Radioactive Investigation
Name ____________________________
Purpose:
In part 1 You will measure background radiation at our school lab using a
digital Geiger counter.
In part 2 You will be altering the distance of the radioactive source from
the Geiger probe to see if distance from the source makes any significant
difference in the reading. You will also block each source with paper & note
any
differences.
In part 3 You will measure radiation in different parts of our school using a digital Geiger counter.
Background:
Alpha decay: nucleus spontaneously emits an alpha particle (symbol: α particle), which is 2 p+ and 2 n (or also
the same as a Helium (He) atom).
Result: atomic number decreases by 2 (lost 2 p+)
Result: atomic mass decreases by 4 (lost 2 p+ and 2n = 4 amu)
Beta decay: neutron in nucleus spontaneously emits a beta particle (symbol: β particle), which is essentially an
electron trapped in a neutron. The neutron, therefore, turns itself into a proton.
Result: atomic number increases by 1 (gained 1 p+)
Result: atomic mass stays same (no mass lost or gained: β particle or electrons have no mass)
Beta or electron capture: proton in nucleus captures a beta particle (symbol: β particle), which is essentially an
electron that can become part of a neutron. The proton, therefore, turns itself into a neutron.
Result: atomic number decreases by 1 (lost 1 p+)
Result: atomic mass stays same (no mass lost or gained: β particle or electrons have no mass)
Procedure:
1. Get a Geiger counter.
2. Test the lab area that you will be working for background radiation. Record!
3. Obtain a radioactive source. Test the radiation at different distances. Record!
4. Try blocking the radiation with a piece of paper, plastic, and Pb foil. Record!
5. Return your sample.
6. Wander around the campus and anywhere there are “spikes” write down exactly where and what the
reading was. Record!
Data: Background radiation reading in lab_____________________________________c.p.m.
A. Radioactive source_______________________________
Less than 2 cm away 1 meter away
1 lab table away
Reading
c.p.m.
c.p.m.
c.p.m.
Reading, covered
w/paper
c.p.m.
Reading w/ 0.5 cm
lead
c.p.m.
Reading with plastic
c.p.m.
Reading with book
c.p.m.
B. Radioactive source_______________________________
Less than 2 cm away 1 meter away
1 lab table away
Reading
c.p.m.
c.p.m.
c.p.m.
Reading, covered
w/paper
c.p.m.
Reading w/ 0.5 cm
lead
c.p.m.
Reading with plastic
c.p.m.
Reading with book
c.p.m.
C.
School “HOT” spots
Place – be very
descriptive
What was the
reading?
Why do you think
these are “hot” spots?
1st Hot Spot
2nd Hot Spot
c.p.m.
3rd Hot Spot
c.p.m.
c.p.m.
Analysis:
1. Fill in the table:
Give the nuclear What stops this?
symbol
What radiation do you believe was
given off by each sample that you
tested?
Sample A
Sample B
alpha
beta
gamma
2. List several sources of background radiation.
3. Explain the differences you would observe in the effectiveness of plastic vs. lead in stopping gamma
radiation. Why do you think one is better than the other?
4. Nuclear reactor containment walls are lined with thick concrete, stainless steel, and sometimes even
lead!! What type of radiation do you suppose could be found inside which would warrant such extreme
shielding measures?
5. What are the units of the readings you took? ___________
6. Explain why smoke detectors, which contain radioactive americium, poses no serious health risk.
7. Given Thorium-232 has a half life of of 14 billion (14x109) years, and decays by alpha emission, with
accompanying gamma radiation.
a. Write an equation for this reaction.
b. How much of a 45.0 mg sample would remain after 3.4 billion years?
8. State the number of neutrons and protons in each of the following nuclei:
Protons
Neutrons Electrons
2
1H
12
6
C
56
26
197
79
Fe
Au
9. Complete the following nuclear reactions:
a. 226
+ 01 e
88 Ra 
b.
209
84
c.
238
92
d.
234
90
e.
Po 
205
82
+ 24 He
U
Th 
+
Pb +
234
91
14
7
Pa +
N  178 O + 11 H
f.
When isotope bismuth-213 emits an alpha particle:
i. Write out the nuclear equation:
_______________________________________
ii. Which is the parent element? _____________________________
iii. Which is the daughter element? ___________________________
iv. What new element results if the isotope, instead, emits a beta particle?
10. Looking at the decay of Uranimum-235 to Lead-207. What is the minimum time needed to decay all
the way, skipping the first 700 million years?
β 26 hours
Uranium-235
α
Protactinium-231
α
700 million years
Thorium-231
Actinium-227
α
33,00 years
β
Thorium-227
22 years
α
22 years
Uranium-235
β
22 minutes
19 days
Radium-223
α
11 days
Radon-219
α
4.0 seconds
Polonium-215
α
700 million years
Bismuth-211
α
Uranium-235
2.1 minutes
Thallium-207
β
α
36 minutes
β 4.8 minutes
Lead-211
α
Lead-207 (stable)
Conclusion: (What did you learn?)
1.8 milliseconds
700 million years
Answer: