426 research outputs found
Design and commissioning of a timestamp-based data acquisition system for the DRAGON recoil mass separator
The DRAGON recoil mass separator at TRIUMF exists to study radiative proton
and alpha capture reactions, which are important in a variety of astrophysical
scenarios. DRAGON experiments require a data acquisition system that can be
triggered on either reaction product ( ray or heavy ion), with the
additional requirement of being able to promptly recognize coincidence events
in an online environment. To this end, we have designed and implemented a new
data acquisition system for DRAGON which consists of two independently
triggered readouts. Events from both systems are recorded with timestamps from
a MHz clock that are used to tag coincidences in the earliest possible
stage of the data analysis. Here we report on the design, implementation, and
commissioning of the new DRAGON data acquisition system, including the
hardware, trigger logic, coincidence reconstruction algorithm, and live time
considerations. We also discuss the results of an experiment commissioning the
new system, which measured the strength of the
keV resonance in the NeNa radiative proton
capture reaction.Comment: 11 pages, 7 figures, accepted for publication in EPJ A "tools for
experiment and theory
Double-beta decay Q values of 130Te, 128Te, and 120Te
The double-beta decay Q values of 130Te, 128Te, and 120Te have been
determined from parent-daughter mass differences measured with the Canadian
Penning Trap mass spectrometer. The 132Xe-129Xe mass difference, which is
precisely known, was also determined to confirm the accuracy of these results.
The 130Te Q value was found to be 2527.01(32) keV which is 3.3 keV lower than
the 2003 Atomic Mass Evaluation recommended value, but in agreement with the
most precise previous measurement. The uncertainty has been reduced by a factor
of 6 and is now significantly smaller than the resolution achieved or foreseen
in experimental searches for neutrinoless double-beta decay. The 128Te and
120Te Q values were found to be 865.87(131) keV and 1714.81(125) keV,
respectively. For 120Te, this reduction in uncertainty of nearly a factor of 8
opens up the possibility of using this isotope for sensitive searches for
neutrinoless double-electron capture and electron capture with positron
emission.Comment: 5 pages, 2 figures, submitted to Physical Review Letter
Mass measurements near the -process path using the Canadian Penning Trap mass spectrometer
The masses of 40 neutron-rich nuclides from Z = 51 to 64 were measured at an
average precision of using the Canadian Penning Trap mass
spectrometer at Argonne National Laboratory. The measurements, of fission
fragments from a Cf spontaneous fission source in a helium gas catcher,
approach the predicted path of the astrophysical process. Where overlap
exists, this data set is largely consistent with previous measurements from
Penning traps, storage rings, and reaction energetics, but large systematic
deviations are apparent in -endpoint measurements. Differences in mass
excess from the 2003 Atomic Mass Evaluation of up to 400 keV are seen, as well
as systematic disagreement with various mass models.Comment: 15 pages, 16 figures. v2 updated, published in Physical Review
C+O sub-barrier radiative capture cross-section measurements
We have performed a heavy ion radiative capture reaction between two light
heavy ions, C and O, leading to Si. The present experiment
has been performed below Coulomb barrier energies in order to reduce the phase
space and to try to shed light on structural effects. Obtained -spectra
display a previously unobserved strong feeding of intermediate states around 11
MeV at these energies. This new decay branch is not fully reproduced by
statistical nor semi-statistical decay scenarii and may imply structural
effects. Radiative capture cross-sections are extracted from the data.Comment: 4 pages, 7 figures, to appear as proceedings of FUSION 2011
conference at St-Malo, Franc
Measurement of radiative proton capture on F 18 and implications for oxygen-neon novae reexamined
Background: The rate of the F18(p,γ)Ne19 reaction affects the final abundance of the radioisotope F18 ejected from novae. This nucleus is important as its abundance is thought to significantly influence the first-stage 511-keV and continuum γ-ray emission in the aftermath of novae. No successful measurement of this reaction existed prior to this work, and the rate used in stellar models had been calculated based on incomplete information from contributing resonances. Purpose: Of the two resonances thought to provide a significant contribution to the astrophysical reaction rate, located at Ec.m.=330 and 665 keV, the former has a radiative width estimated from the assumed analog state in the mirror nucleus, F19, while the latter resonance does not have an analog state assignment, resulting in an arbitrary radiative width being assumed. As such, a direct measurement was needed to establish what role this resonance plays in the destruction of F18 at nova temperatures. This paper extends and takes the place of a previous Letter which reported the strength of the Ec.m.=665 keV resonance. Method: The DRAGON recoil separator was used to directly measure the strength of the important 665-keV resonance in this reaction, in inverse kinematics, by observing Ne19 reaction products. A radioactive F18 beam was provided by the ISAC facility at TRIUMF. R-matrix calculations were subsequently used to evaluate the significance of the results at astrophysical energies. Results: We report the direct measurement of the F18(p,γ)Ne19 reaction with the reevaluation of several detector efficiencies and the use of an updated Ne19 level scheme in the reaction rate analysis. The strength of the 665-keV resonance (Ex=7.076 MeV) is found to be an order of magnitude weaker than currently assumed in nova models. An improved analysis of the previously reported data is presented here, resulting in a slightly different value for the resonance strength. These small changes, however, do not alter the primary conclusions. Conclusions: Reaction rate calculations definitively show that the 665-keV resonance plays no significant role in the destruction of F18 at nova temperatures
Synthetic routes, characterization and photophysical properties of luminescent, surface functionalized nanodiamonds
The functionalization of small diameter (ca. 50 nm) polycarboxylated nanodiamond particles using amide coupling methodologies in both water and acetonitrile solvent has been investigated. In this manner, the surfaces of nanodiamond particles were adorned with different luminescent moieties, including a green fluorescent 1,8-naphthalimide species (Nap-1), and a red emitting ruthenium(II) tris-bipyridine complex (Ru-1), as well as dual functionalization with both luminophores. Comprehensive characterization of the surface functionalized nanodiamonds has been achieved using a combination of dynamic light scattering, nanoparticle tracking analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, zeta potential measurements, microwave plasma atomic emission spectroscopy and time-resolved photophysics. The tendency of the functionalized nanodiamonds to aggregate reflects the degree of surface substitution, yielding small aggregates with typical particle sizes ca. 150 nm. This is likely to be driven by the reduction of the zeta potential, concomitant with the conversion of surface charged carboxylate groups to neutral amide functions. The results show that luminescent nanodiamond materials can be synthesised with tuneable photophysical properties
The ethics of uncertainty for data subjects
Modern health data practices come with many practical uncertainties. In this paper, I argue that data subjects’ trust in the institutions and organizations that control their data, and their ability to know their own moral obligations in relation to their data, are undermined by significant uncertainties regarding the what, how, and who of mass data collection and analysis. I conclude by considering how proposals for managing situations of high uncertainty might be applied to this problem. These emphasize increasing organizational flexibility, knowledge, and capacity, and reducing hazard
The abundance of 44Ti in core collapse supernovae : Measuring the 44Ti(α, p)47V reaction
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