RADIATION*Penetrating rays emitted by a radioactive source *Ranges from Cosmic and Gamma Rays to Radio Waves

RADIOACTIVE DECAY*Unstable atoms have excess internal energy.*the nucleus can undergo a spontaneous change towards a more stable form.

3 types of RADIATION3 types of RADIATION

αα – radiation – radiation(alpha radiation)(alpha radiation)

ß– radiation– radiation(beta radiation)(beta radiation)

γγ – radiation – radiation(gamma radiation)(gamma radiation)

αα – decay: – decay:*Emission of an *Emission of an αα – particle – particle*Particle is a Helium nucleus*Particle is a Helium nucleus

*Element changes to a *Element changes to a new element – a new element – a TransmutationTransmutation occurs occurs

44

22HHee

ααoror 42

αα – decay – decay equationequation

Atomic mass decreases by 4Atomic mass decreases by 4

Atomic number decreases by Atomic number decreases by 22

234

92UU

230

90

TThh

++4

2HeHe

αα – decay – decay

226

88 RaRa 222

86 RnRn ++4

2 HeHe

αα – decay – decay

*Particle carries a positive *Particle carries a positive chargecharge

*Large, heavy particle - *Large, heavy particle - moves slowlymoves slowly

*Little penetrating power *Little penetrating power

*stopped by skin or a sheet *stopped by skin or a sheet of paperof paper

ß -ß - decaydecay

*Emission of a beta - particle*Emission of a beta - particle

*Particle is an electron*Particle is an electron

*A transmutation occurs - a *A transmutation occurs - a neutron changes into a proton neutron changes into a proton and an electronand an electron

00

-1-1ee oror

oo

--11

ß

ß -ß - decay equationdecay equation

*Atomic mass stays the same*Atomic mass stays the same

*Atomic number increases by *Atomic number increases by 11

14

6

C o

-1e

14

7

N +

ß -ß - decaydecay

ß -ß - decaydecay

*Particle carries a negative *Particle carries a negative chargecharge

*Small, light-weight particle*Small, light-weight particle

**fast-movingfast-moving*Penetrates 1-2 cm of skin *Penetrates 1-2 cm of skin or or water water

*can be stopped by metal sheet *can be stopped by metal sheet a few mm thicka few mm thick

γγ – radiation – radiation

Emission of Emission of electromagnetic energyelectromagnetic energy

from an atom’s nucleusfrom an atom’s nucleus

No particles are emittedNo particles are emitted

A transmutation does A transmutation does not occurnot occur

γγ – radiation – radiationIdentical to X-raysIdentical to X-raysEnergy transmitted in Energy transmitted in

waveswavesGreat penetrating Great penetrating

power - can pass power - can pass through human through human bodybody

γγ – radiation – radiation

*Thick barriers of lead,*Thick barriers of lead,

concrete, or water concrete, or water are used as are used as protection against protection against them them

Graph of unstable nuclei Too many neutrons

Tend to beta decay

Too many protons and neutrons

Tend to alpha decayToo many protons

Capture e- to convert p+ to n0

Many radioactive Many radioactive elements have to elements have to go through a go through a series of decays series of decays to reach a stable to reach a stable isotopeisotope

Detecting Radiation

Radiation is ionizing radiation – it knocks electrons off of the substances it hits to produce ionsInstruments can detect this process

Detecting Radiation

Geiger counter – uses gas to detect radiation. Ionized gas particles conduct electricity and produce audible clicks

Detecting Radiation

Scintillation counter - uses phosphor to detect radiationPhosphors produce flashes of light when hit by ionizing radiation

Detecting Radiation

Film badge – uses photographic film to detect radiationWorn by personnel working near radiation sources to monitor exposure

Half – lifeHalf – life

The Half-life is the time it takes The Half-life is the time it takes for half of the atoms of a for half of the atoms of a radioactive substance to decay.radioactive substance to decay.

After one half-life the level of After one half-life the level of radioactivity of a substance is radioactivity of a substance is halved, after two half-lives it is halved, after two half-lives it is reduced to one quarter, and so onreduced to one quarter, and so on

Half-lifeGraph

FissionFission

Fission is a nuclear process in Fission is a nuclear process in which a heavy nucleus splits which a heavy nucleus splits into two smaller nuclei after into two smaller nuclei after being bombarded with being bombarded with neutronsneutrons

nn1

0++ 235

92 UU236

92 UU

142

56 BBaa

91

36 KrKr

1

0nn

++1

0nn

1

0nn

Fission ReactionFission Reaction

Fission reactionsFission reactions

Controlled fission is used Controlled fission is used in Nuclear Reactors to in Nuclear Reactors to produce useful energyproduce useful energy

FusionFusion

Fusion occurs when two Fusion occurs when two nuclei combine to produce nuclei combine to produce a nucleus with a heavier a nucleus with a heavier massmass

2

1H +

3

1 H4

2 HeHe +1

0 nn + energy

Fusion ReactionFusion Reaction FusionFusion

reactionsreactions release morerelease more energy thenenergy then fission fission reactions reactions