PHYS212-071
HW # 11 (Chapter 13)
(Numbers refer to 2nd Edition of Textbook)
15. Calculate the binding energy per nucleon for the nuclei
20
40
93
(a)10
Ne, (b) 20
Ca, (c) 41
Nb, (d )197
79 Au
Answer:
BE / A  Zm p  ( A  Z )mn  M ( ZAX )  931.4943 / A
Ne-20: 8.03 MeV/nucleon
Ca-40: 8.55 MeV/nucleon
Nb-93: 8.66 MeV/nucleon
Au-197: 7.92 MeV/nucleon

22. The half-life of

131
I is 8.04 days. (a) Calculate the decay constant for this isotope.
(b) Find the number of I nuclei necessary to produce a sample with an activity of 0.5 Ci.
131
Answer:
(a)  = 0.693/T1/2 = 0.693/ (8.04 x 24 x 3600) s-1 = 9.97 x 10-7 s-1
(b) A = N  N = A/ = (0.5 x 10-6 x 3.7 x 1010)/ (9.97 x10-7)  2 x 1010 nuclei
26. How many radioactive atoms are present in a sample that has an activity of 0.2 Ci
and a half-life of 8.1 days?
Answer:
N = A/ = A x T1/2/0.693 = (0.2 x 10-6 x 3.7 x 1010) x (8.1 x 24 x 3600)/0.693  8 x109
41. Find the energy released in the alpha decay of 238
92 U :
4
U  234
90Th  2 He
238
92
Answer:
If we neglect the recoil energy of the heavy Thorium nucleus, then the energy of the
alpha particle is just the Q of the reaction; namely
Q = (M (U-238) – M (Th-234) – M (He-4)) x 931.4943 MeV = 4.3 MeV
1
50. Starting with 235
92 U , the sequence of decays shown in Figure P13.50 is observed,
ending with the stable isotope 207
82 Pb . Enter the correct isotope symbol in each open
square.
2