ACT Science Practice Test 102

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


Radioactive decay is a natural process by which an atom of a radioactive isotope (chemical element) spontaneously decays into another element. The unstable nucleus disintegrates by emitting alpha or beta particles, or gamma rays. This process changes the composition of the nucleus and continues to take place until a stable nucleus is reached. Half-life refers to the amount of time it takes for half (50%) of the atoms in a sample to decay.

Figure 1 shows the decay from Radon 222 to Polonium 218 and other decay products.

Figure 1

Figure 2 shows the decay from Mercury 206 to Thallium 206 to Lead 206.

Figure 2

Table 1 shows decay products and associated energy in MeV, million electron volts, and the type of particle emitted from the decay.

1. According to Figure 1, what is the approximate half-life of Radon 222?

F. 2 days
G. 4 days
H. 12 days
J. 16 days

2. Based on the passage, radioactive decay:

A. is unstable.
B. does not occur in nature.
C. is a natural process.
D. only occurs in half of the atoms.

3. Based on Table 1, what is the relationship between decay energy and the type of particle emitted?

F. Beta particles tend to have higher decay energies.
G. Alpha particles tend to have lower decay energies.
H. Alpha particles tend to have higher decay energies.
J. There is no apparent relationship between type of particle and decay energy.

4. When Technetium 98 decays into Ruthenium 98, the decay energy is 1.796 MeV. According to the data in Table 1, the decay particle type is most likely:

A. an alpha particle.
B. a beta particle.
C. similar to that of Radon 222.
D. extremely stable.

5. According to the passage, approximately when do Radon 222 and Polonium 218 have the same percent of atoms remaining?

F. On Day 2.
G. On Day 4.
H. On Day 8.
J. On Day 16.

6. What statement best explains the meaning of the shape of the Radon 222 curve in Figure 1 and the Mercury 206 curve in Figure 2?

A. The rate of decay is erratic.
B. The rate of decay starts off slowly and then speeds up.
C. The rate of decay occurs very quickly at first and slows as the number of atoms is reduced.
D. The rate of decay occurs at a fairly steady rate over time.