Name:
Section:
Pre-Lab 3: Nuclear Chemistry
Answer the following questions after reading the background information at the
beginning of the lab. This should be completed before coming to lab.
1. Show the symbols, with mass number and atomic number, for the following types of
radioactive decay particle:
a) Alpha Particle
b) Beta Particle
b) Positron
d) Gamma Ray
e) Proton
f) Neutron
2. If 242
Am undergoes an Alpha particle emission, what element is leftover?
95
3. If the SI unit Gray = 100 rad, how many Gray are in 140006 mrad?
4. If the half life of 131I is 8.0 days, how long will 25.0 g of 131I take to decay to less than
3.0 g?
Lab 3: Nuclear Chemistry
Objective: The objective of this experiment is to learn about the different types of
radiation and their properties as well as determine a radioactive element’s half-life.
Background Information: Elements with atomic number <19 have for the most part
stable nuclei. Above this atomic number, however are many unstable nuclei. To
remove this instability, the nuclei undergo radioactive decays to stabilize themselves.
These radioactive decay can result in the ejection of different radioactive particle.
These different types of particles are an alpha particle (α, 42He), a beta particle (β, -10e),
a positron( β+, 10e), a proton (p, 11H), neutron(n, 10n), or gamma radiation (γ, 00γ). These
particles have different properties and thus have different health risks depending on
the type of radiation.
Part 1. Determination of the Background Radiation.
There is radiation all around us, known as background radiation. In order to make
radioactivity measurements, the naturally occuring background radiation must be
determined so we can remove it from subsequent measurements.
Materials Needed:
Vernier Digital Radiation Monitor
Procedure:
1. Turn the radiation monitor on, and set it to the counts per minute setting (CPM).
2. Wait 1 min then begin taking a reading every minute for 5 minutes.
3. Average the values to get the Average Background Radiation.
1st Minute
2nd Minute
3rd Minute
Show the work for the averaging of the counts:
4th Minute
5th Minute
Average
Counts
Part 2. Determination of the Type of Radiation from a Source.
This experiment will determine the penetrating ability of the 3 main types of emitted
radiation: alpha, beta and gamma.
Materials Needed:
Vernier Digital Radiation Monitor, Source kit with 3 radiation sources, 1 piece of paper,
aluminum foil.
Procedure:
1. Turn the radiation monitor on, and set it to the counts per minute setting (CPM).
2. Position the source directly under the radiation counter.
3. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
4. Get a piece of paper and position it between the source and the radiation counter.
5. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
6. Remove the paper and replace it with a sheet of aluminum foil.
7. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
Source 1:
Shielding
Material
1st Minute
2nd Minute
Average
Counts
Background
Corrected Avg.
1st Minute
2nd Minute
Average
Counts
Background
Corrected Avg.
Source 2:
Shielding
Material
Source 3:
Shielding
Material
1st Minute
2nd Minute
Average
Counts
Background
Corrected Avg.
Question: Which source has the most penetrating radiation and why?
Question: Which source has the least penetrating radiation?
Part 3. Gamma Radiation.
Gamma radiation is the most penetrating type of radioactive emission.
This experiment will determine the penetrating ability of the 3 main types of emitted
radiation: alpha, beta and gamma.
Materials Needed:
Vernier Digital Radiation Monitor, Gamma radiation source disk (60Co), shielding kit,
shield holder, ring stand, ruler.
Procedure:
Effects of Shielding
1. Turn the radiation monitor on, and set it to the counts per minute setting (CPM).
2. Position the source at the bottom of the shield holder, directly under the radiation
counter.
3. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
4. Get a piece of aluminum foil from the shield kit and position it between the source and
the radiation counter.
5. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
6. Remove the shield and get another, thicker, aluminum foil piece.
7. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
8. Remove the second aluminum foil and get a thin lead foil piece.
9. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
10. Remove the shield and get another, thicker, lead foil piece.
11. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
Shield
Density
1st Minute
2nd Minute
Average
Counts
Background
Corrected
No Shielding
Aluminum
Sheet 1
Aluminum
Sheet 2
Lead Foil 1
Lead Foil 2
Question: Lead is significantly denser than aluminum. What affect does this have on the
gamma radiation?
Question: When you get an X-ray, they put a heavy blanket containing a metal covering
what isn’t being X-rayed. Why is this and which metal is most likely in the blanket?
Effects of Distance
1. Next remove the source and lay it on the desk. Use a ruler to determine 10 cm above
the source. Hold the radiation counter at this height.
2. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
3. Move the radiation counter to 20 cm above the source.
4. Wait 1 min then begin taking a reading every minute for 2 minutes. Average the
counts. Then subtract the average background radiation determined in Part 1.
5. Repeat this for distances of 30 and 40 cm.
1st Minute
2nd Minute
Average
Counts
Background
Corrected
Distance 1.
10 cm
Distance 2.
20 cm
Distance 3.
30 cm
Distance 4.
40 cm
5. Plot the results for the distance vs count rate below, with distance in cm as the bottom
axis and counts as the left axis.
Distance Plot:
Question: What is the relationship between the distance of
the detector and the count rate? Is it a linear response, or
something else, explain:
Part 4. Determination of the Half-Life of 137Ba.
Radioactive materials decay at different rates. This rate is measured in terms of a halflife, where 1 half-life is the time necessary for ½ of the original material to have
transformed into a different element. 137Ba has a short half-life; we will use a solution of
137
Ba to determine this half-life value.
Materials Needed:
Vernier Digital Radiation Monitor, metal tray for solution.
Procedure:
1. Turn the radiation monitor on, and set it to the counts per minute setting (CPM).
2. Position the radiation counter in the ring stand to stand 1cm above the metal tray.
3. Have the instructor distribute drops of the radioactive solution.
4. Wait 1 minute and then begin taking reading every 30 seconds for 18 minutes.
Time
Counts
Background
Adjusted Counts
5. Graph the results on the space below. The side axis is counts per minute (CPM) and
the bottom axis is time (in Minutes)
6. Draw in a best fitting line that matches the data.
Graph of results
Determination of the half-life of 137Ba
1. On the graph, read the counts/min at time 2 minutes.
2. Find the time at which the count rate is half of the count rate at 2 minutes.
3. Record this time in the chart below.
4. Pick another time between 3-5 minutes.
5. Find the time at which the count rate is half of the count rate at this point.
6. Record these values in the chart below.
7. Pick a third time between 5-8 minutes.
8. Find the time at which the count rate is half of the count rate at this point.
9. Record these values in the chart below.
10. Average the 3 measured changes in time to give the half-life of 137Ba.
Initial Time
1st
Determination
2 minutes
2nd
Determination
3rd
Determination
Count Rate
Half the Rate
Time graph
for half-rate
∆Time
Average Change in
Time
Question: When calculating the half-life, what could potentially cause the variations in
time determinations?
Question: How long will it take the sample of 137Ba to be emitting at background
radiation levels?
Name:_________________
Nuclear Chemistry Report Sheet
Partner:________________
Section:________________
Part 1. Determination of the Background Radiation
What was the determined average background radiation level?
Part 2. Determination of the Type of Radiation from a Source.
Which source was stopped by a single piece of paper?
Which source showed the most penetration radiation?
Part 3. Gamma Radiation.
Did the aluminum or metal have more absorption of the
gamma radiation?
What is the relationship between the distance between
the source and the counter and the count rate?
Part 4. Determination of the Half-Life of 137Ba
What is the average half-life determined for 137Ba?
How long does it take for the 137Ba sample to decay
down to background levels?
Part 5. Additional Questions
1. 241Am is used in smoke detectors as an alpha source. Write the balanced equation for
an alpha particle emission from americium.
2. 238U, in its decay cycle, undergoes an alpha particle loss followed by 2 separate beta
particle losses, followed by 2 more alpha particle losses. What elements exist at each
point of this decay cycle?