Fe Reaction Research Articles

Precise measurement of the neutron capture reaction 54Fe(n,γ)55Fe via AMS

The measurement of cross sections relevant to nuclear astrophysics has become one main research topic at the VERA (Vienna Environmental Research Accelerator) facility. The technique applied, accelerator mass spectrometry (AMS), offers excellent sensitivity for the detection of long-lived radionuclides through ultra-low isotope ratio measurements. We discuss the potential and preliminary results of ongoing precision measurements of neutron-capture cross sections of 54Fe. Such measurements might help to clarify the recently found discrepancy of s-process nucleosynthesis at lower-mass nuclei (A<120), which might be attributed to a systematic offset in previous experimental data. Samples were irradiated with neutrons from thermal to MeV energies. After the irradiations, the amount of produced long-lived 55Fe (t1/2 = 2.72 yr) was analyzed using AMS. At VERA, detection of 55Fe was developed with a reproducibility of about 1%, which makes the 54Fe(n,γ)55Fe reaction a precise and unique laboratory measurement, which can serve as a reference to complementary techniques. In this regard a new 55Fe standard for AMS measurements was produced. The final cross-section data are expected to be accurate to better than 3%. We report a preliminary, however, already significantly improved thermal neutron cross section value of (2.32 ± 0.10) barn, and a value of (6.3 ± 0.6) mbarn for En = (520 ± 50) keV.

Dynamics of nuclear interaction in the reaction 56Fe(α, xn)

The spectra and angular distributions of neutrons from the reaction 56Fe(α, xn) were measured at the alpha-particle energies of 12.3, 16.3, 18.3, 26.8, and 45.2 MeV. The measurements were performed with time-of-flight fast-neutron spectrometers at pulsed accelerators of charged particles. The measured data were analyzed within models of equilibrium, preequilibrium, and direct reaction mechanisms. The calculations were performed by using an exact formalism of Hauser-Feshbach statistical theory. The required nuclear-level densities in nickel isotopes excited in this reaction were determined on the basis of new experimental data on low-lying levels, neutron resonances, and spectra of evaporated neutrons. The contributions of equilibrium, preequilibrium, and direct neutron emission were studied over a broad range of alpha-particle energies.

Role of cross-shell excitations in the reaction 54Fe( $$ \vec d $$ , p)55Fe

The reaction 54Fe(\( \vec d \), p)55Fe was studied at the Munich Q3D spectrograph with a 14MeV polarized deuteron beam. Excitation energies, angular distributions and analyzing powers were measured for 39 states up to 4.5MeV excitation energy. Spin and parity assignments were made and spectroscopic factors deduced by comparison to DWBA calculations. The results were compared to predictions by large-scale shell model calculations in the full pf -shell and it was found that reasonable agreement for energies and spectroscopic factors below 2.5MeV could only be obtained if up to 6 particles were allowed to be excited from the f 7/2 orbital into p 3/2 , f 5/2 , and p 1/2 orbitals across the N = 28 gap. For levels above 2.5MeV the experimental strength distribution was found to be significantly more fragmented than predicted by the shell model calculations.

Bulk properties of iron isotopes

Nuclear level densities and radiative strength functions (RSFs) in 56Fe and 57Fe were measured using the 57Fe(3He, αγ) and 57Fe(3He, 3He′γ) reactions, respectively, at the Oslo Cyclotron Laboratory. A low-energy enhancement in the RSF below 4-MeV energy was observed. This finding cannot be explained by common theoretical models. In a second experiment, two-step cascade intensities with soft primary transitions from the 56Fe(n, 2γ) reaction were measured. The agreement between the two experiments confirms the low-energy enhancement in the RSFs. In a third experiment, the neutron evaporation spectrum from the 55Mn(d, n)56Fe reaction was measured at 7-MeV deuteron energy at the John Edwards Accelerator Laboratory at Ohio University. Comparison of the level density of 56Fe obtained from the first and third experiments gives an overall good agreement. Furthermore, observed enhancement for soft γ rays is strengthened by the last experiment.

Retrospective Dosimetry of Fast Neutrons Focused on the Reactions 93Nb(n,n′)93Nbm and 54Fe(n,p)54Mn

Abstract An overview is given of practices for “retrospective” dosimetry based on extraction and counting of niobium and manganese present in typical pressure vessel materials. The main problem of counting structural materials is the overwhelming presence of the nuclide 60Co in the gamma-ray spectra of irradiated materials. Chemical separation of niobium and manganese is needed to determine the induced 93Nbm and 54Mn activities. Procedures have been developed for retrospective dosimetry applicable at normally equipped radiochemical laboratories. Chemical separation procedures have been applied followed by determination of the amount of niobium in dissolution after separation. Special attention has been given to the accurate counting of the very weak X rays of 93Nbm. Different techniques have been applied. Advantages, disadvantages, and the accuracy that can be achieved are discussed. Special attention has been given to the maximum accuracy that can be reached and the minimum amount of niobium that has to be collected to reach this accuracy.

Retrospective Measurement of Neutron Activation within the Pressure Circuit Steelwork of a Magnox Reactor and Comparison with Prediction

Abstract This paper describes a retrospective measurement of neutron activation rates within steel standpipe penetrations of the pressure circuit of the Wylfa nuclear power plant. This was carried out in support of neutron dose calculations. Samples were taken from a length of irradiated thermocouple cable and counted for the fast neutron reactions 54Fe(n,p) 54Mn, and 58Ni(n,p) 58Co, and the thermal neutron reactions 59Co(n,γ) 60Co, 58Fe(n,γ) 59Fe, and 50Cr(n,γ) 50Cr. By isolating clean sheath material and performing elemental analysis, it was possible to obtain absolute neutron flux data from the measurements over a broad range of locations. The measured data were compared with results obtained from a Monte Carlo calculation performed with the code mcbend. Structure observed within the measured and calculated thermal neutron flux distributions was used to confirm the position of the thermocouple samples relative to the reactor geometry. The measurements show that the calculations consistently over-predict fast and thermal neutron reactions. It is concluded that the model predicts spectra without significant bias, and consequently, that the standpipe dose recommendations are similarly over-predicted.

Influence of reaction channel on the isomeric cross-section ratio

Summary The influence of reaction channel on the isomeric cross-section ratio was investigated by analysing the experimental data on the reactions 52Cr(p, n)52m,gMn, 52Cr(3He, t)52m,gMn, 54Fe(d, α)52m,gMn, 54Fe(n, t)52m,gMn and 54Fe(3He, α p)52m,gMn over the incident particle energy range extending up to 35 MeV. The influence is most pronounced when the channels differ widely, for example (p, n) and (3He, t) processes, i.e. when the reaction mechanisms are different. The nuclear model calculational code EMPIRE-II described the isomeric cross-section ratio rather well in the case of a simple nucleon emission reaction, but not when complex reaction channels were involved.

Large Enhancement of Radiative Strength for Soft Transitions in the Quasicontinuum

Radiative strength functions (RSFs) for the (56,57)Fe nuclei below the separation energy are obtained from the 57Fe(3He,alphagamma)56Fe and 57Fe(3He,3He'gamma)57Fe reactions, respectively. An enhancement of more than a factor of 10 over common theoretical models of the soft (E(gamma) less than or approximately equal 2 MeV) RSF for transitions in the quasicontinuum (several MeV above the yrast line) is observed. Two-step cascade intensities with soft primary transitions from the 56Fe(n,2gamma)57Fe reaction confirm the enhancement.

Low-energy magnetic dipole response in 56Fe from high-resolution electron scattering

The 56Fe(e, e′) reaction has been studied for excitation energies up to about 8 MeV and momentum transfers q≃0.4–0.55 fm −1 at the Darmstadt electron linear accelerator (DALINAC) with kinematics emphasizing M1 transitions. Additional data have been taken for q≃0.8–1.7 fm −1 at the electron accelerator NIKHEF, Amsterdam. A PWBA analysis allows spin and parity determination of the excited states. For M1 excitations, transition strengths are derived with a DWBA analysis using shell-model form factors. The resulting B( M1) strength distribution is compared to shell-model calculations employing different effective interactions. The form factor of the prominent low-lying M1 transition at 3.449 MeV demonstrates its dominant orbital nature. It represents a major part of the scissors mode in 56Fe.

Properties of Some Bound States of the 56Fe Nucleus Excited by the 55Mn(p,γ)56Fe Reaction

Radiative decay of 21 resonances in the 55Mn(p,γ)56Fe reaction was studied in the proton beam energy region Ep = (1.3-1.8) MeV. Properties of bound states in the final 56Fe nucleus have been deduced from accurately measured very complex γ-ray spectra. About 150 levels have been firmly established for excitation energy up to ≈ 8 MeV and 93 of them have been observed for the first time or their established energy is substantially more accurate than in former publications or some other information is new. For each of the 57 levels, there has been established its decay and firmly observed at least one decay branch. Spin and parity have been newly determined or appreciated for 35 levels and for 35 levels the mean lifetime has been newly established by the DSAM method. Crude comparison of the observed level density with the statistical Fermi model prediction has been also performed.

Nuclear Model Calculations for the Excitation Functions of Neutron-Induced Reactions on 58Ni in the Energy Range up to 20 MeV

Calculations for the excitation functions of the 58Ni(n, α)55Fe reaction, including those of the ground and first states of 55Fe, 58Ni(n, αp+pα)54Mn, 58Ni(n,2n)57Ni, 58Ni(n,n’)58Ni, and 58Ni(n,np+pn)57Co reactions were carried out using nuclear reaction model codes. The results have been compared with reported measurements and evaluations. The available data on the 58Ni(n,n’)58Ni, 58Ni(n,2n)57Ni, and 58Ni(n,np+pn+d)57Co reactions are described well by using the single-particle model for the calculation of gamma-ray transition probabilities of the excited states of 58Ni.

Experimental study of excitation functions for some reactions induced by deuterons (10–50 Mev) on natural Fe and Ti

Stacks containing high purity natural Fe and Ti foils were irradiated in deuteron beams with incident energies of 30 and 50 MeV. Reactions on Al foils were used for monitoring beam energy and intensity. The excitation functions up to 50 MeV for natTi(d, x) 44m,46,47,48Sc, natFe(d, x) 55,57Co, 52,54Mn, 51Cr are presented and compared with the scarce literature values. No sharp peaks enabling clear identification of contributing reactions on the different naturally occurring isotopes are present. Only for the reactions 56Fe(d, n) 57Co ( Q=−2.1 MeV), 56Fe(d, α or 2p2n) 54Mn ( Q values respectively 5.7 and −22.6 MeV), 48Ti(d, α or 2p2n) 46Sc ( Q values 4 and −24.3 MeV) and 48Ti(d, 2pn) 47Sc ( Q=−13.7 MeV) on the major natural isotopes of Fe and Ti the cross sections reach values higher than 50 mb in the energy region studied.

12C induced transfer reactions on 56Fe

Transfer reactions 56Fe(12C, xN) have been investigated. Angular distributions of particles following elastic scattering, one neutron and one proton transfer reaction channels leading to low lying states in respective residual nuclei have been measured. These are analysed using the coupled reaction channel (CRC) formalism. Starting with a double folded real potential, the elastic scattering angular distribution is calculated using the computer code FRESCO. Inclusion of couplings to first excited states in both the target and the projectile already tends to describe the experimental elastic scattering distribution. Additional coupling of one neutron transfer reaction to first five excited states in 55Fe and one proton transfer reaction to first three low lying states in 57Co improves fit to the elastic scattering angular distribution. Further refinement in fit is brought about by addition of a weak imaginary potential to the complex potential calculated by ERESCO to simulate the absorption effects due to those channels whose coupling is not included explicitly. Such a potential describes the experimental angular distributions for elastic, one neutron and one proton transfer channels correctly in shape and magnitude without any arbitrary normalisation.

Computation of the fluence of fast neutrons in the reactor pressure vessel of Unit I of Kozloduy NPP

The procedure of computation of the fluence of fast neutrons in the pressure vessel of the WWER-440 reactor of Unit I of the Kozloduy NPP, Bulgaria, by the method of the discrete ordinates using the neutron transport code TORT and the cross-section library SAILOR is outlined. The principal results for cycles 16, 17 and 18 are reported, together with a comparison between measured weight specific activities of 54Mn (a product of the reaction 54Fe(n,p) 54Mn) in shavings taken from different locations on the inner surface of weld no.4 of the pressure vessel of unit I after the end of cycles 17 and 18 and the corresponding predicted values on the basis of the computed fluence of fast neutrons at these locations.

Prolate-oblate shape coexistence in 75Kr

The collective bands of 75Kr were extended up to spin 45 2 using the compound reactions 50Cr( 28Si,2pn), 54Fe( 24Mg,2pn) and 58Ni( 20Ne,2pn) 75Kr. Lifetimes were measured by RDDS with nine OSIRIS detectors in coincidence. Mixing ratios were determined by measurements of internal conversion coefficients, angular distribution and correlations. Deviations between different measurements are explained by the short lifetimes leading to angle dependent intensity losses due to Doppler shift. Spins and parities were assigned from angular distributions, excitation functions and DCO ratios measured with the OSIRIS_12 spectrometer. The band head spin of the negative parity yrast band was established as 3 2 via DCO ratios and internal conversion coefficients. Further bands at low excitation energy were found. In accordance to Woods-Saxon cranking model calculations, these weaker populated sidebands are interpreted to be built on oblate deformed intrinsic states ( β 2 ≈ −0.2), while the strongly populated bands are built on prolate deformed states ( β 2 ≈ +0.4). The interpretation of the 1qp g 9 2 yrare band, to be generated from oblate deformation, is further supported by ΔI = 0 transitions into the yrast band and a similar oblate deformed g 9 2 structure in the isotone 73Se. The experimental level energies, branching ratios, transition probabilities and mixing ratios are compared to rotor model calculations. The deviations between experiment and rotor model calculations are interpreted to be based on mixing between prolate and oblate states.

Measurement of cross-sections for the 9Be(n,3n) 7Be and 56Fe(n,p) 56Mn reactions producing background lines in γ-ray astrophysics

The reactions 9Be(n,3n) 7Be and 56Fe(n,p) 56Mn were measured between 28 and 68 MeV and at 28 MeV, respectively. These reactions lead to the emission of γ-rays (478, 847, 1811 keV) that may be disturbing in γ-ray astrophysics missions. Consequences regarding the induced background in detectors are drawn.

The unfolding procedure of the alpha particle spectra of the 58Ni(n, α) 55Fe reaction

The correction of the alpha particle energy spectra which is required because of the alpha particle energy loss, due to the thickness of the sample, is described by an analytical-empirical retrospective relation. This relation can yield a spectrum as it was produced in the sample from a corresponding measured spectrum. The alpha decays of the reaction 58Ni(n, α) 55Fe were used as the source of the alpha particle spectra. The projectile neutrons were produced via the T(p,n) and D(d,n) reactions in the energy range from 2 to 9 MeV. The validity of our assumption for the correctness of the alpha particle spectra was checked by comparing the measured spectrum with the spectrum produced by folding the corrected spectrum with the response function of the system. The calculated folded spectrum appeared to be consistent with the experimental data of the measured spectrum. Typical results are given at the neutron energy of 8 MeV, where the measured data were accumulated from a telescope placed at 79° relative to the neutron beam direction.

Hydrogen generation arising from the 59Ni(n, p) reaction and its impact on fission—fusion correlations

While the influence of transmutant helium on radiation-induced microstructural evolution has often been studied, there is a tendency to overlook the influence of concurrently-generated hydrogen. Recent studies suggest that the influence of hydrogen may be enhanced in the presence of large amounts of helium, especially at lower irradiation temperatures typical of projected ITER operation. This interaction may have an impact on potentially hydrogen-sensitive processes such as irradiation-assisted stress corrosion cracking (IASCC) of stainless steel. In nickel-bearing alloys, one of the major sources of helium in neutron spectra with a significant thermal neutron component is the two-step 58Ni(n, γ) 59Ni(n, α) 56Fe reaction. It has generally been overlooked, however, that the competing (n, p) reaction on 59Ni can dominate the hydrogen production process since about one hydrogen atom is generated for every six helium atoms. Inclusion of the damage energy deposited by the (n, p) reaction in the alloy matrix also requires a slight modification in the 59Ni(n, α) damage enhancement formula published earlier. The impact of the (n, p) reaction on both hydrogen generation and displacement rates is evaluated in this paper for a variety of neutron spectra often employed in fission—fusion correlations.

Study of the flaking‐off phenomenon on a jet Engine's shaft bearing using the thin layer activation technique

AbstractThe Thin Layer Activation technique has been applied in order to study the flake‐off phenomenon on a jet engine's shaft bearing. The external track of the bearing has been activated following the reaction 56Fe(p,n)56Co, over a depth of 80 μm. In spite of a very low activation level, the first signs of flaking‐off were detected 30 min before any significant increase in the vibration level appeared. At that point, the mass of particles leaving the track was measured on line, with a precision of 0.2 mg.

The Evaluation and Calculation of Intermediate Energy Nuclear Data for 56Fe(p,n), 63Cu(p,n), and 65Cu(p,n) Monitor Reactions

Proton monitor reactions have been widely used in accelerator target flux and beam energy monitoring, medical radioisotope production, research on radiation damage, and activation analysis. The excitation functions of 56Fe, 63Cu, and 65Cu(p,n) reactions were calculated and evaluated at incident energies up to 1,200 MeV, 11,500 MeV, and 1,820 MeV, respectively.