Natural Background Radiation and Jawoyn Knowledge of Sickness Country

A Geiger counter can detect radiation beside a granite outcrop, inside a brick house, or on an aircraft. Nobody has brought a radioactive source into the room. So where is the radiation coming from?

Predict which location should give the highest reading: beside the rock, inside the house, or in the aircraft.

There isn’t one automatic winner. The result depends on the local geology, the amount of radon in the air, the building materials, and the altitude. All three locations can expose us to radiation from natural sources.

This is called natural background radiation. It has existed throughout Earth’s history, but understanding where it comes from requires a little nuclear chemistry.

01Why are rocks radioactive?

Start with something familiar: the atoms that make up a rock.

Every atom of an element has a particular number of protons. However, atoms of the same element can have different numbers of neutrons. These different forms are called isotopes.

Some isotopes have stable nuclei. Others have unstable nuclei that spontaneously change into more stable arrangements, releasing energy or particles in a process called radioactive decay.

An unstable isotope is called a radioisotope.

For example:

• Uranium-238 (\(^{238}\mathrm{U}\)) is radioactive.
• Thorium-232 (\(^{232}\mathrm{Th}\)) is radioactive.
• Potassium-40 (\(^{40}\mathrm{K}\)) is radioactive.

These isotopes occur naturally in rocks, soil, minerals, and even living organisms.

If you need to refresh how isotopes differ, see tutorgum’s Why Isotopes Have Similar Chemistry but Different Densities.

What happens when a radioisotope decays?

Think of a radioactive nucleus as a system that can rearrange itself. When it decays, it releases radiation and may become a different element.

This is different from an ordinary chemical reaction.

In a chemical reaction, electrons are rearranged and chemical bonds form or break. In radioactive decay, the nucleus itself changes.

The three main types of radiation you will encounter are:

• Alpha (\(\alpha\)) radiation: A particle containing two protons and two neutrons. It is strongly ionising but has low penetrating power.
• Beta (\(\beta\)) radiation: Usually a high-speed electron or positron emitted during a nuclear transformation.
• Gamma (\(\gamma\)) radiation: High-energy electromagnetic radiation. It has much greater penetrating power than alpha particles.

The differences matter because radiation does not interact with matter in the same way.

For example, alpha particles cannot penetrate intact skin, but alpha-emitting material inside the body can deposit energy over a short distance. Gamma radiation can pass through the body and contribute to external exposure.

What is naturally occurring radioactive material?

Naturally occurring radioactive material, often abbreviated to NORM, describes materials containing radionuclides that exist naturally in the environment.

The most important contributors include uranium, thorium, and potassium-40.

Uranium and thorium are particularly interesting because they decay through a series of radioactive daughter products. Eventually, these decay chains reach stable isotopes of lead.

This means a rock containing uranium can contain several different radioactive substances produced through radioactive decay.

The process is not a single event. It is a sequence of nuclear transformations occurring over extremely long periods.

An important detail: naturally occurring radioactive material does not have to remain untouched.

Mining and mineral processing can concentrate or redistribute naturally occurring radionuclides. The material is still natural in origin, but its concentration and the pathways through which people encounter it can change.

02Where does natural background radiation come from?

Natural background radiation has several different sources. Some come from the ground, some from the atmosphere, and some from inside your own body.

Let’s examine the two sources most closely connected to naturally occurring radioactive material.

1. Radiation from rocks and soil

Uranium and thorium occur naturally in the Earth’s crust. Their concentrations vary between geological regions.

Some rocks contain higher concentrations than others. Granite, for example, can contain naturally occurring uranium, thorium, and potassium-40.

These radionuclides decay and release radiation. Some emissions can travel out of the rock and expose people nearby.

Building materials can contribute too. If a house contains stone or other materials with naturally occurring radionuclides, these can contribute to the radiation exposure of its occupants.

The important point is that the amount of radiation depends on the composition of the material, not simply whether it is classified as a rock or a building material.

2. Radon gas: a radioactive substance that can move through the ground

Radon deserves particular attention.

Radon is a naturally occurring radioactive gas produced during radioactive decay. It is colourless, odourless, and chemically inert.

One important isotope is radon-222 (\(^{222}\mathrm{Rn}\)), which belongs to the uranium-238 decay chain.

Here is the interesting part: unlike solid uranium-containing minerals, radon can move through spaces in soil and rock.

It can escape from the ground into the atmosphere. In enclosed spaces, it can accumulate rather than disperse.

When radon decays, it produces additional radioactive substances called decay products or progeny. Some of these can attach to airborne particles and be inhaled.

This creates a different exposure pathway from simply standing beside a radioactive rock.

It also explains why two buildings in the same geological region can have different radon concentrations. Ground conditions, building design, and ventilation all influence how much radon enters and accumulates indoors.

How much background radiation do Australians receive?

According to the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), the average Australian receives approximately:

\[ \boxed{1.7\ \mathrm{mSv/year}} \]

from natural background radiation.

The unit mSv stands for millisievert. It measures effective radiation dose, which takes account of the biological effects of different types of radiation and their exposure to body tissues.

This average is not a fixed amount received by every Australian.

Local geology, altitude, radon concentrations, building materials, and diet all affect an individual’s exposure.

ARPANSA explains these sources in its background radiation overview.

03Radioactive decay, activity, and half-life

We have established that naturally occurring radioactive materials release radiation through nuclear decay. Now we need to describe how quickly this happens.

There are two quantities that are particularly useful.

Activity measures how many nuclear decays occur per second.

Its SI unit is the becquerel (Bq).

\[ 1\ \mathrm{Bq}=1\ \text{decay per second} \]

A sample with an activity of \(500\ \mathrm{Bq}\) undergoes 500 nuclear decays every second, on average.

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

Different radioisotopes have different half-lives. Uranium-238 has a half-life of approximately 4.5 billion years, whereas radon-222 has a half-life of approximately 3.8 days.

That difference helps explain why uranium can remain in rocks for geological timescales while radon concentrations can change much more rapidly.

For an isolated sample with no additional radioactive material entering it, activity decreases according to:

\[ A=A_0\left(\frac{1}{2}\right)^{t/t_{1/2}} \]

Where:

• \(A\) is the activity after time \(t\), measured in Bq.
• \(A_0\) is the initial activity, measured in Bq.
• \(t\) is the elapsed time.
• \(t_{1/2}\) is the half-life of the isotope.

The equation works because the activity halves after every half-life.

Activity is not the same as radiation dose

This is one of the most important distinctions in this topic.

Activity tells us how frequently nuclear decays occur. Effective dose tells us about the biological effect of radiation exposure.

They are not interchangeable.

Consider two radioactive materials, each with an activity of \(500\ \mathrm{Bq}\).

One mainly emits alpha particles. The other mainly emits gamma radiation.

They have the same activity, but that does not mean they produce the same dose to a person.

The radiation type, energy released, distance from the source, exposure time, and whether the material enters the body all matter.

A becquerel measures nuclear decay. A sievert measures radiation dose.

Keeping those two quantities separate will help you avoid a common mistake in HSC Chemistry questions.

04Aboriginal Knowledge of Sickness Country: The Jawoyn account

Now consider a different kind of knowledge about the natural environment.

In southern Kakadu, in the Northern Territory, there is a region known as Buladjang, or Sickness Country.

This is a particularly important example because it brings together Aboriginal knowledge of Country, geology, naturally occurring radioactive material, and the consequences of disturbing culturally significant places.

The account discussed here belongs specifically to the Jawoyn people of southern Kakadu. It should not be presented as a universal Aboriginal belief or as a story shared identically by every Aboriginal community.

What is Buladjang?

The Kakadu National Park Management Plan 2016-2026 describes Buladjang as an important area to Jawoyn people because the essence of Bula, a major figure associated with the creation era, is located within it.

According to the plan, Jawoyn people believe that disturbing Bula would have catastrophic consequences.

The plan describes Sickness Country as extending over approximately 2,000 square kilometres. It also records that the region coincides with high concentrations of several naturally occurring elements and substances, including:

• Uranium
• Thorium
• Arsenic
• Mercury
• Fluorine
• Radon

These are associated with the region’s rocks, water, and air.

Strict cultural rules and protocols govern access to some sites. The restrictions vary and can depend on a person’s social position and knowledge of the relevant ceremonies and practices.

The plan also recognises the responsibility of traditional owners to protect these places and pass cultural knowledge between generations.

The account is documented in the Kakadu National Park Management Plan 2016-2026, prepared by the Kakadu National Park Board of Management.

A 2023 research paper by Silva Larson and colleagues also discusses Buladjang and Mungguy connections to Country. Importantly, the researchers identify the views presented as those of six Mungguy representatives from the Yurlkmanj, Wurrkbarbar, and Bolmo clans who participated in their research. This is an important distinction when describing community knowledge: the account should be attributed to the people who shared it, rather than generalised to all Aboriginal Australians.

Read the research paper.

Where does chemistry fit into this account?

The geographical overlap between Sickness Country and naturally occurring mineral deposits provides an important connection to chemistry.

Uranium and thorium are radioactive elements. Their radioactive decay contributes to natural background radiation.

Their decay chains also produce radioactive daughter products, including radon.

This gives us a scientific explanation for how certain geological environments can contribute to natural radiation exposure.

However, look carefully at the other substances identified in the Kakadu management plan.

Arsenic, mercury, and fluorine are not automatically radioactive simply because they occur in the same geological region.

They have their own chemical properties and can raise separate questions about environmental contamination and chemical toxicity.

This distinction is important:

• Uranium and thorium can contribute to radiation through radioactive decay.
• Radon is itself a radioactive gas produced through radioactive decay.
• Arsenic, mercury, and fluorine have different chemical properties and should not automatically be treated as radiation sources.

A region can contain several different environmental hazards at once. Explaining one does not automatically explain the others.

What was documented, and what did science explain later?

This is where we need to be particularly careful.

There are two different kinds of information involved.

1. The documented cultural knowledge

The Jawoyn account describes a culturally significant region connected to Bula, with specific responsibilities, restrictions, and consequences associated with disturbing important places.

The Kakadu management plan records these beliefs and the protocols that govern access to Sickness Country.

These are documented aspects of Jawoyn knowledge. They should be understood within their cultural and spiritual context.

2. The scientific explanation

Modern geology and nuclear science can identify naturally occurring uranium and thorium deposits, radioactive decay chains, and radon production.

Scientific measurements can investigate the concentrations of these substances and quantify radiation exposure.

These explanations provide information about the physical properties of the environment. They do not establish that every aspect of Jawoyn knowledge originated as an explanation of radioactivity.

There is also a historical example worth examining.

An AIATSIS research publication, The Right to Protect Sites, by Gareth Lewis and Ben Scambary, records a 1950s account involving uranium exploration near the Jawoyn Sickness Country.

The publication describes a near-fatal outbreak of hookworm anaemia in a work camp at Katherine. Local Aboriginal people attributed the outbreak to uranium exploration and disturbance of the Sickness Dreaming Place at Ngartluk.

This is an important historical record of how local people interpreted the disturbance of a culturally significant place.

However, the account is not a measurement of radiation exposure, nor does it establish that ionising radiation caused the outbreak.

Read the AIATSIS publication.

The distinction is essential. A later scientific explanation of geological conditions should not be used to rewrite an entire cultural knowledge system as though it were simply an early version of nuclear physics.

Nor should every place described as Sickness Country be assumed to have the same environmental conditions or cause of illness.

The chemistry helps explain the natural radioactive materials in a particular region. It does not replace the cultural knowledge, responsibilities, and history associated with that Country.

05Questions and solutions

Question 1

A student measures natural background radiation near a granite building.

Explain why radiation can be detected even though no artificial radioactive source is present. Identify two possible natural contributors to the reading.

Solution 1

The radiation comes from naturally occurring radioactive materials in the surrounding environment.

Granite can contain uranium, thorium, and potassium-40. Their radioactive decay produces ionising radiation.

Two possible contributors are:

1. External radiation from naturally occurring radionuclides in the granite and surrounding soil.
2. Radon gas produced by radioactive decay in the ground, which can enter the building and contribute to exposure through inhalation.

Natural background radiation does not require an artificial source. Radioactive isotopes have existed naturally in the Earth’s crust for billions of years.

Question 2

A sealed sample of radon-222 has an initial activity of \(640\ \mathrm{Bq}\).

After 11.4 days, its activity decreases to \(80\ \mathrm{Bq}\).

Calculate the half-life of radon-222.

Solution 2

The half-life is 3.8 days.

First, compare the initial and final activities:

\[ 640\rightarrow320\rightarrow160\rightarrow80 \]

The activity halves three times.

Therefore, three half-lives have passed.

Using:

\[ t_{1/2}=\frac{t}{n} \]

Substitute:

\[ t_{1/2}=\frac{11.4}{3} \]

\[ \boxed{t_{1/2}=3.8\ \mathrm{days}} \]

The sample has undergone three half-lives in 11.4 days.

Remember that activity measures the number of decays per second, not the radiation dose received by a person.

Question 3

Radium-226 undergoes alpha decay to produce radon-222.

Write a balanced nuclear equation for this process.

Explain why the production of radon creates a different exposure pathway from the presence of solid uranium-containing rock.

Solution 3

The balanced nuclear equation is:

\[ {}^{226}_{88}\mathrm{Ra} \rightarrow {}^{222}_{86}\mathrm{Rn} + {}^{4}_{2}\mathrm{He} \]

The emitted alpha particle is represented by:

\[ {}^{4}_{2}\mathrm{He} \]

Step 1: Check conservation of mass number.

\[ 226=222+4 \]

The total mass number is conserved.

Step 2: Check conservation of atomic number.

\[ 88=86+2 \]

The total atomic number is also conserved.

Step 3: Explain the different exposure pathway.

Radium is a solid radioactive substance found in uranium decay chains.

Radon-222, however, is a gas. It can escape from rocks and soil, move through spaces in the ground, and enter enclosed buildings.

This means radon can be inhaled, creating an internal exposure pathway that is different from external exposure to radiation emitted by nearby rocks.

The nuclear equation demonstrates how one radioactive substance can produce another substance with different physical and chemical properties.

Question 4

Two radioactive sources each have an activity of \(500\ \mathrm{Bq}\).

• Source X emits mainly alpha particles.
• Source Y emits mainly gamma radiation.

A student argues that both sources must produce the same radiation dose because they undergo the same number of nuclear decays per second.

Assess this argument for:

(a) A person standing one metre away from each source.

(b) A situation where radioactive material from each source enters the body.

Explain why activity alone is insufficient to compare radiation doses.

Solution 4

The student’s argument is incorrect. Equal activity does not mean equal radiation dose.

Both sources undergo 500 nuclear decays per second, but the radiation they emit interacts with matter differently.

(a) External exposure

Alpha particles have low penetrating power. They travel only a short distance through air and cannot penetrate intact skin.

Gamma radiation is much more penetrating and can travel through the body.

Therefore, the gamma-emitting source can produce a greater external exposure under the stated comparison, although the exact dose still depends on factors such as radiation energy, geometry, shielding, and distance.

(b) Internal exposure

The comparison changes when radioactive material enters the body.

Alpha particles are strongly ionising. If an alpha-emitting radionuclide is inhaled and retained in the body, its emissions can deposit substantial energy over a short distance.

Gamma radiation is more penetrating and can travel further through body tissues.

The resulting dose depends on the radionuclide, radiation energy, amount taken into the body, retention time, and the tissues exposed.

The key principle: activity measures the frequency of nuclear decay, while effective dose accounts for the biological effects of the radiation.

You cannot calculate or compare effective doses using activity alone.

Question 5

An environmental team investigates two hypothetical locations in the same broad geological region.

Both locations have the same measured uranium concentration in their bedrock and the same external gamma dose rate.

The measurements are:

A surveyor spends four hours at each location. Assume the radon readings represent the conditions during the survey, and the surveyor has the same breathing rate at both locations.

A student makes three claims:

1. Both locations must produce the same total natural radiation dose because their uranium concentrations and external gamma dose rates are identical.
2. Site B must contain ten times as much uranium as Site A because its radon concentration is ten times higher.
3. The Jawoyn understanding of Sickness Country must therefore be an early scientific description of radioactive uranium deposits.

Evaluate all three claims.

Identify what can reasonably be concluded from the measurements, what cannot be established, and what additional information would be needed to compare total effective doses.

Solution 5

Site B has the greater radon-related inhalation exposure under the stated conditions. However, the student’s three claims are not justified.

The important distinction is between the amount of radioactive material in the rock, the amount of radon present in the air, and the total radiation dose received by a person.

Claim 1: Both locations must produce the same total radiation dose.

This is incorrect.

The external gamma dose rates are identical:

\[ 0.10\ \mathrm{\mu Sv/h} \]

For four hours at either location, the external dose contribution is:

\[ D=0.10\times4 \]

\[ D=0.40\ \mathrm{\mu Sv} \]

Therefore, the external gamma dose contributions are equal.

However, the radon concentrations are different.

At Site B, the concentration is:

\[ \frac{400}{40}=10 \]

The radon concentration is ten times higher.

Because the surveyor spends equal time at both sites and has the same breathing rate, Site B produces greater radon-related inhalation exposure.

Assuming other exposure pathways are equal, Site B would therefore be expected to produce the greater total radiological exposure.

The important limitation is that the exact effective dose cannot be calculated from these measurements alone. Additional information about radon decay products and appropriate dose-conversion factors would be required.

Claim 2: Site B must contain ten times as much uranium.

This is also incorrect.

Both locations have the same measured uranium concentration.

The difference in radon concentration can arise from differences in the physical environment.

For example:

• The permeability of the surrounding rock can affect how easily radon escapes.
• Cracks and fractures can provide pathways for radon to move.
• Moisture conditions can affect radon movement through soil.
• Ventilation affects how quickly radon disperses or accumulates.

Site B is enclosed, so radon can accumulate more readily.

This demonstrates an important distinction: the amount of radioactive material present does not automatically determine the concentration of its radioactive decay products in the surrounding air.

A similar uranium concentration can produce different environmental radon concentrations.

Claim 3: Jawoyn knowledge of Sickness Country must be an early scientific description of uranium deposits.

This conclusion goes beyond the evidence.

The geological relationship between naturally occurring radioactive materials and Sickness Country is scientifically significant.

However, the documented Jawoyn account is about much more than the chemical composition of rocks.

It involves Bula, the significance of particular places, cultural responsibilities, and rules governing access and disturbance.

The Kakadu National Park Management Plan also identifies substances such as arsenic, mercury, and fluorine in the region. These have chemical properties that cannot simply be explained through radioactive decay.

The existence of uranium and thorium deposits does not establish that traditional knowledge originated as a theory of nuclear radiation.

It would be equally inaccurate to assume that every place described as Sickness Country has the same geological characteristics or that every account of sickness has a radiological explanation.

What additional scientific information would help?

To compare the total effective doses more accurately, investigators would need information about:

• Radon decay-product concentrations and their relationship to radon gas.
• Appropriate dose-conversion factors.
• The amount of time people spend in each environment.
• Other radioactive materials, including thorium and potassium-40.
• Other exposure pathways, such as ingestion of naturally occurring radionuclides.

The final lesson is that a single measurement rarely explains an entire environmental system.

The uranium concentration tells us something about the rock. The radon concentration tells us something about radioactive gas in the air. The effective dose tells us something about the resulting radiation exposure.

These are connected quantities, but they are not interchangeable.

06Where to next?

Natural background radiation provides a useful application of several important nuclear chemistry concepts: isotopes, radioactive decay, half-life, nuclear equations, and the different properties of alpha, beta, and gamma radiation.

The next step is to trace complete radioactive decay chains and practise balancing nuclear equations. Once you can follow how one isotope transforms into another, you can explain how naturally occurring materials such as uranium and thorium contribute to radiation in the environment.

Most importantly, you can distinguish what a nuclear equation tells you from what a geological measurement or a cultural account tells you. Each provides different information about the same natural world.