Radioactivity and Decay Processes

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Questions and Answers

What occurs when a nucleus captures one of its closest orbital atomic electrons?

It emits a gamma ray.

It experiences electron capture. (correct)

It splits into smaller nuclei.

It undergoes beta decay.

What does the decay constant ($ au$) represent in the context of radioactive decay?

The total number of atoms in a sample.

The amount of energy released during decay.

The time taken to decay to zero.

The probability of an atom decaying per unit time. (correct)

What is the relationship between the half-life ($t_{1/2}$) and the decay constant ($ au$)?

They are directly proportional.

They are inversely related. (correct)

They are mathematically independent.

They are equal for all radionuclides.

What is used to measure activity in radioactive decay?

Curie (Ci) and Becquerel (Bq). Signup and view all the answers

Which of the following statements is true regarding the radioactive decay law?

Decay follows a random and independent process. Signup and view all the answers

What does the mean life ($ au$) of a radioactive nucleus refer to?

The average time before a nucleus decays. Signup and view all the answers

After how many half-lives will the amount of a radioactive substance be reduced to a quarter of its original quantity?

Two half-lives. Signup and view all the answers

What distinguishes gamma decay from other decay processes?

It leads to a loss of energy only. Signup and view all the answers

What characterizes a radioactive atom?

It emits radiation due to excess internal energy in its nucleus. Signup and view all the answers

Which type of decay results in the emission of an alpha particle?

Decay involving an excess of neutrons resulting in the release of a helium nucleus. Signup and view all the answers

How does beta decay alter the nucleus of an atom?

It transforms a neutron into a proton and emits an electron. Signup and view all the answers

What type of radiation is described as having no mass and no charge?

Gamma radiation. Signup and view all the answers

What is the outcome of alpha decay on atomic numbers and mass numbers?

Atomic number decreases by 2; mass number decreases by 4. Signup and view all the answers

What does positive beta decay produce?

A positron, a neutron, and a neutrino. Signup and view all the answers

Why do certain elements naturally exhibit radioactivity?

They possess unstable nuclei with excess energy. Signup and view all the answers

What is the primary trigger for an atom to undergo decay?

The presence of an excess of protons or neutrons in the nucleus. Signup and view all the answers

Study Notes

Radioactivity or Radioactive Decay

Radioactivity is the process where an unstable atom's nucleus loses energy by emitting radiation.
Unstable nuclei decay, emitting alpha, beta, and gamma radiation.
Henri Becquerel discovered natural radioactivity in 1896.

Types of Radioactive Decays

Atoms are either stable or unstable.
Instability results from excess neutrons or protons.
Radioactive atoms achieve stability by emitting nucleons (protons or neutrons) or other particles, or by releasing energy.
Four main decay types: alpha, beta (negative and positive), gamma, and electron capture.

Alpha Decay

An alpha particle is a highly energetic helium nucleus.
It's emitted when the neutron-to-proton ratio is too low in an unstable atom.
Alpha particles are positively charged, massive particles made of two protons and two neutrons.
Atomic and mass numbers are conserved, resulting in a daughter atom with a different atomic number and mass number.
Example: Uranium-238 decays to Thorium-234 plus an alpha particle.

Beta Decay

Negative Beta Decay: A neutron transforms into a proton, electron (beta particle), and an antineutrino. This happens when the nucleus has extra neutrons.
Positive Beta Decay: A proton converts to a neutron, positron (beta+ particle), and a neutrino. This occurs in nuclei with excess protons.

Gamma Decay

Gamma rays are high-energy photons emitted from an excited nucleus.
They have no mass or charge unlike alpha and beta particles.
Gamma emission helps the nucleus to de-excite and reach a lower energy state.
Example: Cobalt-60 undergoes beta-minus decay, then emits gamma photons to reach the ground state.

Electron Capture (EC)

The nucleus captures an orbital electron.
The electron combines with a proton, forming a neutron and emitting a neutrino.
Similar to positive beta decay.

Radioactive Decay Law

Radioactive nuclei decay randomly, independent of time.
Decay follows an exponential law (Radioactive Decay Law).
The number of radioactive nuclei decaying, dN, in a time dt is related to the total number of nuclei, N.
λ (lambda) is the decay constant. It represents the probability of an atom decaying per unit time.
The amount of decaying nuclei depends on the original number of nuclei and the time passed.

Activity

Activity (A) is the rate of decay in a radioactive material.
Measured in Curies (Ci) or Becquerels (Bq).
1 Ci = 3.7 x 10^10 Bq.
1 Bq = 1 disintegration per second.

Half-life

Half-life is the time required for half of the radioactive nuclei to decay.
It is related to the decay constant (λ).
The figure shows the exponential decay of activity over time.
After one, two, or n half-lives... (fraction of initial activity remains)

Average or Mean-Life (τ)

Mean life (τ) is the average lifetime of all nuclei in a specific unstable atomic species.
It's the sum of the lifetimes of all unstable nuclei divided by the initial number of unstable nuclei.
Mean life is 1.443 times the half-life.

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Description

This quiz covers the fundamental concepts of radioactivity, including the types of radioactive decay and the specifics of alpha decay. You'll explore the roles of unstable atoms and the discovery of natural radioactivity by Henri Becquerel. Test your knowledge on the mechanisms behind radioactivity and its various forms.