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1.
The level structure of 184W has been studied from the prompt γ-rays emitted following the capture of both thermal and 2 keV neutrons by 183W. Energies and intensities were measured for both the primary and the secondary (low-energy) prompt γ-rays. From these data, a level scheme is proposed for 184W in which all the Iπ = 0+, 1+ and 2+ states below ≈ 2.0 MeV are observed. Where possible, rotational-band assignments have been made to these and other levels. Additional evidence is presented which confirms the 1130 keV state as being the band head of a Kπ = 2? octupole vibrational band. Admixed Kπ = 0+ and 2+ bands are established at 1322 and 1386 keV, respectively, with the Iπ = 2+ states (at 1431 and 1386 keV) having a mutual admixture of ≈ 12%. In the energy region above 1.5 MeV, the following bands and band-head energies are identified: Kπ = 1+, 1613 keV; Kπ = 0+, 1614 keV; Kπ = 1+, 1713 keV; Kπ = 2+, 1877 keV. The neutron binding energy in 184W has been determined to be 7411.1±0.6 keV. The band structure of the 1613 keV (1+) and 1614 keV (0+) bands is observed to be strongly distorted, the observed A ( h?2/2I) values being ≈ 3.6 keV and ≈ 32 keV, respectively. This strong distortion is shown to be explainable in terms of Coriolis coupling of reasonable strength between the two bands. A similar explanation is shown to account for the somewhat less anomalous A-values (22.8 keV and 14.0 keV, respectively) of the 2+ band at 1386 keV and the 3+ band at 1425 keV. The results of a phenomenological fiveband-mixing analysis involving the Kπ = 0+ and 2+ bands below ≈ 1.5 MeV are presented and discussed. These calculations indicate, among other things, that the direct E2 matrix element connecting the 1322 keV, Kπ = 0+ band and the ground-state band is quite small, possibly zero. They also indicate that a nonzero E2 matrix element exists between this excited Kπ = 0+ band and the γ-vibrational band and that the magnitude of this element is comparable with that between the γ-vibrational and ground-state bands. Arguments favoring and apparently refuting the interpretation of the 1322 keV, 0+ band as a “two-phonon γ-vibration” are presented.  相似文献   

2.
The electron-capture decay of228Pa to levels in228Th has been studied using mass-separated sources and high-resolutionγ-ray and conversion-electron spectroscopy. A level at 979.5 keV is assigned as 2+ member of a second excited Kπ=0+ band, with the 0+ band head at 938.6 keV. The 2+ and 3+ members of a second excited Kπ=2+ band at 1153.5 and 1200.5 keV, which decay by strongE0 transitions to the 969 keVγ-vibrational band, are confirmed. In addition we tentatively propose a Kπ=1+ band at 944 keV. The Kπ=0?, 1? and 2? members of the octupole quadruplet are confirmed, and theγ decay of these levels is analysed in an approach, in which the mixing of the octupole bands by the Coriolis interaction is taken into account. It is suggested that octupole correlations might be important for theE1 transition moments. A total of 29 levels is observed between ~1.4 and ~2.0 MeV, for which the nuclear structure, and the possible assignment to rotational bands, is unclear.  相似文献   

3.
Theγ-decays of levels in26Mg have been investigated up to 12.5 MeV excitation energy by proton-γ-ray coincidence measurements in the23Na(α, pγ) reaction at 14.2 and 16 MeV bombarding energy. Lifetime-measurements, made with the Doppler-shift attenuation method, and proton-γ-ray angular-correlation measurements were performed at Eα=14.2 MeV. Many high-spin states were observed, among them levels at 6,978 (5+), 7,283(4?), 7,395(5+), 7,953(5?), 8,202(6+), 8,472(6+), 9,065(5), 9,112(6+), 9,169(6?), 9,383 (6+), 9,542(5), 9,829(7+), 9,989(6+) and 12,479(8+, 7?) keV excitation energy. The spectrum of positive-parity states and their electromagnetic properties are reproduced with good accuracy by shell-model calculations which employ a unifieds-d shell Hamiltonian and the unrestricted configuration space of the 0d 5/2 1s 1/2 0d 3/2 shell. Members of five inferred rotational bands, withK π=0+, 2+, 3+, 0+ and 3? have been observed up to at leastI=6. TheK π=2+ band shows strong anomalies of excitation energies andE2 transition rates near theI=6 state. The static intrinsic quadrupole moments calculated from the shell model wave functions indicate transitions from prolate to oblate deformation within theK π=2+ band and also the ground state band. The lowest lyingI π=4+ state appears to be “spherical” and cannot be associated with a rotational band.  相似文献   

4.
The energy levels of 234U and 236U have been studied through the inelastic scattering of 16 MeV douterons. A magnetic spectrograph was used to momentum-analyse the scattered deuterons at θ = 90° and 125°. Excited in both 234U and 236U were the ground state bands up to and including the 8+ members, the Kπ = 0+β-vibrations, the Kπ = 2+γ-vibrations, and the Kπ = 0? octupole vibrational bands. In 234U, additional levels at 1023 and 1126 keV are ascribed to a Kπ = 2? band, levels at 1238, 1312, and 1446 keV are identified as members of either a Kπ = 0? or 1? configuration, and other tentative assignments are made for members of Kπ = 1? and 3? configurations. Relative reduced transition probabilities, B(E2), to the 2+ rotational and γ-vibrational states are generally found to be in good agreement with Coulomb excitation measurements. Relative B(E3) values for the 3? states excited are slightly higher than the predictions of a microscopic theory of octupole vibrations.  相似文献   

5.
Evidence is given for the existence of a spin-5 boson resonance from the analysis of the reaction π?p→K+K?n at 62 GeV incident momentum. A simplified amplitude analysis with a Breit-Wigner ansatz leads to a mass 2307 ± 6 MeV and a width of 245 ± 20 MeV. The quantum numbers of the resonance are JP = 5?, C = ?1, and very probably IG = 1+.  相似文献   

6.
New shell model calculations have predicted several high-spin (I π=5+ and 6+) levels in28Si near 10 MeV excitation energy which are missing from or ambiguous in existing experimental studies. Angular distributions, linear polarizations and Doppler-shifts ofγ-rays have been measured for theγ-decay of theE p=1,911 and 2,073 KeV resonances of the27Al(p, γ) reaction in an attempt to discover these missing states or confirm the discrepancies between experiment and theory. The excitation energies and spin-parities of the resonances were determined as 13,424.4±0.2 keV,I π=5+ and 13,582.3±0.5 keV,I π=6+. States populated in theγ-decay of these resonances were assigned spins and parities as follows: 11,777 keV,I π=5+; 11,331 keV,I π=6+; 10,417 keV,I π=5+; 9,417 keV,I π=4+ and 8,945 keV,I π=5+. On the basis ofγ-ray transition rates T=1 is assigned to the 13,424 keV level and T=0 to the 10,417 and 11,777 keV levels. With the new data excellent agreement is achieved between the experimental spectrum of28Si and the new shell model predictions. These data provide evidence for aK π=3+ rotational band comprised by the 6,276, 6,889, 8,945 and 11,331 keV levels. This band emerges also from the shell model wave functions as do theK π=0+ bands based on the ground state and the 6,691 keV state.  相似文献   

7.
A search for high-spin states in28Si has been performed byn?y coincidence measurements in the25Mg(α,nγy) reaction atE α=14 and 15.5 MeV. Spin-parity assignments of the observed levels were obtained fromn?γ angular correlation and lifetime measurements atE α=14.5 MeV. Theγ-decay of the 9,164 keV level was investigated separately with the27Al(p, γ) reaction at theE p=2,160 and 2,312 keV resonances. Rotational bands withK π=3? (comprising levels atE x=6,879, 8,413, 10,188 and 12,204 keV),K π =5? (comprising levels atE x=9,702, 11,577 and 13,741 keV) andK π=0+ (comprising levels atE x=6,691, 7,381, 9,164 and 11,509 keV) were observed. The finding of the latter band supports the idea of coexisting oblate and prolate shapes in28Si. A level at 14,643 keV excitation energy has the properties of theI π=8+ member of the ground state band. There are additional positive-parity high-spin states which do not fit into rotational bands. All types of positive-parity states are well accounted for by shell model calculations.  相似文献   

8.
The bandhead energies of twenty two-quasiparticle states expected to occur in the low-energy excitation spectrum of the doubly odd nucleus 250Bk are calculated using a zero-range residual interaction and the results are compared with the available experimental information. Configuration assignments to nine intrinsic states reported in earlier studies are confirmed. Our calculations support the excitation energy of 115 keV for the Kπ = 3+ state and also the characterisation of the 317 keV 5+ state as the Kπ = 5+ bandhead. In addition, we suggest acceptable two-particle configurations for the 175 keV 1+ state and the 216 keV 0+ state. The expected location of eight as yet unobserved two-quasiparticle states is predicted.  相似文献   

9.
A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of 178Hf in the Kπn = 16+ isomeric state has been performed at 4.77 MeV/u 208Pb beam energy. The first excited Iπ = 17+ state has been observed at an excitation energy of 357.4 ± 0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment of Q 0 = 8.2 ± 1.1 b has been derived from the experimental data within the rigid rotor model.  相似文献   

10.
A resonance is observed in the 27Al(p, γ)28Si reaction at Ep=2876±2 keV, which corresponds to an excitation energy of 14356±2 keV. The 14.36 MeV level decays to a new level at 11577±2 keV, which is turn decays to the known level at 9701.8±0.5 keV. With previous information on the 9.70 MeV level and the present γ-ray angular distributions, obtained from singles spectra as recorded by a 40 cm3 Ge(Li) detector, the spins of the three levels can be limited to J=5, 6; J=6; and J=5, respectively. Transition strength arguments based on measurements of the strength of the 2876 keV resonance and the lifetime of the 11.58 MeV level indicate that the 14.36 MeV level has Jπ=6?, T=1 and that the 11.58 MeV level has Jπ=6?, T=0.  相似文献   

11.
Rotational sidebands in 166Er were observed using the 24 MeV 164Dy(α, 2nγ) reactions. The ground-state band was observed up to spin 16+ and does not backbend. A strong backbend is, however, observed in a Kπ = (O+) sideband, indicating that the 12+ state of the previously unknown S-band is at 2656 keV. The γ-band shows significant rotational alignment above I = 10+. Levels of at least two negative-parity bands, one of which is primarily the Kπ = 2? octupole vibration, are also observed.  相似文献   

12.
Vibrational bands in 226Ra were studied by Coulomb excitation and by the 226Ra(d,pnγ) reaction. The first-excited K π = 0+ and 1? bands with known band heads at 825 and 1049 keV, respectively, were extended up to the 8+ and 7? levels. A new 2+ level at 1110 keV and the known 2+ level at 1156 keV were observed following Coulomb excitation and interpreted as γ vibration and possible member of a second-exited K π = 0+ band, respectively. The E1 and E2 branching ratios from these vibrational bands to the ground and first-excited 0? band are explained within the rotational model including band mixings. No evidence was found for a 0+ level at 650 keV proposed earlier.  相似文献   

13.
A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of178Hf in the Kπ = 16+ isomeric state has been performed at 4.77 MeV/u208Pb beam energy. The first excited Iπ = 17+ state has been observed at an excitation energy of 357.4±0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment ofQ 0=8.2±1.1 b has been derived from the experimental data within the rigid rotor model.  相似文献   

14.
Vibrational bands in226Ra were studied by Coulomb excitation and by the226Ra(d,pnγ) reaction. The first-excitedK π = 0+ and 1? bands with known band heads at 825 and 1049 keV, respectively, were extended up to the 8+ and 7? levels. A new 2+ level at 1110 keV and the known 2+ level at 1156 keV were observed following Coulomb excitation and interpreted asγ vibration and possible member of a second-exitedK π = 0+ band, respectively. TheE1 andE2 branching ratios from these vibrational bands to the ground and first-excited 0? band are explained within the rotational model including band mixings. No evidence was found for a 0+ level at 650 keV proposed earlier.  相似文献   

15.
The γ-rays following the β?-decay of 228Fr have been studied by means of γ-ray singles including multi-spectrum analysis and γ-γ coincidence measurements using Ge(Li) spectrometers. Most of the observed γ-transitions could be placed in the level scheme of 228Ra. The accuracy the energy of the first-excited state in 228Ra has been improved and 35 new excited levels have been established, 11 of them grouped into the ground-state band, the low-lying Kπ = 0? band with the head at 474.14 keV and two excited Kπ = 0+ bands with heads at 721.17 and 1041.9 keV. Candidates for two close-lying Kπ = 2+ bands have also been found. It is concluded that the ground state octupole deformation, if any, is less pronounced in 228Ra than in lighter radium isotopes.  相似文献   

16.
Low and high energy spectra from thermal neutron capture in 237Np have been studied over the energy ranges 25 to 650 keV and 2600 to 5500 keV. Primary transitions from neutron capture in four resonances have been observed between about 4800 and 5400 keV. Using 12 MeV deuterons, (d, p) spectra at three angles have been observed with a magnetic spectrograph. A nuclear level scheme for 238Np has been constructed by combining the results of the above measurements with previous data from a study of the 242mAm α-decay. The Nilsson model has been used to interpret the level structure. Including results from the previous α-decay study, nine rotational bands can be assigned. The Nilsson configurations (Kπ [Nn3ΛΣ]) and band-head energies are: 2+π[642↑]?ν[631↓], 0.0 keV; 3+π[642↑]+ν[631↓], 86.6 keV; 3?π[523↓]+ν[631↓], 136.0 keV; 2?π[523↓]?ν[631↓], 182.8 keV; 5+π[642↑]+ν[622↑], 278.1 keV; 0+π[642↑]?ν[622↑], 332.5 keV; 5?π[523↓]+ν[622↑], 342.6 keV; 0?π[523↓]?ν[622↑], 286.0 keV; 6?π[642↑]+ν[743↑], 301 keV. The measured (d, p) reaction cross sections are compared with theoretical calculations based on these assignments. The Gallagher-Moszkowski rule is found to be valid in the four cases where we have observed both parallel and antiparallel coupled bands with K+ = Ωpn and K? = |Ωpp|. The lowest levels of the two K = 0 bands have spin I = 1; Newby odd-even shifts can be determined in both cases.  相似文献   

17.
The reaction232Th(γ,f) is studied using bremsstrahlungγ-beams in the (5.45–6.85) MeV end point energy range. Fragments angular distributions are measured and yield components with opposite parities are separated. The unfolded cross sections have resonant behaviour which indicates the existence of low damped vibrational states. Furthermore, a near degeneracy forK π =0+ andK π = 0? resonances at ~5.5 MeV and ~6 MeV is observed. Data are analysed in terms of a double humped barrier configuration within the doorway state model for fission. For each component maxima with almost equal heights and a shallow intermediate minimum are determined. Moreover almost equal potential barriers withK=0 and opposite parities are found. This is a signature for mass-asymmetric shapes and seems a clear indication for a threehumped barrier configuration with a low inner maximum and a third mass asymmetric shallow minimum due to the fragmentation of the normal mass-asymmetric second maximum.  相似文献   

18.
Excitation functions for the (α, γ) and (p, γ) reactions leading to 10B have been measured at θ = 0° in the energy range from Ex = 6.7 to 7.6 MeV. Two resonances corresponding to levels at 6.88 and 7.44 MeV are observed. Branching ratios extracted from γ-ray spectra are the same in both reactions for the 6.88 MeV (1?, T = 0 + 1) level, but different at 7.44 MeV. The T = 0 + 1 level at 7.44 MeV (Γ = 90±10keV) is assigned 2? or 2+ from its strong branch to the 3+ ground state. We find no evidence for a second isospin mixed 1? state.  相似文献   

19.
The level structure of 158Gd has been studied using the prompt γ-rays and conversion electrons emitted following neutron capture in 157Gd. The γ-ray energy and intensity measurements were made using both Ge(Li) detectors and a curved-crystal spectrometer. Conversion-electron energy and intensity measurements were made using two separate magnetic spectrometers: one to measure the primary electron spectrum and the other to measure the lower energy secondary electron spectrum. Some γ-γ coincidence measurements were also made among the secondary γ-rays. From these data, a neutron separation energy of 7937.1 ± 0.5 keV has been determined for 158Gd. A level scheme containing 59 excited states with energies < 2.25 MeV, for which de-excitation modes have been identified, is proposed for 158Gd. Many of these states have been grouped into rotational bands. A total of thirteen excited rotational bands with band-head energies below 2.0 MeV are contained in the level scheme. Features of the proposed level scheme include: the Kπ = 0?, 1? and 2? octupole-vibrational bands with band-head energies of 1263, 977 and 1793 keV, respectively; the γ-vibrational band at 1187 keV; three excited Kπ = 0+ bands with band-head energies of 1196, 1452 and 1743 keV; several two-quasiparticle bands with band-head energies in keV (and Kπ assignments) of 1380 (4+), 1636 (4?), 1847 (1+), 1856 (1?), 1920 (4+) and 1930 (1+). An analysis of (d, p) reaction data is presented which permits definite two-quasiparticle configuration assignments to be made to most of these latter bands. Evidence is presented which suggests strong mixing of some two-neutron and two-proton bands. A phenomenological four-band mixing analysis is made of the energy and E2 transition-probability data for the ground-state band and the three lowest-lying excited collective positive-parity bands. Good agreement with experiment is obtained. A Coriolis-mixing analysis of the octupole bands has been carried out and good agreement with the data on level energies and E1 transition probabilities to the ground-state band has been achieved. Values of Z, the ratio of the E1 transition matrix element with ΔK = 1 to that with ΔK = 0, involving the octupole bands and the first four 0+ bands are derived. For three of these 0+ bands, absolute values of these matrix elements are deduced. An interesting alternation in the sign of Z is observed for these four 0+ bands.  相似文献   

20.
Highly excited states in30Si were investigated using the27Al(α, p γ) reaction. Proton-γ ray angular correlations were measured atE α=12, 14.1 and 15MeV. At 15MeV linear polarizations ofγ-rays were measured in coincidence with protons using a five-crystal Compton-polarimeter. Lifetimes were measured atE α=14.6 MeV using the Dopper-shift attenuation method. Unambigious spin-parity assignments were obtained for the levels at 6,865 (3+), 7,001 (5+), 7,079 (3+), 7,810 (4), 9,371 (6+), 7,613 (4?), 8,196 (5?), 8,596 (4?), 8,963 (5?), 9,111 (6?), 9,350 (4?), 9,507 (5?), 9,777 (6?), 10,188 (5?), 10,305 (3?), 10,561 (6?), 10,725 (7?), 11,477 (6?) and 11,544 (7?)keV excitation energy, respectively. The structure of30Si is understood both in terms of the shell model and the collective model. The levels at 5,487, 6,505, 8,196, 9,777 and 11,544keV, respectively, are theI π=3? through 7? members of a well developedK π=3? rotational band with intrinsic quadrupole moment |Q 0|=350 ?70 +250 mb. There is evidence of further rotational bands, among them aK π=3? band with |Q 0|=800 ?80 +422 mb.  相似文献   

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