It can affect you in many differnt ways, first or main would be damage over time, next would be slower rate of mining and moving, probally the most annoying is blured vison anything that is past 1 block will be very blurry including mobs so if a creeper is right infront of you, you proably wont notice him till he goes SSSSSSSSssssSSSSssssssS BOOM! To know how much radition you have in your system there will be a radtion bar aboveyour life bar.
But there is way to prevent it..... wearing full armor hazmat suit bade of advance mobile alloy(technicaly advance alloy that has been been bonded on a molecular with wool and leather using a molecular bonder) it will absorb radition to certian point then it will no longer protect you, now how do you take out the radition from your hazmat suit :D?? Well you can make a wonderfull de-contamnation staion :D(lol it ryhemd) now just insert your self or the hazmat suit into it and just wait about 3 minuets and you or you hazmat suit will be radition free What if you dont have a high tech de-contamnation staion??? Well you can get inexpensive radition pills to counter the affect of radtion(well you have to take one every 5 min)
How do get radition?? well if come in the radtion field of uranuim or if you have a un shielded nuke reactor or if it goes boom.
Ok well this is acutually of topic but while writing about the molecular bonder i had an idea were you can bond types of materiels and reinforce them or create new things