共查询到20条相似文献,搜索用时 46 毫秒
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G. Auger G. Albouy C. Roulet H. Sergolle A. Kerek Th. Lindblad 《Zeitschrift für Physik A Hadrons and Nuclei》1980,294(4):319-322
The isotope shift in the Ca-intercombination line withλ=6,573 Å was measured for all isotopes between40Ca and48Ca with the only exception of 47Ca. The combination of the results with muonic x-ray data yields highly accurate values for the changes of the mean square nuclear charge radii. In addition, the nuclear quadrupole moments of the three isotopes41Ca,43Ca and45Ca have been determined from the hyperfine structure splitting of the 4s 4p 3 P 1 state. 相似文献
3.
D. J. Horen J. Lisantti R. L. Auble F. E. Bertrand B. L. Burks E. E. Gross R. O. Sayer D. K. McDaniels K. W. Jones J. B. McClelland S. J. Seestrom-Morris L. W. Swenson 《Zeitschrift für Physik A Hadrons and Nuclei》1989,333(1):39-43
Spin-dipole strength in40Ca has been studied by inelastic scattering of 500-MeV protons and the dipole response in40Ca is compared with the spin-dipole data from the40Ca(p, n) reaction and nonspin-dipole data from photonuclear studies. 相似文献
4.
H. Löhner H. Eickhoff D. Frekers G. Gaul K. Poppensieker R. Santo A. G. Drentje L. W. Put 《Zeitschrift für Physik A Hadrons and Nuclei》1978,286(1):99-106
Elasticα-scattering angular distributions have been measured atE α=36.2 MeV, 39.6 MeV, 42.6 MeV, 49.5 MeV, 61.0 MeV for40Ca and atE α=36.2 MeV, 42.6 MeV, 49.5 MeV and 61.0 MeV for44Ca, respectively. At backward angles the data display an oscillatory structure forE α<50 MeV and more smoothly decreasing slopes atE α =61.0 MeV resembling the data obtained at higher energies. The40Ca data belowE α =50 MeV show the well known backward enhancement, which at 42.6 MeV and 49.5 MeV can be fitted by aP 14 2 and aP 16 2 respectively. Together with previous data,P L 2-structures have now been observed for allL-values betweenL=8 andL=16. The slope of the curveL(L+1) versus excitation energy is slightly smaller forL>12 than forL<12. Optical model analyses (within a Woods-Saxon-folding model) lead to large differences between the44Ca and40Ca parameters. Furthermore, in our parametrization, the40Ca real potential depth shows dramatic changes with energy. This feature seems outside the domain of the optical model and requires consideration of additional effects (e.g. antisymmetrization) not included in the standard optical model. Present microscopic calculations on the basis of the Resonating Group Method are discussed in connection with the characteristic features ofα-scattering from40Ca. 相似文献
5.
Excitation functions have been measured for 40Ca(p, p)40Ca, in the energy range from Ep = 2.35 to 4.85 MeV at four angles. The R-matrix formalism for multilevel cross sections was used to analyse the data; spins, parities, proton widths and reduced widths were extracted for thirty levels. Several new spin values have been deduced. A detailed comparison of the levels in the mirror system 41Ca?41Sc is given. 相似文献
6.
《Nuclear Physics B》1988,307(2):221-273
Fermionic string perturbation theory is known to suffer from an ambiguity in the form of a total derivative in the moduli space. For a class of backgrounds (including R10, orbifolds and theories with no U(1) factors in gauge group) we show that these ambiguities for the partition function of heterotic string theory at any genus are proportional to massless physical tadpoles in the theory at lower genera and hence vanish in stable vacua. We also find that in R10 the cosmological constant at a given genus is proportional to the cosmological constant at lower genera. This enables us to give an inductive argument for the vanishing of the cosmological constant in R10 to all orders in string perturbation theory. We also address the ambiguity and finiteness of n-point functions. Our results indicate that in R10 the ambiguity can be absorbed by a renormalization of the string coupling constant and the string tension. The expected sources of divergence in the n-point function in arbitrary tachyon-free backgrounds, besides the usual infrared divergences for d ≤ 4, are shown to be proportional to tadpoles of physical massless fields. For type II strings in arbitrary backgrounds, we show by explicit calculations that the ambiguity vanishes at g = 2. 相似文献
7.
A Barrelet-zero analysis is presented of data on in the momentum range 1 to 2 GeV/c. With π?π+ data alone, the slope for ambiguity is very large, but the addition of π0π0 information enables the number of solutions to be reduced to just a few. Although the alternative solutions differ considerably, they significant common features, in particular, with plausible extra assumptions, all solutions appear to be dominated by resonances in all spin states from J = 1 to 5. 相似文献
8.
(3He, 7Be) cross sections have been measured on A = 4n target nuclei between 12C and 40Ca. An α-particle pick-up spectroscopic factor is extracted from the data through a finite-range DWBA analysis. It is concluded that the overall changes of Sα between 12C and 40Ca are moderate, but that local variations exist; Sα is lower in the middle of the sd shell and higher for 40Ca. 相似文献
9.
The energy spectrum and α-spectroscopic factors of40Ca are calculated by using an α+36Ar orthogonality condition model. Overall agreement is obtained with the experimental data. The model successfully produces the parity-doubletK π=O + and O? α+36Ar cluster bands. It is shown that the coexistence and interference of α-cluster states and shell-model states are indispensable to understand the structure of40Ca. 相似文献
10.
M.E. Sevior M.R. Anderson L.W. Mitchell S.R. Kennett D.G. Sargood 《Nuclear Physics A》1982,378(2):349-363
The yield of γ-rays from the reaction 41K(p, γ)42Ca has been measured as a function of bombarding energy over the range 0.68–2.48 MeV and from the reaction 41K(p, αγ)38Ar over the range 1.20–2.48 MeV, and the yield of neutrons from the reaction 41K(p, n)41Ca has been measured from threshold to a bombarding energy of 2.48 MeV. The energy dependence of the cross sections is compared with statistical-model calculations with global optical-model parameters in all particle channels. The calculations seriously overestimate the cross section for the neutron channel and underestimate those for the other channels. A reduction in the imaginary well depth in the neutron channel leads to good agreement with all the data. Statistical-model calculations with this modified set of parameters are then carried out to provide cross sections for the astrophysically interesting reactions 41Ca(n, p)41K, 41Ca(n, α)38Ar, and 41Ca(n, γ)42Ca. Thermonuclear reaction rates are calculated for all six reactions over the temperature range 5 × 108–1010K which includes the range of temperatures of interest in nucleosynthesis calculations. 相似文献
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D. Pelte U. Winkler J. Pochodzalla M. Bühler A. Gorks B. Weissmann 《Nuclear Physics A》1985,438(2):582-604
The reactions 35Cl + 58Ni,40Ca, 27Al are studied at 385 MeV bombarding energy. The experiment employs 6 large-area ionization chambers which are set up to detect fragments with nuclear charge in coincidence multiplicity m ≦ 6. The highest multiplicity observed is m = 4; a detailed analysis of the data is performed for m = 2 and m = 3 events. The 58Ni data contain reactions with 2 fragments (σ = 1350±500 mb) and 3 fragmentes (σ = 175±90 mb) in the exit channel. The three fragments appear to have their origin in two different processes: a sequential-fragmentation process and a fast break-up process. A similar conclusion is reached for the 27Al data, whereas in the 40Ca data only the sequential fragmentation could be identified. 相似文献
13.
A. Chatterjee S. Kailas S. Saini S. K. Gupta M. K. Mehta 《Zeitschrift für Physik A Hadrons and Nuclei》1984,317(2):209-213
The absolute differential cross sections for the40Ca(α,α)40Ca reaction have been measured in the bombarding energy range from 4.33 to 5.68 MeV at the four laboratory angles 85°, 125°, 141° and 165°. An analysis of the data using multilevelR matrix theory has provided the spin-parities and widths of 29 levels in the compound nucleus44Ti. A comparison has been made with the levels deduced from the (α,γ) reaction and existing theoretical calculations of44Ti levels. 相似文献
14.
J.L. Zyskind J.M. Davidson M.T. Esat R.H. Spear M.H. Shapiro William A. Fowler C.A. Barnes 《Nuclear Physics A》1979,315(3):430-444
Absolute cross sections have been measured for the reaction 48Ca(p, γ)49Sc for 0.579 MeV ≦ Ep, lab ≦ 2.670 MeV and for the reaction 48Ca(p, n)48Sc for 0.956 MeV ≦ Ep, lab ≦ 2.670 MeV. Substantial competition effects in the cross section for 48Ca(p, γ)49Sc were observed at the thresholds for neutron emission to the 623 keV (3+), 1143 keV (2+) and 1402 keV (2?) excited states of 48Sc. Thermonuclear reaction rates were calculated from the measured cross sections for 0.1 ≦ T9 ≦ 10.0. The new rates differ considerably from those used in earlier calculations of the production of the rare, neutron-rich intermediate mass nuclides during explosive carbon burning. In particular, the new rates may change the predicted abundances for 48Ca, 49, 50Ti and 50V substantially. The good agreement between current global Hauser-Feshbach models and the experimental data indicates that Hauser-Feshbach calculations can provide sufficiently reliable rates for astrophysical calculations in cases where experimental data are non-existent. 相似文献
15.
Elastic scattering angular distributions for 10, 11B + 40Ca at Elab = 46.6 and 51.5 MeV and12C+39K at Elab = 54 and 63 MeV have been measured and compared with Woods-Saxon and double-folding optical models. The oscillatory structure observed previously for 12C + 40Ca disappears when the projectile is changed to 10,11B or the target is changed to 39K. The angular distributions are adequately reproduced by a double-folding analysis, which employs the nucleon-nucleon potential of Bertsch et al., with a range of real normalizations NR = 1.0–1.38. This same range of real normalizations was also able to describe previously measured 10,11B, 12C + 27A1 data. The double-folding analysis of 12C + 40Ca scattering indicates that this system behaves differently from neighboring systems. 相似文献
16.
Excitation functions of the 40Ca(d, p)41Ca and 40Ca(d, d)40Ca reactions have been measured at 45°, 90°, 135° and 170° from Ed = 4.50 to 5.43 MeV in 10 keV steps. Angular distributions of these reactions have been taken at Ed = 4.70, 5.00 and 5.30 MeV from 25° to 170° in 5° steps. Transitions were observed to the excited states for the range 0.0 ≦ Ex ≦ 3.74 MeV in 41Ca. Rapid fluctuations in the excitation functions and strong variations of the angular distributions with the incident energy were observed, suggesting that the contribution from compound nucleus processes is very large. Various quantities extracted from the experimental data were compared to the predictions of the statistical theories combined with the DWBA theory for the calculation of the direct reaction amplitudes. The results of the present analysis are consistent with the predictions of the standard statistical theories based on the neglect of the channel-channel correlation. 相似文献
17.
U. Klingbeil J. Kowalski F. Träger H. -B. Wiegemann G. zu Putlitz 《Zeitschrift für Physik A Hadrons and Nuclei》1979,290(2):143-148
The isotope shift40Ca-43Ca in the 4s 2 1 S 0-4s4p 3 P 1 intercombination line as well as the hyperfine structure splitting of the 4s4p 3 P 1 state of43Ca have been remeasured by saturation spectroscopy with a tunable stabilizedcw dye laser and an atomic beam of natural Ca as absorber. The nuclear charge radius of43Ca obtained here reconciles our result with the radius obtained from measurements in muonic Ca-atoms and in the Ca resonance line. It reconfirms the fact that the charge radius of43Ca is considerably smaller than the ones of both neighbouring even isotopes. The discrepancy of our previous measurement for this charge radius was due to a wrong assignment of so far unobserved absorption lines of probably molecular origin occuring in the neighbourhood of the atomic resonances under study. 相似文献
18.
L.W. Mitchell R.W. Kavanagh M.E. Sevior C.I.W. Tingwell D.G. Sargood 《Nuclear Physics A》1985,443(3):487-498
The yield of γ-rays from the reaction 42Ca(α, γ)46Ti has been measured as a function of bombarding energy over the range Eα = 3.42–5.62 MeV and from 42Ca(α, pγ)45Sc over the range Eα = 4.06–5.92 MeV, and the yield of protons from the reaction 42Ca(α, p)45Sc has been measured over the range Eα = 4.78–5.92 MeV. Cross sections for all three reactions have been extracted from the data and compared with global statistical-model calculations. The agreement is good. Thermonuclear reaction rates under stellar conditions appropriate for silicon burning are calculated and their significance for the approach to and bridging of the mass-45 bottleneck in the upward flow of nucleosynthesis is discussed. 相似文献
19.
The reactions48Ca(d, t)47Ca and48Ca(3He, α)47Ca have been measured at incident energies of 17 and 18 MeV, respectively and analysed by DWBA. Besides strong transitions to the groundstate and two unresolved states at aboutE x =2.60 MeV relatively strong transitions withl=2 are observed at higher excitation energies in the (3He, α) reaction. The observedl=1 and higherl=3 transitions are rather weak indicating that particle-hole components in the48Ca groundstate are relatively small. 相似文献
20.
The theoretical proton-40Ca optical potential is constructed based on theα-particle model of the nucleus. With this potential, the differential cross section, analysing power and the spin rotation function for 200 MeV proton-40Ca elastic scattering are calculated. The results are in good agreement with the experimental data. 相似文献