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1) The rest mass of an electron is 0.511 MeV, so the minimum energy for an electron - positron pair production is ......... (A) 0.511 MeV (B) zero (C) L022 MeV (D) 2.04 Mev 2) In the radioactive secular equilibrium (A) N2/N1=21/72 (B) N2/N1=1 (C) N2/N20 (D) N2/N1= 12/21 3) The element emitting neutral radioactivity is called (A) radio element (B) active element (C) nuclear element (D) radioactive element 4) A charged particle passing through atoms interacts mainly by the (A) compton scattering (B) Coulomb forces with the electrons of the atoms. (C) loss of K.E. in a collision with the nucleus (D) emission of bremsstrahlung or braking radiation 5) ........ is the energy lost by the incident particle per unit length of its path in a substance. (A) The mean range (B) Specific ionization (C) The Stopping Power (D) Straggling 6) The activity of 1 gram of radium is approximately.... (A) 37000 MB (B) 1 Bq (C) 3.7 MB (D) 370 MB a 7) Which of these models accounts for nuclear mass calculation? (A) shell model (B) liquid drop model (C) collective model (D) Fermi gas model