Teach lesson
Radioactivity 2/2: shielding and penetration
Students compare seven remote-lab configurations, calculate the percentage of the detected count that remains, and use the pattern to identify evidence consistent with alpha, beta, and gamma radiation.
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Learning Outcomes
Compare absorbers while keeping distance, duration, and number of repeats constant.
Calculate the percentage of the detected count that remains relative to the control for the same source.
Relate penetration patterns to evidence consistent with alpha, beta, and gamma radiation in this setup.
Distinguish detector counts, the dominant detected pattern consistent with alpha-, beta-, or gamma-like behaviour, and risk to a person.
Write a short conclusion containing a claim, evidence, reasoning, and a limitation.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Materials do not affect all radiation in the same way
6 min
Paper, aluminium, and lead are not simply three versions of the same shield.
A light material may reduce the detected count for one pattern almost to zero,
while counts still remain for another pattern with the denser material in place.
This contrast lets you investigate the dominant pattern detected by this setup.
It does not prove that an isotope emits only one type of radiation, and it
cannot be used to calculate a personal dose.
In this prediction, relative decrease means the change from the no-absorber
control for that same source. A larger decrease would leave a smaller percentage.
Before measuring, in which comparison do you expect the largest relative
decrease in detected count?
Give one brief reason for your choice. You are assessed for making a reasoned
prediction, not for guessing the result correctly before measuring.
Compare each source with itself
4 min
Set the distance to 20 mm, the duration to 5 s, and the number of repeats to 3.
To find the effect of an absorber, compare its mean with the no-absorber control
for the same source. Do not compare the initial counts from different
sources directly.
Which comparison allows you to attribute the change to the absorber?
Run seven checks
28 min
You will run three controls and four measurements with an absorber. For each
configuration, the lab returns three counts. Calculate the mean on paper or
with a calculator; in TEACH, enter only the mean and the percentage of the
detected count that remains.
Open the Radioactivity lab
Open the lab from this activity and choose advanced mode (
Modo avanzado).Keep 20 mm (
Distancia), 5 s (Duración), and 3 repeats (Repeticiones) throughout the series.Measure the no-absorber (
Ninguno) controls for Americium-241, Strontium-90, and Cobalt-60.Then measure Americium-241 + paper (
Papel); Strontium-90 + paper; Strontium-90 + aluminium disc (Disco de aluminio); Cobalt-60 + lead disc (Disco de plomo).For each row, calculate the mean of the three readings before moving to the next one.
Do not use the sheet, x2, or x4 options in this activity.
Sources in advanced mode
Select all three sources during the series. The Strontium-90 highlight in the
screenshot is only an example, not the only source to use. The interface may
show Fuente, meaning source.
Controls and absorbers
Complete exactly seven rows. Enter 100% for each no-absorber control. For every other row, calculate: mean with absorber / mean of the no-absorber control for the same source x 100. The result is the percentage of the detected count that remains, not a direct measurement of the percentage of radiation transmitted. If extra rows appear, leave them blank.
| Source | Absorber | Mean of 3 readings counts | Detected count remaining % |
|---|---|---|---|
Use your Americium-241 rows. Enter the percentage of the detected count that
remains with paper, and show the calculation using the no-absorber control for
the same source. Round to one decimal place.
From the observed pattern to the model
7 min
Now that you have data, use the penetration model. In general, an alpha-like
pattern produces almost no detected counts after a light barrier; a beta-like
pattern passes through paper but is greatly reduced by aluminium; and a
gamma-like pattern is more penetrating, so dense shielding reduces it without
guaranteeing that it disappears.
Penetration model for interpreting the data
The diagram is a general model. The classification below refers to the dominant
pattern detected in this setup, not to every possible emission from each
isotope.
The dominant pattern detected for Americium-241 is most consistent with...
The dominant pattern detected for Strontium-90 is most consistent with...
The dominant pattern detected for Cobalt-60 is most consistent with...
Conclusion and safety limitation
8 min
Write one integrated conclusion in four short sentences:
1. I claim that... summarise what the absorbers reveal.
2. I know this because... select two percentages from two different sources.
3. This means that... connect those two contrasting cases to the alpha/beta/gamma model.
4. One limitation is... identify variation, the small number of repeats, or the fact that counts are not dose.
Polonium-210 shows why low penetration does not mean no risk. External alpha
irradiation generally has little effect on intact skin, but the eyes, wounds,
and contamination matter. If an alpha-emitting substance enters the body by
inhalation or ingestion, it can deposit energy in a highly localised area.
Activity, exposure time, route of exposure, and chemical form also matter.
Which conclusion is scientifically responsible?