Evidence for the Exchange Effect Down to Very Low Energy in the Beta Decays of ^{63}Ni and ^{241}Pu

Metallic magnetic calorimeters have been used for several years for the determination of the shapes of beta spectra. Experimental spectra of the beta decays of \(^{63}\) Ni and \(^{241}\) Pu exhibit, at very low energy, strong deviations from standard theoretical calculations including corrections for screening, radiative, and nuclear size effects. These discrepancies can be attributed to the atomic exchange effect. In particular the spectrum of \(^{63}\) Ni measured with an electroplated \(^{63}\) Ni source is in excellent agreement with theory including the exchange effect. This underlines the quality of the experimental spectrum as well as the correctness of the calculation of the exchange effect.     

Beta Spectrometry with Magnetic Calorimeters

Absolute activity measurements of alpha, beta and gamma emitting radioactive sources are important in numerous fields such as therapeutic radiology and the characterization of nuclear waste. Conventional ionization and liquid scintillation detectors, which are commonly used for these applications, have an energy dependent quantum efficiency and severe limitations in energy resolution. As a novel alternative we have developed a detector based on a metallic magnetic calorimeter (MMC) with a gold absorber that covers the full solid angle of 4π around the radioactive source. Deposition of energy in the absorber causes a temperature rise and results in a change of magnetization of a parametric Au:Er sensor, which can be measured by a low-noise high-bandwidth dc-SQUID. The detector has equal sensitivity for beta and gamma radiation. In this paper we describe a detector which has a deviation from linear behavior for energies up to 700 keV of smaller than 0.5% and an overall quantum efficiency for beta particles in this energy range close to unity. We show the data of our experiments measuring the decay of ³⁶Cl and compare the results to the theoretically expected spectrum for this second order forbidden non-unique β-decay. We discuss the observed contributions to noise, the quantum efficiency and the achieved energy resolution.     

Development of Decay Energy Spectroscopy for Radionuclide Analysis Using Cryogenic 4π Measurements

We report the recent progress in the development of decay energy spectroscopy for radionuclide analysis using a metallic magnetic calorimeter. In the present analysis, sample radionuclides were completely enclosed by a 4π steradian absorber. The use of a 4π absorber composed of gold foil guarantees that the total energy associated with radioactive decay is converted into thermal energy in the absorber. A paramagnetic temperature sensor was attached to the absorber to accurately measure the temperature change due to radioactive decay. The plutonium isotopes ²³⁸Pu, ²³⁹Pu, and ²⁴⁰Pu were readily identified in the decay energy spectrum because each isotope creates a single peak at its characteristic Q value. Two clear peaks were observed for ²³⁹Pu and ²⁴⁰Pu, and a 6.3?keV FWHM was obtained. The energy resolution of the method was affected by the low-energy tail of the spectrum at the left-hand side of the peaks. A 4.1?keV FWHM of a Gaussian fit was obtained for the right-hand side of the peak. Slow heat release to the absorber due to heat flow mechanisms is discussed to explain the low-energy tailing effect.     

Scattering of electrons in beta-spectroscopy sources

Experimental spectra of the¹⁶⁹Yb conversion lines having kinetic energies of 3.7–18.4 keV and the beta spectrum from the decay of²⁴¹Pu are compared with calculations by the Monte Carlo method which take into account the individual elastic and inelastic scattering processes of the electrons in the source, in the substrate, and in a carbon layer contaminating the source. Good agreement is obtained between the theoretical and experimental results. It is also shown that the scattering of the electrons depends on their emission angle. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 63–65, August. 1997.     

Influence of condensed water on heat radiation absorptivity at cryogenic temperatures

Influence of water deposit on heat radiation absorptivity of a metallic surface was measured in a device designed for investigation of thermal radiative properties of materials at cryogenic temperatures. In this device heat transfer between planparallel surfaces of radiator and absorber is measured. An aluminium sample of 40 mm in diameter was used as absorber. A radiator consisting of an organic composite on a copper disk was used in two experiment stages. At temperature of 298 K, water outgassed from the organic layer formed the deposit on the absorber. Then the heat emitted from the radiator at temperatures from 45 K up to 250 K was used for the absorptivity measurement. Substantial influence of deposit of 85 mg/m² on the sample absorptivity was found.     

Cryogenic micro-calorimeters for low energy beta spectroscopy

We are using calorimeters with completely encapsulated sources to study low energy beta spectra. Our devices work as true calorimeters in the sense that they totally absorb and sum all the various quanta released in a decay into a single temperature pulse with amplitude proportional to the total energy deposited. We use a neutron transmutation doped (NTD) germanium thermistor as the temperature sensor and superconducting NbTi leads, which form a weak thermal link to the cold stage (80 mK). We have been using superconducting tin as our absorber material, and we discuss various techniques for source and absorber preparation. Annealing the absorber leads to shorter pulses with larger amplitude, and significantly improves detector performance. The production of a device to study the beta decay of¹⁰⁷Pd presented special difficulties due to the low specific activity of this isotope (halflife 6.5×10⁶ y), and the low enrichment (15%) that was available. This meant it was necessary to incorporate a large amount of palladium into our tin absorber. We found we could avoid a corresponding increase in heat capacity by forming a superconducting PdSn alloy.     

A Compendium on the NIST Radionuclidic Assays of the Massic Activity of 63Ni and 55Fe Solutions Used for an International Intercomparison of Liquid Scintillation Spectrometry Techniques

The National Institute of Standards and Technology recently participated in an international measurement intercomparison for ⁶³Ni and ⁵⁵Fe, which was conducted amongst principal national radionuclidic metrology laboratories. The intercomparison was sponsored by EUROMET, and was primarily intended to evaluate the capabilities of liquid scintillation (LS) spectrometry techniques for standardizing nuclides that decay by low-energy β-emission (like ⁶³Ni) and by low-Z (atomic number) electron capture (like ⁵⁵Fe). The intercomparison findings exhibit a very good agreement for ⁶³Ni amongst the various participating laboratories, including that for NIST, which suggests that the presently invoked LS methodologies are very capable of providing internationally-compatible standardizations for low-energy β-emitters. The results for ⁵⁵Fe are in considerably poorer agreement, and demonstrated the existence of several unresolved problems. It has thus become apparent that there is a need for the various international laboratories to conduct rigorous, systematic evaluations of their LS capabilities in assaying radionuclides that decay by low-Z electron capture.     

Evidence for an intermediate state in the production of energetic neutral excitations in He II

It has been shown that energetic neutral excitations are produced when a tritium (^– emitter) source is immersed in He II. These neutrals have the same characteristics as those observed by Surko and Reif for a ²¹⁰ Po ( emitter) source. However, a strong electric field in the ionization region of the source is required in the tritium case to produce neutrals. Using this effect it is possible to produce pulses of neutrals and obtain information about their physical properties. We suggest a three-level decay scheme with an intermediate state to explain our experimental results.This work was supported by the National Science Foundation (GP-29659).Tektronix Fellow.Alfred P. Sloan Fellow.     

Analyzing the ZnO and CH₃NH₃PbI₃ as Emitter Layer for Silicon Based Heterojunction Solar Cells

Today, it has become an important task to modify existing traditional silicon-based solar cell factory to produce high-efficiency silicon-based heterojunction solar cells, at a lower cost. Therefore, the aim of this paper is to analyze CH₃NH₃PbI₃ and ZnO materials as an emitter layer for p-type silicon wafer-based heterojunction solar cells. CH₃NH₃PbI₃ and ZnO can be synthesized using the cheap Sol-Gel method and can form n-type semiconductor. We propose to combine these two materials since CH₃NH₃PbI₃ is a great light absorber and ZnO has an optimal complex refractive index which can be used as antireflection material. The photoelectric parameters of n-CH₃NH₃PbI₃/p-Si, n-ZnO/p-Si, and n-Si/p-Si solar cells have been studied in the range of 20–200 nm of emitter layer thickness. It has been found that the short circuit current for CH₃NH₃PbI₃/p-Si and n-ZnO/p-Si solar cells is almost the same when the emitter layer thickness is in the range of 20–100 nm. Additionally, when the emitter layer thickness is greater than 100 nm, the short circuit current of CH₃NH₃PbI₃/p-Si exceeds that of n-ZnO/p-Si. The optimal emitter layer thickness for n-CH₃NH₃PbI₃/p-Si and n-ZnO/p-Si was found equal to 80 nm. Using this value, the short-circuit current and the fill factor were estimated around 18.27 mA/cm² and 0.77 for n-CH₃NH₃PbI₃/p-Si and 18.06 mA/cm² and 0.73 for n-ZnO/p-Si. Results show that the efficiency of n-CH₃NH₃PbI₃/p-Si and n-ZnO/p-Si solar cells with an emitter layer thickness of 80 nm are 1.314 and 1.298 times greater than efficiency of traditional n-Si/p-Si for the same sizes. These findings will help perovskites materials to be more appealing in the PV industry and accelerate their development to become a viable alternative in the renewable energy sector.     

ZrO2微粉表面化学镀镍动力学研究

化学镀法制备Ni包覆ZrO     

Beta spectrum studies with cryogenic micro-calorimeters

Low energy beta spectra are studied with sources encapsulated in a superconducting Sn absorber. An NTD germanium thermistor measures the temperature transient (5 msec) caused by individual beta decays, and the total energy not given to the neutrino is determined with a resolution of 0.5 keV (FWHM) and a threshold of 5 keV. The response function is determined from the mono-energetic electron capture and internal conversion source¹⁰⁹ Cd, both separately and simultaneously with the beta spectrum. The endpoint of the unique first-forbidden decay¹⁰⁷ Pd ¹⁰⁷ Ag+e ^–+ _e is found to be37.5±0.1 keV. High statistics results are compared to the unique first-forbidden shape and the atomic exchange correction. The latter is seen for the first time. Preliminary results of a search for heavy neutrino admixtures are0.15±0.33%.     

A CVD Process for Producing Atomic Current Sources Based on <Superscript>63</Superscript>Ni

A CVD process was developed for producing ⁶³Ni-based atomic batteries by deposition of active ⁶³Ni layers onto semiconductor silicon supports. Tetrakis(trifluorophosphine)nickel synthesized from ⁶³Ni metal and phosphorus trifluoride was used as the volatile precursor. The influence of the support temperature and working pressure on the characteristics of the ⁶³Ni coating was examined.     

Studies on the Properties of Manganese Substituted Nickel Ferrite Nanoparticles

Mn²⁺-substituted Ni ferrite nanoparticles were synthesized by sol-gel auto combustion method. The synthesized samples were annealed at 800 ^°C and characterization studies were carried out by XRD, VSM, electron paramagnetic resonance (EPR), field emission scanning electron microscopy (FE-SEM) and FT-IR spectroscopy. The XRD patterns revealed that Mn ²⁺-substituted Ni ferrite crystallizes in cubic spinel phase and addition of α-Fe ₂ O ₃ phase was also observed. The average crystallite sizes were found to be from 42 to 56 nm using a Scherer equation. The coercivity and remanent magnetization decreases when Mn ²⁺ ion concentration is increased. The EPR spectrum shows the phase homogeneity of the samples. The FE-SEM images revealed that particles are both spherical in shape and particle sizes varied from 22 to 41 nm. The FT-IR spectrum confirmed the two main metal ion vibrations of nickel ferrite near 550 to 560 cm ^?1 (A site) and 441 to 460 cm ^?1 (B site).     

Silicon heterojunction solar cells: Optimization of emitter and contact properties from analytical calculation and numerical simulation

The key constituent of silicon heterojunction solar cells, the amorphous silicon/crystalline silicon heterojunction (a-Si:H/c-Si), offers a high open-circuit voltage (V_oc) potential providing that both the interface defect passivation and the band bending in the c-Si absorber are sufficient. We detail here analytical calculations of the equilibrium band bending in c-Si (ψ_c-Si) in Transparent Conductive Oxide (TCO)/a-Si:H emitter/c-Si absorber structures. We studied the variation of some electronic parameters (density of states, work function) according to relevant experimental values. This study introduces a discussion on the optimization of the doped emitter layer in relation with the work function of the TCO. In particular, we argue on the advantage of having a highly defective (p)a-Si:H emitter layer that maximizes ψ_c-Si and reduces the influence of the TCO on V_oc.     

Microgrid Electrode for Si Microwire Solar Cells with a Fill Factor of Over 80%

Here, a novel microgrid top electrode for highly efficient radial‐junction Si microwire solar cells is demonstrated. The microgrid electrode minimizes optical and electrical losses, thus ensuring proper function of the shallow (sheet resistance of ≈100 Ω sq⁻¹) junction emitter. This leads to effective collection of the photocarriers from the shallow junction emitter through the top electrode without severe Auger/surface recombination, improving the overall power conversion efficiency of the Si microwire solar cell. With an optimized microgrid structure, 1 cm² microwire solar cells show a conversion efficiency of up to 16.5%, with an open‐circuit voltage of 565.2 mV and a short‐circuit current density of 35.9 mA·cm⁻²; this conversion efficiency is 72% higher than that of solar cells with an edge electrode (9.6%). Further, an ≈1 μm thick Ni electrode that is formed by electroplating considerably reduces the metal and contact resistances, which reproducibly yields a fill factor of over 80% (max 81.2%). Thus, the use of a novel microgrid to construct an ideal metal/emitter interface presents a unique opportunity to develop highly efficient microwire solar cells.     

High ductilities in physically vapor-deposited nickel

Two thick films of physically vapor-deposited Ni were prepared on either side of the Movchan-Demchishin T₁ transition temperature. Both deposits were fine grained and columnar, but the lower temperature deposit contained a fine dispersion of pores. During high temperature deformation, the fully dense deposit behaved erratically owing to abnormal grain growth. The porous deposit transformed to a microstructure consisting of fine equiaxed grains interspersed with voids. This transformed structure deforms by grain boundary sliding. The measured activation energy is 116 kJ mol^?1 corresponding to grain boundary self-diffusion. The creep stress exponent is found to be 3, and the grain size exponent is -1. This porous physically vapor-deposited Ni attains steady state elongations that are far superior to those of conventionally processed or larger-grained Ni.     

Development of Metallic Magnetic Calorimeters for High Precision Measurements of Calorimetric 187Re and 163Ho Spectra

The measurement of calorimetric spectra following atomic weak decays, beta?(β) and electron capture (EC), of nuclides having a very low Q-value, can provide an impressively high sensitivity to a non-vanishing neutrino mass. The achievable sensitivity in this kind of experiments is directly connected to the performance of the used detectors. In particular an energy resolution of a few eV and a pulse formation time well below 1?μs are required. Low temperature Metallic Magnetic Calorimeters (MMCs) for soft X-rays have already shown an energy resolution of 2.0?eV FWHM and a pulse rise-time of about 90?ns for fully micro-fabricated detectors. We present the use of MMCs for high precision measurements of calorimetric spectra following the β-decay of ¹⁸⁷Re and the EC of ¹⁶³Ho. We show results obtained with detectors optimized for ¹⁸⁷Re and for ¹⁶³Ho experiments respectively. While the detectors equipped with superconducting Re absorbers have not yet reached the aimed performance, a first detector prototype with a Au absorber having implanted ¹⁶³Ho ions already shows excellent results. An energy resolution of 12?eV FWHM and a rise time of 90?ns were measured.     

Development of cryogenic alpha spectrometers using metallic magnetic calorimeters

Cryogenic particle detectors have recently been adopted in radiation detection and measurement because of their high energy resolution. Many of these detectors have demonstrated energy resolutions better than the theoretical limit of semiconductor detectors. We report the development of a micro-fabricated magnetic calorimeter coupled to a large-area particle absorber. It is based on a planar, 1 mm² large paramagnetic temperature sensor made of sputtered Au:Er, which covers a superconducting meander-shaped pickup coil coupled to a low-noise dc-SQUID to monitor the magnetization of the sensor. A piece of gold foil of 2.5×2.5×0.07 mm³ was glued to the Au:Er film to serve as an absorber for incident alpha particles. The detector performance was investigated with an ²⁴¹Am source. The signal size comparison for alpha and gamma peaks with a large difference in energy demonstrated that the detector had good linear behavior. An energy resolution of 2.83±0.05 keV in FWHM was obtained for 5.5 MeV alpha particles.     

Investigation of microstructures and tensile properties of a Sn-Cu lead-free solder alloy

In recent years, the pollution of environment from lead (Pb) and Pb-containing compounds in microelectronic devices attracts more and more attentions in academia and industry, the lead-free solder alloys begin to replace the lead-based solders in packaging process of some devices and components. In this work, microstructures and mechanical properties of the lead-free solder alloy Sn99.3Cu0.7(Ni) are investigated. This paper will compare the mechanical properties of the lead-based with lead-free solder alloys (Sn99.3Cu0.7(Ni) and 63Sn37Pb). The tensile tests of lead-based and lead-free solder alloys (Sn99.3Cu0.7(Ni) and Sn63Pb37) were conducted at room and elevated temperature at constant strain rate; the relevant tensile properties of Sn99.3Cu0.7(Ni) and Sn63Pb37 were obtained. Specifically, the tensile strength of this lead-free solder- Sn99.3Cu0.7(Ni) in 25^∘C, 50^∘C, 75^∘C, 100^∘C, 125^∘C was investigated; and it was found that tensile strength of the lead-free solder decreased with the increasing test temperature at constant strain rate, showing strong temperature dependence. The lead-free solder alloy Sn99.3Cu0.7(Ni) was found to have favorable mechanical properties and it may be able to replace the lead-based solder alloy such as Sn63Pb37 in the packaging processes in microelectronic industry.     

Effect of sintering temperature on the emission-spectrum-shape-evolution of Sr<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript> phosphor

Color rendering index and color temperature are the key factors for the LEDs application. The two points are closely related to the emission spectrum shape of phosphors. As the key factors for the LEDs application, both the above aspects are closely dependent on the emission spectrum shape of phosphors. In this study, the emission spectrum shape has been adjusted via a home designed route. A combination of structural, morphological, and optical characterization techniques has been used to study the shape evolution mechanism. The structural results show that the Sr₂SiO₄ phase has not been changed with the sintering temperature increasing, but the emission spectrum shape has changed dramatically, meanwhile, the colorimetric coordinate moves from blue-green to green region. Gaussian fitting method has been used to treat the emission spectrum, and the as-obtained results indicate the emission spectrum contains two single bands, which come from the 4f⁷(⁷S_7/2)–4f⁶(⁷F_J)5d¹ transition of Eu²⁺ on the different Sr sites in the Sr₂SiO₄ crystal. The intensity of the two single bands is driven by sintering temperature, because of the difference between the energy barrier of the Eu²⁺ occupying the different Sr sites in the matrix crystal. Moreover, the mechanism of the above phenomenon has also been studied by means of first principles method, and the obtained results agree well with the former deduction.