Dislocations in high-purity germanium and its relation to γ-ray detector performance

The presence of dislocations in high-purity germanium influences the resolution of radiation detectors made from it. The four dislocation types found with electron microscopy are studied by DLTS to understand their influence on trapping in a -ray detector. Only three DLTS bands were found in commercially produced material.Statistical correlation with the detector resolution reported by various detector manufacturers finally yielded useful specifications with respect to the crystallographic perfection to be met in detector grade HP-Ge. The specification limits are discussed in view of the DLTS data.Work performed with financial support from the IWONL     

Quantum efficiency calibration of opto-electronic detector by means of correlated photons method

A new calibration method of detectors can be realized by using correlated photons generated in spontaneous parametric down-conversion (SPDC) effect of nonlinear crystal.An absolute calibration system of detector quantum efficiency is performed.And its principle and experimental setup are introduced.A continuous- wave (CW) ultraviolet (351 nm),diode-pumped,frequency-doubled,and solid-state laser is used to pump BBO crystal.The quantum efficiencies of the photomultiplier at 633,702,and 789 nm are measured respectively.The coincidence peaks are observed using coincidence circuit.Some measurement factors including the filter bandwidth of trigger channel,the detector position alignment and polarization of the pump light are analyzed.The uncertainties of this calibration method are also analyzed,and the relative uncertainties of total calibration are less than 5.8%.The accuracy of this method could be improved in the future.     

Heat capacity of high-purity isotope-enriched germanium-76 in the temperature range of 2–15 K

The heat capacity of high-purity isotopically-enriched germanium Ge-76 has been measured in the range of 2.5–15 K. In this range, the heat capacity of Ge-76 is 6–15% higher than the heat capacity of germanium of the natural isotopic composition, which is determined by a change in the average mass.     

Modeling the efficiency of neutron detection scintillators in the energy range of 5–70 MeV

The instrumental functions for neutron godoscope detectors used in studying the nd-breakup reaction are obtained. The effect on light output of contributions from different processes that occur in a scintillator under the effect of neutrons is examined at different energies of the incident neutrons. The relationship between the detector??s efficiency and neutron energies ranging from 5 to 70 MeV is obtained for different thresholds.     

The quantum efficiency of the photo-electric effect in germanium for the 0.3–2 μ wavelength region

The absolute value of the quantum efficiency of the internal photoelectric effect in germanium in the 0.3–2 wavelength region was measured by means of the photovoltaic effect on a p-n junction. Two different regions were found. In the region from the infra-red absorption edge of germanium to a wavelength of 5750Å a practically constant number of electron-hole pairs, approximately equal to one, is produced per photon absorbed. In the second region from a wavelength of 5750Å and lower the number of generated pairs of current carriers is proportional to the total energy absorbed. In this region an energy of 2.5 eVis necessary to form an electron-hole pair.     

Measurement of attenuation cross-sections of some fatty acids in the energy range 122–1330 keV

The mass attenuation coefficients (μ_m) have been measured for undecylic acid (C₁₁H₂₂O₂), lauric acid (C₁₂H₂₄O₂), tridecylic acid (C₁₃H₂₆O₂), myristic acid (C₁₄H₂₈O₂), pentadecylic acid (C₁₅H₃₀O₂) and palmitic acid (C₁₆H₃₂O₂) using ⁵⁷Co, ¹³³Ba, ¹³⁷Cs, ⁶⁰Co and ²²Na emitted γ radiation with energies 122, 356, 511, 662, 1170, 1275 and 1330 keV, respectively. The accurate values of the effective atomic number (Z_eff), atomic cross-section (σ_t,), electronic cross-section (σ_e) and the effective electron density (N_eff) have great significance in radiation protection and dosimetry. These quantities were obtained by utilizing experimentally measured values of mass attenuation coefficients (μ_m). A NaI(Tl) scintillation detector with 8.2% (at 662 keV) resolution was used for detecting of attenuated γ-photons. The variation in Z_eff and N_eff of fatty acids with energy is discussed. The experimental and theoretical results are in good agreement within 2% deviation.     

Angular distribution of atoms sputtered from germanium by 1–20 keV Ar ions

The angular distribution of atoms sputtered from germanium under 1–20 keV Ar⁺ ion bombardment (normal incidence) has been studied experimentally and using computer simulations. A collector technique combined with Rutherford backscattering to analyze the distribution of collected material was used. In addition, the surface topography was under control. It was found that the experimental angular distribution of sputtered atoms (E ₀=3–10 keV) could be approximated by the function cos ⁿ θ with n≈ 1.65. Such a high value of n is connected with the surface scattering of ejected atoms and a noticeable contribution of backscattered ions to the formation of the sputter flux (the mass effect). The target surface was found to be practically flat even at ion fluencies ～10¹⁸ ions/cm². The results obtained are compared with data from the literature, including our recent data on Si sputtering.     

Optimum condition of efficiency functions for HPGe γ-ray detectors in the 121-1408 keV energy range

The optimum condition of three commonly used functions in the Genie 2000 γ spectra analysis software have been studied in the 121-1408 keV energy range. The three functions are applied for fitting the full-energy peak efficiency of the HPGe gamma-ray detector. A detailed procedure to obtain the optimum condition is described. The HPGe detector is calibrated at 11 cm by three radioactive sources of point form （^152Eu, ^137Cs, ^60Co） providing 11 energy peaks. After data processing, results shows that the three functions used in the Genie 2000 gamma spectra analysis software fit best at orders 3-5. Lastly the standard radioactive source 133Ba is chosen to validate the results. Differences between the standard activity of 133Ba and the result obtained from the fitting functions are below 1.5%. Therefore the optimum orders of the three functions used in the Genie 2000 3, spectra analysis software are 3-5 with the 11 energy peaks.     

Optimum condition of efficiency functions for HPGe γ-ray detectors in the 121-1408 keV energy range

The optimum condition of three commonly used functions in the Genie 2000 γ spectra analysis software have been studied in the 121-1408 keV energy range.The three functions are applied for fitting the full-energy peak effciency of the HPGe gammaray detector.A detailed procedure to obtain the optimum condition is described.The HPGe detector is calibrated at 11 cm by three radioactive sources of point form(152Eu,137Cs,60Co) providing 11 energy peaks.After data processing,results shows that the three functions used in the Genie 2000 gamma spectra analysis software fit best at orders 3-5.Lastly the standard radioactive source 133Ba is chosen to validate the results.Differences between the standard activity of 133Ba and the result obtained from the fitting functions are below 1.5%.Therefore the optimum orders of the three functions used in the Genie 2000 γ spectra analysis software are 3-5 with the 11 energy peaks.     

Calibrated binding energies of some core levels in the energy range between 1.5–4 keV

A commercial photoelectron spectrometer equipped with four interchangeable anodes (Mg, Al, Ag, Ti) has been utilized after careful calibration for accurately measuring binding energies of several deep core levels in the energy range between 1.5–4 keV.     

Absolute frequency measurement of acetylene transitions in the region of 1540 nm

An optical frequency comb has been used to measure the frequency of a diode laser system, locked to the P(10), P(11), P(15), P(16), P(20), and P(21) transitions in the ₁+₃ overtone band of ¹³C₂H₂. When locked to any of these transitions, the laser frequency showed a stability of 4×10^-12 in 1 s and a reproducibility of better than 1 kHz. The frequency of the reference P(16) transition was found to be P(16)=194369569383.83 kHz with an uncertainty of 0.32 kHz, based on measurements of a single system, and 2.5 kHz, based on the reproducibility of independent systems. PACS 06.30.Ft; 33.20Ea; 42.62.Fi     

Electron excitation of hydrogen atom by ions impact in the energy range 20–1000 keV/amu

We have calculated the electron excitation cross sections of hydrogen atom by the impact of protons, alpha particles and He⁺ ions using the boundary corrected continuum intermediate state approximation in the intermediate and high energies. The calculated results are compared with other theoretical and experimental results. The angular influence of excitation to the H atom at the intermediate energy is also discussed. The distortion effects due to the projectile charges in reactions of electron excitation to bound states of the target H atom are shown in the intermediate and high collision energy.     

Preferential etching of Si–Si bond in the microcrystalline silicon germanium

Hydrogenated microcrystalline silicon germanium (μc-Si_1?xGe_x:H) films were investigated as a bottom cell absorber in multi-junction solar cells. μc-Si_1?xGe_x:H films were prepared using very high frequency (VHF, 60 MHz) plasma enhanced chemical vapor deposition (PECVD) systems working pressure of about 1.5 Torr. The precursor flow rates were carefully controlled to determine the phase transition point and to improve the crystallinity of μc-Si_1?xGe_x:H. A relatively high plasma power was necessary to have the high hydrogen (H₂) dilution. Raman spectroscopy study showed transition steps from amorphous to microstructure morphology as hydrogen dilution increasing. Crystallite Si–Ge and Ge–Ge bonds were occurred at relatively higher H₂ dilution compare to crystallite Si–Si bond. The rapidly increased Ge content as increasing the H₂ dilution is believed mainly due to the different decomposition rate of silane (SiH₄) and germane (GeH₄). The other reason of high Ge content even at the low GeH₄ precursor flow rate is probably due to the preferential etching of silicon atom by H₂. The preferential etching of Si–H possibly occurred in very highly concentrated H₂ plasma due to the preferential attachment of Si–H. The compositions of μc-Si_1?xGe_x:H films measured using RBS were Si_0.83Ge_0.17, Si_0.67Ge_0.33 and Si_0.59Ge_0.41 at H₂/SiH₄ flow rate of 60, 80 and 100, respectively. μc-Si_1?xGe_x:H films showed the dark (σ_d) and photo conductivity (σ_p) of about 10^?7 and 10^?5 S/cm, respectively and photo response (σ_p/σ_d) was about 10². This study will present the comprehensive evaluation of crystallization behavior of μc-Si_1?xGe_x:H films.     

Measurement of the total spectrum of electrons and positrons in the energy range of 300–1500 GeV in the PAMELA experiment with the aid of a sampling calorimeter and a neutron detector

A method based on the use of a sampling calorimeter was developed for measuring the total energy spectrum of electrons and positrons from high-energy cosmic rays in the PAMELA satellite-borne experiment. This made it possible to extend the range of energies accessible to measurements by the magnetic system of the PAMELA spectrometer. Themethod involves a procedure for selecting electrons on the basis of features of a secondary-particle shower in the calorimeter. The results obtained by measuring the total spectrum of cosmic-ray electrons and positrons in the energy range of 300–1500 GeV by the method in question are presented on the basis of data accumulated over a period spanning 2006 and 2013.

     

Ionization of M subshells of Pb atoms by electron impact in an energy range of 5–30 keV

The relative intensities of the M ₅ N and M ₄ N satellites of Pb under electron bombardment of thick targets in the range of accelerating voltages U = 5?30 kV are experimentally investigated. Based on the previously proposed model of M X-ray emission, the relative intensities of these satellites are calculated using the total ionization cross sections of M subshells under electron impact found in different approximations. It is established that, among the models yielding analytical expressions for calculating total ionization cross sections, the model of classical binary collisions provides the best agreement with experimental data in the electron energy range under study. The parameters of the semiempirical Bethe formula for calculating the ionization cross sections of Pb M subshells under electron impact are determined.     

XPS study of the chemical bonding in hydrogenated amorphous germanium–carbon alloys

A systematic study of the chemical bonding in hydrogenated amorphous germanium–carbon (a-Ge_1-xC_x:H)alloys using X-ray photoelectron spectroscopy (XPS) is presented. The films, with carbon content ranging from 0 at. % to 100 at. %, were prepared by the rf co-sputtering technique. Raman spectroscopy was used to investigate the carbon hybridization. Rutherford backscattering spectroscopy (RBS) and XPS were used to determine the film stoichiometry. The Ge 3d and C 1s core levels were used for investigating the bonding properties of germanium and carbon atoms, respectively. The relative concentrations of C–Ge, C–C, and C–H bonds were calculated using the intensities of the chemically shifted C 1s components. It was observed that the carbon atoms enter the germanium network with different hybridization, which depends on the carbon concentration. For concentrations lower than 20 at. %, the carbon atoms are preferentially sp³ hybridized, and approximately randomly distributed. As the carbon content increases the concentration of sp² sites also increases and the films are more graphitic-like. Received: 4 May 1999 / Accepted: 24 November 1999 / Published online: 24 March 2000     

Pion-Nucleus potentials in the energy range of 0–80 MeV

Data for the elastic scattering of 30–80 MeV positive and negative pions by a wide range of nuclei is analysed with an Ericson-Ericson MSU type optical potential. By use of consistent sets of data for π⁺ and π⁻ and of experimental results for total reaction cross sections we obtain for the first time optical potentials that describe well all the data without the need of introducing non-standard charge-dependent effects.     

Solid-state traveling-wave amplifiers and oscillators in the THz range: effect of electron collisions

Due to their high plasma frequencies, drifting semiconductor plasmas interacting with slow electromagnetic waves hold promise for terahertz amplifiers and oscillators. In these devices, the gain and the type of instabilities are influenced by electron collisions. To study the effect of collisions, we developed a two-wave model describing the interaction between drifting solid-state plasmas and electromagnetic waves. This paper analyzes the two-wave dispersion relation for representative examples. As the examples show, convective and absolute instabilities can occur at high and low collision frequencies depending on the relationship between the collision frequency and the coupling coefficient. Surprisingly, an absolute instability occurs when collision-dominated plasmas interact with backward waves. The model can be used to determine the potential of a particular configuration in a solid-state amplifier or oscillator.     

Vacancy generation in silicon in the temperature range 100–633 K under electron irradiation

The processes of radiation defect formation in Si with 1 MeV electron irradiation in the temperature range 100–633 K have been investigated. It is established that the generation efficiency of vacancies λ_V increases with temperature, then starts to saturate at temperatures of 250 K and finally stays constant at T>300 K. It is shown that at high temperatures, the λ_V dependence can be caused by the additional scattering of “hot” interstitial atoms on acoustical and optical phonons, the numbers of which increase with the temperature. An explanation, based on the creation of quasi-molecule of “hot” interstitial and lattice atoms, is proposed.