High School Teachers at CERN
WWW.CERN.CH	TEACHING MATERIALS VISITING CERN	LINKS & BOOKS HST

Radiation Protection

This is the science of measuring radiation exposure and protecting people from it so that they stay within safe exposure limits. As a rule-of-thumb these safe limits are set at half what is thought to be dangerous to health. 

CERN is a radiation risk area. For example, when the accelerator beams are switched on, the tunnels are closed and bolted and the system will automatically shut down if the doors are opened. 

Substantially the radiation is contained by the fabric of the tunnel. The level of radiation experienced by a visitor is extremely low and of no significant danger as compared with the background radiation we all receive every day.. However for workers at CERN who may spend their working time in these areas it is necessary to monitor radiation levels and to have their own exposure checked using film badges; you will also find other types of radiation detector spread around the experimental areas which measure environmental radiation levels. 

In much the same way the radiation experienced by having a single chest X-ray or a teeth x-ray is minimal, but for those operating the machinery day after day the risks are much higher unless sensible precautions are taken. 

There is a Department at CERN whose job is radiation safety. 

For measuring the exposure two quantities are used, the DOSE and the DOSE EQUIVALENT. 

DOSE is the energy absorbed per unit mass. Unit: Gray (Gy) 

1 Gy = 1 J/kg

Lethal dose is between 1 Gy and 10 Gy depending on the type of radiation. 

There exists a biological recovery factor to photon radiation (i.e. gamma rays). This is because biological systems can repair (some) of the damage caused by gamma rays, but generally not the damage caused by alpha particles or beta particles. 

Dose rate (Gy/min) can also affect the outcome. 

 

Effects on Humans.

DOSE (Gy)	Life Expectancy	System damaged
1000	1 hour	Central Nervous System
10 - 100	3 days	Gastrointestinal Tract
3 - 10	30 days	Bone Marrow
< 1	> 10 years	Cancer risk

DOSE EQUIVALENT is the effective dose an organism receives, taking into account the differing biological effects of different types of radiation. Unit: Sieverts (Sv) 

Dose Equivalent = Dose x Q

Q is the Quality Factor and depends on the radiation type, dose rate and biological type involved. 

Q is the most difficult thing to measure in radiation protection. 

Typically, alpha particles have Q = 20, for neutrons Q = 10, and beta particles and gamma rays have Q = 1. 

Background dose equivalent is in the range of 1 to 2.5 mSv per year depending on location. Professional workers in radiation 'hot' environments are limited to 15 mSv per year (CERN, 1999). 

Radiation damage can add to existing risks (if it affects the DNA), or, it can multiply existing risks (if it affects the immune system). 

RADIATION PROTECTION MEASURES ARE VERY EFFECTIVE. IN TOTAL ONLY AROUND 600 PEOPLE IN THE WHOLE WORLD HAVE EVER DIED FROM DIRECT RADIATION CAUSES.