Radioactivity and Radioactivity and Nuclear Reactions Nuclear Reactions
Jan 03, 2016
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).