14 Radiation

8/12/2019 14 Radiation

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Biological Effects of

Ionizing Radiation


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Biological Effects of Ionizing

Radiation

Photons or moving particles that have

sufficient energy to knock electrons out of

atoms / molecules These include x-rays, gamma rays, alpha

particles, and beta particles.

Harmful to humans because these canalter significantly the structure of

molecules in cells.


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Radiation

The energy absorbed by

biological tissues per unit mass.

SI Unit = gray (Gy) = 1 J/kg, butthe unit most often used is the

rad = 0.01 Gy = 0.01 J / kg.

The amount of biological damage

depends on the type of ionizing

radiation. To make a comparison, we

use...

effectbiologicalsame

theproducesthatradiationofDose

effectbiologicalcertainaproducetorays-xkeV200ofDose

RBE


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Radiation

Type of Radiation RBE

200 keV x-rays 1

gamma rays 1beta particles 1

protons 10

alpha particles 10-20

slow neutrons 2

fast neutrons 10 A 200 Gy dose of x-rays

does the same amount of

damage as a 20 Gy dose of

fast neutrons.


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Radiation

The RBE is often used in conjunction with the absorbed

dose to give the Biologically Equivalent Dose (BED) in rems.

BED = AD RBE

This reflects the damage-producing character of the radiation.

Source of Radiation BED (mrem/yr)

cosmic rays 28

earth & air 28

internal nuclei (C, K) 39

inhaled radon ~200

consumer products 10

medical diagnostics 39

nuclear medicine 14

360


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Radiation

For the kinds of low doses of radiation

that we receive every day, cells can

usually repair the damage.

At higher doses (up to 100 rem), thecells may not be able to repair the

damagethey are either damaged or

dead. Dead cells do not matter since

they can be replaced.

Damaged cells may produce abnormalcells when they divide. Under the right

circumstances, these cells can become

cancerous. This is the origin of our

increased risk of cancer due to radiation

exposure.


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Radiation

At even higher doses, the cells cannot be replaced and

tissues fail to function.

> 100 remwhole body

Radiation Sickness...intestinal damage, nausea,

general weaknes

>300 rem whole body

immune system damage

>400 rem

whole bodyno medical attention will result in death for 50 %

of people in this condition within 60 days

>1000 rem whole body

vascular damage and death for 100 % of people

...but with adequate safety measures in place, no one is expected

to receive more than 5 rem in a year. So, the real risks we need

to consider are the long term ones...


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Radiation

What about non-ionizing radiation?

Type of Radiation effects

UV chemical changes

visible heating

microwaves more heating

very long waves molecular changes?

...not the same kind of damage that ionizing radiation does...


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Radiation

How much will radiation exposure increase my chances of death

from cancer?

The current US death rate from cancer is 20 %.So, out of every 100 people 20 of them, through random

processes will die from cancer.

If I take 10 000 people and expose them to 1 rem to their

whole body, eight additional people will get cancer, sostatistically we would expect around 2008 cancer deaths.

If the exposure is over the course of a year, then there will

be only 2 to 4 additional cases.

A better way to look at risks is by the number of days

lost to an average life in a population...

smoking 20 cigarettes per day 6 years

15 % overweight 2 years

alcohol (average US consumption) 1 yearall accidents 207 days

natural hazards 7 days

occupational dose (300 mrem/yr) 15 days

occupational dose (1 rem/yr) 51 days

You can do the same thing with risks on the job:

all industries 60 days

agriculture 320 daysconstruction 227 days

mining / quarrying 167 days

manufacturing 40 days


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Radiation

Receiving 10 mrem of radiation will cause death for one in one

million persons. This same rate is achieved by...

smoking 1.4 cigarettes

eating 40 tablespoons of peanut butter

spending 2 days in New York City (air pollution)

driving 40 miles in a car

flying 2500 miles in a jetcanoeing for 6 minutes


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Radiation

So what about nuclear power?

US public exposure from nuclear power

is < 0.1 mrem/yr

coal burning power plant 0.165 mrem/yr

x-rays from TVs 0.500 mrem/hr

airplane ride (39 000 ft) 0.500 mrem/hr

nuclear power plant site 0.600 mrem/yr

natural gas in your home 9 mrem/yr

Three Mile Island event 80 mrem/event

at the plant


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Radiation

So, how do I minimize my risk?

minimize time of exposure

maximize your distance from the source

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14 Radiation