Atomic Interactions and Generation of Radiation

Atomic Dimensions and Structure

Imagine scaling an atom up to the size of a football stadium; the would be just a single marble sitting in the centre.

The radius of an atom is approximately $1 \times 10^{-10}$ metres.
The is incredibly small in comparison, measuring less than 1/10,000 of the atomic radius (approximately $1 \times 10^{-15}$ metres).
Almost all the mass of an atom is concentrated in this central , while the orbiting electrons have a negligible mass.
Electrons orbit the at specific, fixed distances called (or shells).

Absorption and Emission of Radiation

Electrons can jump between like climbing rungs on a ladder, but they must gain or lose exactly the right amount of energy to make the leap.

: When an atom takes in electromagnetic (EM) radiation, an electron gains energy and undergoes , moving to a higher energy level further from the .
: When an atom releases EM radiation, an electron undergoes , losing energy and dropping to a lower energy level closer to the .
The energy of the absorbed or emitted radiation corresponds exactly to the difference in energy between the two levels.

The relationship between energy and frequency is shown by the equation:

\Delta E = hf

Where $\Delta E$ is the energy change, $h$ is Planck's constant, and $f$ is the frequency. A large electron energy drop produces a high-frequency (such as an X-ray), while a small drop produces a low-frequency (such as ).

Where Does Radiation Come From?

Not all radiation is born in the same place; some types come from the deep core of the atom, while others are generated in the outer electron clouds.

: These are generated by . When a has excess energy (an excited state), particles shift into a more stable configuration and release a high-energy gamma . This involves no change to the mass or atomic number.
, , and : These are generated entirely by when electrons lose energy and drop to lower , completely independent of the .

A classic example of a nuclear rearrangement equation is:

{^{60}_{27}Co^*} \rightarrow {^{60}_{27}Co} + {^0_0\gamma}

(Note: The asterisk denotes the is in an excited state. Emitting a gamma ray allows it to lose energy and become stable without changing its particles).

Additionally, UV radiation interacts with our atmosphere. It is absorbed by oxygen to produce ( $O_3$ ). The resulting layer then absorbs further incoming UV radiation, protecting life on Earth.

Ionisation by High-Energy Radiation

If an electron absorbs enough energy, it does not just jump to a higher energy level—it breaks free from the atom entirely.

includes high-energy EM waves at the high-frequency end of the spectrum, specifically , , and high-energy ultraviolet.
occurs when an atom becomes a positively charged ion by losing one or more outer electrons.
The radiation transfers enough energy to an outer electron to overcome the electrostatic attraction of the , effectively knocking it out of the atom.

The risk of harm to the human body from this process depends on both the type of radiation and the size of the dose. Radiation dose is measured in (Sv) or (mSv).

Exam Tips

Common Mistake
Students confuse the origins of X-rays and gamma rays; remember that gamma rays come strictly from the nucleus, whereas X-rays come from electron transitions.
2
When explaining emission, you must explicitly state that the electron moves closer to the nucleus AND loses energy to secure the marks.
3
For OCR Physics B, you must use the exact phrase 'losing outer electrons' when defining ionisation, as vague terms like 'losing charge' will not score the mark.

Key Terms(18)

Nucleus: The tiny, massive central core of an atom that contains protons and neutrons.
Energy levels: Fixed distances from the nucleus where electrons are found; electrons further away possess higher potential energy.
Absorption: The process of an electron taking in EM radiation energy to move to a higher energy level further from the nucleus.
Emission: The process of an electron releasing energy as an EM radiation photon to move to a lower energy level closer to the nucleus.
Excitation: The process of an electron moving to a higher energy level by absorbing energy.
De-excitation: The process of an electron falling back to a lower energy level, releasing energy as a photon of EM radiation.
Photon: A discrete packet or quantum of electromagnetic energy.
Gamma rays: High-energy, high-frequency electromagnetic waves emitted from the nucleus of an atom.
Nuclear rearrangements: The process where the particles inside an excited nucleus shift to a more stable configuration, releasing excess energy as a gamma photon.
X-rays: High-energy, high-frequency electromagnetic waves generated by electron transitions involving large energy drops.
Ultraviolet (UV): Electromagnetic radiation generated by electron transitions, with a frequency higher than visible light.
Visible light: The portion of the electromagnetic spectrum detectable by the human eye, generated by smaller electron transitions.
Electron transitions: The movement of electrons between different energy levels within an atom.
Ozone: A molecule consisting of three oxygen atoms ( $O_3$ ) produced when oxygen absorbs UV radiation in the upper atmosphere.
Ionising radiation: High-energy EM radiation (such as gamma, X-rays, and high UV) that carries enough energy per photon to completely remove an outer electron from an atom.
Ionisation: The process by which an atom becomes a positively charged ion by losing one or more outer electrons due to the absorption of high-energy radiation.
Sieverts: The unit of measurement used to quantify the risk of harm to the body from a dose of radiation.
Millisieverts: A unit of measurement for radiation dose, equal to one-thousandth of a Sievert.

Previous NoteProperties of the Electromagnetic Spectrum Next NoteUses and Hazards of Electromagnetic Waves

Back to Risks and benefits of radiation

Put your knowledge into practice — try past paper questions for Physics B

Key Terms(18)

Nucleus: The tiny, massive central core of an atom that contains protons and neutrons.
Energy levels: Fixed distances from the nucleus where electrons are found; electrons further away possess higher potential energy.
Absorption: The process of an electron taking in EM radiation energy to move to a higher energy level further from the nucleus.
Emission: The process of an electron releasing energy as an EM radiation photon to move to a lower energy level closer to the nucleus.
Excitation: The process of an electron moving to a higher energy level by absorbing energy.
De-excitation: The process of an electron falling back to a lower energy level, releasing energy as a photon of EM radiation.
Photon: A discrete packet or quantum of electromagnetic energy.
Gamma rays: High-energy, high-frequency electromagnetic waves emitted from the nucleus of an atom.
Nuclear rearrangements: The process where the particles inside an excited nucleus shift to a more stable configuration, releasing excess energy as a gamma photon.
X-rays: High-energy, high-frequency electromagnetic waves generated by electron transitions involving large energy drops.
Ultraviolet (UV): Electromagnetic radiation generated by electron transitions, with a frequency higher than visible light.
Visible light: The portion of the electromagnetic spectrum detectable by the human eye, generated by smaller electron transitions.
Electron transitions: The movement of electrons between different energy levels within an atom.
Ozone: A molecule consisting of three oxygen atoms ( $O_3$ ) produced when oxygen absorbs UV radiation in the upper atmosphere.
Ionising radiation: High-energy EM radiation (such as gamma, X-rays, and high UV) that carries enough energy per photon to completely remove an outer electron from an atom.
Ionisation: The process by which an atom becomes a positively charged ion by losing one or more outer electrons due to the absorption of high-energy radiation.
Sieverts: The unit of measurement used to quantify the risk of harm to the body from a dose of radiation.
Millisieverts: A unit of measurement for radiation dose, equal to one-thousandth of a Sievert.

Atomic Interactions and Generation of Radiation

Atomic Dimensions and Structure

Imagine scaling an atom up to the size of a football stadium; the would be just a single marble sitting in the centre.

The radius of an atom is approximately $1 \times 10^{-10}$ metres.
The is incredibly small in comparison, measuring less than 1/10,000 of the atomic radius (approximately $1 \times 10^{-15}$ metres).
Almost all the mass of an atom is concentrated in this central , while the orbiting electrons have a negligible mass.
Electrons orbit the at specific, fixed distances called (or shells).

Absorption and Emission of Radiation

Electrons can jump between like climbing rungs on a ladder, but they must gain or lose exactly the right amount of energy to make the leap.

: When an atom takes in electromagnetic (EM) radiation, an electron gains energy and undergoes , moving to a higher energy level further from the .
: When an atom releases EM radiation, an electron undergoes , losing energy and dropping to a lower energy level closer to the .
The energy of the absorbed or emitted radiation corresponds exactly to the difference in energy between the two levels.

The relationship between energy and frequency is shown by the equation:

\Delta E = hf

Where Does Radiation Come From?

Not all radiation is born in the same place; some types come from the deep core of the atom, while others are generated in the outer electron clouds.

: These are generated by . When a has excess energy (an excited state), particles shift into a more stable configuration and release a high-energy gamma . This involves no change to the mass or atomic number.
, , and : These are generated entirely by when electrons lose energy and drop to lower , completely independent of the .

A classic example of a nuclear rearrangement equation is:

{^{60}_{27}Co^*} \rightarrow {^{60}_{27}Co} + {^0_0\gamma}

(Note: The asterisk denotes the is in an excited state. Emitting a gamma ray allows it to lose energy and become stable without changing its particles).

Additionally, UV radiation interacts with our atmosphere. It is absorbed by oxygen to produce ( $O_3$ ). The resulting layer then absorbs further incoming UV radiation, protecting life on Earth.

Ionisation by High-Energy Radiation

If an electron absorbs enough energy, it does not just jump to a higher energy level—it breaks free from the atom entirely.

includes high-energy EM waves at the high-frequency end of the spectrum, specifically , , and high-energy ultraviolet.
occurs when an atom becomes a positively charged ion by losing one or more outer electrons.
The radiation transfers enough energy to an outer electron to overcome the electrostatic attraction of the , effectively knocking it out of the atom.

The risk of harm to the human body from this process depends on both the type of radiation and the size of the dose. Radiation dose is measured in (Sv) or (mSv).

Exam Tips

Common Mistake
Students confuse the origins of X-rays and gamma rays; remember that gamma rays come strictly from the nucleus, whereas X-rays come from electron transitions.
2
When explaining emission, you must explicitly state that the electron moves closer to the nucleus AND loses energy to secure the marks.
3
For OCR Physics B, you must use the exact phrase 'losing outer electrons' when defining ionisation, as vague terms like 'losing charge' will not score the mark.

Key Terms(18)

Nucleus: The tiny, massive central core of an atom that contains protons and neutrons.
Energy levels: Fixed distances from the nucleus where electrons are found; electrons further away possess higher potential energy.
Absorption: The process of an electron taking in EM radiation energy to move to a higher energy level further from the nucleus.
Emission: The process of an electron releasing energy as an EM radiation photon to move to a lower energy level closer to the nucleus.
Excitation: The process of an electron moving to a higher energy level by absorbing energy.
De-excitation: The process of an electron falling back to a lower energy level, releasing energy as a photon of EM radiation.
Photon: A discrete packet or quantum of electromagnetic energy.
Gamma rays: High-energy, high-frequency electromagnetic waves emitted from the nucleus of an atom.
Nuclear rearrangements: The process where the particles inside an excited nucleus shift to a more stable configuration, releasing excess energy as a gamma photon.
X-rays: High-energy, high-frequency electromagnetic waves generated by electron transitions involving large energy drops.
Ultraviolet (UV): Electromagnetic radiation generated by electron transitions, with a frequency higher than visible light.
Visible light: The portion of the electromagnetic spectrum detectable by the human eye, generated by smaller electron transitions.
Electron transitions: The movement of electrons between different energy levels within an atom.
Ozone: A molecule consisting of three oxygen atoms ( $O_3$ ) produced when oxygen absorbs UV radiation in the upper atmosphere.
Ionising radiation: High-energy EM radiation (such as gamma, X-rays, and high UV) that carries enough energy per photon to completely remove an outer electron from an atom.
Ionisation: The process by which an atom becomes a positively charged ion by losing one or more outer electrons due to the absorption of high-energy radiation.
Sieverts: The unit of measurement used to quantify the risk of harm to the body from a dose of radiation.
Millisieverts: A unit of measurement for radiation dose, equal to one-thousandth of a Sievert.

Previous NoteProperties of the Electromagnetic Spectrum Next NoteUses and Hazards of Electromagnetic Waves

Back to Risks and benefits of radiation

Put your knowledge into practice — try past paper questions for Physics B

Key Terms(18)

Nucleus: The tiny, massive central core of an atom that contains protons and neutrons.
Energy levels: Fixed distances from the nucleus where electrons are found; electrons further away possess higher potential energy.
Absorption: The process of an electron taking in EM radiation energy to move to a higher energy level further from the nucleus.
Emission: The process of an electron releasing energy as an EM radiation photon to move to a lower energy level closer to the nucleus.
Excitation: The process of an electron moving to a higher energy level by absorbing energy.
De-excitation: The process of an electron falling back to a lower energy level, releasing energy as a photon of EM radiation.
Photon: A discrete packet or quantum of electromagnetic energy.
Gamma rays: High-energy, high-frequency electromagnetic waves emitted from the nucleus of an atom.
Nuclear rearrangements: The process where the particles inside an excited nucleus shift to a more stable configuration, releasing excess energy as a gamma photon.
X-rays: High-energy, high-frequency electromagnetic waves generated by electron transitions involving large energy drops.
Ultraviolet (UV): Electromagnetic radiation generated by electron transitions, with a frequency higher than visible light.
Visible light: The portion of the electromagnetic spectrum detectable by the human eye, generated by smaller electron transitions.
Electron transitions: The movement of electrons between different energy levels within an atom.
Ozone: A molecule consisting of three oxygen atoms ( $O_3$ ) produced when oxygen absorbs UV radiation in the upper atmosphere.
Ionising radiation: High-energy EM radiation (such as gamma, X-rays, and high UV) that carries enough energy per photon to completely remove an outer electron from an atom.
Ionisation: The process by which an atom becomes a positively charged ion by losing one or more outer electrons due to the absorption of high-energy radiation.
Sieverts: The unit of measurement used to quantify the risk of harm to the body from a dose of radiation.
Millisieverts: A unit of measurement for radiation dose, equal to one-thousandth of a Sievert.