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Register a new userAlpha spectrometric characterization of thin $^{233}$U sources for $^{229text{(m)}}$Th production
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Four different techniques were applied for the production of $^{233}$U alpha recoil ion sources, providing $^{229}$Th ions. They were compared with respect to a minimum energy spread of the $^{229}$Th recoil ions, using the emitted alpha particles as an indicator. The techniques of Molecular Plating, Drop-on-Demand inkjet printing, chelation from dilute nitric acid solution on chemically functionalized silicon surfaces, and self-adsorption on passivated titanium surfaces were used. All fabricated sources were characterized by using alpha spectrometry, radiographic imaging, and scanning electron microscopy. A direct validation for the estimated recoil ion rate was obtained by collecting $^{228}$Th recoil ions from $^{232}$U recoil ion sources prepared by self-adsorption and Molecular Plating. The chelation and the self-adsorption based approaches appear most promising for the preparation of recoil ion sources delivering monochromatic recoil ions.
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Radioactive $^{233}$U alpha recoil sources are being considered for the production of a thorium ion source to study the low-energy isomer in $^{229}$Th with high-resolution collinear laser spectroscopy at the IGISOL facility of the University of Jyvaskyla. In this work two different $^{233}$U sources have been characterized via alpha and gamma spectroscopy of the decay radiation obtained directly from the sources and from alpha-recoils embedded in implantation foils. These measurements revealed rather low $^{229}$Th recoil efficiencies of only a few percent. Although the low efficiency of one of the two sources can be attributed to its inherent thickness, the low recoil efficiency of the second, thinner source, was unexpected. Rutherford backscattering spectrometry (RBS) was performed to investigate the elemental composition as a function of depth revealing a contamination layer on top of the thin source. The combination of spectroscopic methods proves to be a useful approach in the assessment of alpha recoil source performance in general.
Thin uniform arsenic targets suitable for high-fidelity cross section measurements in stacked-target experiments were prepared by electrodeposition of arsenic on titanium backings from aqueous solutions. Electrolytic cells were constructed and capable of arsenic deposits ranging in mass from approximately 1 to 29 mg (0.32-7.22 mg/cm$^2$, 0.57-12.62 $mu$m). Examination of electrodeposit surface morphology by scanning electron microscopy and microanalysis was performed to investigate the uniformity of produced targets. Brief studies of plating growth dynamics and structural properties through cyclic voltammetry were also undertaken. An alternative target fabrication approach by vapor deposition was additionally conducted. We further introduce a non-destructive characterization method for thin targets by neutron activation, which is independent of neutron flux shape, environmental factors, and source geometry, while correcting for any potential scatter or absorption effects.
Simultaneous measurement of phonon and light signatures is an effective way to reduce the backgrounds and increase the sensitivity of CUPID, a next-generation bolometric neutrinoless double-beta decay ($0 ubetabeta$) experiment. Light emission in tellurium dioxide (TeO$_2$) crystals, one of the candidate materials for CUPID, is dominated by faint Cherenkov radiation, and the high refractive index of TeO$_2$ complicates light collection. Positive identification of $0 ubetabeta$ events therefore requires high-sensitivity light detectors and careful optimization of light transport. A detailed microphysical understanding of the optical properties of TeO$_2$ crystals is essential for such optimization. We present a set of quantitative measurements of light production and transport in a cubic TeO$_2$ crystal, verified with a complete optical model and calibrated against a UVT acrylic standard. We measure the optical surface properties of the crystal, and set stringent limits on the amount of room-temperature scintillation in TeO$_2$ for $beta$ and $alpha$ particles of 5.3 and 8 photons / MeV, respectively, at 90% confidence. The techniques described here can be used to optimize and verify the particle identification capabilities of CUPID.
The Jiangmen Underground Neutrino Observatory will build the worlds largest liquid scintillator detector to study neutrinos from various sources. The 20 kt liquid scintillator will be stored in a $sim$600 t acrylic sphere with 35.4 m diameter due to the good light transparency, chemical compatibility and low radioactivity of acrylic. The concentration of U/Th in acrylic is required to be less than 1 ppt (10$^{-12}$ g/g) to achieve a low radioactive background in the fiducial volume of the JUNO detector. The mass production of acrylic has started, and the quality control requires a fast and reliable radioassay on U/Th in acrylic. We have developed a practical method of measuring U/Th in acrylic to sub-ppt level using the Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The U/Th in acrylic can be concentrated by vaporizing acrylic in a class 100 environment, and the residue will be collected and sent to ICP-MS for measuring U/Th. All the other chemical operation is done in a class 100 clean room, and the ICP-MS measurement is done in a class 1000 clean room. The recovery efficiency is studied by adding the natural nonexistent nuclei $^{229}$Th and $^{233}$U as the tracers. The resulting method detection limit (MDL) with 99% confidence can reach 0.02/0.06 pg $^{238}$U/$^{232}$Th /g acrylic with $sim$75% recovery efficiency. This equipment and method can not only be used for the quality control of JUNO acrylic, but also be further optimized for the radioassay on other materials with extremely low radioactivity, such as ultra-pure water and liquid scintillator.
The GERDA experiment at the Laboratori Nazionali del Gran Sasso (LNGS) searches for the neutrinoless double beta decay of 76-Ge. In view of the GERDA Phase II data collection, four new 228-Th radioactive sources for the calibration of the germanium detectors enriched in 76-Ge have been produced with a new technique, leading to a reduced neutron flux from ( alpha; n ) reactions. The gamma activities of the sources were determined with a total uncertainty of 4 percent using an ultra-low background HPGe detector operated underground at LNGS. The emitted neutron flux was determined using a low background LiI(Eu) detector and a 3-He counter at LNGS. In both cases, a reduction of about one order of magnitude with respect to commercially available 228-Th sources was obtained. Additionally, a specific leak test with a sensitivity to leaks down to 10 mBq was developed to investigate the tightness of the stainless steel capsules housing the sources after their use in cryogenic environment.
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