Topic: Radioactivity. H 2 atom. The mass of 1

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1. Calculate the binding energy for 1 H 2 atom. The mass of 1 H 2 atom is 2.014102 amu, where 1n and 1p have their weights 2.016490 amu. Neglect mass of electron. 2.2232 MeV. 2. The atomic masses of Li, He and proton are 7.

1 1. Calculate the binding energy for 1 H 2 atom. The mass of 1 H 2 atom is amu, where 1n and 1p have their weights amu. Neglect mass of electron MeV. 2. The atomic masses of Li, He and proton are amu, amu, amu respectively. Calculate the energy evolved in the reaction, Given 1 amu = 931 MeV MeV. 3 Li7 + 1 p He 4 + E 3. Calculate the energy released in joules and MeV in the following nuclear reaction: 2 1H H 3 2 H n Assume that the masses of 2 1 H, 3 2 H and neutron (n) respectively are , and in amu J 4. Calculate the mass defect and binding energy per nucleon for an alpha particle whose mass is amu. m P = and m N = amu. Mass defect = amu B.E./nucleon = MeV 5. Calculate mass no., atomic no. and group in the periodic table for RaC in the following change. α 88 Ra226 Rn α RaA β RaB α RaC At. no. of RaC = 83 Mass no. of RaC = 214 PHYSICAL CHEMISTRY by: SHAILENDRA KR. Classes at: - SCIENCE TUTORIALS; Opp. Khuda Baksh Library, Ashok Rajpath, Patna PIN POINT STUDY CIRCLE; House No. 5A/65, Opp. Mahual Kothi, Alpana Market, Patna Topic: Radioactivity Group of element RaC is V from configuration 2, 8, 18, 32, 18, 5. The no. of electrons in outer shell suggest for group. Meq. Approach Page No.: 1

2 6. Calculate no. of α and β-particles emitted when 92 U 238 changes into radioactive 82 Pb 206. No. of α-particles = 8 No. of β-particles = 6 7. The atomic mass of Th is and its atomic number is 90. In terms of its radioactive disintegration six α and β-particles four are emitted. What is mass no. and at. no. of products? X has at. no. = 82 Mass no. = Calculate the group of elements formed in the final stage of radioactive changes given below: α β (a) 92 U Th231 (b) 90 Th X231 III gp. III gp. (c) 91 X 231 α 89 Ac227 (d) 90 Th α Ra227 III gp (a) Th is in III gp. (b) 91 X 231 is also in III gp. (c) 89 Ac 227 is also in III gp. (d) 88 Ra 227 is also in II gp. 9. One g of 79 Au 198 (t 1/2 = 65 hr) decays by β-emission to produce stable Hg. (a) Write nuclear reaction for process. (b) How much Hg will be present after 260 hr. (a) 79 Au Hg e 0 (b) 15/16 g Hg. 10. The half life period of 53 I 125 is 60 days. What % of radioactivity would be present after 180 days? 12.5% 11. One of the hazards of nuclear explosion is the generation Sr 90 and its subsequent incorporation in bones. This nucleoid has a half life of 28.1 year. Suppose one microgram was absorbed by a new-born child, how much Sr 90 will remain in his bones after 20 year? g 12. The activity of a radioactive isotope falls to 12.5% in 90 days. Compound the half life and decay constant of isotope. 30 days 13. The activity of a radioactive sample drops to 1/64th of its original value in 2 hr. Find the decay constant for sample. Ans : sec 1 Page No.: 2

3 14. Calculate the time i which activity of an element reduces to 90% of its original value. The half life period of element is year year 15. The activity of the hair of an egyption mummy is 7 disintegration minute 1 of C 14. Find the age of mummy. Given t 0.5 of C 14 is 5770 year and distegration rate of fresh sample of C 14 is 14 disintegration minute year 16. What mass of C 14 with t 1/2 = 5730 year has activity equal to one curie? g 17. The decay constant for an α-decay of Th 232 is sec 1. Find out the no. of α-decays that occur from 1 g sample in 365 days α-atom 18. The disintegration rate of a certain radioactive sample at any instant is 4750 dpm. Five minutes later, the rate becomes 2700 dpm. Calculate half life of sample minute 19. A certain radio isotope Z X A (t 1/2 = 10 days) decays to give Z-2 Y A-4. If one g atom of Z X A is kept in a sealed vessel, how much He will accumulate in 20 days at STP? ml He g atoms of an α-active radioactive isotope are disintegrating in a sealed container. In one hour, the He gas collected at STP is 11.2 cm 3. Calculate half life of radioactive isotope hours 21. A solution contains 1 millicurie of L-phenyl alanine C 14 (uniformly labelled) in 2.0 ml solution. The activity of labelled sample is given as 150 milli curie/milli mole. Calculate: (a) the concentration of sample in the solution in mole/litre (b) the activity of the solution in terms of counting per minute/ml at a counting efficiency of 80%. (a) M (b) cpm/ml 22. The 6 C 14 and 6 C 12 ratio in a piece of wood is 1/16 part that of atmosphere. Calculate the age of wood. t 1/2 of C 14 is 5577 year year 23. The isotope U 238 and U 235 occur in nature in the ratio 140:1. Assuming that at the time of earth formation, they were present in equal ratio, make an estimation of the age of earth. The half life period of U 238 and U 235 are and year respectively year Page No.: 3

4 24. The half life period of C 14 is 5760 year. A piece of wood when buried in the earth had 1% C 14. Now as charcoal it has only 0.25% C 14. How long has the piece of wood been buried? year 25. (a) On analysis a sample of uranium ore was found to contain g of 82 Pb 206 and g of 92 U238. The half life period of U 238 is year. If all the lead are assumed to have come from decay of 92 U 238, What is the age of earth? (b) An ore of 92 U 238 is found to contain 92 U 238 and 82 Pb 206 in the weight ratio of 1 : 0.1. The half life period of 92 U 238 is year. Calculate the age of ore. (a) year (b) year 26. In nature a decay chain series starts with 90 Th 232 and finally terminates at 82 Pb 208. A thorium ore sample was found to contain ml of He at STP and g of Th 232. Find the age of ore sample assuming that source of He to be only due to decay of Th 232. Also assume complete retention of He within the ore. t 1/2 Th 232 = year year 27. In a sample of radioactive element, radium disintegrates at an average rate of α- particles per minute. Each α-particle takes up 2 electrons from the air and becomes a neutral helium atom. After 420 days, the He gas collected was 0.5 ml measured at 27 C and 750 mm of mercury pressure. From the above data, calculate Avogadro s no particle/mol 28. A solution contains a mixture of isotopes of X A 1 (t 1/2 = 14 days) = X A 2 (t 1/2 = 25 days). Total activity is 1 curie at t = 0. The activity reduces by 50% in 20 days. Find: (a) the initial activities of X A 1 and X A 2. (b) the ratio of their initial no. of nuclei. (a) (b) What amount of energy is evolved by a curie of Rn (an α-emitter) in (a) one hour (b) its mean life? Given that kinetic energy of one α-particle is 5.5 MeV and λ = sec 1 for Rn. (a) J (b) J 30. A small amount of solution containing Na 24 radio nucleide with activity A = dps was administered into blood of a patient in a hospital. After 5 hours, a sample of the blood drawn out from the patient showed an activity of 16 dpm per c.c t 1/2 for Na 24 = 15 hr. Find Page No.: 4

5 (a) Volume of the blood in patient. (b) Activity of blood sample drawn after a further time of 5hr. (a) ml (b) dps per ml 31. It is known that 1 g of Ra 226 emits atoms of a per year. Given the half life of Ra 226 be 1600 year. Compute the value of Avogadro s no At radioactive equilibrium, the ratio between two atoms of radioactive elements A and B are : 1. If half life period of A is year, what is half life of B? 6.45 year 33. The mean lives of a radioactive substance are 1620 year and 405 year for α-emission and β-emission respectively. Find out the time during which three fourth of a sample will decay if it is decaying both by α-emission and β-emission simultaneously year 34. Ac 227 has a half life of 22 year with respect to radioactive decay. The decay follows two parallel paths, one leading the Th 227 and the other leading to Fr 223. The percentage yields of these two daughters nucleides are 2% and 98.0% respectively. What is the rate constant in y 1, for each of the separate paths? yr Cu (half life = 12.8 h) decays by β emission (38%), β + emission (19%), and electron capture(43%). Write the decay products and calculate partial half lives for each of the decay processes. β emission = hr β emission = hr t 1/2 for electron capture = hr 36. Match the following : 1. Isotopes A. 8 O 16 and 8 O Isobars B. Na +, Mg 2+, F 3. Nuclear isomers C. 1 H 2 and 2 He 3 4. Isosters D. U A and U Z 5. Isotones E. CO 2 and N 2 O 6. Isoelectronics F. A X Z, A-2 X Z-4 7. Isodiaphers G. 20 Ca 40 and 19 K 40 Do Yourself Page No.: 5

MockTime.com. Ans: (b) Q6. Curie is a unit of [1989] (a) energy of gamma-rays (b) half-life (c) radioactivity (d) intensity of gamma-rays Ans: (c)

MockTime.com. Ans: (b) Q6. Curie is a unit of [1989] (a) energy of gamma-rays (b) half-life (c) radioactivity (d) intensity of gamma-rays Ans: (c) Chapter Nuclei Q1. A radioactive sample with a half life of 1 month has the label: Activity = 2 micro curies on 1 8 1991. What would be its activity two months earlier? [1988] 1.0 micro curie 0.5 micro