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1.
Total fusion cross sections have been measured for the following reactions and energy intervals: 12C + 10B, Ec.m. = 2.10–5.38 MeV; 12C + 11B, Ec.m. = 2.10–5.99 MeV; 14N + 10B, Ec.m. = 2.64–5.97 MeV. Absolute cross sections were extracted from the prompt γ-rays emitted by the various residual nuclei and measured by two large NaI detectors. No resonance structure was observed in the three reactions. The elastic scattering excitation function was also measured at θc.m. = 90.4° for 12C + 10B over the energy range Ec.m. = 3.18–6.82 MeV. Optical model potentials were found which could consistently describe both the fusion and elastic scattering data. 相似文献
2.
Total fusion cross sections for the 10B + 12C and 11B + 12C reactions have been determined over a 5 MeV (c.m.) energy range extending to ≈ 3 MeV below the Coulomb barrier. Absolute γ-ray yields for specific transitions in the de-excitation of the heavy products following compound nucleus decay were measured using a Ge(Li) detector. Statistical model calculations of the decay modes of the compound nucleus have been used to deduce, from the γ-ray data, cross sections for single proton, neutron and α-particle emission, and to determine total cross sections for compound nucleus formation. No evidence has been found for sub-Coulomb resonances in either reaction. The total reaction cross sections are compared with optical model calculations using different parameter sets and the observed trend in the very low energy cross sections is discussed relative to other reactions in the same mass region. 相似文献
3.
Total fusion cross sections for the 14N+12C and 14N+16O reactions have been measured in the c.m. energy ranges 3.6–9.2 MeV and 5.6–12.6 MeV, respectively. Cross sections are also reported for important individual exit channels which were studied by observing discrete γ-ray transitions in the evaporation residues with a Ge(Li) detector. Excitation functions reveal no evidence of intermediate structure in these reactions. The fusion cross sections for 14N induced reactions on 12C, 14N and 16O are compared with an IWB calculation using recently published semi-empirical parameters for the real ion-ion interaction potential. Such a comparison supports the view that low-energy fusion studies may be sensitive probes of the nuclear potential in the interior of the interaction barrier. 相似文献
4.
The total reaction cross sections for 11B + 9Be and 13C + 9Be have been measured by the total γ-ray yield method over the energy intervals Ec.m. = 1.4–4.4 MeV and Ec.m. = 2.0–5.2 MeV, respectively. The cross sections for the neutron transfer reactions 11B(9Be, 8Be)12B, leading to the 12B 0.953 and 1.674 MeV states, and 13C(9Be, 8Be)14C, leading to the 14C 6.094, 6.728 and 6.902 MeV states, have been obtained from the yields of the characteristic γ-rays. The α-transfer reaction 11B(9Be, 5He)15N, leading to many unresolved 15N states, has been observed with large cross section. There is, however, no evidence for the 13C(9Be, 5He)17O transfer process in the 17O + nα channels. This different behaviour of the 11B + 9Be and 13C + 9Be systems seems to indicate that the α-transfer reaction at sub-barrier energies is not a direct transfer process, and that it probably occurs via molecular state formation. 相似文献
5.
Particle and particle-γ measurements were performed to determine the cross sections for population of the 8.87 (2?), 10.35 (4+), 11.08 (3+) and 11.096 MeV (4+) states in 16O by the 12C(6Li, d) and 13C(6Li, t) reactions in the energy range from 20—34 MeV. In general, statistical compound nuclear calculations correctly predict the magnitude of the cross sections of the unnatural parity states and underpredict those for the natural parity states. The population of the 10.35 MeV 4+ state in the 13C(6Li, t) reaction is correctly predicted by these calculations. These measurements support earlier claims that the large 12C(6Li, d) cross section to the 11.096 MeV 4+ state is a result of multistep processes. 相似文献
6.
Calculations are presented of the elastic scattering and fusion cross sections for the astrophysically interesting reactions 12C+12C, 12C+16O and 16O+16O. The calculations are performed using the incoming wave boundary condition (IWB) and a real ion-ion interaction potential. The results are compared with the available experimental data for the energy region near and below the Coulomb barrier. With values of two adjustable potential parameters (the radial position of the l = 0 barrier and the diffuseness) determined by fitting elastic scattering data, good agreement is obtained for the average energy dependence of the 12C+12C and 12C+16O fusion cross sections. In the case of 16O+16O, both the calculated absolute magnitude and the energy dependence of the fusion cross section are inconsistent with the data and this discrepancy is discussed. 相似文献
7.
A measurement of the residues from the 12C + 7Li reaction has been obtained for 7Li energies from 10 to 38 MeV. From these measurements the fusion cross sections and critical angular momenta for the 12C + 7Li system have been deduced. Cross sections for the 7Li(12C, t)16O reaction have been obtained for 12C energies from 54 to 62 MeV at θlab = 2.7°. The critical angular momenta obtained from the fusion cross sections have been used to perform Hauser-Feshbach calculations for the 12C(7Li, t)16O reaction. These calculations have been compared to measured angular distributions over a wide energy range. By comparing the fusion cross sections required by the Hauser-Feshbach calculations to fit the 12C(7Li, t)16O(8.87 MeV) reaction and the measured residue cross section it is estimated that at least 80 % of the measured residues are fusion products. The calculations also indicate that direct processes dominate the population of many 16O levels at forward angles and the 10.35 MeV state at backward angles. The necessity for using a critical angular momentum in Hauser-Feshbach calculations is discussed. 相似文献
8.
The reaction 12C(12Li, α)14N was studied to investigate the isospin mixing of high-lying levels in 18F. Excitation functions and angular distributions of the α-transitions to the ground, first and second excited states in 14N were measured for bombarding energies from 3.2 to 8.0 MeV. The isospin-forbidden cross section for the excitation of the lowest T = 1 state in 14N at 2.31 MeV was found to lie between 1–2 % of that of the allowed transitions. A partial wave analysis of the α1 angular distribution data revealed a strong resonance with Jπ = 2+ at Ex = 15.99 MeV. Arguments are presented which tentatively identify this resonance as being due to two close-lying 2+ levels with different isospin. 相似文献
9.
Cross sections for several (n, 2n) reactions at 14 Mev 总被引:1,自引:0,他引:1
D. R. Nethaway 《Nuclear Physics A》1972,190(3):635-644
Precision measurements of the cross sections of the (n, 2n) reactions to produce 44mSc, 88Y, 89Zr, 92Nb, 150Eu(35y), 168Tm, 174m+gLu and 196Au were made for a range of neutron energies from 13.7 to 15.0 MeV. The samples were irradiated at various positions on the surface of a 20 cm radius sphere centered at the 2H–3H neutron source. This allowed a range of neutron energies to be obtained with good energy resolution. The 27Al(n, )24Na reaction was used to monitor the neutron fluence in the target samples. Particular attention was given to the accurate measurement of the (n, 2n) products, using calibrated Ge(Li) and NaI(Tl) detectors. An uncertainty of about ±5% is assigned to the results, except those for 150Eu and 174Lu, which have an additional uncertainty in their decay schemes. 相似文献
10.
Đ Miljanić E. Andrade J. Hudomalj-Gabitzsch G.S. Mutchler G.C. Phillips 《Nuclear Physics A》1977,290(1):27-44
The three-body reactions induced by low energy deuterons on 6Li have been studied. The contributions from the sequential processes through the excited states of the intermediate 4He, 5Li, 6Li and 7Li nuclei dominate the coincidence spectra. The quasi-free d + d → d + d, d + α → d + α, and d + d → p + t reactions have been observed and compared with plane wave impulse approximation (PWIA) calculations. 相似文献
11.
12.
Total fusion cross sections have been measured for 18, 17, 16O + 27Al systems at bombarding energies 27–42 MeV. The evaporation residues were detected in the angular range 4°–25° (lab) using a counter telescope. Barrier radii extracted from total fusion and elastic scattering cross sections are found to increase with the projectile mass. The effect of the yrast levels on the isotopic yields in the evaporation cascade is investigated. 相似文献
13.
C. Beck F. Haas R.M. Freeman B. Heusch J.P. Coffin G. Guillaume F. Rami P. Wagner 《Nuclear Physics A》1985,442(2):320-360
Kinetic energy spectra, angular distributions, and elemental yield distributions have been measured for the 12 C + 16 O, 12 C + 18 O and 13 C + 17 O reaction products over an energy range from 2 to 7 times the Coulomb barrier energy. A careful kinematic analysis of the evaporation residues and comparisons with statistical-model calculations show that fusion proceeds with full momentum transfer followed by a statistical decay of the compound nucleus. The competition between complete fusion process and peripheral reactions in the 12 C + 16 O system is less important than for the 12 C + 18 O and 13 C + 17 O reactions. The unexpectedly high 12 C + 16 O complete fusion cross sections are related to the possible occurrence of a superdeformation of the 28 Si compound nucleus. 相似文献
14.
The 16O + 9Be reactions have been studied from Ec.m. = 2.0 MeV to 5.1 MeV, an energy near the top of the Coulomb barrier. The cross section for the neutron transfer reaction 9Be(16O,17O1 (0.87 MeV))8Be has been measured over this range by detecting the prompt 0.87 MeV γ-rays. The total fusion cross section has been determined from Ec.m. = 2.8 to 5.1 MeV by observing individual γ-ray transitions in the evaporation residues with a Ge(Li) detector, and then summing the separate yields. Direct processes are found to dominate the reaction yield below Ec.m. = 4 MeV. A comparison of the energy dependence of the fusion cross section for this reaction and the 12C + 13C reaction, which proceeds via the formation of the same compound nucleus, 25Mg, reveals differences at sub-barrier energies. Optical model and incoming-wave boundary condition calculations are presented. Data have also been obtained for the near optimum Q-value neutron-transfer reactions 9Be(12C, 13C1)8Be and 9Be(19F, 20F)8Be, and these are discussed in terms of a simple model of sub-barrier direct reactions. 相似文献
15.
Y.-D. Chan H. Bohn R. Vandenbosch K.G. Bernhardt J.G. Cramer R. Sielemann L. Green 《Nuclear Physics A》1978,303(3):500-520
The γ-ray yield of discrete transitions from evaporation residues formed in the reaction 16O + 12C has been measured between Ec.m. = 6 and 31 MeV. Data for a backed and self-supporting target were compared to check the consistency of the observed results. Channels in which α-particles are emitted carry most of the oscillatory structure which was previously observed for the total fusion cross section. Relative yields of the different evaporation channels can be reproduced by statistical model calculations. Optical model calculations with a parity-dependent exchange contribution reproduce the periodicity of the gross structure but underestimate the magnitude of the oscillations. 相似文献
16.
The cross sections for the 10B(13C, 12C)11B neutron-transfer reaction, leading to the 11B 4.45 and 6.74 MeV and 12C 4.44 MeV excited states, and for 13C + 10B fusion have been measured by the characteristic and total γ-ray yield methods, respectively, over the energy (c.m.) interval 2.4–5.8 MeV. For 13C + 11B, with no transfer reactions present, the fusion cross sections have been measured between Ec.m. = 2.3 and 6.4 MeV. The fusion cross sections for 13C + 10B and 13C + 11B are found to be almost equal and slightly enhanced with respect to those for 12C + 10B and 12C + 11B. 相似文献
17.
The elastic scattering of 6Li ions from a variety of targets, A = 12 to 208, has been measured at a bombarding energy of 50.6 MeV. The angular distributions are characteristic of strongly absorbed particles, such as 3He and heavy ions, and less diffractive than for 4He. A simple optical model with Woods-Saxon real and imaginary volume potentials is adequate to fit the data. Spin-orbit effects are not apparent in the data. 相似文献
18.
Closely spaced angular distributions have been measured for the reaction between Eα = 17.39 and 20.5 MeV in a search for 8+ strength in 16O. No evidence of 8+ strength is found, but evidence is found for a narrow 7? resonance at 21.52 MeV excitation. 相似文献
19.
J. Cook L.C. Dennis K.W. Kemper T.R. Ophel A.F. Zeller C.F. Maguire Z. Kui 《Nuclear Physics A》1984,415(1):114-126
The elastic scattering of 6Li + 16O at 48 MeV has been measured and fitted with an optical model calculation. Measurements have been made of the 16O(6Li, α)F reaction at 48 MeV populating the 1+ g.s., 3+ 0.927 MeV and 5+ 1.122 MeV states in 18F. The data exhibit cross sections at large angles comparable to those at forward angles, and have been compared with exact finite-range DWBA calculations. Exchange contributions were included for the 1+ g.s. and were unable to account for the large-angle data. Calculated statistical compound nucleus cross sections were approximately a factor of 100 below the data. The same conclusions are reached for previously published data at 34 MeV. 相似文献
20.
Elastic scattering data have been measured for the 7Li + 90Zr, 6Li + 90Zr, and 6Li + 91Zr systems at E(Li) = 34 MeV. Inelastic scattering data for the 7Li + 90Zr and 6Li + 90Zr systems were also measured for the 2+(2.18 MeV) and 3?(2.75 MeV) states in 90Zr and the state in 7Li. Optical model analyses of the elastic scattering data and DWBA analyses for the states in 90Zr were performed. The deduced deformation lengths for the 2+ state agreed with those extracted in other studies but the deformation length for the 3? state was smaller. The 90Zr(7Li, 6Li)91Zr angular distributions were measured for the 1.21 and 2.03 MeV states and the 2.19 MeV doublet in 91Zr. Also, 90Zr(7Li, 6He)91Nb angular distributions were measured for the ground states, 0.10, 3.41 and 4.82 MeV states in 91Nb. The transitions well matched in angular momentum were described by finite-range DWBA calculations, while other transitions displayed the same phase problems seen with heavier ions. The extracted spectroscopic information was consistent with the results of other reaction studies. At the present energy, it was not possible to determine whether the l = 1 phase problem that occurs for heavy-ion single-nucleon transfer reactions on 2s-1d shell nuclei occurs in 91Zr also. 相似文献