Define radioactive decay .

Radioactive decay is the spontaneous disintegration of a nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle.

Define a spontaneous process.

A spontaneous process is one which cannot be influenced by environmental factors.

Define a random process.

A random process is one in which the exact time of decay of a nucleus cannot be predicted.

What experimental evidence demonstrates the randomness of radioactive decay?

The count rate recorded by a Geiger-Muller (GM) tube placed near a radioactive source fluctuates irregularly and cannot be predicted, since each count represents the decay of an unstable nucleus.

Name three environmental factors that do not affect the rate of radioactive decay.

Temperature Pressure Chemical conditions

Although the exact decay time of an individual nucleus cannot be predicted, it has a constant .......... of decaying in a given time interval.

Although the exact decay time of an individual nucleus cannot be predicted, it has a constant probability of decaying in a given time interval.

True or False? The exact time at which a specific nucleus will decay can be predicted.

False. Radioactive decay is random - an individual nucleus has a constant probability of decaying in a given time, but its exact decay time cannot be predicted. However, the behaviour of a large number of nuclei can be predicted statistically.

Define the decay constant , λ.

The decay constant is the probability that an individual nucleus will decay per unit of time.

Define the becquerel (Bq).

One becquerel is equal to one radioactive decay per second (1 s -1 ); it is the unit of activity .

Besides the number of undecayed nuclei, which two other quantities can be represented in exponential decay form?

Activity : A = A 0 e -λt Count rate : C = C 0 e -λt

In radioactive decay, the number of undecayed nuclei falls very rapidly but never reaches .......... .

In radioactive decay, the number of undecayed nuclei falls very rapidly but never reaches zero .

True or False? A steeper radioactive decay curve indicates a smaller decay constant.

False. A steeper decay curve indicates a larger decay constant λ, since the number of undecayed nuclei falls more quickly.

Half-life is the time taken for the initial number of nuclei in a sample to reduce by half.

What does a short half-life indicate about a sample's decay constant and rate of decay?

A short half-life means the sample has a larger decay constant and therefore decays at a faster rate , since half-life and decay constant are inversely proportional .

If a sample has an initial activity A 0 , what fraction of A 0 remains after two half-lives have passed?

One quarter (¼) of the initial activity, A 0 , remains after two half-lives.

Activity is proportional to the number of undecayed nuclei, so after one half-life has passed, the activity of a sample will also .......... .

Activity is proportional to the number of undecayed nuclei, so after one half-life has passed, the activity of a sample will also halve .

True or False? The half-life of a radioactive isotope depends on the initial number of nuclei in the sample.

False. Half-life is a constant property of a radioactive isotope; it does not depend on the initial number of nuclei, N 0 , or the sample's activity.

A LevelPhysicsCambridge (CIE)Flashcards23. Nuclear PhysicsRadioactive Decay

Radioactive Decay (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontThe Random Nature of Radioactive Decay
Define radioactive decay.

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Cards in this collection (20)

Define radioactive decay.
Radioactive decay is the spontaneous disintegration of a nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle.
Define a spontaneous process.
A spontaneous process is one which cannot be influenced by environmental factors.
Define a random process.
A random process is one in which the exact time of decay of a nucleus cannot be predicted.
What experimental evidence demonstrates the randomness of radioactive decay?
The count rate recorded by a Geiger-Muller (GM) tube placed near a radioactive source fluctuates irregularly and cannot be predicted, since each count represents the decay of an unstable nucleus.
Name three environmental factors that do not affect the rate of radioactive decay.
- Temperature
- Pressure
- Chemical conditions
Although the exact decay time of an individual nucleus cannot be predicted, it has a constant .......... of decaying in a given time interval.
Although the exact decay time of an individual nucleus cannot be predicted, it has a constant probability of decaying in a given time interval.
True or False?
The exact time at which a specific nucleus will decay can be predicted.
False.
Radioactive decay is random - an individual nucleus has a constant probability of decaying in a given time, but its exact decay time cannot be predicted. However, the behaviour of a large number of nuclei can be predicted statistically.
Define the decay constant, λ.
The decay constant is the probability that an individual nucleus will decay per unit of time.
What equation relates the activity of a sample to the decay constant and the number of undecayed nuclei?
$A = \frac{Δ N}{Δ t} = - λ N$
where A is the activity (Bq), ΔN is the number of decayed nuclei, Δt is the time interval (s), λ is the decay constant (s^-1) and N is the number of nuclei remaining
Define the becquerel (Bq).
One becquerel is equal to one radioactive decay per second (1 s^-1); it is the unit of activity.
What is the equation for the number of undecayed nuclei remaining after time t?
$N = N_{0} e^{- λ t}$
where N₀ is the initial number of undecayed nuclei and λ is the decay constant (s^-1)
Besides the number of undecayed nuclei, which two other quantities can be represented in exponential decay form?
- Activity: A = A₀e^-λt
- Count rate: C = C₀e^-λt
In radioactive decay, the number of undecayed nuclei falls very rapidly but never reaches ...........
In radioactive decay, the number of undecayed nuclei falls very rapidly but never reaches zero.
True or False?
A steeper radioactive decay curve indicates a smaller decay constant.
False.
A steeper decay curve indicates a larger decay constant λ, since the number of undecayed nuclei falls more quickly.
Define half-life.
Half-life is the time taken for the initial number of nuclei in a sample to reduce by half.
What equation relates half-life to the decay constant?
$t_{1 / 2} = \frac{\ln 2}{λ}$
where t_½ is the half-life (s) and λ is the decay constant (s^-1)
What does a short half-life indicate about a sample's decay constant and rate of decay?
A short half-life means the sample has a larger decay constant and therefore decays at a faster rate, since half-life and decay constant are inversely proportional.
If a sample has an initial activity A₀, what fraction of A₀ remains after two half-lives have passed?
One quarter (¼) of the initial activity, A₀, remains after two half-lives.
Activity is proportional to the number of undecayed nuclei, so after one half-life has passed, the activity of a sample will also ...........
Activity is proportional to the number of undecayed nuclei, so after one half-life has passed, the activity of a sample will also halve.
True or False?
The half-life of a radioactive isotope depends on the initial number of nuclei in the sample.
False.
Half-life is a constant property of a radioactive isotope; it does not depend on the initial number of nuclei, N₀, or the sample's activity.

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