2n Reaction Research Articles

Production of [13N]ammonia from [13C]methanol on a 7.5 MeV cyclotron using 13C(p, n)13N reaction: Detection of myocardial infarction in a mouse model

[13N]Ammonia is commonly produced using 16O(p, α)13N reaction but one of the limiting factor of this reaction is the relatively small nuclear cross-section at proton energies of <10 MeV. An alternative production method using 13C(p, n)13N reaction, which has a higher nuclear cross-section at low proton energies, is more suitable for a preclinical PET imaging facility equipped with a <10 MeV cyclotron. Here, we report a novel method to produce [13N]ammonia from [13C]methanol for preclinical use on a 7.5 MeV cyclotron. A tantalum solution target (80 μl) consisting of a havar window supplied by the cyclotron manufacturer for the production of [18F]fluoride was used without any modifications. The final bombardment parameters were optimized as follow: [13C]methanol concentration in target solution – 10%, bombardment time – 8 min, and beam current – 2.2 μA. These parameters provided doses of [13N]ammonia which were sufficient to conduct preclinical PET imaging studies in a mouse model of myocardial infarction. Under optimized conditions, the operational lifetime of the target was approximately 150 μAmin. Radionuclide identity of the product as 13N was confirmed by measuring the decay half-life and its radionuclide purity was confirmed by γ-ray spectroscopic analysis. Gas chromatography revealed that the final [13N]ammonia dose was not distinguishable from water, showing no traces of methanol. As expected, PET/CT imaging in healthy CD-1 mice indicated the accumulation of [13N]ammonia in myocardial tissue; mice with myocardial infarction created by left ascending coronary ligation showed clear perfusion deficit in affected tissue. This work demonstrates the proof-of-concept of using 13C(p, n)13N reaction to produce [13N]ammonia from [13C]methanol with a <10 MeV cyclotron, and its diagnostic application in imaging cardiac perfusion.

Suprathermal nuclear effects in the solar core: overall view

The present paper completes a series of works on the influence on solar processes of fast charged particles produced in exoergic reactions in the solar core. The general picture of suprathermal effects triggered by the most energetic of them—MeV protons and α-particles—is composed. All reactions in the pp chain and the CNO cycle induced by these particles are examined. It is shown that some opposite suprathermal (p, α) and (α, p) reactions can be balanced, but their rates can exceed the rates of the respective thermal processes, affecting some points of nuclear fusion in the solar core. In particular, the suprathermal channels of p + 17O α + 14N reactions increase the total energy released in these processes by a factor of 1.64, and enhance the mass fractions of 17O and 18O by ∼1–4 times at radii . The same result is also obtained for the 18F abundance, leading to the proportional enhancement of the 18F neutrino emission rate. At the same time, integral characteristics like the total energy production and neutrino generation in the solar core remain unchanged.

Measurement of the 58Ni(n, p)58Co and 58Ni(n, 2n)57Ni reaction cross-sections for fast neutron energies up to 18 MeV

The 58Ni(n, p) and 58Ni(n, 2n) reaction cross-sections were measured from threshold to 18MeV neutron energies using the activation and off-line $\gamma$ -ray spectroscopic technique. The quasi-monoenergetic neutron beam was generated using the 7Li(p, n) reaction. The results from the present work were compared with those of the literature and with the evaluated data from different libraries, like ENDF-B/VII.1, JENDL-4.0, CENDL-3.1, and JEFF-3.3. Nuclear model codes, like TALYS-1.9 and EMPIRE-3.2.3-Malta, were also used for a better description of the present work and literature data. The uncertainties in the measured cross-section were evaluated using the covariance analysis. The present experimental results were found to be in good agreement with those of the literature and with the evaluated data. The nuclear model code TALYS-1.9 was found successful in reproducing the experimental data for both reactions. However, the EMPIRE-3.2.3-Malta model code was found to be able to reproduce only the trend of the 58Ni(n, p) reaction excitation function. The present work provides a better insight on the comparison of both nuclear model codes. The present work is also essential for the production cross-section and the dose rate estimation of the medical isotope 58Co.

New Data on the Photodisintegration of 140, 142Ce and 153Eu Nuclei

Experimental data for 140, 142Се and 153Eu nuclei are analyzed jointly using the cross sections for total and partial photoneutron reactions obtained with quasimonoenergy photon beams formed during the annihilation of relativistic positrons. The results from an experiment performed on a bremsstrahlung beam are also used for such an analysis for the 153Eu nucleus. Well-known systemic discrepancies between the results of different experiments are analyzed using the objective physical criteria of data reliability, and ways of allowing for them are considered. New data on the cross sections of (γ, 1n) and (γ, 2n) reactions for 140, 142Се nuclei, on the cross section of (γ, 3n) reaction for 153Eu nucleus, and on the cross section of total photoneutron reaction for all three nuclei were obtained additionally the cross sections of partial reactions that satisfy the established criteria of reliability. It was shown that substantial deviations of the experimental reaction cross sections from those evaluated are due to an unreliable sorting of neutrons between the channels with a multiplicity of 1, 2 due to the abovementioned systematic uncertainties.

Tritium breeding capability of water cooled ceramic breeder blanket with different container designs

Water cooled ceramic breeder (WCCB) blankets have been regarded as a primary concept in Japan. We investigated the tritium breeding capability of a WCCB blanket with a cylindrical structure, an advantageous shape for withstanding high coolant pressure, in this study. The breeding area in the blanket was modeled as a homogeneous mixture or heterogeneous structures. Nuclear analyses with Monte Carlo method were conducted for evaluating the tritium breeding ratio (TBR) of the blanket. The neutron balance of the blanket was analyzed to elucidate the mechanism related to the increase in TBR when an additional thin breeding layer (envelope) was applied to the blanket. The neutron multiplication in (n, 2n) reaction increased concomitantly with increase of the beryllium volume ratio. However, numerous neutrons were not used efficiently for tritium production, but were captured by the container, which was made of the reduced activation ferritic martensitic steel, F82H. Capture by the container can be reduced by introducing an envelope. The effect of the envelope was considerable when modeling the internal structure such as U-shaped pipes in the breeding area. The envelope was also applied to a blanket with different container designs. An increase in TBR was shown irrespective of blanket design. The envelope effect was remarkable when it was difficult to achieve the internal configuration, which was equivalent to the homogeneous mixture in the breeding area.

Increased Uptake of At-211 in Thyroid Gland by the Preparation with Ascorbic Acid for Targeted Alpha Therapy of Thyroid Cancer

Astatine-211 (211At) is an alpha-emitting radionuclide suitable for targeted alpha therapy. Because At is a heavier homolog of iodine, astatide ion (At-) is expected to be applied to the treatment of thyroid cancer. In this study, 211At was treated by ascorbic acid (AA) as reducing agent to prepare At-. We aimed to evaluate the uptake change in the thyroid after the preparation of 211At solutions with AA and demonstrate the treatment effect in the differentiated thyroid cancer xenograft mice. Astatine-211 was produced in the 209Bi(α, 2n) reaction and supplied through Shortlived RI Supply Platform. Produced 211At was then separated from the target materials by a dry distillation method and dissolved in pure water. The aliquot of 211At solution was mixed with 1% AA solution to prepare At-. The radiochemical yield was checked by radio-TLC. The crude 211At solution or 211At with AA solution was administered to normal rats (n=3 for both solution) through tail vein under isoflurane anesthesia. In vivo imaging of 211At in the normal rats was then carried out using a gamma camera at 0.5, 3, 6 and 24 hrs after administration. The 211At solution with AA was also administered to mice with implanted K1 cells (human papillary thyroid carcinoma) expressing sodium iodide symporter (NIS). Mice were divided into 4 groups according to the injected dose [1 MBq (n=6), 0.4 MBq (n=6), 0.1 MBq (n=6), control (n=6)]. Distribution of 211At administered in the mice was investigated at 3 and 24 hrs after administration by the gamma camera. The radiochemical yield of At- checked by radio-TLC increased from approximately 20% to 90% after treatment of the crude 211At solution with AA. In vivo imaging of 211At in the normal rats showed high uptakes in the thyroid, the stomach, and the bladder. Uptake of At with AA in thyroid gland was 2–3 times higher compared to crude 211At solution. In the xenograft mice, there was a stable accumulation in the thyroid tumor at 3 and 24 hrs post administration (23 ± 11 %ID and 13 ± 7 %ID, respectively). Tumor growth was immediately inhibited after administration of 211At in a dose-dependent manner. Suppression of tumor growth was maintained until 17, 31, and 41 days after administration of 211At in 0.1, 0.4, and 1 MBq groups, respectively. Uptake of 211At can be enhanced in the normal thyroid by increasing the radiochemical purity of At-. The administered 211At showed good treatment effect in thyroid cancer xenograft, suggesting that 211At solution with AA is promising for the targeted alpha therapy for the thyroid cancer.

Proton induced differential cross sections on 14N and 28Si from 3 to 4 MeV

In this work commercially available self-supporting thin silicon-nitride films were applied to measure the differential cross sections for the reactions 28Si(p,p′γ)28Si (Eγ = 1779 keV) and 14N(p,p′γ)14N (Eγ = 2313 keV) in the proton energy range of 3–4 MeV. For an additional validation of the data, the cross section from the present work and from the literature were integrated and compared to experimental thick target yields. Gamma-rays were detected simultaneously with backscattered particles using a HPGe detector at 55° and an ion implanted Si detector at 135° with respect to the beam direction. As a by-product, differential gamma-ray and particle production cross sections were measured for the first time in the 29Si(p,p′γ)29Si (Eγ = 1273 keV) reaction at 55°, as well as in the natN(p,po)natN, natSi(p,po)natSi and 28Si(p,p1)28Si elastic and inelastic scatterings at 135° from 3 to 4 MeV proton energies.

Activation cross-sections for the 185Re(n, 2n) reaction and the isomeric cross-section ratio of 184m,gRe in the neutron energy range of 13\u201315 MeV

.Cross-sections and their isomeric ratios ( sigma_{mathrm{m}}/sigma_{mathrm{g}}) for the 185Re(n, 2n)184mRe and 185Re(n, 2n)184gRe reactions in the 13–15 MeV range were measured. The neutron activation technique was applied using the K-400 neutron generator at the Chinese Academy of Engineering Physics (CAEP). Natural Re samples and Nb monitor foils were activated jointly to determine the reaction cross-section and the incident neutron flux. The 3H(d, n)4He reaction was used to generate the neutron beam. The pure cross-section of the ground state was derived from the absolute cross-section of the metastable state using residual nuclear decay analysis. Numerical calculations using the nuclear-model-based computer code TALYS-1.8 with six level density models were used to obtain 185Re(n, 2n)184m, gRe reaction excitation functions and their isomeric cross-section ratios. Finally, experimentally determined cross-sections were compared with corresponding literature data.

Pure hydrogen references synthesized by low energy ion implantation into amorphous silicon

We developed a hydrogen standard by ion implantation in amorphous silicon, produced by implantation of 170 keV 28Si with 2·1015 at./cm2 in a silicon wafer (1 0 0) to obtain an amorphous depth of a few hundred of nanometers. The tilt and twist angles of the target were fixed to avoid channeling and the sample was cooled during the implantation. The amorphous silicon was then irradiated successively with hydrogen at 3.0 and 1.5 keV with doses 1.0 and 0.7·1017 at./cm2 respectively. The characteristics of the standards (retained dose, depth profile and stability under irradiation) were investigated by elastic recoil detection analysis (ERDA) and resonant nuclear reaction analysis (RNRA) with a 1H(15N,αγ)12C reaction at 6.385 MeV. These properties were compared with another previously developed standard (hydrogen implantation in monocrystalline silicon (1 0 0)). Results showed that, for the same implanted dose, the retained dose is about 55% larger in amorphous silicon. Furthermore, we showed these new standards are stable under beam irradiation for low current (10 nA/mm2) and could be used as IBA reference. Stability for higher currents (100 nA/mm2) showed a 10% release after an integrated charge about 2 mC. We showed that this release which occurs at the beginning of irradiation is due to desorption of the H-contamination layer on the surface. Implanted hydrogen remains stable under irradiation. We conclude that those standards are suitable target to study nuclear reactions of astrophysical interest, namely the 1H(13C,γ)14N reaction.

Improved astrophysical rate for the 18O(p,α)15N reaction by underground measurements

The 18O(p,α)15N reaction affects the synthesis of 15N, 18O and 19F isotopes, whose abundances can be used to probe the nucleosynthesis and mixing processes occurring deep inside asymptotic giant branch (AGB) stars. We performed a low-background direct measurement of the 18O(p,α)15N reaction cross-section at the Laboratory for Underground Nuclear Astrophysics (LUNA) from center of mass energy Ec.m.=340 keV down to Ec.m.=55 keV, the lowest energy measured to date corresponding to a cross-section of less than 1 picobarn/sr. The strength of a key resonance at center of mass energy Er=90 keV was found to be a factor of 10 higher than previously reported. A multi-channel R-matrix analysis of our and other data available in the literature was performed. Over a wide temperature range, T=0.01–1.00 GK, our new astrophysical rate is both more accurate and precise than recent evaluations. Stronger constraints can now be placed on the physical processes controlling nucleosynthesis in AGB stars with interesting consequences on the abundance of 18O in these stars and in stardust grains, specifically on the production sites of oxygen-rich Group II grains.

Cross sections for formation of 139mCe radioisotope through the 140Ce (n, 2n) reaction over 13.73–14.77 MeV neutrons

Cross sections for the formation of metastable state of 139Ce through 140Ce(n, 2n)139mCe reaction were measured at five neutron energies over 13.73–14.77 MeV range using the activation method and off-line gamma-ray spectrometric technique. These cross sections were in agreement with the corresponding theoretical cross sections estimated over 10–20 MeV neutrons by EMPIRE-3.2 code, using LEVEDEN 4 and strength function GSTRFN 0 parameters, and TALYS-1.8 code using ldmodel 5 and preeqmode 4 parameters. The estimated most probable excitation energies of 139Ce were 1.320–3.877 MeV, respectively over 13.73 MeV and 14.77 MeV neutron energies.

About chemical form and binding energy of 14C in irradiated graphite of uranium-graphite nuclear reactors

Issues associated with handling irradiated graphite of uranium-graphite nuclear reactors are examined. It is demonstrated that selection of approaches, methods and means for handling irradiated graphite are determined by the form of occurrence and binding energy of long-lived 14C radionuclide with graphite crystalline lattice. The purpose of the present study is the determination of possible chemical compounds in which 14C can be found and assessment of fastness of its binding in the structure of irradiated graphite. Indigent and foreign experience of handling graphite radioactive wastes was analyzed, calculations and measurements were performed. Information was provided on the channels of accumulation of 14C in the structure of reactor graphite and it was demonstrated that the largest quantities of the radionuclide in question are generated according to the reaction 14N(n, p)14C. Here, most part of radioactive carbon is generated on 14N nuclei found in the form of impurities in non-irradiated graphite and in the composition of gas used for purging nuclear reactor in the process of operation. 14C radionuclide generated according to 14N(n, p)14C nuclear reaction is localized in the near subsurface graphite layer (in the near subsurface layer of pores) at the depth of not more than 50 nm. Analysis was performed of possible chemical compounds which may incorporate radioactive carbon. It was established that the form of occurrence is determined by the operational properties of specific graphite element in the reactor core. 14C binding energy in the structure of irradiated graphite was evaluated and depth of its penetration in the structure was calculated. It was established that selective extraction of this radionuclide is possible only under elevated temperatures in weakly oxidizing environment which is explained by the binding energy reaching up to 800 kJ/mole in the process of chemical sorption of 14C on the surface of graphite and depth of its occurrence equal to ~ 70 nm in the course of ion implantation. It was demonstrated that radioactive carbon generated according to 13C(n, γ)14C nuclear reaction is uniformly distributed among graphite elements and possesses binding energy ~477 kJ/mole. Its selective extraction is possible only under the condition of destruction of graphite crystalline lattice and organization of the process of isotopic separation. The obtained results allow recommending the most efficient methods of handling irradiated graphite during decommissioning uranium-graphite reactors.

The Role of 14-MeV Neutrons in Light Element Nucleosynthesis

The 14-MeV neutron-induced nuclear reactions which might contribute to better understanding of the so-called “cosmological lithium problem” have been discussed. The big bang nucleosynthesis theory predicted 7Li overestimated value could be lowered by 2n-induced reactions on Li isotopes and/or 7Be destruction via resonance in the d + 7Be → 9B process. Proposals for 6Li + 2n and 7Li + 2n reactions’ cross section evaluations and measurements are discussed in some details. In addition, we discuss also a preliminary measurements of n–n coincidences from the 10B(n,2n) 9B reaction with two neutron detectors placed outside the cone of 14-MeV tagged neutron beam. From the time-of-flight measurements and known geometry, we tried to deduce the neutron energies and calculate the 9B missing mass spectrum. Improvements for better measurements are suggested.

Study of differential cross-sections of the 14N(d,α0,p0,α1) reactions suitable for NRA

In the present work the differential cross-sections of the 14N(d,α0,p0,α1) reactions were studied in projectile energy range Ed,lab = 900–2000 keV (in energy steps of ∼50 keV) and for six detector angles between 145° and 170° (in steps of 5°). The target used was a 75 nm self-supported thin Si3N4 foil (Silson Ltd). The measurements were performed using the 5.5 MV TN11 HV Tandem Accelerator of N.C.S.R. “Demokritos”, Athens, Greece and a high-precision goniometer. The results were compared with already existing ones in literature, as well as with evaluated values.

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.

Modelling of the neutron production in a mixed beam DT neutron generator

Compact DT neutron generators based on accelerators are often built on the principle of a mixed beam operation, meaning that deuterium (D) and tritium (T) are both present in the ion beam and in the target. Moreover, the beam consists of a mixture of ions and ionized molecules (D, T ions, and ionized D-D, T-T and D-T molecules) so the relevant source components come from T(d, n), D(t, n), D(d, n) and T(t, 2n) reactions at different ion energies.The method for assessing the relative amplitudes of different source components (DD, DT, TT) is presented. The assessment relies on the measurement of the neutron spectrum of different DT components (T(d, n) and D(t, n) at different energies) using a high resolution neutron spectrometer, e.g. a diamond detector, fusion reaction cross-sections, and simulations of neutron generation in the target. Through this process a complete description of the neutron source properties of the mixed beam neutron generator can be made and a neutron source description card, in a format suitable for Monte Carlo code MCNP, produced.

Investigation of the excitation functions for the (n, 2n) reactions on the structural fusion material 58,60 – 62,64Ni

Abstract The theoretical prediction of the cross-sections in the determination of the structure materials used in the fission and fusion technology is very important in terms of reactor safety. Also, theoretical cross-sections are necessary to evaluate the performance of structure materials, especially, in the lack or absence of experimental data. Nickel base alloys are one of the wide ranges of structural materials used in fission and fusion reactors. Therefore, the excitation functions of the (n, 2n) reactions on the structure material nickel with neutrons producing via fusion reactions are investigated in this study. Thus, the excitation functions for 58,60 – 62,64Ni(n, 2n) reactions are calculated using some pre-equilibrium models which are the hybrid, the geometry depended hybrid and the two-component excitation models. The calculations are performed in the ALICE/ASH and the Talys 1.8 codes. Also, the equilibrium and pre-equilibrium effects on these reactions are investigated in this study. The obtained cross-sections are discussed and compared with the experimental data and the theoretical predicted data.

Direct underground measurement of the 17O(p,α)14N reaction at LUNA

The 17O(p, α)14N reaction plays a role in a number of stellar sites, including giant branch stars and novae. In particular, a narrow and isolated resonance at Ep=70 keV dominates the reaction rate at stellar temperatures around T9=0.01-0.1. A direct measurement of the 17O(p,α)14N reaction has been recently performed at the underground LUNA-400 accelerator in the Gran Sasso Laboratory, Italy. Protons were accelerated on a solid Ta2O5 target and the alpha particles emitted were detected with an array of silicon detectors. The background reduction afforded by the underground environment was instrumental in successfully carrying out the measurement. The setup was simulated and commissioned exploiting two well-known resonances at Ep=151 and 193 keV in 18O(p,α)15N and 17O(p,α)14N respectively. The strengths of the two resonances were found to be respectively meV and ωγ(193)=1.68±0.03stat±0.12 syst meV in good agreement with the literature. Analysis of data acquired on the Ep=70 keV resonance in 17O(p,α)14N reaction is currently underway.

New perspectives for undoped CaF2 scintillator as a threshold activation neutron detector

In this paper we present the prompt photofission neutron detection performance of undoped CaF2 scintillator using Threshold Activation Detection (TAD). The study is carried out in the frame of C-BORD Horizon 2020 project, during which an efficient toolbox for high volume freight non-intrusive inspection (NII) is under development. Technologies for radiation monitoring are the part of the project. Particularly, detection of various radiological threats on country borders plays an important significant role in Homeland Security applications. Detection of illegal transfer of Special Nuclear Material (SNM) - 235U, 233U and 239Pu - is particular due to the potential use for production of nuclear weapon as well as radiological dispersal device (RDD) V known also as a “dirty bomb”. This technique relies on activation of 19F nuclei in the scintillator medium by fast neutrons and registration of high-energy β particles and γ-rays from the decay of reaction products. The radiation from SNM is detected after irradiation in order to avoid detector blinding. Despite the low 19F(n,α)16N or 19F(n,p)19O reaction cross-section, the method could be a good solution for detection of shielded nuclear material. Results obtained with the CaF2 detector were compared with the previous study done for BaF2 and 3He detector. These experimental results were obtained using 252Cf source and 9 MeV Varian Linatron M9 linear accelerator (LINAC). Finally, performance of the prompt neutron detection system based on CaF2 will be validated at Rotterdam Seaport during field trails in 2018.

First radioactive beams at ACCULINNA-2 facility and first proposed experiment

New fragment separator ACCULINNA-2 was installed at the primary beam line of the U-400M cyclotron in 2016. Recently, first radioactive ion beams were obtained. The design parameters of new facility were experimentally confirmed. Intensity, purity and transverse profile of several secondary beams at the final focal plane were studied. The intensities obtained for the secondary beams of 14B, 12Be, 9;11Li, 6;8He in the fragmentation reaction 15N (49.7 AMeV) + Be (2 mm) are in average 15 times higher in comparison to the ones produced at its forerunner ACCULINNA separator. The ACCULINNA-2 separator will become a backbone facility at the FLNR for the research in the field of light exotic nuclei in the vicinity of the nuclear drip lines. The planned first experiment, aimed for the observation of the 7H nucleus at ACCULINNA-2, is outlined.