[ WP ] You are invincible exactly 50 % of the time

Every time I get attacked, I am either invincible or just a human, with 50/50 chance. Well, that was a superpower easy to exploit. 
 
 I could n't withstand multiple attacks, because half of them would kill me, but if I got lucky and became invincible this time, I could withstand one continuous attack as long as I wanted. Solution popped into my head immediately. 
 
 I went to a nuclear waste repository in anti-radiation suit, and grabbed myself a small piece of uranium. I enclosed it in a small case and went home. 
 
 I pierced my hand with a needle - ouch! Then I pierced it again and felt nothing - excellent, I'm invincible now. I've opened the case, grabbed a piece of uranium, and put int on a small chain around my neck. Now I would be constantly exposed to radiation, therefore - forever invincible.
