Measurement of the spectroscopic quadrupole moment of the second 2+ state of 184186W, by means of Coulomb excitation

In a particle-gamma coincidence experiment, a thick tungsten target of natural isotopic abundance was bombarded, first with alpha particles, then with 16O ions. From analysis of the de-excitation gamma rays following Coulomb excitation, the spectroscopic quadrupole moment of the second 2+ state (the 2+' state) was measured for 184,186W. In a separate Coulomb excitation experiment, a thin, isotopically enriched 186W target was bombarded with 16O ions. From an analysis of the projectiles scattered elastically and inelastically, the quadrupole moment of the 2+' state of 186W was determined. The quadrupole moment of the 2+' state was found to be opposite in sign to that of the 2+ state, for both isotopes studied. However, its magnitude decreases rapidly in going from 186W to 184W. This should be compared with the predictions of the rotation-vibration model and the asymmetric rotor model, which predict the quadrupole moment to increase slowly with decreasing mass. The microscopic theory of Kumar and Baranger does predict the experimental trend qualitatively. Thus the present results are interpreted as being evidence of the strong coupling of the β and γ degrees of freedom in the tungsten isotopes which, according to the theory of Kumar and Baranger, is the source of the reduced value of the quadrupole moment