Ionising radiation harms people in two distinct ways: a large dose received in a short time causes acute radiation sickness within hours to weeks, and smaller doses, acute or accumulated, raise the risk of cancer years later. The severity of acute sickness tracks the dose, and at high doses the outcome is poor whatever care is available.
Part of Radiation Safety
Radiation injures through damage to DNA and cells; the body’s response depends on how much energy is absorbed, how fast, and which tissues receive it.
Cells Are Damaged, Killed Or Changed
The parent article, Nuclear Safety, says ionising radiation damages DNA, kills cells and causes cancer. The fast-dividing tissues, bone marrow and the lining of the gut, are hit first and hardest, which is why the parent’s acute-syndrome table moves from low blood-cell counts to gut destruction as dose rises.
A Large Dose In A Short Time Causes Acute Radiation Syndrome
Large doses received over a short time cause acute radiation syndrome (ARS), commonly called radiation sickness. Severity depends on dose; the full picture is in Acute Radiation Syndrome and the dose bands are in Dose Thresholds. Below a threshold dose no acute effect appears; above it, severity rises with dose.
Smaller Doses Raise Cancer Risk With No Safe Threshold Assumed
The effect that does not have a clear threshold is cancer. Standard radiation protection assumes the chance of cancer rises in proportion to dose, with no dose that is risk-free; that is a modelling assumption, not a measured fact at very low doses. It appears years to decades after exposure. See Chronic Exposure.
Where The Source Is Matters
Gamma radiation from outside irradiates the whole body. Alpha and beta emitters do most harm when swallowed, inhaled or lodged in a wound, where they irradiate the nearest tissue at short range. Some isotopes also seek out particular organs: iodine-131 concentrates in the thyroid and strontium-90 deposits in bone (parent article). See Contamination vs Irradiation.
Who Is Most Vulnerable
Children, pregnant women and the unborn are generally regarded as more sensitive than healthy adults, and the thyroid of a child is the usual reason iodine blocking is considered at all; see Treatment Protocols. This is standard radiation-protection teaching rather than a figure from the parent article, and no sensitivity ratio is given here.
Common Mistakes
- Waiting for symptoms to decide whether you were exposed. Symptoms of a high dose can start within minutes to hours; symptoms of a damaging but survivable dose can be delayed or absent. See Biological Indicators.
- Treating a patient as radioactive. An irradiated person is not a hazard to others.
- Assuming “no symptoms” means “no cancer risk”. The parent table says the lowest band causes no symptoms but a slightly increased cancer risk.
Safety
No treatment in this guide reverses a large whole-body dose
There is no field treatment that changes the outcome of a large whole-body dose. The practical lesson is prevention: distance, shelter and time, decided before exposure. See Treatment Protocols.
What’s Next
- Learn next: Acute Radiation Syndrome — symptoms, stages and prognosis
- Combine with: Chronic Exposure — the long-term cancer risk