40Ca+58Fe,58Ni反应中的径向膨胀流研究

利用同位旋相关的Boltzmann-Langevin方程研究了⁴⁰Ca+⁵⁸Fe和⁴⁰Ca+⁵⁸Ni两个反应系统在53,100,150和200MeV/u入射能量下对心碰撞的径向膨胀流.发现对于丰中子系统⁴⁰Ca+⁵⁸Fe的径向膨胀流系统性地小于稳定系统⁴⁰Ca+⁵⁸Ni的径向膨胀流.在假定轰击能量与反应体系的压缩密度呈抛物线关系时,能够解释入射能量和径向膨胀流之间呈现的直线关系.提取了出现径向膨胀流的轰击能量阈值,发现对丰中子系统⁴⁰Ca+⁵⁸Fe得到的能量阈值小于稳定系统⁴⁰Ca+⁵⁸Ni所得到的能量阈值.     

Levels of 41Sc from the 40Ca(p,p)40Ca reaction

Excitation functions have been measured for ⁴⁰Ca(p, p)⁴⁰Ca, in the energy range from E_p = 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.     

Giant resonances in the fused system induced by 40Ca + 40Ca reactios

The giant quadrupole resonance of the fused system obtained in a ⁴⁰Ca + ⁴⁰Ca reaction is investigated in the framework of the TDHF approximation. A large splitting of the resonance due to the deformation of the composite system is observed. These results are confirmed by a direct fluid-dynamical calculation of the resonance. An estimation of the energy stored in the resonance is also presented.     

Proton direct capture on 40Ca

Excitation functions for the ⁴⁰Ca(p, γ)⁴¹Sc reaction have been measured at 0° and 90° in the proton energy range E_p = 2.1–3.1 MeV. The experimental results have been interpreted in terms of the direct capture process to the first excited state of ⁴¹Sc. The direct capture transition to the ground state has been observed only at a few proton energies. The spectroscopic factor of the first excited state in ⁴¹Sc has been found to be 1.0 ± 0.3. The direct capture cross section to the ground state is consistent with the spectroscopic factor reported from stripping reactions.     

Two-step processes in the 40Ca(α, 3He)41Ca reaction

The ⁴⁰Ca(α, ³He) reaction has been studied at 36 MeV incident energy. About fifty levels have been observed up to 7.1 MeV excitation energy and angular distributions were measured from 6–60° using a split-pole spectrometer. A local zero-range DWBA analysis has been carried out, and the deduced l-assignments and spectroscopic factors are compared with those obtained from previous neutron stripping experiments. Core-excited states in ⁴¹Ca with a [3^? ? f_7,2], [2⁺ ? f_7,2] and [5^? ? f_7,2] component previously observed in inelastic scattering experiments, are selectively excited by the (α, ³He) reaction. Their angular distributions are compared with coupled-reaction-channel calculations, assuming a pure two-step reaction mechanism. The agreement between theory and experiment may be considered as rather satisfactory for a number of levels. In particular the $\text{1}\text{2}{}^{\mathrm{+}}\text{and}\text{3}\text{2}{}^{\mathrm{+}}$ levels and the high-spin states with $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{?}}\text{,}\text{11}\text{2}{}^{\mathrm{+}}\text{,}\text{15}\text{2}{}^{\mathrm{+}}\text{and}\text{17}\text{2}{}^{\mathrm{+}}$ are successfully described within the framework of the weak-coupling model.     

Particle-hole multiplets in 40Ca observed in the 41Ca(τ, α) reaction

Energy levels in ⁴⁰Ca up to 10.2 MeV have been studied in the neutron pickup reaction ⁴¹Ca(τ, α)⁴⁰Ca with 20 MeV bombarding energy. Thirty excited states have been identified and angular distributions have been measured in the interval from 5° to 40° by means of a split-pole magnetic spectrometer. The angular distributions together with DW calculations have been used to extract l_n values and spectroscopic factors. The l_n = 2 strength distribution for the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$ particle-hole levels is compared to the l_p = 3 strength distribution from pr stripping data.     

Generator-coordinate study of elastic 16O + 40Ca scattering

Elastic ¹⁶O + ⁴⁰Ca phase shifts are calculated using a generator-coordinate method. A rotational band of molecular resonances is found with a rotational constant of about 30 keV. The width of these resonances should make them observable in the energy range 30 to 50 MeV. These features can be approximately reproduced by a shallow local potential. Properties of the imaginary part of the optical potential are discussed qualitatively. The optical potential should be transparent in a window of J-values comprised between about 16 and 25. Odd-even effects are shown to be negligible in the real part of the potential but might be important in its imaginary part. A possible confirmation of these predictions is found in an experimental excitation function.     

A study of the ground-state energy of 40Ca

The ⁴⁰Ca ground state is studied in the 176-dimensional model space of 0 + 2 ?ω excitations. In this space diagonalization is compared to the sum of linked graphs to all orders. Both the original and the saturating Sussex matrix elements are used and the effect on the order-by-order convergence of modifying the unperturbed single-particle energies is studied.     

Atomic antiproton states in 16O, 18O, 32S, 40Ca, 44Ca and 122Sn

Atomic levels for the systems p? plus ¹⁶O, ¹⁸O, ³²S, ⁴⁰Ca, ⁴⁴Ca and ¹²²Sn are calculated in optical potentials based on the N?N interaction of Dover and Richard.     

α-clustering in the ground state of 40Ca

The anomalous large angle scattering observed in ⁴⁰Ca(α,α) is studied in the frame of a semi-microscopic model taking into account the presence of α-correlations in the ground state of ⁴⁰Ca. The calculations, performed between 18 and 29 MeV, assert the potential, non resonant nature of the phenomenon.     

Quasimolecular states in the elastic α-scattering on 40Ca

Resonance states seen in α-⁴⁰Ca elastic scattering are treated in a microscopic model which describes the fragments by displaced oscillator shell model functions. The minima of the energy expectation value for various angular momenta are in good agreement with the experimental resonance energies, thus confirming the concept of an underlying quasimolecular structure.     

On the predictions of the coexistence model for the reaction 42Ca(p,t)40Ca

The coexistence model as formulated by Gerace and Green for ⁴⁰Ca has been shown to predict cross sections for the reaction ⁴²Ca(p,t)⁴⁰Ca in strong disagreement with experiment. In the present letter we demonstrate how a much improved agreement can be obtained by introducing additional kinds of basis states. Especially important are triaxially deformed components, which contain admixtures of the $\text{1}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states.     

Shell model study of 0+ states in 40Ca

Low-lying positive parity levels of calcium-40 are discussed in the framework of the shell model. An inert ³²S core is assumed, and $\text{Od}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{Of}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ are taken as active orbits. As effective interactions we assumed those used by Federman and Pittel. Effect of many-particle and many-hole configurations up to 8p–8h states are shown to be important even for the very low-lying 0⁺ states.     

Neutron emission in muon capture by 40Ca

The neutron spectrum and asymmetry have been calculated for ⁴⁰Ca with different wave functions for the bound proton and the emitted neutron. The asymmetry is shown to be very sensitive to the behaviour of the wave functions near the nuclear surface while the spectrum is mostly sensitive to the strength of the real part of the neutron optical potential.     

Anomalous L = 0 transition observed in the reaction 40Ca(p,t)38Ca

An anomalous L = 0 transition to the 3.06 MeV state in ³⁸Ca is observed in the reaction ⁴⁰Ca(p,t) at E_p = 52 MeV. Its angular distribution and relative intensity can be explained by the cancellation of form factors.     

The decay of isoscalar giant resonances in 24Mg and 40Ca

In this paper we present data on the charged-particle decay of the isoscalar 2⁺ strength between 10 and 20 MeV excitation energy (E_x) in ²⁴Mg and ⁴⁰Ca. The isoscalar strength was excited by inelastic scattering of 120MeV α-particles at 14° and 12.5° for ²⁴Mg and ⁴⁰Ca, respectively. The charged particles originating from the decay were detected in coincidence with the α′ particles at several angles in the scattering plane. J^π assignments of the decaying states were made on the basis of the angular correlation pattern of the α₀ decay to the ground state of ²⁰Ne and ³⁶Ar, respectively, using a DWBA calculation for the m-state population of the decaying state.For ⁴⁰Ca, about 40% of the E2 EWSR is found to be located in the interval E_x = 13.5 ± 1.5 MeV, which is similar to what has been found from previous inelastic scattering experiments at E_x = 18 ± 2 MeV, but much more than such experiments located in the region E_x = 12–15 MeV. The difference for the region E_x < 16 MeV is due to the fact that from our α₀ angular correlation pattern we conclude that virtually no continuum is excited in the (α, α′) process up to E_x = 16 MeV while all previous inelastic hadron scattering experiments assumed such a continuum to be present. The E2 strength distribution for ⁴⁰Ca thus obtained is very different from what previous theoretical calculations predict. For ²⁴Mg about 30% of the E2 EWSR is present in the interval 12.5 ? E_x ? experiments. 16.5 MeV which again is about twice as much as deduced from previous inelastic scattering The observed branching ratios are compared with calculated ones assuming statistical decay. Reasonable agreement was obtained for ⁴⁰Ca, but for ²⁴Mg especially the α₀-decay branch and to a lesser extent also the p₁ one are much stronger than the statistical calculations predict, indicating that especially the α₀ decay occurs mainly in a non-statistical way.A similar conclusion can be drawn from the behaviour of the forward-backward asymmetry in the angular correlations of the decay particles as a function of the excitation energy FBA(E_x). For ⁴⁰Ca, FBA(E_x) for all decay channels increases smoothly on the average once E_x is above a well-defined threshold, which is due to the onset of knock-out processes. For ²⁴Mg, however, the FBA(E_x) for the α₀ shows a large fluctuation as a function of E_x, indicating an interference process between semi-direct decay and knock-out processes.     

Variation of the α-particle pick-up spectroscopic factor from 12C to 40Ca

(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 S_α between ¹²C and ⁴⁰Ca are moderate, but that local variations exist; S_α is lower in the middle of the sd shell and higher for ⁴⁰Ca.     

The isospin forbidden 1− → 0+ transition in 40Ca

The isospin forbidden transition 1^? (6.95 MeV) → 0⁺ (g.s.) in ⁴⁰Ca is explained within a model that mixes isospin through single-particle energy differences and the two-body Coulomb interaction. There is no need to introduce an isospin non-conserving part of the nucleon-nucleon interaction to explain this anomalously fast transition.     

Alpha capture to the giant dipole resonances of 42Ca, 44Ca and 52Cr

Differential cross sections for the ${}^{38}\text{Ar}\text{(α, γ}{}_0\text{)}{}^{42}\text{Ca}\text{,}{}^{40}\text{Ar}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{44}\text{Ca and}{}^{48}\text{Ti}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{52}\text{Cr}$ reactions were measured at 90° to the beam direction in 50 or 100 keV steps over the bombarding energy ranges 6.0–15.0 MeV, 5.5–11.1 MeV and 6.0–12.0 MeV respectively. Gamma-ray angular distributions were measured at forty bombarding energies. These show that the (α, γ₀) reaction proceeds through 1^? levels and to a lesser extent 2⁺ levels, whereas the (α, γ₁) reaction most probably proceeds through 1^? and 3^? levels. It is deduced that 〈Γ〉/〈D〉 ≦ 1 for the ⁴⁰Ar(α, γ)⁴⁴Ca. reaction whereas the fine structure observed in the ⁴⁸Ti(α, γ)⁵²Cr reaction is probably due to fluctuations. From a comparison with other data it is shown that the (α, γ) reaction is most probably statistical in nature. Using Hauser-Feshbach theory it is deduced that the ³⁶Ar(α, γ)⁴⁰Ca. reaction is inhibited by isospin selection rules and an estimate is made of isospin mixing in the ⁴⁰Ca giant dipole resonance. The ${}^{38}\text{Ar}\text{(α, γ)}{}^2{}^{42}\text{Ca and}{}^{40}\text{Ar}\text{(α, γ)}{}^{44}\text{Ca}$ data are considered with respect to theories of isosopin splitting of the giant dipole resonance.