The count rate is higher when the shield is removed because the shield is designed to absorb or block radiation from external sources, such as cosmic rays and naturally occurring radioactive materials in the surroundings. Without the shield, the Geiger-Muller tube is exposed to these external sources, resulting in a higher number of ionizing events and therefore a higher count rate.

A method to determine the background radiation count rate involves measuring the count rate of the Geiger-Muller tube when it is exposed to no radiation source (i.e., the shield is present or the tube is shielded from all known sources). This background count rate is the count rate due to naturally occurring radiation in the environment and the inherent sensitivity of the Geiger-Muller tube.

To calculate a corrected count rate, the measured count rate (e.g., 25 CPM when the shield is removed) is subtracted from the background count rate. The corrected count rate represents the count rate due *only* to the radiation from the specific source being investigated. The formula is: Corrected Count Rate = Measured Count Rate - Background Count Rate.

It is important to shield ourselves from background radiation because prolonged exposure to high levels of radiation can be harmful to living organisms.

Radiation can damage cells, potentially leading to:

• Increased risk of cancer: Radiation can damage DNA, increasing the likelihood of cancerous cell development.
• Genetic mutations: Radiation can cause changes to genetic material.
• Other health problems: Exposure to high doses can cause acute radiation sickness.

Shielding materials, such as lead or concrete, can absorb or deflect radiation, reducing the amount that reaches our bodies.

To calculate the background radiation count rate, we subtract the unshielded count rate from the shielded count rate. This is because the shielded count rate represents the radiation from the source *plus* the background radiation. Therefore, subtracting the unshielded count rate isolates the background radiation.

Background Radiation Count Rate = Shielded Count Rate - Unshielded Count Rate

Background Radiation Count Rate = 10 counts/minute - 40 counts/minute = -30 counts/minute

There appears to be an error in the provided data, as the background radiation count rate cannot be negative. The unshielded count rate should be *lower* than the shielded count rate. Assuming the data is correct, the calculation would yield -30 counts/minute. However, in a real experiment, the unshielded count rate should be significantly higher than the shielded count rate. A more realistic scenario would be, for example, Shielded = 10 CPM and Unshielded = 50 CPM, resulting in a background rate of 40 CPM.