Au Reactions Research Articles

Results of the ASY-EOS experiment at GSI: The symmetry energy at suprasaturation density

Directed and elliptic flows of neutrons and light charged particles were measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector LAND, combined with parts of the CHIMERA multidetector, of the ALADIN Time-of-flight Wall, and of the Washington-University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA, was used for complementary measurements of the isotopic composition and flows of light charged particles. From the comparison of the elliptic flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value \gamma = 0.72 \pm 0.19 is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of supra-saturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation.

Flux trap effect study in a sub-critical neutron assembly using activation methods

ABSTRACTThe neutron flux trap effect was experimentally studied in the subcritical assembly of the Atomic and Nuclear Physics Laboratory of the Aristotle University of Thessaloniki, using delayed gamma neutron activation analysis. Measurements were taken within the natural uranium fuel grid, in vertical levels symmetrical to the Am–Be neutron source, before and after the removal of fuel elements, permitting likewise a basic study of the vertical flux profile. Three identical flux traps of diamond shape were created by removing four fuel rods for each one. Two (n, γ) reactions and one (n, p) threshold reaction were selected for thermal, epithermal and fast flux study. Results of thermal and epithermal flux obtained through the 197Au (n, γ) 198Au and 186W (n, γ) 187W reactions, with and without Cd covers, to differentiate between the two flux regions. The 58Ni (n, p) 58Co reaction was used for the fast flux determination. An interpolation technique based on local procedures was applied to fit the cross sections data and the neutron flux spectrum. End results show a maximum thermal flux increase of 105% at the source level, pointing to a high potential to increase in the available thermal flux for future experiments. The increase in thermal flux is not accompanied by a comparable decrease in epithermal or fast flux, since thermal flux gain is higher than epithermal and fast neutron flux loss. So, the neutron reflection is mainly responsible for the thermal neutron increase, contributing to 89% at the central axial position.

Gold nanoparticles production using reactor and cyclotron based methods in assessment of 196,198Au production yields by 197Au neutron absorption for therapeutic purposes

Medical nano-gold radioisotopes is produced regularly using high-flux nuclear reactors, and an accelerator-driven neutron activator can turn out higher yield of 197Au(n,γ)196,198Au reactions. Here, nano-gold production via radiative/neutron capture was investigated using irradiated Tehran Research Reactor flux and also simulated proton beam of Karaj cyclotron in Iran. 197Au nano-solution, including 20nm shaped spherical gold and water, was irradiated under Tehran reactor flux at 2.5E+13n/cm2/s for 196,198Au activity and production yield estimations. Meanwhile, the yield was examined using 30MeV proton beam of Karaj cyclotron via simulated new neutron activator containing beryllium target, bismuth moderator around the target, and also PbF2 reflector enclosed the moderator region. Transmutation in 197Au nano-solution samples were explored at 15 and 25cm distances from the target.The neutron flux behavior inside the water and bismuth moderators was investigated for nano-gold particles transmutation. The transport of fast neutrons inside bismuth material as heavy nuclei with a lesser lethargy can be contributed in enhanced nano-gold transmutation with long duration time than the water moderator in reactor-based method. Cyclotron-driven production of βeta-emitting radioisotopes for brachytherapy applications can complete the nano-gold production technology as a safer approach as compared to the reactor-based method.

Thermal neutron radiative capture cross-section of 186W(n, γ)187W reaction

The thermal neutron radiative capture cross section for 186W(n, γ)187W reaction was measured by the activation method using the filtered neutron beam at the Dalat research reactor. An optimal composition of Si and Bi, in single crystal form, has been used as neutron filters to create the high-purity filtered neutron beam with Cadmium ratio of Rcd = 420 and peak energy En = 0.025 eV. The induced activities in the irradiated samples were measured by a high resolution HPGe digital gamma-ray spectrometer. The present result of cross section has been determined relatively to the reference value of the standard reaction 197Au(n, γ)198Au. The necessary correction factors for gamma-ray true coincidence summing, and thermal neutron self-shielding effects were taken into account in this experiment by Monte Carlo simulations.

Near-barrier neutron transfer in reactions with 3He nucleus

Experimental cross sections for the formation of 196,198Au isotopes in the 3He + 197Au reaction and 44,46Sc isotopes in the 3He + 45Sc reaction are analyzed. To calculate transfer probabilities and cross sections, the time-dependent Schrodinger equation is numerically solved for the external neutrons of the 3He, 45Sc, and 197Au nuclei. It is shown that the contribution from the fusion channel with subsequent evaporation is important for the 3He + 45Sc reaction and negligibly small for the 3He + 197Au reaction. Fusion–evaporation is taken into account using the NRV and PACE codes. Calculation results demonstrate overall satisfactory agreement with experimental data.

Selective oxidation of fatty alcohol ethoxylates with H2O2 over Au catalysts for the synthesis of alkyl ether carboxylic acids in alkaline solution

In this paper, we report a green and selective route for the direct oxidation of alcohol ethoxylates (AEOs) into alkyl ether carboxylic acids over supported noble metal catalysts using H2O2 as an oxidant in the presence of a base. The catalytic performance of supported Au, Pt and Pd was assessed in the oxidation of AEO7 consisting of C12–C14-alcohol polyethyleneglycol ether with average 7 EO units. Among the different catalysts tested, Au/Al2O3 and Au/TiO2 displayed a yield up to 88% to polyoxyethylene(7) lauryl ether carboxylic acid (AECA6) at 80°C. The effect of Au particle size, reaction temperature, reaction time, catalyst loading and base amount on the activity, selectivity and stability of Au/Al2O3 was explored in detail. Hydroxyl radicals were generated during the reaction as suggested by a series of poisoning tests using 2,2,6,6-tetramethylpiperidinoxyl and 1,4-benzoquinone as radical scavengers. Au/Al2O3 and Au/TiO2 could only be reused in two consecutive runs, showing a strong deactivation in the third run and beyond due to Au leaching and partial nanoparticle sintering as inferred by combined TEM and ICP-AES analysis. The Au stability could be highly promoted over a bimetallic AuPt/TiO2 formulation, showing a good recyclability and reuse for at least 10 consecutive catalytic cycles.

Measurement of flux-weighted average cross sections for 197Au(γ, xn) reactions and isomeric yield ratios of 196m,gAu with bremsstrahlung

Photo-neutron cross sections of 197Au were experimentally determined for the bremsstrahlung end-point energies of 50, 60, and 70 MeV, by utilizing activation and off-line γ-ray spectrometric technique, using the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Pohang, Korea. The 197Au(γ, xn; x=1–6) reaction cross sections were calculated as a function of the bombarding photon energy by using the TALYS 1.6 computer code with default parameters. The flux-weighted average cross sections were obtained from the literature data and the theoretical values of TALYS 1.6 and TENDL-2014, for mono-energetic photons, and are found to be in good agreement with the present data. Isomeric yield ratios of 196m2,gAu from the 197Au(γ, n) reaction were also determined for the bremsstrahlung end-point energies of 50, 60, and 70 MeV, from the reaction cross sections of m2- and g-states, based on the present experimental data, and are found to be in good agreement with the theoretical values based on TALYS 1.6 and TENDL-2014.

Decay Properties of New Isotopes 234Bk and 230Am, and Even–Even Nuclides 234Cm and 230Pu

A neutron-deficient berkelium isotope of 234Bk produced via 197Au(40Ar,3n) reaction and the daughter product of 230Am were newly identified. Alpha-decay energies of eleven 234Bk were found at 7.62–7.96 MeV, and six fission events that correlated with the α-decay of 234Bk were observed. The half-lives of 234Bk and 230Am were determined to be \(19_{ - 4}^{ + 6}\) s and \(32_{ - 9}^{ + 22}\) s, respectively. The 234Cm followed by the β-decay of 234Bk was also identified.

Investigation of the Freeze-out Configuration in the $^{197}$Au + $^{197}$Au Reaction at 23 $A$\,MeV

Investigation of the Freeze-out Configuration in the $^{197}$Au + $^{197}$Au Reaction at 23 $A$\,MeV

Fusion and neutron transfer reactions with weakly bound nuclei within time-dependent and coupled channel approaches

The time-dependent Schrödinger equation and the coupled channel approach based on the method of perturbed stationary two-center states are used to describe nucleon transfers and fusion in low-energy nuclear reactions. Results of the cross sections calculation for the formation of the 198Au and fusion in the 6He+197Au reaction and for the formation of the 65Zn in 6He+64Zn reaction agree satisfactorily with the experimental data near the barrier. The Feynman’s continual integrals calculations for a few-body systems were used for the proposal of the new form of the shell model mean field for helium isotopes.

Neutron capture cross section and capture gamma-ray spectra of89Y

The neutron capture cross section of 89 Y was measured by the time-of-flight method in an energy range from 15 to 100 keV. A pulse-height weighting technique was applied to derive the capture yield. The absolute cross section was determined based on the standard reaciotn 197 Au(n , γ )198 Au reaction. The neutron capture γ -ray spectrum was derived by unfolding the pulse-height spectrum with detector response functions.

Freeze-out configuration properties in theAu197+Au197reaction at23AMeV

Data from the experiment on the 197Au + 197Au reaction at 23 AMeV are analyzed with an aim to find signatures of exotic nuclear configurations such as toroid-shaped objects. The experimental data are compared with predictions of the ETNA code dedicated to look for such configurations and with the QMD model. A novel criterion of selecting events possibly resulting from the formation of exotic freeze-out configurations, "the efficiency factor", is tested. Comparison between experimental data and model predictions may indicate for the formation of flat/toroidal nuclear systems.

Sub-threshold ϕ and production by high mass resonances with UrQMD

We present a possible explanation for the deep sub-threshold, ϕ and production yields measured with the HADES experiment in Ar+KCl reactions at A GeV and present predictions for Au+Au reactions at A GeV. To explain the surprisingly high yields of ϕ and hadrons we propose new decay channels for high mass baryon resonances. These new decay channels are constrained by elementary cross sections, and production in p+Nb. Based on the fits to the elementary reactions one obtains a satisfactorily description of ϕ and production in deep sub-threshold Ar+KCl reactions as well as the observed nuclear transparency ratio in proton-induced ϕ production in cold nuclear matter. The results implicate that no new medium effects are required to describe the rare strange particle production data in low energy nuclear collisions.

A new integral experiment on copper with DT neutron source at JAEA/FNS

In order to validate copper nuclear data, an integral experiment on copper with the DT neutron source at JAEA/FNS had been performed over 20 years ago. The experiment had showed that ratios of the calculated values to the experimental ones (C/Es) related to lower energy neutrons had been drastically smaller than unity. In order to reveal reasons of the small C/Es, we newly performed the integral experiment on copper with the DT neutron source at JAEA/FNS. A quasi-cylindrical copper assembly of 315mm in radius and 608mm in depth was covered with Li2O blocks of 51mm in thickness for the front and side parts and 153mm in thickness for the rear part to exclude background neutrons which might affect the measured data. We measured reaction rates with 5 activation foils and fission rates with 2 micro fission chambers at the center of the assembly. The experiment was analyzed by using MCNP5-1.40 with the recent nuclear data libraries, ENDF/B-VII.1, JEFF-3.2 and JENDL-4.0. As a result, the C/E of the reaction rate of the 197Au(n,γ)198Au reaction improved by 10% from the previous result and the combination of the 63Cu data in JEFF-3.2 and 65Cu data in JENDL-4.0 increased the C/E by more 10% because of the resonance data of the 63Cu in JEFF-3.2. Moreover, the calculated result with the 63Cu data in JEFF-3.2 and 65Cu data in JENDL-4.0 with 10% larger elastic scattering cross section data and 10% smaller capture cross section data between 100eV and 0.3MeV agreed with the measured one related to lower energy neutrons very well. The copper data should be reassessed.

Quantum description of coupling to neutron-rearrangement channels in fusion reactions near the Coulomb barrier

The fusion cross sections for the 17,18O+27Al, 18O+58Ni, and 6He+197Au reactions were calculated by the coupled-channel method. The radial dependence of matrices that describe coupling to valence-neutron-rearrangement channels was determined with the aid of two-center wave functions. The coupling-strength parameters were evaluated on the basis of numerically solving the time-dependent Schrodinger equation. Satisfactory agreement with experimental data was obtained.

Measurement of 197Au(n,γ)198gAu reaction cross-section at the neutron energies of 1.12, 2.12, 3.12 and 4.12 MeV

Abstract The 197Au(n, γ)198Au reaction cross-sections at the neutron energies of 1.12, 2.12, 3.12 and 4.12 MeV were determined by using activation and off-line γ-ray spectrometric technique. The mono-energetic neutron energies of 1.12–4.12 MeV were generated from the 7Li(p, n) reaction by using the proton energies of 3 and 4 MeV from the folded tandem ion beam accelerator (FOTIA) at BARC as well as 5 and 6 MeV from the Pelletron facility at TIFR, Mumbai. The 115In(n,γ)116mIn reaction cross-section was used as the neutron flux monitor. The 197Au(n, γ)198Au reaction cross-section at the neutron energies of 3.12 and 4.12 MeV are reported for the first time. The 197Au(n, γ)198Au reaction cross-sections at 1.12 and 2.12 MeV are close to the literature data of in between neutron energies. The 197Au(n, γ)198Au cross-section was also calculated theoretically by using the computer code TALYS 1.6 and found to be higher than the experimental data of present work and literature data within the neutron energies of 0.8 to 4 MeV.

Thermal neutron capture and resonance integral cross sections of 45Sc

The thermal neutron cross section (σ0) and resonance integral (I0) of the 45Sc(n,γ)46Sc reaction have been measured relative to that of the 197Au(n,γ)198Au reaction by means of the activation method. High-purity natural scandium and gold foils without and with a cadmium cover of 0.5mm thickness were irradiated with moderated pulsed neutrons produced from the Pohang Neutron Facility (PNF). The induced activities in the activated foils were measured with a high purity germanium (HPGe) detector. In order to improve the accuracy of the experimental results the counting losses caused by the thermal (Gth) and resonance (Gepi) neutron self-shielding, the γ-ray attenuation (Fg) and the true γ-ray coincidence summing effects were made. In addition, the effect of non-ideal epithermal spectrum was also taken into account by determining the neutron spectrum shape factor (α). The thermal neutron cross-section and resonance integral of the 45Sc(n,γ)46Sc reaction have been determined relative to the reference values of the 197Au(n,γ)198Au reaction, with σo,Au=98.65±0.09barn and Io,Au=1550±28barn. The present thermal neutron cross section has been determined to be σo,Sc=27.5±0.8barn. According to the definition of cadmium cut-off energy at 0.55eV, the present resonance integral cross section has been determined to be Io,Sc=12.4±0.7barn. The present results are compared with literature values and discussed.

A novel route to produce a homogeneous certified reference material for k0-neutron activation analysis: Application to the certification of gold mass fraction in an Al–0.1% Au alloy

Reliable certified reference materials (CRM) are required for neutron dosimetry in k0-neutron activation analysis (k0-NAA). In the past, levitation melting was employed to produce highly homogeneous alloys used in the production of CRMs. This publication describes a novel and more efficient way of processing such alloys using the example of an Al–Au alloy, the evaluation of the efficacy with respect to achieving homogeneity and avoiding micro- and macrosegregation and the final certification of the Au mass fraction. First, Al–5% Au alloy was melted by arc melting and then diluted into Al–0.1% Au with high purity Al in a resistance furnace under the protection of high purity argon gas. The as-casted Al–0.1% Au was then heat-treated at about 635°C for 48h. No significant macrosegregation and no intermetallic phase (AuAl2) were observed in the heat-treated alloy. Using this approach, a new CRM for gold mass fraction in Al–0.1% Au was produced in the form of wires and foils (ERM-EB530A, B and C). The relative uncertainty from gold inhomogeneity in the material was assessed using a randomised block design and inductively coupled plasma optical emission spectrometry (ICP-OES) and was found to be 0.3%. The characterisation of the gold mass fraction was performed by an interlaboratory comparison of expert laboratories. Sixteen laboratories participated using instrumental neutron activation analysis (197Au(n,γ)198Au), fire assay and ICP-OES. Alternative INAA reactions (197Au(n,2n)196Au) and calibration strategies were tested but not retained for the characterisation study as they did not meet the strict performance criteria set for the study. After evaluation of homogeneity and characterisation, the Au mass fraction in ERM-EB530A, B and C was certified to be 1005±7mg/kg (k=2), which is a lower uncertainty than for previous similar materials. This demonstrates the suitability of the new production route, which should also be applicable to other binary alloys required for neutron dosimetry.

Measurement of the 115In(n,γ)116m In reaction cross-section at the neutron energies of 1.12, 2.12, 3.12 and 4.12 MeV

The 115In(n,γ)116m In reaction cross section at neutron energies of 1.12, 2.12, 3.12 and 4.12 MeV was determined by using an activation and off-line γ-ray spectrometric technique. The monoenergetic neutron energies of 1.12 − 4.12 MeV were generated from the 7Li(p,n) reaction by using proton beam with energies of 3 and 4 MeV from the folded tandem ion beam accelerator (FOTIA) at Bhabha Atomic Research Centre (BARC) and with energies of 5 and 6 MeV from the Pelletron facility at Tata Institute of Fundamental Research (TIFR), Mumbai. The 197Au(n,γ)198Au reaction cross-section was used as the neutron flux monitor.The 115In(n,γ)116m In reaction cross section at neutron energies of 1.12, 2.12, 3.12 and 4.12 MeV was determined by using an activation and off-line γ-ray spectrometric technique. The monoenergetic neutron energies of 1.12 − 4.12 MeV were generated from the 7Li(p,n) reaction by using proton beam with energies of 3 and 4 MeV from the folded tandem ion beam accelerator (FOTIA) at Bhabha Atomic Research Centre (BARC) and with energies of 5 and 6 MeV from the Pelletron facility at Tata Institute of Fundamental Research (TIFR), Mumbai. The 197Au(n,γ)198 Au reaction cross-section was used as the neutron flux monitor. The 115In(n,γ)116m In reaction cross-sections at neutron energies of 1.12 – 4.12 MeV were compared with the literature data and were found to be in good agreement with one set of data, but not with others. The 115In(n,γ)116m In cross-section was also calculated theoretically by using the computer code TALYS 1.6 and was found to be slightly lower than the experimental data from the present work and the literature.)198Au reaction cross-section was used as the neutron flux monitor. The 115In(n,γ)116m In reaction cross-sections at neutron energies of 1.12 − 4.12 MeV were compared with the literature data and were found to be in good agreement with one set of data, but not with others. The 115In(n,γ)116m In cross-section was also calculated theoretically by using the computer code TALYS 1.6 and was found to be slightly lower than the experimental data from the present work and the literature.

Systematic effects on cross-section data derived from reaction rates at a cold neutron beam

The methodology to derive cross-section data from measurements in a cold neutron beam was studied. Mostly, capture cross-sections at thermal energy are derived relative to a standard cross-section, e.g. the cross-section of the 1H(n,γ), 14N(n,γ), or 197Au(n,γ) reaction, and proportionality between the standard and the measured cross-section, evaluated at different energies in the sub-thermal region, is often assumed. Due to this assumption the derived capture cross-section at thermal energy can be biased by more than 10%. Evidently the bias depends on how much the energy dependence of the cross-section deviates from a direct proportionality with the inverse of the neutron speed. The effect is reduced in case the cross-section is not derived at thermal energy but at an energy close to the average energy of the cold neutron beam. Nevertheless, it is demonstrated that the bias can only be avoided in case the energy dependence of the cross-section is known and proper correction factors are applied. In some cases the results are also biased when the attenuation of the neutron beam within the sample is neglected in the analysis. Some of the cross-section data reported in the literature suffer from such bias effects. Hence, the results have to be corrected using the correction factors presented in this paper.