Laser fluorescence on radio-active isotopes produced in very low yield

East particle-photon coincidence techniques, developed at Daresbury with strontium isotopes, allow ultrasensitive laser fluorescence spectroscopy of beams of radio-active isotopes which can only be produced in very low yields. The technique has now been applied to neutron-deficient barium isotopes down to120Ba. From measured hyperfine splittings and isotope shifts, nuclear moments and changes in mean square radii have been determined. The work has revealed an abrupt increase in the mean square radius for121Ba large enough to disrupt the systematic staggering of nuclear size seen for the series. In a recent experiment an isomeric state of127Ba with a half-life of about 2 seconds has been produced in a very low yield; nevertheless we have succeeded in obtaining a fluorescence spectrum.