31 research outputs found
Sinter-Resistant Gold-144 Iron(III) Oxide Core-Shell Structures: Synthesis, Characterization, and Application via Heterogeneous Catalysis
In the realm of catalysis, small nanoparticles have been an area of interest due to their high surface-to-volume ratio. This is even more so with gold nanoparticles in that gold only becomes catalytically active with small particles sizes. Thus, gold clusters are desirable given their uniformity, high surface-to-volume ratio, and high catalytic activity. Given the nature of small gold particles to sinter, it was found to be advantageous to protect the particles using a gold-metal oxide core-shell configuration. Core-shell heterostructures have been utilized as a catalyst that is thermally stable and exhibits a synergistic effect between core and shell, resulting in increased catalytic activity. The research contained in this document discusses the synthetic procedure of a gold-144 cluster using a variation of the Brust-Schiffrin method followed by an iron oxide coating via post-selective oxidative treatment to create a gold-144 iron oxide core-shell structure. Shell thickness is varied depending on the amount of iron precursor used and studied under the particle’s catalytic efficiency with carbon monoxide oxidation. The gold-144 iron oxide particles with Au:Fe mass ratios of 1:2, 1:4, and 1:6 were synthesized and then deposited onto silica via colloidal deposition. Using CO oxidation, each gold-144 iron oxide catalyst loaded onto silica gave varying degrees of full CO conversion depending on the thickness of the iron oxide layer. The 1:4 gold-144 iron oxide catalyst produced the best catalytic activity and was further investigated using 2-propanol conversion as well as thermal treatments using CO oxidation. Under CO oxidation, the 1:4 structure calcined at 300 degrees Celsius presented the best results, and the 1:4 ratio was still active at 100 degrees Celsius after thermal treatments. Under 2-propanol conversions, the data seems to suggest that core-shell structure provides a synergistic effect for acetone production, however, this cannot be concluded until further testing is accomplished
Precision measurement of Zn electron-capture decays with the KDK coincidence setup
Zn is a common calibration source, moreover used as a radioactive
tracer in medical and biological studies. In many cases, -spectroscopy
is a preferred method of Zn standardization, which relies directly on
the branching ratio of via electron capture (EC*). We measure the relative
intensity of this branch to that proceeding directly to the ground state
(EC) using a novel coincidence technique, finding
. Re-evaluating the decay
scheme of Zn by adopting the commonly evaluated branching ratio of
we obtain , and
I_\text{EC^0} = (48.50 \pm 0.06) \%. The associated 1115 keV gamma intensity
agrees with the previously reported NNDC value, and is now accessible with a
factor of ~2 increase in precision. Our re-evaluation removes reliance on the
deduction of this gamma intensity from numerous measurements, some of which
disagree and depend directly on total activity determination. The KDK
experimental technique provides a new avenue for verification or updates to the
decay scheme of Zn, and is applicable to other isotopes.Comment: Uses similar methodology to the 40K measurement by the KDK
Collaboration (Stukel et al PRL 2023, arXiv:2211.10319; Hariasz et al PRC
2023, arXiv:2211.10343), as such there may be some similarity in figures and
tex
Evidence for ground-state electron capture of K
Potassium-40 is a widespread isotope whose radioactivity impacts estimated
geological ages spanning billions of years, nuclear structure theory, and
subatomic rare-event searches - including those for dark matter and
neutrinoless double-beta decay. The decays of this long-lived isotope must be
precisely known for its use as a geochronometer, and to account for its
presence in low-background experiments. There are several known decay modes for
K, but a predicted electron-capture decay directly to the ground state
of argon-40 has never been observed, while theoretical predictions span an
order of magnitude. The KDK Collaboration reports on the first observation of
this rare decay, obtained using a novel combination of a low-threshold X-ray
detector surrounded by a tonne-scale, high-efficiency -ray tagger at
Oak Ridge National Laboratory. A blinded analysis reveals a distinctly nonzero
ratio of intensities of ground-state electron-captures () over
excited-state ones () of
(68% CL), with the null hypothesis rejected at 4 [Stukel et al.,
DOI:10.1103/PhysRevLett.131.052503]. This unambiguous signal yields a branching
ratio of
,
roughly half of the commonly used prediction. This first observation of a
third-forbidden unique electron capture improves understanding of low-energy
backgrounds in dark-matter searches and has implications for nuclear-structure
calculations. A shell-model based theoretical estimate for the
decay half-life of calcium-48 is increased by a factor of . Our
nonzero measurement shifts geochronological ages by up to a percent;
implications are illustrated for Earth and solar system chronologies.Comment: This is a companion submission to Stukel et al (KDK collaboration)
"Rare K decay with implications for fundamental physics and
geochronology" [arXiv:2211.10319; DOI: 10.1103/PhysRevLett.131.052503]. As
such, both texts share some figures and portions of text. This version
updates the text following its review and production proces
A novel experimental system for the KDK measurement of the K decay scheme relevant for rare event searches
Potassium-40 (K) is a long-lived, naturally occurring radioactive
isotope. The decay products are prominent backgrounds for many rare event
searches, including those involving NaI-based scintillators. K also
plays a role in geochronological dating techniques. The branching ratio of the
electron capture directly to the ground state of argon-40 has never been
measured, which can cause difficulty in interpreting certain results or can
lead to lack of precision depending on the field and analysis technique. The
KDK (Potassium (K) Decay (DK)) collaboration is measuring this decay. A
composite method has a silicon drift detector with an enriched, thermally
deposited K source inside the Modular Total Absorption Spectrometer.
This setup has been characterized in terms of energy calibration, gamma tagging
efficiency, live time and false negatives and positives. A complementary,
homogeneous, method is also discussed; it employs a KSrI:Eu
scintillator as source and detector.Comment: 20 pages, 24 figures, Submitted to NIM
Progress in Diamond Detector Development
Detectors based on Chemical Vapor Deposition (CVD) diamond have been used successfully in Luminosity and Beam Condition Monitors (BCM) in the highest radiation areas of the LHC. Future experiments at CERN will accumulate an order of magnitude larger fluence. As a result, an enormous effort is underway to identify detector materials that can operate under fluences of 1 · 1016 n cm−2 and 1 · 1017 n cm−2. Diamond is one candidate due to its large displacement energy that enhances its radiation tolerance. Over the last 30 years the RD42 collaboration has constructed diamond detectors in CVD diamond with a planar geometry and with a 3D geometry to extend the material's radiation tolerance. The 3D cells in these detectors have a size of 50 µm×50 µm with columns of 2.6 µm in diameter and 100 µm×150 µm with columns of 4.6 µm in diameter. Here we present the latest beam test results from planar and 3D diamond pixel detectors
A study of the radiation tolerance of cvd diamond to 70 mev protons, fast neutrons and 200 mev pions
We measured the radiation tolerance of commercially available diamonds grown by the Chemical Vapor Deposition process by measuring the charge created by a 120 GeV hadron beam in a 50 μm pitch strip detector fabricated on each diamond sample before and after irradiation. We irradiated one group of samples with 70 MeV protons, a second group of samples with fast reactor neutrons (defined as energy greater than 0.1 MeV), and a third group of samples with 200 MeV pions, in steps, to (8.8±0.9) × 10 protons/cm, (1.43±0.14) × 10 neutrons/cm, and (6.5±1.4) × 1014 pions/cm, respectively. By observing the charge induced due to the separation of electron–hole pairs created by the passage of the hadron beam through each sample, on an event-by-event basis, as a function of irradiation fluence, we conclude all datasets can be described by a first-order damage equation and independently calculate the damage constant for 70 MeV protons, fast reactor neutrons, and 200 MeV pions. We find the damage constant for diamond irradiated with 70 MeV protons to be 1.62±0.07(stat)±0.16(syst)× 10−18 cm/(pμm), the damage constant for diamond irradiated with fast reactor neutrons to be 2.65±0.13(stat)±0.18(syst)× 10−18 cm/(nμm), and the damage constant for diamond irradiated with 200 MeV pions to be 2.0±0.2(stat)±0.5(syst)× 10−18 cm/(πμm). The damage constants from this measurement were analyzed together with our previously published 24 GeV proton irradiation and 800 MeV proton irradiation damage constant data to derive the first comprehensive set of relative damage constants for Chemical Vapor Deposition diamond. We find 70 MeV protons are 2.60 ± 0.29 times more damaging than 24 GeV protons, fast reactor neutrons are 4.3 ± 0.4 times more damaging than 24 GeV protons, and 200 MeV pions are 3.2 ± 0.8 more damaging than 24 GeV protons. We also observe the measured data can be described by a universal damage curve for all proton, neutron, and pion irradiations we performed of Chemical Vapor Deposition diamond. Finally, we confirm the spatial uniformity of the collected charge increases with fluence for polycrystalline Chemical Vapor Deposition diamond, and this effect can also be described by a universal curve
Beam test results of 3D pixel detectors constructed with poly-crystalline CVD diamond
As a possible candidate for extremely radiation tolerant tracking devices we present a novel detector design - namely 3D detectors - based on poly-crystalline CVD diamond sensors with a pixel readout. The fabrication of recent 3D detectors as well their results in recent beam tests are presented. We measured the hit efficiency and signal response of two 3D diamond detectors with 50 × 50 μm cell sizes using pixel readout chip technologies currently used at CMS and ATLAS. In all runs, both devices attained efficiencies >98 % in a normal incident test beam of minimum ionising particles. The highest efficiency observed during the beam tests was 99.2 %