Cross sections of 43Sc, 44Sc, 46Sc isotopes formed in the 45Sc + 3He reaction

Reactions ⁴⁵Sc(³He, αn)⁴³Sc, ⁴⁵Sc(³He, α)⁴⁴Sc and ⁴⁵Sc(³He, 2p)⁴⁶Sc in the ³He energy range of 5 to 24 MeV are investigated in experiments performed with a ³He ion beam during the irradiation of U-120M cyclotron scandium targets. Activation is used to determine the yield of nascent Sc isotopes. The γ activity induced in targets is measured using a high-resolution HPGe detector. The character of the excitation function changes during the formation of these ions and differs from the excitation functions for deuterons, despite the low bond energy of ³He and the positive values of the Q reactions leading to the formation of ⁴⁴Sc and ⁴⁶Sc isotopes. The cross sections of ⁴⁴Sc formation reach their maximum value at the Coulomb barrier of the reaction, due to the stable ⁴He nucleus that accompanies the formation of ⁴⁴Sc. The contribution from different reaction mechanisms to the cross sections of ⁴³Sc, ⁴⁴Sc, and ⁴⁶Sc isotope formation are considered.     

Cross sections for production of 43Sc, 44Sc, and 46Sc isotopes in the 45Sc + 3He reaction

Reactions ⁴⁵Sc(³He, αn)⁴³Sc, ⁴⁵Sc(³He, α)⁴⁴Sc, and ⁴⁵Sc(³He, 2p)⁴⁶Sc, resulting from the irradiation of scandium targets with a beam of ³He ions with energy from 5 to 24 MeV, are investigated in experiments on the U120M cyclotron of the Nuclear Physics Institute (Rez, Czech Republic). The activation technique is used to find the yield of the produced Sc isotopes. The induced γ activity in the targets is measured using a high-resolution HPGe detector. Despite the low binding energy of ³He and positive reaction Q values, which leads to formation of the ⁴⁴Sc and ⁴⁶Sc isotopes, the behavior of the excitation functions for the formation of these isotopes differs from the behavior of the excitation function for deuterons. Scandium-44 formation cross sections reach their maximum at the reaction Coulomb barrier. This is because not only ⁴⁴Sc but also a stable ⁴He nucleus is formed in the reaction.     

Activation cross-sections of titanium isotopes at neutron energies of 13.5–14.8 MeV

The cross-sections for ~(46) Ti(n,2 n)~(45) Ti, ~(46) Ti(n,p)~(46 m+g) Sc+~(47) Ti(n,d*)~(46 m+g) Sc, ~(46)Ti(n,p)~(46 m+g) Sc, ~(47) Ti(n,p)~(47) Sc+~(48) Ti(n,d*)~(47) Sc, ~(47) Ti(n,p)~(47) Sc, ~(48) Ti(n,p)~(48) Sc+~(49) Ti(n,d*)~(48) Sc,~(48) Ti(n,p)~(48) Sc, and ~(50) Ti(n,α)~(47) Ca reactions were investigated around neutron energies of 13.5–14.8 Me V by means of the activation technique. Fast neutrons were produced by the~3 H(d,n)~4 He reaction. Neutron energies from different directions in the measurements were obtained in advance using the method of cross-section ratios for ~(90) Zr(n,2 n)~(89 m+g) Zr and ~(93) Nb(n,2 n)~(92 m) Nb reactions. The results obtained are analyzed and compared with the experimental data provided by the literature and verified nuclear data in the JEFF-3.3,CENDL-3.1, ENDF/B-VIII.0 libraries, as well as results calculated by Talys-1.9 code.     

The structure and properties of45Sc at low excitation energies

The spins and electromagnetic properties of levels in⁴⁵Sc up to 2,352 keV were studied by means of inelastic proton scattering using a 3-parameter coincidence arrangement and Coulomb excitation with³He and⁴He beams. Relevant experimental results are discussed in terms of the Thankappen-True core-plus-particle model.     

The45Sc(3He,d)46Ti reaction. DWBA analysis of transitions to states between 7.6 and 11.0 MeV

Angular distributions of transitions to 29 states in⁴⁶Ti between 7.6 and 11.0 MeV excitation energy from the⁴⁵Sc (³He,d) reaction at 15 MeV have been compared with DWBA predictions. The results support previously suggestedT=2 states in⁴⁶Ti.     

Single-particle and core-excited states in 49Sc: (I). The 48Ca(3He,d)49Sc reaction

The ⁴⁸Ca(³He, d)⁴⁹Sc reaction has been studied at 25 MeV incident energy. Angular distributions have been measured from 5° to 40° using a split-pole spectrometer, for about 160 levels located up to 18 MeV excitation energy. A local zero-range DWBA analysis has been carried out, using Gamow functions as form factors in the case of unbound states; l-assignments and spectroscopic factors are obtained for a large number of levels, most of them previously unknown. The summed experimental spectroscopic strengths for the T_<, l = 1 and l = 3 levels are in good agreement with the shell-model sum-rule limits for 1f-2p proton states, and their energy centroids have been determined. The $\text{lg}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ strength in ⁴⁹Sc is strongly fragmented: about 27% of the T_< strength is carried by twenty-three levels located between 6.5 and 13.5 MeV. Spectroscopic factors for analog states are compared with those from previous (p, p), (³He, dp) and (d, p) experiments.     

Near-barrier neutron transfer in reactions <Superscript>6</Superscript>He + <Superscript>45</Superscript>Sc, <Superscript>64</Superscript>Zn,and <Superscript>197</Superscript>Au

Experimental cross sections of formation of isotopes ⁴⁶Sc (in reaction ⁶He + ⁴⁵Sc), ^196,198Au (in reaction ⁶He + ¹⁹⁷Au), and ⁶⁵Zn (in reaction ⁶He + ⁶⁴Zn) are analyzed. The time-dependent Schrödinger equation for the outer neutrons of ⁶He and ¹⁹⁷Au nuclei is solved numerically to calculate the probability of neutron transfer and transfer cross sections. In reaction ⁶He + ¹⁹⁷Au, the contribution of fusion and subsequent evaporation to experimental data can be neglected, while the corresponding contributions to reactions ⁶He + ⁴⁵Sc and ⁶He + ⁶⁴Zn are considerable. Fusion–evaporation is taken into account using the computational code of the NRV knowledge base. The results of calculations are in satisfactory agreement with the experimental data.     

Fusion and transfer cross sections of 3He induced reaction on Pt and Au in energy range 10–24.5 MeV

In experiments performed by accelerated ion ³He-beam irradiated gold and platinum targets on the cyclotron U-120M of the Nuclear Physics Institute of the Czech Academy of Sciences, ?e?, reactions of complete and incomplete fusion and nucleon transfer reactions in the ³He energy range from 10 to 24.5 MeV have been investigated. To determine the yield of the nuclides resulting from the nuclear reaction, the activation technique has been used. The obtained data are analyzed using models based on statistical calculations and compared with similar results for other light stable particles. Transfer reactions with positive Q values have relatively high cross sections in the energy range below the Coulomb barrier. These cross sections continue to grow with increasing ³He energy, and, in the case of capturing neutron from target nucleus by a nucleus of ³He, the excitation functions of these reactions reach their maximum almost at the Coulomb barrier of the reactions.     

Single-particle and core-excited states in 49Sc: (II). The 48Ca(α, t)49Sc reaction

The ⁴⁸Ca(α, t)⁴⁹Sc reaction has been studied at 36 MeV incident energy. About eighty levels have been observed up to 7.5 MeV excitation energy and angular distributions were measured from 6° to 58°, 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 the (³He, d) reaction. In the other hand, a large number of angular distributions cannot be reproduced by the DWBA calculations; they have been compared with the results of coupled-reaction-channel calculations, assuming two-step excitation of weak coupling states with a [${}^{48}\text{Ca}{}^1\text{?}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$] structure. Good agreement between experimental angular distributions and two-step predictions is obtained for several ⁴⁹Sc levels, suggesting spin and parity assignments. Moreover, as rather large cross sections are predicted for two-step excitations, it is concluded that, generally, these processes cannot be neglected in the analysis of (α, t) reactions.     

The46Ti(d,τ)45Sc reaction

The⁴⁶Ti(d, τ)⁴⁵Sc reaction has been investigated at an incident energy of 52 MeV. Angular distributions have been taken for 14 τ-groups corresponding to excitation energies below 4 MeV in⁴⁵Sc. Spectroscopic factors were extracted through DWBA calculations. Spins and parities of 5/2⁺ are proposed for states at 1.30, 1.80, 2.91, 3.48, and 3.72 MeV. The hole state spectrum of⁴⁵Sc closely resembles that of⁴⁷Sc. A strong fractionation of the 1d _3/2 strength was not observed in contrast to other recent work. The data provide evidence for (1f _7/2 · 1f _5/2 ¹) components in the ground state wave function of⁴⁶Ti, which demonstrates that such configurations are not restricted to neutron excitations.     

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.     

Special features of nuclear reactions induced by loosely bound <Superscript>6</Superscript>He and <Superscript>6,7</Superscript>Li nuclei in the vicinity of the Coulomb barrier height

Excitation functions are measured for complete-fusion and transfer reactions induced by the interaction of ⁶He and ⁶Li with ²⁰⁶Pb, ²⁰⁹Bi, and Pt. Data obtained for fusion reactions induced by ⁶He ions deviate from the predictions of the statistical model of compound-nucleus decay at projectile energies in the vicinity of the Coulomb barrier height. A strong enhancement of cross sections for fusion reactions induced by the interaction of ⁶He with target nuclei is observed. The cross sections for reactions of cluster transfer, neutron transfer from ⁶He, and deuteron transfer from ⁶Li at deep-subbarrier energies are also found to be enhanced. These results are discussed from the point of view of the effect of the cluster structure of nuclei on the interaction probability at energies in the vicinity of the Coulomb barrier height.     

Excitation functions of some neutron threshold reactions on isotopes of molybdenum

Cross sections were measured for (n,p) reactions on ^{92, 95, 96, 97, 98}mo, (n, α) reactions on ^{92, 98}Mo, and (n, 2n) reaction on ¹⁰⁰Mo for the first time in the neutron energy range of 5.9 to 9.6 MeV. The quasi-monoenergetic neutrons were produced via the ²H(d, n)³He reaction using a deuterium gas target at a compact cyclotron. Use was made of the activation technique in combination with high-resolution γ-ray spectroscopy. Some systematic trends observed in the excitation functions are discussed. For the various isotopes of molybdenum, with increasing mass of the target nucleus, the thresholds of (n,p) and (n,α) reactions increase and the magnitudes of cross sections near the maxima of the excitation functions appear to decrease. Hauser-Feshbach calculations show that in general the excitation functions of (n, p) and (n, α) reactions are described within a factor of 2 by the statistical model only up to about 8 MeV; the (n,2n) reaction on ¹⁰⁰Mo, however, is reproduced well from threshold up to 15 MeV by this model.     

The excitation functions of complete and incomplete fusion reactions of 6Li with Pt nuclei

Experimental results from measuring the energy dependences of cross sections of fusion and transfer reactions for ⁶Li beams and Pt targets are presented. The experiments were performed using the MSP-144 magnetic analyzer; stacks of platinum foils were installed at the focal plane of this analyzer. In the energy range 22.5–42.5 MeV, the energy resolution of the beam hitting the target stack was not worse than 0.25 MeV and that of the transmitted beam was not worse than 0.40 MeV. The yields of products of neutron and deuteron transfer reaction on target nuclei were measured using the γ activity induced in the platinum targets. Thus, excitation functions for transfer reactions were obtained in a wide energy range, including near the Coulomb barrier. It was shown that the basic reaction channel is the deuteron capture from ⁶Li. In this case, the maximum of the excitation function for ⁶Li breakup and subsequent deuteron capture lies near the Coulomb barrier of the reaction.     

Level structure of 47Ti from the (d,p) reaction in 46Ti

The reaction ⁴⁶Ti(d, p) is studied at 10 MeV using the Aldermaston tandem Van de Graaff accelerator and a multichannel magnetic spectrograph. A total of 180 levels are observed up to an excitation of ≈ 7.2 MeV and the stripping angular distributions are analysed in terms of the DWBA theory of direct reactions using the NL/FR optical model potential. Spins, parities and spectroscopic factors are deduced for various levels. Summed spectroscopic factors and quasiparticle energies are obtained for shell model states. Properties of low-lying levels in ⁴⁷Ti are compared with the MBZ and Coriolis coupling models and also with those of the isotonic nuclei ⁴⁵Ca and ⁴⁶Sc.     

Excitation functions for complete fusion and transfer reactions in the interaction of 6He with 197Au nuclei

The excitation functions for the fusion reactions with subsequent neutron evaporation, ¹⁹⁷Au(⁶He, xn)^{203 ? xn}Tl (x = 2?7), and the neutron transfer reactions with production of the ¹⁹⁶Au and ¹⁹⁸Au isotopes have been measured. Unusually high cross section of the ¹⁹⁸Au isotope production at energies below the Coulomb barrier has been observed. Possible mechanisms of production and decay of the transfer reaction products are considered.     

9Be(3He,n)11C and 11B(3He,n)13N Reactions at Energies below Coulomb Barrier

Angular distributions have been measured for ⁹Be(³He, n)¹¹C and ¹¹B(³He, n)¹³N reactions for the neutron group leading to the ground state at E_3He = 0.90, 1.00, 1.20, 1.40 MeV and 1.70, 1.90 MeV respectively. To fit the experimental data, the theory of two nucleon stripping reactions below the Coulomb barrier has been considered. Taking Coulomb distorted wave functions for the interacting particles in the initial channel, a closed analytical form for the differential cross-section has been obtained. The other two cases using the plane wave Born approximation and the distorted wave Born approximation are also applied to the experimental data. The agreement between the Coulomb distorted wave calculations and the experimental data is better than with the PWBA and DWBA. The spectroscopic factors are extracted by fitting the experimental data with the theoretical calculations.     

Coulomb-nuclear interference in the scattering of 3He and α-particles by 122,124Te, 124Sn and 114Cd

Angular distributions and excitation functions of the elastic and inelastic scattering of ³He and α-particles by ^122,124Te, ¹²⁴Sn and ¹¹⁴Cd at incident energies around the Coulomb barrier were measured. The experimental results were analyzed in the framework of the optical model and DWBA taking into account the interference between nuclear and Coulomb excitation. Nuclear and charge deformation parameters were deduced.     

Fusion and transfer reactions in beams of light loosely bound nuclei at energies in the vicinity of the Coulomb barrier

Experiments devoted to studying cross sections for fusion and transfer reactions induced by the interaction of beams of halo-like (⁶He), cluster (⁶Li and ⁷Li), and loosely bound (³He) nuclei with nuclei of light and heavy elements are described. The cross sections obtained experimentally for such reactions are analyzed. Special features in the behavior of the cross sections for the formation of evaporation residues and products of transfer reactions at energies in the vicinity of the Coulomb barrier are revealed. In particular, an increase in the cross sections for fusion and transfer reactions involving halo-like nuclei and proceeding at energies in the subbarrier region is observed. The cross sections for neutron-transfer and light-cluster-transfer reactions reachmaximum values at an energy in the vicinity of the Coulomb barrier for the reaction being considered.     

The 42Ca(α, γ)46Ti and 42Ca(α, p)45Sc cross sections and the mass-45 bottleneck

The yield of γ-rays from the reaction ⁴²Ca(α, γ)⁴⁶Ti has been measured as a function of bombarding energy over the range E_α = 3.42–5.62 MeV and from ⁴²Ca(α, pγ)⁴⁵Sc over the range E_α = 4.06–5.92 MeV, and the yield of protons from the reaction ⁴²Ca(α, p)⁴⁵Sc has been measured over the range E_α = 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.