Spectroscopic quadrupole moments of 25Mg and 27Al from muonic X-rays

Abstract With the crystal spectrometer at Muon Channel I at SIN we measured the 3d 5 2 -2p 3 2 X-ray transitions in muonic 25 Mg and 27 Al. The h.f.s. of the 2p 3 2 was resolved and the spectroscopic quadrupole moment of the nuclear ground states determined: Q( 25 Mg ) = +0.201 ± 0.003 b , Q( 27 Al ) = +0.150 ± 0.006 b . We find agreement between the intrinsic quadrupole moment value derived from Q( 25 Mg ) with those calculated from measured B (E2) values. This indicates that for 25 Mg the strong-coupling limit of the rotational model with an axially symmetric charge distribution is realized in the lower part of the ground-state rotational band. We combine the quadrupole moments Q with the quadrupole coupling constants measured in electronic atoms of 25 Mg and 27 Al and derive the electric field gradients at the nucleus (in units of e · a 0 −3 , where a 0 is the Bohr radius): 〈 d E d z 〉 = 0.339± 0.005 for the 3P 2 state of 25 Mg, 〈 d E d z 〉 = 0.54± 0.02 for the 2 P 3 2 state of 27 Al. From Hartree-Fock calculations of the 2 P 3 2 state of Al we derive values for the Sternheimer correction factor R and compare them with calculated values.