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1.
The reaction26Mg(p, γ)27Al has been investigated atE p (lab)=80–355 keV. The existence of the resonances atE p =292 and 338 keV has been verified and new resonances were found atE p =227 and 275 keV. Information on branching and mixing ratios,ωγ values, total widths, andJ π assignments for the observed resonances is given. Upper limits on theωγ strengths for expected resonances in the energy range covered are presented. The astrophysical aspects of the data are discussed in the light of the26Mg(26Al) isotopic anomaly.  相似文献   

2.
The reaction25Mg(p,γ)26Al has been investigated atE p (lab)=80-350keV. The existence of the resonance atE p =317keV has been verified and new resonances have been found atE p =198, 255 and 304 keV. TheE p = 304keV resonance represents a new compound state in26A1. Information on branching ratios,Ωγ values, total widths andJ π assignments for the observed resonances as well as upper limits on themy strengths for the expected resonances atE p =97 and 134 keV are given. The astrophysical aspects of the data are discussed in the light of the renewed interest in the precise location of26A1 nucleosynthesis.  相似文献   

3.
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   

4.
The yield curve of the reaction56Fe(p,γ)57Co has been measured over the energy rangeE p =1,300–1,900 keV and the decay of nine resonances has been investigated. For twelve of the resonances the strengths have been determined. The angular distributions of the gamma rays have been recorded for resonances atE p =1,599, 1,623, 1,643 and 1,649 keV, giving spin-parity assignmentsJ π=3/2? for all four resonances. The resonances atE p =1,623, 1,643 and 1,649 keV have been identified as the split analogue resonances of the 367 (J π=3/2?) states in57Fe. TheM1 transition strengths to the corresponding antianalogue states have been measured and compared with theoretical predictions.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
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   

8.
Measurements of resonance strengths and ofγ-ray angular distributions or anisotropies have been performed on selected resonances of the25Mg(p, γ) reaction in the rangeE p=2–4 MeV,E x=8.2?10.1 MeV with an emphasis on high-spin andT=1 analog resonances. EightT=1 states are identified, among them high-spin states at 8747 keV (I=6), 9286 KeV (I=5), and 9986 keV (I π = 7+, 6+). Shell model calculations in thes-d basis space reproduce the branching ratios of these states and clarify the nature of final states. New high-spinT=0 states are observed at 9720 keV (I π = 7+), 8602 keV (I = 6), and 6695 keV (I π = 7+). TheI π assignments to severalE x = 6–8 MeV states are revised and the role of two-particle excitations into thef-p shell is elucidated. A revised spectrum of 73 positive-parity,T = 0 states is compared to the predictions of shell-model calculations in thes-d basis space using the universals-d shell Hamiltonian.  相似文献   

9.
Co54m (T 1/2=1.43 min) was produced in iron-foils by irradiation withdE=19 MeV deuterons. The gamma ray spectrum was investigated using a NaJ(Tl) scintillation spectrometer, a coincidence circuit and a Ge(Li)-counter. There were observed three gamma rays having the following energies and intensities per Co54m decay: 411 keV (0.97±0.07), 1130keV (0.98±0.05), 1407 keV (1.00±0.05). The directional correlation between the pairs of gamma rays were determined. These results correspond to spin and parityJ π=2+ for the 1407 keV,J π=4+ for the 2537 keV, andJ π=6+ for the 2948 keV energy level of Fe54. The last-mentioned level was not excited in previous scattering experiments. Our results are compatible withE=210keV andJ π=6+ or 7+ of the isomeric state of Co54m .  相似文献   

10.
An extended level scheme of109Sn is presented showing high-spin states up to Ex≈ 8 MeV and spins up to=(41/2+). Their decay to the 5/2+ ground state has been observed identifying a 12.8 keV 7/2+ → 5/2+ transition. A half-life of T1/2=7(1) ns has been measured for the 17/2+ state atE x =2114 keV. The experimental data are compared with the predictions of shell-model calculations.  相似文献   

11.
《Nuclear Physics A》1986,459(1):61-76
Thin target yield curves with good statistics have been measured for the 25Mg(p, γ)26Al and 25Mg(p, p′)25Mg reactions in the Ep = 310–1845 keV region. Altogether 76 resonances have been observed, of which 45 only in (p, γ), 30 in both (p, γ) and (p, p′), and one only in (p, p′). Several of these resonances had not been observed previously in either of the two reactions, and several of the previously observed resonances turned out to be doublets. All 39 25Mg(p, p0)25Mg resonances found previously in the Ep = 700–1845 keV region resonate in (p, γ) and many also in (p, p′). Resonance strengths have been derived relative to that of the Ep = 593 keV resonance.The analysis of weak (p, p1) and (p, p2) resonance yields has been supported by a calculation of the yields in the continuum (in between resonances) due to the Breit-Wigner tails of strong and broad resonances in the neighbourhood (with interference between resonances with the same Jπ; T taken into account), and to Coulomb excitation.  相似文献   

12.
The yield curve and resonance strengths of resonances in the24Mg(p, γ)25Al reaction for the proton energy rangeE p=800 keV toE p=1,830 keV, have been determined and the existence of a resonance atE p=1.184 MeV confirmed. Single energy spectra as well as decay schemes and branching ratios are given for these resonances. An upper level of 2.0×10?15 sec for the lifetime of the 3.079 MeV level in25Al results from a Doppler shift attenuation measurement carried out on the 2.624 MeV gamma line originating in the 3.070 MeV→0.455 MeV transition in25Al.  相似文献   

13.
Resonances in the reaction60Ni(p, γ)61Cu have been studied in the proton energy rangesE p=1840–1880 keV and 2220–2300 keV. Decay schemes and branching ratios have been determined for a number of resonances, three of which are identified as analogue fragments of the 283 keV (1/2?) and 656 keV (3/2?) states in61Ni. The split analogue components of the 283 keV state atE x≈6.6 MeV are seen to decay significantly to a group of states in the region of excitation 3–4 MeV. Gamma ray angular distributions yield the following resonance spins:E p=2248 keV,J=3/2;E p=2263 keV,J=5/2. Also, the61Cu ground stateβ + decay to parent levels in61Ni has been compared to the respective analogue stateM1 gamma decay to the61Cu ground state.  相似文献   

14.
Angular correlation measurements for the58Ni(p, p′ γ) reaction were performed atE p =8.1 MeV. Method II of Litherland and Ferguson was used to determine multipole mixing ratios of the γ-radiation and spins of most of the excited levels up to 4.11 MeV. The results confirm for the most part recent measurements of van Patteret al.; the 2775 keV state was verified to have a spin ofJ=2. Several discrepancies and additional information concerning the 3531, 3774, 3898 and 4108 keV levels are discussed. A spin value ofJ=1 is assigned to the 3531 keV level, clearly ruling out former assignments of 4+ and 0+. AJ=4 assignment is proposed for the 3774 keV state, contrary to the generally assumed value ofJ=3, which these measurements do not support.  相似文献   

15.
The absolute resonance strengths of the 24–26Mg(p, γ)25–27Al reactions have been studied. The absolute values Sc.m.=1.03 ± 0.11, 2.3 ± 0.2 and 2.2 ± 0.2 eV for the frequently used standard resonances at Ep=823, 434 and 454 keV in the reactions 24–26Mg(p, γ)25–27Al, respectively, have been determined. In addition, absolute values for use as standards were determined for the 684 keV 25Mg(p, γ)26Al and 840 and 1966 keV 26Mg(p, γ)27Al resonances. New relative values were determined for the strengths of the if25Mg(p, γ)26Al resonances at ifEp = 0.3–1.7 MeV and the 26Mg(p, γ)27Al resonances at Ep = 0.3–2.1 MeV. The resonance energies and total widths obtained in the present work are also given. The branching ratios and angular distributions of the γ-rays used in the absolute strength determinations were obtained in the same set-up as the absolute strength measurement. Using the revised resonance strengths, the astrophysical reaction rates of hydrogen burning of 24–26Mg in explosive carbon burning in the stellar temperature region of T = (0.1–5.0) × 109 K are compared with Hauser-Feshbach calculations. The present reaction rates are also discussed in the frame of the MgAl cycle.  相似文献   

16.
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.  相似文献   

17.
The resonance in the12C+12C system atE c.m.=19.3 MeV has been studied in the neutron and proton decay channels. From(p, γ), (n, p) and (n, γ) coincidence measurements high spin states could be localized inA=23 nuclei, in23Mg up to possibly 21/2+. These states were resonantly populated. The present data favorJ π=17/2+ for the 9.61 MeV state in23Mg and therefore also for the probable parent state at 9.81 MeV in23Na. AJ π=12+ assignment to the resonance is supported and evidence was found that the resonant excitation of the lowest 15/2+ and 17/2+ states in mass 23 nuclei is caused by a change of the intrinsic structure of the Yrast levels aroundJ π=15/2+ towards larger deformation.  相似文献   

18.
Angular distribution measurements of gamma-rays from the22Ne(p, γ)23Na reaction on theE p =897, 1006, 1091 and 1278 keV resonances have been made. Spin and parity assignments for several bound states are presented together with multipole mixing ratios for transitions from resonance and bound states. The level at 6617 keV (7/2+) is proposed to be a member of the rotational band based on the Nilsson orbit 5(K π=5/2+).  相似文献   

19.
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.  相似文献   

20.
The16O(3He,?γ)18F reaction atE(3He)=2.95 MeV was used to study the low-lying states in18F belowE x =3.2 MeV. A combination of γ-ray angular distribution and linear polarization measurements using a single planar Ge(Li) polarimeter resulted in aJ π =1? assignment to the 3134 keV state. In addition, the positive parity assignments to the 937(3+) and 1702(1+) keV states have been verified. Information on branching and mixing ratios as well as on lifetimes are reported. The results are discussed in terms of the weak-coupling and strong-coupling models.  相似文献   

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