Gerry Klinglesmith
Nuclear Science & Technology Workshop
Lesson Plan for June 6, 2002
NATURAL RADIOACTIVE SERIES
Grade Level: Grades 6 – 12
Target Class Size: 15 to 30
Objectives:
Students will understand alpha and beta particles
Students will understand what happens to elements as they undergo alpha and beta
decays
Materials Required:
Sheet of large-square graph paper for each student (1 cm graph paper works
well)
Procedure: Lecture
1.
Alpha particle is composed of 2 protons and 2 electrons, therefore it has an atomic number of 2 and an
atomic mass of 4 (it is the same as a Helium nucleus). When an the nucleus of an element undergoes
alpha decay its atomic mass decreases by 4 and its atomic number decreases by 2, changing it to a
different element.
2.
A beta particle is an electron, it is formed when a neutron in the nucleus of a particular atom breaks
down into a proton and an electron. The electron is the beta, particle which escapes, and the proton
formed remains in the nucleus. In this process, the atomic mass of the original element remains the
same (the neutron is now a proton and each has an atomic mass of one). But, the atomic number of the
nucleus goes up by one because the nucleus now has one more proton and it is the number of protons
in a nucleus that determines the atomic number, therefore the original element undergoing decay
becomes a new element.
3.
Work through a number of examples on the chalk board or overhead showing equations such as
Alpha Decay
238
U
92

4
He
2
+
134
Th
90

234
Pa
91
Beta Decay
134
Th
90
4.
0

e
-1
Have students chart the path of the U-238 decay series on 1 cm graph paper.
x-axis labeled from 124 to 146 (going up by increments of 2 or 4)
y-axis labeled from 81 to 92 (going up by increments of 1/2 or 1)
(Remind them, if necessary, that the atomic mass is the number of protons plus the number of neutrons
in a nucleus and the name of the element is determined by the number of protons in the nucleus of an
atom.)
5.
They will need to know the sequence of decays that occur going from U-238 to Pb-206, which is:
alpha beta
beta
alpha alpha alpha alpha alpha beta
beta
alpha
beta
beta
alpha
that is: 1 alpha, 2 betas, 5 alphas, 2 betas, 1 alpha, 2 betas, 1 alpha
DECAY CHAIN OF URANIUM-238
Step
Element
Event
New element
1.
Uranium (at. Mass 238, at. # 92)
alpha particle
+ Th (at. Mass 234, at # 90)
2.
Thorium (at. Mass 234, at # 90)
beta particle
+ Pa (at. Mass 234, at. # 91)
3.
Protactinium (at. Mass 234, at. #
91)
beta particle
+ U (at. Mass 234, at. # 92)
4.
Uranium (at. Mass 234, at. # 92)
alpha particle
+ Th (at. Mass 230, at. # 90)
5.
Thorium (at. Mass 230, at. # 90)
alpha particle
+ Ra (at. Mass 226, at. # 88)
6.
Radium (at. Mass 226, at. # 88)
alpha particle
+ Rn (at. Mass 222, at. # 86)
7.
Radon (at. Mass 222, at. # 86)
alpha particle
+ Po (at. Mass 218, at. # 84)
8.
Polonium (at. Mass 218, at. # 84)
alpha particle
+ Pb (at. Mass 214, at. # 82)
9.
Lead (at. Mass 214, at. # 82)
beta particle
+ Bi (at. Mass 214, at # 83)
10.
Bismuth (at. Mass 214, at # 83)
beta particle
+ Po (at. Mass 214, at. # 84)
11.
Polonium (at. Mass 214, at. # 84)
alpha particle
+ Pb (at. Mass 210, at. # 82)
12.
Lead (at. Mass 210, at. # 82)
beta particle
+ Bi (at. Mass 210, at. # 83)
13.
Bismuth (at. Mass 210, at. # 83)
beta particle
+ Po (at. Mass 210, at. # 84)
14.
Polonium (at. Mass 210, at. # 84)
alpha particle
+ Pb (at. Mass 206, at. #82)
Pb-206 is a stable isotope and does not decay
Evaluation:
Grade charts for accuracy (correct decays, at. Mass and at. Numbers.