1718_H2_Nuclear_Physics_timed_practice_with_soln

9749 H2 PHYSICS Topical Timed Practice Nanyang Junior College 1 Chapter 20 NUCLEAR PHYSICS Name: ___________________________ CT: __________ Duration: 30 minutes Data and Formulae Section A: Multiple Choice Questions (2 marks each) Fill in the answers in the boxes below. 1 2 3 4 5 6 D C D C D C 1 The deviation of α-particles by thin metal foils through angles that range from 0 o to 180o can be explained by A scattering from free electrons. B diffuse reflection from the metal surface. C diffraction from the crystal lattice. D scattering from small but heavy regions of positive charge. Ans: D speed of light in free space c = 3.00 × 108 m s−1 elementary charge e = 1.60 × 10−19 C unified atomic mass constant u = 1.66 × 10−27 kg rest mass of electron me = 9.11 × 10−31 kg rest mass of proton mp = 1.67 × 10−27 kg the Avogadro constant NA = 6.02 × 1023 mol−1 radioactive decay x = xo exp (−λt) decay constant λ = ln2 / t1/2 25

9749 H2 PHYSICS Topical Timed Practice Nanyang Junior College 2 2 A nucleus has a nucleon number A, a proton number Z and a binding energy B. The masses of the neutron and proton are mn and mp respectively, and c is the speed of light. The mass of the nucleus is given by the expression A 2n p BAm Zm c  B 2n p BAm Zm c  C   2n p BA Z m Zm c   D   2n p BA Z m Zm c   Ans: C 3 The rest mass of the deuteron, 2 1H , is equivalent to an energy of 1876 MeV. The rest mass of a proton is equivalent to 939 MeV and the rest mass of a neutron is equivalent to 940 MeV. A deuteron may disintegrate to a proton and a neutron if it A emits a  -ray photon of energy 1 MeV. B captures a  -ray photon of energy 1 MeV. C emits a  -ray photon of energy 3 MeV. D captures a  -ray photon of energy 3 MeV. Ans: D Since Reactants ProductsM M   , a photon must be absorbed whose energy is equal to the difference   2 Products ReactantsM M c  . 4 At time t, a sample of radioactive substance contains N atoms of a particular nuclide. At time (t + Δt), where Δt is a short period of time, the number of atoms of the nuclide is (N – ΔN). Which expression is equal to the decay constant of the nuclide? A N N  B N t   C N N t   D N N t   Ans: C Decay constant  = probability of decay per unit time Probability of decay = N N  Hence N N t   OR Activity A = rate of decay = N t   Since A N => A N N N t   

9749 H2 PHYSICS Topical Timed Practice Nanyang Junior College 3 5 The graph shows how the activities of two isotopes X and Y vary with time. What will be the ratio activity of X activity of Y after each has decayed for 8 hours? A 9 10 B 10 9 C 81 100 D 100 81 Ans: D Isotope X (4) 1 900 1000 0.0263 hr X X e       After 8 hrs, (0.0263)(8)1000 810