Prof.Dr.Tarek Elnimr

L 3& L4Presented to the

Biology Departments in Faculty of

Scienceson February 15 ,

2009

Electromagnetic Waves vs. Particle RadiationRadiation

Energy transfer through matter or spaceClassification of Radiation Energy

Electromagnetic Made of electric and magnetic fields Radio, UV, microwave, gamma rays, visible light, x-

rays, and infra red (listed in order from lowest frequency)

Spring 2008 3

Electromagnetic Radiation

Interrelated electric and magnetic fields traveling through space

All electromagnetic radiation travels at c = 3108 m/s in vacuum – the cosmic speed limit!real number is 299792458.0 m/s exactly

Electromagnetic Spectrum

Diagram of EM spectrum (w/ color)

Radioactivity: Gamma RaysThe Electromagnetic Spectrum

Stratospheric Ozone and Ultraviolet Radiation (UVR)Ultra-violet radiation (UVR) high energy electromagnetic wave emitted from the

sun. It is made up of wavelengths ranging from 100nm to 400nm.

UV radiation includes UV-A, the least dangerous form of UV radiation, with a wavelength range between 315nm to 400nm, UV-B with a wavelength range between 280nm to 315nm, and UV-C which is the most dangerous between 100nm to 280nm. UV-C is unable to reach Earth’s surface due to stratospheric ozone’s ability to absorb it. (Last, 2006)

for visible light is approximately 100 nm

red 750 - 610 nm long - low

purple 450 - 400 nm short - high

Wavelength UnitsMeters

More commonly in nanometers (1 nm = 10-9

meters)Angstroms still used

Named for Swedish Astronomer who first named these wavelengths

1 nanometer = 10 Ao

THE ENERGIES OF ELECTROMAGNETIC WAVES

THE ENERGIES OF ELECTROMAGNETIC WAVES

hcNc

hNhNE

hcc

hhE

c

AAA

1

hcNc

hNhNE

hcc

hhE

c

AAA

1

(nu-bar) represents wavenumber, the number of wavelengths in 1 cm

4) Characteristics of Waves

- wavelength - distance between consecutive peaks - crests - measured in m, nm, angstroms.

• All life is dependent on small doses of electromagnetic radiation.

• For example, photosynthesis and vision use the suns radiation.

Low HighENERGY

Radio waves

Microwaves

Radar

Infrared

Visible light

Ultra-violet

X-ray

Gamma-ray

Non-ionizing radiation

Ionizing radiation

Radiation is EnergyRadiation is EnergyThe energy is given off by unstable

(radioactive) atoms and some machines.

• For this talk, we will be focusing on ionizing radiation and its health effects.

frequency - (nu) - number of times per second a crest passes a given point (cycles per second)

1 Hz = 1 cycle per second = 1/sec =sec-1

u = speed = X

nm/wave X wave/sec = nm/sec

for light - speed of electromagnetic radiation in a vacuum is a constant - c - 2.998 X 108 m/sec

X = c for light

nu is inversely proportional to the wavelength. What does this mean?

The range of frequencies or wave lengths is called the electromagnetic spectrum - it ranges from gamma rays to TV, FM, AM radio waves.

Forms of RadiationForms of RadiationWhen unstable atoms transform, they often eject particles from their nucleus. The most common of these are: Alpha Radiation

High energy, but short range (travels an inch in air, not an external hazard)

Beta RadiationLonger range (10 – 20 feet in air) and can be a skin and eye hazard for high activity beta sources.

Gamma Rays (electromagnetic radiation) Often accompany particle radiation. This “penetrating” radiation is an external hazard and can travel 100s of feet in air.

gamma

gamma

NonionizingUltraviolet, visible, infrared, microwaves, radio & TV, power transmission

IonizingRadiation capable for producing ions when interacting with matter – x-rays, alpha, beta, gamma, cosmic rays

NonionizingUltraviolet, visible, infrared, microwaves, radio & TV, power transmission

IonizingRadiation capable for producing ions when interacting with matter – x-rays, alpha, beta, gamma, cosmic rays

Sources• Ultraviolet light• Visible light• Infrared radiation• Microwaves• Radio & TV• Power transmission

• Ultraviolet – Black light – induce fluorescence in some materials

• Vision – very small portion that animals use to process visual information

• Heat – infrared – a little beyond the red spectrum

• Radio waves – beyond infrared• Micro waves• Electrical power transmission – 60

cycles per second with a wave length of 1 to 2 million meters.

Ionizing Electromagnetic Radiation

Ionizing Electromagnetic Radiations do have enough energy to remove electrons from atoms, such as:•X-rays•Gamma rays•Neutrons•Alpha Particles

Ionization

Atom

Electron

IonizingRadiation

Ion

More Reactive !!

Biological Effect

The process by which a neutral atom acquires a positive or negative charge

Ionization

electron is stripped from atom

-

-

-

-

The neutral atom gains a + charge= an ion

+

+

Alpha Particle

IonizationIonization by a Beta particle:

-

-

-

-

The neutral absorber atom acquires a positive charge

Beta Particle

-

CollidingCoulombic Fields

ejected electron

Radiation and Radioactive Material are a Radiation and Radioactive Material are a Natural Part of Our LivesNatural Part of Our LivesWe are constantly exposed to low levels of radiation from outer space, earth, and the healing arts.

Low levels of naturally occurring radioactive material are in our environment, the food we eat, and in many consumer products.

Some consumer products also contain small amounts of man-made radioactive material.

SmokeDetector

Non-Ionizing Electromagnetic Radiation Non-Ionizing Electromagnetic Radiations do not have enough energy to remove electrons from atoms, such as:•Ultraviolet Radiation•Light•Infrared Radiation•Microwaves•Radio Waves

Microwaves 3 major uses in our society

Cooking (Ovens)

Microwaves 3 major uses in our society

Cell phones Radar

Infrared Radiation (Heat)

• Energy between 750 nm to 0.3 cm• The energy of heat – Heat is the transfer

of energy• Can damage – cornea, iris, retina and

lens of the eye (glass workers – “glass blower’s cataract”)

• Energy between 400 and 750 nm• High energy – bright light produces of

number of adaptive responses• Standards are set for the intensity of

light in the work place (measured in candles or lumens)

• Sun light• Most harmful UV is absorbed by the

atmosphere – depends on altitude• Fluorescent lamps• Electric arc welding

Can damage the eye (cornea)• Germicidal lamps• Eye damage from sun light• Skin cancer

• High ultraviolet – kills bacterial and other infectious agents

• High dose causes - sun burn – increased risk of skin cancer

• Pigmentation that results in suntan • Suntan lotions contain chemicals that

absorb UV radiation• Reaction in the skin to produce Vitamin D

that prevents rickets• Strongly absorbed by air – thus the danger

of hole in the atmosphere

Too much ultra-violet light can result in:Skin cancerEye damage such as cataractsImmune system damageReduction in phytoplanktonDamage to the DNA in various life-forms

this has been as observed  in Antarctic ice-fish that lack pigments to shield them from the ultra-violet light (they've never needed them before)

Possibly other things too that we don't know about at the moment

Ionization Defined

Radiation capable for producing ions when interacting with matter – in other words enough energy to remove an electron from an atom.

Sources – x-rays, radioactive material produce alpha, beta, and gamma radiation, cosmic rays from the sun and space.

Radioactive Material

Either natural or created in nuclear reactor or accelerator

Radioactive material is unstable and emits energy in order to return to a more stable state (particles or gamma-rays)

Half-life – time for radioactive material to decay by one-half

Hazards of Radiation“Radiation is radiation. It cannot be seen; it

cannot be felt; it cannot be smelled; it cannot be heard; and it cannot be touched. Yet it exisits, and though its proper use has been immeasurable benefit to mankind, its abuse or improper use presents great hazards.”

The process by which a neutral atom acquires a positive or negative charge

Ionization

electron is stripped from atom

-

-

-

-

The neutral atom gains a + charge= an ion

+

+

Alpha Particle

Alpha Particles Two neutrons and two protons Charge of +2 Emitted from nucleus of radioactive

atoms Transfer energy in very short

distances (10 cm in air) Shielded by paper or layer of skin Primary hazard from internal

exposure Alpha emitters can accumulate in

tissue (bone, kidney, liver, lung, spleen) causing local damage

Radioactivity: Beta Rays

Beta Particles Small electrically charged

particles similar to electrons Charge of -1 Ejected from nuclei of radioactive

atoms Emitted with various kinetic

energies Shielded by wood, body

penetration 0.2 to 1.3 cm depending on energy

Can cause skin burns or be an internal hazard of ingested

Gamma-rays Electromagnetic photons or

radiation (identical to x-rays except for source)

Emitted from nucleus of radioactive atoms – spontaneous emission

Emitted with kinetic energy related to radioactive source

Highly penetrating – extensive shielding required

Serious external radiation hazard

X-rays Overlap with gamma-rays Electromagnetic photons or radiation Produced from orbiting electrons or

free electrons – usually machine produced

Produced when electrons strike a target material inside and x-ray tube

Emitted with various energies & wavelengths

Highly penetrating – extensive shielding required

External radiation hazard Discovered in 1895 by Roentgen