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This section focuses on how we can detect and measure radioactive emissions, particularly by measuring background radiation and determining a corrected count rate.
Background radiation is the naturally occurring radiation that surrounds us. It comes from various sources, including cosmic rays, naturally occurring radioactive isotopes in the Earth's crust, and even within our own bodies.
A Geiger-Müller tube is a common instrument used to detect and measure ionizing radiation. It works by detecting the ionization produced when radiation passes through it, resulting in a detectable electrical pulse. The count rate is the number of these pulses detected per unit time (usually per minute).
When measuring the radioactivity of a sample, it's crucial to account for the background radiation. This is done by measuring the count rate in the absence of the sample and then subtracting this background count rate from the count rate obtained with the sample. This gives a corrected count rate that is due to the sample being measured.
The corrected count rate ($C$) can be calculated using the following formula:
$$C = \text{Count rate with sample} - \text{Background count rate}$$
| Measurement | Value (counts/minute) |
|---|---|
| Background Count Rate (no sample) | 15 |
| Count Rate with Sample | 285 |
| Corrected Count Rate | $285 - 15 = 270$ counts/minute |
In this example, the corrected count rate of the sample is 270 counts per minute.