232Th Reaction Research Articles

Observation of near-scission “polar” and “equatorial” proton emission in heavy-ion induced fission

Proton and α-particle energy spectra were measured in coincidence with fission fragments at different relative angles in 16O (96 MeV) + 232Th reaction. The multiplicity spectra were analyzed within the framework of a Moving Source Disentangling Analysis (MSDA) to determine contributions from different emission stages. The MSDA conclusively shows “Near Scission Emission (NSE)” as an essential component in the multiplicity spectra. In contrast to NSE α particles which emit mainly perpendicular (“equatorial emission”), the NSE protons are observed to be emitted perpendicular as well as parallel (“polar emission”) to the fission axis with similar intensities (~20% for each). Thus, around 40% of total pre-scission protons are emitted near the scission stage, whereas the same fraction for α particles is only around 10%. The inevitable presence of “polar” and “equatorial” NSE protons in a heavy-ion induced fission has been observed for the first time. Present results open up a new avenue to study the heavy-ion induced fission dynamics.

Study of binary fragmentation dynamics of 260Rf compound nucleus at an excitation energy of 85.7 MeV

The fission dynamics has been studied for a near super heavy compound nucleus 260Rf populated through 28Si + 232Th reaction at an excitation energy of 85.7 MeV. Full momentum transfer binary events were separated from the transfer induced fission events. The contribution from transfer induced fission has been found to be 7±2%. Mas ratio distribution, mass-total kinetic energy (TKE), and mass angle correlation have been extracted for the full momentum transfer events using two body kinematics. The experimentally extracted width of mass distribution is higher than the mass width calculated theoretically using the saddle-point model, which indicates the presence of non-compound nuclear fission in the reaction under study. The mass-TKE distribution obtained for 260Rf nucleus matches with the theoretical predictions from the Viola systematics and GEneral description of Fission observables (GEF) model. The mass-angle distribution for the reaction under study indicates no significant correlation between the mass and emission angles of the fission fragments.

Measurements of 232Th(n,2n) 231Th reaction cross-sections in the neutron energy of 12–18.5 MeV

Measurements of 232Th(n,2n) 231Th reaction cross-sections in the neutron energy of 12–18.5 MeV

Evaluation of Neutron Cross-Section Data Using Gaussian Mixture Model and Digital Filter

For the accurate estimation of neutron cross-section data, evaluation of nuclear data is mandatory to fulfill the need of nuclear science and technology. In this work, the evaluation of 232Th(n,2n)231Th, 241Am(n,2n)240Am, 100Mo(n,2n)99Mo, and 96Mo(n,p)96Nb reaction cross-section data is carried out using a novel method. This novel method of evaluation employs a cluster-based piecewise evaluation followed by a digital filter for merging the evaluated curves. The clusters in the experimental data and model data are identified using the probabilistic method of the Gaussian Mixture Model. The clustered experimental data are then regressed using the polynomial regression technique. The model data are generated using the Talys 1.9 code, and the model deficiency due to the complex random nature of nuclear reactions is also accounted here using chi-squared analysis. Evaluation in each cluster is then carried out independently using the popular Kalman filter technique. For obtaining a single smooth evaluated curve for the whole energy range, the popular smoothing digital filter, the Savitzky-Golay Filter, is employed for the first time in nuclear data evaluation. The proposed evaluated curves and existing evaluated curves of 232Th(n,2n)231Th, 241Am(n,2n)240Am, 100Mo(n,2n)99Mo, and 96Mo(n,p)96Nb reactions from nuclear data libraries such as ENDF/BVIII.0, JEFF-3.3, JENDL-4.0, CENDL-3.1, and TENDL 2021 are compared and found to be in good agreement. It is also found that generally, evaluation methods are data dependent, and so, a single evaluation method may not be applicable for all reactions of all nuclides. Since piecewise evaluation is cluster dependent, selecting the appropriate cluster makes this method robust for almost all reactions of all nuclides. Also, it is proven that this novel method of evaluation is a promising method demonstrating the potential of this approach for evaluation based on the chi-squared goodness-of-fit test with respect to standard evaluated library ENDF/BVIII.0 and experimental data.

SHELL EFFECTS IN THE FISSION OF <sup>236</sup>U* NUCLEI, FORMED IN THE REACTION <sup>232</sup>Th(α,f) AT INCIDENT ALPHA PARTICLES ENERGY OF 29 MeV

Mass and energy distribution of fission fragments of 236U* nuclei, formed in the reaction 232Th(α,f) at incident alpha energy of 29 MeV were studied to reveal the influence of shell effects. The experiment was carried out by 2E method at U-150M accelerator at Institute of Nuclear Physics, Almaty city. Acquired experimental data was decomposed into yields of separate shells, including deformed shells, assuming that the shell yield has the form of gauss distribution. The manifestation of deformed shells N84, Z52 and deformed shells Z36, Z38 was revealed.

New signature of non-equilibrium fission from pre-scission α-particle emission

The pre-scission α-particle multiplicity (αpre), measured in 16O (96 MeV) + 232Th reaction, is observed to be significantly lower than the global trend reported earlier. Statistical model calculations also show a much shorter fission-time to reproduce the experimental αpre. By assimilating the previous measurements, it is observed that the αpre makes a changeover from high to a very low value while crossing the Businaro Gallone point in mass asymmetry in the entrance channels in heavy-ion induced fission of 232Th. Similar discontinuous behavior with respect to the entrance channel mass asymmetry was observed earlier in fission fragment angular anisotropy data, and it was attributed to “pre-equilibrium fission”. The present results on αpre provide compelling evidence for an admixture of non-equilibrium fission which depends on the entrance channel dynamics.

Production of 230Pa as a Source for Medical Radionuclides 230U and 226Th Including Isolation by Liquid–liquid Extraction

ABSTRACT Liquid–liquid extraction of protactinium with different extractants (1-octanol, MIBK, aliquat 336) was studied depending on concentration of nitric and hydrochloric acids, presence of bulk amount of thorium, fluoride ions, and addition of boric acid or Al3+ ions as a masking agent. The extraction with 1-octanol followed by back-extraction with 7 M HCl + 0.1 M HF solution proved to be appropriate for selective 230Pa isolation from thorium irradiated with medium-energy protons. The proposed procedure provided simultaneous production of medical 225Ac and 230Pa/230U from the same Th-target. The experimental cross-sections of 230Pa formation in the reaction 232Th(p,3n)230Pa were determined for the protons energy range of 140–35 MeV and compared with literature data. The yield of 230U and impurities of 232U and 233U depending on the energy of protons entering a thick thorium target were estimated.

On the volatility of protactinium in chlorinating and brominating gas media

Abstract A multi-target recoil chamber technique was applied to study online chemical properties of protactinium in chlorinating and brominating gas media using 226Pa (T 1/2 = 1.8 min) decaying by alpha emission (74%) and β+/EC decay (26%). A 58 MeV proton beam passing 15 × 50 μg/cm2 thick 232Th targets enabled production of 226Pa formed in the reaction 232Th(p,7n). Isothermal gas chromatography in quartz columns allowed for the determination of adsorption enthalpies of oxohalides and pure halides of Pa5+ compounds. On the basis of empirical correlations, these adsorption enthalpies (ΔH0 ads) could be converted to sublimation enthalpies (ΔH0 subl). Resulting values for the assumed compounds PaCl5, PaOCl3, PaBr5, and PaOBr3 were 113 ± 15, 329 ± 16, 165 ± 5 and 235 ± 17 kJ/mol, respectively. These values are rather similar to known ΔH0 subl data for group-5 elements Nb, Ta and Db in support of the assumption that Pa is a pseudo-group 5 element.

The Neutron Facility at NCSR "Demokritos"- Implementation in the Case of the 232Th(n,2n) and 241Am(n,2n) Reactions

In the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" monoenergetic neutron beams can be produced in the energy ranges 120-650 keV, 4-11.5 MeV and 16-20.5 MeV by using the 7Li(p,n), 2H(d,n) and 3H(d,n) reactions, respectively. The corresponding beam energies and ions delivered by the accelerator, are 1.92-2.37 MeV protons, 0.8-9.6 MeV deuterons and 0.8-3.7 MeV deuterons, for the three reactions, respectively. Experimental results for neutron energies from threshold up to 11.5 MeV and at 17.1 MeV will be given for the 232Th(n,2n)231Th reaction, while for the 241 Am(n,2n)240 Am reaction, preliminary cross section data at 10.4, 10.6 and 17.1 MeV will be discussed. In the framework of the CERN n-TOF collaboration, the cross section of these reactions have been measured relative to the 197Au(n,2n)196Au, 27Al(n,a)24Na and 93Nb(n,2n) reaction cross sections, by using the activation method. In addition to the experimental work, theoretical Statistical model calculations are being carried out using the computer code STAPRE/F. The results are compared to the experimental data.

Statistical model calculations of the 232Th(n,2n) reaction

On the context of the Cern n_TOF collaboration the 232Th(n,2n)231Th reaction cross section has been measured relative to the 56Fe(n,p)56Mn and 27Al(n,a)24Na reaction cross sections by the activation method for neutron energies up to 11 MeV. The neutrons were produced via the 2H(d,n) reaction using a deuterium filled gas-cell, at the 5.5MV TANDEM Accelerator of NCSR "Demokritos". In addition to the experimental work, theoretical Statistical model calculations have been performed using the computer code STAPRE/F. The code STAPRE is designed to calculate energy averaged cross sections for particle induced nuclear reactions with several emitted particles and gamma rays under the assumption of sequential evaporation. For the first evaporation step preequilibrium emission is taken into account while population of states resulting from the first equilibrium evaporation step is calculated using the Hauser-Feschbach theory. Fission process competition is also taken into account in the evaporation steps. Sensitive parameters for the calculation, like level density parameters, have been adopted after fitting experimental data for the competing (n,f) reaction. The results are being compared to the experimental data.

Measurement and covariance analysis of 232Th(n, 2n)231Th reaction cross sections at the effective neutron energies of 8.97 and 16.52 MeV

The $${}_{ }^{ 2 3 2} {\text{Th(n, 2n)}}{}_{ }^{ 2 3 1} {\text{Th}}$$ reaction cross sections relative to the $${}_{ }^{ 2 3 2} {\text{Th}}$$ (n, f)97Zr monitor reaction at the effective neutron energies of 8.97 and 16.52 MeV have been measured by using the activation and off-line $$\gamma$$ -ray spectrometry. The neutron beams were generated from the $${}_{ }^{7} {\text{Li}}\left( {{\text{p}}, {\text{n}}} \right){}_{ }^{7} {\text{Be}}$$ reaction by using the proton beam energies of 11 and 18.8 MeV. Correction factors for the low energy neutrons were taken care by considering the thickness of sample and non mono-energetic neutrons. The covariance analysis in the uncertainty of the reaction cross section was carried out by using error propagation and micro-correlation technique. The present data were compared with the literature data, evaluated data and theoretical values based on TALYS-1.8 code.

Benchmark experiments on breeding properties of thorium

Thorium is a fertile element that can be applied in the conceptual blanket design of a fusion-fission hybrid reactor. It is essential to validate 232Th nuclear data and obtain the breeding properties of macroscopic thorium assemblies by conducting integral neutronics benchmark experiments. The thorium assemblies with a D-T fusion neutron source consist of a polyethylene shell, depleted uranium shell, and thorium oxide powder cylinder. The 232Th (n, γ), 232Th (n, f), and 232Th (n, 2n) reaction rates in the assemblies are measured by ThO2 foil activation technique. The experimental uncertainties are about 3.1% for 232Th capture rates, 5.3–5.5% for 232Th fission rates, and 6.8–7.0% for 232Th (n, 2n) reaction rates. From 232Th reaction rates, the fuel and neutron breeding properties of thorium under different neutron spectra are obtained and compared. The experiments are simulated by using the MC code with different evaluated data. The ratios of calculation to experimental values for the reaction rates are analyzed.

Determination of the 232Th(n,2n)231Th reaction rate in thorium oxide cylinder assembly under D-T neutron source

Aiming at verifying the evaluated cross-section of 232Th(n,2n) reaction for the conceptual design of thorium based subcritical blanket in fusion–fission hybrid reactor, an integral experiment was carried out using activation technique with D-T neutrons. 232Th(n,2n) reaction rates were measured in a ThO2 cylinder assembly with relative uncertainty of 8.0%. The experiment was simulated by MCNP code combining with ENDF/B-VII.0, ENDF/B-VII.1, CENDL-3.1 and JENDL-4.0 databases. The calculated 232Th(n,2n) reaction rates employing JENDL-4.0 show low discrepancy with the measured ones. The results could provide reference to the re-evaluation of 232Th(n,2n) cross-section and the design of fusion–fission hybrid reactor.

Measurement and analysis of 232Th(n,2n)231Th reaction rate in the thorium oxide cylinder with a D-T neutron source

Aiming at providing reference to verify the 232Th(n,2n)231Th cross sections in different evaluated nuclear databases in the neutron energy range of 14.5–15.5MeV, a dedicated integral experiment was carried out on a thorium cylinder setup with D-T neutrons using activation technique. 5 thorium foils were placed at 0° direction to the incident D+ beam, and the 232Th(n,2n)231Th reaction rates were determined with relative uncertainties of about 7.0%. The experiment was simulated by the MCNP code employing ENDF/B-VI, ENDF/B-VII.0, ENDF/B-VII.1, CENDL-3.1 and JENDL-4.0 libraries. The calculated 232Th(n,2n)231Th reaction rates employing JENDL-4.0 library agreed with the measured ones within experimental uncertainty, while those employing ENDF/B-VI, ENDF/B-VII.0, ENDF/B-VII.1, CENDL-3.1 libraries were all smaller than the measured ones by as much as 27.1%, 24.9%, 24.0%, 23.3% on average, respectively. The results could provide reference to the validation of 232Th(n,2n)231Th cross sections in different evaluated libraries as well as the design of thorium fuel based reactor.

Dynamic picture of the formation of spins of induced fission fragments

A way of calculating the average spins of induced fission fragments is developed, based on the dynamic model of their angular distributions. The range of relaxation times for the degree of freedom associated with the orientation of the axis of symmetry of a fissioning nucleus relative to its total angular momentum is determined by analyzing experimental data on the energy dependences of average spins and the anisotropy of the angular distributions of fission fragments for the 12C, 16O + 232Th reactions at E сm = 55–150 MeV.

The spins of induced-fission fragments within the dynamic approach

A new approach to calculating the mean spins of induced-fission fragments is proposed. This approach, which has the key dynamic aspects of induced fission factored in, was used to analyze experimental data on the angular and energy dependences of mean spins and on the anisotropy of the angular distributions of fission fragments for the 16O + 232Th reaction at Ecm = 80–150 MeV. The range of relaxation times that provide a consistent description of the experimental data was determined for the degree of freedom associated with the orientation of the symmetry axis of a fissioning nucleus with respect to the total angular momentum.

Fission fragments mass distributions of nuclei populated by the multinucleon transfer channels of the 18O +232Th reaction

Abstract It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multinucleon transfer channels of the 18O + 232Th reaction are used to study fission of fourteen nuclei 231,232,233,234Th, 232,233,234,235,236Pa, and 234,235,236,237,238U. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions are measured for each transfer channel, in selected bins of excitation energy. In particular, the mass distributions of 231,234Th and 234,235,236Pa are measured for the first time. Predominantly asymmetric fission is observed at low excitation energies for all studied cases, with a gradual increase of the symmetric mode towards higher excitation energy. The experimental distributions are found to be in general agreement with predictions of the fluctuation–dissipation model.

Measurement and calculation of U and Th reaction rates in uranium mock assemblies

The conceptual blanket based on a subcritical reactor for a fusion–fission hybrid energy reactor with magnetic confinement fusion is being studied. To validate nuclear data and code of neutronics calculation for the blanket design, measurement of reaction rates for U and Th is performed by integral experiments. Based on the fission blanket, the uranium mock assemblies are established, and include the depleted uranium shell, the depleted-uranium/polyethylene/graphite shell and the natural uranium cube. A depleted-uranium/polyethylene/graphite assembly of 131mm in inner radius and 365mm in outer radius consists of three layers of depleted uranium shells, two layers of polyethylene shells and a graphite shell, and these shells are arranged alternatively. A D–T fusion neutron source is centered of the spherical assemblies. The U reaction rates for capture, fission and ratio of capture to fission in the assemblies are measured by depleted uranium foils and an HPGe gamma spectrometer. The 232Th reaction rates for capture, fission and ratio of capture to fission are measured by ThO2 foils put into the depleted uranium shell. The measured results are compared to the calculated ones by using MCNP code with ENDF/B-VII.0 library data.

Pre-neutron-emission Mass Distributions for Reaction 232Th(n, f) up to 60 MeV

The pre-neutron-emission mass distributions for reaction 232Th(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependences of the peaks and valleys of the pre-neutron-emission mass distributions are described by the exponential expressions based on the newly measured data. The energy dependence of evaporation neutrons before scission, which plays a crucial role for the reasonable description of the mass distribution, is also considered. Both the double-humped and triple-humped shape of the measured pre-neutron-emission mass distributions for reaction 232Th(n, f) are reasonably well reproduced at incident energies up to 60 MeV. The mass distributions at unmeasured energies and the critical energies at which the humped pre-neutron-emission mass distributions are transformed into each other are also predicted.

Measurement of 232Th(n,5n γ) cross sections from 29 MeV to 42 MeV

The excitation function of the reaction 232 Th(n, 5nγ)228 Th from 29 to 42 MeV has been measured for the first time at the quasi-monoenergetic neutron beam of the UCL cyclotron CYCLONE employing the 7Li(p,n) source reaction. Taking advantage of the good energy resolution of the planar High-Purity Germanium (HPGe) detectors, prompt γ-ray spectroscopy was used to detect the γ-rays resulting from the decay of excited states of nuclei created by the (n,xn) reactions. The neutron beam was characterized by a combination of time of flight measurements carried out using a liquid scintillation detector and a 238U fission ionization chamber. Fluence measurements were performed using a proton recoil telescope. The results are compared with TALYS-1.4 code calculations.