Give any two important sources of background radiation.

Explanation

**Step-by-Step Text Solution:**

1. **Identify Background Radiation**: Background radiation is the ionizing radiation present in the environment that originates from various natural and artificial sources.

2. **Source 1 - Radioactive Substances**: One important source of background radiation is radioactive substances found in the earth's crust and in living organisms. Examples include:
- Potassium-40 (K-40): A naturally occurring isotope of potassium that contributes to background radiation.
- Carbon-14 (C-14): A radioactive isotope of carbon that is present in the atmosphere and is absorbed by living organisms.
- Radium-226 (Ra-226): A radioactive element that can be found in some soils and rocks.
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