Spectroscopy of 46Ar by the (t,p) two-neutron transfer reaction
K. Nowak, K. Wimmer, S. Hellgartner, D. Mücher, V. Bildstein, J. Diriken, J. Elseviers, L. P. Gaffney, R. Gernhäuser, J. Iwanicki, J. G. Johansen, M. Huyse, J. … 展开作者
K. Nowak, K. Wimmer, S. Hellgartner, D. Mücher, V. Bildstein, J. Diriken, J. Elseviers, L. P. Gaffney, R. Gernhäuser, J. Iwanicki, J. G. Johansen, M. Huyse, J. Konki, T. Kröll R. Krücken, R. Lutter, R. Orlandi, J. Pakarinen, R. Raabe, P. Reiter, T. Roger, G. Schrieder, M. Seidlitz, O. Sorlin, P. Van Duppen, N. Warr, H. De Witte, M. Zielinska
States in the $N=28$ nucleus $^{46}$Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive $^{44}$ at an energy of 2.16~AMeV and a tritium loaded titanium target were used to populate $^{46}$ by the t($^{44}$,p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in $^{46}$ have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695~keV has been identified as $J^π= 0^+$. The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell model calculations using state-of-the-art effective interactions.
A new method is proposed to deduce the neutron radii of neutron-rich nuclei. This method requires measuring the reaction cross sections of both the neutron-rich nucleus and its stable isotope at the same energy on a proton target. Using this method and the available experimental data of $^{12,22}$C + $p$ and $^{9,14}$Be + $p$ at 40$A$ MeV, the neutron radii of $^{22}$C and $^{14}$Be have been deduced for the first time.
The relative importance of neutron transfer and breakup process in reaction around Coulomb barrier energies have been studied for the $^{7}$Li+$^{124}$Sn system. Coupled channel calculations have been performed to understand the one neutron stripping and pickup cross sections along with the breakup in the $^{7}$Li+$^{124}$Sn system. The systematics of one and two neutron striping and pickup cross sections with $^7$Li projectile on several targets show an approximate universal behaviour that have been explained by a simple model. Complete reaction mechanism have been studied by comparing the re…
Background: Eclipse effect of the neutron and proton in a deuteron target is essential to correctly describe high-energy deuteron scattering. The nucleus-deuteron scattering needs information not only on the nucleus-proton but also the nucleus-neutron interaction, for which no direct measurement of the nucleus-neutron cross sections is available for unstable nuclei. Purpose: We systematically evaluated the total reaction cross sections by a deuteron target to explore the feasibility of extracting the nucleus-neutron interaction from measurable cross sections. Methods: High-energy nucleus-deute…
We investigate the contributions of various reaction channels to the interaction, reaction, charge-changing and neutron-changing cross sections. The goal is to investigate the relation between microscopic interactions and the symmetry energy component of the equation of state (EoS) of interest for the structure of neutron stars. We have made a comparison of the neutron skins extracted from diverse experimental techniques with those obtained with Hartree-Fock-Bogoliubov calculations with 23 Skyrme and with 8 density-dependent interactions used in the relativistic mean field method. We have show…
Probabilities for two-neutron transfer reactions, $P_{\rm 2n}$, are often discussed in comparison with the square of the corresponding probabilities for one-neutron transfer process, $(P_{\rm 1n})^2$, implicitly assuming that $(P_{\rm 1n})^2$ provides the probability of two-neutron transfer reactions in the absence of the pairing correlation. We use a schematic coupled-channels model, in which the transfers are treated as effective inelastic channels, and demonstrate that this model leads to $P_{\rm 2n}=(P_{\rm 1n})^2/4$, rather than $P_{\rm 2n}=(P_{\rm 1n})^2$, in the pure sequential limit. W…
Background: Multi-nucleon transfer reactions have recently attracted attention as a possible path to the synthesis of new neutron-rich heavy nuclei. Purpose: We study transfer reactions involving massive nuclei with the intention of understanding if the semi-classical model GRAZING coupled to an evaporation and fission competition model can satisfactory reproduce experimental data on transfer reactions in which fission plays a role. Methods: We have taken the computer code GRAZING and have added fission competition to it (GRAZING-F) using our current understanding of $Γ_n/Γ_f$, fission barrier…
Knockout reactions with heavy ion targets in inverse kinematics, as well as "quasi-free" (p,2p) and (p,pn) reactions are useful tools for nuclear spectroscopy. We report calculations on \textit{ab-initio} many-body wavefunctions based on the no-core shell model to study the nucleon removal reactions in light nuclei, including beryllium, carbon, and oxygen isotopic chains, and explore the importance of using an \textit{ab-initio} method. Our study helps clarifying how the extraction of spectroscopic factors from the experiments depend on the details of the many-body wavefunctions being probed. …
Cross sections for neutron-induced reactions from surrogate data: revisiting the Weisskopf-Ewing approximation for $(n,n^{\prime})$ and $(n,2n)$ reactions
The contribution of one neutron stripping cross section to the total reaction cross section has been studied for $^9$Be projectile incident on $^{169}$Tm, $^{181}$Ta, $^{187}$Re and $^{197}$Au targets around Coulomb barrier energy. The measured one neutron stripping cross sections for these systems have been compared with the coupled channel calculations. The recently developed global set of optical model potential parameters for $^9$Be projectile has been used in the present calculations. The cumulative of measured complete fusion (CF), incomplete fusion (ICF), one neutron stripping and calcu…
Interference effect of neutron capture cross section between the compound and direct processes is investigated. The compound process is calculated by resonance parameters and the direct process by the potential mode. The interference effect is tested for neutron-rich $^{82}$Ge and $^{134}$Sn nuclei relevant to $r$-process and light nucleus $^{13}$C which is neutron poison in the $s$-process and produces long-lived radioactive nucleus $^{14}$C ($T_{1/2}=5700$ y). The interference effects in those nuclei are significant around resonances, and low energy region if $s$-wave neutron direct capture …
Using adiabatic distorted-wave approximation (ADWA) with nonlocal optical potentials (NLOP) for $(d,p)$ transfer reactions [G.W. Bailey, N.K. Timofeyuk, and J.A. Tostevin, Phys. Rev. Lett. 117, 162502 (2016)] reported strong sensitivity to the $n$-$p$ force model. This sensitivity disappears in rigorous three-body Faddeev-type results. Some shortcomings of ADWA with NLOP are pointed out.
Background: One-nucleon knockout reactions provide insightful information on the single-particle structure of nuclei. When applied to one-neutron halo nuclei, they are purely peripheral, suggesting that they could be properly modeled by describing the projectile within a Halo Effective Field Theory (Halo-EFT). Purpose: We reanalyze the one-neutron knockout measurements of $^{11}$Be and $^{15}$C-both one-neutron halo nuclei-on beryllium at about 60MeV/nucleon. We consider Halo-EFT descriptions of these nuclei which already provide excellent agreement with breakup and transfer data. Method: We i…
Gamma-strength function essentially distinguishes the reaction mechanisms of charged particle inelastic and neutron capture reactions, reflecting from the ratios of transition of neutron capture to low-lying states. The extraordinary quenching of gamma_0 transition of p-wave neutron resonance reaction in 3s-region nucleus 57Fe is observed, for the first time, due to the non-forming 2p-1h doorway state activation which raises the strong intensities of gamma_1 and gamma_2. The enhancement of low energy gamma-strength function doesn't emerge in the neutron capture reaction resulting from the popu…
Direct hard photon emissions from incoherent proton-neutron bremsstrahlung in collisions of the neutron-rich projectile $^{50}$Ca with $^{12}$C and $^{40}$Ca targets are simulated in the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. By adjusting the diffuseness parameter of neutron density in the droplet model to obtain different neutron skin thicknesses for $^{50}$Ca, the effects of neutron skin thickness on direct hard photon emission are investigated via several probes. The results show that more direct hard photons are produced with increasing neutron skin thi…
We propose a novel method for producing very-neutron-rich hypernuclei and corresponding resonance states by employing charge-exchange reactions via pp($^{12}$C, $^{12}$N $K^+$)n$Λ$ with single-charge-exchange and ppp($^{9}$Be, $^{9}$C $K^+$)nn$Λ$ with double-charge-exchange, both of which produce $ΛK^+$ in a target nucleus. The feasibility of producing very-neutron-rich hypernuclei using the proposed method was analysed by applying an ultra-relativistic quantum molecular dynamics model to a $^6$Li+$^{12}$C reaction at 2 $A$ GeV. The yields of very-neutron-rich hypernuclei, signal-to-background…
Two-neutron transfer reactions are studied within the interacting boson model based on the nuclear energy density functional theory. Constrained self-consistent mean-field calculations with the Skyrme energy density functional are performed to provide microscopic input to completely determine the Hamiltonian of the IBM. Spectroscopic properties are calculated only from the nucleonic degrees of freedom. This method is applied to study the $(t,p)$ and $(p,t)$ transfer reactions in the assorted set of rare-earth nuclei $^{146-158}$Sm, $^{148-160}$Gd, and $^{150-162}$Dy, where spherical-to-axially…
We propose a novel method to measure the neutron-neutron scattering length using the $^{6}$He$(p,pα)nn$ reaction in inverse kinematics at high energies. The method is based on the final state interaction (FSI) between the neutrons after the sudden knockout of the $α$ particle. We show that the details of the neutron-neutron relative energy distribution allow for a precise extraction of the $s$-wave scattering length. We present the state-of-the-art in regard to the theory of this distribution. The distribution is calculated in two steps. First, we calculate the ground-state wave function of $^…
We present a reaction model to describe the fast removal of the $α$-particle core in $^8$He nucleus with eventual emission of four neutrons. The obtained four neutron energy distributions allows to explain the sharp low energy peak observed by studying the missing mass spectra of four neutrons in [Nature Vol. 606, p. 678], as a consequence of dineutron-dineutron correlations.
The 15N(p,n) reaction is a promising candidate for the production of monoenergetic neutrons with energies of up to 5.7 MeV at the facilities where the T(p,n)3He reaction cannot be used. The characteristic properties of this reaction were studied focusing on its suitability as a source of monoenergetic neutrons for the measurement of differential scattering cross sections in the neutron energy range of 2 MeV to 5 MeV. For this purpose differential and integral cross sections were measured and the choice of optimum target conditions was investigated. The reaction has already been used successful…
Within the minimum model of neutron stars (NS) consisting of neutrons, protons and electrons, a new approach is proposed for inferring the symmetry energy of super-dense neutron-rich nucleonic matter above twice the saturation density $ρ_0$ of nuclear matter directly from integrating iteratively barotropic pressures in both neutron stars and heavy-ion reactions. Simultaneously, the proton fraction of NSs at $β$ equilibrium is extracted as a function of baryon density from the same procedure. An application of this approach using the NS pressure from GW170817 and the pressure in cold symmetric …
The average prompt-fission-neutron multiplicity $\barν$ is of significance in the areas of nuclear theory, nuclear nonproliferation, and nuclear energy. In this work, the surrogate-reaction method has been used for the first time to indirectly determine $\barν$ for $^{239}$Pu($n$,$f$) via $^{240}$Pu($α$,$α^{\prime}f$) reactions. A $^{240}$Pu target was bombarded with a beam of 53.9-MeV $α$ particles. Scattered $α$ particles, fission products, and neutrons were measured with the NeutronSTARS detector array. Values of $\barν$ were obtained for a continuous range of equivalent incident neutron en…
$^{1}S_{0}$ \textit{nn}-scattering length has been measured in the \textit{nd}-breakup reaction at 60 MeV. The experiment was performed in the final state interaction geometry with registration of all three secondary particles. The scattering length $a_{nn} = -16.3 \pm 0.5$~fm was obtained from a comparison of the experimental dependence of the \textit{nd}-breakup yield on the relative energy of \textit{nn}-pair with the simulation results. An analysis of this value of scattering length together with the data obtained in other experiments on \textit{nd}- and \textit{dd}-breakup confirms the hy…
Modeling direct and pre-equilibrium processes of neutron-induced reactions with noniterative finite amplitude method and distorted-wave Born approximation
We discuss the possibility to build a neutron target for nuclear reaction studies in inverse kinematics utilizing a storage ring and radioactive ion beams. The proposed neutron target is a specially designed spallation target surrounded by a large moderator of heavy water (D$_2$O). We present the resulting neutron spectra and their properties as a target. We discuss possible realizations at different experimental facilities.
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 a…
PINO - a tool for simulating neutron spectra resulting from the 7Li(p,n) reaction
7 Li（p，n）反应与3.7 MV的Van de Graaff加速器相结合，在FZK常规使用，以进行激活以及keV区域中子的飞行时间测量。计划中的具有更高质子电流的新装置（如SARAF和FRANZ）以及液体锂靶技术的可用性将引发这种方法的复兴。详细了解中子能谱不仅在实验计划阶段很重要，而且在活化实验分析过程中也很重要。因此，基于蒙特卡罗的程序PINO（质子在中子出）的开发，它允许考虑设置的几何形状和质子能量分布的中子谱的模拟。
A ThO$_{2}$ sample and a nickel activation foil were irradiated in the leakage neutron field of CFBR-II reactor. The activities of the activation products were measured after irradiation to obtain the reaction rates. The normalized reaction rates were also calculated based on the ENDF/B-VII.1, CENDL-3.1, JENDL-4.0, BROND-2.2 databases. The experimental reaction rate ratio is 4.37 with an uncertainty of 3.9\% which is coincident with each of the ratios calculated based on the ENDFB-VII. 1, JENDL-4.0, BROND-2.2 databases, but is 11.2\% larger than that based on CENDL-3.1 database.
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 f…
