keV State Research Articles

Comment on "Double-octupole excitations in the N=84 nuclei 144Nd and 146Sm"

Results of proton and electron inelastic scattering suggest that the interpretation of the ${5}_{1}^{\mathrm{\ensuremath{-}}}$-${7}_{1}^{\mathrm{\ensuremath{-}}}$-${9}_{1}^{\mathrm{\ensuremath{-}}}$ sequence in $^{144}\mathrm{Nd}$ as simple quadrupole-octupole-coupled states neglects large \ensuremath{\nu}(${\mathit{f}}_{7/2}$${\mathit{i}}_{13/2}$${)}_{5,7,9}$ components and, therefore, that the interpretation of the ${12}^{+}$ state at 4354 keV as a double-octupole-phonon state (${6}_{1}^{+}$\ensuremath{\bigotimes}octupole\ensuremath{\bigotimes}octupole) given by Bargioni et al. [Phys. Rev. C 51, R1057 (1995)] may be too simple. It is suggested that measurements of the ${9}_{1}^{\mathrm{\ensuremath{-}}}$ state via single-neutron-stripping reactions and intermediate energy proton scattering can help determine the underlying structure of the 4354 keV state. \textcopyright{} 1996 The American Physical Society.

Yrast states in the doubly-odd nucleus100Tc

High spin states up toJ=14 and excitation energy up toE *=3076 keV have been observed in the odd-odd nucleus100Tc with the reaction96Zr(7Li, 3n), at bombarding energies between 21 and 31 MeV, by in-beam γ spectroscopy and conversion-electron measurements. A ΔJ=1 negative parity band similar to that observed in theN=57 isotone102Rh, and based on the 8−, 708 keV state has been identified. The observed band can be interpreted in terms of collective core excitations based on a two-quasiparticle state of(πg9/2 ⊗ νh11/2) configuration. Comparison with IBFM-2 calculations have been performed.

Lifetime of the two-phonon vibrational state in232Th

We report on a measurement of the lifetime of the 1414 keV state in232Th by the Doppler-shift recoil-distance method. This 4+ state shows all characteristics of a nearly-harmonic two-phononγ-vibrational excitation. The result for the B(E2) value obtained from the lifetime,τ=3.2 ± 0.7 ps, is in agreement with an earlier estimate of the collectivity from Coulomb-excitation yields and supports the interpretation of the 1414 keV state as a two-phononγ-vibrational excitation.

Multiparticle-hole states of high spin in N < 50, A ≈ 90 nuclei: 2. Nanosecond isomeric states in 87,89Nb, 89Mo and 91Tc

Abstract The lifetimes of the 21 2 + and 17 2 − yrast states in 89Nb, 89Mo and 91Tc and of the 334 keV 5 2 − state in 87Nb were determined via the electronic timing method. The nuclei were populated by means of the VICKSI pulsed 36Ar beam impinging on a 58Ni target. The lifetimes measured for the first time are: 89Mo: 2271 keV 17 2 − τ = 1.6(4) ns ; 2584 keV 21 2 + τ = 13.7(3) ns ; 87Nb: 334 keV 5 2 − τ = 41(3) ns . The resulting B(E2) values of stretched E2-decay γ-rays largely confirm predictions of multiparticle shell model calculations carried out within the ( g 9 2 ,p 1 2 ) single-particle space and with the Gross-Frenkel residual interaction. The long lifetime of the 334 keV state in 87Nb arises from an f 5 2 excitation.

Beta-decay of 20Mg

The β-decay of 20Mg was investigated. A secondary beam of 20Mg ions, produced in reactions between a 95 A·MeV24Mg-beam and a natNi-target, was isotopically separated by means of the LISE3 spectrometer at GANIL. This secondary beam was implanted into a silicon detector array surrounded by germanium γ-detectors. The β-delayed proton and γ-ray data, measured for this short-lived nucleus (T12 = 95 ± 3 ms), were incorporated into an improved 20Mg→20Na decay scheme. The 2645 keV level in 20Na is of importance for the breakout from the astrophysical hot CNO-cycle and the onset of the rapid proton capture process via the reaction 19Ne(p,γ)20Na. An upper limit of 0.1% for the β-decay feeding of the 2645 keV level and a lower limit for the corresponding log ft value of 6.24 were determined. The implications of this result for the spin and parity assignment of the 2645 keV state are discussed. By comparing the 20Mg β-decay into the proton-unbound 3001 keV state in 20Na and the isospin-mirrored decay into the particle-bound 3488 keV level in 20F, an asymmetry ft+ft− − 1 = 1.69−0.65+0.86 was observed. The comparison of the experimentally determined B(GT) values for the Gamow-Teller β-decay of 20Mg with a calculation performed in a full sd-shell model space yields an overall quenching of the Gamow-Teller strength of 0.84, corresponding to an observed fraction of 71% of the calculated strength. The measured Gamow-Teller strength above excitation energies of 3 MeV is more fragmented than predicted by the shell-model calculation.

Retardation of single-particle E1 transitions from the 622 keV broad d-wave neutron resonance in 9Be

Capture gamma rays from the 622 keV d-wave neutron resonance in 9Be with large reduced neutron width have been observed by means of a time-of-flight method, employing an anti-Compton NaI(TI) detector. Partial radiative widths have been derived for the strong primary E1 transition to the 3368 keV (2 +) state in 10Be and also for the weak one to the 5958 keV (2 +) state. Those widths were compared with predictions of the Lane-Mughabghab valence-capture model. As a consequence we found certain evidence to show that the 3368 keV state transition is appreciably hindered. The discrepancy can be removed by using a renormalized neutron effective charge which takes into account the coupling between the d-state neutron single-particle motion and the E1 giant resonance excitation of the target nucleus.

A Study on Hyperfine Magnetic Field at117In (←117Cd) in Fe3O4by γ-γ Time-Differential Perturbed Angular Correlation

Hyperfine magnetic fields, H hf , at 117 In arising from 117 Cd were measured in Fe 3 O 4 by time-differential perturbed angular correlation (TDPAC) of 90–345 keV γ-rays through the intermediate 660 keV state (3/2+). The values of H hf were found to be 123 and 138 kOe at 295 and 77 K, respectively. The present work is the frrst one which measured H hf at 117 In in magnetically ordered materials, and demonstrates the applicability of TDPAC of this nuclide in the field of magnetism.

TDPAD measurements with highly oriented pyrolytic graphite using the19F(p, p′)19F* and19F(α, n)22Na* reactions

The TDPAD technique has been used to investigate quadrupole interactions of19F*(E x =197 keV,J π=5/2+,T 1/2=88.5 ns) and22Na*(E x =583 keV,J π=1+,T 1/2=243 ns) in highly oriented pyrolytic graphite (HOPG). For19F* a single static quadrupole interaction was found with field gradientV ZZ =3.24(19) × 1018 V/cm2. For the case of22Na* no quadrupole interaction was detected, leading to the conclusion that |QV ZZ |<5.2(5) × 1015 b V/cm2. TakingQ=0.06 b for the 583 keV state on the basis ofB(E2) measurements and theoretical estimates, we find that |V ZZ | <8.7(8) × 1016 V/cm2. The data demonstrate the advantages of using HOPG as a host material for the study of quadrupole interactions.

A comparison of angular distributions for charge exchange reactions to analogue states in 20Na and 20F

Differential cross sections are presented for the analogue charge exchange reactions 20Ne(3He,t)20Na and 20Ne(t,3He)20F at an incident energy of 33.4 MeV. The angular distributions are very similar for states of the same spin-parity assignment. On this basis, the analogue of the 2646 keV state in 20Na is identified with the 2966 keV state (3+) in 20F.

Core vibration of99Tc

The gyromagnetic ratios and the half-lifes of the 141 keV and 181 keV states of99Tc have been remeasured. The results,g(141 keV)=+1.280(44);g(181 keV)=+1.446(20) andT1/2(141 keV)=0.205(4)ns;T1/2(181 keV)=3.44(3) ns are in only fair agreement with prior published data but more precise. They confirm that both states are members of the ground state core vibration multiplet. The hyperfine field of TcFe has been determined asBhf10K (TcFe)=30.42 (30)T;Bhf290K (TcFe)=29.47 (29)T

73Ge: a new high resolution PAC probe

Long lens electron spectrometers were used to make electron-gamma and electron-electron PAC measurements for the 5/2+ 13.3 keV state of73Ge. Sources of73As were produced in the decay of73Se implanted at the CERN/ISOLDE facility. The magnetic interaction in nickel was determined as ωL=74.2(7) Mrad s−1 and the quadrupolar frequency in antimony asv Q =19.7(2) MHz. The nuclear moments derived are μ=−1.08(3) μN and |Q|=0.70(8) b.

Gamow-Teller strength in A=37 nuclei.

A comparison is made of the recent ${\mathrm{\ensuremath{\beta}}}^{+}$-decay measurements of Garc\'{\i}a et al. and the 1981 $^{37}\mathrm{Cl}$(p,n${)}^{37}$Ar measurements of Rapaport et al. in order to see whether the experiments are consistent. Garc\'{\i}a et al. were not able to determine the amount of Gamow-Teller strength in the isobaric analog state (IAS) or the Coulomb mixing of Fermi strength to a state near the IAS, and were forced to determine the amount of Gamow-Teller strength in the daughter 1371 keV state by making the branching ratios sum to unity. This approach leaves a range of possible values open for these quantities which we investigate. We find that the experiments could be consistent within a theoretically unlikely part of this range. We also examine the effect of this range of allowed values on solar and supernova neutrino cross sections of $^{37}\mathrm{Cl}$ and find weak dependence on the uncertainties described here. We discuss how the consistency of the two experiments can be tested more conclusively.

Level scheme and mixed-symmetry states of 134Ba from in-beam (n, n′γ) measurements

The decay properties of the existed states of 134Ba below 3 MeV have been studied with the (n, n′γ) reaction. From γ-ray excitation function and angular distribution measurements, several new levels, spin-parity values and multipole mixing ratios were obtained. Lifetimes were measured by the Doppler-shift attenuation method, and reduced transition probabilities were calculated for a number of levels using the proton-neutron interacting boson model. The 2029 and 2088 keV states appear to share the properties of the lowest mixed-symmetry 2 + state.

Beta -delayed proton decay of 20Mg and its astrophysical implications.

We have studied the {beta}-delayed proton decay of {sup 20}Mg to search for the 2645 keV state in {sup 20}Na. This state is of astrophysical interest, because any proton capture through this state would dominate the stellar reaction rate of the reaction {sup 19}Ne({ital p},{gamma}){sup 20}Na. This reaction determines the break out from the hot CNO cycle. Several proton groups have been observed and their log{ital ft} values have been determined. No protons from the 2645 keV state were seen and a lower limit of log{ital ft}{ge}5.85 has been established. The impact of this result on the {sup 19}Ne({ital p},{gamma}) rate is discussed.

Atmospheric neutrino fluxes and sterile neutrinos

Abstract We show that the Kamiokande and IMB atmospheric neutrino flux data, together with the nucleosynthesis constraint on neutrino oscillations, implies an unambiguous v μ − v τ mixing. We discuss the implications of such a mixing for the solar neutrino problem, hot dark matter and the 17 keV state and argue, that a simultaneous solution for the atmospheric and solar neutrino problems, with a neutrino as a hot dark matter candidate, requires a new sterile, non-interacting neutrino species.

High spin isomer in 151Sm

An investigation of the high spin isomer in 151Sm was performed via the 150Nd(α, 3nγ) reaction at a projectile energy of 35 MeV. A new γ-transition, 693.6 keV was identified having an exponential delayed component. The transition feeds the 1912 keV state of the negative parity band built on the h11/2 state. This transition was also observed in coincidence with γ-rays belonging to 151Sm in the γ-γ coincidence experiment at E α =37 MeV. A new isomeric state having energy E x =2605.8 keV and half life T1/2=23.1±3.5 ns is proposed.

Measurement ofK-electron capture probability (P k ) in the decay of197Hg (64.1 h)

TheK-electron capture probability (P K ) for the 268.7 and 77.3 keV states of197Au in the decay of197Hg (64.1h) have been determined from theKX-ray gamma ray summing in a HPGe X-ray detector. The measured values,P k (268.7)=0.746±0.033 andP k (77.3)=0.774±0.036 are found to be in good agreement with the theoretical results.

Angular distributions of γ-rays from four resonances of the55Mn(p, γ)56Fe reaction

Four resonances in the55Mn(p, γ)56 Fe reaction at the centre-of-mass proton beam energy E P CM =1320, 1504, 1508 and 1649 keV were studied. Angular distributions for some strong γ-rays following the radiative decay of the resonances were measured and analysed in terms of the channel-spin formalism. Spin-parity assignmentI r π =3+, 4+ and 3+ was acquired for the 1320, 1504 and 1649 keV resonances, respectively. No definite assignment was established for the 1508 keV resonance and the resonance is assumed to be a very tight multiplet. Analysis of primary transitions to bound states of the Fe final nucleus permited us to assign these states. The 2+, 2+, 2+, 6+ and 4+ assignments were ascribed to the states at excitation energyE x =5705, 5303, 4738, 4692 and 4658 keV, respectively, while for the 5132 keV state ambiguous assignment 3+ or 4+ was found. Multipole mixing ratioδ was established for some primaries. The coupling of angular momenta of proton and target nucleus in the formation of the 3+ resonances was also roughly discussed.

Mössbauer gamma echo

By applying stepwise phase modulation of recoilless gamma radiation in a coincidence experiment, constructive interference is produced in transmission geometry between the source and the absorber fields. The resulting regenerated decay signal is called a gamma echo. Here it is demonstrated that during the decay of the 14.4 keV state of57Fe multiple echo signals can be generated.

Core polarization in the 203 keV [formula omitted] resonance capture by 32S

We have observed gamma-ray spectra from neutron capture in the 203 keV p 1 2 - wave resonance of 32S with an anti-Compton NaI(Tl) detector, employing a neutron time-of-flight technique. Partial radiative widths were measured for the strong E1 transitions to the ground ( 3 2 +) and 840 keV ( 1 + 2 ) states, and for the weak M1 transition to the 3220 keV ( 3 2 −) state. The observed E1 transitions are in a marked discrepancy with predictions of the Lane-Mughabghab valence-capture model. However, those transitions are well explained by a particle-vibrator coupling model, in which an explicit account is taken of the core polarization due to quadrupole and octupole one-phonon excitation in the resonance state. In particular we emphasize that the 2 +⊗ f 5 2 ) configuration component in a model wave function of the resonance state plays an important role for the E1 transitions. A brief discussion is also presented on the M1 transition.