In health physics and radiation protection, the rem (Roentgen Equivalent Man) is a CGS unit used to measure the biological effect of ionizing radiation. Unlike the rad, which measures the amount of energy absorbed by physical matter, the rem accounts for the specific biological damage that different types of radiation inflict on human tissue.
The REM Calculation Formula
The calculation of dose equivalent is straightforward but requires knowledge of the radiation type's "Quality Factor" (Q). The formula used by this calculator is:
If a technician is exposed to 0.05 rad of alpha particle radiation, we use the quality factor of 20 for alpha particles. The calculation would be:
0.05 rad × 20 = 1.0 rem
This means that while the physical energy absorbed was small, the biological impact is equivalent to 1 rem of X-ray exposure.
Safety Limits and Context
To put these numbers into perspective, the average person receives approximately 0.62 rem (620 mrem) per year from natural and medical sources combined. The occupational limit for radiation workers in the United States is generally 5 rem per year, though many facilities aim for much lower levels following the ALARA (As Low As Reasonably Achievable) principle.
Rem vs. Sievert (Sv)
The rem is an older unit still widely used in the United States. The International System of Units (SI) equivalent is the Sievert (Sv). The conversion is simple:
1 Sievert = 100 rem
1 rem = 0.01 Sievert (or 10 millisieverts)
function calculateRem() {
var absorbedDose = document.getElementById('absorbedDose').value;
var qualityFactor = document.getElementById('radiationType').value;
var resultDiv = document.getElementById('remResult');
var remDisplay = document.getElementById('remValue');
var mremDisplay = document.getElementById('mremValue');
var sievertDisplay = document.getElementById('sievertValue');
if (absorbedDose === "" || isNaN(absorbedDose)) {
alert("Please enter a valid number for the absorbed dose.");
return;
}
var doseValue = parseFloat(absorbedDose);
var qValue = parseFloat(qualityFactor);
if (doseValue < 0) {
alert("Dose cannot be negative.");
return;
}
// Calculation logic
var remTotal = doseValue * qValue;
var mremTotal = remTotal * 1000;
var svTotal = remTotal / 100;
// Displaying results
remDisplay.innerHTML = remTotal.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 5});
mremDisplay.innerHTML = mremTotal.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
sievertDisplay.innerHTML = svTotal.toLocaleString(undefined, {minimumFractionDigits: 4, maximumFractionDigits: 7});
resultDiv.style.display = "block";
}