E3 - Radioactive Decay

What are isotopes?

Nuclei that have the same number of protons but different numbers of neutrons.

What is isotopic data?

The relative amounts of different isotopes of an element present within a substance.

What is radioactive decay?

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

What are the characteristics of radioactive decay?

Can be spontaneous and random:

1. Spontaneous = process which cannot be influenced by environmental factors.

• Radioactive decay can’t be affected by environmental factors like temperature, pressure, and chemical conditions.

2. Random = process which the exact time of decay of a nucleus cannot be predicted.

What is background radiation?

Ionising radiation present in the environment.

1. Natural Sources

2. Artificial Sources

What are natural sources of background radiation?

Radon gas from rocks and buildings

Cosmic rays from space

Carbon-14 in biological material

Radioactive material in food and drink

What are artificial sources of background radiation?

Nuclear medicine

Nuclear waste

Nuclear fallout from nuclear weapons

Nuclear accidents

What is an alpha particle?

High-energy helium nucleus that contains 2 protons and 2 nucleons, with a mass of 4u and +2e.

When are alpha particles usually emitted?

Alpha particles are usually emitted by large, unstable nuclei with to many nucleons.

When an alpha particle is emitted, the nucleus loses 2 protons and 4 nucleons.

What is beta-minus decay?

High-energy electron that contains -1 protons and 0 nucleon, with a mass of 0.0005u and charge of -1e.

When are beta-minus usually emitted?

Beta-minus particles are usually emitted by unstable nuclei with too many neutrons.

Beta-minus decay is when a neutron turns into a proton and emits an electron and an anti-neutrino.

Proton number increase by 1 and nucleon number stays the same.

What is beta-plus decay?

High-energy positron that contains +1 protons and 0 nucleons. With a mass of 0.0005u and a charge of +1e.

When is beta-plus usually emitted?

Beta-plus particles are usually emitted by unstable nuclei with too many protons.

Beta-plus decay is when a proton turns into a neutron and emits a positron and an electron neutrino.

Proton number decreases by 1 and nucleon number stays the same.

What is gamma radiation?

High-energy electromagnetic radiation.

When is gamma radiation usually emitted?

Gamma-radiation is usually emitted by nuclei that needs to lose some energy.

Gamma particles are photons, so they have a proton number of 0 and a nucleon number of 0.

Properties of alpha particles?

Highly ionising = highest charge.

Weakly penetrating.

Small range (3-7 cm).

Absorbed by paper.

Properties of beta particles?

Moderately ionising = charge of 1e.

Moderately penetrating.

Moderate range (20 cm - 3 m).

Absorbed by aluminium foil (3 mm).

Properties of gamma particles?

Weakly ionising = no charge.

Highly penetrating.

High range (infinite).

Absorbed by thick lead or concrete.

What is ionising ability?

If any type of radiation collides with an atom, it can knock out electrons, ionising the atoms.

What is penetrating power?

The distance radiation can travel before losing most, or all, of its energy.

What are deflection in electric and magnetic fields?

When a charged particles enters an electric field it will undergo a deflection.

1. Alpha particles = deflected towards the negative plate.

2. Beta particles = deflected towards the positive plate.

3. Gamma radiation = doesn’t deflect as it goes through the between.

When a charged particles moves in a magnetic field, it will undergo a deflection. The faster-moving particles move in larger circular paths according to Bqv = mv²/r. The larger the circular path, the greater the deflection.

Reasons for radioactive decay?

1. Too many neutrons = beta-minus emission.

2. Too many protons = beta-plus emission.

3. Too many nucleons = alpha emission.

4. Too much energy = gamma emission.

What are electron neutrinos?

Type of subatomic particle with no charge and negligible mass that is emitted from the nucleus. This is produced during B+ decay.

What are anti-neutrinos?

Antiparticle of a neutrino. This is produced during B- decay.

What is the activity of radioactive samples?

The number of nuclei which decays in a given time, this is measured in becquerels (Bq).

What is half-life?

The time taken for half the undecayed nuclei to decay or the activity of a source of decay to half.

What is mass defect?

Difference between measured mass of a nucleus and the sum total of the masses of its constituents.

What is binding energy?

The energy required to break a nucleus into its constituent protons and neutrons.

Einsteins theory of relativity

1. mass can be converted into energy.

2. energy can be converted into mass.

E = mc²

What is the atomic mass unit?

used to express the mass of subatomic particles. It is exactly 1/12 of the mass of a neutral atom of carbon-12.