Nuclear structure investigations of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Es</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>253</mml:mn><mml:mo>?</mml:mo><mml:mn>255</mml:mn></mml:mrow></mml:mmultiscripts></mml:math> by laser spectroscopy

Laser resonance ionization spectroscopy was performed on the rare einsteinium isotopes $^{253\ensuremath{-}255}\mathrm{Es}$ at RISIKO mass separator in Mainz. With low sample sizes ranging down to femtograms, prominent 352 nm-ground-state transition measured all three isotopes, and four additional ground-state transitions were $^{254}\mathrm{Es}$. Hyperfine-structure analysis resulted assigned spin values of $I(^{254}\mathrm{Es})=7$ $I(^{255}\mathrm{Es})=7/2$. From extracted coupling constants, nuclear magnetic dipole moments ${\ensuremath{\mu}}_{I}(^{254}\mathrm{Es})=3.42(7)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{N}$ ${\ensuremath{\mu}}_{I}(^{255}\mathrm{Es})=4.14(10)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{N}$ as well spectroscopic electric quadrupole ${Q}_{s}(^{254}\mathrm{Es})=9.6(1.2)\phantom{\rule{0.16em}{0ex}}e\mathrm{b}$ ${Q}_{s}(^{255}\mathrm{Es})=5.1(1.7)\phantom{\rule{0.16em}{0ex}}e\mathrm{b}$ derived. Our value for $^{254}\mathrm{Es}$ deviates from $|{\ensuremath{\mu}}_{I}(^{254}\mathrm{Es})|=4.35(41)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{N}$ angular anisotropy $\ensuremath{\alpha}$-radiation emitted by