2n Reaction Research Articles

Development of irradiation-resistant enriched 12C targets for astrophysical [formula omitted] reaction measurements

The production of irradiation-resistant enriched 12C target is one of the key technologies in the direct measurement of the 12C(α,γ)16O reaction at energies of astrophysical interest. In this work, we produced the enriched Ti12C targets on Ta substrates via the filter cathodic vacuum arc (FCVA) technology. The target stability under the bombardment of a high-intensity 4He beam was investigated by monitoring the γ-ray yields of the 12C(p,γ)13N reaction regularly. A 25% deterioration of 12C in the target was observed after bombardment by a 740 keV, 500 μA 4He2+ beam with a charge of 280 C, which is stronger than the implanted targets developed before. Furthermore, the 13C/12C ratio in the Ti12C target was measured to be (1.1±0.3)×10−4, which can meet the requirement of the 12C(α,γ)16O measurement at the China JinPing underground Laboratory (CJPL).

Measurements of natCd(γ, x) reaction cross sections and isomer ratio of 115m,gCd with the bremsstrahlung end-point energies of 50 and 60 MeV * *Supported by the National Research Foundation of Korea (NRF) through a grant provided by the Ministry of Science and ICT (NRF-2017R1D1A1B03030484, NRF-2013M7A1A1075764, NRF-2018R1A6A1A06024970)

The flux-weighted average cross sections of natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions were measured at the bremsstrahlung end-point energies of 50 and 60 MeV. The activation and off-line γ-ray spectrometric technique was carried out using the 100 MeV electron linear accelerator at the Pohang Accelerator Laboratory, Korea. The natCd(γ, xn) reaction cross sections as a function of photon energy were theoretically calculated using the TALYS-1.95 and the EMPIRE-3.2 Malta codes. Then, the flux-weighted average cross sections were obtained from the theoretical values of mono-energetic photons. These values were compared with the flux-weighted values from the present study and were found to be in general agreement. The measured experimental reaction cross-sections and integral yields were described for cadmium and silver isotopes in the natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions. The isomeric yield ratio (IR) of 115g,mCd in the natCd(γ, xn) reaction was determined for the two bremsstrahlung end-point energies. The measured isomeric yield ratios of 115g,mCd in the natCd(γ, xn) reaction were also compared with the theoretical values of the nuclear model codes and previously published literature data of the 116Cd(γ, n) and 116Cd(n, 2n) reactions. It was found that the IR value increases with increasing projectile energy, which demonstrates the characteristic of excitation energy. However, the higher IR value of 115g,mCd in the 116Cd(n, 2n) reaction compared to that in the 116Cd(γ, n) reaction indicates the role of compound nuclear spin alongside excitation energy.

Characterization of Nitrite-Related Reaction Products in Beer.

The effect of nitrites in foods and beverages still raises discussion due to the possible formation of harmful nitroso compounds. However, as most of these compounds in beer were not structurally characterized yet, the research about their toxicological relevance for consumers is limited. This study is focused on identification of the products formed by nitrite (or isotopically labeled nitrite 15N) reactions in beer using gas chromatography with tandem mass spectrometry. In total, 19 products were identified, and some of them were structurally characterized and confirmed by comparing retention indices and mass spectra of standard/synthesized compounds. Identified compounds were representatives of nitroso, nitro, oxime, and even cyano compounds. For the peaks which were not structurally identified, primary structural characteristics were also listed. Found products were further screened in 16 authentic beer samples which showed the apparent occurrence of found compounds in non-treated beers.

Measurement of HFETR reactor power by improved 16N gamma spectrum analysis method

To increase redundancy and diversity of the reactor power measurement, a system for the measurement of reactor power can be established based on neutron activation analysis using 16O(n,p)16N reaction. In this work, gamma spectrums from the coolant of HFETR core are continuously detected by 16N monitor with NaI(Tl) detector and the count rates in the spectrum range of 4.5 MeV-7.5 MeV are obtained. Meanwhile, the overlapping peaks in the given spectrum range are decomposed with Levenberg-Marquardt method during the operation of HFETR. The results confirm that the count rates of full-energy peak, single-escape peak and double-escape peak of 6.13 MeV gamma spectrums is proportionate to the increased reactor power measured by other monitors such as compensated ionization chamber and thermal power. It is possible to achieve the absolute nuclear power measurement by adopting the count rate of 16N 6.13 MeV peak, detection efficiency of detector and 16N source term.

I<sub>N</sub>RACM: incorporating <sup>15</sup>N into the Regional Atmospheric Chemistry Mechanism (RACM) for assessing the role photochemistry plays in controlling the isotopic composition of NO<sub><i>x</i></sub>, NO<sub><i>y</i></sub>, and atmospheric nitrate

Abstract. Nitrogen oxides, classified as NOx (nitric oxide (NO) + nitrogen dioxide (NO2)) and NOy (NOx+ NO3, N2O5 HNO3, + HNO4+ HONO + Peroxyacetyl nitrate (PAN) + organic nitrates + any oxidized N compound), are important trace gases in the troposphere, which play an important role in the formation of ozone, particulate matter (PM), and secondary organic aerosols (SOA). There remain many uncertainties in the origin and fate of atmospheric N compounds including the understanding of NOy cycling, NOx emission budgets, unresolved issues within the heterogeneous uptake coefficients of N2O5, and the formation of organic nitrates in urban forests, to name a few. A potential tool to resolve some of these uncertainties are using natural abundance N isotopes in NOy compounds. Here we have developed a photochemical mechanism used to simulate tropospheric photochemistry to include 15N compounds and reactions as a means to simulate δ15N values in NOy compounds. The 16 N compounds and 96 reactions involving N used in the Regional Atmospheric Chemistry Mechanism (RACM) were replicated using 15N in a new mechanism called iNRACM. The 192 N reactions in iNRACM were tested to see if isotope effects were relevant with respect to significantly changing the δ15N values (±1 ‰) of NOx, HONO, and/or HNO3. The isotope fractionation factors (α) for relevant reactions were assigned based on recent experimental or calculated values. Each relevant reaction in the iNRACM mechanism was tested individually and in concert in order to assess the controlling reactions. The controlling reactions and their diurnal importance are discussed. A comparison between iNRACM predictions and observed δ15N NO3- in particulate matter from Tucson, Arizona, suggests the model, and isotope fractionation factors incorporated into it, are accurately capturing the isotope effects occurring during the photochemistry of NOy. The implication is that measurements of δ15N in NOy compounds may be a new way of tracing in situ N chemistry and a means of assessing NOx emission budgets.

Isomeric Ratios 109m,gPd in the (γ, n) and (n, 2n) Reactions

The method of induced activity of the investigated cross-sections of excitation of isomeric states in the 110Pd(y,n)109m,gPd and 110Pd(n,2n)109m,gPd reactions in the energy range 12–35 MeV is studied. The experimental results are compared with those of calculations carried out using the software package TALYS-1.6.

Semi-empirical systematics formulas for the (n, p), (n, α), and (n, 2n) reaction cross-sections at 14.5 MeV

New Semi-empirical mass formulas were developed for the (n, p), (n, α), and (n, 2n) reaction cross-sections at 14.5 MeV neutron energy by using the literature data available on EXFOR library. The new formulas were derived on the basis of the statistical model considering Q − value dependence. The results obtained from the present exercise were compared with other systematic formulas developed in past years as well as with the experimental literature data reported on EXFOR library. The comparison has been done on the basis of statistical model as well as on the asymmetry parameter dependence. The present work offers an alternative to reproduce nuclear data at 14.5 MeV incident neutron energies.

Systematic study of the [formula omitted]([formula omitted],p)[formula omitted] reaction for NRA applications

The differential cross sections of the first two proton groups of the 12C(3He,p)14N reaction were determined within the 3He energy range 1.34–2.86 MeV and for backward angles from 107o107o to 164o with 2o steps using two double sided silicon strip detectors. The results are presented in graphical form and they are also given as tables in the Appendix. Aiming to assist in the enrichment of the reaction database and the improvement of the differential cross section data quality, the determined cross sections were benchmarked with the measurement of thick target reaction yields from a pure glassy carbon target at two 3He energies, 2.0 and 2.7 MeV. Furthermore, the data were accompanied by R-Matrix theory calculations, allowing for cross section data interpolation with sufficient accuracy.

Study of (n, 2n) reaction cross sections for 107Ag within the energy range of 9–22 MeV

Study of (n, 2n) reaction cross sections for 107Ag within the energy range of 9–22 MeV

Application of photofission reaction to identify high-enriched uranium by bremsstrahlung photons

The applicability of the photofission reaction ratio (PFRR) method to identify high-enriched uranium is studied by switching the photon source from the Gaussian spectrum to a bremsstrahlung spectrum. The combination of 6 and 11 MeV Gaussian photon energy was used in previous study for applying PFRR method because the photofission cross sections between 235U and 238U at these two energies differ significantly. A parametric study was conducted with the incident electron energy 7.0 MeV and the result showed that these electrons generate similar photofission reactions as that of 6.0 MeV Gaussian photons, while 13.5 MeV electrons is found to give even better results for PFRR considering the measurement noise contributed by multiple neutron emission, (γ, 2n) reaction. Bremsstrahlung photons were injected into a 1 mm thick uranium metal target with varying uranium enrichment. The PFRR increases linearly with uranium enrichment, and is found to provide a higher sensitivity than the Gaussian photons owing to higher total photofission reactions.

Real-time nuclear activation detectors for measuring neutron angular distributions at the National Ignition Facility (invited).

The Real Time Nuclear Activation Detector (RTNAD) array at NIF measures the distribution of 14MeV neutrons emitted by deuterium-tritium (DT) fueled inertial confinement fusion implosions. The uniformity of the neutron distribution is an important indication of implosion symmetry and DT shell integrity. The array consists of 48 LaBr3(Ce) crystal gamma-ray spectrometers mounted outside the NIF target chamber, which continuously monitor the slow decay of the 909 keV gamma-ray line from activated 89Zr located in Zr cups surrounding each crystal. The measured decay rate dramatically increases during a DT implosion in proportion to the number of 14MeV neutrons striking each Zr cup. The neutrons produce activated 89Zr through an (n, 2n) reaction on 90Zr, which is insensitive to low energy neutrons. The neutron flux along the detector line-of-sight at shot time is determined by extrapolating the fitted 909 keV decay curve back to shot time. Automatic analysis algorithms were developed to handle the non-stop data stream. The large number of detectors and the high statistical accuracy of the array enable the spherical harmonic modes of the neutron angular distribution to be measured up to L ≤ 4 to provide a better understanding of implosion dynamics. In addition, these data combined with measurements of the down-scattered neutrons can be used to derive fuel areal density distributions. This paper will describe the RTNAD hardware and analysis procedures.

Аналіз впливу вигоряння ядерного палива реактора ВВЕР-1000 на швидкість утворення 16N в теплоносії першого контуру

The developed model of the WWER-1000 reactor using MCNP6.2 (Monte Carlo N-Particle Transport Code) includes the detailed core taking into account the design of the fuel assemblies, as well as the baffle, the lower plenum, the fuel support columns, the core barrel, a downcomer, and the reactor pressure vessel. It allows implementing multifunctional calculations such as recriticality with various fuel configurations, the critical concentration of boric acid, determination of the axial and radial peaking factor in the reactor core, etc. For obtaining the more precise result of the cumulation nitrogen-16 formation rate, the contribution from different water volumes was taken into account: in the core, above the fuel and the top nozzle, in the top nozzle of the fuel assembly, in the bottom nozzle, between the fuel and the bottom nozzle, in the axial channels of the baffle, in the reflector. In order to obtain the realistic boundary conditions, the change of the isotopic composition in the fuel assemblies during one fuel cycle was calculated using the ORIGEN-ARP of SCALE software. Therefore, the influence of the nuclear fuel depletion of fuel assemblies in the WWER-1000 reactor on the change of the basic neutron-physical characteristics was determined such as the distribution of the neutron flux density with the energies necessary to initiate the 16O(n,p)16N reaction, the average number of neutrons per fission, the neutron spectrum and average fission energy. As a result, the dependence of the nitrogen-16 formation rate in the primary coolant system on the nuclear fuel burnup is obtained.

3D1D hydro-nucleosynthesis simulations – I. Advective–reactive post-processing method and its application to H ingestion into He-shell flash convection in rapidly accreting white dwarfs

ABSTRACT We present two mixing models for post-processing of 3D hydrodynamic simulations applied to convective–reactive i-process nucleosynthesis in a rapidly accreting white dwarf (RAWD) with [Fe/H] = −2.6, in which H is ingested into a convective He shell. A 1D advective two-stream model adopts physically motivated radial and horizontal mixing coefficients constrained by 3D hydrodynamic simulations. A simpler approach uses diffusion coefficients calculated from the same simulations. All 3D simulations include the energy feedback of the 12C(p, γ)13N reaction from the H entrainment. Global oscillations of shell H ingestion in two of the RAWD simulations cause bursts of entrainment of H and non-radial hydrodynamic feedback. With the same nuclear network as in the 3D simulations, the 1D advective two-stream model reproduces the rate and location of the H burning within the He shell closely matching the 3D simulation predictions, as well as qualitatively displaying the asymmetry of the XH profiles between the upstream and downstream. With a full i-process network the advective mixing model captures the difference in the n-capture nucleosynthesis in the upstream and downstream. For example, 89Kr and 90Kr with half-lives of $3.18\,\,\mathrm{\mathrm{min}}$ and $32.3\,\,\mathrm{\mathrm{s}}$ differ by a factor 2–10 in the two streams. In this particular application the diffusion approach provides globally the same abundance distribution as the advective two-stream mixing model. The resulting i-process yields are in excellent agreement with observations of the exemplary CEMP-r/s star CS31062-050.

Measurement of the [formula omitted]O(n,p)[formula omitted]N cross sections for validating the water activation experiment for ITER at the Frascati neutron generator

Water activated by fast neutrons emits both high energy gammas from 16N and delayed neutrons from 17N. The radioisotopes 16,17N are produced through the 16O(n,p)16N and 17O(n,p)17N reactions (thresholds about 10 MeV) and decay through the reactions 16N (T1∕2=7.13±2 s) →16O + γ (67% @ 6.13 MeV, 5% @ 7.12 MeV) and 17N (T1∕2=4.173±4 s) →17O→16O + n (37.7% @ 0.386 MeV, 0.6% @ 0.886 MeV, 49.8% @ 1.16 MeV, 6.9% @ 1.69 MeV), γ (3.7% @ 0.87 MeV), respectively. Activated water, flowing throughout a nuclear plant distributes the radioactivity to many critical components where personnel and/or instrumentation can be located thus depositing additional radiation dose which requires a proper shielding. This source of radiation represents an issue for a D-T fusion device like ITER which uses water as the main cooling fluid for components such as e.g. first wall and divertor.Owing to the scarce experimental information available for the cross sections of the 16O(n,p)16N and 17O(n,p)17N reactions and few benchmark validations, large uncertainties are affecting the calculations of the water activation induced by DT neutrons in a tokamak. In the attempt to improve the available nuclear data Fusion for Energy (F4E) tasked ENEA to carry on a benchmark experiment to validate the water activation calculations presently performed for ITER. This benchmark experiment was carried out in the year 2019 irradiating with the 14 MeV neutrons produced by the Frascati Neutron generator (FNG) a small size ITER First Wall mock-up. Demineralized water was circulating inside the mock-up and downstream of the irradiation zone the 16N gamma-rays decay and the 17N neutrons decay were measured using proper detectors. The experiment was simulated using the MCNP and the FISPACT codes. The obtained C/E values are in a range close to unit for both 16,17N isotopes. However, due to the large uncertainty on the 16O(n,p)16N and 17O(n,p)17N reactions cross-sections, for some of the used cross-section data base, e.g. ENDF/B-VIII.0, the C/E is affected by large uncertainty. This is especially true for the case of 17N which production cross-section is affected by ±60% uncertainty. In the attempt to measure and validate the cross-section data for 16,17N production, the water activation experiment was repeated at FNG so to measure directly the 16,17O(n,p)16,17N reaction cross-sections at almost monochromatic energies. The results of this new experiment are presented in this paper and compared to the data currently used by ITER project for calculating the water activation.

Сравнение коллективного ускорения протонов и дейтронов в диоде Люса с полиэтиленовым анодом

Collective acceleration of protons and deuterons is compared in the same geometry of a Luce diode with a polyethylene anode at an accelerating diode voltage of 250 kV, current and pulse duration of relativistic electrons up to 30 kA and 90 ns, respectively. The accelerated ions were intercepted by B4C, BN, and AlN plates, in which analytical radionuclides were produced according to nuclear reactions 10B( p , α)7Be, 12C( p, γ)13N, 10B( d , n )11C, 12C( d , n )13N, 14N( d , n )15O and 27Al( d , p )28Al. The ion energy was determined according to the ratios of activity of the analytical radionuclides, while the number of accelerated ions was calculated from the number of induced nuclei of the radionuclides. It was found that the velocities of the main group of protons and deuterons were the same within the measurement error, and the average number of ions accelerated in one pulse was, on average, 3 times higher when protons were accelerated.

Phase transition between the isovector to isoscalar pairing correlations in deformed N = Z nuclei

We investigate the pairing correlations on N = Z nuclei. In particular, the isoscalar (IS) pairing mode in neutron-proton (np) pairing is discussed in detail because the IS np pairing is closely related to the tensor force in the nucleon-nucleon interaction. Recent experiments demonstrated that the IS pairing might be enhanced from the M1 spin strength distribution data and deuteron, which is a consequence of the IS pairing, can be detected in 16O(p,p’d)14N reaction. The present study illustrates that the IS np pairing can be condensed not only in S=0, L = odd states but also in S=1, L=even states. The former is usually treated as T=0 np pairing. The latter is associated with deuteron and has not been fully treated in the BCS theory for the nuclear structure. In particular, the latter np pairing can be ejected as deuteron from the energetic probes in the experiments. Detailed analyses of the np pairing are performed mainly on 16O and extended to other N = Z nuclei.

Indirect Measurements of n- and p-Induced Reactions of Astrophysical Interest on Oxygen Isotopes

Observations of abundances and isotopic ratio determinations in stars yield powerful constraints on stellar models. In particular, the oxygen isotopic ratios are of particular interest because they are affected not only by nucleosynthesis but also by mixing processes. This review is focused on the measurements via the Trojan Horse Method (THM) that have been carried out to investigate the low-energy cross sections of proton and neutron-induced reactions on 17O as well as the proton-induced reaction on 18O, overcoming extrapolation procedures and enhancement effects due to electron screening. The (p,a) reactions induced on these oxygen isotopes are of paramount importance for the nucleosynthesis in many stellar sites, including red giants (RGs), asymptotic giant branch (AGB) stars, massive stars, and classical novae. The indirect measurement of the 17O(p,a)14N reaction was performed. The strength of the narrow resonance at 65 keV was evaluated and it was used to renormalize the corresponding resonance strength in the 17O+p radiative capture channel. The reaction rate was evaluated for both the 17O(p,a)14N and the 17O(p,g)18F, and a significant difference of 30% and 20% with respect to the literature was found in the temperature range relevant for RG, AGB and massive stars nucleosynthesis. Regarding the 18O(p,a)15N reaction, the strength of the 20 keV resonance was extracted, which is the main contribution to the reaction rate for astrophysics. This approach allowed us to improve the data accuracy of a factor 8.5, as it is based on the measured strength instead of extrapolations or spectroscopic measurements. Finally, the 17O(n,a)14C reaction was studied because of its role during the s-process nucleosynthesis as a possible neutron poison. This study represents the extension of THM to resonant neutron-induced reactions. In this measurement, the subthreshold level centered at -7 keV in the center-of-mass, corresponding to the 8.039 MeV 18O excited level, was observed. Moreover, the THM measurements showed a clear agreement with the available direct measurements because of the additional contribution of the 8.121 MeV 18O level, strongly suppressed in direct measurements because of its l=3 angular momentum. The contributions to the total reaction rate were than evaluated for future astrophysical applications.

Global R-matrix analysis of the 11B(α,n)14N reaction

Reactions that populate the 15N system have implications for nucleosynthesis through the 11B(α, n)14N and 14N(n, p)14C reactions and the 14N(n, p)14C reaction is also a key component in modeling atmospheric 14C production. A convenient characteristic of this system is that the α-particle, proton, and neutron separation energies are all within ≍1 MeV of one another. Further, it has been observed that 11B+α, 14N+n and 14C+p induced reactions all populate many of the same resonances near their reaction thresholds. This strongly facilitates the simultaneous analysis of data for all three of these entrance partitions using a global R-matrix analysis, which in turn provides a method of comparing the consistency among the different experimental measurements. In this work, a new measurement has been performed for the 11B(α, n)14N reaction, which gives a more accurate description of the cross section, in particular over an important interference region. This new data is combined with results from previous measurements, which populate a similar excitation energy range in the 15N system, to produce a global fit that includes 11B(α, n)14N reaction data for the first time.

Activation Measurements of the Integral Cross Sections of the 12C(d,X)13N, 14N(d,X)15O, 14N(d,X)13N, 14N(d,X)11C, and 16O(d,X)17F Reactions

Cross sections of the 12C(d,X)13N (β+, T1/2 = 9.965 min), 14N(d,X)15O (β+, T1/2 = 122 s), 14N(d,X)13N (β+, T1/2 = 9.965 min), 14N(d,X)11C (β+, T1/2 = 20.39 min), and 16O(d,X)17F (β+, T1/2 = 64.5 s) reactions are measured at the electrostatic tandem accelerator via activation method at deuteron energies of 1–12 MeV. (C5Н4О2) mylar films (5 ± 1%) μm thick and layers of atmospheric air of 2.1, 5.1, and 7.1 mm thick are used as targets.

Measurement of delayed neutron emission from water activated by 14 MeV neutrons in a FW mock-up of ITER

Water activated by 14 MeV neutrons emits both high energy gammas from 16N and delayed neutrons from 17N. The isotopes 16,17N are produced through the 16O(n,p)16N (T1/2 = 7.13 s) and 17O(n,p)17N (T1/2 = 4.1 s) reactions, respectively. These sources of radiation represent one of the main issues for ITER having large impact on the design of the machine and on the qualification of components. To validate the calculation methodology used for ITER and to reduce the safety factors applied to the calculation results a water activation experiment was commissioned by F4E to ENEA and performed at the 14 MeV Frascati neutron generator (FNG). The experimental set-up consisted of a closed water loop, about 40 m long, where the cooling water, while transiting through an ITER FW mock-up, was irradiated by the D-T neutrons produced at FNG. 6.73 MeV gamma-rays from 16N and delayed (fast) neutrons from 17N were measured using a large CsI gamma-ray detector and an array of absolutely calibrated 3He detectors, respectively. This paper reports on the measurements of the delayed neutrons emission from 17N. The calibration of the 3He detector array and the experimental set-up are first discussed. Then the experimental results (E) for the delayed neutrons as well as the comparison with the calculation (C) performed using the MCNP Monte Carlo code (coupled to the FENDL3.1 data library) and the EASY-2007 inventory code are presented. The C/E ratio results close to unity, however it is affected by a very large error (> ±60 %) to be ascribed mainly to the uncertainty on the nuclear data used for calculation.