Radioactivity and Nuclear Reactions Chp 18 Section 1 Radioactivity.

Radioactivity and Radioactivity and Nuclear ReactionsNuclear Reactions

Chp 18 Section 1Chp 18 Section 1

RadioactivityRadioactivity

ContentsContents

Section 1 Radioactivity slides 3-31Section 1 Radioactivity slides 3-31 Section 2 Nuclear Decay Section 2 Nuclear Decay slides 32-55slides 32-55 Section 3 Detecting Radioactivity Section 3 Detecting Radioactivity

slides 56-74slides 56-74 Section 4 Nuclear Reactions Section 4 Nuclear Reactions

slides 75-106slides 75-106

1 Radioactivity1 Radioactivity

What You’ll LearnWhat You’ll Learn What particles make up an atom and What particles make up an atom and

its nucleusits nucleus How the nucleus is held togetherHow the nucleus is held together What radioactivity isWhat radioactivity is The properties of radioactive and The properties of radioactive and

stable nucleistable nuclei

The NucleusThe Nucleus

The atom is made up of protons, The atom is made up of protons, neutrons and electrons.neutrons and electrons.



Positively-charged protons and Positively-charged protons and electrically neutral neutrons are electrically neutral neutrons are located in the nucleus.located in the nucleus.



Positively-charged protons and Positively-charged protons and electrically neutral neutrons are electrically neutral neutrons are located in the nucleus.located in the nucleus.

Each proton has one positive charge Each proton has one positive charge or +1 so each nucleus has a positive or +1 so each nucleus has a positive charge equal to the number of charge equal to the number of protons that it has.protons that it has.


The number of protons is called the The number of protons is called the element’s atomic number.element’s atomic number.



Atoms contain the same number of Atoms contain the same number of protons as negatively-charged protons as negatively-charged electrons.electrons.



Atoms contain the same number of Atoms contain the same number of protons as negatively-charged protons as negatively-charged electrons.electrons.

The electric attraction of opposites The electric attraction of opposites pulls the electrons close to the pulls the electrons close to the nucleus.nucleus.

Is the nucleus the largest part of an Is the nucleus the largest part of an atom?atom?

Protons and neutrons are packed Protons and neutrons are packed together tightly so that the nucleus together tightly so that the nucleus takes up only a tiny part of an atom.takes up only a tiny part of an atom.



If an atom were the size of a football If an atom were the size of a football stadium, its nucleus would be the stadium, its nucleus would be the size of a marble!size of a marble!



If an atom were the size of a football If an atom were the size of a football stadium, its nucleus would be the stadium, its nucleus would be the size of a marble!size of a marble!

Despite taking little space, the Despite taking little space, the nucleus contains almost all the mass nucleus contains almost all the mass of the atom. of the atom.


A proton or neutron has about 2,000 A proton or neutron has about 2,000 times the mass of an electron.times the mass of an electron.

Modeling an AtomModeling an Atom

To create a To create a model or model or drawing of an drawing of an atom visit this atom visit this site: site: education.jlab.org/education.jlab.org/qa/atom_model.htqa/atom_model.htmlml

The Strong ForceThe Strong Force

The force that makes protons and The force that makes protons and neutrons attract each other and stay neutrons attract each other and stay together.together.– 100 times stronger than the electric force100 times stronger than the electric force– Only works when particles are closeOnly works when particles are close

How do forces work in a small How do forces work in a small nucleus?nucleus?

In a small nucleus, the particles are In a small nucleus, the particles are close together so that the strong close together so that the strong force holds the protons and neutrons force holds the protons and neutrons tightly together.tightly together.

How do forces work in a large How do forces work in a large nucleus?nucleus?

In a large nucleus, the strong force In a large nucleus, the strong force holds together only the particles that holds together only the particles that are closest to one another.are closest to one another.


In a large nucleus, the strong force In a large nucleus, the strong force holds together only the particles that holds together only the particles that are closest to one another.are closest to one another.

In a nucleus with many protons, the In a nucleus with many protons, the electric force repels protons that are electric force repels protons that are far apart.far apart.


In a large nucleus, the strong force holds In a large nucleus, the strong force holds together only the particles that are closest together only the particles that are closest to one another.to one another.

In a nucleus with many protons, the In a nucleus with many protons, the electric force repels protons that are far electric force repels protons that are far apart.apart.

This increased repulsive force causes the This increased repulsive force causes the particles in a large nucleus to be held less particles in a large nucleus to be held less tightly than those in a small nucleus.tightly than those in a small nucleus.


When the strong force can hold a When the strong force can hold a nucleus together forever, the nucleus nucleus together forever, the nucleus is stable.is stable.



If not, the nucleus becomes unstable If not, the nucleus becomes unstable and can break apart or decay by and can break apart or decay by emitting particles and energy.emitting particles and energy.



If not, the nucleus becomes unstable If not, the nucleus becomes unstable and can break apart or decay by and can break apart or decay by emitting particles and energy.emitting particles and energy.

Large nuclei are more unstable; all Large nuclei are more unstable; all with more than 83 protons are with more than 83 protons are radioactive.radioactive.

What are isotopes?What are isotopes?

Atoms of the same Atoms of the same element may have element may have different numbers different numbers of neutrons in the of neutrons in the nucleus.nucleus.

What are isotopes?What are isotopes? Atoms of the same Atoms of the same

element may have element may have different numbers of different numbers of neutrons in the neutrons in the nucleus.nucleus.

The atoms of all The atoms of all isotopes of an element isotopes of an element have the same have the same numbers of protons & numbers of protons & electrons & the same electrons & the same chemical properties.chemical properties.

What makes nuclei unstable?What makes nuclei unstable?

The ratio of neutrons to protons The ratio of neutrons to protons determines whether a nucleus is determines whether a nucleus is stable or unstable.stable or unstable.– Small isotopes 1 neutron:1 protonSmall isotopes 1 neutron:1 proton– Large isotope 3 neutrons: 2 protonsLarge isotope 3 neutrons: 2 protons– Generally, nuclei with too many or too Generally, nuclei with too many or too

few neutrons compared to the numbers few neutrons compared to the numbers are unstable or radioactive.are unstable or radioactive.

How is a nucleus described?How is a nucleus described?

Atomic number= Atomic number= proton numberproton number

Mass number= Mass number= protons + neutronsprotons + neutrons

How is an atom’s information How is an atom’s information shown?shown?

Scientists use Scientists use symbols to write symbols to write information about information about atoms.atoms.

C is the symbol for C is the symbol for carbon with 6 carbon with 6 protons and 6 protons and 6 neutrons in the neutrons in the isotope C-12. isotope C-12. Stable w/ 1:1 ratioStable w/ 1:1 ratio

How is an atom’s information How is an atom’s information shown?shown?

This isotope is This isotope is carbon-14 with 6 carbon-14 with 6 protons and 14 -6 protons and 14 -6 or 8 neutrons; the or 8 neutrons; the ratio is 8:6 so this ratio is 8:6 so this is unstable or is unstable or radioactive.radioactive.

Who discovered radioactivity?Who discovered radioactivity?

In 1896, Henri Becquerel accidentally left In 1896, Henri Becquerel accidentally left pieces of uranium salt in a drawer on a pieces of uranium salt in a drawer on a photographic plate. When he developed photographic plate. When he developed the plate, he saw an outline of the the plate, he saw an outline of the uranium salt on it. He realized that it must uranium salt on it. He realized that it must have given off rays that darkened the film.have given off rays that darkened the film.

http://www.hulu.com/watch/113908/milesthttp://www.hulu.com/watch/113908/milestones-in-science-and-engineering-radioactiones-in-science-and-engineering-radioactivity-%E2%80%93-henri-becquerel-marie-avity-%E2%80%93-henri-becquerel-marie-and-pierre-curiend-pierre-curie


Two years later Two years later Marie and Pierre Marie and Pierre Curie discovered Curie discovered two new elements, two new elements, polonium and polonium and radium, both radium, both radioactive.radioactive.


Two years later Marie and Pierre Two years later Marie and Pierre Curie discovered two new elements, Curie discovered two new elements, polonium and radium, both polonium and radium, both radioactive.radioactive.

It took them >3 years to get 0.1g of It took them >3 years to get 0.1g of radium from several tons of the radium from several tons of the mineral pitchblende.mineral pitchblende.

2 Nuclear Decay2 Nuclear Decay

What You’ll LearnWhat You’ll Learn How alpha, beta, and gamma How alpha, beta, and gamma

radiation are similar and differentradiation are similar and different What the half-life of a radioactive What the half-life of a radioactive

material ismaterial is How radioactive dating is usedHow radioactive dating is used

Nuclear RadiationNuclear Radiation

When an unstable nucleus decays, it When an unstable nucleus decays, it breaks apart emitting particles and breaks apart emitting particles and energy as it decays.energy as it decays.

Nuclear RadiationNuclear Radiation

When an unstable nucleus decays, it When an unstable nucleus decays, it breaks apart emitting particles and breaks apart emitting particles and energy as it decays.energy as it decays.

Three types of nuclear radiation:Three types of nuclear radiation:– Alpha particlesAlpha particles– Beta particlesBeta particles– Gamma radiation electromagnetic waveGamma radiation electromagnetic wave

Alpha ParticlesAlpha Particles

AnAn alpha particle alpha particle is made of 2 is made of 2 protons & 2 neutrons.protons & 2 neutrons.



The decaying nucleus emits an alpha The decaying nucleus emits an alpha particle ( particle ( 44

22He) with a mass number He) with a mass number of 4 & atomic number of 2.of 4 & atomic number of 2.



The decaying nucleus emits an alpha The decaying nucleus emits an alpha particle ( particle ( 44

22He) with a mass number He) with a mass number of 4 & atomic number of 2.of 4 & atomic number of 2.

An alpha particle is the same as the An alpha particle is the same as the nucleus of a Helium (He) atom.nucleus of a Helium (He) atom.


Alpha particles have much more mass than Alpha particles have much more mass than beta or gamma radiationbeta or gamma radiation– with an electric charge of +2.with an electric charge of +2.– Penetrate or pass through matterPenetrate or pass through matter– Attract negatively charged electrons away Attract negatively charged electrons away

from atoms they passfrom atoms they pass– Lose energy quickly & slow downLose energy quickly & slow down– Heavier & move more slowly than Heavier & move more slowly than ββ or or

gammagamma– Sheet of paper can stop alpha particlesSheet of paper can stop alpha particles

How can alpha particles harm you?How can alpha particles harm you?

Think of alpha particles like bowling Think of alpha particles like bowling balls moving in slow motion – they balls moving in slow motion – they may not penetrate deeply but they may not penetrate deeply but they can do lots of damage to whatever can do lots of damage to whatever they hit.they hit.

Released inside the human body Released inside the human body they can damage cells causing illness they can damage cells causing illness & disease.& disease.

How can alpha particles help you?How can alpha particles help you?

Smoke detectors work by emitting Smoke detectors work by emitting alpha particles which collide with alpha particles which collide with molecules in the air forming ions that molecules in the air forming ions that flow within the detector to create an flow within the detector to create an electric circuit. Smoke particles electric circuit. Smoke particles break this circuit causing the alarm break this circuit causing the alarm to sound.to sound.

What is transmutationWhat is transmutation

After an alpha particle is emitted, the After an alpha particle is emitted, the nucleus has 2 fewer protons & nucleus has 2 fewer protons & neutrons than it had.neutrons than it had.

TransmutationTransmutation is the process of is the process of changing one element to a different changing one element to a different element by the decaying process.element by the decaying process.

2102108484Po – Po – 4 4

22He = He = 2062068282Pb Pb

The polonium atom has become a The polonium atom has become a lead atom.lead atom.

Beta ParticlesBeta Particles

A second type of radioactive decay, A second type of radioactive decay, beta radiation, a neutron decays into beta radiation, a neutron decays into a proton by emitting an electron (a proton by emitting an electron (00

--

11e). Beta decay is caused by the e). Beta decay is caused by the weak force.weak force.

Beta ParticlesBeta Particles

A second type of radioactive decay, A second type of radioactive decay, beta radiation, a neutron decays into beta radiation, a neutron decays into a proton by emitting an electron (a proton by emitting an electron (00

--

11e). Beta decay is caused by the e). Beta decay is caused by the weak force.weak force.

An atom that loses a beta particle An atom that loses a beta particle undergoes transmutationundergoes transmutation

1311315353I I 00

-1-1e + e + 1311315454Xe Here iodine Xe Here iodine

becomes xenon.becomes xenon.

How can beta particles harm you?How can beta particles harm you?

Beta Particles are faster than alpha Beta Particles are faster than alpha because they’re smaller & lighter so because they’re smaller & lighter so they penetrate deeper into material they penetrate deeper into material they hit.they hit.– Pass through paperPass through paper– Aluminum foil will stop a beta particleAluminum foil will stop a beta particle– Can damage human cells if released Can damage human cells if released

inside the bodyinside the body

Gamma RaysGamma Rays

Gamma radiation is emitted as Gamma radiation is emitted as electromagnetic waves.electromagnetic waves.

Gamma rays Gamma rays are EM waves with the are EM waves with the highest frequencies & the shortest highest frequencies & the shortest wavelength in the EM spectrum.wavelength in the EM spectrum.

The symbol for a gamma ray is the The symbol for a gamma ray is the Greek letter Greek letter γγ gamma. gamma.

Gamma RaysGamma Rays

Have no mass & no charge.Have no mass & no charge. Travel at the speed of light.Travel at the speed of light. Emitted by nucleus when alpha or Emitted by nucleus when alpha or

beta particle is created.beta particle is created. Takes thick blocks of concrete or Takes thick blocks of concrete or

lead to stop gamma rays.lead to stop gamma rays. Cause less damage to cells inside the Cause less damage to cells inside the

body than alpha or beta particles.body than alpha or beta particles.

Radioactive Half-LifeRadioactive Half-Life

The measure of the time it takes for The measure of the time it takes for half of the radioactive nuclei in a half of the radioactive nuclei in a sample to decay is called a sample to decay is called a half-life.half-life.

The remaining nucleus is called the The remaining nucleus is called the daughter nucleus.daughter nucleus.

Various isotopes decay at different Various isotopes decay at different rates.rates.

Half-LifeHalf-Life

Radioactive bismuth Radioactive bismuth (210Bi) can undergo (210Bi) can undergo alpha decay to form alpha decay to form the thallium (206Tl) the thallium (206Tl) with a half-life equal with a half-life equal to 5 days. If we start to 5 days. If we start with 100 g of with 100 g of bismuth in a sealed bismuth in a sealed lead container, after lead container, after 5 days we will have 5 days we will have 50 g of bismuth & 50 g of bismuth & 50 g of thallium in 50 g of thallium in the jar. After the jar. After another 5 days, another 5 days,

One-half of the remaining bismuth will decay & we will be left with 25 g of bismuth & 75 g of thallium in the jar.

Radioactive DatingRadioactive Dating

Scientists often want to know the ages Scientists often want to know the ages of rocks & fossils using radioactive of rocks & fossils using radioactive isotopes & their half-lives. isotopes & their half-lives.

Radioactive DatingRadioactive Dating

Scientists often want to know the ages Scientists often want to know the ages of rocks & fossils using radioactive of rocks & fossils using radioactive isotopes & their half-lives. isotopes & their half-lives.

The amount of the radioactive isotope The amount of the radioactive isotope in object is measured, then the in object is measured, then the amount of the daughter nuclei is amount of the daughter nuclei is measured. With these the number of measured. With these the number of half-lives or age of the object can be half-lives or age of the object can be calculated.calculated.

How is carbon used to date How is carbon used to date objects?objects?

Carbon-14, with a half-life of 5,730 Carbon-14, with a half-life of 5,730 years is often used to estimate the age years is often used to estimate the age of plant & animal remains.of plant & animal remains.



COCO22 which plants use in photosynthesis which plants use in photosynthesis contains C-14 which stays in the same contains C-14 which stays in the same ratio while alive.ratio while alive.



COCO22 which plants use in photosynthesis which plants use in photosynthesis contains C-14 which stays in the same contains C-14 which stays in the same ratio while alive.ratio while alive.

Once it dies, C-14 decreases as the C-Once it dies, C-14 decreases as the C-12 increases over time. The ratio 12 increases over time. The ratio estimates ages up to 50,000 years.estimates ages up to 50,000 years.

How is uranium used to date How is uranium used to date objects?objects?

Some rocks can be dated using the Some rocks can be dated using the amount of radioactive uranium amount of radioactive uranium isotopes that have decayed into lead.isotopes that have decayed into lead.

How is uranium used to date How is uranium used to date objects?objects?

Some rocks can be dated using the Some rocks can be dated using the amount of radioactive uranium amount of radioactive uranium isotopes that have decayed into lead.isotopes that have decayed into lead.

The ratio of the amounts of U The ratio of the amounts of U isotopes & and their daughter nuclei isotopes & and their daughter nuclei are compared to estimate the age of are compared to estimate the age of the rock.the rock.

3 Detecting Radioactivity3 Detecting Radioactivity

What You’ll LearnWhat You’ll Learn How cloud and bubble chambers are How cloud and bubble chambers are

used to detect radioactivityused to detect radioactivity How an electroscope is used to How an electroscope is used to

detect radiationdetect radiation How a Geiger counter measures How a Geiger counter measures

radiationradiation

Radiation DetectorsRadiation Detectors

Special instruments detect the Special instruments detect the electric charge of the ions formed by electric charge of the ions formed by the radioactive particles as they pass the radioactive particles as they pass through matter.through matter.

How does a cloud chamber detect How does a cloud chamber detect radiation?radiation?

A A cloud chamber, cloud chamber, a rectangular box a rectangular box with transparent sides containing with transparent sides containing water or ethanol vapor, can be used water or ethanol vapor, can be used to detect to detect αα or or ββ radiation. radiation.


A A cloud chamber, cloud chamber, a rectangular box a rectangular box with transparent sides containing with transparent sides containing water or ethanol vapor, can be used water or ethanol vapor, can be used to detect to detect αα or or ββ radiation. radiation.

A radioactive sample placed in the A radioactive sample placed in the cloud chamber emits charged cloud chamber emits charged αα or or ββ particles which pull electrons off particles which pull electrons off atoms in the air leaving a trail of atoms in the air leaving a trail of ions. ions.


Vapor condenses Vapor condenses around these ions around these ions forming small forming small drops along their drops along their path.path.– Beta leave long, Beta leave long,

thin trailsthin trails– Alpha leave shorter, Alpha leave shorter,

thicker trailsthicker trails

What is a bubble chamber?What is a bubble chamber?

A A bubble chamber bubble chamber contains contains superheated liquid under high superheated liquid under high pressure so that it does not boil.pressure so that it does not boil.

What is a bubble chamber?What is a bubble chamber?

A A bubble chamber bubble chamber contains contains superheated liquid under high superheated liquid under high pressure so that it does not boil.pressure so that it does not boil.

When a radioactive particle passes When a radioactive particle passes through, it leaves a trail of ions that through, it leaves a trail of ions that causes the liquid to boil along the ion causes the liquid to boil along the ion trail.trail.

Bubble ChamberBubble Chamber When a charged When a charged

particle passes through particle passes through superheated liquid, it superheated liquid, it leaves a trail of tiny gas leaves a trail of tiny gas bubbles that can be bubbles that can be illuminated & illuminated & photographed. The photographed. The track of a charged track of a charged particle can be used to particle can be used to identify the particle & identify the particle & to analyze complex to analyze complex events. events.

How does an electroscope detect How does an electroscope detect radiation?radiation?

Nuclear radiation can cause an Nuclear radiation can cause an electroscope to lose its charge.electroscope to lose its charge.

How does an electroscope detect How does an electroscope detect radiation?radiation?

Nuclear radiation Nuclear radiation can cause an can cause an electroscope to electroscope to lose its charge.lose its charge.

Leaves stay apart Leaves stay apart until their extra until their extra negative charges negative charges can combine with can combine with positive charges positive charges creating positive creating positive ions in the air.ions in the air.

Tevatron AcceleratorTevatron Accelerator

Measuring RadiationMeasuring Radiation

A Geiger counter A Geiger counter has a negatively has a negatively charged Cu tube charged Cu tube with a positively with a positively charged wire charged wire running through it.running through it.


The tube is filled The tube is filled with gas at low with gas at low pressure. pressure.

Radiation knocks Radiation knocks electrons off the electrons off the gas which are gas which are attracted to the attracted to the wire producing a wire producing a current.current.


An amplifier An amplifier strengthens the strengthens the current producing current producing a clicking sound or a clicking sound or a flashing light.a flashing light.

The number of The number of clicks or flashes clicks or flashes per second tell how per second tell how strong the strong the radiation is.radiation is.

Background RadiationBackground Radiation

The air, the ground, & even the walls The air, the ground, & even the walls of your home give off radiation in of your home give off radiation in small amounts.small amounts.

Background RadiationBackground Radiation

The air, the ground, & even the walls The air, the ground, & even the walls of your home give off radiation in of your home give off radiation in small amounts.small amounts.

Radioactive isotopes that occur in Radioactive isotopes that occur in nature emit background radiation nature emit background radiation from rocks, soil, air, bricks, wood, from rocks, soil, air, bricks, wood, stone, food, water, animals, plants, stone, food, water, animals, plants, etc.etc.

Where does background radiation Where does background radiation come from?come from?

The circle graph The circle graph shows sources shows sources received on received on average by a average by a person living in the person living in the US. Decay of U-US. Decay of U-238 in the soil 238 in the soil produces radon produces radon gas which can gas which can move into houses move into houses & basements.& basements.

55%

11%

8%

4%

8%

3%

11

Where does background radiation Where does background radiation come from?come from?

Cosmic radiation is Cosmic radiation is greater at higher greater at higher elevations where elevations where there is less there is less atmosphere to atmosphere to absorb it.absorb it.

Background Background radiation comes radiation comes from natural from natural processes.processes.

55%

11%

8%

4%

8%

3%

11

4 Nuclear Reactions4 Nuclear Reactions

What You’ll LearnWhat You’ll Learn What nuclear fission isWhat nuclear fission is What nuclear fusion isWhat nuclear fusion is How radioactive tracers can be used How radioactive tracers can be used

in medicinein medicine How nuclear reactions can help treat How nuclear reactions can help treat

cancercancer

Nuclear FissionNuclear Fission

1934- Enrico Fermi bombards U 1934- Enrico Fermi bombards U nuclei with neutrons.nuclei with neutrons.



1938- Otto Hahn & Fritz Strassmann 1938- Otto Hahn & Fritz Strassmann split U-235 into smaller nuclei.split U-235 into smaller nuclei.




1939- Lise Meitner theorized that 1939- Lise Meitner theorized that splitting occurs when the nucleus splitting occurs when the nucleus becomes so unstable that it splits.becomes so unstable that it splits.




1939- Lise Meitner theorized that 1939- Lise Meitner theorized that splitting occurs when the nucleus splitting occurs when the nucleus becomes so unstable that it splits.becomes so unstable that it splits.

The process of splitting a nucleus The process of splitting a nucleus into smaller nuclei- into smaller nuclei- nuclear fissionnuclear fission

What nuclei can split during nuclear What nuclei can split during nuclear fission?fission?

Only large nuclei Only large nuclei like U or plutonium like U or plutonium can split apart can split apart during nuclear during nuclear fission.fission.

What nuclei can split during nuclear What nuclei can split during nuclear fission?fission?

U-236 is so U-236 is so unstable that it unstable that it immediately splits immediately splits into barium & into barium & krypton nuclei, krypton nuclei, several neutrons & several neutrons & a large amount of a large amount of energyenergy

How are mass & energy related?How are mass & energy related?

Einstein proposed that mass & Einstein proposed that mass & energy are related & can be changed energy are related & can be changed from one to the other.from one to the other.



His special theory of relativity says His special theory of relativity says that energy in joules is equal to mass that energy in joules is equal to mass in kg multiplied by the speed of light in kg multiplied by the speed of light squared. squared.



His special theory of relativity says His special theory of relativity says that energy in joules is equal to mass that energy in joules is equal to mass in kg multiplied by the speed of light in kg multiplied by the speed of light squared. squared.

Energy (joules) = mass (kg) X speed Energy (joules) = mass (kg) X speed of light (m/s)of light (m/s)2 2 or E= mcor E= mc22

What is a chain reaction?What is a chain reaction?

Free neutrons produced by fission Free neutrons produced by fission can hit other nuclei emitting more can hit other nuclei emitting more neutrons repeating the reaction over neutrons repeating the reaction over and over.and over.


Free neutrons produced by fission Free neutrons produced by fission can hit other nuclei emitting more can hit other nuclei emitting more neutrons repeating the reaction over neutrons repeating the reaction over and over.and over.

A series of fission reactions is called A series of fission reactions is called a a chain reaction.chain reaction.


Free neutrons produced by fission can hit Free neutrons produced by fission can hit other nuclei emitting more neutrons other nuclei emitting more neutrons repeating the reaction over and over.repeating the reaction over and over.

A series of fission reactions is called a A series of fission reactions is called a chain reaction.chain reaction.

An uncontrolled chain reaction releases a An uncontrolled chain reaction releases a huge amount of energy in a short time & huge amount of energy in a short time & requires a requires a critical mass critical mass of starting of starting material to produce more reactions.material to produce more reactions.

Nuclear FusionNuclear Fusion

Splitting one nucleus of U-235 Splitting one nucleus of U-235 releases about 30 million times more releases about 30 million times more energy than when one molecule of energy than when one molecule of dynamite explodes.dynamite explodes.



In a In a nuclear fusion nuclear fusion reaction, two reaction, two small, light nuclei combine to form small, light nuclei combine to form one larger, heavier nucleus.one larger, heavier nucleus.



In a In a nuclear fusion nuclear fusion reaction, two reaction, two small, light nuclei combine to form small, light nuclei combine to form one larger, heavier nucleus.one larger, heavier nucleus.

Fusion combines nuclei & fission Fusion combines nuclei & fission splits them apart.splits them apart.

How are temperature & fusion How are temperature & fusion related?related?

How can two nuclei get close enough How can two nuclei get close enough to combine? to combine?


How can two nuclei get close enough How can two nuclei get close enough to combine? They must be moving to combine? They must be moving very fast.very fast.


How can two nuclei get close enough How can two nuclei get close enough to combine? They must be moving to combine? They must be moving very fast.very fast.– All nuclei positively chargedAll nuclei positively charged– Thus repel each otherThus repel each other


How can two nuclei get close enough How can two nuclei get close enough to combine? They must be moving to combine? They must be moving very fast.very fast.– All nuclei positively chargedAll nuclei positively charged– Thus repel each otherThus repel each other– KE must overcome electric force to push KE must overcome electric force to push

them close enough to combinethem close enough to combine– KE increases as temperature increasesKE increases as temperature increases


How can two nuclei get close enough How can two nuclei get close enough to combine? They must be moving to combine? They must be moving very fast.very fast.– All nuclei positively chargedAll nuclei positively charged– Thus repel each otherThus repel each other– KE must overcome electric force to push KE must overcome electric force to push

them close enough to combinethem close enough to combine– KE increases as temperature increasesKE increases as temperature increases– Temp must be millions of °C like Sun & Temp must be millions of °C like Sun &

other starsother stars

How does the Sun produce How does the Sun produce energy?energy?

The Sun, made The Sun, made mostly of H mostly of H produces its produces its energy by fusion of energy by fusion of H nucleiH nuclei

2 protons (H-1) 2 protons (H-1) fuse to make a H fuse to make a H isotope (H-2); then isotope (H-2); then H-1 + H-2 form an H-1 + H-2 form an isotope of He-3.isotope of He-3.

How does the Sun produce How does the Sun produce energy?energy?

To complete the To complete the process, 4 H nuclei process, 4 H nuclei combine into 1 He combine into 1 He nucleus during nucleus during which a small which a small amount of matter amount of matter changes into a changes into a huge amount of huge amount of energy.energy.

Fusion on the SunFusion on the Sun

The heat & light Earth receives The heat & light Earth receives comes from this process.comes from this process.

About 1% of the Sun’s hydrogen has About 1% of the Sun’s hydrogen has been changed into energy. been changed into energy.

Sun has enough H to continue fusion Sun has enough H to continue fusion reactions for another 5 billion years.reactions for another 5 billion years.

Using Nuclear Reactions in Using Nuclear Reactions in MedicineMedicine

A A tracertracer is a radioactive isotope is a radioactive isotope used to find or keep track of a used to find or keep track of a molecule as it moves through your molecule as it moves through your body.body.

How are iodine tracers used?How are iodine tracers used?

If the thyroid gland in your neck is If the thyroid gland in your neck is not working properly, you get sick. not working properly, you get sick. The radioactive isotope I-131 is used The radioactive isotope I-131 is used to see if the thyroid is working to see if the thyroid is working properly. The I-131 decays giving off properly. The I-131 decays giving off gamma rays which can be detected.gamma rays which can be detected.

How can cancer be treated with How can cancer be treated with radioactivity?radioactivity?

Radiation can be used to stop some Radiation can be used to stop some cells from growing into tumors.cells from growing into tumors.



Sometimes a radioactive isotope can Sometimes a radioactive isotope can be placed inside or near a tumor; be placed inside or near a tumor; other times, tumors can be treated other times, tumors can be treated from outside the body.from outside the body.



Sometimes a radioactive isotope can Sometimes a radioactive isotope can be placed inside or near a tumor; be placed inside or near a tumor; other times, tumors can be treated other times, tumors can be treated from outside the body.from outside the body.

The radiation emitted when particles The radiation emitted when particles decay can turn nearby atoms into decay can turn nearby atoms into ions.ions.


If a source of radiation is placed near If a source of radiation is placed near cancer cells, atoms in those cells can cancer cells, atoms in those cells can be ionized such as atoms in DNA or be ionized such as atoms in DNA or RNA which can stop the tumor from RNA which can stop the tumor from growing or even kill it.growing or even kill it.


If a source of radiation is placed near If a source of radiation is placed near cancer cells, atoms in those cells can cancer cells, atoms in those cells can be ionized such as atoms in DNA or be ionized such as atoms in DNA or RNA which can stop the tumor from RNA which can stop the tumor from growing or even kill it.growing or even kill it.

Because cancer cells grow quickly, Because cancer cells grow quickly, radiation affects them more than radiation affects them more than other cells. Patients receiving other cells. Patients receiving radiation suffer side effects when it radiation suffer side effects when it ionizes healthy cells.ionizes healthy cells.

Fission Both Fusion

Complete the Venn diagram by listing one thing that fission & fusion have in common, one thing that applies only to fission, & one thing that applies only to fusion,

Fission Both Fusion

Complete the Venn diagram by listing one thing that fission & fusion have in common, one thing that applies only to fission, & one thing that applies only to fusion,

Reactions produce energy

Process of splitting a nucleus into smaller nuclei

2 small, light nuclei combine to form one larger, heavier nucleus

Date post:	18-Dec-2015
Category:	Documents
Upload:	moris-nash
View:	240 times
Download:	5 times

Radioactivity and Nuclear Reactions Chp 18 Section 1 Radioactivity.

Documents