1 Curie is equal to
(1) 3×1010 disintegrations/sec
(2) 3.7×107 disintegrations/sec
(3) 5×107 disintegrations/sec
(4) 3.7×1010 disintegrations/sec
The electron emitted in beta radiation originates from
(1) Inner orbits of atoms
(2) Free electrons existing in nuclei
(3) Decay of a neutron in a nucleus
(4) Photon escaping from the nucleus
When a radioactive substance emits an α-particle, its position in the periodic table is lowered by
(1) One place
(2) Two places
(3) Three places
(4) Four places
A radioactive nucleus emits a beta particle. The parent and daughter nuclei are
(1) Isotopes
(2) Isotones
(3) Isomers
(4) Isobars
If a radioactive substance reduces to 116 of its original mass in 40 days, what is its half-life
(1) 10 days
(2) 20 days
(3) 40 days
(4) None of these
A radioactive nucleus with Z protons and N neutrons emits an α-particle, 2β-particles and 2 gamma rays. The number of protons and neutrons in the nucleus left after the decay respectively, are
(1) Z – 3, N – 1
(2) Z – 2, N – 2
(3) Z – 1, N – 3
(4) Z, N – 4
99% of a radioactive element will decay between
(1) 6 and 7 half lives
(2) 7 and 8 half lives
(3) 8 and 9 half lives
(4) 9 half lives
The half-life of a radioactive substance against α-decay is 1.2×107 s. What is the decay rate for 4×1015 atoms of the substance
(1) 4.6×1012 atoms/s
(2) 2.3×1011 atoms/s
(3) 4.6×1010 atoms/s
(4) 2.3×108 atoms/s
In a sample of radioactive material, what percentage of the initial number of active nuclei will decay during one mean life
(1) 69.3%
(2) 63%
(3) 50%
(4) 37%
The S.I. unit of radioactivity is
(1) Roentgen
(2) Rutherford
(3) Curie
(4) Becqueral