Health Effects of Radiation

The degree of damage caused by radiation depends on many factors – the dose, the dose rate, the type of radiation, the part of the body being exposed, the exposed person's age and health, etc. Embryos including human fetuses are particularly sensitive to radiation damage.

The lowest level of radiation dose which could conceivably increase one's likelihood of developing cancer is above 100 mSv per year. Sudden large dose of radiation of 1,000 mSv or above to the body will also cause acute radiation injuries. This will in turn result in short-term symptoms like nausea, vomiting, extreme tiredness and hair loss. A short dose of 10,000 mSv or more can be fatal unless proper medical attention is available.

The units to measure the dose of radiation to individuals are millisievert (mSv, i.e. 1/1000Sv). We are typically exposed to about 3mSv per person per year in Hong Kong.

Radiation Comes in Both Ionising and Non-ionising Forms
Non-ionising Radiation: Contains low-energy electromagnetic waves. Common examples include ultrasound, microwave, visible light and ultraviolet light. As the energy level of each type is relatively low, non-ionising radiation generally only manages to cause molecules to vibrate and induce heat effects.
Ionising Radiation: Consists of high-energy electromagnetic waves and charged atomic particles. Causes chemical changes in materials from the high energy. In high quantities, ionising radiation can damage living tissues and destroy human cells. In general, "radiation" refers to this form.
Is it possible to stop this chain reaction?

YES. The control rods in a nuclear reactor are used to control the speed of the chain reaction and can capture free neutrons before they collide with U235 atoms. The control rods are also used to shut down the reactor and can stop a nuclear chain reaction within 2 seconds.