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1.
Angular distributions of protons from the 12C(α, p)15N reaction have been measured over the angular range from 10–70° at an α-particle bombarding energy of 96.8 MeV. Well defined particle groups are observed up to an excitation energy of 18 MeV in 15N. The relatively small number of states excited implies a selectivity both in the reaction mechanism and in structure effects. DWBA calculations using a semi-microscopic three-nucleon form factor have been performed using several different sets of wave functions. Good agreement in the ratio σexp/σth is obtained for most states using the 15N wave functions of de Meijer. The strongest state in the (α, p) spectrum is observed at 15.397 MeV in 15N and DWBA calculations give good agreement for a assignment. This state has been observed only in other three-nucleon transfer reactions involving heavy ions. The recent discovery of a state at 10.693 MeV in a p+14C resonance measurement is supported by our analysis. 相似文献
2.
High spin states of 57Co have been studied via prompt γ-ray spectroscopy in the reactions 48Ti(12C, p2n) and 54Fe(α, p) at 26–48 MeV and 12–24 MeV, respectively. The energies and decay modes of these levels were determined from the analysis of γ-ray singles and γ-γ coincidence spectra, excitation functions, angular distributions and correlations. The relevant lifetimes were measured by the Doppler-shift attenuation method. The new levels established in this work are at 4037, 4814 and 5918 keV with the most probable Jπ assignment of , if and , respectively. The previously known level at 2524 keV was assigned to have . These together with the known (1224 keV) and (1690 keV) levels constitute the yrast states of 57Co. The measured lifetimes of the above six levels are (in order of increasing energies) 0.085±0.030, 0.32±0.10, 0.16±0.06, 0.10?0.07+0.06, 1.5?0.54 and 0.17?0.07+0.08 ps, respectively. Comparisons with some theoretical calculations are presented. 相似文献
3.
The energy dependence of the fusion cross section has been measured over the range Ec.m. = 3.05–6.88 MeV by detecting the γ-rays from residual nuclei in a 4π geometry. Analyzing the 1.37 MeV photopeak, originating from , the cross sections for 24Mg+2n channel were also deduced. The measured fusion cross sections have been compared with those for 12C + 12C and 12C + 13C systems and found to be significantly different. For 13C+13C the fusion cross sections agree with the standard optical-model prediction down to the lowest measured energies, while for 12C + 12C and 12C + 13C they are, at the lowest energies, too low. It is suggested that the unpaired valence nucleons facilitate fusion at energies well below the Coulomb barrier. 相似文献
4.
By γ-γ coincidence measurements following the 57Fe(12C, 2nγ) reaction at E12C = 40 MeV several new states above 1.5 MeV excitation energy in 67Ge have been established. Spin and parity assignments on the basis of the angular distribution, linear polarization and γ-ray yield function indicate very similar structures in 67, 69Ge. The positive-parity states can be followed up to the state at Ex = 3.07 MeV followed by a sequence of negative-parity high-spin states at nearly the same excitation energy relative to the single-particle state as in the neighbouring nucleus 69Ge where these states were found to have strong single-particle admixtures. A reinvestigation of the spin of the Ex = 2.75 MeV level in 69Ge resulting in a change of its spin from and for all spins above, removed the discrepancy concerning the spin assignments of corresponding levels in 67, 69Ge. The excitation pattern of the Ge isotopes with 34 ≦ N ≦ 39 clearly indicate same structures probably due to the strong competition between collective and single-particle excitations along the whole chain similar to the results for the Zn isotopes. 相似文献
5.
H.H. Eggenhuisen L.P. Ekström G.A.P. Engelbertink H.J.M. Aarts W.G.J. Langeveld 《Nuclear Physics A》1978,299(1):175-188
Yrast states of 41K and 41Ca have been investigated with the 26Mg(18O, p2nγ)41K and 26Mg(18O, 3nγ)41Ca reactions at a beam energy of 34 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of , , , , and to the 41K levels at Ex = 1.68, 2.53, 2.76, 2.77, 4.27 and 4.98 MeV and of to the 41Ca levels at Ex = 3.20, 3.37 and 3.83 MeV, respectively, have been obtained. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The main features of the 41K and 41Ca level and decay schemes are reproduced in a 2p-1h and 3p-2h shell-model calculation. 相似文献
6.
Energy and angular distributions of neutrons from the reaction 14C(d, n)15N have been measured at 6.5 MeV deuteron energy. The DWBA analysis yielded l-values and absolute spectroscopic factors for fifteen states in 15N below 10 MeV excitation energy. For the 9.23 MeV level Jπ is determined to be + or +, for the 9.93 MeV level the data suggest . The spectroscopic factors are in qualitative agreement with pure jj coupling and in semi-quantitative agreement with shell-model calculations. 相似文献
7.
P. Sperr D. Evers K. Rudolph W. Assmann E. Spindler P. Konrad G. Denhöfer 《Physics letters. [Part B]》1974,49(4):345-347
A strong selectivity of the 12C(12C,n)23Mg reaction is observed in a resonance at . The neutron spectra and n-γ coincidence measurements show evidence for population of high-spin members of the ground- state rotational band in 23Mg. 相似文献
8.
H.J.M. Aarts G.A.P. Engelbertink H.H. Eggenhuisen L.P. Ekström 《Nuclear Physics A》1979,321(2):515-532
High-spin states of 38Ar have been studied with the 35Cl(α, pγ)38Ar reaction at Eα = 18 MeV and with the 24Mg(16O, 2pγ)38Ar reaction at . The 38Ar level scheme is obtained with the former reaction from a proton-γ coincidence measurement. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization experiments have been performed with a Ge(Li)-Na(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of to the 38Ar levels at Ex = 7.51, 8.08, 8.57, 8.97, 10.17 and 11.61 MeV, respectively, are obtained. The 8.57 MeV, 8+ level has a mean life below 0.8 ps. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The experimental results are compared with shell-model calculations. 相似文献
9.
Sugimitsu Tsuyoshi 《Nuclear Physics A》1974,224(1):199-220
Excitation functions of γ-rays from the 75As(p, n)75Se reaction were measured with 2.0 to 3.6 MeV protons to establish the level scheme of 75Se up to about 1.5 MeV excitation energy. Internal conversion electrons following the same reaction were measured at 4.5 and 5.0 MeV proton energy. Using theoretical predictions of the statistical compound nucleus model together with deduced internal conversion coefficients, unique spin assignments were obtained for the and levels. Probable spins were proposed to the for one of the doublet and or for the other), 579.4 or , or and or levels. Alow-lying level was tentatively assigned at 133.2 keV energy. It was found that a low-lying level which appears systematically in other odd Se nuclei is absent in 75Se. 相似文献
10.
L.K. Fifield T.J.M. Symons C.H. Zimmerman M.J. Hurst F. Watt K.W. Allen 《Physics letters. [Part B]》1977,68(2):125-128
Levels at 7.17, 8.29, 8.96 and 9.88 MeV in 19F have been assigned spin and parity , , and , respectively, from resonance strength and γ-ray angular distribution measurements employing the 15N(α,γ) 19F reaction. An earlier assignment of to the 8.96 MeV level is incorrect. The measured properties of the states are compared with the results of both SU (3) shell model and cluster model calculations. 相似文献
11.
Total cross sections for the reaction have been measured by observation of the positron decay of the residual 13N nuclei. These cross sections, covering the c.m. energy range 5.4 ≦ E ≦ 9.9 MeV, allow determination of reaction rates of astrophysical interest at temperatures in the neighborhood of 4 × 109°K. 相似文献
12.
H.H. Eggenhuisen L.P. Ekström G.A.P. Engelbertink H.J.M. Aarts 《Nuclear Physics A》1978,305(1):245-261
High-spin states of 39K and 42Ca have been investigated with the 28Si(16O, αpγ)39K and 28Si(16O, 2pγ)42Ca reactions at a beam energy of 45 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. High-spin states of 39K at Ex = 7.14,7.78and8.03 and of 42Ca at Ex = 7.75MeV are established. Unambiguous spin-parity assignments of to the 39K levels at Ex = 5.35, 5.72, 6.48, 7.14, 7.78 and 8.03 MeV and of 6?, 7?, 8?, 9? and(8, 10)? to the 42Ca levels at Ex = 5.49, 6.15, 6.41, 6.55 and 7.37 MeV, respectively, have been obtained. Further spin-parity restrictions, lifetime limits, excitation energies, branching ratios and multipole mixing ratios are reported. Discrepancies with previous Jπ assignments are discussed in detail. 相似文献
13.
The nuclear structure of 5125Mn was studied by γ-ray spectroscopy in the 54Fe(p, α)51 Mn reaction (Ep = 9.0–13.2 MeV) and the 14N+39K, 16O+40Ca and 14N+40Ca fusion-evaporation reactions (Ebeam = 36 MeV). In the 54Fe(p, αγ)51Mn reaction γ-rays were detected in coincidence with α-particles emitted near 180°; mean lifetimes and γ-ray mixing and branching ratios were deduced from Doppler shift attenuation and α-γ angular correlation measurements, respectively. Definite spin assignments are: 237 and 2416 keV, ; 1140 keV, ?; 1488 keV, ?; 1825 and 2140 keV, ?. The results for other states below 3 MeV are consistent with the existence of rotational bands (/kh2/2/OI/t~ 95 keV) built on the (+) 1817 keV and + 2276 keV hole states. The various measurements together with an earlier value for the lifetime of the first-excited state determine unambiguously the B(M1) and B(E2) values for all of the decay branches of the ?, ? and ? lowest three excited states. From the γ-singles and γ-γ coincidence observations with fusion-evaporation reactions, the yrast cascade proceeds through these three states and higher states at 2957, 3250,3680 and 4139 keV which are suggested to have , ?,? and ?, respectively. The various experimental results for the ? → (?) yrast states are in good overall agreement with shell-model calculations in the (f1 space. 相似文献
14.
H.H. Eggenhuisen L.P. Ekström G.A.P. Engelbertink H.J.M. Aarts J.A.J. Hermans 《Nuclear Physics A》1977,285(1):167-188
Yrast levels in 40K and 40Ar have been investigated with the 26Mg(16O, pnγ)40K and 26Mg(16O, 2pγ)40Ar reactions at a beam energy of 34 MeV. Gamma-ray angular distribution and γ-γ coincidence measurements have been performed with a high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer. Gamma-ray linear polarizations have been measured with a three-crystal Ge(Li) Compton polarimeter. The 40K decay scheme involves new high-spin levels at Etx = 4365.6±0.3, 4875.6±0.4 and 6227.0±0.5 keV with lifetime limits of < 1, < 1 and < 2ps, respectively. Unambiguous spin-parity assignments of to the 40K levels at Ex = 0.89, 2.88, 4.37, 4.88 and 6.23 and of levels at Ex = 2.89 and 3.46 MeV, respectively, have been obtained. Branching ratios and multipole mixing ratios are reported. 相似文献
15.
Excitation functions of the capture reaction 12C(p, γ0)13N have been obtained at θγ = 0° and 90° and Ep = 150–2500 keV. The results can be explained if a direct radiative capture process, E1(s and d → p), to the ground state in 13N is included in the analysis in addition to the two well-known resonances in this beam energy range and 1699 . The direct capture component is enhanced through interference effects with the two resonance amplitudes. From the observed direct capture cross section, a spectroscopic factor of C2S(l = 1) = 0.49 ± 0.15 has been deduced for the ground state in 13N. Excitation functions for the reaction have been obtained at θγ = 0° and 90° and Ep = 610–2700 keV. Away from the 1699 keV resonance the capture γ-ray yield is dominated by the direct capture process E1 (p → s) to the unbound state. Above Ep = 1 MeV, the observed excitation functions are well reproduced by the direct capture theory to unbound states (bremsstrahlung theory). Below Ep = 1 MeV, i.e., Ep → 457 keV, the theory diverges in contrast to observation. This discrepancy is well known in bremsstrahlung theory as the “infrared problem”. From the observed direct capture cross sections at , a spectroscopic factor of C2S(l = 0) = 1.02 ± 0.15 has been found for the unbound state. A search for direct capture transitions to the and unbound states resulted in upper limits of C2S(l = 1) ≦ 0.5 and C2S(l = 2) ? 1.0, respectively. The results are compared with available stripping data as well as shell-model calculations. The astrophysical aspect of the 12C(p, γ0)13N reaction also is discussed. 相似文献
16.
A complete coupled-reaction-channel method is applied to molecular orbital phenomena of the valence nucleon in the scattering of 12C on 13C, i.e. in elastic and inelastic transitions to the single-particle states of 13C1(gr., ; 3.086 MeV, ; 3.854 MeV, ) with consi 12C core-exchange process. The system is analyzed with respect to the occurrence of higher-order transitions of the direct (inelastic) and transfer (core-exchange) processes of the valence nucleon in 13C. It is found in the states of positive total parity that the transfer and direct processes act additively and lead to extreme higher-order steps of the multi-interactions, if the ground state (1p) and the excited states (2s and 1d) are taken into account. Transitions between the excited subchannels show strong-coupling effects, which are due to the reorientations of the d orbitals. The reoriented system couples to the ground channel (l-parity mixing) so favourably that the multi-interaction series hardly converges. The consequence of these observations are discussed in terms of the formation of molecular nucleon orbitals based on the polarization and the hybridization of the original orbitals. 相似文献
17.
The characteristics of the decay sequences are discussed for the two sharp levels of 12C1 at excitation energies of 12.7 MeV (Jf = 1+, T = 0) and 16.11 MeV (Jf = 2+, T = 1), which are observed prominently in this decay process. The transition rates for these processes and the angular correlations in the final four-particle state αααπ? are discussed quantitatively, using the intermediate coupling model for both the 12ΛB and 12C1 systems, as a function of the 12ΛB spin J. Three distinct tests are proposed, which are sensitive to the spin J for ground-state 12ΛB, and which have been used by the European K? Collaboration to deduce that J = 1 for 12ΛB. The implications of this conclusion for the ΛN and ΛNN interactions are briefly discussed. 相似文献
18.
N.H. Hamann 《Nuclear Physics A》1985,433(2):198-214
Excited states of 16F have been investigated with the reaction 14N(3He, np)15O at E = 10.5 and 12 MeV in kinematically complete experiments. Proton groups corresponding to the decays of intermediate 16F states were observed at various angles with counter telescopes in time coincidence with the associated neutrons detected at θnlab = 0° with a time-of-flight spectrometer. Excitation energies and decay widths Γp0 of these states have been extracted from the proton spectra. Lower limits for the orbital angular momentum in the decay channel and for the spin of the states have been deduced from the obtained angular correlations. By comparison with the reaction 14N(3He, pp)15N measured at E = 13 MeV, pairs of parent/16O analog states have been identified. Jπ assignments and shell-model configurations are discussed on the basis of the selectivity of the reactions measured. 相似文献
19.
A.J. Rutten A. Holthuizen W.A. Sterrenburg C.P.M. Van Engelen G. Van Middelkoop 《Nuclear Physics A》1981,359(2):442-454
The g-factor and mean life of the state at 3.85 MeV in 13C have been determined by a recoil-into-vacuum plunger measurement. The state was populated by the 2H(12C, p) reaction at E = 15.0 MeV. The analysis of the time-differential deorientation effect on the p-γ angular correlation leads to a g-factor of . For the mean lifetime a value of τ = 12.2 ± 0.4ps is obtained. 相似文献
20.
An isomeric 587.3 keV transition was investigated using several target-ion combinations: 197Au+12C, 193Ir+16O and 196Pt+15N. From the measured excitation functions for the At reaction it follows that this transition belongs to 204At. The isomeric level is ascribed to the 10? state of the configuration π(h)3ν(i)?1. 相似文献