An equation was derived for the fractionQof the incident x‐ray powerPwhich escapes as kinetic energy of electrons.Q=0.140&tgr;S(1+e−&mgr;l)r−1r1−&lgr;&lgr;K3+1r1−&lgr;&lgr;L3+1.20(1−wK)(r−1)r&lgr;&lgr;K&agr;−&lgr;&lgr;L3,where &tgr; and &mgr; are, respectively, the linear true and total absorption coefficients for the incident wave‐length &lgr;,Sis the range of an electron having an energyh&ngr;corresponding to the wave‐length &lgr;,ris theKabsorption jump ratio andwKis theKfluorescent yield. &lgr;K&agr;, &lgr;Kand &lgr;Lare, respectively, the wave‐lengths of theKlines, theKabsorption limit and theLabsorption limit. This equation can be used to eliminate the necessity of guard electrodes.