Measurement of the cross sections for the production of the isotopes <Superscript>74</Superscript>As, <Superscript>68</Superscript>Ge, <Superscript>65</Superscript>Zn,and <Superscript>60</Superscript>Co from natural and enriched germanium irradiated with 100-MeV protons

The cross sections for the production of the radioactive isotopes ⁷⁴As, ⁶⁸Ge, ⁶⁵Zn, and ⁶⁰Co in metallic germanium irradiated with 100-MeV protons were measured, the experiments being performed both with germanium of natural isotopic composition and germanium enriched in the isotope ⁷⁶Ge. The targets were irradiated with a proton beam at the facility for the production of radionuclides at the accelerator of the Institute for Nuclear Research (INR, Moscow). The data obtained will further be used to calculate the background of radioactive isotopes formed by nuclear cascades of cosmic-ray muons in new-generation experiments devoted to searches for the neutrinoless double-beta decay of ⁷⁶Ge at underground laboratories.     

Beiträge zu den Niveauschemata der Ge-Isotope71Ge,73Ge,74Ge und75Ge aus der Untersuchung von (n, γ)-Reaktionen in natürlichem Germanium

Low energy γ-spectra from neutron capture in natural germanium have been studied with several high resolution Ge(Li)-detectors. Measurements have been made with two different target configurations. In the first measurement a normal Ge-target was irradiated with neutrons; no neutrons were allowed to enter the Ge(Li)-detector. In the second measurement the Ge(Li)-detector was used simultaneously as target and as γ- ande ^?-detector. By combination of the results convertion coefficients of several transitions in⁷³Ge have been determined. Several unknown low energy transitions in Ge isotopes have been found with the aid of the second method. The level schemes of⁷¹Ge,⁷³Ge,⁷⁴Ge and⁷⁵Ge have been revised by means of coincidence measurements with a Ge(Li)-Ge(Li)-coincidence system of high efficiency and resolution.     

Raman scattering in germanium at high pressure: Isotope effects

The first-order Raman scattering in isotopically enriched samples of germanium ⁷⁰Ge, ⁷²Ge, and ⁷⁴Ge and germanium with the natural isotopic composition is investigated at high pressures. It is found that the isotopic dependence of the frequency of the LTO(Γ) mode in isotopically pure germanium samples can be described in the harmonic approximation (ν∝m ^−1/2). At the same time, the frequency of the LTO(Γ) mode of germanium of natural isotopic composition apparently contains a contribution due to isotopic disorder effects. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 211–214 (10 February 1999)     

Ab initio determination of crystal lattice constants and thermal expansion for germanium isotopes

The temperature dependence of the equilibrium lattice constants for five isotopically pure Ge crystals (⁷⁰Ge, ⁷²Ge, ⁷³Ge, ⁷⁴Ge and ⁷⁶Ge) and naturally occurring Ge were calculated from ab initio electronic theory within the quasiharmonic approximation. It is shown that at very low temperature, calculations including zero point motions contribution to the free energy correctly reproduced the experimental unit cell parameters for the five isotopes. For ⁷⁰Ge, ⁷⁴Ge, ⁷⁶Ge and naturally occurring Ge, the predicted thermal expansion coefficients agree very well with experiments. The calculated thermal expansitivity for ⁷³Ge does not agree well with experiment. It is speculated that this anomaly may due to the non-zero nuclear spin of the ⁷³Ge isotope.     

The Raman spectroscopy of neutron transmutation doping isotope Germanium nanocrystals embedded in SiO2 matrix

We have succeeded in doping arsenic (As) impurities into isotope germanium nanocrystals (nc-⁷⁴Ge) uniformly dispersed in a SiO₂ matrix by using the neutron transmutation doping (NTD) method. The samples’ inner structural transmutation is studied by combining Raman scattering, X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS) and Transmission electron microscope (TEM) methods. The Raman spectrum of the doped sample exhibits a relative intensity increase of the low frequency tail, blue shift of the main Raman peak (∼300 cm⁻¹) and a high frequency tail, while the undoped sample does not. Together with the XRF, XPS and TEM, we believe that the relative intensity increase of the low frequency tail arises from an increase of amorphous ⁷⁴Ge (a-⁷⁴Ge) induced by the irradiation damage. The blue shift of the main Raman peak comes from the mismatch of the crystal lattice which arose from the As impurity introduction. And the high frequency tail is due to transmuted-impurities (As) in the nc-⁷⁴Ge which was introduced by NTD.     

Neutron interactions as seen by a segmented germanium detector

The GERmanium Detector Array (GERDA) is designed for the search for “neutrinoless double-beta decay” ( 0ν2β with germanium detectors enriched in ⁷⁶Ge . An 18-fold-segmented prototype detector for GERDA Phase II was exposed to an AmBe neutron source to improve the understanding of neutron-induced backgrounds. Neutron interactions with the germanium isotopes themselves and in the surrounding materials were studied. Segment information is used to identify neutron-induced peaks in the recorded energy spectra. The Geant4-based simulation package MaGe is used to simulate the experiment. Though many photon peaks from germanium isotopes excited by neutrons are correctly described by Geant4, some physics processes were identified as being incorrectly treated or even missing.     

Low-field anomalous muonium depolarization in isotopically enriched germanium

The depolarization rate of anomalous muonium, Mu^*, in germanium isotopically enriched in⁷⁴Ge (I=0) was measured as a function of field. The concentration of⁷³Ge (I=9/2) was about 9 times less than natural abundance. The depolarization rate at 10 K in this isotopically enriched crystal for both lines of those Mu^* centers whose symmetry axes make an angle of 90° to the field is less than 1sec^–1 at all fields down to the lowest one measured, 14.5 gauss. This is in sharp contrast to the wide lines reported at low field in germanium having natural isotopic abundance. The spectrum of Mu^* in the isotopically enriched Ge crystal was also seen at zero field. These results confirm that the increased depolarization rate for Mu^* at low fields arises from unresolved nuclear hyperfine structure. The depolarization rates observed were consistent with an average hyperfine interaction with a single⁷³Ge nucleus of 2.5 MHz, a value requiring nearly 1% of the spin density to be on a typical atom.     

用从头算方法研究GeCl2分子的非谐振力场和光谱常数

用从头算方法的MP2和CCSD（T）方法结合cc-pVTZ基组计算了二氯化锗同位素（⁷⁰GeCl₂、⁷²GeCl₂和⁷⁶GeCl₂）分子的平衡结构、光谱常数和非谐振力场.二氯化锗的几何结构、转动常数、振转相互作用常数、谐频、非谐振常数、四次和六次离心畸变常数、三次和四次力常数的计算结果与实验结果符合较好,二氯化锗分子的同位素效应较小,可能的原因是Ge同位素的质量变化相对较小.两种方法计算的结果均与实验结果符合,但CCSD（T）方法比MP2计算结果的偏差稍大一些,可能的原因是CCSD（T）方法在描述过共价Cl原子的电子相关时不够充分.     

Hexagonal germanium formed via a pressure‐induced phase transformation of amorphous germanium under controlled nanoindentation

We have studied the stable end phase formed in amorphous germanium (a‐Ge) films that have been subjected to a pressure‐induced phase transformation under indentation loading using a large (20 µm) spherical indenter. After indentation the samples have been annealed at room temperature to remove any residual unstable R8 and BC8 phases. Raman spectroscopy indicates a single broad peak centred around 292 cm^–1 and we have used first principles density functional perturbation theory calculations and simulated Raman spectra for nano‐crystalline diamond cubic germanium (DC‐Ge) to help identification of the final phase as hexagonal diamond germanium (HEX‐Ge). Transmission electron microscopy and selected area diffraction analysis confirmed the presence of a dominant HEX‐Ge end phase. These results help explain significant inconsistencies in the literature relating to indentation‐induced phase transitions in DC‐ and a‐Ge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

73Ge NMR spectra in germanium single crystals with different isotopic composition

We have studied the influence of isotopic disorder on the local deformations in Ge single crystals from both experimental and calculation points of view. The nuclear magnetic resonance (NMR) spectra of⁷³Ge nuclei (the nuclear spin equals 9/2) in perfect single crystals of germanium with different isotopic content were measured at temperatures 80, 300 and 450 K. Abnormal broadening of the spectrum was found to occur when the magnetic field was aligned along the [111] axis of a crystal. The observed specific angular dependence of the quadrupole broadening was attributed to isotopic disorder among atoms of germanium sited around the⁷³Ge NMR probe. Local lattice deformations in germanium crystal lattice due to isotopic impurity atoms were calculated in the framework of the adiabatic bond charge model. The results obtained were applied to study random noncubic crystal field interactions with the nuclear quadrupole moments and corresponding effects in NMR spectra. Simulated second and fourth moments of resonance frequency distributions caused by the magnetic dipole-dipole and electric quadrupole interactions are used to analyze the lineshapes, theoretical predictions agree qualitatively with the experimental data.     

A study of the 70, 72, 74, 76Ge(d,p)71, 73, 75, 77Ge reactions using polarized deuterons

Differential cross sections and vector analyzing powers were measured at an incident deuteron energy of 12.0 MeV for the ^{70, 72, 74, 76}Ge(d, p)^{71, 73, 75, 77}Ge reactions. The data were analyzed with the distorted-wave Bom approximation. Spin and parity assignments were made to 13 states in ⁷¹Ge, 19 states in ⁷³Ge, 13 states in ⁷⁵Ge and 11 states in ⁷⁷Ge. Spectroscopic factors were extracted and a simple sum rule analysis was applied to the data.     

Vibrational density of states of hen egg white lysozyme

The resonant Raman scattering in GeSi/Si structures with GeSi quantum dots has been analyzed. These structures were formed at various temperatures in the process of molecular-beam epitaxy. It has been shown that Raman scattering spectra recorded near resonances with the E₀ and E₁ electronic transitions exhibit the lines of Ge optical phonons whose frequencies differ significantly from the corresponding values in bulk germanium. In the structures grown at low temperatures (300–400°C), the phonon frequency decreases with increasing excitation energy. This behavior is attributed to Raman scattering, which is sensitive to the size of quantum dots, and shows that quantum dots are inhomogeneous in size. In the structures grown at a higher temperature (500°C), the opposite dependence of the frequency of Ge phonons on excitation energy is observed. This behavior is attributed to the competitive effect of internal mechanical stresses in quantum dots, the localization of optical photons, and the mixing of Ge and Si atoms in structures with a bimodal size distribution of quantum dots.     

Exciton molecule in semiconductors by phonon-assisted two-photon absorption

Direct creation of bi-excitonic states by photon-assisted two-photon absorption in indirect-gap semiconductors is investigated theoretically. The symmetry of the indirect bi-exciton states and of the phonon used are given for the case of Ge. A numerical application to the case of Si shows that the indirect two-photon absorption coefficient for bi-excitonic α²_I (bi-ex) transitions is several orders of magnitude larger than both indirect two-photon interband, α²_I (band), and excitonic, α²_I (exc), transitions. It becomes smaller than both indirect one-photon interband, α¹_I (band), and excitonic, α¹_I (exc), transitions for available laser intensities. The essential contribution to this enhancement of α²_I (bi-ex) is found to be from the resonance effect in the first process and from both the resonance effect and matrix elements included in the second process.     

Normal and “Anomalous” isotope shifts of phonon frequencies in mono- and polyisotopic germanium crystals

The shifts of the phonon frequencies in ⁷⁰Ge and ⁷⁴Ge monoisotopic crystals have been studied using inelastic neutron scattering. It has been shown that the frequency shifts for all of the branches are normal, i.e., inversely proportional to √M. At the same time, the gap between acoustic and optical frequencies in monoisotopic crystals appears to be much wider (by about 2 meV in the [111] direction) than that in natural polyisotopic crystals containing “isotopic defects.” In this case, the phonon frequencies undergo “anomalous” shifts; i.e., the oscillation frequency of the heavier isotope is higher than that for the lighter isotope. The effect is in qualitative agreement with old theoretical calculations of the effect of mass defects on the phonon spectra of diatomic lattices.     

Local Vibrations of Oxygen-Containing Thermal Donors in Germanium

The vibrational absorption bands associated with some types of double thermal donors (TD) in Ge enriched with the oxygen isotopes ¹⁶O and ¹⁸O have been identified. The thermal donors were formed during heat treatment of Ge:O crystals at 300 and 350°C. Absorption spectra were measured at room temperature and at 10 K. The formation of the thermal donors was accompanied by the appearance of three absorption bands, which in the Ge:¹⁶O spectra at room temperature are located at 600, 740, and 780 cm^–1. In low-temperature measurements, the bands at 600 and 780 cm^–1 exhibited splitting into series of narrow lines (up to 9) associated with some types of thermal donors (TD1–TD9). The absorption spectra measured at 10 K after different cooling conditions display bistability of the first four types of thermal donors (TD1–TD4). In the samples cooled by illumination with light in the region of frequencies of the fundamental absorption of Ge, pairs of lines are observed that belong to the bistable thermal donors in the helium-like configuration of double donors (DD). After cooling the samples in the dark, these pairs of lines are replaced by three new bands, which belong to local vibrational modes of bistable thermal donors in the low-energy neutral configuration. Based on the isotopic shift of the local vibrational modes of the thermal donors in Ge:¹⁶O and Ge:¹⁸O, a rigorous proof of the oxygen atoms entering into the composition of thermal donors is obtained.     

Precise atomic mass difference determinations between some stable isotopes of Ge,As and Se

The 1 m radius, high-resolution mass spectrometer at the University of Manitoba (“Manitoba II”) has been used to determine 11 atomic mass differences between some stable isotopes of Ge, As and Se. These values are of greater accuracy and precision than existing data. Their consistency has been checked by a major least-squares adjustment involving relevant data in the region. Results include improved S_2n values for several nuclides and the energies available for the ββ decays of ⁷⁶Ge and ⁷⁴Se, respectively.     

Raman spectra of two new modifications of germanium: Allo-germanium and 4H-Ge

The Raman spectra of allogermanium and 4H germanium have been measured. Allogermanium shows a band which mimics the density of states of diamond-like Ge(Ge?I). 4H-Ge shows a peak at 287 cm^-1 which can be assigned to an E₂ phonon. This phonon corresponds to a TO-mode of Ge-I at the $\text{(}\text{π}\text{2}\text{a}\text{) (1|1)}$ point of the Brillouin zone.     

The role of interdiffusion and spatial confinement in the formation of resonant raman spectra of Ge/Si(100) heterostructures with quantum-dot arrays

The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beam epitaxy in an apparatus integrated with a chamber of the scanning tunneling microscope into a single high-vacuum system are investigated using Raman spectroscopy. It is revealed that the Ge-Ge and Si-Ge vibrational modes are considerably enhanced upon excitation of excitons between the valence band Λ₃ and the conduction band Λ₁ (the E ₁ and E ₁ + Δ₁ transitions). This makes it possible to observe the Raman spectrum of very small amounts of germanium, such as one layer of quantum dots with a germanium layer thickness of ≈10 Å. The enhancement of these modes suggests a strong electron-phonon interaction of the vibrational modes with the E ₁ and E ₁ + Δ₁ excitons in the quantum dot. It is demonstrated that the frequency of the Ge-Ge mode decreases by 10 cm^?1 with a decrease in the thickness of the Ge layer from 10 to 6 Å due to the spatial-confinement effect. The optimum thickness of the Ge layer for which the size dispersion of quantum dots is minimum is determined.     

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.     

Mass and excited levels of the neutron-rich nuclei 73Zn and 74Zn studied with the 76Ge(14C, 17O) and (14C, 16O) reactions

The ⁷⁶Ge(¹⁴C, ^{16, 17}O)^{74, 73}Zn reactions have been studied at 72 MeV bombarding energy. The mass excesses of ⁷³Zn and ⁷⁴Zn were determined to be ?65.41 ± 0.04 and ?65.62 ± 0.04 MeV, respectively. In addition, previously unknown excited levels were identified in both nuclei. The structure of ⁷³Zn is discussed in terms of HFB calculations.