Fragments productions in spallation reactions are key infrastructure data for various applications. Based on the empirical parameterizations {\sc spacs}, a Bayesian-neural-network (BNN) approach is established to predict the fragment cross sections in the proton induced spallation reactions. A systematic investigation have been performed for the measured proton induced spallation reactions of systems ranging from the intermediate to the heavy nuclei and the incident energy ranging from 168 MeV/u to 1500 MeV/u. By learning the residuals between the experimental measurements and the {\sc spacs} predictions, the BNN predicted results are in good agreement with the measured results. The established method is suggested to benefit the related researches in the nuclear astrophysics, nuclear radioactive beam source, accelerator driven systems, and proton therapy, etc.
The ratio of pairing-energy coefficient to temperature ($a_{p}/T$) of neutron-rich fragments produced in spallation reactions has been investigated by adopting an isobaric yield ratio method deduced in the framework of a modified Fisher model. A series of spallation reactions, 0.5$A$ and 1$A$ GeV $^{208}$Pb + $p$, 1$A$ GeV $^{238}$U + $p$, 0.5$A$ GeV $^{136}$Xe + $d$, 0.2$A$, 0.5$A$ and 1$A$ GeV $^{136}$Xe + $p$, and $^{56}$Fe + $p$ with incident energy ranging from 0.3$A$ to 1.5$A$ GeV, has been analysed. An obvious odd-even staggering is shown in the fragments with small neutron excess ($I\e…
We studied the complete dynamics of the proton-induced spallation process with the microscopic framework of the Constrained Molecular Dynamics (CoMD) Model. We performed calculations of proton-induced spallation reactions on 181Ta, 208Pb, and 238U targets with the CoMD model and compared the results with a standard two-step approach based on an intranuclear cascade model (INC) followed by a statistical deexcitation model. The calculations were also compared with recent experimental data from the literature. Our calculations showed an overall satisfactory agreement with the experimental data an…
The Bayesian neural network (BNN) method is used to construct a predictive model for fragment prediction of proton induced spallation reactions with the guidance of a simplified EPAX formula. Compared to the experimental data, it is found that the BNN + sEPAX model can reasonably extrapolate with less information compared with BNN method. The BNN + sEPAX method provides a new approach to predict the energy-dependent residual cross sections produced in proton-induced spallation reactions from tens of MeV/u up to several GeV/u.
Based on the Boltzmann-Uehling-Uhlenbeck (BUU) transport model coupled with a phase-space coalescence afterburner, spallation reaction of $p+^{197}Au$ at the incident beam energy of E$_{beam}$= 800 MeV/nucleon is studied. We find that the number of test particles per nucleon has minor effects on the neutron to proton ratio (n/p) of the produced heavier fragments while it affects much on their yields. The external strong magnetic field affects the production of heavier fragments much than the n/p of produced fragments. The n/p of free nucleons is greatly affected by the strong magnetic field, e…
Rules for in-medium complex particle production in nuclear reactions are proposed. These rules have been implemented in two models to simulate nucleon-nucleus and nucleus-nucleus reactions around the Fermi energy. Our work emphasizes the effect of randomness in cluster formation, the importance of the nucleonic Fermi motion as well as the role of conservation laws. The concepts of total available phase-space and explored phase-space under constraint imposed by the reaction are clarified. The compatibility of experimental observations with a random clusterization is illustrated in a schematic s…
We investigate the prompt emission of few intermediate-mass fragments in spallation reactions induced by protons and deuterons in the 1 GeV range. Such emission has a minor contribution to the total reaction cross section, but it may overcome evaporation and fission channels in the formation of light nuclides. The role of mean-field dynamics and phase-space fluctuations in these reactions is investigated through the Boltzmann-Langevin transport equation. We found that a process of frustrated fragmentation and re-aggregation is a prominent mechanism of production of IMFs which can not be assimi…
The CEM2k and LAQGSM codes have been recently developed at Los Alamos National Laboratory to simulate nuclear reactions induced by particles and nuclei for a number of applications. We have benchmarked our codes against most available measured data at projectile energies from 10 MeV/A to 800 GeV/A and have compared our results with predictions of other current models used by the nuclear community. Here, we present a brief description of our codes and show illustrative results obtained with CEM2k and LAQGSM for A+p and A+A spallation, fission, and fragmentation reactions measured recently at GS…
Different reaction mechanisms contribute to the production of light fragments (LF) from nuclear reactions. Available models cannot accurately predict emission of LF from arbitrary reactions. However, the emission of LF is important for many applications, such as cosmic-ray-induced single event upsets, radiation protection, and cancer therapy with proton and heavy-ion beams, to name just a few. The cascade-exciton model (CEM) and the Los Alamos version of the quark-gluon string model (LAQGSM), as implemented in the CEM03.03 and LAQGSM03.03 event generators used in the Los Alamos transport code …
The dynamics of high-energy proton-induced spallation reactions on target nuclides of $^{136}$Xe, $^{59}$Ni, $^{56}$Fe, $^{208}$Pb, $^{184}$W, $^{181}$Ta, $^{197}$Au and $^{112}$Cd, are investigated with the quantum molecular dynamics transport model. The production mechanism of light nuclides and fission fragments is thoroughly analyzed. The statistical code GEMINI is employed in conjunction to the model for managing the decay of primary fragments. For the treatment of cluster emission during the preequilibrium stage, a surface coalescence model is implemented into the model. It is found that…
The LAQGSM code has been recently developed at Los Alamos National Laboratory to simulate nuclear reactions for proton radiography applications. We have benchmarked our code against most available measured data both for proton-nucleus and nucleus-nucleus interactions at incident energies from 10 MeV to 800 GeV and have compared our results with predictions of other current models used by the nuclear community. Here, we present a brief description of our code and show illustrative results obtained with LAQGSM for neutron spectra measured recently by Nakamura's groups for reactions induced by li…
One of considered nowadays scenarios of proton - nucleus reaction is spallation. Its motivation is based on experimental final-state observations of one heavy nucleus, a small number of light fragments and numerous individual nucleons. It is theoretically described as two step process involving energy deposition in the target nucleus and subsequent evaporation. Several models, based on different assumptions, have been constructed in order to describe the spallation process. The main subject of this work is description of global average properties of proton induced spallation reactions in wide …
Heavy nuclei bombarded with protons and deuterons in the 1 GeV range have a large probability of undergoing a process of evaporation and fission; less frequently, the prompt emission of few intermediate-mass fragments can also be observed. We employ a recently developed microscopic approach, based on the Boltzmann-Langevin transport equation, to investigate the role of mean-field dynamics and phase-space fluctuations in these reactions. We find that the formation of few IMF's can be confused with asymmetric fission when relying on yield observables, but it can not be assimilated to the statist…
We have used an extended version of the Cascade-Exciton Model (CEM) to analyze more than 600 excitation functions for proton induced reactions on 19 targets ranging from C-12 to Au-197, for incident energies ranging from 10 MeV to 5 GeV. We have compared the calculations to available data, to calculations using approximately two dozen other models, and to predictions of several phenomenological systematics. We present here our conclusions concerning the relative roles of different reaction mechanisms in the production of specific final nuclides. We comment on the strengths and weaknesses of th…
The induced-activity investigations in off-line analysis performed in different experiments, concerning pre-actinide and actinide nuclei, are here presented and discussed. Generalized expressions for the determination of independent yields/cross sections of radioactive nuclei, formed in the targets, are derived and analysed. The fragment mass distribution from U-238, Th-232 and Ta-181 photofission at the bremsstrahlung end-point energies of 50 and 3500 MeV, and from Am-241, U-238 and Np-237 fission induced by 660-MeV protons, are scrutinized from the point of view of the multimodal fission app…
We use particle-transport simulations to show that secondary pions play a crucial role for the development of the hadronic cascade and therefore for the production of neutrons and photons from thick spallation targets. In particular, for the n_TOF lead spallation target, irradiated with 20 GeV/c protons, neutral pions are involved in the production of ~90% of the high-energy photons; charged pions participate in ~40% of the integral neutron yield. Nevertheless, photon and neutron yields are shown to be relatively insensitive to large changes of the average pion multiplicity in the individual s…
The ability to describe production of light fragments (LF) is important for many applications, such as cosmic-ray-induced single event upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams. The Cascade-Exciton Model (CEM) and the Los Alamos version of the Quark-Gluon String Model (LAQGSM) event generators in the LANL transport code MCNP6, describe quite well the spectra of fragments with sizes up to 4He across a broad range of target masses and incident energies (up to ~ 5 GeV for CEM and up to ~ 1 TeV/A for LAQGSM). However, they do not predict the high-energ…
Isotope production cross sections from the 500 MeV p + 136Xe interactions measured recently at GSI in inverse kinematics have been simulated with MCNP6 using the CEM03.03 event generator. MCNP6 reproduces reasonably well most of the measured cross sections. However, the isotopes with a charge number greater than the charge number on the target by two units is overestimated significantly by CEM03.03. We found also an underestimation for the production of isotopes in the deep spallation region, far from the target-nucleus. Further investigations and further improvement of CEM03.03 with a possibl…
We present the current status of the improved Cascade-Exciton Model (CEM) code CEM2k and of the Los Alamos version of the Quark-Gluon String Model code LAQGSM. To describe fission and light-fragment (heavier than He4) production, both CEM2k and LAQGSM have been merged with the GEM2 code of Furihata. We present some results on proton- and deuteron-induced spallation, fission, and fragmentation reactions predicted by these extended versions of CEM2k and LAQGSM. We show that merging CEM2k and LAQGSM with GEM2 allows us to describe many fission and fragmentation reactions in addition to the spalla…
In nuclear reactions induced by hadrons and ions of high energies, nuclei can disintegrate into many fragments during a short time (~100 fm/c). This phenomenon known as nuclear multifragmentation was under intensive investigation last 20 years. It was established that multifragmentation is an universal process taking place in all reactions when the excitation energy transferred to nuclei is high enough, more than 3 MeV per nucleon, independently on the initial dynamical stage of the reactions. Very known compound nucleus decay processes (sequential evaporation and fission), which are usual for…
We present a statistical-model description of fission, in the framework of compound-nucleus decay, which is found to simultaneously reproduce data from both heavy-ion-induced fusion reactions and proton-induced spallation reactions at around 1 GeV. For the spallation reactions, the initial compound-nucleus population is predicted by the Liège Intranuclear Cascade Model. We are able to reproduce experimental fission probabilities and fission-fragment mass distributions in both reactions types with the same parameter sets. However, no unique parameter set was obtained for the fission probability…
The formation of fragments in proton-induced reactions at low relativistic energies within a combination of a covariant dynamical transport model and a statistical approach is investigated. In particular, we discuss in detail the applicability and limitations of such a hybrid model by comparing data on fragmentation at low relativistic $SIS/GSI$-energies.
The atomic numbers and the masses of fragments formed in quasi-fission reactions have been simultaneously measured at scission in 48 Ti + 238 U reactions at a laboratory energy of 286 MeV. The atomic numbers were determined from measured characteristic fluorescence X-rays whereas the masses were obtained from the emission angles and times of flight of the two emerging fragments. For the first time, thanks to this full identification of the quasi-fission fragments on a broad angular range, the important role of the proton shell closure at Z = 82 is evidenced by the associated maximum production…
Current r-process models under-produce A<130 nuclei. P-process models either underproduce A<100 and 150<A<165 p-nuclei, or have other limitations. We argue that the puzzles in these two mechanisms can be solved by heavy-ion spallation. Spallation happens in the explosive phase transition from a neutron star to a quark star - the quark-nova. The quark-nova triggers the r-process which creates abundant A>130 nuclei, and spallation fragments these isotopes into A<130 nuclei and all 35 p-nuclei. Our model is universal in relation to a star's age, metallicity, and chemistry.
Two NaI (85% 129-I and 15% 127-I) targets were exposed to a beam of 660-MeV protons. Cross sections for formation of 76 residual nuclei were obtained by the induced activity method. The results are compared with other experimental data on 127-I and theoretical calculations by eleven models contained in the codes LAHET3 (using the Bertini+Dresner, ISABEL+Dresner, INCL+Dresner, and INCL+ABLA options), CASCADE, CEM95, CEM2K, LAQGSM+GEM2, CEM2k+GEM2, LAQGSM+GEMINI, and CEM2k+GEMINI. Most of the models describe spallation products with masses close to the target reasonably well while the reliabilit…
We review recent results on intermediate mass cluster production in heavy ion collisions at Fermi energy and in spallation reactions. Our studies are based on modern transport theories, employing effective interactions for the nuclear mean-field and incorporating two-body correlations and fluctuations. Namely we will consider the Stochastic Mean Field (SMF) approach and the recently developed Boltzmann-Langevin One Body (BLOB) model. We focus on cluster production emerging from the possible occurrence of low-density mean-field instabilities in heavy ion reactions. Within such a framework, the …
The jet fragmentation function describes the longitudinal momentum distribution of hadrons inside a reconstructed jet. We study the jet fragmentation function in proton-proton collisions in the framework of soft-collinear effective theory (SCET). We find that, up to power corrections, the jet fragmentation function can be expressed as the ratio of the fragmenting jet function and the unmeasured jet function. Using renormalization group techniques, we are able to resum large logarithms of jet radii R in the perturbative expansion of the cross section. We use our theoretical formalism to describ…
Use of deuteron-induced spallation reactions at intermediate energies has recently been proposed for transmutation of several long-lived fission products (LLFPs). In the design study of a transmutation system using a deuteron primary beam, accurate cross section data of deuteron-induced reactions on the LLFPs are indispensable. Reliable model predictions play an important role in completing the necessary cross section data since currently available experimental data are very limited. Under the circumstances, we have been developing a code system dedicated for deuteron-induced reactions, which …
The light fragment production reactions for 10 MeV to 3 GeV protons incident on O-16, Al-27, Fe, Nb-93, and Ag are analyzed by a combination of an intranuclear cascade model and a generalized evaporation model which includes light nuclei up to Mg as ejectiles. It is concluded that evaporation is the dominant process by which particles lighter than or equal to Be are produced from targets heavier than O.
Recent data on the deutron and $^3$He production in central Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS) energies measured by the NA49 collaboration are analyzed within the model of the three-fluid dynamics (3FD) complemented by the coalescence model for the light-fragment production. The simulations are performed with different equations of state---with and without deconfinement transition. It is found that scenarios with the deconfinement transition are preferable for reproduction rapidity distributions of deuterons and $^3$He, the corresponding results well agree with the exp…
Intermediate mass fragment (IMF) formation in the 12 GeV proton induced reaction on Au target is analyzed by using a combined framework of a transport model (JAM/MF) and a newly developed non-equilibrium percolation (NEP) model. In this model, we can well reproduce the mass distribution of fragments. In addition, the sideward peaked angular distribution would emerge under the condition that the fragment formation time is very short, around 20 fm/c. Within this short time period, the un-heated part of the residual nucleus is kept to have doughnut shape, then the Coulomb repulsion from this shap…
We propose a method to calculate the two-dimensional (2D) fission-fragment yield $Y(Z,N)$ versus both proton and neutron number, with inclusion of odd-even staggering effects in both variables. The approach is to use Brownian shape-motion on a macroscopic-microscopic potential-energy surface which, for a particular compound system is calculated versus four shape variables: elongation (quadrupole moment $Q_2$), neck $d$, left nascent fragment spheroidal deformation $ε_{\rm f1}$, right nascent fragment deformation $ε_{\rm f2}$ and two asymmetry variables, namely proton and neutron numbers in eac…
It is demonstrated that the fragmentation functions at large momentum fraction play a key role in hard hadron production from relativistic proton-proton collisions. We find that this region of the fragmentation functions is not strongly constrained by the electron-positron data. This freedom can be used (together with the transverse momentum distribution of partons) to reproduce hard pion-to-proton ratio data in relativistic proton-proton collisions.
A brief description of our improvements and refinements that led from the CEM95 version of the Cascade-Exciton Model (CEM) code to CEM97 and to CEM2k is given. The increased accuracy and predictive power of the code CEM2k are shown by several examples. To describe fission and light-fragment (heavier than 4He) production, the CEM2k code has been merged with the GEM2 code of Furihata. We present some results on proton-induced fragmentation and fission reactions predicted by this extended version of CEM2k. We show that merging CEM2k with GEM2 allows us to describe many fission and fragmentation r…
The production cross sections of various fragments from proton-induced reactions on $^{56}$Fe and $^{27}$Al have been analyzed by the Quantum Molecular Dynamics (QMD) plus Statistical Decay Model (SDM). It was found that the mass and charge distributions calculated with and without the statistical decay have very different shapes. These results also depend strongly on the impact parameter, showing an importance of the dynamical treatment as realized by the QMD approach. The calculated results were compared with experimental data in the energy region from 50 MeV to 5 GeV. The QMD+SDM calculatio…
The time evolution of protons and $^3$He fragments from Au+Au/Pb+Pb reactions at 0.25, 2, and 20 GeV$/$nucleon is investigated with the potential version of the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model combined with the traditional coalescence afterburner. In the coalescence process, the relative distance $R_0$ and relative momentum $P_0$ are surveyed in the range of 3-4 fm and 0.25-0.35 GeV$/$c, respectively. For both clusters, a strong reversed correlation between $R_0$ and $P_0$ is seen and it is time-dependent as well. For protons, the accepted ($R_0$, $P_0$) bands lie in…
Background: Neutron stars are astronomical systems with nucleons submitted to extreme conditions. Due to the long range coulomb repulsion between protons, the system has structural inhomogeneities. These structural inhomogeneities arise also in expanding systems, where the fragment distribution is highly dependent on the thermodynamic conditions (temperature, proton fraction, ...) and the expansion velocity. Purpose: We aim to find the different regimes of fragment distribution, and the existence of infinite clusters. Method: We study the dynamics of the nucleons with a semiclassical molecular…
One-proton removal from 15O at intermediate energies (56 A MeV) is studied in the eikonal approximation of the Glauber model. The production of the 14N core fragment in the ground and excited states is regarded. The calculated proton removal cross section, the 15O interaction cross section, and the longitudinal momentum distribution of the 14N fragments are compared to recent experimental data [1]. [1] H. Jeppesen, R. Kanungo, B. Abu-Ibrahim it et al, Nucl. Phys. A 739, 57 (2004).
A short review of simulation results of anti-proton-proton and anti-proton-nucleus interactions within the framework of Geant4 FTF (Fritiof) model is presented. The model uses the main assumptions of the Quark-Gluon-String Model or Dual Parton Model. The model assumes production and fragmentation of quark-anti-quark and diquark-anti-diquark strings in the mentioned interactions. Key ingredients of the model are cross sections of string creation processes and an usage of the LUND string fragmentation algorithm. They allow one to satisfactory describe a large set of experimental data, especially…
