A typical chest X ray exposes a patient to an effective dose of 0.02 mSv. How many rem is this, and how many chest X rays would a patient have to receive before biological effects would be observed? (The limit from Table 11.6 is >25 rem.)

Verified step by step guidance

1. Step 1: Understand the relationship between millisieverts (mSv) and rem. The conversion factor is 1 mSv = 0.1 rem. This means you can convert the given dose in mSv to rem by multiplying the mSv value by 0.1.
2. Step 2: Convert the effective dose of 0.02 mSv to rem using the formula: $\mathrm{rem}=\mathrm{mSv}\times 0.1$. Substitute 0.02 mSv into the equation.
3. Step 3: Determine the total number of chest X-rays required to reach the biological effects threshold (>25 rem). Use the formula: $n=\frac{\mathrm{Threshold}}{\mathrm{Effective\; Dose\; per\; X-ray}}$. Substitute the threshold value of 25 rem and the effective dose per X-ray (in rem) into the equation.
4. Step 4: Perform the division to calculate the number of X-rays required. This will give you the number of chest X-rays a patient would need to receive before biological effects are observed.
5. Step 5: Interpret the result. If the calculated number of X-rays is a whole number, that is the exact count. If it is a decimal, round appropriately based on the context (e.g., to the nearest whole number if partial X-rays are not possible).

Key Concepts

Effective Dose and Conversion

Effective dose is a measure of the biological effect of ionizing radiation on human tissue, expressed in sieverts (Sv) or millisieverts (mSv). To convert mSv to rem, a conversion factor of 1 mSv = 0.1 rem is used. Therefore, a chest X-ray dose of 0.02 mSv equates to 0.002 rem.

Biological Effects of Radiation

Biological effects of radiation refer to the potential damage that ionizing radiation can cause to living tissues, which may lead to health issues such as cancer. The threshold for observable biological effects is often set at 25 rem, indicating that doses above this level may increase the risk of adverse health outcomes.

Cumulative Dose Calculation

Cumulative dose calculation involves determining the total radiation exposure a patient receives over multiple X-ray procedures. To find out how many chest X-rays would lead to biological effects, one can divide the threshold dose (25 rem) by the dose per X-ray (0.002 rem), resulting in the number of X-rays needed to reach or exceed this threshold.