Experimental Research to Confirm the Excitation of Gamov–Teller Resonance in Compound Nucleus <Superscript>118</Superscript>Sb

At proton energies of 4–9 MeV, trial experimental investigations were performed to confirm the excitation of Gamov–Teller resonance (GTR) 1⁺ in the compound nucleus ¹¹⁸Sb discovered by B.Ya. Guzhovskiy’s research group in the ¹¹⁷Sn(p,xn) reaction at proton energies of 7.2 MeV (the first component is GTR1) and 9.9MeV (the second component is GTR2). The ¹¹⁷Sn(p,xn) reaction was used, whose neutrons and background neutrons were registered by an all-wave long counter arranged at an angle of 140° to the direction of the proton beam propagation. Simultaneously, along with the registration of neutrons, elastically and inelastically scattered protons at angles of 20° and 160° were registered. At the proton energy equal to ~7.2 MeV, in the excitation functions for ¹¹⁷Sn(p,xn), ¹¹⁷Sn(p,p₀), and ¹¹⁷Sn(p,p₄)¹¹⁷Sn* (1004.5 keV, 3/2⁺), a resonance with a width of ≈1.2 MeV having an energy structure was discovered. Its possible quantum numbers are 1⁺.     

Synthesis of Ge-Sn at high pressure and high temperature in a laser-heated diamond anvil cell

Ge–Sn compound is predicted to be a direct band gap semiconductor with a tunable band gap. However, the bulk synthesis of this material by conventional methods at ambient pressure is unsuccessful due to the poor solubility of Sn in Ge. We report the successful synthesis of Ge–Sn in a laser-heated diamond anvil cell (LHDAC) at ~7.6 GPa &; ~2000 K. In situ Raman spectroscopy of the sample showed, apart from the characteristic Raman modes of Ge TO (Г) and β-Sn TO (Г), two additional Raman modes at ~225 cm^?1 (named Ge–Sn₁) and ~133 cm^?1 (named Ge–Sn₂). When the sample was quenched, the Ge–Sn₁ mode remained stable at ~215 cm^?1, whereas the Ge–Sn₂ mode had diminished in intensity. Comparing the Ge–Sn Raman mode at ~225 cm^?1 with the one observed in thin film studies, we interpret that the observed phonon mode may be formed due to Sn-rich Ge–Sn system. The additional Raman mode seen at ~133 cm^?1 suggested the formation of low symmetry phase under high P–T conditions. The results are compared with Ge–Si binary system.     

The structure of 113Sn from proton and alpha- particle induced reactions

The results of in-beam investigations of ¹¹³ Sn using the (p,n), (p,3n), (α,n) and (α,2n) reactions are summarized. Excited states have been identified until E _x = 4715 MeV and J ^π = (27/2^{t -}). For a large number of levels mean lifetimes τ have been determined with the DSA method. For the J ^k = 25/2⁺ state at E _x = 4059 MeV, τ = 1.0(4) ns has been measured with the γ-RF method. The experimental results are compared with the predictions of shell-model calculations. Most of the positive-parity states may be considered as one-or three-quasiparticle neutron excitations of the 2d_5/2, 1_g7/2, 3_s1/2 and 2d_3/2 shells, the negative-parity states as the coupling of one 1h_11/2 neutron to the two- or four-quasiparticle neutron excitations in the even-mass ¹¹²Sn core. For the 25/2⁺ isomer the three-quasiparticle neutron configuration ν(h ₁₁ ^2/2 g ₇ ^2/?1 ) has been proposed on the basis of a shell-model analysis using the mass-formula formalism. The experimentally observed yrast states in ₅₀ ¹¹³ Sn₆₃ are compared with the corresponding states in the valence mirror nucleus ₆₃ ¹⁴⁵ Eu82 giving remarkable similarities although the parameters for the shell-model calculations differ considerably. The analysis of nearest-neighbour spacing distributions of experimentally obtained 5/2⁺ states in ¹¹³Sn does not allow definite conclusions about regularity or chaos.     

Effect of oxygen deficiency on the radiation sensitivity of sol-gel Ge-doped amorphous SiO2

We report experimental investigation by electron paramagnetic resonance (EPR) measurements of room temperature γ-ray irradiation effects in sol-gel Ge doped amorphous SiO₂. We used materials with Ge content from 10 up to 10⁴ part per million (ppm) mol obtained with different preparations. These latter gave rise to samples characterized by different extents of oxygen deficiency, estimated from the absorption band at ~5.15 eV of the Ge oxygen deficient centers (GeODC(II)). The irradiation at doses up to ~400 kGy induces the E'-Ge, Ge(1) and Ge(2) paramagnetic centers around g ~ 2 with concentrations depending on Ge and on GeODC(II) content. We found correlation between Ge(2) and GeODC(II) contents, supporting the suggestion that the latter defect is the precursor of Ge(2). Even if the concentration of E'-Ge and Ge(1) defects cannot be strictly related to GeODC(II) one, the concentration growth of these paramagnetic defects with irradiation evidences that the radiation sensitivity is enhanced by the oxygen deficiency for Ge doping above 1000 ppm mol and it is reduced below 100 ppm mol. Moreover, the investigation of samples with different GeODC(II) concentration but fixed Ge content has shown that the oxygen deficiency enhances the overall radiation sensitivity for [GeODC(II)]/[Ge] in the range 10^-3 10^-2.     

Defect structures of ion-implanted α-tin

Single crystalline and polycrystalline -tin has been implanted at room temperature with 80-keV ions of radioactive^119m Sn,¹¹⁹Sb, and^119m Te. The radioactive nuclei decay to the Mössbauer level of¹¹⁹Sn. Mössbauer spectra of the emitted 24-keV radiation have been measured for different source temperatures by resonance counting techniques. Five individual lines in the spectra are characterized mainly by their isomer shifts and Debye temperatures. From these parameters the radiogenic¹¹⁹Sn atoms are concluded to be located in regular substitutional and interstitial lattice sites and in defect complexes. Simple models for the defects are proposed: A Sn-vacancy pair consists of Sn atoms on (nearly) substitutional sites with a dangling bond into an adjacent vacancy. In a complex oxygen-containing defect the Sn atoms have approximately a 5s ² configuration withp-bonds to two nearest neighbour atoms. Sn atoms, having an atomic 5s ² 5p ² configuration and large vibrational amplitudes, are concluded to be in non-bonding regular interstitial sites. For special implantation conditions minor fractions of SnO₂ molecules are formed in the bulk. The interstitial¹¹⁹Sn and the¹¹⁹Sn-vacancy pairs are proposed to represent elementary point defects in -tin. Conclusions are also drawn concerning the lattice location and the defects created in the implantation process of the implanted parent isotopes.     

An ENDOR study of radical spin adducts derived from novel 2-substituted-5,5-dimethyl-pyrroline-N-oxide spin traps

ENDOR spectra of a series of carbon- and oxygen-centered radical adducts of 2-substituted DMPO-type nitrones are reported. They include the novel cyclic nitrones, 2-phenyl-5,5-dimethyl-pyrroline-N-oxide (2-Ph-5,5-M₂PO), 2,5,5-trimethyl-l-pyrroline-N-oxide (2,5,5-M₃PO), and 2-phenyl-3,3,5,5,-tetramethyl-l-pyrroline-N-oxide (2-Ph-3,3,5,5-M₄PO). Electron paramagnetic resonance (EPR) was used to ascertain the nitrogen hyperfine splittings (hfs’s) while¹H ENDOR was employed to determine the long-range (γ) hydrogen hfs’s. The magnitude of the nitrogen hfs combined with the numbers and sizes of the long-range γ-H hfs’s of spin adducts of these new spin traps are shown to help disclose the identities of various added radicals (or radical addends). It should be noted that the three new spin traps presented here are keto-nitrones not aldo-nitrones. Thus, there is alkyl (e.g. CH₃) or aryl (e.g. C₆H₅) substitution at the 2-position of the pyrroline-N-oxide ring. This feature is part of our search for modified spin traps that yield spin adducts with greater stability.     

Paramagnetic resonance in irradiated Sr(NO3)2 single crystal

Paramagnetic resonance absorption of centres with spin 1/2 centered aboutg=2 is reported in gamma-irradiated single crystals of Sr(NO₃)₂. At room temperature four centres are detected which appear to exhibit axial symmetry about the [111] crystal direction. Two of the observed centres have a resolved hyperfine structure of N¹⁴. This hyperfine structure and axial symmetry of the centres indicate that they could be irradiation products of the nitrate ion. To find the number of trapped electrons, a simplified calculation of the molecular orbitals of planar and pyramidal NO₃ is carried out. Centres with a resolved hyperfine structure are then identified as pyramidal NO ₃ ^? and a NO₂ molecule rotating about the [111] direction. Two centres without hyperfine structure are not identified exactly.     

Temperature dependence of the quadrupole interaction of67Ge and67Zn ins-p metals

The temperature dependence of the electric quadrupole interaction was measured on the 9/2⁺ isomeric state of⁶⁷Ge in metallic Zn, Cd, In, and Sn and on the 9/2⁺ isomeric state of⁶⁷Zn in Cd metal. For all investigated systems, the temperature dependence reproduces very well aT ^1.5-relation. The analysis shows that the strength of the temperature dependence in the pure metals is correlated to 1/(M _D ² ) ( _D =Debye-temperature). This favours lattice vibrations as the main component of the temperature dependence of the electric field gradient. The strength of the temperature dependence measured on an impurity atom generally differs from the value of the pure host. Possible explanations for this effect are discussed.     

Spin-diffusion lengths in dilute Cu(Ge) and Ag(Sn) alloys

We used current-perpendicular-to-plane (CPP) exchange-biased spin valves to directly measure spin-diffusion lengths ?_sf^N for N=Cu(2.1 at% Ge) and Ag(3.6 at% Sn) alloys. We found ?_sf^{Cu(2% Ge)}=117₋₆⁺¹⁰ nm and ?_sf^{Ag(4% Sn)}=39±3 nm. The good agreement of this ?_sf^{Cu(2% Ge)} with the value ?_sf^{Cu(2% Ge)}=121±10 nm derived from an independent spin-orbit cross-sectional measurement for Ge in Cu quantitatively validates the use of Valet-Fert theory for CPP-MR data analysis to layer thicknesses several times larger than had been done before. From the value of ?_sf^{Ag(4% Sn)}, we predicted the ESR spin-orbit cross-section for Sn impurities in Ag.     

High spin states in131Ce

Gamma ray spectra from the¹¹⁷Sn(¹⁸O,4n)¹³¹ Ce reaction have been studied with the NORDBALL array of 15 Compton-suppressed Ge detectors. States up to I=51/2 , E8 MeV are populated. Observed bands are interpreted in terms of quasiparticle configurations.     

Phase diagram and LPE growth of strongly Sn- and Te-doped InGaAs

Sn and Te are used as n-type dopants in LPE In_0.53Ga_0.47 As contact layers, and carrier concentrations up to 2.2·10¹⁹ cm^–3 are obtained for both dopants. The distribution coefficients are k_Sn=(1.55±0.10)·10^–3 and k_Te0.11, respectively. With Sn a better control of the doping level is achieved than with Te, but the large amount of Sn necessary strongly affects the phase diagram. In order to facilitate the growth of InGaAs:Sn, the phase equilibria in the system In-Ga-As-Sn near 600° C are established. The liquid interaction parameters (Ga-Sn) and (As-Sn) are determined as 700 and -2050 cal/mole, respectively.     

Magnetic hyperfine fields in the Heusler alloys Co2 YZ (Y=Sc,Ti, Hf,V, Nb; Z=Al,Ga, Si,Ge, Sn)

The magnetic hyperfine field acting on Ta at the non-magnetic transition element site has been investigated in the Heusler alloys Co₂(Sc, Hf, V)Sn, Co₂ScGa, Co₂(V, Nb)Al and Co₂Ti(Si, Ge) by TDPAC measurements utilizing the 133–482 keV gamma-gamma cascade in¹⁸¹Ta following the ^– decay of¹⁸¹Hf. An important conclusion is that the reduced mhf either on the non-magnetic transition element site or on the s-p element site depends mainly on the chemical nature of the non-magnetic transition element rather than any other factor, e.g. the local moment _Co of the alloy.Supported by a fellowship from CNPq.Supported by a fellowship from FAPESP.     

Neutron interactions with germanium isotopes and amorphous and crystalline GeO2

Coherent neutron scattering lengths and total cross sections have been measured on elemental and oxide samples of ordinary Ge and of isotopically enriched substances. From the experimental results the following values were obtained:

the coherent scattering lengths (in fm) of the bound atoms Ge(8.185±0.020);⁷⁰Ge(10.0±0.1);⁷²Ge(8.51±0.10);⁷³Ge(5.02±0.04);⁷⁴Ge(7.58±0.10) and⁷⁶Ge(8.2 ±1.5);

the absorption cross sections at 0.0253 eV (in barn) for Ge(2.20±0.04);⁷⁰Ge(2.9±0.2);⁷²Ge(0.8±0.2);⁷³Ge(14.4±0.4) and⁷⁴Ge(0.4±0.2);

the free cross sections for epithermal neutrons and the zero energy scattering cross sections.

On the basis of this data, the isotopic- and spin-incoherent cross sections and thes-wave resonance contributions to the coherent scattering lengths have been determined and discussed. Transmission measurements at 0.57 meV on amorphous and crystalline GeO₂ yielded for the amorphous sample an inelastic cross section eight times larger than for the crystalline samples. This effect corresponds to a clearly higher density of low energy states in the amorphous than in the crystalline substances.     

Spin-wave resonance in Ge<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films exhibiting percolation ferromagnetism

Magnetic properties of Ge_{1 ? x} Mn _x (x = 0.02, 0.04, 0.08) thin films obtained by ion-implanting Mn⁺ ions into single-crystal Ge plates are investigated. The contributions of the subsystem of dispersed Mn²⁺ ions, Ge³Mn⁵ ferromagnetic clusters, and Mn-enriched ferromagnetic domains of Ge to the magnetic moment of Ge_{1 ? x} Mn _x films are distinguished. In the subsystem of dispersed Mn²⁺ ions in Ge_{1 ? x} Mn _x films at temperatures below 10 K, a spin-wave resonance is observed in the magnetically ordered state due to percolation ferromagnetism. It is established that, in the films with percolation ferromagnetism, the exchange integrals determined from static measurements correspond to those determined by dynamic measurements.     

Transition probabilities and energy levels in heavy odd-mass isotopes of Sn (A=119–125)

The de-excitation of levels in^119–125Sn populated in the decay of In isotopes has been studied using on-line isotope separators. Level half-lives have been measured in^119–123Sn. a near cancellation of the matrix element for B(E2; g_7/2→ d_3/2) is observed to occur in¹²¹Sn and is probably due to pairing effects. Very low lying 9/2^? levels have been observed in^121–125Sn and are suggested in^{127, 129}Sn. These levels have been interpreted as three quasi-particle states based on the unique parity h_11/2 level. A possible mixing of theg _7/2 level with a close lying 7/2⁺ three quasi-particle state in¹²³Sn is discussed. Radioactivity.^119–125In from²³⁵U(n, f) and²³⁸U(α, f), isotope separated sources; measuredE _γ ,I _γ , E_ce, I_ce,γγ-coin,Βγ-delay, deduced multipolarities.^119–123Sn deduced levels,I, π, B(λ). Ge(Li), Si(Li), NaI(Tl) and plastic detectors, Ge(Li)-Ge(Li) coin, plastic detector — NaI(Tl) delay.     

Segregation of Sn and Sb in a ternary Cu(1 0 0)SnSb alloy

Surface segregation studies of Sn and Sb in Cu(1 0 0)-0.14 at.% Sn-0.12 at.% Sb ternary alloy, have been done by making use of Auger Electron Spectroscopy. The method of Linear Temperature Ramp (LTR) was employed, whereby the sample was heated and cooled linearly at a constant rate. The positive heating rate showed both a kinetic segregation profile, as well as a narrow equilibrium segregation region, at higher temperatures. The equilibrium segregation profile was extended by cooling the sample. Sn was first to segregate to the surface due to its higher diffusion coefficient, mainly from a smaller activation energy E_Sn. Sb, due to its higher segregation energy, eventually replaced Sn from the surface. The modified Darken model was used to simulate the profile yielding the following segregation parameters: D_o(Sn) = 6.3 × 10⁻⁶ m²/s, D_o(Sb) = 2.8 × 10⁻⁵ m²/s; E_Sn = 175.4 kJ/mol, E_Sb = 186.3 kJ/mol; , ; Ω_Cu-Sn = 3.4 kJ/mol, Ω_Cu-Sb = 15.9 kJ/mol and Ω_Sn-Sb = −5.4 kJ/mol.     

Time-differential observation of quadrupole interactions following recoil implantation of a Ge-probe into Cd,In, Sn,and Sb

We have measured the quadrupole interactions of excited⁶⁷Ge nuclei in the polyvalent metals Cd, In, Sn, and Sb. The experiments have been performed by the time-differential angular distribution technique, following the reaction⁶⁴Zn(, n)⁶⁷Ge to produce and implant the Ge nuclei into the different metals (DIMPAD). A sandwich target system is used, which allows the application of the DIMPAD-technique for low recoil energies. The extracted electric field gradients are found to depend on the host metal as well as on the solute Ge, an interpretation is suggested on the basis of charge screening effects.     

Transition probabilities and the structure of some negative-parity states in 126,130Xe and 132Ba

The lifetimes of several negative-parity states in ^126,130Xe and ¹³²Ba have been determined by means of the generalized centroid-shift method. The reactions ^124,128Te(α, 2n) and ¹²²Sn(¹³C, 3n) have been used. Following results were obtained: T_1/2(2758 keV) = 1.3 ± 0.2 ns in ¹²⁶Xe, T_1/2 (2060 keV) = 0.20 ± 0.10 ns, T_1/2 (2104 keV) = 0.50 ± 0.10 ns, T_1/2 (2376 keV) = 0.30 ± 0.10 ns and T_1/2 (2973 keV) = 4.6 ± 0.4 ns in ¹³⁰Xe as well as T _1/2(2120 keV) = 0.40 _?0.10 ^+0.20 ns in ¹³²Ba. A systematics of the B(E2; 7 ₁ ^? ? 5 ₁ ^? ) values in the N = 76 nuclei is presented. Electric dipole and quadrupole transition rates are discussed in terms of octupole and quadrupole collectivity. The structure of the 5 ₁ ^? and 7 ₁ ^? states is considered. Nuclear reactions: ^124,128Te(α, 2n), E = 26 MeV, ¹²²Sn (¹³C, 3n), E = 53 MeV; measured E_{gg}, I_{gg}, γ-r.f. Deduced T_1/2, B(σL) in ^126,130Xe and ¹³²Ba. Ge detectors. Generalized centroid-shift analysis.     

Mössbauer study of the ternary system (Fe1−xVx)3 Ge

Three crystallographically different structures of (Fe_1–xV_x)₃ Ge have been studied by⁵⁷Fe Mössbauer spectroscopy. The hexagonal phase, stable for low values ofx, is ferromagnetic with the spins parallel to thec-axis above a critical temperature, where a spin flip to thec-plane takes place. A V/Fe substitution in the near surrounding of an iron atom leads to a decrease in the isomer shift of –0.02 mm/s and an estimated reduction in the magnetic moment of 0.31 _B from 2.07 _B. A result for the intermediate cubic closed packed structure is that V populates only one type of metal sites. Furthermore, from similarities with-Fe the average value of the change in isomer shift is found to be +0.075 mm/s and +0.02 mm/s per Ge/Fe substitution in the 1nn and 2nn shells, respectively. The spin polarization effect on the magnetic hyperfine field for iron is –8.6%, –0.4%, and –0.6% per Ge/Fe (1nn), Ge/Fe (2nn) and V/Fe (3nn) substitutions, respectively. The simple cubic compound (Fe_0.7V_0.3)₃ Ge is non-magnetic down to at least 5 K. Here a decrease in the isomer shift of –0.05 mm/s is found for a V/Fe (1nn) substitution.On leave from the Department of Nuclear Physics, University of Madras, Madras, India.On leave from the Physics Department, Punjabi University, Patiala, India.