Radioactivity and Radioactivity and Nuclear ReactionsNuclear Reactions

RadioactivityRadioactivity Protons and Neutrons are attracted to each other in Protons and Neutrons are attracted to each other in

the nucleus of an atom by the “strong force”the nucleus of an atom by the “strong force” The total force between these particles depends on The total force between these particles depends on

how far apart they arehow far apart they are Smaller nuclei have a stronger attraction to each Smaller nuclei have a stronger attraction to each

other and are more stableother and are more stable Larger nuclei are held together less tightly and the Larger nuclei are held together less tightly and the

strong force may not be enough to keep the atom strong force may not be enough to keep the atom stable. stable.

When the “strong force” is not enough to hold a When the “strong force” is not enough to hold a nucleus together, the nucleus begins to decay and nucleus together, the nucleus begins to decay and give ff matter and energy.give ff matter and energy.

This is called radioactivityThis is called radioactivity

Radioactive decay Radioactive decay is the process is the process by which the unstable nuclei lose by which the unstable nuclei lose mass and/or energy by emitting mass and/or energy by emitting radiation. radiation.

Eventually unstable nuclei Eventually unstable nuclei achieve a more stable state achieve a more stable state when they are transformed into when they are transformed into atoms of a atoms of a different elementdifferent element..

All nuclei that contain more than 83 All nuclei that contain more than 83 protons are radioactiveprotons are radioactive

Almost all elements with more than 92 Almost all elements with more than 92 protons don’t exist naturally on Earth and protons don’t exist naturally on Earth and are only produced in laboratoriesare only produced in laboratories

These are called synthetic elements and These are called synthetic elements and decay soon after they are created due to decay soon after they are created due to being unstablebeing unstable

Radioactivity is all around you, even in Radioactivity is all around you, even in your bodyyour body

It cannot be detected by smell, sight, It cannot be detected by smell, sight, sound, taste, or touchsound, taste, or touch

Radioactivity can be captured on Radioactivity can be captured on photographic plates (x-rays)photographic plates (x-rays)

RadioactivityRadioactivity Radioactivity was 1Radioactivity was 1stst

discovered by Antoinediscovered by Antoine

Becquerel, when Becquerel, when

a photographic plate a photographic plate

never exposed to never exposed to

Sunlight in his lab had become exposed. Sunlight in his lab had become exposed. The only possible culprit was a nearby The only possible culprit was a nearby uranium salt sitting on the bench top.uranium salt sitting on the bench top.

Nuclear DecayNuclear Decay

There are three types of nuclear radiationThere are three types of nuclear radiation AlphaAlpha BetaBeta Gamma radiationGamma radiation

Alpha and Beta are particlesAlpha and Beta are particles

Gamma radiation behaves like a wave of light at Gamma radiation behaves like a wave of light at a very high frequencya very high frequency

Transmutation is changing one element to Transmutation is changing one element to another by nuclear decayanother by nuclear decay

In Alpha decay, two protons and two In Alpha decay, two protons and two neutrons are lost from the nucleus so the neutrons are lost from the nucleus so the new element has an atomic number two new element has an atomic number two less than that of the original elementless than that of the original element

Alpha ParticlesAlpha Particles

Alpha Particles are the least penetrating Alpha Particles are the least penetrating form of radiation. They can be stopped by form of radiation. They can be stopped by a piece of papera piece of paper

Ex. Smoke detectors give off alpha Ex. Smoke detectors give off alpha particles that ionize the surrounding air. particles that ionize the surrounding air. Smoke particles absorb the ions and Smoke particles absorb the ions and electrons and break a circuit which causes electrons and break a circuit which causes the alarm to go offthe alarm to go off

Alpha Particle Emission (Alpha Particle Emission (αα))

HeThU 42

23490

23892

Uranium - 238 Thorium - 238 Alpha Particle (α)

Beta ParticlesBeta Particles

Beta particles are faster and more Beta particles are faster and more penetrating than alpha particles. They can penetrating than alpha particles. They can pass through paper and are stopped by a pass through paper and are stopped by a sheet of aluminum foilsheet of aluminum foil

During Beta decay an electron is emitted During Beta decay an electron is emitted from the atom and a new element is from the atom and a new element is formedformed

BETA EMISSION BETA EMISSION A beta particle (a high energy electron, A beta particle (a high energy electron, charge of -1) is generated in the charge of -1) is generated in the nucleus as a neutron is converted into nucleus as a neutron is converted into a proton.a proton.

eNC 01

147

146

Carbon - 14

Nitrogen - 14 BetaParticle

Gamma RaysGamma Rays

The most penetrating form of radiation are The most penetrating form of radiation are gamma raysgamma rays

Gamma rays carry energyGamma rays carry energy Thick blocks of lead and concrete are Thick blocks of lead and concrete are

required to stop gamma raysrequired to stop gamma rays

Gamma Emission (Gamma Emission (λλ))

Generally accompanies other radioactive radiation because it is the energy lost from settling within the nucleus after a change.

Penetrating Power of Penetrating Power of RadiationRadiation

Radioactive Half-LifeRadioactive Half-Life

Half-Life (tHalf-Life (t1/21/2) is ) is the time the time required for required for half half of the atoms of of the atoms of a radioisotope a radioisotope to emit radiation to emit radiation and to decay to and to decay to productsproducts..

Half-Life ExampleHalf-Life ExampleIt takes 4.5 X 10It takes 4.5 X 1099 years for one half of a years for one half of a sample of uranium-238 to decay to lead-206. sample of uranium-238 to decay to lead-206. Therefore, it would take another 4.5 X 10Therefore, it would take another 4.5 X 1099 years for one half of the remaining uranium to years for one half of the remaining uranium to decay, et cetera, et cetera, et cetera.decay, et cetera, et cetera, et cetera.

PbU

PbU

PbU

PbU

20682

23892

20682

23892

20682

23892

20682

23892

100g 50g

50g

1 half-life

25g

25g12.5g

12.5g 6.25g

2nd half-life

3rd half-life

4th half life

How many atoms of a 2.97g. sample of How many atoms of a 2.97g. sample of molybdenum-91 would remain after 62 min. if molybdenum-91 would remain after 62 min. if the half-life of molybdenum-91 is 15.49 min.?the half-life of molybdenum-91 is 15.49 min.?How many ½ lives is this?How many ½ lives is this?

# Half-Lives# Half-Lives Time Spent Time Spent (min)(min)

Amount Amount Remaining (g)Remaining (g)

00 00 2.972.97

11 15.49 15.49 1.491.49

22 30.9830.98 0.740.74

33 46.47 46.47

0.370.37

44 61.9661.96 0.190.19Answer = 0.19 g 4 half-lives

Types of Nuclear ReactionsTypes of Nuclear Reactions

There are two types of nuclear reactionsThere are two types of nuclear reactions Fission – splitting the nucleusFission – splitting the nucleus Fusion – fusing or combining of nucleiFusion – fusing or combining of nuclei

Nuclear FissionNuclear Fission

Fission is the breaking apart of a very heavy nucleus into parts.

nBaKrU 10

14156

9236

23592 2

Fusion Fusion is the combining of 2 small is the combining of 2 small nuclei into 1 larger one. nuclei into 1 larger one.

Fusion of hydrogen into helium Fusion of hydrogen into helium occurs in the sun. occurs in the sun.

Fusions reactions should produce Fusions reactions should produce much more energy than fission and much more energy than fission and use much more accessible fuels. use much more accessible fuels. However, currently many problems However, currently many problems exist in fusion reactions such as the exist in fusion reactions such as the extremely extremely high high temperature needed temperature needed

for the reaction.for the reaction.

Radiation DetectionRadiation Detection

Film badges Film badges are used to are used to monitor the monitor the amount of amount of radiation radiation exposure exposure people have people have received.received.

Geiger CounterGeiger Counter

Instrument that detects radiationby measuring current produced by gas particles ionized by radioactivity

Scintillation CounterScintillation Counter

Instrument that converts light to an electric signal

for detecting radiation.

Uses for Nuclear RadiationUses for Nuclear Radiation

Since the physical and chemical Since the physical and chemical properties of radioisotopes of an properties of radioisotopes of an

element are the same as stable ones, element are the same as stable ones, many uses for radioactive nuclides are many uses for radioactive nuclides are

possible.possible.

In medicine radioactive nuclides are used to In medicine radioactive nuclides are used to destroy cancer cells and as tracers to tract destroy cancer cells and as tracers to tract

substances through the body or identify substances through the body or identify cancer and other diseases.cancer and other diseases.

Cobalt - 60 Radioactive Tracer

In agriculture, In agriculture, radioactive radioactive nuclides are nuclides are used as tracers used as tracers in fertilizer to in fertilizer to determine the determine the effectiveness or effectiveness or to prolong shelf to prolong shelf life of food by life of food by irradiating to irradiating to destroy destroy microorganisms.microorganisms.

In dating In dating radioactive radioactive nuclides are nuclides are used to used to determine determine the age of the age of objects. objects. Example: Example: Carbon -14 Carbon -14 is used to is used to date date organic organic materials.materials.

In energy production, currently nuclear In energy production, currently nuclear fission is used to create energy. fission is used to create energy. Example: Comanche Peak nuclear Example: Comanche Peak nuclear power plant in Glen Rose produces power plant in Glen Rose produces energy that is used by TXU.energy that is used by TXU.

Nuclear WasteNuclear WasteNuclear fission produces radioactive Nuclear fission produces radioactive wastes that must be contained and wastes that must be contained and stored on-site (temporary) or disposed stored on-site (temporary) or disposed of (permanent).of (permanent).