arXiv subjects

A. Andreyev

Publications and source records attributed to A. Andreyev.

5 recordsLinked to original sources

arXiv2026

Fission mode identification in the 180Hg region: derivative analysis approach

Experimental setups commonly used to study fission properties of nuclei in the exotic neutron-deficient 180Hg region are based on the time-of-flight technique for the fission-product identification. The nuclei of interest are created via fusion reactions at excitation energies of several tens of MeV and identified with limited mass resolution. The deduced final fission-fragment mass distributions are in general structureless, which makes the identification of fission modes, along with their properties, ambiguous and author-dependent. The standard functional-analysis technique applied to the simulated limited-resolution fusion-fission data appears to provide consistent results on the number and parameters of fission modes, even in cases of strong symmetric-mode dominance, i.e. for Gaussian-like fission-fragment mass distribution shapes. The method is shown to work also on data sets with limited statistics (real experimental data with integral of a few tens of thousands of events).

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arXiv2024

Beta delayed neutron emission of $N=84$ $^{132}$Cd

Using the time-of-flight technique, we measured the beta-delayed neutron emission of $^{132}$Cd. From our large-scale shell model (LSSM) calculation using the N$^3$LO interaction [Z.Y. Xu et al., Phys. Rev. Lett. 131, 022501 (2023)], we suggest the decay is dominated by the transformation of a neutron in the $g_{7/2}$ orbital, deep below the Fermi surface, into a proton in the $g_{9/2}$ orbital. We compare the beta-decay half-lives and neutron branching ratios of nuclei with $Z<50$ and $N\geq82$ obtained with our LSSM with those of leading "global" models such as Finite-Range Droplet Model (FRDM). Our calculations match known half-lives and neutron branching ratios well and suggest that current leading models overestimate the yet-to-be-measured half-lives. Our model, backed by the $^{132}$Cd decay data presented here, offers robust predictive power for nuclei of astrophysical interest such as $r$-process waiting points.

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arXiv2024

Detailed study of the decay of $^{21}$Mg

Beta-delayed proton and gamma emission in the decay of $^{21}$Mg has been measured at ISOLDE, CERN with the ISOLDE Decay Station (IDS) set-up. The existing decay scheme is updated, in particular what concerns proton transitions to excited states in $^{20}$Ne. Signatures of interference in several parts of the spectrum are used to settle spin and parity assignments to highly excited states in $^{21}$Na. The previously reported $\beta$p$\alpha$ branch is confirmed. A half-life of 120.5(4) ms is extracted for $^{21}$Mg. The revised decay scheme is employed to test mirror symmetry in the decay and to extract the beta strength distribution of $^{21}$Mg that is compared with theory.

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arXiv2011

Simulations of a micro-PET System based on Liquid Xenon

The imaging performance of a high-resolution preclinical microPET system employing liquid xenon as the gamma ray detection medium was simulated. The arrangement comprises a ring of detectors consisting of trapezoidal LXe time projection ionization chambers and two arrays of large area avalanche photodiodes for the measurement of ionization charge and scintillation light. A key feature of the LXePET system is the ability to identify individual photon interactions with high energy resolution and high spatial resolution in 3 dimensions and determine the correct interaction sequence using Compton reconstruction algorithms. The simulated LXePET imaging performance was evaluated by computing the noise equivalent count rate, the sensitivity and point spread function for a point source, and by examining the image quality using a micro-Derenzo phantom according to the NEMA-NU4 standard. Results of these simulation studies included NECR peaking at 1326 kcps at 188 MBq (705 kcps at 184 MBq) for an energy window of 450 - 600 keV and a coincidence window of 1 ns for mouse (rat) phantoms. The absolute sensitivity at the center of the field of view was 12.6%. Radial, tangential, and axial resolutions of 22Na point sources reconstructed with a list-mode maximum likelihood expectation maximization algorithm were <= 0.8 mm (FWHM) throughout the field of view. Hot-rod inserts of < 0.8 mm diameter were resolvable in the transaxial image of a micro-Derenzo phantom. The simulations show that a liquid xenon system would provide new capabilities for significantly enhancing PET images.

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arXiv2008

Beta-delayed deuteron emission from 11Li: decay of the halo

The deuteron-emission channel in the beta-decay of the halo-nucleus 11Li was measured at the ISAC facility at TRIUMF by implanting post-accelerated 11Li ions into a segmented silicon detector. The events of interest were identified by correlating the decays of 11Li with those of the daughter nuclei. This method allowed the energy spectrum of the emitted deuterons to be extracted, free from contributions from other channels, and a precise value for the branching ratio B_d = 1.30(13) x 10-4 to be deduced for E(c.m.) > 200 keV. The results provide the first unambiguous experimental evidence that the decay takes place essentially in the halo of 11Li, and that it proceeds mainly to the 9Li + d continuum, opening up a new means to study of the halo wave function of 11Li.

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