22. - UJYA J) 3.9 pm 490.59 pm If 10% of a radioactive material decays in 5 days then the amount of the original material left after 20 days is approximately 1) 60 % 2) 65 % 3) 70% 4) 75% A freshly prepared radioactive source of half-life 2 hours emits radiation of intensity 1. in timon the nermissible safe level. The minimum times after which it would 3.