Decay spectroscopy of the odd-proton nuclei
249
Md and
251
Md has been performed. High-
K
isomeric states were identified for the first time in these two nuclei through the measurement of their ...electromagnetic decay. An isomeric state with a half-life of 2.8(5) ms and an excitation energy
≥
910
keV was found in
249
Md. In
251
Md, an isomeric state with a half-life of 1.4(3) s and an excitation energy
≥
844
keV was found. Similarly to the neighbouring
255
Lr, these two isomeric states are interpreted as 3 quasi-particle high-
K
states and compared to new theoretical calculations. Excited nuclear configurations were calculated within two scenarios: via blocking nuclear states located in proximity to the Fermi surface or/and using the quasiparticle Bardeen–Cooper–Schrieffer method. Relevant states were selected on the basis of the microscopic-macroscopic model with a deformed Woods–Saxon potential. The most probable candidates for the configurations of
K
-isomeric states in Md nuclei are proposed.
The new neutron-deficient nuclei 240Es and 236Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from 240Es produced in the ...fusion–evaporation reaction 209Bi(34S,3n)240Es. Half-lives of 6(2)s and 22−6+13s were obtained for 240Es and 236Bk, respectively. Two groups of α particles with energies Eα=8.19(3)MeV and 8.09(3)MeV were unambiguously assigned to 240Es. Electron-capture delayed fission branches with probabilities of 0.16(6) and 0.04(2) were measured for 240Es and 236Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilities in more neutron-deficient isotopes.
Decay spectroscopy of the odd-proton nuclei $^{249}$Md and $^{251}$Md has
been performed. High-$K$ isomeric states were identified for the first time in
these two nuclei through the measurement of ...their electromagnetic decay. An
isomeric state with a half-life of $2.8(5)$ ms and an excitation energy $\geq
910$ keV was found in $^{249}$Md. In $^{251}$Md, an isomeric state with a
half-life of $1.4(3)$ s and an excitation energy $\geq 844$ keV was found.
Similarly to the neighbouring $^{255}$Lr, these two isomeric states are
interpreted as 3 quasi-particle high-$K$ states and compared to new theoretical
calculations. Excited nuclear configurations were calculated within two
scenarios: via blocking nuclear states located in proximity to the Fermi
surface or/and using the quasiparticle Bardeen-Cooper-Schrieffer method.
Relevant states were selected on the basis of the microscopic-macroscopic model
with a deformed Woods-Saxon potential. The most probable candidates for the
configurations of $K$-isomeric states in Md nuclei are proposed.
The odd-\(Z\) \(^{251}\)Md nucleus was studied using combined \(\gamma\)-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the \(5211/2^-\) ...configuration, another rotational structure has been identified using \(\gamma\)-\(\gamma\) coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a \(5147/2^-\) single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of \(\simeq\) 60% was well reproduced by simulating a set of unresolved excited bands. Moreover, a detailed analysis of the intensity profile as a function of the angular momentum provided a method for deriving the orbital gyromagnetic factor, namely \(g_K = 0.69^{+0.19}_{-0.16}\) for the ground-state band. The odd-\(Z\) \(^{249}\)Md was studied using \(\gamma\)-ray in-beam spectroscopy. Evidence for octupole correlations resulting from the mixing of the \(\Delta l = \Delta j = 3\) \(5213/2^-\) and \(6337/2^+\) Nilsson orbitals were found in both \(^{249,251}\)Md. A surprising similarity of the \(^{251}\)Md ground-state band transition energies with those of the excited band of \(^{255}\)Lr has been discussed in terms of identical bands. Skyrme-Hartree-Fock-Bogoliubov calculations were performed to investigate the origin of the similarities between these bands.
In the study of the odd-\(Z\), even-\(N\) nuclei \(^{243}\)Es and \(^{249}\)Md, performed at the University of Jyv\"askyl\"a, the fusion-evaporation reactions ...\(^{197}\)Au(\(^{48}\)Ca,2\(n\))\(^{243}\)Es and \(^{203}\)Tl(\(^{48}\)Ca,2\(n\))\(^{249}\)Md have been used for the first time. Fusion-evaporation residues were selected and detected using the RITU gas-filled separator coupled with the focal-plane spectrometer GREAT. For \(^{243}\)Es, the recoil decay correlation analysis yielded a half-life of \(24 \pm 3\)s, and a maximum production cross section of \(37 \pm 10\) nb. In the same way, a half-life of \(26 \pm 1\) s, an \(\alpha\) branching ratio of 75 \(\pm\) 5%, and a maximum production cross section of 300 \(\pm\) 80 nb were determined for \(^{249}\)Md. The decay properties of \(^{245}\)Es, the daughter of \(^{249}\)Md, were also measured: an \(\alpha\) branching ratio of 54 \(\pm\) 7% and a half-life of 65 \(\pm\) 6 s. Experimental cross sections were compared to the results of calculations performed using the KEWPIE2 statistical fusion-evaporation code.
Decay spectroscopy of the odd-proton nuclei \(^{249}\)Md and \(^{251}\)Md has been performed. High-\(K\) isomeric states were identified for the first time in these two nuclei through the measurement ...of their electromagnetic decay. An isomeric state with a half-life of \(2.8(5)\) ms and an excitation energy \(\geq 910\) keV was found in \(^{249}\)Md. In \(^{251}\)Md, an isomeric state with a half-life of \(1.4(3)\) s and an excitation energy \(\geq 844\) keV was found. Similarly to the neighbouring \(^{255}\)Lr, these two isomeric states are interpreted as 3 quasi-particle high-\(K\) states and compared to new theoretical calculations. Excited nuclear configurations were calculated within two scenarios: via blocking nuclear states located in proximity to the Fermi surface or/and using the quasiparticle Bardeen-Cooper-Schrieffer method. Relevant states were selected on the basis of the microscopic-macroscopic model with a deformed Woods-Saxon potential. The most probable candidates for the configurations of \(K\)-isomeric states in Md nuclei are proposed.
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