Pre-compound neutron evaporation in low energy heavy ion fusion reactions

Inclusive and exclusive neutron evaporation spectra have been studied from the fusion reactions at 80 MeV C-12 on Ti-46 and 131 MeV 31 p on Al-27, populating the compound nucleus Ni-58 at the excitation energy of 79.5 MeV but in different angular momentum ranges. The evaporation residues Fe-53, Fe-55 and (CO)-C-56 were identified by their characteristic gamma-rays. The measured energy spectra of evaporated neutrons were compared with the predictions from statistical-model calculations. In case of the asymmetric system C-12 + Ti-46, the neutron spectra are well reproduced, when compared with the results from statistical-model calculations with level density parameter a = A/8 MeV-1. On the contrary, the experimental spectra for the symmetric system 31 p + Al-27 are found to be harder than the theoretical predictions with a = A/8 MeV-1. In this case, a lower value of the level density parameter a = A/10 MeV-1 seems to be required to reproduce the experimental results. The dependence of the energy spectra on the entrance channel is taken as an indication that, in case of the symmetric system, the neutrons are in part emitted from a temperature equilibrated di-nuclear complex at a higher temperature before the formation of the compound nucleus

Pre-compound neutron evaporation in low energy heavy ion fusion reactions

Inclusive and exclusive neutron evaporation spectra have been studied from the fusion reactions at 80 MeV 12C on 46Ti and 131 MeV 31P on 27Al, populating the compound nucleus 58Ni at the excitation energy of 79.5 MeV but in different angular momentum ranges. The evaporation residues 53Fe, 55Fe and 56Co were identified by their characteristic \u3b3 -rays. The measured energy spectra of evaporated neutrons were compared with the predictions from statistical-model calculations. In case of the asymmetric system 12C + 46Ti, the neutron spectra are well reproduced, when compared with the results from statistical-model calculations with level density parameter a = A/8MeV 121. On the contrary, the experimental spectra for the symmetric system 31P + 27Al are found to be harder than the theoretical predictions with a = A/8MeV 121. In this case, a lower value of the level density parameter a = A/10 MeV 121 seems to be required to reproduce the experimental results. The dependence of the energy spectra on the entrance channel is taken as an indication that, in case of the symmetric system, the neutrons are in part emitted from a temperature equilibrated di-nuclear complex at a higher temperature before the formation of the compound nucleus

Entrance channel effects in fission of (TI)-T-197

The pre- and post-scission neutron multiplicities are measured for (16)O+(181)Ta and (19)F+(178)Hf systems where the same compound nucleus (197)Tl is formed at the same excitation energies (E(*)=72, 76, and 81 MeV). The measured pre-scission neutron multiplicities are found to be different for the two reactions and this difference in neutron yield increases with the excitation energy of the compound nucleus. The experimental pre-scission neutron yield is compared with predictions from the statistical model of compound nuclear decay containing the strength of nuclear viscosity as a free parameter. The magnitude of nuclear viscosity required to fit the experimental yield is found to be different for the two reactions. Because the two systems under consideration lie on the two sides of the Businaro-Gallone point, this observation indicates that the entrance channel mass asymmetry plays an important role in determining the number of neutrons emitted prior to scission in fusion-fission reactions

Role of nuclear dissipation and entrance channel mass asymmetry in pre-scission neutron multiplicity enhancement in fusion-fission reactions

Pre-scission neutron multiplicities are measured for (12)C + (204)Pb and (19)F + (197)Au reactions at laboratory energies of 75-95 MeV for the (12)C beam and 98-118 MeV for the (19)F beam. The chosen projectile-target combinations in the present study lie on either side of the Businaro-Gallone mass asymmetry (alpha(BG)) and populate the (216)Ra compound nucleus. The dissipation strength is deduced after comparing the experimentally measured neutron yield with the statistical model predictions which contains the nuclear viscosity as a free parameter. Present results demonstrate the combined effects of entrance channel mass asymmetry and the dissipative property of nuclear matter on the pre-scission neutron multiplicity in fusion-fission reactions

Measurement of neutron multiplicity from fission of U-228 and nuclear dissipation

Pre- and post-scission neutron multiplicities are measured at different excitation energies of the compound nucleus (228)U populated using the (19)F+(209)Bi reaction. The measured yield of pre-scission and total neutrons are compared with the statistical model calculation for the decay of a compound nucleus. The statistical model calculations are performed using the Bohr-Wheeler transition state fission width as well as the dissipative dynamical fission width due to Kramers. Comparison between the measured and the calculated values shows that, while the Bohr-Wheeler fission width grossly underestimates the pre-scission neutron yield, a large amount of dissipation is required in the Kramers width to fit the experimental pre-scission multiplicities. Various factors contributing to the large excitation energy dependence of the fitted values of the dissipation coefficient are discussed

CRISPLD2 variants including a C471T silent mutation may contribute to nonsyndromic cleft lip with or without cleft palate

Objective: To assess the association between nonsyndromic (NS) cleft lip with or without cleft palate (CL(P)) and single-nucleotide polymorphisms (SNPs) within the CRISPLD2 gene (cysteine-rich secretory protein LCCL domain containing 2). Design: Four SNPs within the CRISPLD2 gene domain (rs1546124, rs8061351, rs2326398, rs4783099) were genotyped to test for association via family-based association methods. Participants: A total of 5826 individuals from 1331 families in which one or more family member is affected with CL(P). Results: Evidence of association was seen for SNP rs1546124 in U.S. (p = .02) and Brazilian (p = .04) Caucasian cohorts. We also found association of SNP rs1546124 with cleft palate alone (CP) in South Americans (Guatemala and ECLAMC) and combined Hispanics (Guatemala, ECLAMC, and Texas Hispanics; p = .03 for both comparisons) and with both cleft lip with cleft palate (CLP; p = .04) and CL(P) (p = .02) in North Americans. Strong evidence of association was found for SNP rs2326398 with CP in Asian populations (p = .003) and with CL(P) in Hispanics (p = .03) and also with bilateral CL(P) in Brazilians (p = .004). In Brazilians, SNP rs8061351 showed association with cleft subgroups incomplete CL(P) (p = .004) and unilateral incomplete CL(P) (p = .003). Prediction of SNP functionality revealed that the C allele in the C471T silent mutation (overrepresented in cases with CL(P) presents two putative exonic splicing enhancer motifs and creates a binding site AP-2 alpha, a transcription factor involved in craniofacial development. Conclusions: Our results support the hypothesis that variants in the CRISPLD2 gene may be involved in the etiology of NS CL(P)

Fission and binary fragmentation reactions in Se-80+Pb-208 and Se-80+Th-232 systems

Fission and binary fragmentation of the excited nuclear systems of Z=116 and 124 were investigated using the reactions induced by Se-80 beams on Pb-208 and Th-232 targets at bombarding energies ranging from 470 to 630 MeV. The mass and kinetic energy of the binary reaction products were reconstructed by measuring their velocities by the time-of-flight method and the angles of emission using multiwire proportional chambers. Total neutron multiplicities were measured in coincidence with the fragments, using an array of neutron detectors. The fragment mass-energy correlation was studied for the two systems. The average total kinetic energy (TKE) of fragments for the Se-80+Pb-208 system agrees with earlier measurements and with Viola's systematics in the mass symmetric region for compound nucleus fission, whereas for the Se-80+Th-232 system, the TKE values are significantly lower. This is also consistent with higher values of total neutron multiplicities observed for the case of Se-80+Th-232 at comparable available energies. From an extrapolation of the measured total neutron multiplicities for the mass symmetric region to zero compound nucleus excitation energy, the average number of prompt neutrons expected to be emitted in the spontaneous fission of the superheavy Z=116 has been estimated to be nu(sf)(tot)=10 +/- 2, which is consistent with the value derived for the same compound nucleus populated in the Fe-56+Th-232 reaction in an earlier work. In the case of the Se-80+Th-232 system, similar analysis was carried out by taking the average TKE from Viola's systematics for estimating the available energy for particle emission corresponding to compound nucleus fission. In this way, by extrapolating the observed neutron multiplicities to zero compound nucleus excitation energy, a value of nu(sf)(tot)=15 +/- 2 was obtained for the spontaneous fission of the superheavy Z=124 nucleus. The increase in the average number of neutrons emitted in fission as a function of the atomic number of the nucleus in the superheavy mass region was confirmed by comparing the results of the present work with published data