Download P 3.5 Answers #3

FORM SEVEN PHYSICS (P 3.5 -ATOMIC/NUCLEAR)
ANSWERS
WORKSHEET THREE: NUCLEAR PHYSICS
1.
28 protons and 32 neutrons.
2.
Isotopes are atoms of the same element with different numbers of neutrons.
3.
Fusion is a nuclear reaction in which two smaller nuclei join together to form a
larger nucleus.
4.
Fission is a nuclear reaction in which a large nuclei splits into smaller ones.
5.
For a chain reaction to occur, the nucleus needs to release 3 or more neutrons per
decay event. The decay needs to be initiated by collision with a neutron and there
needs to be more than the critical mass of material present.
6
(a)
241
95
7.
(a)
14
6
8.
(a)
Gamma
9.
(a)
Mass alpha particle = 6.64591 x 10-27
Am 
C
237
93

Np +
14
7
4
2
He
N
+
(b)
Beta
Total mass of nucleons
0
1
e
(c)
Ra

222
86
Cu

0
1
(b)
226
88
(b)
60
29
Gamma
(d)
e
Rn +
+
60
28
4
2
He
Ni
Alpha
= 2( 1.67338 x 10-27) + 2(1.67483 x 10-27)
= 3.3467 x 10-27 + 3.34966 x 10-27
= 6.69624 x 10-27
(b)
10.
Mass deficit
= 0.05051 x 10-27
Binding energy
= 0.05051 x 10-27 x (3 x 108)2 = 4.5459 x 10-12 J
Binding energy per nucleon = 1.136475 x 10-12 J
Rest mass of products = 6.6443 x 10-27 + 1.6747 x 10-27 = 8.3190 x 10-27 kg
Rest mass of reactants = 3.3434 x 10-27 + 5.0 x 10-27 = 8.3434 x 10-27 kg
Mass deficit = 2.44 x 10-29 kg
Binding energy = energy released = 2.44 x 10-29 x (3 x 108)2 = 2.196 x 10-12 J
11.
(a)
Mass of 1 amu = 1.6604 x 10-27 kg
(b)
Energy equivalent = mc2 = 1.6604 x 10-27 x (3 x 108)2 = 1.49436 x 10 –10 J
(c)
In eV = 9.340 x 108 eV = 934 MeV
12.
Binding energy
per nucleon
Fe
He
U
H
Mass Number
(a)
Iron. Iron has the highest binding energy per nucleon and so the iron
nucleus needs more energy input per nucleon than any other nucleus to
separate into its individual nucleons.
(b)
Elements to the right of iron become progressively less stable in their larger
nuclei and so by splitting (fission) their nuclei can become smaller and
more stable and release energy in doing so.
Elements to the left of iron have less stable small nuclei and so by joining
two smaller nuclei together (fusion) to form a larger nuclei there can be an
increase in stability and a release of energy.