Spallation Reactions Research Articles

Isotope production in proton-, deuteron-, and carbon-induced reactions on Nb93 at 113 MeV/nucleon

Isotope-production cross sections for p-, d-, and C-induced spallation reactions on Nb93 at 113 MeV/nucleon were measured using the inverse-kinematics method employing secondary targets of CH2, CD2, and C. The measured cross sections for Mo90, Nb90, Y86,88 produced by p-induced reactions were found to be consistent with those measured by the conventional activation method. We performed benchmark tests of the reaction models INCL-4.6, JQMD, and JQMD-2.0 implemented in the Particle and Heavy Ion Transport code System (PHITS) and of the nuclear data libraries JENDL-4.0/HE, TENDL-2017, and ENDF/B-VIII.0. The model calculations also showed generally good agreement with the measured isotope-production cross sections for p-, d-, and C-induced reactions. It also turns out that, among the three nuclear data libraries, JENDL-4.0/HE provides the best agreement with the measured data for the p-induced reactions. We compared the present Nb93 data with the Zr93 data, that were measured previously by the same inverse kinematics method (Kawase et al., Prog. Theor. Exp. Phys. 2017, 093D03 (2017)2050-391110.1093/ptep/ptx110), with particular attention to the effect of neutron-shell closure on isotope production in p- and d-induced spallation reactions. The isotopic distributions of the measured production cross sections in the Zr93 data showed noticeable jumps at neutron number N=50 in the isotopic chains of ΔZ=0 and -1, whereas no such jump appeared in isotopic chain of ΔZ=0 in the Nb93 data. From INCL-4.6 + GEM calculations, we found that the jump formed in the evaporation process is smeared out by the intranuclear cascade component in Nb91 produced by the Nb93(p,p2n) and (d,d2n) reactions on Nb93. Moreover, for Nb93, the distribution of the element-production cross sections as a function of the change in proton number ΔZ is shifted to smaller ΔZ than for Zr93, because the excited Nb prefragments generated by the cascade process are more likely to emit protons than the excited Zr prefragments, due to the smaller proton-separation energies of the Nb isotopes.

Cosmogenic 3He production rate in ilmenite and the redistribution of spallation 3He in fine-grained minerals

Cosmogenic nuclide surface exposure dating and erosion rate measurements in basaltic landscapes rely primarily on measurement of ^3He in olivine or pyroxene. However, geochemical investigations using ^3He have been impossible in the substantial fraction of basalts that lack separable olivine or pyroxene crystals, or where such crystals were present, but have been chemically weathered. Fine-textured basalts often contain small grains of ilmenite, a weathering-resistant mineral that is a target for cosmogenic ^3He production with good He retention and straightforward mineral separation, but with a poorly constrained production rate. Here we empirically calibrate the cosmogenic ^3He production rate in ilmenite by measuring ^3He concentrations in basalts with fine-grained (∼20 μm cross-section) ilmenite and co-existing pyroxene or olivine from the Columbia River and Snake River Plain basalt provinces in the western United States. The concentration ratio of ilmenite to pyroxene and olivine is 0.78 ± 0.02, yielding an apparent cosmogenic ^3He production rate of 93.6 ± 7.7 atom g^(−1) yr^(−1) that is 20–30% greater than expected from prior theoretical and empirical estimates for compositionally similar minerals. The production rate discrepancy arises from the high energy with which cosmic ray spallation reactions emit tritium and ^3He and the associated long stopping distances that cause them to redistribute within a rock. Fine-grained phases with low cosmogenic ^3He production rates, like ilmenite, will have anomalously high production rates owing to net implantation of ^3He from the surrounding, higher ^3He production rate, matrix. Semi-quantitative modeling indicates implantation of spallation ^3He increases with decreasing ilmenite grain size, leading to production rates that exceed those in a large grain by ∼10% when grain radii are <150 μm. The modeling predicts that for the ilmenite grain size in our samples, implantation causes production rates to be ∼20% greater than expected for a large grain, and within uncertainty resolves the discrepancy between our calibrated production rate, theory, and rates from previous work. The redistribution effect is maximized when the host rock and crystals differ substantially in mean atomic number, as they do between whole-rock basalt and ilmenite.

Spallation reactions induced by 4.4 GeV deuterons on lead isotopes

Independent and cumulative production cross sections for radioactive nuclear fragments from the deuteron-irradiation of isotopically enriched lead (204Pb, 206Pb, 207Pb, and 208Pb) targets were obtained for the first time. The experiment has been performed with a 4.4 GeV deuteron beam from the Nuclotron of the Laboratory of High Energy Physics (LHE), Joint Institute for Nuclear Research (JINR) at Dubna. The production cross sections of target fragments were determined by off-line γ-ray spectroscopy. Charge dispersion and mass-yield distributions were deduced from these data. The results are discussed in terms of the relative importance of different reaction mechanisms (evaporation–spallation, fission and multifragmentation). Comparison of our results with the data from the reaction induced by protons of about the same kinetic energy per nucleon, has been performed. The coexistence of the different decay modes in the formation of the reaction residues, such as spallation, fission and multifragmentation is suggested.

The analytical study of inventories and physicochemical configuration of spallation products produced in Lead-Bismuth Eutectic of Accelerator Driven System

Lead-Bismuth Eutectic (LBE) is used as a spallation neutron target and coolant material of Accelerator Driven System (ADS), and many kinds of elements are produced as spallation products via spallation reactions in LBE of ADS. It is important to evaluate the release and transport behavior of the spallation products in the LBE coolant system of ADS from the viewpoints of the radiological hazard both in the cases of normal operation and accident. The physicochemical configuration of the spallation products is essential to evaluate the release and transport behavior because the physical and chemical properties such as solubility in LBE and volatility depend on the configuration. The inventories and the physicochemical configuration of the spallation products produced in LBE have been investigated for an LBE loop to be installed in the ADS Target Test Facility (TEF-T) in the Japan Proton Accelerator Research Complex (J-PARC). The inventories of the spallation products in the LBE were estimated using the PHITS code based on the technical design specifications and the operation program of TEF-T. The physicochemical configuration of the spallation products in the LBE was calculated using the Thermo-Calc code under the conditions of the operation temperatures of LBE from 350 °C to 500 °C and the oxygen concentrations in LBE from 10 ppb to 10 ppm. From the results of the PHITS code evaluation, 18 elements were evaluated as the important elements from the viewpoint of these large inventories and the radiation hazards of their radionuclide. The results of the Thermo-Calc calculation showed the 8 elements of Rb, Tl, Tc, Os, Ir, Pt, Au and Hg were soluble in LBE under the all given conditions and any kinds of compound were not formed in LBE. It was suggested that the oxides of Ce, Sr, Zr and Y were stable as CeO2, SrO, ZrO2, Ce2O3 and Y2O3 in the LBE. The validity of these results was discussed compared with the previous experimental and theoretical work.

Imaging of fragment particles in water by nuclear spallation during carbon-ion irradiation

Recently we found that the luminescence imaging of water during carbon-ion irradiation was possible using a cooled charge-coupled device (CCD) camera and the method could be used for range estimation of the beam. In the luminescence image, we found luminescence from the fragment particles produced by the nuclear spallation reaction of carbon ions. The luminescence may be used for the estimation of the distribution of the fragment particles by the nuclear spallation. For this purpose, we irradiated carbon ions of 241.5 MeV u−1 to a water phantom and measured the luminescence image of water using a CCD camera. Then, we carefully observed the luminescence distribution after the Bragg peak to find the luminescence from the nuclear spallation reaction. In the luminescence image, we could clearly observe the luminescence from the fragment particles produced by the nuclear spallation reaction during irradiation of carbon ions. The beam widths of the luminescence image of the nuclear spallation were compared with those measured by the ionization chamber. The relative difference of the beam width at FWHM between luminescence image and ionization chamber was 23%. With these results, we conclude that the luminescence image of water during carbon-ion irradiation has a potential to be a new and efficient method for the width estimation of the fragment particles by the nuclear spallation reaction.

The N = 126 factory: A new facility to produce very heavy neutron-rich isotopes

A new facility, the N = 126 factory, is currently under construction at Argonne National Laboratory. It will use multi-nucleon transfer reactions to create neutron-rich isotopes of very heavy elements for studies of interest to the formation of the A ∼ 195 abundance peak in the r-process. This region of the nuclear chart is difficult to access by standard fragmentation or spallation reactions and as a result has remained mostly unexplored. The nuclei of interest, very neutron-rich isotopes around Z = 70–95, will be produced by multi-nucleon exchange of a high intensity 10 MeV/u heavy-ion beam on the most neutron-rich stable isotopes of heavy elements such as 198Pt and 238U. This reaction mechanism can transfer a large number of neutrons and create very neutron-rich isotopes with larger than mb cross-section. The reaction mechanism is a nuclear surface process and the reaction products come out close to the grazing angle, which makes them very difficult to collect. The N = 126 factory circumvents this difficulty by using a unique large high-intensity RF gas catcher, similar to the one currently in operation at CARIBU, to collect the target-like reaction products and transform them into a low-energy beam that will then be mass separated with a medium resolution electromagnetic separator (ΔM/M ≃ 1/1500), followed by an RFQ buncher and an MR-TOF (ΔM/M ≃ 1/100,000) system. The extracted radioactive beams will be essentially pure and available at low-energy for mass measurements with the CPT mass spectrometer or decay study with the X-array.

Microscopic description of proton-induced spallation reactions with the constrained molecular dynamics (CoMD) model

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 followed by a statistical deexcitation model. The calculations were also compared with recent experimental data from the literature. Our calculations showed agreement with some aspects of the experimental data and suggest further improvements in the models. We point out that this CoMD study represents the first complete dynamical description of spallation reactions with a microscopic N-body approach and may lead to advancements in the physics-based modeling of the spallation process.

Measurement of fast neutrons with 238U-coated fission chamber

A fission chamber with two layers of 238U fissile materials has been developed for the measurements of fast neutrons. The developed fission chamber has been tested by 60Co gamma source and 252Cf neutron source. The results have indicated that it is very easy to cut off the gamma rays from the neutrons by using a discriminator, when the fission chamber works in the pulse mode. The detector works well, even if the static air is used as the filling gas. To discuss the application of the detector, Monte Carlo simulations have been performed by considering four 238U-coated fission chambers located outside the spallation target for the fast neutron measurement from spallation reaction. The simulation results have indicated that the detector can be used to measure the fast neutron flux and neutron flux ratio of four fission chambers. Furthermore, a 238U-coated fission chamber can be used within a reactor for longer time, in comparison with a 235U-coated fission chamber.

Corrigendum: Comparison of spallation reaction models based on multiple-criteria decision analysis. https://doi.org/10.3897/nucet.4.31869

Corrigenda: Comparison of spallation reaction models based on multiple-criteria decision analysis. https://doi.org/10.3897/nucet.4.31869

Systematic study of proton-induced spallation reactions with microscopic and phenomenological models

Proton induced spallation reactions on 238U, 208Pb, 181Ta and 197Au targets at high energies were investigated using the microscopic Contrained Molecular Dynamics (CoMD) model and the phenomenological models INC and SMM. We have calculated the total fission cross sections, the ratio fission cross section to residue cross section, the mass yield curves and the excitation energy after the intranuclear cascade using the CoMD model and the INC/SMM phenomenological models. We made a comparison between the models and the experimental data from the liter- ature. Our calculations showed satisfactory agreement with available experimental data and suggest further improvements in the models. Our study with the CoMD code represents the first complete dynamical description of the spallation process with a microscopic code based on an effective nucleon-nucleon interaction.

Systematic study of proton-induced spallation reactions with the Constrained Molecular Dynamics (CoMD) model

Proton – induced spallation reactions on 238U, 208Pb, 181Ta and 197Au targets at high energies were studied and investigated using the microscopic Contrained Molecular Dynamics (CoMD) model. Total fission cross sections, the ratio fission cross section to residue cross section, mean kinetic energy of fission fragments, mass yield curves and the number of nucleons emitted, before and after scission, as well as the total nucleon multiplicity were calculated using the CoMD model and compared with experimental data from the literature. Some of our calculations showed satisfactory agreement with available experimental data.The calculations of cross sections and the ratio fission cross section to residue cross section as a function of the proton energy gave us the opportunity to estimate observables for unmeasured nuclides.

Spallation of 56Fe by 1.0 GeV Protons

Mass, charge and isotopic distributions observed in spallation reactions of 56Fe with 1 GeV protons are analysed in the framework of the intranuclear cascade code ISABEL coupled with the sequential binary decay code MECO. The code MECO provides a description of the equilibrated nuclear decay by the emission of gamma-rays, light-mass particles and clusters as well as intermediate mass fragments emitted in their ground, excited bound and excited unbound states (continuum) according to a generalized Weisskopf formalism. A good overall description of the experimental data is obtained with a global Fermi gas level density parameter and inverse cross sections based on the Christensen and Winther nuclear potential. Multifragmentation decay events are simulated with the code SMM and their influence on the above observables is discussed.

Meteoritic evidence of a late superflare as source of 7Be in the early Solar System

Fossil meteoritic records of short-lived, now-extinct radionuclides provide crucial high-resolution temporal information about the events, processes and activity of the Sun during the early phases of Solar System formation1. The proposed genesis of one such radionuclide,10Be, by spallation reactions of carbon and oxygen2–5 led to the hypothesis of enhanced irradiation in the early Solar System6–8. An alternative scenario of production of 10Be (half-life t1/2 = 1.386 ± 0.016 million years9) by a neutrino process in a supernova arising from the core collapse of a low-mass star (11.8 solar masses, M⊙) has recently been suggested10 and can explain the observed abundance of 10Be in the early Solar System. Here, we report well-resolved excesses in 7Li/6Li of up to ~21.5% in a calcium- and aluminium-rich inclusion (CAI) from the Efremovka meteorite that correlate with 9Be/6Li, suggestive of in situ decay of 7Be. The in situ decay of 7Be to 7Li, with a characteristic half-life of 53.12 ± 0.07 days11, entails multiple episodes of enhanced irradiation in the early Solar System, which have been observed recently in other Sun-like stars12,13. The short half-life of 7Be limits its production by interaction of solar energetic particles (SEPs) with the nebular gas and solids, and provides constraints on the genealogy and chronology of CAIs. Irradiation of the solid and gaseous precursors of CAIs of solar composition by a superflare (X-ray luminosity approximately 1032 erg s−1) during the terminal phase of class I or II of the pre-main-sequence stages of the Sun explains the isotopic properties, distinctive petrographic features and diffusivity constraints in the CAI. Li and Be isotopic measurements of calcium–aluminium inclusions (CAIs) in the Efremovka meteorite suggest that the solid and gaseous precursors of CAIs were irradiated by a superflare during the last stages of the pre-main-sequence evolution of the Sun.

Positron Annihilation Spectroscopy of Active Galactic Nuclei

This paper focuses on the interpretation of radiation fluxes from active galactic nuclei. The advantage of positron annihilation spectroscopy over other methods of spectral diagnostics of active galactic nuclei (therefore AGN) is demonstrated. A relationship between regular and random components in both bolometric and spectral composition of fluxes of quanta and particles generated in AGN is found. We consider their diffuse component separately and also detect radiative feedback after the passage of high-velocity cosmic rays and hard quanta through gas-and-dust aggregates surrounding massive black holes in AGN. The motion of relativistic positrons and electrons in such complex systems produces secondary radiation throughout the whole investigated region of active galactic nuclei in form of cylinder with radius R= 400-1000 pc and height H=200-400 pc, thus causing their visible luminescence across all spectral bands. We obtain radiation and electron energy distribution functions depending on the spatial distribution of the investigated bulk of matter in AGN. Radiation luminescence of the noncentral part of AGN is a response to the effects of particles and quanta falling from its center created by atoms, molecules and dust of its diffuse component. The cross-sections for the single-photon annihilation of positrons of different energies with atoms in these active galactic nuclei are determined. For the first time we use the data on the change in chemical composition due to spallation reactions induced by high-energy particles. We establish or define more accurately how the energies of the incident positron, emitted γ-quantum and recoiling nucleus correlate with the atomic number and weight of the target nucleus. For light elements, we provide detailed tables of all indicated parameters. A new criterion is proposed, based on the use of the ratio of the fluxes of γ-quanta formed in one- and two-photon annihilation of positrons in a diffuse medium. It is concluded that, as is the case in young supernova remnants, the two-photon annihilation tends to occur in solid-state grains as a result of active loss of kinetic energy of positrons due to ionisation down to thermal energy of free electrons. The singlephoton annihilation of positrons manifests itself in the gas component of active galactic nuclei. Such annihilation occurs as interaction between positrons and K-shell electrons; hence, it is suitable for identification of the chemical state of substances comprising the gas component of the investigated media. Specific physical media producing high fluxes of positrons are discussed; it allowed a significant reduction in the number of reaction channels generating positrons. We estimate the brightness distribution in the γ-ray spectra of the gas-and-dust media through which positron fluxes travel with the energy range similar to that recorded by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) research module. Based on the results of our calculations, we analyse the reasons for such a high power of positrons to penetrate through gas-and-dust aggregates. The energy loss of positrons by ionisation is compared to the production of secondary positrons by high-energy cosmic rays in order to determine the depth of their penetration into gas-and-dust aggregations clustered in active galactic nuclei. The relationship between the energy of γ-quanta emitted upon the single-photon annihilation and the energy of incident electrons is established. The obtained cross sections for positron interactions with bound electrons of the diffuse component of the non-central, peripheral AGN regions allowed us to obtain new spectroscopic characteristics of the atoms involved in singlephoton annihilation.

Nuclear spallation in active galaxies

A number of works point to the presence of narrow emission features at unusual energies in the X-ray spectra of active galactic nuclei (AGN) or to potentially low iron abundances as possible evidence for the spallation of iron. With the imminence of high-resolution calorimeter spectroscopy, the potential to test spallation models in astrophysical sources will soon be possible. Previously determined nuclear spallation reactions of Fe are recalculated making use of improved total inelastic and partial reaction cross sections that result in different absolute and relative abundances of the main spallation elements Mn, Cr, V, and Ti. The effects of ionisation and dynamics near the black hole are examined in simulated spectra with CCD and calorimeter (i.e. Hitomi) resolution. With high-resolution, differences in relative abundances and ionisation should be detectable if spallation is originating at large distances from the black hole (e.g. torus or disc wind) where blurring is not significant. If spallation were occurring in the inner accretion disc, it would likely be undetected as blurring effects would cause significant blending of spectral features.

Qualification of the ANET Code for Spallation Neutron Yield and Core Criticality in the KUCA ADS

Innovative nuclear reactor concepts such as the Accelerator Driven Systems (ADSs) have imposed extra requirements of simulation capabilities on the existing stochastic neutronics codes. The combination of an accelerator and a nuclear reactor in the ADS requires the simulation of both subsystems for an integrated system analysis. Therefore, a need arises for more advanced simulation tools, able to cover the broad neutron energy spectrum involved in these systems. ANET (Advanced Neutronics with Evolution and Thermal hydraulic feedback) is an under development stochastic code for simulating conventional and hybrid nuclear reactors. Successive testing applications performed throughout the ANET development have been utilized to verify and validate the new code capabilities. In this context, the ANET reliability in simulating the spallation reaction and the corresponding neutron yield as well as computing the multiplication factor of an operating ADS are here examined. More specifically, three cores of the Kyoto University Critical Assembly (KUCA) facility in Japan were analyzed focusing on the spallation neutron yield and the neutron multiplication factor. The ANET-produced results are compared with independent results obtained using the stochastic codes MCNP6.1 and MCNPX. Satisfactory agreement is found between the codes, confirming thus ANET’s capability to successfully estimate both the neutron yield of the spallation reaction and the keff of a realistic ADS.

New study of various target neutron yields from spallation reactions using a high-energy proton beam

The spallation target plays an important role in the construction of an accelerator-driven system. Its purpose is to generate a neutron flux produced by cascaded spallation reactions using heavy nuclei, the latter being bombarded by the high-intensity proton beam. In this study, we have examined several heavy materials, such as uranium, thorium, tungsten, tantalum, lead, bismuth and mercury. The aim of this is to optimise a high-intensity neutron flux to be useful in several fields of applications, such as medicine and transmutation of nuclear waste. In this paper, we have shown when the spallation target changes the neutron flux varies. For example, uranium and thorium two materials producing a very intense amount of neutrons followed by lead, tungsten, mercury and bismuth and lately tantalum. We found these results by the variation of the proton beams energy from 0.1 GeV to 3 GeV, then with the variation of the geometry. Finally, we validated this study with experimental and theoretical results.

Proton-induced spallation of mercury and xenon targets for neutron flux produced between CEM03.01 and INCL4-ABLA spallation packages

Accelerator-Driven Subcritical (ADS) reactors are one of the pathways considered for the incineration of minor actinides. They use a proton beam accelerator up to a GeV energy, bombarding a spallation target, usually made of a material of high atomic number (W, Pb, Ta or U). The neutrons generated during the spallation reactions are then multiplied. The main goal of this study is to make a comparison between two models of physical packages via the Monte Carlo code MCNP6. The first package is the INCL4-ABLA and the second one is the CEM03.01, and we have deduced the best package according to the neutron production rate. In this study, we are interested in two cylindrical targets of natural mercury and xenon 20cm in height and 20 in diameter and a proton beam varies from 0.1 to 1.5 GeV.

Proton-induced spallation of mercury and xenon targets for neutron flux produced between CEM03.01 and INCL4-ABLA spallation packages

Accelerator-Driven Subcritical (ADS) reactors are one of the pathways considered for the incineration of minor actinides. They use a proton beam accelerator up to a GeV energy, bombarding a spallation target, usually made of a material of high atomic number (W, Pb, Ta or U). The neutrons generated during the spallation reactions are then multiplied. The main goal of this study is to make a comparison between two models of physical packages via the Monte Carlo code MCNP6. The first package is the INCL4-ABLA and the second one is the CEM03.01, and we have deduced the best package according to the neutron production rate. In this study, we are interested in two cylindrical targets of natural mercury and xenon 20cm in height and 20 in diameter and a proton beam varies from 0.1 to 1.5 GeV.

Calculations of current and yield of neutrons using several targets and different proton beam energies

Spallation reactions provide the neutrons which are useful for fundamental research and for several desired applications. It is specifically dedicated to applied research with a neutron flux for driving the subcritical nuclear reactors also for the transmutation of nuclear wastes. The choice of spallation target remains as a nuclear research activity that is more efficient, more adaptable and more coherent to the parameters related to theory and practice through the MC simulation. In this research, we investigated cylindrical spallation targets: beryllium, tin, lead, tungsten, and uranium, which are bombarded by high-energy proton beams. In this work, we focused on the target type of accelerator-driven systems by calculating important parameters such as yield, current, and neutron spectrum using the MCNP code and comparing the results found with theoretical and experimental results, to approve the proper application of an ADS project.