Determination of 8B(p, γ )9C Reaction Rate From 9C Breakup

The astrophysical factor of the ⁸B(p, γ )⁹C reaction at zero energy, S ₁₈(0), is determined from three-body model analysis of ⁹C breakup processes. The elastic breakup ²⁰⁸Pb(⁹C,p ⁸B)²⁰⁸Pb at 65 MeV/nucleon and the one-proton removal reaction of ⁹C at 285 MeV/nucleon on C and Al targets are calculated with the continuum-discretized coupled-channels method (CDCC) and the eikonal reaction theory (ERT), respectively. As a result of the present analysis, S ₁₈(0) extracted from the two reactions shows good consistency, in contrast to in the previous studies.     

Investigation of the level structure of17O

The reactions¹²C(⁷Li,d) and¹³C(⁷Li,t) have been studied atE _C.M.=13.3. MeV. Spin assignments have been extracted from the integrated cross sections of the first reaction. The latter reaction has been analysed in terms of a modified-DWBA code.     

Selective population of the lowest-lying negative parity states in23Na in the12C(12C,p)23Na reaction

The¹²C(¹²C,p)²³Na reaction was investigated in the vicinity of the Coulomb barrier. The lowest-lying negative parity states in²³Na were found to be preferentially populated at energies for which correlated resonances exist in the excitation functions of theα, p, n andγ exit channels of the¹²C+¹²C reaction. If these negative parity states are assumed to consist of ap _1/2 hole coupled to a²⁰Ne quartet state, this selectivity can be explained with the existence ofα-particle doorway states.     

A study of the 12N 2.43 MeV level

We have measured the differential cross sections for the reactions ¹²C(τ, τ′)¹²C(17.77 MeV 0⁺T=1) and ¹²C(τ, t)¹²N(2.43 MeV) at E_τ=44 MeV. The similar shapes of the angular distributions and the relative magnitudes of the cross sections suggest that the ¹²N 2.43 MeV level is the 0⁺T=1 analog to the ^q12C 17.77 MeV level. We have also studied the reaction ¹⁴N(p,t) ¹²N(2.43 MeV) at E_p=52 MeV. The strength with which this level is excited in this reaction is consistent with reasonable two-step calculations assuming the 2.43 MeV level to have J^π=0⁺.     

First study of the (14C, 12C) reaction: Selectivity of the reaction and the energy levels of 28Mg and 30Si

The first measurements are reported for (¹⁴C, ¹²C) two-neutron stripping reactions. Energy spectra up to an excitation energy of 12 MeV have been measured at 69 MeV for the ²⁶Mg(¹⁴C, ¹²C) and ²⁸Si(¹⁴C, ¹²C) reactions. A strong selectivity of this reaction is observed. Using this selectivity, the comparison of the spectra suggests J^π assignments for several ³⁰Si and ²⁸Mg states. The results from the other two-neutron stripping reactions, (t, p) and (¹⁸O, ¹⁶O) are compared with those of the (¹⁴C, ¹²C) reaction.     

Investigation of one-nucleon transfer reactions between complex nuclei at incident energies between 3 and 8

Angular distributions of the ground state transitions in the reactions ¹¹B(¹⁴N, ¹⁵O)¹⁰Be, ¹¹B(¹⁴N, ¹³C)¹²C, ¹²C(¹¹B, ¹²C)¹¹B and ¹³C(¹²C, ¹³C)¹²C have been measured with a magnetic spectrometer as an identification system. The first two reactions (angular momentum transfer l = 2) measured at 41, 77 and 113 MeV show a clear damping of the oscillatory structures in the angular distributions. This effect was qualitatively reproduced by DWBA calculations which take into account a recoil phase, thus showing that the damping of the structures is due to the recoil of the transferred particle on the system. The reaction ¹¹B(¹²C, ¹¹B)¹²C (l = 2) at 87 MeV with Q = 0 is well reproduced by the calculations, whereas the ¹³C(¹²C, ¹³C)¹²C reaction as the only l = 0 transition is in complete disagreement with theoretical expectations.     

Spin determination of the 12C + 12C resonance at Ec.m. = 6.25 MeV

The J^π value of the ¹²C + ¹²C resonance at E_c.m. = 6.25 MeV has been determined to be 2⁺. This is in contrast to several theoretical predictions which give J^π = 0⁺. In addition, J^π values of several sub-Coulomb resonances of the ¹²C + ¹²C reaction have been determined for the first time.     

Defect-dominated optical emission and enhanced ultraviolet photoconductivity properties of ZnO nanorods synthesized by simple and catalyst-free approach

We report on the defect-dominated light emission and ultraviolet (UV) photoconductivity characteristics of ZnO nanorods (NRs) fabricated using a facile, cost-effective, and catalyst-free thermal decomposition route under varying reaction temperatures. The morphological and structural studies reveal the formation of homogeneous quality nanorods in large scale at the highest reaction temperature of 600 ^°C. The luminescence feature of the nanorods is dominated by the defect related emission over the typical band edge emission. The variation of band-edge and native defect-related emission response of the samples has been correlated to the morphology and microstructure. In photoconductivity studies, the I–V characteristics of the ZnO NRs prepared at different reaction temperatures in dark and under UV illumination (λ=365 nm) follow the power law, i.e., IαV ^r . An enhanced ultraviolet photodetection has been observed in the nanorods fabricated at the highest reaction temperature of 600 ^°C. The sample prepared at highest reaction temperature of 600 ^°C exhibits UV photosensitivity value (photo-to-dark current ratio) of around 1.18×10³, which is much higher in magnitude compared to that of the samples prepared at lower reaction temperatures. The enhanced photoconductivity may be assigned to the development of uniformity and homogeneity of the nanorods. Further development of such ZnO nanostructures can form the basis of promising prototype luminescent and UV photodetecting devices.     

12C + 7Li Reaction measurements and the 12C(7Li,t)16O reaction

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 θ_lab = 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.     

22Ne(a,n)25Mg reaction in CONe mantle of massive stars at high temperatures

The effectiveness of²²Ne (a, n)²⁵Mg reaction as a neutron source is examined at high temperatures 0.8?T ₉?3.0 (T ₉ is the temperature in units of 10⁹ K). An assembly consisting of¹²C,¹⁶O, and²²Ne is considered at the end of helium burning in some massive stars. Alpha particles necessary for this neutron producing reaction are assumed to be due to reactions involving¹²C and¹⁶O nuclei. Assuming²²Ne as the only neutron absorber, the number density of neutrons is calculated. The mantles outside the cores of massive stars are possibly the physical sites for these reactions.     

Solution of the10Li-Puzzle

The mass of¹⁰Li has been measured with two different reactions:⁹Be(¹³C,¹²N)¹⁰Li,E _Lab=336 MeV, and¹³C(¹⁴C,¹⁷F)¹⁰Li,E _Lab=337 MeV. The mass excess of 33.445(50) MeV is deduced from theQ-value measurement.¹⁰Li is found to be particle-unstable with respect to one-neutron emission by 0.42(5) MeV. In the analysis of the first reaction a low lying excited state is found at 0.38(8) MeV. This state and the ground state can be most probably identified as the 1⁺/2⁺-doublet coupled from the [π 1p3/2 ?ν 1p 1/2] configuration, the 1⁺-state being the ground state. The (¹³C,¹²N)-reaction populates the 1⁺-state strongly due to a spin-isospin-flip character of the dominant part of the transition amplitude. The 2⁺-member corresponds to the mass given by Wilcox et al. A second excited state is observed at 4.05(10) MeV with a width of 0.7(2) MeV, it can be associated with theν 1d 5/2-strength. The second reaction is fully supporting the interpretation of the ground state doublet. The excited state at 4.05 MeV is not observed in this reaction and indeed it should not, because the reaction does not populate in first order excited neutron configurations. The levels are well described by mean field calculations including pairing correlations. The lowest resonance in the calculations is theν 1/2^?-configuration, whereas theν 1/2⁺-configuration shows at the neutron threshold a strong non-resonant contribution.     

Investigation of quasimolecular states in 24Mg* through the analysis of the angular dα correlations in the 12C(14N, d)24Mg(α)20Ne reaction

Theoretical analysis of the differential cross sections and angular correlation functions in the ¹²C(¹⁴N, d)²⁴Mg*(α)²⁰Ne reaction at the energy of the incident nitrogen ions E _lab=29–42 MeV is performed in the models of the direct transfer of ¹²C cluster and the compound nucleus. Amplitudes of the reduced widths for the excited quasimolecular states like ¹²C ? ¹²C* in the ²⁴Mg nucleus are obtained. The effect of various states of the relative motion of nuclei in the ¹²C + ¹²C* configuration on the angular dα-correlation functions is studied.     

Study of the reaction 12C(γ, n 3He)2α

The possibility of separating, with the aid of photoemulsion, channels of the reaction ¹²C(γ, n ³He)2α that involve the formation of ⁷Be and ⁸Be intermediate nuclei in excited states is studied. The experimental energy distributions of these nuclei are obtained. The relative yields from these reaction channels are estimated.     

Resonant effects in the12C+12C→8Be gs +16O gs reaction aroundE cm=32.5 MeV

The¹²C+¹²C→⁸Be _gs +1¹⁶O _gs reaction has been studied at c.m. energies of 27.9, 32.5 and 35.0 MeV. The energy dependence of the cross section is consistent with a resonant behaviour like the one observed for two¹²C nuclei excited in a very deformed state in the final channel. The angular distributions for the two reactions show also a similar oscillatory behaviour. The analysis suggests that the reaction proceeds through the formation of an intermediate state with a complex nature, involving largely deformed configurations as well as almost spherical ones.     

Coupled-channels analysis of energy-dependent isospin violation in the 12C(d, α)10B(1.74 MeV,T = 1) reaction

We have studied the isospin non-conserving ¹²C(d, α)¹⁰B(1.74 MeV, 0⁺, T= 1) reaction at several incident energies of 9 ≦ E_d ≦ 16 MeV in terms of a coupled-channels method. The reaction processes involved in the present analysis are the successive single-nucleon pick-up processes as well as the inelastic scattering of deuterons from ¹²C. It is assumed that the isospin violation should occur in the intermediate mirror cluster states of ³He + ¹¹B and t + ¹¹C, due to the Coulomb interaction. The calculation reproduces fairly well the observed features of the reaction, i.e. the decreasing cross section with increasing incident energy, and the variation of the angular distribution. We also note that the calculation shows the energy-dependent localization of isospin violation in the angular momentum space, i.e. a specifically narrow localization at the lower incident energies studied and its broadening at the higher energies. This fact is associated with the variation of the angular distribution from a forward-backward symmetry at the lower incident energies to a forward peak at the higher energies.     

Angular-momentum analysis of pionic nucleon capture

The pionic capture reaction A(N, π)(A + 1) is analyzed in terms of the Mandelstam model for pion production by two nucleons. The results are applied to the proton-capture reactions ¹²C(p, π⁺)¹³C and ⁴He(p, π⁺)⁵He, and comparisons are made with experiments.     

Discovery of the First 2- State in 16C via Neutron Knockout Reaction

The ¹⁶C nucleus has been investigated by the neutron knockout reaction of ¹⁷C on a liquid hydrogen target. Applying the invariant mass method in inverse kinematics and γ-ray spectroscopy, the energy spectrum was reconstructed by triple-coincidence measurement, in which neutrons, charged fragments, and γ rays from the decay of the reaction residue (¹⁶C*) were detected. A peak at 0.47 MeV was observed in the invariant mass spectrum in coincidence with a peak at 0.74 MeV in the γ-ray spectrum, which indicates the presence of an unbound state with an excitation energy of 5.46 MeV. Comparison of the experimental cross section with the value derived by a theoretical calculation provided evidence that the spin-parity of this state is 2^?.     

Isospin violation in α-induced reactions

A study has been made of the reactions ¹²C(α, α')¹²C and ¹⁰B(α, d)¹²C which lead to the 12.71 MeV T = 0 and the 15.11 MeV T = 1 levels in ¹²C. Significant structure is observed in the yield curves of the reactions ¹²C(α, α') ¹²C for both the isospin allowed and forbidden reactions up to the maximum available α-energy of 27 MeV; this structure is attributed to compound nucleus formation. No significant structure is observed in the reaction ¹⁰B(α, d)¹²C.     

Study of spin-orbit interaction of13C and15N nuclei in14C induced transfer reactions on138Ba

Angular distributions of single nucleon transfer reactions populating single particle states in the reactions¹³⁸Ba(¹⁵C,¹⁴N)¹³⁷Cs and¹³⁸Ba(¹⁴C,¹³C)¹³⁹Ba have been studied. The shapes of the angular distributions show differences for different final configurations. Using the reaction asymmetry it is possible to describe these differences consistently for all transitions by a spin-orbit potential. The polarisation of the outgoing fragments is discussed and its dependence on final configurations is explained. The spin-orbit potentials deduced from the reaction asymmetry are large, as compared to predictions of folding potentials. They are, however, consistent with measurements of spin-flip probabilities. The origin of theL-S interaction is to be found in coupling effects of second order in the heavy ion reaction.