A very interesting document. Unfortunately you can&#x27;t trivially copy-paste text from it, so instead I&#x27;ll like to direct readers to page 4, to the text that starts below figure 5. It seems that most of the size&#x2F;weight of the nuclear pacemaker was because of shielding, that was designed to withstand even an airplane crash or getting hit by a bullet - all because plutonium is a substance from hell that will kill you if you let it in your blood or expose to air. OTOH radiation was <i>not</i> a concern, measured levels under normal operation were way below safety limits.