N. Vermeulen

Precision measurement of the electric quadrupole moment of 31Al and determination of the effective proton charge in the sd-shell

Abstract The electric quadrupole coupling constant of the 31 Al ground state is measured to be ν Q = | e Q V z z h | = 2196 ( 21 ) kHz using two different β -NMR (Nuclear Magnetic Resonance) techniques. For the first time, a direct comparison is made between the continuous rf technique and the adiabatic fast passage method. The obtained coupling constants of both methods are in excellent agreement with each other and a precise value for the quadrupole moment of 31 Al has been deduced: | Q ( Al 31 ) | = 134.0 ( 16 ) mb . Comparison of this value with large-scale shell-model calculations in the sd and sdpf valence spaces suggests that the 31 Al ground state is dominated by normal sd-shell configurations with a possible small contribution of intruder states. The obtained value for | Q ( Al 31 ) | and a compilation of measured quadrupole moments of odd- Z even- N isotopes in comparison with shell-model calculations shows that the proton effective charge e p = 1.1 e provides a much better description of the nuclear properties in the sd-shell than the adopted value e p = 1.3 e .

g-factor measurement of the 9/2+ isomeric state in 65Ni

We report on the first measurement of the g factor of the Jπ = 9/2+ isomeric state in 65Ni. (d,p) reactions on enriched 64Ni and 62Ni have been used in order to populate and spin orient the Jπ = 9/2+ isomeric states in 65Ni and 63Ni. The hyperfine field of the Ni target, oriented by an external magnetic field, was used in order to obtain a sufficient number of spin precessions within the relatively short life time of the isomers. The g factor obtained, g(65mNi) = −0.296(3), is in good agreement with the g factors of other 9/2+ states in the region and with shell-model calculations.

g factors of {sup 17}N and {sup 18}N remeasured

The g factors of the {sup 17}N and {sup 18}N ground states were remeasured using the {beta}-nuclear magnetic resonance ({beta}-NMR) technique on spin-polarized fragment beams at the LISE fragment separator at GANIL. Based on the g-factor results, the magnetic moments of {sup 17}N (I{sup {pi}}=1/2{sup -}) and {sup 18}N (I{sup {pi}}=1{sup -}) were deduced: |{mu}({sup 17}N)|=0.3551(4) {mu}{sub N} and |{mu}({sup 18}N)|=0.3273(4) {mu}{sub N}. Both results are in good agreement with and more precise than the earlier observed values.

First isomeric quadrupole moment measured in fragmentation reactions: The case of {sup 61}Fe{sup m}(9/2{sup +})

This paper demonstrates the feasibility of quadrupole moment measurements on isomeric levels populated in projectile fragmentation reactions. The neutron-rich {sup 61}Fe(9/2{sup +}) [E*= 861 keV, T{sub 1/2}= 239(5) ns] isomer was produced and spin aligned by the intermediate energy fragmentation of a {sup 64}Ni beam and implanted in a Cd single crystal. Its spectroscopic quadrupole moment |Q{sub s}|=41(6) e fm{sup 2} agrees with mean-field based calculations using the finite-range Gogny force, suggesting a moderately deformed shape characterized by an intrinsic charge quadrupole moment Q{sub 0}=-85 e fm{sup 2} or Q{sub 0}=+115 e fm{sup 2}. The present measurement paves the way for future determinations of isomeric quadrupole moments in more exotic nuclei.