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  • 11
    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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  • 12
    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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  • 13
    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
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The38Ar levels at Ex=5350, 7289 and 9341 keV have been investigated using the35Cl(α,pγ) reaction at Eα=l4 and 14.5 MeV. From particle-γ-ray angular correlations the spin assignments J(5350)=4, J(7289)=6,4 and J(9341)=8,6,4 have been obtained. Life-time measurements using the Doppler-shift attenuation method yielded τ(9341)=106±25 fs and τ(7289)=77±30 fs, while the lifetime τ(5350)=200±50 fs was known previously. All levels have positive parity and decay by enhanced E2 transitions. Hence we propose that they are the Jπ=4+, 6+ and 8+ members, respectively, of a Kπ=0+ rotational band which has the Ex=3377keV, Jπ=0+ and the 3937 keV, Jπ=2+ levels as further members. The enhancement of inband E2 transitions is 30 −6 +10 W.u. (4→2), 35 −14 +30 W.u. (6→4) and 20–36 W.u. (8 → 6), respectively, yielding an average intrinsic quadrupole moment Q0=850 −125 +200 mb. The moment of inertia is given by h22θ=92 keV. The present data are in good agreement with the predictions of a deformed state in38Ar that coexists with the spherical states.
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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
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The excited states of27Mg have been investigated up toE x =7976 keV using the26Mg(d, pγ) reaction. A measurement of proton-γ-ray angular correlations atE d =6.5 MeV has yielded spin-parity assignments or restrictions of levels up toE x =6508 keV and accurate excitation energies and branching ratios of levels up toE x =7976keV, respectively. The Doppler-shift attenuation ofγ-rays has been measured atE d ==5.5 MeV yielding information on the lifetimes of levels up toE x =6009keV. The properties of positive-parity levels up toE x =5 MeV are successfully reproduced by recent shell-model calculations. The rotational model is also applicable to the description of collective properties without reaching the overall agreement of the shell model. The negative-parity states are well described by the rotational model.
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  • 17
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The45Sc(α, p γ) reaction has been investigated atE α=11, 12 and 13MeV. Theγ-decay of 198 levels in48Ti up to 8,323 keV excitation energy has been observed. High-spin states were investigated by proton-γ ray angular correlation measurements atE=11 and 13MeV and by DSAM lifetime measurements atE=11 MeV. From the combined evidence spin (-parity) assignments were obtained for the levels atE x =8,323 keV (J= 10,8,6), 8,091(12, 10, 8, 6), 7,668(10, 8), 7,427(9, 7), 7,374(11, 9, 7), 6,906(10, 8, 6), 6,172(8+,6+), 6,102(10+,8+), 6,039(6), 6,034(9+, 7+), 5,630(7), 5,197(8+), 5,169(7+), 5,155(5), 4,404(5), 4,398(6+) and 4,046keV (5). Most of the ambiguous spin assignments become unique if the 8,091 keV level hasJ=12, an assumption which is favoured by its excitation function. The level spectrum thus obtained is well reproduced by shell model calculations in the pure (f 7/2)8 configuration space. Discrepancies exist in the reproduction ofγ-decay modes. The reason is found in low-lying high-spin intruder states which include the 7,427 and 8,323 keV levels. The spectrum of negative-parity states is understood qualitatively by a comparison with46Ti and42Ca.
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  • 18
    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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  • 19
    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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  • 20
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Inorganica Chimica Acta 149 (1988), S. 171-175 
    ISSN: 0020-1693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
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