IB Physics Radioactive decay Practice Questions

Q: A sample has an activity of $800\,\text{Bq}$. After $3$ half-lives, the activity is:

$100\,\text{Bq}$. Each half-life halves the activity: $800\to 400\to 200\to 100\,\text{Bq}$.

Question 1

An alpha particle is identical to:

Accepted Answer

A helium-4 nucleus. An alpha particle is a helium-4 nucleus, consisting of two protons and two neutrons.

Question 2

Which type of radiation is the most penetrating?

Accepted Answer

Gamma. Gamma radiation is the most penetrating, requiring thick lead or concrete; alpha is stopped by paper, beta by aluminium.

Question 3

The half-life of a radioactive isotope is the time taken for:

Accepted Answer

Half of the nuclei present to decay. The half-life is the time for half of the original radioactive nuclei in a sample to decay.

Question 4

When a nucleus emits an alpha particle, its nucleon number:

Accepted Answer

Decreases by 4. Alpha emission removes 2 protons and 2 neutrons, so the nucleon number decreases by 4 and proton number by 2.

Question 5

In beta-minus decay, a neutron in the nucleus changes into a:

Accepted Answer

Proton, emitting an electron and antineutrino. In $\beta^{-}$ decay a neutron becomes a proton, emitting an electron and an antineutrino, so the proton number increases by 1.

Question 6

A sample has an activity of $800\,	ext{Bq}$. After $3$ half-lives, the activity is:

Accepted Answer

$100\,	ext{Bq}$. Each half-life halves the activity: $800	o 400	o 200	o 100\,	ext{Bq}$.

Question 7

The time taken for half the radioactive nuclei in a sample to decay is called the _____.

Accepted Answer

half-life / half life. Half-life is constant for a given isotope and independent of the amount present.

Question 8

After 3 half-lives, the fraction of the original radioactive nuclei remaining is _____.

Accepted Answer

1/8 / one eighth / 0.125. Each half-life halves the number: $\left(\frac{1}{2}\right)^{3}=\frac{1}{8}$.

Question 9

When a nucleus undergoes alpha decay, how do its proton number Z and nucleon number A change?

Accepted Answer

Z decreases by 2 and A decreases by 4. An alpha particle removes 2 protons and 2 neutrons, so Z decreases by 2 and A decreases by 4.

Question 10

In beta-minus decay, which change occurs inside the nucleus?

Accepted Answer

A neutron changes into a proton. In beta-minus decay a neutron changes into a proton, emitting an electron and an antineutrino.

IB Physics: Radioactive decay — Practice Questions & Answers

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