266 Step 4. Review the Knowledge You Need to Score High
Answers and Explanations
- What is the missing product in the following
nuclear reaction? - Which of the following statements are correct
concerning βparticles?
I. They have a mass number of zero and a
charge of –1.
II. They are electrons.
III. They are less penetrating than αparticles.
(A) I and II
(B) I and III
(C) II and III
(D) I only
(E) II only - An atom of undergoes radioactive decay by
αemission. What is the product nuclide? - If 75% of a sample of pure decays in
24.6 years, what is the half-life of?
(A) 24.6 yr
(B) 18.4 yr
(C) 12.3 yr
(D) 6.15 yr
(E) 3.07 yr
1
(^31) H
(^3) H
(E) 238230 Pu
(D)^23091 Pa
(C)^23092 U
(B)^23490 Th
(A)^23090 Th
92
(^238) U
(E) Nb 4198
(D) Zr 4098
(C) Y^9639
(B) Sr 3896
(A) Y^9039
92
236
0
1
53
UnI→++ 4 136 _____
- D—The mass should be 226 −(4 + 4 + 0 +4) =
214. The atomic number should be 88 −(2 + 2 −
1 +2) =83. - B—Mass difference = 234 − 230 =4, and atomic
number difference = 92 − 90 =2. These corre-
spond to an αparticle. - C—Alpha particles are the least penetrating, and
gamma rays are the most penetrating. - C—Mass difference = 236 −4(1) − 136 =96.
Atomic number difference = 92 −4(0) − 53 =39.
5. A—In nuclear reactions the mass of a βparticle
is treated as 0, with a charge of −1. Electrons and
βparticles are the same thing.
6. B—Mass number = 238 − 4 =234, and atomic
number = 92 − 2 =90.
7. C—After one half-life, 50% would remain.
After another half-life this would be reduced by
one-half to 25%. The total amount decayed is
75%. Thus, 24.6 yr must be two half-lives of
12.3 yr each.