Chapter 18Chapter 18Nuclear ReactionsNuclear Reactions

Chemical ReactionsChemical Reactions

Occur in the outer electron energy levelOccur in the outer electron energy level

Valance electronsValance electrons

Nuclear ReactionsNuclear Reactions

Occur in the nucleus of the atomOccur in the nucleus of the atom

Involve the Involve the NUCLEONSNUCLEONS

Nucleons = protons & neutronsNucleons = protons & neutrons

Strong Nuclear ForceStrong Nuclear Force

Protons are positively charged and repel Protons are positively charged and repel each other each other

←←+ ++ +→→ Strong Nuclear ForceStrong Nuclear Force = the force that = the force that

causes the protons and neutrons in the causes the protons and neutrons in the nucleus to stick together and holds the nucleus to stick together and holds the nucleus tightly together.nucleus tightly together.

RadioactivityRadioactivity

When the strong force of an atom is not When the strong force of an atom is not strong enough to hold the nucleus strong enough to hold the nucleus together, then the atom tends to decaytogether, then the atom tends to decay

The atoms are considered unstable, or The atoms are considered unstable, or radioactiveradioactive

The process of decay is called The process of decay is called radioactivity and in the process particles radioactivity and in the process particles and energy are released and the atom is and energy are released and the atom is changed into another type of atomchanged into another type of atom

ISOTOPESISOTOPES

Atoms of the same element Atoms of the same element with a different number of with a different number of neutrons.neutrons.

Ex: carbon-12 & carbon-14Ex: carbon-12 & carbon-14 Carbon-12Carbon-12

6 protons6 protons 6 neutrons6 neutrons 6 electrons6 electrons

Carbon-14Carbon-14 6 protons6 protons 8 neutrons8 neutrons 6 electrons6 electrons

Carbon 12 is a stable isotope of carbon. Carbon-14 is unstable or radioactive because the addition of the two neutrons have disrupted the strong force and made the nucleus start to decay, or break apart.

3 Types of Radioactivity3 Types of RadioactivityRadioactive DecayRadioactive Decay

ALPHA PARTICLE ALPHA PARTICLE ((αα))

BETA PARTICLE BETA PARTICLE ((ββ))

GAMMA RAYS GAMMA RAYS ((γγ))

ALPHA ALPHA PARTICLEPARTICLE 2 protons & 2 neutrons2 protons & 2 neutrons nucleus of a helium atomnucleus of a helium atom weakest type of radiationweakest type of radiation can be stopped by a piece of papercan be stopped by a piece of paper 12 inches max. distance travel12 inches max. distance travel

What happens to the numbers What happens to the numbers of particles in the nucleus after of particles in the nucleus after alpha decay?alpha decay?

BETA BETA PARTICLEPARTICLE

an electron emitted from around the nucleusan electron emitted from around the nucleus A neutron splits into a proton & electronA neutron splits into a proton & electron The electron is expelled out of the nucleusThe electron is expelled out of the nucleus The proton stays and increases the number of protons The proton stays and increases the number of protons

by one.by one. The atomic number of the element increases by oneThe atomic number of the element increases by one The element changes into the next higher element on The element changes into the next higher element on

the periodic table.the periodic table. 100x stronger than an alpha particle100x stronger than an alpha particle

What happens to the numbers of particles in What happens to the numbers of particles in the nucleus after beta decay?the nucleus after beta decay?

Gamma Gamma RaysRays

An electromagnetic waveAn electromagnetic wave A packet of energyA packet of energy The energy readjustment in the nucleusThe energy readjustment in the nucleus Most powerful form of radiationMost powerful form of radiation The sun is a great source of gamma radiationThe sun is a great source of gamma radiation

Gamma Radiation, ContGamma Radiation, Cont

Gamma rays are very harmful to cells. They can Gamma rays are very harmful to cells. They can damage the DNA of your cells and mutate them, damage the DNA of your cells and mutate them, which can cause cancerwhich can cause cancer

High amounts of gamma ray exposure can High amounts of gamma ray exposure can cause deathcause death

Low amounts are normal and you are exposed Low amounts are normal and you are exposed to them all the timeto them all the time

Cannot be easily blocked. Inches of concrete Cannot be easily blocked. Inches of concrete lined with lead can stop a gamma raylined with lead can stop a gamma ray

Gamma Ray Photography From SpaceGamma Ray Photography From Space

REMEMBER! Gamma rays are REMEMBER! Gamma rays are light!light!

AntoineAntoine Henri Henri BecquerelBecquerel

In 1896, radioactivity was In 1896, radioactivity was first discovered.first discovered.

Used uranium salts = placed Used uranium salts = placed them near a photographic them near a photographic film plate.film plate.

exposed the film exposed the film (below)(below)

Awarded Nobel Prize in Awarded Nobel Prize in 1903 in Physics1903 in Physics

Pierre & Marie CuriePierre & Marie Curie (1898) (1898)

Discover the radioactive properties of radium & poloniumDiscover the radioactive properties of radium & polonium Together awarded the Nobel Prize in 1903 (Together awarded the Nobel Prize in 1903 (physicsphysics) along with Henri ) along with Henri

BecquerelBecquerel Marie is award a second Nobel Prize in 1911 (Marie is award a second Nobel Prize in 1911 (chemistrychemistry)) Pierre is killed in an accident in 1906, Marie continues working with Pierre is killed in an accident in 1906, Marie continues working with

radioactive substances. She eventually dies of cancerradioactive substances. She eventually dies of cancer

TransmutationTransmutation

= changes from one element to another = changes from one element to another element during element during αα and and ββ decay. decay.

Alpha DecayAlpha Decay = mass number decreases = mass number decreases by 4 and the atomic number decreases by by 4 and the atomic number decreases by 22

Beta DecayBeta Decay = mass number does not = mass number does not change and the atomic number increases change and the atomic number increases by 1by 1

Alpha DecayAlpha Decay

Uranium-238 has 92 protonsUranium-238 has 92 protons

After alpha decay After alpha decay ((2 protons & 2 neutrons leave the nucleus2 protons & 2 neutrons leave the nucleus))

Becomes Thorium-234 and has 90 protonsBecomes Thorium-234 and has 90 protons

Beta DecayBeta Decay

Carbon-14 has 6 protons & 8 neutronsCarbon-14 has 6 protons & 8 neutrons

After beta decayAfter beta decay (a neutron is split into a proton and electron (a neutron is split into a proton and electron

& the electron is expelled from the nucleus)& the electron is expelled from the nucleus)

Becomes Nitrogen-14 and has 7 protons and 7 neutronsBecomes Nitrogen-14 and has 7 protons and 7 neutrons

Half LifeHalf Life

= the time it takes for one half of the mass of a = the time it takes for one half of the mass of a radioactive substance to decay.radioactive substance to decay.Ex: carbon-14 = 5730 yearsEx: carbon-14 = 5730 years

100 gram sample100 gram sample – In 5730 yrs = In 5730 yrs = 50 grams50 grams C-14 & C-14 & 50 grams50 grams N-14 N-14– In11,460 yrs = In11,460 yrs = 25 grams25 grams C-14 & C-14 & 75 grams75 grams N-14 N-14– In 17,190 yrs = In 17,190 yrs = 12.5 grams12.5 grams C-14 & C-14 & 87.5 grams87.5 grams N-14 N-14

Radioactive DatingRadioactive Dating

Half life is used by scientists to find out Half life is used by scientists to find out how old a fossil or a rock ishow old a fossil or a rock is

Carbon 14 is often used to date fossilsCarbon 14 is often used to date fossils

What type of isotope used depends on the What type of isotope used depends on the material being datedmaterial being dated

Uranium is often used to date rocks Uranium is often used to date rocks because many rocks contain uranium because many rocks contain uranium alreadyalready

Detecting RadioactivityDetecting Radioactivity

Cloud chambers track Cloud chambers track alpha and beta alpha and beta particlesparticles

Chamber is filled with Chamber is filled with a cloud of vapora cloud of vapor

Alpha particles leave Alpha particles leave short thick trailsshort thick trails

Beta particles leave Beta particles leave long thin trails long thin trails

Bubble ChamberBubble Chamber

Holds a super heated Holds a super heated liquid that doesn’t boil liquid that doesn’t boil due to high pressuredue to high pressure

When a radioactive When a radioactive particle passes particle passes through the liquid, through the liquid, trails of bubbles formtrails of bubbles form

Geiger CounterGeiger Counter

Pops or clicks in the Pops or clicks in the presence of radiationpresence of radiation

Uses electricity and Uses electricity and current to cause a current to cause a flow of electronsflow of electrons

The current is The current is amplified to produce a amplified to produce a clicking soundclicking sound

Background RadiationBackground Radiation

You are exposed to radiation every dayYou are exposed to radiation every day

Sources of background radiation vary and Sources of background radiation vary and amounts are usually not harmfulamounts are usually not harmful

Nuclear ReactionsNuclear Reactions

Nuclear FissionNuclear Fission

Nuclear FusionNuclear Fusion

Nuclear FissionNuclear Fission

the splitting of the nucleus into two smaller the splitting of the nucleus into two smaller nucleinuclei

Neutrons are used to split the nucleusNeutrons are used to split the nucleus Additional neutrons are released to continue on Additional neutrons are released to continue on

to hit/split other nucleito hit/split other nuclei

Chain ReactionsChain Reactions

Critical MassCritical Mass ( (requiredrequired) = concentration of ) = concentration of radioactive atoms in a sample.radioactive atoms in a sample.Controlled Chain ReactionControlled Chain Reaction = many of the neutrons = many of the neutrons

that are produced are absorbed in “control rods” that are produced are absorbed in “control rods” prevent excess energy to be released.prevent excess energy to be released.

Ex. Nuclear Power PlantsEx. Nuclear Power Plants

Uncontrolled Chain ReactionUncontrolled Chain Reaction = all the neutrons = all the neutrons are allowed to continue to hit/split other nuclei are allowed to continue to hit/split other nuclei causing massive amounts of energy to be released causing massive amounts of energy to be released all at once.all at once.Ex. Atomic Bomb (used on Japan in 1945)Ex. Atomic Bomb (used on Japan in 1945)

Controlled Chain Controlled Chain ReactionReaction

Generating ElectricityGenerating Electricity

Nuclear power is only one way to generate Nuclear power is only one way to generate electricityelectricity

It is often cheaper and easier than other It is often cheaper and easier than other forms of energy (ie using wind or coal or forms of energy (ie using wind or coal or water)water)

However, there are safety concerns that However, there are safety concerns that you must take into consideration you must take into consideration

Nuclear ReactorsNuclear Reactors

Used to generate electricity Used to generate electricity

Used to power ships, submarines Used to power ships, submarines

Risk of meltdown, must be kept cool Risk of meltdown, must be kept cool to prevent uncontrolled chain to prevent uncontrolled chain reactionsreactions

Nuclear ReactorNuclear Reactor

Three Mile Island AccidentThree Mile Island Accident

March 28, 1979– March 28, 1979– Harrisburg PA– Three Harrisburg PA– Three Mile Island Nuclear Mile Island Nuclear Power Plant: A partial Power Plant: A partial meltdown occurred in meltdown occurred in one reactor due to a one reactor due to a stuck valve. Negligible stuck valve. Negligible amounts of radiation amounts of radiation were released into the were released into the environmentenvironment

Chernobyl - April 26,1986Chernobyl - April 26,1986

Power Plant in the UkrainePower Plant in the Ukraine

Explosion and fire that was caused by a Explosion and fire that was caused by a power surgepower surge

31 people died of acute radiation sickness31 people died of acute radiation sickness

You still can’t live in that area todayYou still can’t live in that area today

Crops were affected, many cases of Crops were affected, many cases of cancer recorded, especially in children cancer recorded, especially in children

ChernobylChernobyl

Pripyat, Ukraine

Fukushima - March 11, 2011Fukushima - March 11, 2011

Ongoing nuclear accident in Japan at the Ongoing nuclear accident in Japan at the Fukushima power plantFukushima power plant

Caused partial or full meltdown to reactor, Caused partial or full meltdown to reactor, thanks to earthquake and Tsunamithanks to earthquake and Tsunami

Power failure to coolant main causePower failure to coolant main cause

Effects of the disaster are ongoing and Effects of the disaster are ongoing and unknown at this timeunknown at this time

Uncontrolled Chain Uncontrolled Chain ReactionReaction

Nuclear FusionNuclear Fusion

= the joining of two smaller nuclei into a single = the joining of two smaller nuclei into a single larger nucleuslarger nucleus

Powers the sun, very hard to duplicate on Earth Powers the sun, very hard to duplicate on Earth because of the high pressure and temperature because of the high pressure and temperature neededneeded

Extremely more powerful release of energy Extremely more powerful release of energy than fissionthan fission

Also known as a Also known as a thermonuclear reactionthermonuclear reaction ex: H-bomb and the sun/starsex: H-bomb and the sun/stars

Fusion ExplosionsFusion Explosions