I believe it is current. An ammeter is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes (A), hence the name. Instruments used to measure smaller currents, milliampere or microampere range, are designated as milliammeters or microammeters.
There are 3 major types of radiation. The Alpha, Beta and Gamma radiation. It is the Alpha radiation that can be stopped by a piece of paper or fabric. Beta on the other hand can be stopped by plastic or a thin sheet of metal and Gamma by a piece of aluminum foil or lead.
Iodine 131 and iodine 126 are the same in the sense that, they both have the same number of electrons and protons in their atoms, it is only the number of their neutrons that is different. Iodine 131 has 78 neutrons while iodine 126 has 73 neutrons.
