5925
However , radioactivity of this nuclear isomer has never been observed , and only a lower limit on its half-life of 2.0 " × " 10 " years has been set .
 time: half-life
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 time: half-life