Superconductivity of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ with and without artificial disorder over the entire doping range*

Effects of electron irradiation on superconducting transition temperature and in-plane London penetration depth were studied in single crystals of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (x= 0.22, 0.34, 0.47, 0.56, 0.65, 0.80, 0.82, 0. 90, 0.92, 1.0). Electron irradiation introduces point - like disorder that gives insight into the superconducting gap structure by studying the effects of increasing scattering. We studied the entire superconducting ``dome'' and find distinctly different behaviours in underdoped, optimal, and overdoped compositions and unusual behaviour near x = 0.7 - 0.8.