A new facility, the N = 126 factory, is currently under construction at Argonne National Laboratory. It will use multi-nucleon transfer reactions to create neutron-rich isotopes of very heavy ...elements for studies of interest to the formation of the A ∼ 195 abundance peak in the r-process. This region of the nuclear chart is difficult to access by standard fragmentation or spallation reactions and as a result has remained mostly unexplored. The nuclei of interest, very neutron-rich isotopes around Z = 70–95, will be produced by multi-nucleon exchange of a high intensity 10 MeV/u heavy-ion beam on the most neutron-rich stable isotopes of heavy elements such as 198Pt and 238U. This reaction mechanism can transfer a large number of neutrons and create very neutron-rich isotopes with larger than mb cross-section. The reaction mechanism is a nuclear surface process and the reaction products come out close to the grazing angle, which makes them very difficult to collect. The N = 126 factory circumvents this difficulty by using a unique large high-intensity RF gas catcher, similar to the one currently in operation at CARIBU, to collect the target-like reaction products and transform them into a low-energy beam that will then be mass separated with a medium resolution electromagnetic separator (ΔM/M ≃ 1/1500), followed by an RFQ buncher and an MR-TOF (ΔM/M ≃ 1/100,000) system. The extracted radioactive beams will be essentially pure and available at low-energy for mass measurements with the CPT mass spectrometer or decay study with the X-array.
•We develop a joint seat allocation and bid pricing mathematical formulation.•We obtain time-dependent bid prices with corresponding resource allocations.•We develop a column generation algorithm to ...solve large-scale problems.•We develop an efficient heuristic procedure for solving the NP-hard sub problem.
Firms selling perishable products use a variety of techniques to maximize revenue through the dynamic control of their inventories. One of the most powerful and simple approaches to address this issue consists of assigning threshold values (“bid prices”) to each resource, and to accept requests whenever their revenue exceeds the sum of the bid prices associated with its constituent resources. In this context, we propose a new customer choice-based mathematical program to estimate time-dependent bid prices. In contrast with most approaches from the current literature, ours is characterized by its flexibility. Indeed, it can easily embed technical and practical constraints that occur in most central reservation systems (CRS). To solve the model, we develop a column generation algorithm, in which the NP-hard subproblem is addressed via an efficient heuristic procedure. Our computational results illustrate the performance of the method, through comparisons with alternative proposals.
The Canadian Penning Trap mass spectrometer at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility was used to measure the masses of eight neutron-rich isotopes of Nd and Sm. These ...measurements are the first to push into the region of nuclear masses relevant to the formation of the rare-earth abundance peak at A∼165 by the rapid neutron-capture process. We compare our results with theoretical predictions obtained from "reverse engineering" the mass surface that best reproduces the observed solar abundances in this region through a Markov chain Monte Carlo technique. Our measured masses are consistent with the reverse-engineering predictions for a neutron star merger wind scenario.
The CARIBU gas catcher Savard, G.; Levand, A.F.; Zabransky, B.J.
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
06/2016, Letnik:
376, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The CARIBU upgrade of the ATLAS facility provides radioactive beams of neutron-rich isotopes for experiments at low and Coulomb barrier energies. It creates these beam using a large RF gas catcher ...that collects and cools fission fragments from an intense 252Cf fission source and transforms them into a low-emittance monoenergetic beam. This beam can then be purified, reaccelerated and delivered to experiments. This technique is fast and universal, providing access to all fission fragment species independently of their chemical properties. The CARIBU gas catcher has been built to operate at high ionization density and in the presence of the contamination from the source. A brief overview of the CARIBU concept is given below, together with a more detailed description of the CARIBU gas catcher and the performance it has now achieved.
SUMMARY
Irazú and Turrialba are a twin volcanic complex that marks a distinct stop in volcanism along the Central America volcanic arc. We present a new traveltime velocity model of the crust beneath ...Irazú and Turrialba volcanoes, Costa Rica, and interpret it considering the results of previous ambient noise tomographic inversions. Data were acquired by a temporary seismic network during a period of low activity of the Irazú–Turrialba volcanic complex in 2018–2019. Beneath the Irazú volcano, we observe low P-wave velocities (VP = 5 km s−1) and low velocity ratios (VP/VS = 1.6). In contrast, below the Turrialba volcano, we observe low S-wave velocities (VS = 3 km s−1) and a high VP/VS (= 1.85) anomaly. We found that locations of low VP and VS anomalies (−15 %) correspond well with shear wave velocity anomalies retrieved from ambient noise tomography. At shallower depths, we observe high VP and VS anomalies (+15 %) located between the summits of the volcanoes. Subvertical velocity anomalies are also observed at greater depths, with high VP and VS anomalies appearing at the lower limits of our models. We propose a complex structure of an intermediate magmatic reservoir, presenting multiphase fluid states of a liquid-to-gas transition beneath Irazú and a juvenile store of magmatic fluid beneath Turrialba, while shallow fluid transport provides evidence of magmatic–hydrothermal interactions.
We employ 130 low‐frequency earthquake (LFE) templates representing tremor sources on the plate boundary below southern Vancouver Island to examine LFE magnitudes. Each template is assembled from ...hundreds to thousands of individual LFEs, representing over 269,000 independent detections from major episodic‐tremor‐and‐slip (ETS) events between 2003 and 2013. Template displacement waveforms for direct P and S waves at near epicentral distances are remarkably simple at many stations, approaching the zero‐phase, single pulse expected for a point dislocation source in a homogeneous medium. High spatiotemporal precision of template match‐filtered detections facilitates precise alignment of individual LFE detections and analysis of waveforms. Upon correction for 1‐D geometrical spreading, attenuation, free surface magnification and radiation pattern, we solve a large, sparse linear system for 3‐D path corrections and LFE magnitudes for all detections corresponding to a single‐ETS template. The spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12–24 h of LFE activity during an ETS episode when tidal sensitivity is low. The remainder is released in bursts over several days, particularly as spatially extensive rapid tremor reversals (RTRs), during which tidal sensitivity is high. RTRs are characterized by large‐magnitude LFEs and are most strongly expressed in the updip portions of the ETS transition zone and less organized at downdip levels. LFE magnitude‐frequency relations are better described by power law than exponential distributions although they exhibit very high b values ≥∼5. We examine LFE moment‐duration scaling by generating templates using detections for limiting magnitude ranges (MW<1.5, MW≥2.0). LFE duration displays a weaker dependence upon moment than expected for self‐similarity, suggesting that LFE asperities are limited in fault dimension and that moment variation is dominated by slip. This behavior implies that LFEs exhibit a scaling distinct from both large‐scale slow earthquakes and regular seismicity.
Key Points
Moment magnitudes estimated for almost 270,000 LFE detections below southern Vancouver Island
Moment variation in space, time, and frequency is examined
LFE moment‐duration scaling is distinct from both slow earthquakes and regular seismicity
We present an apparatus for detection of cyclotron radiation yielding a frequency-based β± kinetic energy determination in the 5 keV to 2.1 MeV range, characteristic of nuclear β decays. The ...cyclotron frequency of the radiating β particles in a magnetic field is used to determine the β energy precisely. Our work establishes the foundation to apply the cyclotron radiation emission spectroscopy (CRES) technique, developed by the Project 8 Collaboration, far beyond the 18-keV tritium endpoint region. We report initial measurements of β–’s from 6He and β+’s from 19Ne decays to demonstrate the broadband response of our detection system and assess potential systematic uncertainties for β spectroscopy over the full (MeV) energy range. To our knowledge, this is the first direct observation of cyclotron radiation from individual highly relativistic β’s in a waveguide. Furthermore, this work establishes the application of CRES to a variety of nuclei, opening its reach to searches for new physics beyond the TeV scale via precision β-decay measurements.
An experiment was performed at Lawrence Berkeley National Laboratory's 88-in. Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two ...α-decay chains, produced via the ^{243}Am(^{48}Ca,xn)^{291-x}Mc reaction, that were separated by mass-to-charge ratio (A/q) and identified by the combined BGS+FIONA apparatus. One event occurred at A/q=284 and was assigned to ^{284}Nh (Z=113), the α-decay daughter of ^{288}Mc (Z=115), while the second occurred at A/q=288 and was assigned to ^{288}Mc. This experiment represents the first direct measurements of the mass numbers of superheavy elements, confirming previous (indirect) mass-number assignments.
For the past two decades the Canadian Penning Trap mass spectrometer (CPT) has been utilized to study various disciplines of nuclear physics through precision mass measurements. Since moving to the ...Californium Rare Isotope Breeder Upgrade (CARIBU) facility, the CPT experimental program has focused on neutron-rich nuclei whose masses may play an important role in the astrophysical r process. Through a recent upgrade of the detector system, the phase-imaging ion-cyclotron-resonance (PI-ICR) technique has been successfully implemented. This method offers several benefits which drastically improve the experimental sensitivity of the CPT to the most neutron-rich nuclei produced at CARIBU. Here we describe the PI-ICR procedure at the CPT, give an overview of the systematic sources of uncertainty in the system, and provide new mass results for 142I, 146La, and 163Gd which were made possible through this upgrade.
•A two-stage stochastic extension of a generic pricing model.•Reformulation as a single-stage bilevel program, and next as a mixed integer program.•Analysis of the theoretical properties of the ...model.•Sensitivity analysis with respect to a parameter that limits the difference between first and second-stage tariffs.
We consider a two-stage stochastic extension of the bilevel pricing model introduced by Labbé et al. (1998). In the first stage, the leader sets tariffs on a subset of arcs of a transportation network, with the aim of maximizing profits while, at the lower level, flows are assigned to cheapest paths of a multicommodity transportation network. In the second stage, the situation repeats itself under the constraint that tariffs should not differ too widely from those set at the first stage, a condition that frequently arises in practice. We analyze properties of the model, provide numerical illustrations, and open avenues for further research into this area.
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