Good question, I really don't know for sure. I'll make some form of educated guess here.
Graphite is carbon - specifically a type of carbon where each atom has a molecular bond to three other carbon arms, which are stacked in layers. 'Lead' pencils are graphite - you rub layers off as you write. Diamond has four bonds for each atom, the maximum possible.
Carbon-12 (6 protons, 6 neutrons) and Carbon-13 (6 protons, 7 neutrons) are the stable, non-radioactive version. Most of the radioactive isotopes of Carbon have very short half-lifes, except for Carbon-14. That is a byproduct of nuclear power generation and nuclear explosions; mostly by the Nitrogen-14 having a neutron knocked off it.
Carbon-14 is itself a beta emitter and it's most famously used for 'carbon date' because of the 5,730 year half-life. However, C-14 isn't that dangerous; it's stopped by less than a foot of air and can be used on a lab bench without any shielding:
The bigger problem was probably that the graphite, due to its presence in the core, was coated with all the other radiation sources from the reactor, like the Plutonium-241 in it.
45
u/columbus8myhw May 09 '19
The closer you are to it, the stronger it is. When his hand was millimeters away from the graphite, the graphite's radiation was much stronger.
Imagine putting your eyes millimeters away from a lightbulb, verses standing a few feet away.