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. The text was submitted by the authors in English.     

Gamma-ray transitions in56Ni induced by the54Fe(3He,n)56Ni reaction

Ten gamma-ray transitions have been observed in the⁵⁴Fe(³He,n γ)⁵⁶Ni reaction. A new level at 3925±10 keV is established in⁵⁶Ni. Spin-parity assignments of 0⁺, 4⁺ and 2⁺ are proposed for the levels at 3.925, 3.958 and 5.352 MeV, respectively. Branching ratios are given.     

Investigation of excited states in56Co with the54Fe(3He,pγ)56Co reaction

The two-particle stripping reaction⁵⁴Fe(³He,p γ)⁵⁶Co at \(E_{3_{He} } \) =15.15 MeV was used to investigate theγ-ray transitions and to determine branching ratios, possible spin assignments and mean lifetimes of levels in⁵⁶Co up to 5.5 MeV excitation energy. Gamma-rays for both angular correlations and lifetime measurements were observed with a 43 cm³ Ge(Li) detector in coincidence with proton-groups detected at 0°. The level scheme and lifetime values are compared with the predictions of various shell model calculations.     

Study of the ground state doublet in57Fe

The⁵⁶Fe(d,p)⁵⁷Fe reaction has been studied at an incident energy of about 10 MeV. The ground state doublet of⁵⁷Fe has been resolved using the Heidelberg Q 3 D magnetic spectrograph and the Minnesota split-pole spectrograph. The ratio of the spectroscopic strengths (2J+1)S for the transitions to the first excited state at 14.4 keV excitation energy (J ^π=3/2^?) and the ground state (J ^π=1/2^?) has been determined to be 5.80±0.5. This number is of special interest with respect to a possible deformation of the nucleus⁵⁷Fe and in connection with the corresponding analogue resonances in⁵⁷Co.     

Optically stimulated luminescence and thermoluminescence efficiencies for high-energy heavy charged particle irradiation in Al2O3:C

The thermally and optically stimulated luminescence (TL and OSL) response to high energy heavy-charged particles (HCPs) was investigated for two types of Al2O3:C luminescence dosimeters. The OSL signal was measured in both continuous-wave (CW) and pulsed mode. The efficiencies of the HCPs at producing TL or OSL, relative to gamma radiation, were obtained using four different HCPs beams (150 MeV/u 4He, 400 MeV/u 12C, 490 MeV/u 28Si, and 500 MeV/u 56Fe). The efficiencies were determined as a function of the HCP linear energy transfer (LET). It was observed that the efficiency depends on the type of detector, measurement technique, and the choice of signal. Additionally, it is shown that the shape of the CW-OSL decay curve from Al2O3:C depends on the type of radiation, and, in principle, this can be used to extract information concerning the LET of an unknown radiation field. The response of the dosimeters to low-LET radiation was also investigated for doses in the range from about 1-1000 Gy. These data were used to explain the different efficiency values obtained for the different materials and techniques, as well as the LET dependence of the CW-OSL decay curve shape.     

Study of Stretched States Populated by 56,57Fe,59Co(α,d)58,59Co,61Ni Reactions

Spectra and angular distributions of the(α,d)reactions on ⁵⁶Fe ⁵⁷Fe and 59Co have been measured with the △E-E telescopic systems and Q3D magnetic spectrometer at a bombarding energy of 35MeV from the HI-13 Tandem,and analyzed with microscopic DWBA.Among the angular distributions of nine levels strongly populated by ⁵⁶Fe(α,d)⁵⁸Co reaction, the experimental data of 6.79MeV and 6.4MeV levels in ⁵⁸Co were analyzed and discussed. The highest stretched configuration (1g_9/2,1g_9/2)₉ was found and J^π=1⁺ of 6.4MeV level was determined for the first time. No isolated stretched states were observed by ⁵⁷Fe ⁵⁹Co(α,d)reactions.This probably means that the strength of the stretched configuration spreads on a number of states.     

Lifetime measurements in 56Co

Lifetimes of six excited states in ⁵⁶Co below 1.75 MeV have been measured by the Doppler-shift attenuation method. The levels were excited via the ⁵⁴Fe(³He, pγ) reaction with 10.4 MeV ³He particles. Gamma rays were measured in a 45 cm³ Ge(Li) detector in coincidence with protons backscattered near 180°. Reduced transition probabilities extracted from measured lifetimes compare favourably with shell model predictions of McGrory.     

The (He,p) and (d, α) reactions to states in Co

The ⁵⁶Fe(³He, p)⁵⁸Co and ⁶⁰Ni(d, α)⁵⁸Co reactions have been investigated at 12.0 and 7.0 MeV bombarding energies, respectively, using the MIT multiple-gap spectrograph. For the (³He, p) reaction, levels below 6.0 MeV of excitation were observed and analysed using the DWBA to obtain L-values. In the (d, α) reaction, levels up to 3.4 MeV of excitation were observed. A level scheme for ⁵⁸Co is proposed. The ⁵⁸Fe(0.0) analogue was observed, and candidates for the antianalogue level are identified.     

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,)⁵⁶Fe reaction was studied in the proton beam energy region E _p = (1.3-1.8) MeV. Properties of bound states in the final ⁵⁶Fe nucleus have been deduced from accurately measured very complex -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.     

Local states of iron in iron implanted hematite Fe2O3

Powder samples of⁵⁷Fe₂O₃ and⁵⁶Fe₂O₃ were implanted with⁵⁶Fe and⁵⁷Fe ions, respectively. By the use of Conversion Electron Mössbauer Spectroscopy it was possible to observe the local states of implanted ions (⁵⁷Fe in⁵⁶Fe₂O₃) or the states of iron atoms from the target which were displaced during implantation due to the ballistic processes (⁵⁶Fe in⁵⁷Fe₂O₃). The implanted and displaced iron atoms appear in three different states: (i) in regular substitutional positions of Fe₂O₃, (ii) as magnetite Fe₃O₄-type structures and (iii) paramagnetic FeO_1?x state. The observed fractions of each state agree rather well with the calculated values obtained from the local iron atom enrichment at the surface as well as from the analysis of the equilibrium phase diagram for the binary Fe?O system. However, in⁵⁷Fe implanted samples some enhancement of the FeO_1?x fraction was found in comparison with the⁵⁶Fe implanted hematite.     

Single-crystal (57)Fe Q-band ENDOR study of the 4 iron-4 sulfur cluster in its reduced [4Fe-4S](1+) state.

(57)Fe Q-band ENDOR has been used to study the [4Fe-4S](1+) state created by gamma irradiation of single crystals of the synthetic model compound [N(C(2)H(5))(4)](2)[Fe(4)S(4)(SCH(2)C(6)H(5))(4)] enriched in (57)Fe. This compound is an excellent biomimetic model of the active sites of many 4 iron-4 sulfur proteins, enabling detailed and systematic studies of its oxidized [4Fe-4S](3+) and reduced [4Fe-4S](1+) paramagnetic states. Taking advantage of the fact that Q-band ENDOR, in contrast with X-Band ENDOR, allows for a very good separation of the (57)Fe transitions from those of the protons, the complete hyperfine tensors of the four iron atoms for the [4Fe-4S](1+) species has been measured with precision. For each iron atom, the electron orbital and electron spin isotropic contributions have been determined separately. Moreover, it is remarkable that two (57)Fe hyperfine tensors attributed to the ferrous pair of iron atoms are very different. In effect, one tensor presents a much larger anisotropic part and a much smaller isotropic part than those of the other. This difference has been interpreted in terms of a differential electron orbital hyperfine interaction among the two ferrous ions.     

Giant isotope effect in the incoherent tunneling specific heat of the molecular nanomagnet Fe8

Time-dependent specific heat experiments on the molecular nanomagnet Fe8 and the isotopic enriched analogue 57Fe8 are presented. The inclusion of the 57Fe nuclear spins leads to a huge enhancement of the specific heat below 1 K, ascribed to a strong increase in the spin-lattice relaxation rate gamma arising from incoherent, nuclear-spin-mediated magnetic quantum tunneling (MQT) in the ground doublet. Since gamma is found comparable to the expected tunneling rate, the MQT process has to be inelastic. A model for the coupling of the tunneling spins to the lattice is presented. Under transverse field, a crossover from nuclear-spin-mediated to phonon-induced tunneling is observed.     

Study of the57Fe low-energy states

The low energy states of⁵⁷Fe has been studied by means of thermal neutron radiative capture. The gamma-ray spectrum below 3 MeV was measured using a Ge(Li) detector of an intrinsic volume 5.4 cm³. On making use of other experiments beside the good resolution of the Ge(Li) detector it was possible to suggest a decay scheme and to get some valuable informations. The transitions from the levels 366.7keV to the ground- and first-excited states seem to be pureM1 transitions. An evidence for the existence of a transition from the level 1725.5 keV to the 1018.6 keV with an absolute intensity 2.4% is shown.     

Design and gamma sensitivity measurement of a novel dual-emitter vacuum Compton detector

A novel dual-emitter vacuum Compton detector (D-VCD) with higher gamma ray detecting efficiency is proposed. The emitters are made of Ta--Al clad metal. The gamma ray sensitivity is studied by Monte Carlo simulation using the MCNP code. A comparison between calculations and results measured by using the 1.25~MeV gamma ray of Co-60 is also performed. Experimental sensitivities for two sample D-VCDs with the same materials and structures are 1.92×10^ - 20 and 2.02×10^ - 20~C.cm²/MeV separately, which are consistent with the simulation result of 1.98×10^ - 20~C.cm²/MeV and are 4 times higher than that of VCD with a single Fe emitter. According to the simulation results, in a gamma energy range from 0.5 to 3~MeV, the maximum sensitivity variance for the D-VCD is less than 15%, and less than 5% in a range from 1 to 2~MeV in particular. The novel D-VCD is applicable to the detection of intense pulse gamma rays.     

Proton-hole states in 57Co studied with the 58Ni(d, 3He) 57Co reaction at 78 MeV

The ⁵⁸Ni(d, ³He)⁵⁷Co reaction was measured at a bombarding energy of 78 MeV. Energy levels up to 7.0 MeV excitation energy in ⁵⁷Co were studied. Angular distributions of the ³He particles, corresponding to transitions to the ground state and to 42 excited states in ⁵⁷Co, were analyzed in the range of θ_lab = 2.7° to 25°. Exact finite-range DWBA calculations were employed to extract l-values and spectroscopic factors. Shell-model calculations were carried out in an fp-shell model space. In addition, calculations of the energy levels in ⁵⁷Co were performed in the SU(6) particle-vibration model (PTQM). Satisfactory agreement is observed between the experimental results and both theoretical predictions.     

Diagnostics of the region of nuclear interactions of neutrons in the solar flare of January 20, 2005 by gamma-ray lines

Based on an analysis of the time history of the count rate in the 2.223 MeV neutron-capture line from the extreme solar event of January 20, 2005, we investigate the density of the surrounding medium and the 3He content in the area of the 2.223 MeV gamma-line production. The analysis uses data on count rates in the 2.223 MeV gamma-ray line, as well as in lines ranging from 4 to 7 MeV, which were acquired with the AVS-F apparatus from the SONG-D detector onboard the CORONAS-F satellite. It is shown that simulation of the time history of the 2.223 MeV gamma-ray line from the flare event would require an assumption of the elevated abundance of 3He. It is found that in the area of the 2.223 MeV gamma-line production the ratio n(³He)/n(¹H) is (1.4 ± 0.15) × 10^?4, although, based on the data from different flares, on average it is approximately 2 × 10^?5. The elevated abundance of ³He may be considered as an additional indirect argument for the possible presence of reaction products of neutron radiative absorption by the 3He isotope within a small increase in gamma emission in the 15?C21 MeV range over the background level (which was detected previously from the CORONAS-F/AVS-F data).     

Untersuchung von57Co mit der Reaktion57Fe(p,n)57Co

A neutron time-of-flight investigation of the⁵⁷Fe(p, n)⁵⁷Co reaction performed at bombarding energies of 4.9, 5.6 and 6.2 MeV results in new energy levels of⁵⁷Co. In addition, gamma spectra andn-γ-coincidence spectra were taken to complete the decay scheme of⁵⁷Co up to an excitation energy of 4 MeV.     

Der Zerfall des In109m (0,21 sec)

In^109m(0,21±0,01 sec) was produced from natural Ag and enriched Ag¹⁰⁷ byα irradiation and investigated using scintillation spectrometers and coincidence techniques. The mass assignment follows from the excitation function for the (α, 2n) reaction on Ag¹⁰⁷. The following results were obtained: energy of the isomeric level (2,11±0,02) MeV, determined directly by summing up the cascade transitions in a well-type scintillator; four gamma transitions with energies (0,680±0,015) MeV, (0,405±0,015) MeV, (1,035±0,030) MeV and (1,435±0,020) MeV, respectively. The proposed decay scheme contains the isomeric level (19/2⁺) at 2,11 MeV and a further level (13/2⁺) at 1,435 MeV which decays either by the 1,435 MeV transition (80±3)% or by a 0,405–1,035 MeV cascade (20±3)% via an (11/2⁺) level at 1,035 MeV to the 9/2⁺-ground state of In¹⁰⁹.