Search results for "Ph. D."
showing 10 items of 180 documents
Confirmation of the new isotope Pb178
2016
The extremely neutron-deficient isotope $^{178}\mathrm{Pb}$ has been produced. The GREAT spectrometer at the focal plane position of the gas-filled separator RITU was used to study the $\ensuremath{\alpha}$ decay of $^{178}\mathrm{Pb}$ and its $\ensuremath{\alpha}$-decay chain through $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\alpha}$ correlations. The $\ensuremath{\alpha}$ decay was measured to have an energy and half-life of ${E}_{\ensuremath{\alpha}}$= 7610(30) keV and ${t}_{1/2}=0.{21}_{\ensuremath{-}0.08}^{+0.21}$ ms, respectively. The half-life is consistent with recent theoretical calculations using the Coulomb and proximity potential model. The $\ensuremath{\alpha}$-decay…
Search for Electron-Capture Delayed Fission in the New Isotope Md244
2020
The electron-capture decay followed by a prompt fission process was searched for in the hitherto unknown most neutron-deficient Md isotope with mass number 244. Alpha decay with $\ensuremath{\alpha}$-particle energies of 8.73--8.86 MeV and with a half-life of ${0.30}_{\ensuremath{-}0.09}^{+0.19}\text{ }\text{ }\mathrm{s}$ was assigned to $^{244}\mathrm{Md}$. No fission event with a similar half-life potentially originating from spontaneous fissioning of the short-lived electron-capture decay daughter $^{244}\mathrm{Fm}$ was observed, which results in an upper limit of 0.14 for the electron-capture branching of $^{244}\mathrm{Md}$. Two groups of fission events with half-lives of ${0.9}_{\ens…
A triplet of differently shaped spin-zero states in the atomic nucleus 186Pb
2000
Understanding the fundamental excitations of many-fermion systems is of significant current interest. In atomic nuclei with even numbers of neutrons and protons, the low-lying excitation spectrum is generally formed by nucleon pair breaking and nuclear vibrations or rotations. However, for certain numbers of protons and neutrons, a subtle rearrangement of only a few nucleons among the orbitals at the Fermi surface can result in a different elementary mode: a macroscopic shape change. The first experimental evidence for this phenomenon came from the observation of shape coexistence in 16O (ref. 4). Other unexpected examples came with the discovery of fission isomers and super-deformed nuclei…
αdecay studies of the nuclides195Rnand196Rn
2001
The new neutron deficient nuclide ${}^{195}\mathrm{Rn}$ and the nuclide ${}^{196}\mathrm{Rn}$ have been produced in fusion evaporation reactions using ${}^{56}\mathrm{Fe}$ ions on ${}^{142}\mathrm{Nd}$ targets. A gas-filled recoil separator was used to separate the fusion products from the scattered beam. The activities were implanted in a position sensitive silicon detector. The isotopes were identified using spatial and time correlations between implants and decays. Two $\ensuremath{\alpha}$ decaying isomeric states, with ${E}_{\ensuremath{\alpha}}=7536(11)\mathrm{keV}[{T}_{1/2}{=(6}_{\ensuremath{-}2}^{+3})\mathrm{ms}]$ for the ground state and ${E}_{\ensuremath{\alpha}}=7555(11)\mathrm{k…
A Novel Method for the Measurement of Half-Lives and Decay Branching Ratios of Exotic Nuclei
2019
A novel method for simultaneous measurement of masses, Q-values, isomer excitation energies, half-lives and decay branching ratios of exotic nuclei has been demonstrated. The method includes first use of a stopping cell as an ion trap, combining containment of precursors and decay-recoils for variable durations in a cryogenic stopping cell (CSC), and afterwards the identification and counting of them by a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). Feasibility has been established by recording the decay and growth of $^{216}$Po and $^{212}$Pb (alpha decay) and of $^{119m2}$Sb (t$_{1/2}$ = 850$\pm$90 ms) and $^{119g}$Sb (isomer transition), obtaining half-lives and bran…
Electromagnetic transitions andαdecay of the223Panucleus
1999
Actinides with $N\ensuremath{\sim}132$ present the best explored region of pear shape nuclei. Still almost no spectroscopic information is available for the heaviest elements, $Z=91--98,$ which are predicted to be octupole instable. The lack of data for the latter nuclei results from the high fission probability encountered in the heavy-ion reactions used to populate them. In order to overcome this handicap, an $\ensuremath{\alpha}$-decay tagging technique was used to identify $\ensuremath{\gamma}$ rays in ${}^{223}\mathrm{Pa}$ produced through the ${}^{208}\mathrm{Pb}{(}^{19}\mathrm{F},4n)$ reaction. A new value of 4.9(4) ms for the half-life of ${}^{223}\mathrm{Pa}$ was obtained as a by-p…
In-beam γ-ray spectroscopy of 190Po: First observation of a low-lying prolate band in Po isotopes
2003
Gamma rays from excited states of 190Po have been observed using the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated with a collective band which from spin 4 onwards resembles the prolate rotational bands known in the isotones 188Pb and 186Hg. This indicates that in 190Po the prolate configuration becomes yrast above I = 2. The experimental results are interpreted in a two-band mixing calculation and are in agreement with α-decay data and potential energy surface calculations.
Microscopic description of α-like resonances
2000
A description of $\ensuremath{\alpha}$-like resonances is given in terms of single-particle states including narrow Gamow resonances in continuum. The equations of motion are derived within the multistep shell-model approach; the lowest collective two-particle eigenmodes are used as building blocks for the four-particle states. A good agreement with the low-lying states in ${}^{212}\mathrm{Po}$ is obtained. A new technique to estimate the $\ensuremath{\alpha}$-particle formation amplitude for any multipolarity is proposed. The spectroscopic factor of the $\ensuremath{\alpha}$-decay between ground states is reproduced, but the total width is by two orders of magnitude less than the experimen…
In-beam andα-decay spectroscopy of191Poand evidence for triple shape coexistence at low energy in the daughter nucleus187Pb
2002
Prompt gamma rays have been observed for the first time from the neutron-deficient nucleus Po-191 using the recoil-decay tagging technique at the RITU gas-filled separator. In addition improved alp ...
Microscopic description ofα+40Caquasimolecular resonances
2001
A multistep microscopic approach describing the dynamics of quasimolecular resonances is applied to the $\ensuremath{\alpha}{+}^{40}\mathrm{Ca}$ system. The lowest collective two-particle eigenmodes are used as building blocks of the four-particle states. The pair states are built on mean-field single-particle orbitals including also sharp resonances in continuum. The structure of ${}^{44}\mathrm{Ti}$ is analyzed and strong high-lying $\ensuremath{\alpha}$-like resonances are found in good agreement with the experimentally observed quasimolecular spectrum. The resonances turn out to be very collective and contain mostly proton-neutron pairs where the lowest proton single-particle resonance,…