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1.
The cross section for the reaction 12C(12C, n)23Mg has been measured in the energy range Ec.m. = 3.54?4.94 MeV by counting the delayed γ-rays from 23Mg decays (half-life = 11.57 sec), and a theoretical model has been employed to extrapolate the results to threshold (Ec.m = 2.60 MeV). By combining these results with previous measurements of the reactions 12C(12C, p)23Na and 12C(12C, α)20Ne, the neutron branching ratio in the energy interval from threshold to 8 MeV is deduced, and a thermal average is computed that should be valid for use in astrophysical environments characterized by temperatures in the range (0.5–5) × 109 °K. The neutron branching at temperatures appropriate to hydrostatic carbon burning in stars (T ≈ 109 °K) is found to be much smaller than previously estimated. 相似文献
2.
《Physics letters. [Part B]》1986,173(1):39-42
A detailed phase shift analysis of 12C + 12C elastic data from Ecm = 5.5 to 33 MeV has revealed a pronounced sequence of gross structure resonances. They appear to form a rotational band from l = 0 to at least 16ħ, and are the dominant structural feature of the 12C + 12C reaction. The resonances are parametrized by a Breit-Wigner analysis and are simulated by shape-resonances in an optical potential with a secondary minimum at large radius. They are discussed in terms of shape-isometric doorway states in 24Mg. 相似文献
3.
In order to understand the α-nucleus interactions for the α+12C~α+16O systems systematically, α scattering from 12C is studied in a microscopic coupled-channel model using a folding potential and realistic microscopic wave functions of 12C. The experimental angular distributions of elastic and inelastic scattering to the 2+(4.43 MeV), 3? (9.64 MeV), and 0 2 + (7.66 MeV) states in the range of E α = 41–172.5 MeV are analyzed. 相似文献
4.
We have studied the heavy-ion radiative capture reaction12C(12C,γ)24Mg forE cm =4.7–6.0 MeV. Transitions to the ground-, first and unresolved second and third excited states in the final nucleus24Mg have been observed with cross sections as low as 1 nb/sr. Forγ 1 two strong resonance-like structures at 4.9 and 5.0 MeV were found correlated in energy with established 2+ resonances. Statistical model calculations cannot account for the observed yield. The branching ratioΓ γ /Γ associated with theγ 1 decay channel of the 5 MeV resonance was estimated to be 1.1·10?5 yielding aγ-ray strength of 0.8 eV. The experimental result is in agreement with calculations based on the generator coordinate method where broad barrier resonances are viewed as short lived states of quasimolecular nature. 相似文献
5.
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
6.
K. U. Kettner H. Lorenz-Wirzba C. Rolfs 《Zeitschrift für Physik A Hadrons and Nuclei》1980,298(1):65-75
The reaction12C+12C has been studied in the energy rangeE cm=2.45–6.15 MeV byγ-ray spectroscopy. Gamma-ray transitions from a large number of excited states in20Ne,23Na and23Mg were observed, which show strong and rapid yield variations. When the influence of the Coulomb barrier is removed, these structures appear superimposed on a flat reaction yield, which does not show a strong increase at low energies, in contrast to previous work. These results obviate the need for the hypothesis of absorption under the barrier at least down toE cm=2.45 MeV. The nuclear and astrophysical aspects of the data are discussed. 相似文献
7.
The cross section for the reaction 12C(α, γ)16O has been measured for a range of c.m. energies extending from 1.41 MeV to 2.94 MeV, by using 12C targets of high isotopic purity, large NaI(T1) crystals, and the time-of-flight technique for the suppression of prompt neutron background and time-independent background. Gamma-ray angular distributions were measured at c.m. energies of 2.18, 2.42, 2.56 and 2.83 MeV. By means of theoretical fits, which include the coherent effects of the 1? states of 16O at 7.12 MeV, 9.60 MeV, and those at higher energies, the electric-dipole portion of the cross section at astrophysically relevant energies has been determined. A three-level R-matrix parametrization of the data yields an S-factor at Ec.m. = 0.3 MeV, S(0.3 MeV) = 0.14+0.14?0.12 MeV · b. A “hybrid” R-matrix optical-m parameterization yields S(0.3 MeV) = 0.08+0.05?0.04 MeV · b. This S-factor is of crucial importance in determining the abundances of 12C and 16O at the end of helium burning in stars. 相似文献
8.
The 12C + 12C fusion cross section has been studied over the energy range 2.46 ≦ Ec.m. ≦ 5.88 MeV. The yields of the γ-rays emitted from the first excited states of 23Na and 20Ne, following 24Mg compound nucleus decay via proton- and α-emissions, were measured using a Ge(Li) detector. The fusion cross section was obtained by normalizing these yields to previously reported 12C(12C, p)23Na and 12C(12C, α)20Ne cross sections. The data indicate that the cross section below 3.5 MeV is dominated by two or more resonances, and that the average trend in this energy region does not show the absorption-under-the barrier features of the optical model. For astrophysical extrapolations to lower energies, the new results are consistent with the extrapolation proposed by Fowler, Caughlan and Zimmerman. 相似文献
9.
Ahmed A. Ebrahim 《Brazilian Journal of Physics》2011,41(2-3):146-153
Angular distributions of differential cross sections for the 12C(π ±, π ±)12C and 12C(π ±, π ±)12C* reactions at pion kinetic energy ranging from 50 to 260 MeV have been analyzed with the 3α-particle model of 12C. The model provides good fits to a wide range of data. Differential cross sections for inelastic transitions to the (2?+?; 4.44 MeV) and (3???; 9.64 MeV) states in 12C are computed and the deformation lengths δ 2 and δ 3 are extracted. It is found that the extracted deformation lengths are sensitive to the nuclear model used and similar to the corresponding values found with other probes and nuclear models. 相似文献
10.
12C + 28Si elastic scattering angular distributions are smooth functions, relatively easily fit by optical potential predictions, at laboratory bombarding energies, E1ab, within ≈ 10 MeV of the Coulomb barrier (i.e. up to E1ab ≈ 27 MeV). Between E1ab = 27 and 36 MeV the angular distributions show pronounced oscillatory structure which is not easily fit with an optical potential. No optical potential has been found to give a very good account of all the angular distributions simultaneously; the best simultaneous fit to all the data was achieved with a surface-transparent potential whose real and imaginary well depths are energy dependent. 相似文献
11.
12.
R.E. Chrien M. May H. Palevsky R. Sutter P. Barnes S. Dytman D. Marlow F. Takeutchi M. Deutsch R. Cester S. Bart E. Hungerford T.M. Williams L.S. Pinsky B.W. Mayes R.L. Stearns 《Physics letters. [Part B]》1979,89(1):31-35
States of 12ΛC formed in the (K?, π?) reaction have been studied for momentum transfers up to 260 MeV/c, using an incident K? beam of 800 MeV/c momentum. The angular distributions for the g.s. and for a peak at 11 meV have been measured between 0° and 19° in the laboratory. Limits on the splitting of the 11 MeV peak and on the formation of low-lying excited states are given. 相似文献
13.
We observe a yield to the 1+T = 1 level in 12C at 15.11 MeV in the isospin forbidden 12C(d, d') and 10B(α, d) reactions at about 1 % of the yield to the 1+T = 0 level at 12.71 MeV. Observed yields to the T = 12+ level at 16.11 MeV in both reactions at about half the yield to the 15.11 MeV level preclude attributing this observed isospin violation entirely to final state mixing. From the ratios of the spectroscopic factors for the 12.71 and 15.11 MeV levels in 12C and the ground state of 12B from the 13C(d, t) and 13C(d, 3He) reactions, we find a charge dependent matrix element between the 1+ states in 12C of 179 ± 75 keV. 相似文献
14.
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
15.
Excitation functions for 12C(6Li, 6Li)12C (gs, 4.43 MeV) have been measured at 10 angles (40° ? θcm ? 160°) over the energy range 20 MeV < Elab < 36 MeV. A single anomaly of width Γ ≈ 800 keV is observed at Elab = 22.8 MeV. The results casts doubts on the resonant two-step α-exchange mechanism suggested to occur in this system. 相似文献
16.
D. Evers G. Denhöfer W. Assmann A. Harasim P. Konrad C. Ley K. Rudolph P. Sperr 《Zeitschrift für Physik A Hadrons and Nuclei》1977,280(3):287-307
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
17.
18.
Dr. M. A. Fawzi 《Zeitschrift für Physik A Hadrons and Nuclei》1972,250(2):120-144
Alpha particle unstable states in12C have been investigated using the three reactions14N(d, α′)12C,14N(d, α′α)8Be and12C(α, α′)12C. Excitation cross sections and angular distributions have been measured for the reactions14N(d, α′) at 52 MeV and12C(α, α′) at 90 MeV. For a few angle pairs the α-decay of excited states in12C have been observed in a14N(d, α′α) correlation measurement. The reactions selectively excite onlyT=0 states. A previously undetected level with a large α-decay width (Γ=1.2 MeV) has been observed at 15.62 MeV excitation. This level shows up clearly in both reactions and is further distinguished from the nearby 14.08 state in the correlation measurement because of the distinctly different energy distributions of the decay products. On the basis of a particle angular distributions the 15.62 MeV level was assigned spin and parity 4+ and the level at 14.08 was assigned 3?. The latter differs from the value suggest by earlier work. Comparison with DWBA calculations indicates that angular distributions of all other prominent levels are in agreement with their earlier assignments. Two levels at 19.20 and 20.30 MeV (both Γ?0.4 MeV) and three further levels at 21.81, 22.7 and 24.24 MeV also decay predominantly by α-emission. 相似文献
19.
Ch. Setzensack H. Hick K. Tanaka H. Morinaga 《Zeitschrift für Physik A Hadrons and Nuclei》1982,307(2):109-112
The58Ni(12C,γ)70Se capture reaction was studied with beam energies ofE 12C=30 to 42 MeV. The capture events were identified by means of the residual activity produced in the reaction. At a beam energy of 38 MeV the capture cross section has been determined to 1.5±0.7 μb. AtE 12C=30, 34 und 42 MeV we established upper limits of 0.3, 0.5 and 0.6 μb, respectively. The experimental results are compared with a statistical model calculation. 相似文献
20.
G. Ingold H. G. Bohlen M. Clover H. Lettau H. Ossenbrink W. von Oertzen 《Zeitschrift für Physik A Hadrons and Nuclei》1982,309(2):135-142
Level structure of102Cd has been studied via both102In decay and nuclear reactions. Using92Mo+14N at 86 MeV, the nucleus102In was identified and its decay (T 1/2=24 ±4s) studied with the aid of on-line mass separation techniques. Levels of102Cd were also populated with92Mo+12C at 50 MeV and102Pd+3He at 35 MeV reactions and investigated by means of standard in-beam techniques. A level scheme including states up to 4.5 MeV excitation energy is proposed and then discussed in the frame of available calculations. 相似文献