(1a) What is the source of the energy emitted in radioactive decay? (A) absorbed photon energy (B) Conversin of part of the mass of the nucleus to energy (C) Kinetic energy transferred from collision with a high speed neutro (D) De-excitation of electrons from a meta- stable state (E) Kinetic energy of heat (1b) Choose the best definition of the term "half-life" (A) The time halfway between a radioisotopes creation and the moment it disappears. (B) the time after which the radioactivity of a certain nucleus will have decreased by half (C) the time interval in which a certain nucleus has a 50% chance of decaying (D) The time it takes for exactly half of all nuclei in a radioactive sample to decay (1c) About how many half lives have elapsed when a radioactive substance has decayed to less than 1% or it original form? (A) 32 (B) 50 (C) 7 (D) 99 (E) 5 (F) 10 (G) 4 (1d) Food irradiation causes some residual radioactivity in the treated food (A) true (B) False