Binay Dasmahapatra

Fusion cross sections for 12C + 12C, 12C + 13C and 13C + 13C at low energies

Abstract Fusion cross sections for 12 C + 12 C and 12 C + 13 C have been measured by the total-γ-ray- yield method over the c.m. energy intervals 4.2–7.0 MeV and 3.1–6.7 MeV, respectively. Comparing the present 12 C + 12 C fusion cross sections with those obtained previously by various methods, the discrepancies between data are clarified. The fusion cross sections for 12 C + 13 C agree with those of Dayras et al . and confirm the unusual energy dependence below the interaction barrier. The fusion cross sections for the 12 C + 13 C and 13 C + 13 C systems are found to be enhanced with respect to the 12 C + 12 C system more than the increase in the nuclear radius suggests. The enhancement, which is larger for 12 C + 13 C than for 13 C + 13 C, is attributed to the attractive action of the valence neutron of the 13 C nucleus. A new resonance has been observed in the 12 C + 12 C system at E c.m. ≈ 5.22 MeV.

Fusion cross sections for 16O + 13C at low energies

Abstract The energy dependence of the fusion cross section has been measured over the range E c.m. = 3.05–6.88 MeV by detecting the γ-rays from residual nuclei in a 4π geometry. Analyzing the 1.37 MeV photopeak, originating from 24 Mg 1.37 MeV → g.s. transition , the cross sections for 24 Mg+2n channel were also deduced. The measured fusion cross sections have been compared with those for 12 C + 12 C and 12 C + 13 C systems and found to be significantly different. For 13 C+ 13 C the fusion cross sections agree with the standard optical-model prediction down to the lowest measured energies, while for 12 C + 12 C and 12 C + 13 C they are, at the lowest energies, too low. It is suggested that the unpaired valence nucleons facilitate fusion at energies well below the Coulomb barrier.

Cross section measurements for the 9Be+9Be System at subbarrier energies

Abstract The total reaction cross section and the characteristic y-ray cross sections have been measured for the 9 Be+ 9 Be reaction in the energy range E cm = 1.4–3.4 MeV, detecting the prompt γ-rays emitted by the various residual nuclei with two Nal detectors in nearly 4π geometry and with a germanium detector, respectively. The differential elastic cross sections for the same system have also been measured at e c.m. = 2.2, 2.7 and 3.2 MeV. The cross sections calculated with the “standard” and the proximity optical model potentials, which describe well the total reaction cross sections of the light nuclei, agree with the 9 Be + 9 Be elastic-scattering data, but underpredict the total reaction cross section by a factor of 2 to 3. The characteristic γ-ray measurements show that all two-particle emission channels, nα 13 C, nn 16 O, np 16 N and αα 10 Be are enhanced by about that factor, while the single-particle emission channel, p 17 N, is not enhanced.

Reactions with 9Be at subbarrier energies

Abstract The 9 Be+ 9 Be, 9 Be+ 10 B, 9 Be+ 11 B and 9 Be+ 13 C reactions have been studied at subbarrier energies measuring the cross sections for the characteristic γ-rays emitted by the residual nuclei and comparing them with the statistical evaporation prediction. A substantial enhancement in the αn channel, which contains the the α-transfer reaction from 9 Be, has been observed in all the systems studied. Evidence suggesting that the α-transfer reaction is not exclusively a direct transfer process is being presented.

Accurate measurement of target thickness by heavy ion elastic scattering

Abstract The potentiality of heavy ion elastic scattering for the measurement of target thickness has been investigated considering a number of target-projectile combinations. From such studies it is inferred that the target thickness can be measured with an uncertainty of ±5% in most cases.

Total reaction and transfer cross sections for 11B + 9Be and 13C + 9Be reactions at low energies

Abstract The total reaction cross sections for 11B + 9Be and 13C + 9Be have been measured by the total γ-ray yield method over the energy intervals Ec.m. = 1.4–4.4 MeV and Ec.m. = 2.0–5.2 MeV, respectively. The cross sections for the neutron transfer reactions 11B(9Be, 8Be)12B, leading to the 12B 0.953 and 1.674 MeV states, and 13C(9Be, 8Be)14C, leading to the 14C 6.094, 6.728 and 6.902 MeV states, have been obtained from the yields of the characteristic γ-rays. The α-transfer reaction 11B(9Be, 5He)15N, leading to many unresolved 15N states, has been observed with large cross section. There is, however, no evidence for the 13C(9Be, 5He)17O transfer process in the 17O + nα channels. This different behaviour of the 11B + 9Be and 13C + 9Be systems seems to indicate that the α-transfer reaction at sub-barrier energies is not a direct transfer process, and that it probably occurs via molecular state formation.

Cross-section measurements for 7Li + 11B AND 7Li + 13C reactions at low energies

Abstract The 7 Li + 11 B and 7 Li + 13 C reactions have been studied at incident energies below and around the Coulomb barrier, by measurement of the cross sections for the characteristic γ-rays emitted by the residual nuclei. The nα, αα and np emission channels are found to be enhanced with respect to the statistical compound nucleus predictions, while the nn and single-particle emission channels are not enhanced. An unusual energy dependence is observed for the 7 Li + 11 B → nn 16 O 7.12 MeV channel cross section, suggesting the existence of a broad resonance.

Cross-section measurements for the 9Be + 9Be, 7Ll +11B and α + 14C reactions at low energies☆

Abstract The 9Be + 9Be, 7Li+11B and α +14C reactions, leading to the 18O compound state in the excitation energy range between 25 and 31 MeV, have been studied by measurement of the cross sections for the characteristic g-rays emitted by the residual nuclei. The cross sections for the two-particle emission channels (nn, np, na, aa) are much larger in the two heavy-ion reactions, 9e+9Be and 7Li + 11B, than in the a + 14C reaction. It is suggested that the large enhancement in the nn and np channels, which do not include any transfer processes, indicates that 9Be+ 9Be and 7Li + 11B form a largely deformed molecular state, from which only low-energy particles can be emitted. A broad resonance is observed at ∼ 28 MeV 18O excitation energy in the 9Be+9Be→ nn16O 7.12 MeV, 7 Li + 11 B → nn 16 O 7.12 MeV and 9 Be + 9 Be → np 16 N 0.397 MeV reaction channels.

Fusion and neutron-transfer cross sections for 13C + 10B and 13C + 11B reactions at subbarrier energies

Abstract The cross sections for the 10 B( 13 C, 12 C) 11 B neutron-transfer reaction, leading to the 11 B 4.45 and 6.74 MeV and 12 C 4.44 MeV excited states, and for 13 C + 10 B fusion have been measured by the characteristic and total γ-ray yield methods, respectively, over the energy (c.m.) interval 2.4–5.8 MeV. For 13 C + 11 B, with no transfer reactions present, the fusion cross sections have been measured between E c.m. = 2.3 and 6.4 MeV. The fusion cross sections for 13 C + 10 B and 13 C + 11 B are found to be almost equal and slightly enhanced with respect to those for 12 C + 10 B and 12 C + 11 B.

Measurement of cross sections for 12C + 14C reaction at subbarrier energies☆

Abstract The partial cross sections for the 12 C + 14 C reaction have been determined in the energy range E c.m. = 5–8 MeV by measuring, with an HPGe detector, the yields of the characteristic γ-rays emitted from the residual nuclei. Comparison of the partial cross sections with those of the 13 C + 13 C reaction shows that the two reactions proceed mainly via the compound-nucleus formation and subsequent statistical evaporation of particles. The total fusion cross section is well described by the optical-model calculation using standard parameters. A small enhancement observed in the total fusion cross section at E c.m. ⋍ 6 MeV , is correlated with the E x = 25.35 MeV, Γ = 1.75 MeV fine-structure resonance observed in the γ + 26 Mg photonuclear reaction.