Activity determination of 133Xe by gamma-ray spectrometry

As both ¹³³Xe and ¹³³Ba decay to the same daughter nucleus ¹³³Cs, the activity of a ¹³³Xe source can be determined spectrometrically by comparing the gamma-ray count-rate of the 81 keV full energy peak from ¹³³Xe with the same peak of a ¹³³Ba standard source. By choosing the same gamma transition in both cases, the measuring uncertainty is considerably reduced.     

Design and construction of a high pressure xenon time projection chamber

The design and construction of a 300 1 high pressure xenon gas time projection chamber (TPC) is discussed. This detector has been built to perform a sensitive search for double beta decay of ¹³⁶Xe.     

The COBRA double-beta decay experiment

The COBRA experiment aims to use a large quantity of Cadmium–Zinc–Telluride (CdZnTe) semiconductor detectors to search for neutrinoless double-beta decay (0υββ). The current status of the experiment is discussed, and new limits on several double-beta modes are presented. Future plans for a large-scale experiment are also described.     

Concept of Metallic Magnetic Calorimeters for Rare Event Search in the LUMINEU Project

The project LUMINEU is mainly aiming at the search for neutrinoless double-beta decay of the candidate nuclide \(^{100}\) Mo using cryogenic ZnMoO \(_4\) detectors with simultaneous heat and scintillation light detection for radioactive background rejection. It also includes some development for dark matter search using cryogenic Ge detectors with simultaneous heat and ionization detection for background rejection. For both cases, metallic magnetic calorimeters (MMCs) are studied among several thermometer types. In double-beta decay search, the intrinsically fast response of MMCs reading out the light detector may allow for a very fast signal rise time and help to reduce the potential background due to pile-up of two-neutrino double beta decay events. In dark matter search, MMCs reading out the heat channel may improve the energy resolution with respect to the standard NTD Ge thermistor readout and hence the sensitivity of the detectors for low-mass WIMPs.     

Tunable color emission and afterglow in CaGa2S4: Eu, Ho phosphor

The tunable color emission and persistent luminescence lifetime in phosphor CaGa₂S₄: Eu²⁺, Ho³⁺ were achieved through the introduction of alkaline earth elements Mg, Sr and Ba, in which the Ca was partially replaced. The duration of the persistent luminescence of the material CaGa₂S₄: Eu²⁺, Ho³⁺ was remarkably shortened as Al was introduced, substituting for Ga. The luminescent properties were investigated via thermo-luminescence (TL) glow curves, phosphorescence spectra and decay time curves. These results show that vast changes in trap levels and charge density takes place with introduction of other alkaline earth elements or Al. Trap depths and the trap density were also evaluated by simple methodologies.     

Ultrapurification of isotopically enriched materials for 40Ca100MoO4 crystal growth

This paper describes ultrapurification of isotopically enriched calcium and molybdenum compounds and ⁴⁰Ca¹⁰⁰MoO₄ calcium molybdate growth charge in order to remove radioactive uranium, thorium, and radium impurities. ⁴⁰Ca¹⁰⁰MoO₄ single crystals grown from such charges are needed for the fabrication of scintillator elements of the cryogenic detector for the AMoRE project: a search for ¹⁰⁰Mo neutrino-less double-beta decay.     

Study of 132Xe ion tracks in a soda glass detector

Soda glass track detectors have been exposed to ¹³²Xe ion cyclotron beams at the Joint Institute for Nuclear Research, Dubna (USSR). The etch pit diameters are measured for different etching times after etching the detectors in a ‘new etchant’ free of the adverse effect of the etch product layer. The computed values of energy loss, $\text{d}\text{E}\text{d}\text{x}$, in soda glass have been correlated with the track diameter. The energy resolution of soda glass and the critical angle for etching of ¹³²Xe ion tracks in glass detectors have also been determined. The maximum etched track length of Xe ions in soda glass has been compared with the theoretical range. The effects of different annealing conditions on the bulk etch rate, the track etch rate, the etching efficiency, the track diameter and on the range of Xe ions in soda glass have been studied.     

Design of the Ion Trap and Vacuum System for <Superscript>171</Superscript>Yb-ion Optical Frequency Standard

We are developing a frequency standard based on the ultra-narrow electric octupole transition of the ytterbium-ion (¹⁷¹Yb⁺), which is in the optical wavelength region. In this article, we describe optimized design of our end-cap type Paul trap which will be used for trapping single ions for precision frequency metrology. Selection of the materials for fabricating different parts of the trap assembly is also described. Customized design of the ultra-high vacuum chamber, which houses the ion trap, oven producing ytterbium atomic beam, compensation electrodes and high numerical aperture fluorescence collection lens together with four pairs of optical viewports is lastly described.     

Comparison of the low-energy decay mechanisms of C70 and C70

Low-energy multiple-collisional-excitation experiments have been performed on C₇₀⁺ and C₇₀⁻ at the ClusterTrap apparatus. The ions are stored in a Penning trap where they are excited via radial dipolar excitation before undergoing collisions with neutral argon atoms. The dominant decay mechanism for C₇₀⁺ (sequential loss of C₂-units) is compared with the dominant decay process of C₇₀⁻ (thermionic electron emission). A simple model based on the decay rates of the clusters is found to be in reasonable agreement with the experimental data obtained for the fragmentation process of the cationic fullerenes. The same model, when applied to the anions is observed to be in less agreement with the experimental results.     

Energy measurement of gamma rays from 133Ba decay: Consistency with cascade cross-over relations

Energies of gamma rays from ¹³³Ba decay were measured with HPGe and Ge(Li) spectrometers in two independent measurements. Long term electronic instabilities were followed. A statistical procedure using constraint conditions was adopted to fit energy values compatible to cascade cross-over relations in ¹³³Cs.     

Decay of long-lived 129I

The decay of the long-lived fission nuclide ¹²⁹I was reinvestigated with a high-resolution HPGe detector. Accurate values of the energy and the absolute intensity of the 39.58 keV γ-rays are given together with Xe X-ray intensities. The K internal conversion coefficient of the M1 line is also deduced.     

Defect Engineering for Modulating the Trap States in 2D Photoconductors

Defect‐induced trap states are essential in determining the performance of semiconductor photodetectors. The de‐trap time of carriers from a deep trap can be prolonged by several orders of magnitude as compared to shallow traps, resulting in additional decay/response time of the device. Here, it is demonstrated that the trap states in 2D ReS₂ can be efficiently modulated by defect engineering through molecule decoration. The deep traps that greatly prolong the response time can be mostly filled by protoporphyrin molecules. At the same time, carrier recombination and shallow traps in‐turn play dominant roles in determining the decay time of the device, which can be several orders of magnitude faster than the as‐prepared device. Moreover, the specific detectivity of the device is enhanced (as high as ≈1.89 × 10¹³ Jones) due to the significant reduction of the dark current through charge transfer between ReS₂ and molecules. Defect engineering of trap states therefore provides a solution to achieve photodetectors with both high responsivity and fast response.     

Isolation of actinium-225 for medical purposes

A procedure is described for isolation and purification of ²²⁵Ac as a ²²⁹Th daughter decay product using ion exchange. The process includes the following steps: separation of ²²⁹Th from a mixture of ²²⁵Ac and ²²⁵Ra (²²⁵Ac precursor) using an anion-exchange resin; separation of ²²⁵Ac and ²²⁵Ra using a cation-exchange resin; purification of ²²⁵Ac to remove inactive impurity cations (primarily Fe) using an anion-exchange resin; final purification of the product on a column with a cation-exchange resin.     

Measurement of the Neutron Lifetime by Counting Trapped Protons

We measured the neutron decay lifetime by counting in-beam neutron decay recoil protons trapped in a quasi-Penning trap. The absolute neutron beam fluence was measured by capture in a thin ⁶LiF foil detector with known efficiency. The combination of these measurements gives the neutron lifetime: τ_n = (886.8 ± 1.2 ± 3.2) s, where the first (second) uncertainty is statistical (systematic) in nature. This is the most precise neutron lifetime determination to date using an in-beam method.     

Switchable Xe/Kr Selectivity in a Hofmann-Type Metal–Organic Framework via Temperature-Responsive Rotational Dynamics

The development of adsorbents for Kr and Xe separation is essential to meet industrial demands and for energy conservation. Although a number of previous studies have focused on Xe-selective adsorbents, stimuli-responsive Xe/Kr-selective adsorbents still remain underdeveloped. Herein, a Hofmann-type framework Co(DABCO)[Ni(CN)₄] (referred to as CoNi-DAB ; DABCO = 1,4-diazabicyclo[2,2,2]octane) that provides a temperature-dependent switchable Xe/Kr separation performance is reported. CoNi-DAB showed high Kr/Xe (0.8/0.2) selectivity with significant Kr adsorption at 195 K as well as high Xe/Kr (0.2/0.8) selectivity with superior Xe adsorption at 298 K. Such adsorption features are associated with the temperature-dependent rotational configuration of the DABCO ligand, which affects the kinetic gate-opening temperature of Xe and Kr. The packing densities of Xe (2.886 g cm⁻³ at 298 K) and Kr (2.399 g  cm⁻³ at 195 K) inside the framework are remarkable and comparable with those of liquid Xe (3.057 g cm⁻³) and liquid Kr (2.413 g cm⁻³), respectively. Breakthrough experiments confirm the temperature-dependent reverse separation performance of CoNi-DAB at 298 K under dry and wet (88% relative humidity) conditions and at 195 K under dry conditions. The unique adsorption behavior is also verified through van der Waals (vdW)-corrected density functional theory (DFT) calculations and nudged elastic band (NEB) simulations.     

A xenon gas purity monitor for EXO

We discuss the design, operation, and calibration of two versions of a xenon gas purity monitor (GPM) developed for the EXO double beta decay program. The devices are sensitive to concentrations of oxygen well below 1 ppb at an ambient gas pressure of one atmosphere or more. The theory of operation of the GPM is discussed along with the interactions of oxygen and other impurities with the GPM's tungsten filament. Lab tests and experiences in commissioning the EXO-200 double beta decay experiment are described. These devices can also be used on other noble gases.     

129Xe n.m.r. of Y3+-, La3+-, and Ce3+-exchanged X zeolites

The ¹²⁹Xe n.m.r. spectrum of adsorbed xenon has been used to locate the Y³⁺, Ce³⁺, and La³⁺ ions that are exchanged into NaX zeolite. The chemical shift of xenon adsorbed on yttrium-X zeolite follows a concave plot against the adsorbed xenon concentration, very similar to the previous ¹²⁹Xe n.m.r. study of Mg²⁺, Ca²⁺, and Ni²⁺ in Y zeolites. This result suggests strong adsorption of xenon on the Y³⁺ ion located inside the zeolite supercage. In contrast, the ¹²⁹Xe n.m.r. chemical shift for the CeX and LaX zeolites indicates that the cations are located in hexagonal prisms or sodalite cages inaccessible to the xenon atoms. The example of the Y³⁺ cation proves that not all trivalent cations migrate outside the supercages during thermal treatment of the solid.     

Studies on separation of Cs/Ba and Zn/Cu binary mixtures on zirconium antimonate as ion exchanger

Zirconium antimonate (ZrSb) ion exchanger was prepared. Distribution coefficients of metal ions on ZrSb ion exchanger in solutions of various acids (hydrochloric, nitric, acetic, citric, ascorbic) and salts (sodium chloride and sodium nitrate) were determined to evaluate the ion exchange behavior and selectivity to specific ions. ZrSb, as compared to other inorganic ion exchangers, showed increased thermal and chemical stability. ZrSb is an efficient and promising ion exchanger for preparation of ¹³⁷Cs/^137m Ba and ⁶²Zn/⁶²Cu radioisotope generators.     

Reduction of radioactive waste volume using selective crystallization processes

Satisfactory combination of small volume of compositions incorporating ¹³⁷Cs, ⁹⁰Sr, and ²⁴⁴Cm with the admissible heat release rate can be attained by crystallization of definite compounds from high-level solutions. The concentrate of cesium isotopes is obtained by their precipitation in the form of phosphoromolybdate and, after additional storage, in the form of CsMgPO₄·6H₂O; the concentrate of Am, Cm, Sr, Ba, and Ln can be obtained using the known but somewhat modified (increased pH of solution) OXAL process. It is appropriate to remove Am and long-lived Cm isotopes from this concentrate also after storage ensuring the decay of ⁹⁰Sr and ²⁴⁴Cm. The remaining rare-earth elements with traces of Am and Cm and stable isotopes of Sr and Ba can be disposed of, e.g., in the form of a mineral-like phosphate.