Name the noble gas which is obtained from `._(86)^(226)Ra`. Write its main use.
Or Name the noble gas used in radiotherapy.

Explanation

To solve the question, we need to identify the noble gas that is obtained from the radioactive decay of radium-226 (Ra-226) and its main use.

### Step-by-Step Solution:

1. **Identify the Element**:
The question mentions `._(86)^(226)Ra`, which refers to radium with atomic number 86 and mass number 226.

2. **Understand Radioactive Decay**:
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