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  • 11
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 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.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 338 (1991), S. 23-49 
    ISSN: 1434-601X
    Keywords: 27.30.−t ; 21.10.Hw ; 21.60.Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Gamma-decay modes and spin(-parity) assignments of levels in25Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the24Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the22Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2〈I≦15/2. The excitation energies and electromagnetic properties of more than 70 states for which positive parity has been established or is most probable are compared with the results of shell-model calculations which use the complete configuration space of theO d 5/2 — 1s 1/2-O d 3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of25Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of25Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of25Mg in great detail. The prospectiveI π=9/2−, 13/2−, and 15/2− members of the established negative-parity,K=1/2 band are found in levels atE x=7801, 9410, and 8896 keV.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 268 (1974), S. 391-399 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The24Mg(α, p γ) reaction has been studied atα-particle energies of 13, 15, and 15.2 MeV. Using method II of Litherland and Ferguson spin assignments or restrictions thereof could be made to the27Al levels atE x =5500 keV (I=11/2, 7/2), 6950 keV (I=11/2, 7/2), 7226 keV (I=9/2), 7286 keV (I=9/2–13/2), 7399 keV (I=11/2, 7/2) and 7443 keV (I=13/2, 9/2). Using the Doppler-shift attenuation method a lifetimeτ=20–50 fs was obtained for theE x =7399 keV level and a limitτ〈20 fs for the levels atE x =7443, 7286, 7226, 6950, 6718, and 6287 keV, respectively. Further spin assignments in27Al were obtained by a study of the26Mg(p, γ) reaction at the Ep=2174 keV resonance. Fromγ-ray angular distributions the resonance spin was determined as I=9/2 (previous assignmentI=7/2) and the spin of theE x =5959 keV level was determined asI=7/2. Tentative spin assignments were made to the levels atE x =6537 keV (I=7/2) and 6718 keV (I=9/2). From the combined evidence of the24Mg(α, p) and26Mg(p, γ) reactions the spin of the 6287 keV level was found to beI=7/2. The results are compared with shell model calculations and the Nilsson model.
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 276 (1976), S. 295-302 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The42Ca levels at 4,715 and 6,633 keV excitation energy have been investigated using the39 K(α,pγ reaction atE α=14 and 15 MeV. From particle-γ-ray angular correlations the spin assignmentsJ(4,715)=6, 4 andJ(6,633)=8, 6, 4 have been obtained. Lifetime measurements using the Doppler-shift attenuation method yieldedτ (4,715)=120±46 fs andτ(6,633)=52±21 fs. Both levels have positive parity and decay by enhancedE2 transitions. They are interpreted as theJ π=6+ and 8+ members, respectively, of theK π=0+ rotational band which has theE x =1,837, 2,423 and 3,250 keV states as further members. The enhancement of inbandE2 transitions is 50 −16 +35 W.u. (6→4) and 63 W.u. (8→6) respectively. The intrinsic quadrupole moments which have been derived on the basis of the coexistence model, areQ 0=1.13−0.16/+0.37b(8→6) andQ 0=1.36±0.25b(6→4), respectively. TheJ π=10+ member of the rotational band has possibly been observed as a level at 8,856±5 keV excitation energy.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 278 (1976), S. 319-325 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theγ-decay of 9338Ar levels between 6.84 and 10 MeV excitation energy has been measured using the35Cl(α,pγ) reaction atE α=14 MeV. A previous measurement of the same reaction could be exploited in the light of the present results, yielding spin(-parity) assignmentsJ π(7,070)=5-, J(7,507)=7,5,J π(8,077)=7+, J(8,129)=5,6 and J(8,488)=7,5. Theγ-decay modes of yrast levels, which have been previously observed in heavy ion induced reactions, are revised leading to major changes in their spin-parity assignments. New candidates for theJ π=8- and 9+ levels were found in the levels at 9,644 and 9,928 keV excitation energy, respectively. A comparison of yrast levels with shell-model calculations is satisfying.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 294 (1980), S. 51-64 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theγ-decay modes of38Ar levels withE x ≦11,630keV and of42Ca levels withE x ≦10,036keV have been studied using the35Cl(α, pγ) reaction at 16MeV and the39K(α, pγ) reaction at 15.14 MeV, respectively. In both nuclei the number of states withJ≧6 exceeds fifty. Weak coupling calculations of the Bansal and French type reproduce the density of high-spin states. The success of the model implies that the excitations of up to four particles from thed 3/2 into thef 7/2 shell play a role in both nuclei. The structure of deformed states was found to be predominantly 4p/s 6h in38Ar and 4p/s 2h in42Ca, respectively.
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  • 17
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 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.
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  • 18
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theγ-decay of40Ar has been studied by particle-γ-ray coincidence measurements in the37Cl(α, pγ) reaction at 12 and 13 MeV bombarding energy. Particle-γ-ray angular correlations and linear polarizations ofγ-rays were measured at 12 MeV. A lifetime measurement using the Doppler-shift attenuation method was performed at 11 MeV. The coexistence of spherical and deformed states in40Ar could be concluded from the observation of aK π=0+ rotational band which has itsI π=0+ through 6+ members at 2,121, 2,524, 3,515 and 4,959 KeV excitation energy. The intrinsic quadrupole moment derived fromB(E2) values is ∥Q 0∥=1,320 −120 +60 mb. Negative-parity states with high spin were observed at 4,858(5−), 4,494(5−), 4,226(4−) and 4,991 KeV(4−) excitation energy. A complete account of all levels below 5 MeV excitation energy is obtained by a model in which twod 3/2 proton holes couple weakly to the42Ca levels below 4.75 MeV excitation energy.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 266 (1974), S. 55-64 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spin assignments have been made to the25Mg levels in theE x=5–6 MeV region fromγ-ray angular distributions measured in the22Ne(α, n y) reaction atE α=8.0 and 8.8 MeV and fromp-γ angular correlations measured in the24Mg(d, p γ) reaction atE d=6 MeV. Unique spin assignments ofJ=7/2, 5/2, 5/2, and 9/2 could be made to the levels atE x=5005, 5511, 5851, and 5967 keV, respectively. Ambigious assignments have been made to the levels atE x=5245, 5524, 5785, 6032 keV (J=11/2, 7/2), 5455 keVJ=13/2, 9/2), and 5738 keV (J=3/2, 5/2). The present data confirm previous assignments ofJ=1/2 to the levels atE x=5108 and 5466 keV, respectively. Lifetime estimates have been obtained, using the Doppler-shift attenuation method, for the levels atE x=5245 keV (τ=30–60 fs), 5785 keV (τ=50–100 fs), 5967 keV (τ=50–100 fs), and 5455 keV (τ〉1ps). All other levels in theE x=5–6 MeV region haveτ〈60 fs. A breakdown of theK-selection rule has been observed in theγ-decay of some high spin states, indicating a deviation from the strong coupling model.
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 271 (1974), S. 59-64 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The mean lives of25Mg levels have been studied using the Doppler-shift attenuation method in the24Mg(d, pγ) reaction atE d =6 MeV. Except for theE x =6873 keV level, all levels between 2 MeV excitation energy and the neutron binding energy could be investigated, yielding 11 mean lives and 30 limits thereof. A large number of multipole transition rates could be deduced and several parity assignments be made. The relevance of the data with respect to the rotational model is discussed. A serious breakdown of theK-selection rule, which has been proposed earlier for some high-spin states, is confirmed.
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