Spectroscopy of 47K and proton core-excitations in 48Ca from the 48Ca(t, α)47K reaction

The ⁴⁸Ca(t, α)⁴⁷ K reaction has been measured at 33 MeV bombarding energy. Spectroscopic information has been extracted for 13 states in ⁴⁷K and 9 new levels have been observed in this nucleus. A comparison of Spectroscopic factors is made with a recent shell-model calculation and the presence of proton core-excitations in the ground state of ⁴⁸Ca is examined.     

Evidence for proton ground state correlations in48Ca

In a high resolution⁴⁸Ca(d,³He) experiment at 80 MeV evidence has been found for a 7/2^? state at 1.97 MeV in⁴⁷K with a spectroscopic factor of C²S=0.08 corresponding to a ~4% admixture of πf²(s,d)^?2 configurations in the ground state of Ca.     

No evidence for precritical phenomena of pion condensation in A = 48 nuclei

The ⁴⁸Ca(e,e′)(1⁺, 10.24 MeV) reaction, the ⁴⁸Ca(p,p′)(1⁺, 10.24 MeV) reaction and the ⁴⁸Ca(p,n)⁴⁸Sc(1⁺, 16.8 MeV) reaction have been theoretically investigated with respect to the occurrence of precritical phenomena related to pion condensation. No evidence for precritical phenomena is found.     

Analogue states in 47Ca

The ⁴⁸Ca(³He, ⁴He)⁴⁷Ca and ⁴⁸Ca(p, d)⁴⁷Ca reactions were used to observe six levels in ⁴⁷Ca above 12 MeV excitation. Analysis of the data has yielded precise excitation energies for the lowest $\text{T =}\text{9}\text{2}$ levels in ⁴⁷Ca; which are analogs of low-lying levels in ⁴⁷K. Comparison of experimental and calculated Coulomb displacement energies for the K-Ca isotopes is made.     

Cross section measurements and thermonuclear reaction rates for 48Ca(p, γ)49Sc and 48Ca(p,n)48Sc

Absolute cross sections have been measured for the reaction ⁴⁸Ca(p, γ)⁴⁹Sc for 0.579 MeV ≦ E_{p, lab} ≦ 2.670 MeV and for the reaction ⁴⁸Ca(p, n)⁴⁸Sc for 0.956 MeV ≦ E_{p, 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, 50}Ti 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.     

Observation of the proton-pairing vibration in 48Ca

The two-proton transfer reaction (¹⁴C, ¹⁶O) has been investigated at 96 MeV on targets of ⁵⁰Ti and ⁴⁸Ca. The ⁴⁸Ca states at 0 MeV (0⁺), 3.83 MeV (2⁺), 4.28 MeV (0⁺) and 4.50 MeV (3⁻) and the ⁴⁶Ar ground state were excited. The 4.28 MeV 0⁺state has a transfer strength comparable to the g.s. transition to ⁴⁶Ar and a predominant proton vibrational character. The interpretation of the state as the proton-pairing vibrational state is supported by estimates of the excitation energy based on experimental binding energies.     

The reactions48Ca(d,t)47Ca and48Ca(3He, α)47Ca

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.     

The (p-d-t) process in strong (p,t) transitions

The (p-d-t) process in ⁴⁸Ca(p, t)⁴⁸Ca(p, t)⁴⁶Ca(0⁺, g.s.; 2⁺, 1.34 MeV) and ¹¹⁶Sn(p, t)¹¹⁴Sn(0⁺, g.s.) at 20 MeV was investigated. The calculations showed that the two-step process is important in all the transitions investigated, and is enhanced in the Sn transition by the pairing correlations in the BCS ground states.     

Thermonuclear reaction rates for proton induced reactions on 41K and neutron induced reactions on 41Ca

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.     

Excitation functions for48Ca(d,p)49Ca(0) in the rangeE d=3.0–5.5 MeV

Excitation curves for⁴⁸Ca(d, p)⁴⁹Ca(0) have been measured at 12 angles in the energy region from 3.0–5.5 MeV with the aim to investigate the charge exchange effect expected at the analogous (d, n) threshold opening at 4.3 MeV. A broad flat minimum is seen in the 165° excitation curve around this threshold which is however much less significant than the charge exchange cusps observed in theA ≈ 90 mass region. More significant structure is seen atE _d≈5 MeV which possibly may be connected with⁴⁸Ca(4.611) core excitation or due to an intermediate state in⁵⁰Sc.     

Isospin aspects in nuclear reactions involving Ca beams at 25 MeV/nucleon

Isospin dependence of dynamical and thermodynamical properties observed in reactions ⁴⁰Ca+ ^40,48Ca and ⁴⁰Ca + ⁴⁶Ti at 25 MeV/nucleon has been studied. We used the CHIMERA multi-detector array. Strong isospin effects are seen in the isotopic distributions of light nuclei and in the competition between different reaction mechanisms in semi-central collisions. We will show also preliminary results obtained in nuclear collision ⁴⁸Ca + ⁴⁸Ca at 25MeV/nucleon, having very high N/Z value in the entrance channel (N/Z = 1.4). The enhancement of evaporation residue production confirms the strong role played by the N/Z degree of freedom in nuclear dynamics.     

Evaporation residue and total reaction cross sections for the system36S+48Ca

Evaporation residue cross sections for the system³⁶ s +⁴⁸Ca were measured at E_cm=66.4 MeV, 74.4 MeV and 83.5 MeV and are compared with simple model predictions. Compound nucleus formation accounts for 80% of the total reaction cross section; the residual strength is found in the transfer channels.     

The mass of 18C from a heavy ion double-charge-exchange reaction

The mass of ¹⁸C has been measured using the double-charge-exchange reaction ⁴⁸Ca(¹⁸O, ¹⁸C)⁴⁸Ti at an ¹⁸O energy of 112 MeV. The ¹⁸C ions were detected at the focal plane of a magnetic spectrometer. The mass excess of ¹⁸C was found to be 24.923 ± 0.030 MeV, and the first excited state was observed at an excitation energy of 1.62 ± 0.02 MeV. At the same time, an independent measurement of the mass excess of ¹⁷C was obtained from the ⁴⁸Ca(¹⁸O, ¹⁷C)⁴⁹Ti reaction, and the value 21.039 ± 0.020 MeV is in excellent agreement with an earlier measurement. The first excited state of ¹⁷C is at 295 ± 10 keV.     

Cross sections for proton induced reactions on 41K and for the reaction 62Ni(α, p)65Cu

Excitation functions have been measured for ⁶²Ni(α, p)⁶⁵Cu in the energy range 6.5–9.0 MeV, for ⁴¹K(p, α)³⁸Ar in the range 0.8–2.6 MeV, for ⁴¹K(p, γ)⁴²Ca, ⁴¹K(p, αγ)³⁸Ar, ⁴¹K(p, nγ)⁴¹Ca, and ⁴¹K(p, p'γ)⁴¹ in the range 0.6–4.0 MeV, and for ⁴¹K(p, n)⁴¹Ca from threshold to 3.0 MeV. Cross sections have been extracted from the data and these are compared with statistical-model calculations based on global optical model parameters. Alternative parameter sets have been tried for the ⁶²Ni(α, p)⁶⁵Cu data and published data for ⁶²Ni(α, γ)⁶⁶Zn and ⁶²Ni(α, n)⁶⁵Zn, and both these and the global parameters have been used in statistical-model calculations of ⁶⁵Cu(p, γ)⁶⁶Zn, ⁶⁵Cu(p, n)⁶⁵Zn and ⁶⁵Cu(p, α)⁶²Ni cross sections, which are compared with published data for these reactions. Both the global and the alternative parameters lead to very good agreement with experiment for all six reactions. Alternative parameters have been tried for the ⁴¹K + p reactions also. The global parameters lead to agreement to within a factor of 2 and the alternative parameters lead to agreement to within a factor of 1.3. The ⁴¹K + p alternative parameters are used in calculations of ⁴¹Ca(n, γ)⁴²Ca, ⁴¹Ca(n, p)⁴¹K and ⁴¹Ca(n, α)³⁸Ar cross sections, and these and the experimental ⁴¹K + p data are used in calculations of thermonuclear reaction rates under stellar conditions for the ⁴¹Ca + n and ⁴¹K + p reactions.     

Two-proton transfer reaction48Ca(18O,16C)50Ti at 102 MeV

Differential cross sections for¹⁸O elastic scattering and the (¹⁸O,¹⁶C) and (¹⁸O,¹⁷N) reactions on⁴⁸Ca were measured at 102 MeV using a Q3D magnetic spectrograph. The transitions to the 7/2^? ground state (g.s.) of⁴⁹Sc and the 0⁺ (g.s.), 2⁺ (1.554 MeV), 4⁺ (2.675 MeV), and 6⁺ (3.198 MeV) states of⁵⁰Ti were analyzed by DWBA calculations which include finite-range and recoil effects. Simple cluster-transfer calculations were done for all two-proton transfer transitions. For the 0⁺ (g.s.) transition a two-nucleon transfer code employing microscopic wave functions was also used. It was found that absolute cross sections for this kinematically well-matched transition were underrated by a factor of about 7 for a reasonable amount of configuration mixing in the nuclear states involved in this transition. This factor is very close to the value 5 derived for the similarly well-matched⁴⁸Ca(¹⁸O,¹⁶O)⁵⁰Ca reaction.     

Cross sections and thermonuclear reaction rates for 42Ca(p, γ)43Sc, 44Ca(p, γ) 45Sc, 44Ca(p,n) 44Sc and 45Sc(p,n)45Ti

The yield of γ-rays from the reaction ⁴²Ca(p, γ)⁴³Sc has been measured as a function of bombarding energy over the range 0.63–3.01 MeV, from ⁴⁴Ca(p, γ)⁴⁵Sc over the range 0.775–4.00 MeV, from ⁴²Ca(p, p'γ)⁴²Ca over the range 2.24–3.01 MeV, and from ⁴⁴Ca(p, p'γ)⁴⁴Ca over the range 1.90–5.03 MeV. The cross section of the reaction ⁴⁴Ca(p, n)⁴⁴Sc has been measured from threshold to a bombarding energy of 5.05 MeV by observation of the 1157 keV γ-ray associated with the residual ⁴⁴Sc activity, and the cross section of the reaction ⁴⁵Sc(p, n)⁴⁵Ti has been measured from threshold to a bombarding energy of 4.00 MeV both by observation of the annihilation radiation associated with the residual ⁴⁵Ti activity and by measurement of the total neutron yield with a wide-angle BF₃ tube and paraffin detector. All these data are compared with statisticalmodel calculations and satisfactory agreement is achieved. Thermonuclear reaction rates for the (p, γ) and (p, n) reactions are calculated for the temperature range 5 × 10⁸-10¹⁰K and the significance of these results for explosive nucleosynthesis in stars is discussed.     

Untersuchung von40Ca mit der Reaktion39K(p, γ0)40Ca

Excitation functions of the reaction³⁹K(p, γ ₀)⁴⁰Ca at 0° and 90° have been taken in the proton energy range 2.5–6.0 MeV corresponding to an excitation of⁴⁰Ca between 10.8 and 14.1 MeV. Positions and strengths of several resonances appearing in the excitation functions are given. The structure of⁴⁰Ca is compared with predictions from 1 particle — 1 hole calculations.     

Study of electric monopole transitions between the ground state and the first excited 0+ state in 40, 42, 44, 48Ca with high resolution inelastic electron scattering

Monopole transitions from the 0₁⁺ ground states to 0₂⁺ excited states at 3.353 MeV (⁴⁰Ca), 1.837 MeV (⁴²Ca), 1.884 MeV (⁴⁴Ca) and 4.272 MeV (⁴⁸Ca) have been investigated with high resolution inelastic electron scattering (FWHM ≈ 30 keV) at low momentum transfer (0.29 ≦ q ≦ 0.53 fm^?1). The respective monopole matrix elements are 2.53 ± 0.41 fm², 5.24 ± 0.39 fm², 5.45 ± 0.41 fm² and 2.28 ± 0.49 fm². These results are used together with known ground state charge radii and the average number of holes in the sd shell in the ground state to estimate the number of particle-hole excitations in the wave functions of the excited 0⁺ states.