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Register a new userSimultaneous determination of neutron-induced fission and radiative-capture cross sections from decay probabilities obtained with a surrogate reaction
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Reliable neutron-induced reaction cross sections of unstable nuclei are essential for nuclear astrophysics and applications but their direct measurement is often impossible. The surrogate-reaction method is one of the most promising alternatives to access these cross sections. In this work, we successfully applied the surrogate-reaction method to infer for the first time both the neutron-induced fission and radiative-capture cross sections of 239Pu in a consistent manner from a single measurement. This was achieved by combining simultaneously-measured fission and gamma-emission probabilities for the 240Pu(4He,4He) surrogate reaction with a calculation of the angular-momentum and parity distributions populated in this reaction. While other experiments measure the probabilities for some selected gamma-ray transitions, we measure the gamma-emission probability. This enlarges the applicability of the surrogate-reaction method.
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We investigated the 238U(d,p) reaction as a surrogate for the n + 238U reaction. For this purpose we measured for the first time the gamma-decay and fission probabilities of 239U* simultaneously and compared them to the corresponding neutron-induced data. We present the details of the procedure to infer the decay probabilities, as well as a thorough uncertainty analysis, including parameter correlations. Calculations based on the continuum-discretized coupled-channels and distorted-wave Born approximations were used to correct our data from detected protons originating from elastic and inelastic deuteron breakup. In the region where the fission and gamma-decay probabilities compete, the corrected fission probability is in agreement with neutron-induced data, whereas the gamma-decay probability is much higher than the neutron-induced data. The performed statistical-model calculations are not able to explain these results.
Alternative methods to calculate neutron capture cross sections on radioactive nuclei are reported using the theory of Inclusive Non-Elastic Breakup (INEB) developed by Hussein and McVoy [1]. The statistical coupled-channels theory proposed in Ref. [2] is further extended in the realm of random matrices. The case of reactions with the projectile and the target being two-cluster nuclei is also analyzed and applications are made for scattering from a deuteron target [3]. An extension of the theory to a three-cluster projectile incident on a two-cluster target is also discussed. The theoretical developments described here should open new possibilities to obtain information on the neutron capture cross sections of radioactive nuclei using indirect methods.
The capture-fission cross-sections in an energy range of 206-242 MeV of 48Ca-projectiles and mass-energy distributions (MEDs) of reaction products in an energy range of 211-242 MeV have been measured in the 48Ca+208Pb reaction using the double-arm time-of-flight spectrometer CORSET. The MEDs of fragments for heated fission were shown to consist of two components. One component, which is due to classical fusion-fission, is associated with the symmetric fission of the 256No compound nucleus. The other component, which appears as shoulders, is associated with the quasi-fission process and can be named quasi-fission shoulders. Those quasi-fission shoulders enclose light fragments whose masses are 60-90 a.m.u. The total kinetic energy (TKE) of the fragments that belong to the shoulders is higher than the value expected for a classical fusion-fission process. We have come to the conclusion that in quasi-fission, spherical shells with Z=28 and N=50 play a great role. It has also been demonstrated that the properties of the MEDs of fragments formally agree with a well-known hypothesis of two independent fission modes; in this case the modes are normal fusion-fission and quasi-fission processes. A high-energetic Super-Short mode of classical fission has been found at low excitation energies in the mass range of heavy fragments M = 130-135 and TKE = 233 MeV; however the yield associated with this mode is small.
The neutron-capture reaction plays a critical role in the synthesis of the elements in stars and is important for societal applications including nuclear power generation and stockpile-stewardship science. However, it is difficult - if not impossible - to directly measure neutron capture cross sections for the exotic, short-lived nuclei that participate in these processes. In this Letter we demonstrate a new technique which can be used to indirectly determine neutron-capture cross sections for exotic systems. This technique makes use of the $(d,p)$ transfer reaction, which has long been used as a tool to study the structure of nuclei. Recent advances in reaction theory, together with data collected using this reaction, enable the determination of neutron-capture cross sections for short-lived nuclei. A benchmark study of the $^{95}$Mo$(d,p)$ reaction is presented, which illustrates the approach and provides guidance for future applications of the method with short-lived isotopes produced at rare isotope accelerators.
In our previous paper, we predicted $sigma_{rm R}$ for $^{40-60,62,64}$Ca+ $^{12}$C scattering at 280 MeV/u, using the Kyushu (chiral) $g$-matrix folding model with the densities calculated with D1S-GHFB with and without the AMP. Interaction cross sections $sigma_{rm I}$ are available for $^{42-51}$Ca + $^{12}$C scattering, whereas $sigma_{rm R}$ are available for p+$^{48}$Ca scattering. As for $^{48}$Ca, the high-resolution $E1$ polarizability experiment ($E1$pE) yields $r_{rm skin}^{48}(E1{rm pE}) =0.14 sim 0.20~{rm fm}$. We determine $r_{rm skin}^{48}({rm exp})$ from the data on $sigma_{rm R}$ for p+$^{48}$Ca scattering and from the data on $sigma_{rm I}$ for $^{48}$Ca+$^{12}$C scattering. We use the chiral (Kyushu) $g$-matrix folding model with the densities calculated with the Gogny-D1M Hartree-Fock-Bogoliubov with the AMP. The D1M-GHFB+AMP proton and neutron densities are scaled so as to reproduce the data under the condition that the radius $r_{rm p}$ of the scaled proton density equals the data $r_{rm p}({rm exp})$ of the electron scattering. The neutron radius $r_{rm n}$ thus obtained is an experimental value. Our results are $r_{rm skin}^{48}({rm exp})=-0.031sim 0.183$fm for p+$^{48}$Ca and $0.100 sim 0.218$fm for $^{48}$Ca + $^{12}$C scattering. Using the $r_{rm skin}^{48}$-$r_{rm skin}^{208}$ relation with a high correlation coefficient $R=0.99$, we have transformed $r_{rm skin}^{208}({rm PREXII})$ and $r_{rm skin}^{208}(E1{rm pE})$ to the corresponding values $r_{rm skin}^{48}({rm tPREXII})$ and $r_{rm skin}^{48}({rm t}E1{rm pE})$. The transformed data $r_{rm skin}^{48}({rm tPREXII})=0.190 sim 0.268$fm is consistent with $r_{rm skin}^{48}=0.102 sim 0.218$fm for $^{48}$Ca + $^{12}$C. Our final result is $r_{rm skin}^{48}=0.102 sim 0.218$fm determined from $^{48}$Ca + $^{12}$C scattering.
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