Health Physics

1a: Sources of Radiation

Introduction

• Scientists have studied radiation for over 100 years and we know a great deal about it.

• Radiation is part of nature. All living creatures, from the beginning of time, have been, and are still being, exposed to radiation.

We Live (And Have Always Lived) in aWe Live (And Have Always Lived) in a

““Sea of Radiation”Sea of Radiation”

Types of Radiation

Absorbed Dose

Depends on:

• Whether material is inside or outside body

• How long material remains in the body

• How much radioactive material there is

• The type of radiation it emits

• What its half-life is

Natural and Man-Made Radiation Sources

Natural Background Radiation

• Cosmic Radiation

• Terrestrial Radiation

• Internal Radiation

Cosmic Radiation

• The earth, and all living things on it, are constantly being bombarded by radiation from outer space (~ 80% protons and 10% alpha particles).

• Charged particles from the sun and stars interact with the earth’s atmosphere and magnetic field to produce a shower of radiation.

• The amount of cosmic radiation varies in different parts of the world due to differences in elevation and to the effects of the earth’s magnetic field.

Terrestrial Radiation (Uranium, Actinium, Thorium decay series)

• Radioactive material is found throughout nature in soil, water, and vegetation.

• Important radioactive elements include uranium and thorium and their radioactive decay products which have been present since the earth was formed billions of years ago.

• Some radioactive material is ingested with food and water. Radon gas, a radioactive decay product of uranium is inhaled.

• The amount of terrestrial radiation varies in different parts of the world due to different concentrations of uranium and thorium in soil.

Internal Radiation

• People are exposed to radiation from radioactive material inside their bodies. Besides radon, the most important internal radioactive element is naturally occurring K-40, but uranium and thorium are also present as well as H-3 and C-14.

• The amount of radiation from potassium-40 does not vary much from one person to another. However, exposure from radon varies significantly from place to place depending on the amount of uranium in the soil.

• On average, in the United States radon contributes 55% or all radiation exposure from natural and man-made sources. Another 11% comes from the other radioactive materials inside the body.

Enhanced Natural Sources

• Air travel (cosmic rad. is increased)

• Accumulation of rad. material (uranium)

• Consumer products (radium dials, smoke detectors)

Locations of Operating Nuclear Reactors

Transportation Safey

• A 120-ton locomotive, speeding at 80 miles an hour, crashed broadside into a container on a flatbed.

• This photo was taken immediately after impact.

• The impact demolished the train, but hardly dented the container.

Radioactive material is used in:

• Medicine - diagnostic (X-ray, CAT)

• Medicine - therapeutic (Co-60, Linac)

• Medical research (radio-pharmaceuticals, accel.)

• Industry - (X-ray density gauges, well logging)

Man-Made Radiation

Radiation in Medicine

• Radiation used in medicine is the largest source of man-made radiation.

• Most exposure is from diagnostic x-rays.

Man-Made Radiation Sources

• Exposure of selected groups of the public:– diagnostic radiology (X-rays)– nuclear medicine

(radiopharmaceuticals)– radiotherapy (Co-60, Linacs)

Man-Made Radiation Sources

• The Canadian Nuclear Safety Commission regulates exposure from man-made radiation sources. Different regulations apply to two distinct groups:

–Members of the public–Nuclear Energy Workers (NEWs)

Average Annual Effective Dose in US population (1982)

mSvNatural Background

Radon 2.0 other 1.0

Occupational 0.009Medical

diagnostic X-rays 0.39nuclear medicine 0.14

__________________________________Total (rounded) 3.6 mSv / year

From: Mettler et al., Ionizing Radiation

Total: 3.6 mSv/y

Natural Backgroundand Radiation Risk

• Use background radiation to quantify risk to a lay person.

• Background Equivalent Radiation Time (BERT).

• Regulatory limits based on natural radiation (1mSv/year for members of the public).

Radiation Risk

Consent Form:• 5mSv may increase fatal cancer risk by 2 in

10’000 in a lifetime.• Similar risks are associated with:

- smoking 2 packs of cigarettes in a lifetime

- driving 2000 miles by car

- living 100 days in New York

N.B.: natural incidence of fatal cancer is about 1 in 3.

Radiation Use at MNH/I

• Laboratories: 0.1 to 1 mCi

H-3, C-14, P-32, S-35, Cr-51, I-125, Ge-

68 • Gamma Cell: 600 Ci of Cs-137• PET scan: 10 to 100 mCi

C-11, O-15, F-18 (FDG)

• Cyclotron: 100 mCi to 1 Ci

C-11, O-15, F-18, neutrons

Examples on Nonionizing Radiation Sources

• Visible light• Microwaves• Radios• Video Display Terminals• Power lines• Radiofrequency • Lasers

Biological Effects

• Lasers (e.g. in patient alignment equipment)

– Permanent eye injuries– Cataracts and temporary blinding– Skin damage