in medium-heavy mass nuclei

An isospin-self-consistent approach based on the continuum-random-phase approximation (CRPA) is applied to describe the Fermi and Gamow-Teller strength distributions within a wide excitation-energy interval. To take into account nucleon pairing in open-shell nuclei, we formulate an isospin-self-consistent version of the proton-neutron-quasiparticle-CRPA (pn-QCRPA) approach by incorporating the BCS model into the CRPA method. The isospin and configurational splittings of the Gamow-Teller giant resonance are analyzed in single-open-shell nuclei. The calculation results obtained for the ²⁰⁸Bi, ⁹⁰Nb, and Sb isotopes are compared with the available experimental data.     

Measurement of the beta beta-decay rate of 100Mo to the first excited 0(+) State of 100Ru

The double-beta beta beta(2 nu)-decay rate of 100Mo to the first excited 0(+) state of 100Ru has been measured by a gamma-gamma coincidence technique that uses two HPGe detectors to observe the two gamma rays ( E(gamma 1) = 590.76 keV; E(gamma 2) = 539.53 keV) from the 100Ru nucleus as it deexcites to the ground state via the 0(+)-->2(+)-->0(+) sequence. Unlike all previous beta beta-decay experiments, this technique provides data which have a large signal-to-background ratio. After a 440-day measurement of a 1.05-kg isotopically enriched (98.4%) disk of 100Mo, 22 detected coincidence events (with an estimated background of 2.5 events) yield a half-life of [5.9(+1.7)(-1.1)(stat)+/-0.6(syst)] x 10(20) years.     

The spin of Ac from beta-decay experiments

The spin of the odd nucleus has been determined to be I = 3 from the beta circularly-polarized gamma correlation studies on two prominent beta-gamma cascades: (i) the 1.19 MeV beta group (966 and 908) keV gamma rays and (ii) the 1.76 MeV beta group- 3.38 keV gamma ray. The matrix element ratio X for the 1.76 MeV beta transition has been determined to be X = 0.40±0.10.     

High-resolution photoemission from Ag(100), Ag(110), and Ag(111)

Energy distribution curves of photoelectrons emitted normal to (100), (110), and (111) faces of silver have been obtained at photon energies of 21.22, 16.85, and 11.83 eV. The results are compared with Christensen's relativistic band structure calculation of bulk silver yielding a close correspondence between experiment and theory. A surface state in the L gap immediately below the Fermi level is identified.     

Gamow-Teller and dipole strength in the 208Pb(n,p) reaction

Earlier data on the ²⁰⁸Pb(n,p)²⁰⁸Ti reaction at 198 MeV has been analysed using the multipole decomposition technique, and the contributions to the spectra from L = 0 and 1 transitions determined. The L = 0 cross section has been found to be smaller than values given by the calculations of MacFarlane [3] for Gamow-Teller transitions, using three different forms for the population of single particle states about the Fermi energy. Comparison is made with GT-strength values obtained from a more recent mean field calculation of these populations, and with an older nuclear structure calculation of properties of the lead nuclei. The L = 1 strength distribution is also reported.     

Beta decay of 103In: Evidence for the Gamow-Teller resonance near 100Sn

The β decay of the neutron-deficient isotope ¹⁰³In was investigated by using total absorption γ-ray spectrometry on mass-separated sources. The measurement reveals a high-lying resonance of the β-decay strength in striking disagreement with high-resolution γ-ray data. The result is discussed in comparison with shell-model predictions.     

The study of Gamow-Teller transition strength for some Fe and Ni isotopes

The method developed by Pyatov and Salamov has been used to study the Gamow-Teller transition strength in the iron mass region nuclei. Calculations have been performed within the framework of the proton-neutron quasiparticle random-phase approximation with separable Gamow-Teller residual interactions. The obtained results have been compared with other theoretical results and the corresponding experimental data.     

Q EC value and Gamow-Teller strength of the102CdEC/gb+ decay

Within the framework of a systematic study of 0⁺→1⁺ Β-transitions in the¹⁰⁰Sn region, the decay of the neutrondeficient isotope¹⁰²Cd was investigated. This isotope was produced in¹⁶O+⁹²Mo and⁵⁸Ni+⁵⁰Cr heavy-ion reactions and in proton-induced spallation of^natSn, and mass-separated samples were prepared by means of the GSI and the ISOLDE on-line mass separators, respectively. Observations of X-rays,γ-rays, and conversion-electrons studies have led to an improved¹⁰²Cd→¹⁰²Ag decay scheme which includes six 0⁺→1⁺ Gamow-Teller transitions. The half-life of¹⁰²Cd was redetermined with higher accuracy to be 345±8 s. Using a Si(Li)-BGO-Ge spectrometer, theΒ ⁺ endpoint energy of the main decay component was measured, yielding aQ _EC value of 2587±8 keV. This very small uncertainty ofQ _EC, combined with the improved knowledge of half-life and decay scheme, allows an accurate determination of the observed Gamow-Teller decay strengthB _Σ (GT)=1.513±0.055 for¹⁰²Cd. This result is discussed in comparison with predictions from model calculations.     

Breaking of the SU(4) limit for the Gamow-Teller strength in N ∼ Z nuclei

We have performed large-scale shell model calculations of the Gamow-Teller strength distributions in N ∼ Z pf -shell nuclei. These calculations were motivated by the experimental attempts to measure the low-lying GT strength for the even-even N = Z + 2 or N = Z - 2 nuclei ⁴⁶Ti , ⁵⁰Cr , ⁵⁴Fe and ⁶²Ge , where a sizable low-energy GT strength could be interpreted as reminiscence of SU(4) symmetry; in the limit of exact SU(4) symmetry the GT_- strength would be concentrated in a single transition to the lowest T = 0, J = 1⁺ state in the daughter. We confirm that the SU(4) symmetry is strongly broken by the spin-orbit interaction and by increasing neutron excess.