First ionization energy measurements of heaviest actinides, lawrencium and nobelium

Sato, Tetsuya   

We measured the first ionization energy (IE) of nobelium (No, Z = 102) and lawrencium (Lr, Z =103) by exploiting the dependence of the ionization efficiency () on the IE in a surface ionization process. The isotopes No ( = 24.5s) and Lr ( = 27 s), produced in the reaction Cm (C, 4n) and Cf (B, 4n), respectively, were used for studying their ionization. The reaction products recoiling from the targets were transported to a surface ion-source by a He/CdI gas-jet transport system. The products ionized in the ion-source were mass-separated with JAEA-ISOL. The number of ions collected at the end of the ISOL was determined by -particle measurements and was used to evaluate values. With the present system, we successfully ionized and mass-separated No and Lr with efficiencies of (0.5 0.1)% and (36 7)% at 2800 K, respectively. From these values, IE values of No and Lr were determined based on the relationship between and IE. Our values are in good agreement with the predicted ones by theoretical calculations.