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In radiation dosimetry, the equivalent dose is a critical concept that helps us understand the risk produced by exposure to radiation. It is expressed in units of Sieverts (Sv) or rems and considers the biological effect that ionizing radiation has on humans. The conversion between the two units is straightforward: 1 Sievert is equal to 100 rem.

This factor of 100 is used because Sieverts and rems reflect similar concepts but in different measurement systems. To convert from Sieverts to rem, simply multiply the number of Sieverts by 100. For instance, if someone is exposed to a dose of 5.4 Sv, this translates to 5.4 × 100 = 540 rem.

The equivalent dose takes into account the type of radiation we're dealing with. Different types of radiation have different potentials for biological damage. X-rays, for example, have a quality factor of 1, meaning their potential for biological harm is the baseline for comparison with other types of radiation.

The absorbed dose is the amount of radiation energy absorbed per unit mass of an object or tissue, and it is measured in rads or Grays (Gy). While the rad and Gray measure the same concept, they use different scales: 1 rad equals 0.01 Gy.

For the specific case of x-rays, the quality factor is 1. This means that the equivalent dose in rem is numerically the same as the absorbed dose in rad, when dealing with x-rays. Hence, our previous conversion from Sieverts to rem also gives us the absorbed dose in rads. If the absorbed dose is needed in our scenario of a 5.4 Sv exposure, we just convert the equivalent dose of 540 rem directly to 540 rad.

It's important to note that while the absorbed dose tells us how much energy is deposited in tissue, it doesn't convey biological impact—that's where equivalent dose comes into play, by accounting for the type of radiation.

When discussing energy absorption, we refer to the actual energy taken up by a material or tissue as a result of radiation exposure. The energy absorbed by a human body can be calculated once the absorbed dose is known. In this instance, the absorbed dose was calculated as 540 rad.

The formula to compute the total energy absorbed (\[E\]) involves the absorbed dose, mass of the tissue, and the conversion factor of 0.01 J/kg per rad:
\[E = ext{absorbed dose in rad} \times ext{mass in kg} \times 0.01 \, \text{\frac{J}{kg rad}}\]
Substituting the values for a 65 kg person yields:\[E = 540 \, \text{rad} \times 65 \, \text{kg} \times 0.01 \, \text{\frac{J}{kg rad}} = 351 \, \text{J}\]

This shows the total energy absorbed by the body. To put this number into perspective, compare it to the energy required to heat up water. It takes significantly more energy to raise the temperature of water slightly—a common benchmark when considering energy quantities. In this case, heating 65 kg of water by 0.010°C takes much more energy, specifically 2,721 J. This demonstrates that even a lethal dose of radiation corresponds to a surprisingly small amount of energy.