Gamma rays from thermal-neutron capture in natural and K enriched potassium

Gamma rays following thermal-neutron capture in natural and in ³⁹K enriched potassium have been investigated with a Ge(Li) and a Ge(Li)-NaI spectrometer. In the ³⁹K(n,γ)⁴⁰K reaction 222 γ-rays were found, of which 187 could be fitted into the level scheme of ⁴⁰K. Fifteen γ-rays could be ascribed to the ⁴¹K(n, γ)⁴²K reaction. Excitation energies of 54 levels in ⁴⁰K and of 9 levels in ⁴²K have been determined with 0.2−1.0 keV errors. The Q-values of the ³⁹K(n, γ)⁴⁰K and ⁴¹K(n, γ)⁴²K reactions are Q = 7799.7 ±0.8 keV and 7533.9±1.2 keV, respectively.     

Transitions in41K studied with the (n,n′γ) reaction

Singles gamma ray spectra of the⁴¹K(n, n′γ)⁴¹K reaction have been measured with fast reactor neutrons. The populated states and γ-ray intensities are compared with those of the⁴⁰K(n, γ)⁴¹K reaction. About 91% of the observed gamma ray intensity was assigned to the decay of 35 states in⁴¹K. The energy and spin dependence of the gamma ray fluxes in both reactions are discussed.     

Thermonuclear reaction rates for proton induced reactions on 41K and neutron induced reactions on 41Ca

The yield of γ-rays from the reaction ⁴¹K(p, γ)⁴²Ca has been measured as a function of bombarding energy over the range 0.68–2.48 MeV and from the reaction ⁴¹K(p, αγ)³⁸Ar over the range 1.20–2.48 MeV, and the yield of neutrons from the reaction ⁴¹K(p, n)⁴¹Ca has been measured from threshold to a bombarding energy of 2.48 MeV. The energy dependence of the cross sections is compared with statistical-model calculations with global optical-model parameters in all particle channels. The calculations seriously overestimate the cross section for the neutron channel and underestimate those for the other channels. A reduction in the imaginary well depth in the neutron channel leads to good agreement with all the data. Statistical-model calculations with this modified set of parameters are then carried out to provide cross sections for the astrophysically interesting reactions ⁴¹Ca(n, p)⁴¹K, ⁴¹Ca(n, α)³⁸Ar, and ⁴¹Ca(n, γ)⁴²Ca. Thermonuclear reaction rates are calculated for all six reactions over the temperature range 5 × 10⁸–10¹⁰K which includes the range of temperatures of interest in nucleosynthesis calculations.     

Mesures des vies moyennes des niveaux de 1K alimentes par les réactions 39K(t,p) et 27Al(16O, 2p)

Twenty-four levels in ⁴¹K at excitation energies below 5 MeV have been identified in the reactions ³⁹K(t, p)⁴¹K and ²⁷Al(¹⁶O, 2p)⁴¹K, at incident beam energies of 3.0 and 34 MeV respectively. Using the recoil-distance technique and the Doppler-shift attenuation method, mean lifetimes (in ps) were obtained for the following levels: 980 keV, 0.42^0.30_0.15; 1294 keV, > 5; 1560 keV, 0.58 ± 0.22; 1582 keV,> 1.5; 1677 keV, 6⁺³_?1; 1698 keV, 1.3 ± 0.4; 2528 keV, 230 ± 15; 2762 keV, < 2; 2775 keV, 68 ± 4; 4274 keV, < 2; 4983 keV, 95 ± 15. The positive parity states are suggested to have predominantly 2p-1h configurations. As a by-product, mean lifetimes for five levels in ⁴¹Ca, populated via the ²⁷Al(¹⁶O, pn)⁴¹Ca reaction, were also obtained.     

Potassium and potassium oxide monolayers on the platinum (111) and stepped (755) crystal surfaces: A LEED,AES, and TDS study

The adsorption of potassium and the coadsorption of potassium and oxygen on the Pt(111) and stepped Pt(755) crystal surfaces were studied by AES, LEED, and TDS. Pure potassium adlayers were found by LEED to be hexagonally ordered on Pt(111) at coverages of θ = _K0.9–;1. The monolayer coverage was 5.4 × 10¹⁴K atoms/cm² (0.36 times the atomic density of the Pt(111) surface). Orientational reordering of the adlayers, similar to the behavior of noble gas phase transitions on metals, was observed. The heat of desorption of K decreased, due to depolarization effects, from 60 kcal/mole at θ_K <0.1, to 25 kcal/mole at θ_K = 1 on both Pt(111) and Pt(755). Exposure to oxygen thermally stabilizes a potassium monolayer, increasing the heat of desorption from 25 to 50 kcal/mole. Both potassium and oxygen were found to desorb simultaneously indicating strong interactions in the adsorbed overlayer. LEED results on Pt(111) further indicate that a planar K₂O layer may be formed by annealing coadsorbed potassium and oxygen to 750 K.     

Revealing the Spin-Hamiltonian and Characteristic Parameters of Paramagnetic Centers in Cu2+-Doped Potassium Metabisulfite (K2S2O5) Single Crystal by Electron Paramagnetic Resonance Technique

The present study is mainly related to finding out spin-Hamiltonian parameters of Cu²⁺-doped potassium metabisulfite [K₂S₂O₅] single crystals using electron paramagnetic resonance (EPR) technique which has been applied in the temperature range from 297 to 113 K for single and powder crystals of the title compound. The existence of two complexes and two Cu²⁺ sites for each complex was concluded from the angular variation of the EPR spectra. Having constructed the g and the hyperfine tensors, the spin-Hamiltonian parameters have been obtained for these two complexes. Using these parameters, the covalency parameter (α ²), mixing coefficients (α and β) and Fermi contact term (K) have been calculated.     

Analog resonances with J π = 3/2− in the 40Ar(pγ)41 K reaction

γ decay of isobaric analog 2p _3/2 resonances in the ⁴¹K nucleus, observed in the ⁴⁰Ar(pγ)⁴¹K reaction at E _p = 1102, 1839, 1842, 1859, 1875, and 1896 keV, has been experimentally investigated. The decay schemes of these resonances are constructed, the angular distributions of γ rays are measured, and the partial γ widths are determined for the first time. The intensities of single-particle M1 transitions are compared with the results of the calculations within the shell model with surface δ interaction.     

Magnetic hyperfine fields at Gd and in sites in GdPdIn compound

Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the hyperfine interactions in the intermetallic compound GdPdIn using ¹¹¹In→ ¹¹¹Cd and ¹⁴⁰La→ ¹⁴⁰Ce probe nuclei at the In and Gd sites, respectively. The PAC results for ¹¹¹Cd show two well-defined electric quadrupole frequencies above T _C assigned to probes occupying Gd and In sites, with ~50% of site occupation each. The fraction corresponding to In sites increases with temperature reaching 95% around 500 K. Below T _C the measurements for ¹¹¹Cd probe showed combined electric quadrupole plus magnetic dipole interaction with sharp increase in the magnetic field below around 80 K. A pure magnetic interaction with lower hyperfine field values was observed at the Gd sites occupied by ¹⁴⁰Ce below 100 K.     

Observation of weakly coupled 2p-1h states in 41Ca from proton transfer on 40K

The proton transfer on ⁴⁰K has been studied with the ⁴⁰K(³He, d)⁴¹Ca reaction at 13 and 21 MeV bombarding energy and with the ⁴⁰K(d, n)⁴¹Ca reaction at 6.5 MeV bombarding energy. The energy and angular distribution of outgoing particles have been measured. For transitions to 62 levels in ⁴¹Ca the l-values and spectroscopic factors have been derived with DWBA. The excitation energies of levels populated with l = 3 and the qualitative distribution of transfer strength strongly suggest their interpretation as 2p-1h states of the f_{$\text{7}\text{2}$}²d_{$\text{3}\text{2}$}^?1 configuration with weak coupling between the particle pair and the hole. The high-spin states of this configuration (with J^π up to $\text{15}\text{2}{}^{\mathrm{+}}$) are preferentially excited.     

Microscopic magnetic properties of nonstoichiometric V2O3+x—NMR and inelastic spin-flip neutron scattering measurements

The local magnetic properties of the V sites in the nonstoichiometric V₂O_3+x (0 ? x <0.08) have been examined by nuclear magnetic resonance and inelastic spin-flip neutron scattering techniques. The samples with x = 0.01 and 0.02 show a paramagnetic metal (PM)-antiferromagnetic insulator (AFI) transition. In the AFI phase, two distinct ⁵¹V NMR signals with hyperfine fields H_n = 184.9±0.5 kOe and 71±1 kOe were observed at 1.8 K, which were assigned as due to V³⁺ and V³⁺ sites, respectively. On the other hand, the samples with x = 0.04 and 0.06 were metallic down to 1.4K, and showed a paramagnetic (PM)-antiferromagnetic (AFM) transition at about 10 K. In these samples, a ⁵¹V NMR signal with H_n = 58±2 k0e and one with 〈H_n〉 = 9kOe were observed at 1.8 K, which were assigned as due to V³⁺-like sites and the matrix V sites, respectively. These results are entirely consistent with those obtained from the neutron experiment. We propose that in the metallic phase (0.04 ? x < 0.08) the minority V⁴⁺-like sites are magnetically localized in the delocalized V matrix and may be responsible for the antiferromagnetic long range order below 10 K.     

Photoelectron spectroscopy for probing surface reactions at the CO/K/Cu(1 1 5) interface

The adsorption of carbon monoxide on the potassium modified Cu(1 1 5) surface was investigated using photoelectron spectroscopy based on synchrotron radiation. From detailed analysis of the 1s core levels in combination with existing knowledge, the assignment of surface species is performed. It is demonstrated that in dependence of the alkali coverage, several adsorption states of CO are present on the interface at 135 K. From the temperature dependence of the C 1s and O 1s profiles it is established that surface reactions based on CO dissociation start from 223 K over an interface with a potassium coverage close to half a complete K overlayer. The role of potassium as a reordering environment of adsorbed CO, leading to molecule dissociation and disproportionation is proposed. It is observed that a higher density of potassium on the substrate surface blocks adsorption sites for incoming CO molecules and no dissociation takes place.     

Coverage dependence of fe flicker noise: Spectral density functions due to potassium on W(112) and W(111)

Field emission flicker noise spectral density functions W(?) have been determined for potassium on W(112) and W(111) single planes. The coverage dependence of the spectral densities W(?_j) shows pronounced maxima and minima, whereas the slopes ? obtained from double logarithmic plots of W(?) ~ ?^?? vary considerably. Minima and maxima of W(?_j) are assumed to be due to coherent and disordered adlayers, respectively, and the behaviour of the exponents ? supports further the proposed observation of order-disorder transitions of the potassium adsorbate. LEED results for W(112)K and W(111)K are in fair agreement with the corresponding coverages from noise measurements.     

The reactions 2H(40Ar,n)41K and 2H(40Ar,p)40Ar and electromagnetic decays of low-lying states in 41K and 41Ar

The γ-decay of states in ⁴¹K and ⁴¹Ar populated in the reactions ²H(⁴⁰Ar, n)⁴¹K and ²H(⁴⁰Ar, p)⁴¹Ar has been investigated at a bombarding energy of 56 MeV. Using the Doppler shift attenuation method and three different stopping materials, mean lifetimes were determined for the states in ⁴¹K at 980 keV (0.5±0.2 ps), 1560 keV (0.6_?0.2^+0.3ps), 1698 keV (0.1_?0.1^+0.2ps), 2144 keV (0.8_?0.2^+0.3ps) and in ⁴¹Ar at 1354 keV (0.664_?0.08^+0.09ps). Shell-model calculations have been performed for the positive parity states in ⁴¹K using a model space of a proton hole in the $\text{1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ orbits and two neutrons in the $\text{1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ orbit. The resulting excitation energies and electromagnetic properties of the low-lying states are in good agreement with experiment. An empirical value for a [Y₂s]₁ contribution in the effective M1 operator is obtained.     

129I-Mössbauer study of molecular dynamics in the organic superconductor β-(BEDT-TTF)2I3

¹²⁹ I-Mössbauer spectroscopy was applied to study the organic superconductor β _H -(BEDT-TTF)₂ I ₃ withT _c=8 K. The measurements were performed in the temperature range 1.4 K to 160 K. A detailed analysis of the well-resolved spectra, including transmission integral fits, revelas information about the hyperfine interactions and the local binding strength (f-factor) for the terminal and central sites of the linear and symmetricI ₃ ^? anion. A change in the local Debye temperature of both sites of theI ₃ ^? anions is observed around 120 K, where a phase transition was monitored by other methods. Most interesting with respect to the superconducting properties is a change of the relative intensities of the terminal and central iodine sites, which starts below 10 K and increases down to 1.4 K. This behaviour may be attributed to a libral motion of the iodine molecules and seems to be connected with the occurence of superconductivity in this system.     

Experimental and theoretical investigation of the isotope shift of the 4D level in atomic potassium

Doppler-free two-photon laser spectroscopic measurements in the deep red spectral region have been performed on the transition 4² S _1/2→4² D _J in the naturally abundant isotopes 39 and 41 of atomic potassium. The 4D level isotope shift, ?81±12 MHz was obtained by combining the current results with data from Rydberg-state spectroscopy. Many-body perturbation theoretical calculations of the specific mass shift in the measured state are also presented. With the use of Brueckner orbitals the value ?70 MHz was obtained in substantial agreement with the experimental result.     

Radiation widths of resonances in the <Superscript>40</Superscript>Ar(pγ)<Superscript>41</Superscript>K reaction

The excitation function for the ⁴⁰Ar(pγ)⁴¹K reaction at the accelerated proton energy E _p= 450–2700 keV is studied. Positions of 168 resonances identified as levels of the ⁴¹K nucleus are observed in this energy range. The data for the proton energy E _p < 1 MeV and E _p > 2 MeV are obtained for the first time. Relative yields of γ rays observed in the decay of the resonances are calculated from a comparison with the yield of the calibrating resonance at E _p= 1102 keV. Total radiation widths of the resonances are calculated on the basis of the data obtained.     

Investigation of the GdMn2O5 multiferroic by the μSR method

The GdMn₂O₅ multiferroic (a ceramic sample and a sample consisting of a large array of randomly oriented single crystals with linear dimensions 2–3 mm) has been studied by the μSR method within the temperature range 10–300 K. Three anomalies in the temperature behavior of the parameters of the muon polarization relaxation function, namely, close to the phase transition driven by the onset of long-range magnetic order in the manganese ion subsystem (T _N1 = 40–41 K), near the lock-in transition initiated by an abrupt change of the wave vector of magnetic order (T _L = 35 K), and close to the Gd³⁺ ion ordering temperature (T _N2 = 15 K), have been found. An analysis of the time spectra of muon spin precession in the internal magnetic field of the samples has revealed two positions of preferable muon localization sites in samples, which differ in precession frequencies and the character of their behavior with temperature. The lower-frequency precession driven by Mn⁴⁺ ions, ferromagnetic Mn4⁺-Mn⁴⁺ + muonium complexes, and Gd³⁺ions is observed throughout the temperature region T < T _N1 and is practically independent of temperature. At temperatures T < T _L = 35 K, a higher-frequency precession associated with Mn³⁺ ions appears also. It is characterized by a temperature dependence ～(T/T _N1)^β with the index β = 0.39, which is typical of Heisenberg-type 3D magnets. For T < T _N1, a deficiency of the rest total asymmetry is observed. This phenomenon can probably be assigned to formation of muonium, which suggests that charge transfer processes play an important role in formation of long-range magnetic order.     

Magnetic hyperfine fields of (Nd2Fe1-xCox)14B AT x = 0.25 between 100 and 780 K

The ⁵⁷Fe Mössbauer spectra are recorded in Nd₂(Fe_1-xCo_x)₁₄B at x = 0.25 in the temperature range 100 to 780 K. T_c the Curie temperature, B̄_hf, the magnetic hyperfine field average over various Fe nuclei of the unit cell and its temperature coefficient α(B̄_hf) in the vicinity of 300 K are found to be 760(5) K, 34.0(3) T and -0.08(1)% K^-1, respectively. The magnetic moment at Fe atoms is estimated to increase up to 12% as a result of the partial substitution by Co atoms. The dependence of the fields upon temperature is observed to be least at the j₂ and k₂ sites as compared to the other sites of Fe. The results for the variation of B_hf at all of the six sites of Fe with respect to temperature are given. A site preference of Fe atoms for the j₂ sites is observed.     

Precision two-photon spectroscopy of alkali elements

In this paper, we have briefly reviewed the work on two-photon spectroscopy of alkali elements and its applications. The technique of Doppler-free two-photon spectroscopy is briefly summarized. A review of various techniques adopted for measuring absolute frequencies of the atomic transitions and precision measurements of isotope shifts and hyperfine structures (HFS) is presented. Some of the recent works on precision measurements of HFS constants of 6s ² S _1/2 level of ³⁹K and ⁴¹K, 9s ² S _1/2level and 7d ² D _3/2 level of ¹³³Cs are also discussed.     

Cross sections for proton induced reactions on 41K and for the reaction 62Ni(α, p)65Cu

Excitation functions have been measured for ⁶²Ni(α, p)⁶⁵Cu in the energy range 6.5–9.0 MeV, for ⁴¹K(p, α)³⁸Ar in the range 0.8–2.6 MeV, for ⁴¹K(p, γ)⁴²Ca, ⁴¹K(p, αγ)³⁸Ar, ⁴¹K(p, nγ)⁴¹Ca, and ⁴¹K(p, p'γ)⁴¹ in the range 0.6–4.0 MeV, and for ⁴¹K(p, n)⁴¹Ca from threshold to 3.0 MeV. Cross sections have been extracted from the data and these are compared with statistical-model calculations based on global optical model parameters. Alternative parameter sets have been tried for the ⁶²Ni(α, p)⁶⁵Cu data and published data for ⁶²Ni(α, γ)⁶⁶Zn and ⁶²Ni(α, n)⁶⁵Zn, and both these and the global parameters have been used in statistical-model calculations of ⁶⁵Cu(p, γ)⁶⁶Zn, ⁶⁵Cu(p, n)⁶⁵Zn and ⁶⁵Cu(p, α)⁶²Ni cross sections, which are compared with published data for these reactions. Both the global and the alternative parameters lead to very good agreement with experiment for all six reactions. Alternative parameters have been tried for the ⁴¹K + p reactions also. The global parameters lead to agreement to within a factor of 2 and the alternative parameters lead to agreement to within a factor of 1.3. The ⁴¹K + p alternative parameters are used in calculations of ⁴¹Ca(n, γ)⁴²Ca, ⁴¹Ca(n, p)⁴¹K and ⁴¹Ca(n, α)³⁸Ar cross sections, and these and the experimental ⁴¹K + p data are used in calculations of thermonuclear reaction rates under stellar conditions for the ⁴¹Ca + n and ⁴¹K + p reactions.