Efficient Germanium Research Articles

Ultra-broad band antireflection coating at mid wave infrared for high efficient germanium optics

This work mainly demonstrates the development process of an ultra-broad band antireflection (AR) coating that maximizes the optical performance of germanium optical elements. A multilayer stack exhibiting high efficient AR performance on Ge consists of thin multi-layers of aluminum oxide (Al2O3) and germanium (Ge) named as low and high refractive index layer materials. A three-layer design with a very tight thickness tolerance (3%) was optimized by Optilayer software. Al2O3 and Ge layers were deposited by a plasma assisted e-beam evaporation system. Ultra-high efficient multilayer AR coating on Ge has a base reflectance 0.005% at 3550 nm and an average reflectance of 0.256% over the entire mid wave infrared spectrum. Multilayer AR coating on Ge offers lower base and average reflectance than the works reported before. Moreover, AR coating on Ge offers a cost effective process cycle due to its number of layers and its thickness for providing ultra-broadband and high efficient optical performance for mid wave infrared electro-optical applications.

Non-Dispersive Extraction of Ge(IV) from Aqueous Solutions by Cyanex 923: Transport and Modeling Studies

Transport process of germanium from an aqueous solution containing oxalic acid and 100 mg/L Ge was studied. Cyanex 923 immobilized in a polytetrafluoroethylene membrane was employed as a carrier in a flat-sheet supported liquid membrane (FSSLM) system. The speciation of the germanium ion in the oxalic acid medium and related diagrams were applied to study the transport of germanium. The effective parameters such as oxalic acid, carrier concentration, and strip reagent composition were evaluated in this study. Based on the experimental data, the oxalic acid and carrier concentrations of 0.075 mol/L and 20% v/v were the condition in which the efficient germanium transport was achieved, respectively. The concentration range of 0.04–0.1 mol/L was selected for sodium hydroxide (NaOH) as a strip reagent providing the best efficiency to transport germanium through the supported liquid membrane (SLM) system. Furthermore, the permeation model was obtained to calculate the mass transfer resistance of the membrane (Δm) and feed (Δf) phases. According to the results, the values of 1 and 1345 s/cm were found for Δm and Δf, respectively.

EXOGAM at the ILL: the EXILL campaign

Radiative capture reactions on rare targets and prompt spectroscopy of neutron-rich nuclei produced in the neutron-capture induced-fission of 235U and 241Pu have been performed at the Institut Laue-Langevin (ILL). The high efficiency germanium (Ge) EXOGAM array has been used, complemented with Ge detectors from GASP and the ILL. LaBr3 detectors from the FATIMA collaboration have also been coupled to EXOGAM to measure lifetimes of lowlying excited states. The measured characteristics indicate very good performances of the overall setup. Some recent results will be discussed.

Absolute peak-efficiency calibration of a well-type germanium detector using multiple gamma-emitting nuclides with the “Solver” add-in in Excel™

When calibrating absolute peak efficiency and total efficiency functions for high efficient germanium detectors, single gamma-emitting nuclides are used in general to avoid coincidence summing effects. As another approach, Blaauw developed calibration technique using multiple gamma-emitting nuclides with least-square technique (Blaauw, 1993; Blaauw and Gelsema, 2003). In the present study, we tried to calibrate efficiency functions of a well-type germanium detector based on Blaauw's approach using a home-made iteration calculation algorithm with the “Solver” add-in in Excel™.

Ge microdisk with lithographically-tunable strain using CMOS-compatible process.

We present germanium microdisk optical resonators under a large biaxial tensile strain using a CMOS-compatible fabrication process. Biaxial tensile strain of ~0.7% is achieved by means of a stress concentration technique that allows the strain level to be customized by carefully selecting certain lithographic dimensions. The partial strain relaxation at the edges of a patterned germanium microdisk is compensated by depositing compressively stressed silicon nitride layer. Two-dimensional Raman spectroscopy measurements along with finite-element method simulations confirm a relatively homogeneous strain distribution within the final microdisk structure. Photoluminescence results show clear optical resonances due to whispering gallery modes which are in good agreement with finite-difference time-domain optical simulations. Our bandgap-customizable microdisks present a new route towards an efficient germanium light source for on-chip optical interconnects.

Observation of Spin-Dependent Charge Symmetry Breaking in ΛN Interaction: Gamma-Ray Spectroscopy of _{Λ}^{4}He.

The energy spacing between the spin-doublet bound state of _{Λ}^{4}He(1^{+},0^{+}) was determined to be 1406±2±2 keV, by measuring γ rays for the 1^{+}→0^{+} transition with a high efficiency germanium detector array in coincidence with the ^{4}He(K^{-},π^{-})_{Λ}^{4}He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus _{Λ}^{4}H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in ΛN interaction. By combining the energy spacings with the known ground-state binding energies, it is also found that the CSB effect is large in the 0^{+} ground state but is vanishingly small in the 1^{+} excited state, demonstrating that the ΛN CSB interaction has spin dependence.

High precisionγspectroscopy of69,71Zn from (n, γ) reactions using EXILL

Measurement of γ radiation following slow neutron capture on 68 Zn and 70 Zn using very efficient germanium array EXILL was done at Institute Laue-Langevin in Grenoble. New spectroscopic information for 69 Zn (including doorway state) and first results for 71 Zn (accurate energy of β decaying isomer) were obtained. Binding energies for 68 Zn, 69 Zn and 71 Zn were determined with 5-to-70 times higher accuracy than presented in the literature.

The negative parity bands in 156Gd

The high flux reactor of the Institut Laue-Langevin is the world most intense neutron source for research. Using the ultra high-resolution crystal spectrometers GAMS installed at the in-pile target position H6/H7 it is possible to measure nuclear state lifetimes using the gamma ray induced Doppler broadening (GRID) technique. In bent crystal mode, the spectrometers allow one to perform spectroscopy with a dynamic range of up to six orders of magnitude. At a very well collimated external neutron beam it is possible to install a highly efficient germanium detector array to obtain coincidences and angular correlations. These techniques were used to study the first two negative parity bands in . These bands are of interest as they seem to show signatures of a tetrahedral symmetry. A surprisingly high B(E2) value of about 1000 W.u. for the transition was discovered. It indicates that the two first negative parity bands cannot be considered to be signature partners.

Study of collisions of 136Xe + 198Pt for the KEK isotope separator

Multinucleon transfer reactions between two heavy ions are an important tool for production and investigation of exotic neutron-rich nuclei, which are difficult to access by other methods. The 136Xe+198Pt system is a candidate to efficiently produce neutron-rich nuclei around the neutron magic number N=126 for the KEK isotope separation project. In order to confirm this, measurements of the production cross sections with the large acceptance magnetic spectrometer VAMOS++ and de-excitation gamma rays from target-like fragments using the high efficiency germanium array EXOGAM at GANIL are reported. The measured isotopic distributions of the projectile-like fragments are compared with GRAZING calculations. The proton stripping channels show rough agreements between measurements and calculations. For the proton pick-up channels, the measured distributions are shifted toward the heavier masses and show enhanced cross sections in transfers of two or more protons.

Preparation and luminescence of terbium and cerium-doped silica xerogels

Sol-gel chemistry offers a possibility for preparation of optical materials like xerogels, aerogels, or thin films doped with rare earth ions [1–5]. In the case of silicabased materials the physical properties of the produced xerogels depend on the physicochemical processes accompanying the hydrolysis and gelation of tetraethylorthosilicate (TEOS) at different temperatures and time durations. In our previous contributions we demonstrate a higly efficient germanium–terbium energy transfer in silica sol-gel derived glasses [4, 5], the synthesis of transparent holmium-doped silica xerogels [3], as well as the luminescence of silica gels doped with terbium benzoate complexes [4]. The aim of the present investigation is the study of the preparation and luminescence of Ce3+/Tb3+ codoped silica xerogels. Optical materials containing Tb3+ and Ce3+ are important green emitting phosphors due to Ce3+ (5d1) → Tb3+ (4f75d1) energy transfer [6–8]. Despite the intense investigations of polycrystalline Ce3+/Tb3+-doped materials [8], the luminescence of amorphous xerogels remains unexplained so far. The silica xerogels in the present contribution were prepared by acid-catalyzed hydrolyzation of TEOS dissolved in ethanol (EtOH), and then gelation and drying (Techne 3D dry block with 5.6 ml starting amount of TEOS for all samples). Both ethanol addition and doping, followed by hydrolysis with HCl at pH 2 were performed under stirring. The molar ratios were TEOS:EtOH:H2O:HCl = 1:1:4:0.003. The pH of the 0.45 M Tb3+ nitrate solution is 4–5. For the cerium codoping a 1.8 M Ce3+ nitrate solution with pH 4–5 was added to the terbium containing sol. The duration and temperature conditions for all samples of the different sol-gel steps following the cerium codoping are: hydrolysis—1 hr at room temperature, gelation—48 hr at 50 ◦C and drying—120 hr at 50 ◦C. Samples containing 1 mol% Tb/Si and codoped with 0.5, 1, 2, 3, 4, 5, and 7.5 mol% Ce/Si as well as 1, 2, and 5 mol% Ce/Si were

New thermal neutron prompt γ-ray activation analysis instrument at the National Institute of Standards and Technology Center for Neutron Research

A new thermal neutron prompt γ-ray activation analysis (PGAA) instrument was designed and built to replace the original PGAA system at the NIST Center for Neutron Research. By placing a sapphire filter in the neutron beam shutter assembly, the fast neutron fluence rate was reduced by a factor of 5 and low-energy (50–200 keV) γ-ray intensities were reduced by factors of 5–10. The thermal neutron fluence rate was reduced by only a factor of 1.13. A new external beam tube, sample chamber, beam stop, and support structure were built and a new detection system installed. The new beam tube is made of two cylindrical aluminum sections lined with a lithiated polymer. Both sections are kept under vacuum to reduce the number of neutrons scattered by air into the beam tube walls. The sample chamber is also fabricated from aluminum and lined with lithiated polymer, and may be evacuated to minimize the number of neutrons scattered and absorbed by air. The beam tube and sample chamber assembly is suspended from the aluminum support structure. The detection system consists of a 40% efficient (relative) germanium detector (resolution 2.0 at 1332.5 keV) and a bismuth germanate Compton suppressor. The detection system is shielded by lead, surrounded by borated and lithiated polyethylene, and placed on a table attached to the support structure. The new, more compact beam stop is welded to the support structure. Capture γ-ray photopeaks from H, B, C, N, Na, Al, Fe, Ge, I and Pb in the background spectrum were either of lower intensity or eliminated with the new PGAA instrument. The more efficient detection system, positioned closer to the sample, yielded element sensitivity increases of 5–50%. Limits of detection have been greatly reduced compared with those of the original instrument due to reduced Compton and scattered γ-ray backgrounds (especially in the low-energy region), increased sensitivities, and reduction of background γ-ray photopeak intensities.

Development of a Gamma-Ray Box (GARBO)

Isomer decays, β–γ and electron–γ spectroscopy, α–γ fine structure studies, and Coulomb excitation are cases of nuclear structure experiments where the ideal detector is a compact, highly segmented, very efficient germanium (Ge) detector box. In order to develop such a structure, we are working on the R&D of large, segmented, high-purity planar Ge strip detectors (HPGeDSSD) which form the walls of such a box. We have developed a 92mm×92mm×20mm HPGeDSSD, which has 16×16 orthogonal strips of 5mm width. We are in the process of designing a focal plane detector for the Argonne fragment mass analyzer which consists of a five-sided box, each side having a HPGeDSSD backed by a large segmented clover HPGe detector. MCNP simulations indicate this detector would have an efficiency of ∼60% for 122keV gamma rays and ∼15% for 1.33MeV radiation, which is ideal for studying the decays of nuclei far from stability that are usually produced with very low cross-sections.

Photon counting in the 1540-nm wavelength region with a germanium avalanche photodiode

Unexpected results have been obtained in measurements of dark-count rate and quantum efficiency (QE) for a germanium avalanche photodiode operating in the photon counting regime at 1540-nm wavelength. A liquid-nitrogen cooled Ge single-photon avalanche diode (SPAD) exhibited both a low dark-count rate and a QE of the order of 1%, which is at least one order of magnitude higher than the values reported for such a device. The data offer hope for future diodes that might match such performance. Reasons for the device's extraordinarily good performance, a performance level not matched by the other 17 APDs in the collection investigated, are not understood. Such high quantum efficiency germanium devices could be used in one-bit-per-photon communication systems operating in the 1540-nm telecommunications window.

The capture reactions 15N(α,γ) 19F and 20Ne(α,γ) 24Mg at astrophysically relevant energies

The capture reactions 15N(α, γ) 19F and 20Ne(α, γ) 24Mg have been studied using a windowless gas target system and a 100% relative efficiency germanium detector with an active BGO shielding. For the 15N(α, γ) 19F reaction 14 resonances have been analyzed in the range 650 keV < E α,lab < 2650 keV, branching ratios and resonance strengths have been deduced. For the 20Ne(α, γ) 24Mg reaction up to now 10 resonances have been investigated in the range 1640 keV < E α,lab < 2650 keV. Due to the effective background reduction resonance strengths of weak resonances could be deduced. In near future the study will be extended to lower energies.

Optimum geometry of radioactive aqueous sample container for measurement with a germanium detector

High-resolution gamma-ray spectra of radioactive aqueous samples with volume of 0.1–4.0 L were measured using a 20% relative efficiency germanium detector. A total of 308 spectra, covering the photoenergy range of 50–1500 keV, were sorted and analyzed with various sample geometries. The optimum dimensions of a Marinelli-like container were obtained to maximize the count rate of aqueous samples up to 4 L. Relations among the radius, height and volume of the optimum geometry for the Marinelli-like container are established.