Shell effect in Pb isotopes near the proton drip line

A mass formula (BWM) without shell effect is employed to study the variation of the shell effect in Pb isotopes through comparison with the experimental data. Unlike other macroscopic formulae, the BWM reproduces the general trend of the binding energy versus neutron number curves of all the nuclei from Li to Bi. The shell effect in Pb-isotopes reduces to ~56 keV at N=106 but, increases gradually for N<106, indicating increasing shell effect in Pb near the proton drip line.