Discovery of Cesium, Lanthanum, Praseodymium and Promethium Isotopes
  Currently, forty-one cesium, thirty-five lanthanum, thirty-two praseodymium, and thirty-one promethium, isotopes have been observed and the discovery of these isotopes is discussed here. For each isotope a brief synopsis of the first refereed publication, including the production and identification method, is presented. 
E. May and M. Thoennessen
nucl-ex