What are back ground radiations?

Explanation

### Step-by-Step Solution:

1. **Definition of Background Radiation**: Background radiation refers to the ionizing radiation that is present in the environment at all times. It is a natural form of radiation that is not associated with any specific man-made source.

2. **Sources of Background Radiation**: The primary sources of background radiation include cosmic rays from outer space, terrestrial radiation from radioactive isotopes found in the Earth’s crust, and internal radiation from radioactive isotopes present within the human body.

3. **Radioactive Isotopes**: The Earth’s crust contains various isotopes, such as uranium, thorium, and radon, which are naturally radioactive. These isotopes undergo radioactive decay and emit radiation as they transform into more stable forms.

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