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  • 1
    ISSN: 1434-601X
    Keywords: 27.30.+t ; 21.10.Hw ; 21.10.Dr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The systematics ofγ-decay modes and radiative widths of highly excited states in28Si has been extended by takingγ-ray spectra on 60 resonances of the27Al(p,γ) reaction in the range 1097 keV≤E p ≤ 4492 keV (12643 keV≤E x ≤ 15915 keV) and on the24Mg(α,γ) resonances atE α =3355, 3431, 4003 keV (E x =12860, 12925, 13 415 keV). Theγ-decay modes of levels in the sub-resonance region (E x =10−12.5 MeV) were studied with both the27 A1(p, γ) reaction and the27 A1(d, nγ) reaction at Ed=4,5,6 MeV. Information on radiative widths of levels was obtained by measuring the resonance strengthsS γ =(2I+1)Γ p Γ γ/Γ for 52 resonances of the27Al(p, γ) reaction with an emphasis on prospective T=1 states.
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  • 2
    ISSN: 1434-601X
    Keywords: 27.30+t ; 21.10 Hw ; 21.60 Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 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.
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  • 3
    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 assignments of levels in27Al have been investigated by proton-γ-ray angular correlation measurements in the24Mg(α, pγ) reaction at 14.2, 15 and 15.6 MeV bombarding energy and byγ-ray angular distribution measurements on the Ep=1820, 2114, 2293 and 2574 keV resonances of the26Mg(p, γ) reaction. Unique spin assignments were obtained as follows: I=3/2 for the 5827 keV state, I=5/2 for the 6115, 6465, 6765, 7577, 7721, 8097, 8136, 8324 keV states, I=7/2 for the 5433, 6533, 7413, 8037, 8442, 8586 keV states, I=9/2 for the 5418, 6512, 6713, 7997 keV states, I=11/2 for the 5500, 6948, 7400, 8396 keV states. The level scheme and electromagnetic properties of levels are compared with the results of shell model calculations which use the complete configuration space of the 0d5/2-1s1/2-0d3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent and extends into the region of high level density above 7 MeV excitation energy. The total B(M1↑) below 8.5 MeV excitation energy is evaluated, using published resonance fluorescence and (e, e′) data, and quenching relative to the free-nucleon predictions is reexamined. Evidence in favour of a prolate ground state deformation of27Al and implications of this work for the astrophysically interesting26Al(p, γ) reaction are discussed.
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  • 4
    ISSN: 1434-601X
    Keywords: 27.30.+t ; 21.10. Hw ; 21.60. Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theγ-decay of levels in21Ne up to 10 MeV excitation energy has been investigated byn — γ coincidence measurements initiated with the18O(α, nγ) reaction at 12, 13, 14.5 and 15.4 MeV bombarding energies. Spin(-parity) assignments of excited states are obtained by combining then — γ angular correlation measurements performed atE α=11, 11.82 and 13.6 MeV with a consideration of lifetimes, neutron penetrabilities of the unbound states, and information from the mirror nucleus21Na. The resulting values of Ex[keV]−J π are as follows: 4525-5+, 4686-3+, 5431-7+, 5549-3+, 5819-7−, 6175-7+, 6268-9+, 6550-9, 6639-9, 7006-7+, 7041-9, 7356-7 or 9, 7422-11(−), 7648-7+, 7981-11 or (7+), 8154-9, 8240-11, 8664-9− or 11 or 13−, 9401-13−, 9867-13− or 15+, 9941-13− or 15 or 17+. The assignment of mirror levels in21Ne —21Na has been extended to the 6175 keV level of21Ne. Excitation energies, electromagnetic properties, Gamow−Teller matrix elements and spectroscopic factors of positive parity states are compared with the results of shell-model calculations which employ a unifieds—d shell Hamiltonian and the unrestricted configuration space of the 0d 5/2 —1s 1/2—0d3/2 shell. Collective properties contained in shell model wave functions are explored up to the termination of bands atJ=17/2 or 19/2. The spectrum of intruder states in21Ne is observed to begin with a 5628 keV,J π=7/2+ state. The 7422, 8664 and 9401 keV levels are assigned as members of previously established negative-parity rotational bands.
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  • 5
    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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  • 6
    ISSN: 1434-601X
    Keywords: 27.30.+ t ; 21.10.Hw
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New assignments of quantum numbers have been obtained for more than 50 levels in28Si between 8953 and 15915 keV excitation energy. They are based on the measurement of γ-ray angular distributions or anisotropies on 29 resonances of the27Al(p, γ) reaction and on the24Mg(a, γ) resonance atE α=3355 keV. A total of 15 high-spin states withI=5–7 has been obtained and the spectrum ofT=1 states has been identified up to 15915 keV excitation energy and a maximum spinI=6.
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  • 7
    ISSN: 1434-601X
    Keywords: 27.30+t ; 21.60Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 28Si level scheme up to 14.5 MeV excitation energy is reevaluated using information from two preceding papers. It consists of approximately 250 levels which are almost completely characterized according to the quantum numbersI, π, T of the levels. The properties of positive-parity states are compared to the predictions of shell model calculations within the completes-d basis space using the unifieds-d shell Hamiltonian. A spectrum of 48 experimentalT=1 states between 9.3 and 16 MeV is reproduced with a rms deviation of only 150 keV. A calculation of radiative widths and γ-decay modes which uses free-nucleong-factors yields excellent agreement with experiment and confirms that quenching of M1 transitions is only marginal in28Si. The detailed shell model analysis of theT=0 spectrum is extended to the limiting energy whereT=1 wave function admixtures, not contained in the theory, become important experimentally. This happens at 6–8 MeV above the yrast state, depending on the spin value. Altogether it appears that a spectrum of 171 levels below 14.5 MeV, which have positive or unassigned parity, is almost completely accounted for by the model. Apparent intruder states from outside thes-d shell space are observed atE x =10 945 keV (I π=4+) and 12 860 keV (I π=6+) and are interpreted as members of aK π=0+ rotational band.
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  • 8
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    ISSN: 0163-8998
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
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  • 9
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    ISSN: 0163-8998
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
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  • 10
    Publication Date: 2011-08-16
    Keywords: PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Type: Physics Letters; 49B; Apr. 1
    Format: text
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