Hazards and uses of radioactive emissions and of background radiation (physics only)

Radiation: Everywhere and Useful!

Welcome! In this section, we are going to look at the world of radiation that exists all around us. We’ll explore where it comes from, how we measure it, and why doctors actually use it to save lives. Don't worry if this seems a bit "invisible" and tricky at first—we'll break it down into simple steps!

1. Background Radiation

Background radiation is the low-level radiation that is around us all the time. It is like the "background noise" in a busy cafe—it's always there, even if you aren't paying attention to it.

Where does it come from?

It comes from two main places:

1. Natural Sources:
- Rocks: Some rocks, like granite, contain radioactive isotopes that release radon gas.
- Cosmic Rays: High-energy particles from outer space (mostly from the Sun) that hit the Earth.

2. Man-made Sources:
- Fallout: Leftover radiation from nuclear weapons testing.
- Nuclear Accidents: Small amounts released from past accidents at power stations.

What affects your dose?

Not everyone gets the same amount of radiation. Your radiation dose (the amount you absorb) depends on:
- Location: If you live in an area with lots of granite rock, your dose will be higher.
- Occupation: People like pilots (who are closer to cosmic rays) or X-ray technicians have a higher "work-related" dose.

Quick Review: Radiation dose is measured in sieverts (Sv). Because one sievert is a huge amount, we often use millisieverts (mSv).
Remember: \( 1000 \text{ millisieverts (mSv)} = 1 \text{ sievert (Sv)} \)

Did you know? Eating a banana gives you a tiny dose of radiation because bananas contain naturally radioactive potassium! But don't worry—you'd have to eat millions at once for it to be a problem.

2. Half-lives and Hazards

Before we move on, remember that half-life is the time it takes for half of the radioactive atoms in a sample to decay. The length of the half-life determines how dangerous a substance is over time.

Short Half-life: These sources are very radioactive at first (high activity) but become safe quickly. They are like a firecracker—a big bang, then it's over.
Long Half-life: These sources stay radioactive for a very long time. They are more like a slow-burning candle that you can't blow out. These are hazardous because they can contaminate an area for hundreds of years.

Key Takeaway: We must choose radioactive sources carefully based on their half-life. For example, we wouldn't want to inject a patient with something that stays radioactive for 50 years!

3. Using Radiation in Medicine

Even though radiation can be hazardous, it is an incredible tool in hospitals. There are two main ways it's used:

A. Exploration of Internal Organs (Tracers)

Doctors can use gamma-emitting isotopes as "tracers" to see how your body is working.
1. The patient swallows or is injected with a radioactive source.
2. The source travels to a specific organ (like the thyroid or kidneys).
3. A gamma camera outside the body detects the radiation and builds a picture.

Why use Gamma? Gamma radiation is used because it is weakly ionising and can pass easily out of the body to be detected by the camera without causing too much damage to cells.

B. Control or Destruction of Unwanted Tissue

Radiation can be used to kill cancer cells (radiotherapy).
- External Treatment: High-energy gamma rays are aimed precisely at a tumour from many different angles to kill the cancer while minimizing damage to healthy skin.
- Internal Treatment: A radioactive "seed" or liquid is placed right next to or inside a tumour.

Common Mistake to Avoid: Don't confuse "irradiation" with "contamination." If a patient has a gamma-ray beam aimed at them, they are irradiated (exposed to waves), but they do not become radioactive themselves!

4. Evaluating the Risks

When using radiation, scientists and doctors always perform a risk-benefit analysis.
- The Risk: Radiation can enter living cells and ionise atoms, which can damage DNA and cause mutations or cancer.
- The Benefit: It can find life-threatening blockages in organs or destroy a deadly tumour.

Memory Aid: Think of a surgical knife. It is sharp and "dangerous," but in the hands of a doctor, the benefit of the surgery outweighs the risk of the cut. Radiation is the same!

Summary: Quick Review Box

1. Background radiation comes from natural (rocks, space) and man-made (fallout) sources.
2. Radiation dose is measured in sieverts (Sv) and depends on your job and where you live.
3. Half-life affects hazard: long half-lives mean the source stays active for a long time.
4. Tracers use gamma radiation to "see" inside the body because it passes through tissue easily.
5. Radiotherapy uses high doses of radiation to kill cancer cells.
6. Risk vs. Benefit: We use radiation when the benefit (saving a life) is greater than the risk (cell damage).