Radiation Exposure, Effects and Risk

Anthony WakerFaculty of Energy Systems and Nuclear Science

External Exposure The source is external to the body

Types of Exposure

CT Scanner: A few to 10s of mSv per examination

Internal Exposure The source is inside the body

Types of Exposure

Approximately 1 mSv per year

Total Exposure is the sum of all external and all internal doses

Types of Exposure

Approximately 3 mSv per year

Members of the public 1 mSv per year

Nuclear Energy Workers 20 mSv per year (100 mSv in 5 years, 50 mSv in any one year)

Fukushima workers – legal limit has been raised to 250 mSv

Legal Limits of Exposure

Medical Radiation not counted

External doses Calibrated Instruments and dosimeters

Measuring Dose

Calibrated instruments and dosimeters give a direct reading of the radiation dose to the individual

Internal Doses Whole body counters and Bioassay

Measuring Dose

Whole body counters and bioassay are used to determine the intake of radioisotopes; what follows is a complicated calculation to convert an intake into a dose.

Principal Concerns at moderate to low dose (mSv to a few Sv)

Cancer

Hereditary Disease

Radiation Effects on the Fetus

Effects

The risk increases with dose

Principal Concerns at high dose (1 Sv and up)

Radiation Sickness

Bone marrow damage

Gastrointestinal damage

Effects

The severity increases with dose

Risk to humans derived from

Atomic Bomb Survivors (Hiroshima and Nagasaki Life Span Study)

Medically exposed groups (ankylosing spondylitis; repeated fluoroscopic examination of tuberculosis patients in Massachusetts and Nova Scotia)

Occupationally exposed groups (radium dial-painters, uranium miners, former Soviet Union plutonium workers)

Risks at moderate and low doses

Current Assessment of Risk

Cancer (4 to 10% per Sv)

Hereditary Disease (1/10 th of fatal cancer risk)

Radiation Effects on the Fetus (life-time cancer risk 20% per Sv)

Risks at moderate and low doses

Cancer risk estimates apply to populations not to individuals

Risks at moderate and low doses

Risks at moderate and low doses

Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know

PNAS November 25, 2003 vol. 100 no. 24 13761–13766

What is the lowest dose of X-ray or gamma ray radiation for which good evidence exists of increased cancer risk in humans………

Risks at moderate and low doses

Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know

PNAS November 25, 2003 vol. 100 no. 24 13761–13766

………the epidemiological data suggests that it is approximately 10-50 mSv for an acute exposure and 50–100 mSv for a chronic exposure

Effects at high dose result from the killing of stem cells that are used to supply replacement cells in the blood and for the lining of the intestines

Effects at High Dose

Whole-body Irradiation and Radiation Lethality

Acute Radiation Syndrome – Medical Intervention

External exposures Limit the time of exposure Rotation of workers (shifts) Increase the distance from the source Shielding (put something between

you and the source)

Exposure mitigation -workers

Fukushima workers will be using all these measures of reducing dose

Internal exposures Protective clothing and breathing

apparatus Prevent spreading contamination by

not moving out of contaminated area without changing protective clothing and boots; showers

Exposure mitigation - workers

Very High Total Exposures Nursing Anti-biotics Blood transfusions Bone marrow transfusions

Exposure mitigation - workers

External Exposure Distance (exclusion zones and

evacuation plans)

Internal Exposure Staying out of the plume (exclusion) Staying indoors Preventing spread of contamination Using Potassium Iodide

Exposure mitigation - Public