Tiêu đề 28. Nuclei.pdf ✅

1. A nucleus m n X emits one  particle and one 2. A fresh radioactive sample is given at t= 0. Its decay fraction are 1 5 at 1 t instant and 4 5 at 2 t instant. Its mean life is :- 3. The binding energy of deuteron is 2.2 MeV and that of 4 2 He is 28 MeV. If two deuterons are fused to form one 4 2 He then the energy released is : (1) 25.8 MeV (2) 23.6 MeV (3) 19.2 MeV (4) 30.2 MeV 4. Half-life of a radioactive substance is 20 minute. The time between 20% and 80% decay will be (1) 20 min (2) 40 min (3) 30 min (4) 25 min 5. The half-life of a radioactive substance against -decay is 1.2 × 107 s. What is the decay rate for 4.0 × 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 6. Decay rate for a certain mass of a radioactive substance measured at different times varies with time as shown in fig. count rate at t = 8 hr will be :- (1) 25 2 decays/sec (2) 50 decays/sec (3) 500 decays/sec (4) 750 decays/sec 7. When a slow neutron is captured by a U235 nucleus, a fission results which releases 200 MeV of energy. If the output of a nuclear reactor is1.6MW, what is the rate of nuclei (per sec) undergoing fission ? (1) 8 × 10–3 (2) 1 × 1013 (3) 1 × 1025 (4) 5 × 1016 8. A radioactive element X decays into another stable element Y. Half life of X is 2hrs. Initially only X is present. After time t the ratio of atoms of X and Y is found to be 1 : 3, then t in hours is:- (1) 2 (2) 4 (3) 5 (4) 6 9. The radius of a nucleus with nucleon number 16is 3 × 10–15 m. Then, the radius of a nucleus with nucleon number 128 will be :- (1) 3 × 10–15 m (2) 6 × 10–15 m (3) 9 × 10–15 m (4) 24 × 10–15 m A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion. B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion. C. If Assertion is True but the Reason is False. D. If both Assertion & Reason are False. 10. Assertion :- A nucleus contain no electron, but can eject them. Reason :-−rays are emitted by the excited nuclei. (1) A (2) B (3) C (4) D 11. The above is a plot of binding energy per nucleon Eb, against the nuclear mass M; A, B, C, D, E, Nuclei
F correspond to different nuclei. Consider four reactions :- (i) A + B → C +  (ii) C → A + B +  (iii) D + E → F +  (iv) F → D + E +  where is the energy released ? In which reactions is  positive? (1) (ii) and (iv) (2) (ii) and (iii) (3) (i) and (iv) (4) (i) and (iii) 12. A nucleus with Z = 92 emits the following in a sequence               , , , , , , , , , , , , . − − − − + + .The Z of the resulting nucleus is- (1) 76 (2) 78 (3) 82 (4) 74 13. The ratio of N1 to N2 when N2 is maximum is : (1) at no time this is possible (2) 2 (3)1/2 (4) 2 2 n 14. Assuming that about 20 MeV of energy is released per fusion reaction, 1H 2 + 1H 3→0n 1 + 2He4 , the mass of 1H 2 consumed per day in a future fusion reactor of power 1 MW would be approximately (1) 0.09 gm (2) 0.009 gm (3) 9 gm (4) 90 gm 15. The half-life period of a radioactive element is10 days. Then how long does it take for 90% of a given mass of this element to disintegrate - (1) 19 days (2) 27 days (3) 33 days (4) 47 days 16. A certain radioactive material ZX A starts emitting  and  particles successively such that the end product is Z–3Y A–8 . The number of  and  particles emitted are - (1) 4 and 3 respectively (2) 2 and 1 respectively (3) 3 and 4 respectively (4) 1 and 2 respectively 17. There are three lumps of a given radioactive substance. Their activity is in the ratio of1 : 2 : 3 now. What will be the ratio of their activities at any further date - (1) 1 : 2 : 3 (2) 2 : 1 : 3 (3) 3 : 2 : 1 (4) 2 : 3 : 1 18. A radioactive nucleus emits an -particle and a neutron simultaneously with same speed but in opposite direction in order to form a stable nuclei If the speed of emitted particles is v and A is the mass number of radioactive nucleus, then speed of stable nucleus is 19. Two radioactive elements X and Y have half-lifetimes of 50 minutes and 100 minutes, respectively. Samples X and Y initially contain equal numbers of atoms . After 200 minutes, the (1) 4 (2) 2 (3) 1/2 (4) 1/4 20. A nucleus ruptures into two nuclear parts which have their velocity ratio equal to 2 : 1. What will be the ratio of their nuclear sizes- (1) 21/3 : 1 (2) 1 : 21/3 (3) 31/2 : 1 (4) 1 : 31/2 21. Two nucleons are at a separation of 1 fm. The net force between them is F1 if both are neutrons, F2if both are protons, and F3 if one is a proton and the other is a neutron (1) F1 > F2 > F3 (2) F2 > F1 > F3 (3) F1 = F3 > F2 (4) F1 = F2 > F3 22. The number of  and  − emitted during the radioactive decay chain starting from 226 88Ra and ending at 206 82 Pb is (1) 3& 6 − (2) 4& 5 − ()    − ()    −
23. A certain radioactive substance has a half- life of5 years. Thus for a nucleus in a sample of the element, the probability of decay in ten years is (1) 50% (2) 75% (3) 100% (4) 60% 24. A freshly prepared radioactive source of half-life2 hours emits radiation of intensity which is 64times the permissible safe level. The minimum time after which it would be possible to work safely with the source is : (1) 6 hours (2) 12 hours (3) 24 hours (4) 128 hours 25. When a radioactive isotope 228 88Ra decays in series by the emission of 3 alpha particles and a beta particle, the isotope finally formed is 26. The mass defect for the nucleus of helium is0.0303 a.m.u. What is the binding energy per nucleon for helium in MeV? (1) 28 (2) 7 (3) 4 (4) 1 27. The mass density of a nucleus varies with mass number A as (1) A2 (2) A (3) constant (4) 1/A 28. In an  -decay the kinetic energy of - particle is 48 MeV and Q-value of the reaction is 50 MeV. The mass number of the parent s nucleus is (Assume that daughter nucleus is in ground state): (1) 96 (2) 100 (3) 104 (4) None 29. Heavy stable nuclei have more neutrons than protons. This is because of the fact that : (1) Neutrons are heavier than protons (2) Electrostatic force between protons is repulsive (3) Neutrons decay into protons through beta decay (4) Protons decay into neutrons through beta decay 30. Atomic weight of thorium is A = 232 and the atomic number is Z = 90. After disintegration to last element Pb is obtained which has A = 208 and Z = 82. In this process the number of emitted  and  particles are- (1) 4 and 6 (2) 6 and 4 (3) 3 and 2 (4) 2 and 3 31. The decay rate of sample of radioactive nuclide I128 after time 4 min and 36 min is 322 and 161 counts/s. Find half life for this radionuclide. (1) 28 min (2) 32 min (3) 16 min (4) 40 min 32. Consider the following reaction The atomic masses are given as The Q– value of the above reaction will be (1) –4.03 MeV (2) –2.01 MeV (3) 2.01 MeV (4) 4.03 MeV 33. A radioactive material decays by simultaneous emission of two particles with respective half lives 1620 and 810 years. The time (in years) after which one- fourth of the material remains is : (1) 1080 (2) 2430 (3) 3240 (4) 4860 34. Binding energy per nucleon verses mass number curve for nuclei is shown in the figure. W, X, Y and Z are four nuclei indicated on the curve. The process that would release energy is :- (1) Y → 2Z (2) W → X + Z (3) W → 2Y (4) X → Y + Z 35. A radioactive substance is being produced at a constant rate of 10 nuclei/s. The decay constant of the substance is 1 2 s –1 . After what time the number of radioactive nuclei will become 10 from zero ? Assume decay law holds for the sample : (1) 2.45 s (2) log(2) s (3) 1.386 s (4) 1 ln 2 s
36 . Which is not unit of radioactivity : (1) Becquerel (2) Curie (3) Sievert (4) Thomson 37 . There are two radioactive samples A and B with decay constant A and  B. Their activity (R) is plotted against number of active nuclei (N). Which one is correct :- 4) Can't be obtained 38 . How long a nuclear power plant of 10MW power can be operated by using fission energy of 20 kg U235 consider 50% fission energy can be converted in electricity : (1) 6 yrs (2) 3 yrs (3) 6000 yrs (4) 2000 yrs 39 . Which conservation is must in a nuclear reaction: (1) Baryon number (2) Lepton number (3) Charge (4) All of the above 40. In a radioactive disintegration, the ratio of initial number of atoms to the number of atoms present at an instant of time equal to its mean life is :- (1) 1/e2 (2) 1/e (3) e (4) e2 41. The half life of a radioactive isotope 'X' is 50 years. It decays to another element 'Y' which is stable. The two elements 'X' and 'Y' were found to be in the ratio of 1 : 15 in a sample of a given rock. The age of the rock was estimated to be :- (1) 150 years (2) 200 years (3) 250 years (4) 100 years 42. In the nuclear reaction 235 92 U decay to 231 91 Pa , what are the particles emitted :- (1) One  -particle and one proton (2) One  - particle and one electron (3) One deuteron and one positron (4) One electron and one proton 43. Two radioactive nuclei P and Q in a given sample decay into a stable nucleus R. At time t=0,number of P species are 4 N0 and that of Q areN0. Half-life of P (for conversion to R) is 1 minute where as that of Q is 2 minutes. Initially there are no nuclei of R present in the sample. When number of nuclei of P and Q are equal, the number of nuclei of R present in the sample would be :- (1) 2N0 (2) 3N0 (3) 0 9 2 N (4) 0 5 2 N 44. At t = 0, number of active nuclei in a sample is N0.How much no. of nuclei will decay in time between its first mean life and second half life? (1) N0 e (2) 0 0 4 N N e − (3) 0 0 2 N N e − (4) 0 4 N 45. The binding energies of nuclei X and Y are E1 and E2 respectively. Two atoms of X are fused to give one atom of Y and an energy Q is released. Then (1) Q = 2E1 – E2 (2) Q = E2–2E1 (3) Q = 2E1 + E2 (4) Q = 2E2 + E1 46. A radioactive element X with a half-life period of 2 hours decays giving a stable element Y. After a time t the ratio of X to Y atoms is 1 : 7. Then t is:- (1) 4 hr (2) 6 hr (3) Between 4 hr and 6 hr (4) 14 hr