Session D13: Nuclear Reactions:Heavy-ion / Rare Isotope Beams

On Demand

We report the results of a study of multi-nucleon transfer in the reactions of 760 MeV 136Xe with 198Pt and 977 and 1143 MeV 204Hg + 208Pb. In the 136Xe + 198Pt reaction, the Improved Quantum Molecular Dynamics model does an excellent job of describing our results while the predictions of the GRAZING-F and DNS models do not agree with our measurements. In the symmetric 204Hg + 208Pb reaction, none of the models (GRAZING, DNS, ImQMD) describe the measurements adequately. The implications of the model failures for symmetric multi-nucleon transfer reactions for the synthesis of the heaviest nuclei will be discussed.   

On Demand

X-ray superbursts are powered by runaway thermonuclear burning deep inside of a neutron star, where the pycnonuclear fusion of neutron-rich isotopes may be an important heat source. We measured the total fusion cross sections of $^{16}$C + $^{12}$C and $^{16}$C + $^{13}$C for E$_{C.M.}$ = 8 - 22 MeV. The experiment was conducted using the active-target MUlti-Sampling Ionization Chamber (MUSIC) detector at the Argonne Tandem LINAC Accelerator System (ATLAS) facility at Argonne National Lab using a radioactive $^{16}$C beam. The measured cross sections show good agreement with theoretical models. While studies indicate that $^{16}$C has a larger mean radius than $^{15}$C, the $^{16}$C + $^{12, 13}$C cross sections are measured to be smaller than the $^{15}$C + $^{12}$C cross section. This indicates that an enhanced s-wave tail of the $^{15}$C wave function might be increasing the $^{15}$C fusion cross section or that neutron pairing effects in $^{16}$C may reduce the $^{16}$C cross sections.   

On Demand

Under a joint collaboration between TUNL-LANL-LLNL, a set of absolute fission product yield measurements has been performed. The energy dependence of a number of cumulative fission product yields (FPY) have been measured using quasi-monoenergetic neutron beams for three actinide targets, $^{\mathrm{235}}$U, $^{\mathrm{238}}$U and $^{\mathrm{239}}$Pu, between 0.5 and 14.8 MeV. The FPYs were measured by a combination of fission counting using specially designed dual-fission chambers and $\gamma $-ray counting. Each dual-fission chamber is a back-to-back ionization chamber encasing an activation target in the center with thin deposits of the same target isotope in each chamber. This method allows for the direct measurement of the total number of fissions in the activation target with no reference to the fission cross-section, thus reducing uncertainties. Reported are absolute cumulative fission product yields for incident neutron energies of 0.5, 1.37, 2.4, 3.6, 4.6 and 14.8 MeV. New data in the second chance fission region of 5.5 -- 11 MeV are included to complete the measurements in the energy range of interest. These results are compared to previous measurements and theoretical estimates.   

Measurements of short-lived photofission product yields using a rapid transfer system

Photon-induced fission product yield (FPY) studies were conducted on the three major actinide isotopes: $^{\mathrm{235}}$U, $^{\mathrm{238}}$U, and $^{\mathrm{239}}$Pu. Fission was induced at the Triangle Universities Nuclear Laboratory's High Intensity $\gamma $-ray Source using monoenergetic $\gamma $-rays of E$_{\mathrm{\gamma }} \quad =$ 11.2 and 13.0 MeV. To measure the short-lived FPYs, a RApid Belt-driven Irradiated Target Transfer System (RABITTS) was used. The RABITTS is a fully automated 1 m track system which performs cyclic activation by moving the target between irradiation and counting positions. Following $\gamma $-ray activation, the target was rapidly (0.4 s) transferred to two well-shielded Highly Purity Germanium detectors, which measure the induced activity. The irradiation-counting cycle was repeated until the summed data are sufficient for statistical analysis. The counting data was used to validate the half-lives for most identified fission products. More than 40 fission products with half-lives ranging from 1 s to 240 s were uniquely identified, and their yield values computed. The results are compared with previous photon and neutron induced FPY measurements.   

On Demand

Nuclear reaction data collection, evaluation and dissemination have been pioneered at the Brookhaven National Laboratory since the early 50s. These activities gained popularity worldwide, and around 1970 the experimental nuclear reaction data interchange or exchange format (EXFOR) was established. The original EXFOR compilation scope consisted only of neutron reactions and spontaneous fission data, while many other nuclear data sets were ignored. Fission yields play a very important role in applied and fundamental physics, and such data are essential in many applications. The comparative analysis of Nuclear Science References (NSR) and Experimental Nuclear Reaction (EXFOR) databases shows a large number of unaccounted experiments and provides a guide for the recovery of fission cross sections, yields and covariance data sets. The dedicated fission yields data recovery effort is currently underway in the Nuclear Reaction Data Centers (NRDC) network, and includes identification, compilation, storage and Web dissemination of the missing data sets.   

Not Participating

The past few decades witness rapid advancements in intense laser technologies. The promising under-constructing extreme light infrastructure (ELI) of Europe is designed to reach peak laser intensities of about 10$^{\mathrm{24}}$ W/cm$^{\mathrm{2}}$. The corresponding laser electric field strength is comparable to the nuclear Coulomb field at a radius of about 10 to 100 fm Intense laser fields therefore can influence nuclear processes that are sensitive to the Coulomb potential barrier, such as alpha decay. In this presentation, we will analyze the influence of intense laser fields on the nuclear alpha decay process, and present numerical results with the help of quantitative alpha-nucleus potentials. Our results show that alpha decay can indeed be modified by intense external laser fields to some finite extent. A modification on the alpha particle penetrability (or half-life) of 0.1{\%} is predicted for a laser intensity of 10$^{\mathrm{24}}$ W/cm$^{\mathrm{2}}$ Our study provides a scheme where intense lasers meet nuclear physics. In this scheme, the laser influences nuclear physics through its intensity, instead of photon frequency.