Complex sentence: Its longer lifetime insures that tractable amounts of material could be collected into experimental targets that held no hazards for personnel working with the material: 1 micro-gram of 178m2 Hf has an activity of 40 micro-Curies.
Split into simpler sentences: Its longer lifetime also insures that tractable amounts of material could be collected into experimental targets. These samples would hold no hazards for personnel working with the material; 1 micro-gram of 178m2 Hf has an activity of only 40 micro-Curies.