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Energy Changes in Nuclear Reactions. BY…. E=mc². Einstein’s equation that relates mass and energy E=Energy m=mass c=speed of light, 3.00 x 10 8 m/s States that mass and energy are proportional If a system loses mass, it loses energy, and vice versa - PowerPoint PPT Presentation

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Page 1: Energy Changes in Nuclear Reactions

Energy Changes in Nuclear Reactions

BY…

Page 2: Energy Changes in Nuclear Reactions

E=mc²

• Einstein’s equation that relates mass and energy• E=Energy• m=mass• c=speed of light, 3.00 x 108 m/s• States that mass and energy are proportional• If a system loses mass, it loses energy, and vice

versa• Mass and energy changes are much greater in

nuclear reactions than in chemical reactions

Page 3: Energy Changes in Nuclear Reactions

Example of E=mc²• 238 U 234 Th + 4 He• Mass U=238.0003 amu, mass Th=233.9942 amu,

mass He=4.0015 amu• Δm=233.9942g+4.0015g-238.0003=-0.046– Lost mass=exothermic

• Energy change calculated through Einstein’s equation, E=mc²:

• ΔE=Δ(mc2)=c2Δm =(2.9979 x 108 m/s)2(-0.0046 g)(1 kg/100o g) =-4.1 x 1011 kg-m2/s2 = -4.1 x 1011 J

(Note: Δm is converted to kg, SI unit of mass, to get ΔE in joules, SI unit for energy.)

Page 4: Energy Changes in Nuclear Reactions

Nuclear Binding Energies– Energy required to separate a nucleus into its individual

nucleons• Masses of nuclei are always less than the masses of

individual nucleons• Mass defect- difference between a nucleus and its

constituent nucleons• Addition of energy to a system must be joined by a

proportional increase in mass• Larger the binding energy is, the more stable the

nucleus is towards decomposition

Page 5: Energy Changes in Nuclear Reactions

Nuclear Binding Energies Continued

• Binding energies per nucleon initially increases in magnitude as mass number increases

• Nuclei of intermediate mass numbers are more tightly bonded (more stable) than other nuclei that is smaller or has larger mass numbers

• Trend has two consequences – Heavy nuclei gain stability and give off energy if they divide into

two mid-sized nuclei • Fission

– Greater amounts of energy is release when very light nuclei are combined or fused together to give larger nuclei• Fusion

Page 6: Energy Changes in Nuclear Reactions

Biological Effects of Nuclear Radiation

By: Kayla Seider and Hannah Cherry

Page 7: Energy Changes in Nuclear Reactions

Radioactivity • We are continually being bombarded by

artificial and natural radiation• Infrared, UV, visible radiation from the sun, radio

waves, microwaves, and x-rays• There is radioactivity in the soil and other

materials

Page 8: Energy Changes in Nuclear Reactions

Types of Radiation• If matter absorbs radiation, it can cause either excitation or ionization of the

matter• Excitation occurs when absorbed radiation excites electrons to a higher energy

state or increases the motion of molecules• Causes them to move, vibrate, or rotate

• Ionization occurs when the radiation removes an electron from an atom or molecule• Is more harmful than radiation that doesn’t cause ionization

• Non-ionization is lower in energy or slower moving neurons• Radiofrequency electromagnetic radiation

• Most of the energy is absorbed by water molecules in tissue• Most tissue is 70% water by mass

• Can define ionizing radiation as radiation that can ionize water• X-rays, higher-energy UV, alpha, beta, and gamma rays

Page 9: Energy Changes in Nuclear Reactions
Page 10: Energy Changes in Nuclear Reactions

What Happens• When ionization radiation passes through living tissue, electrons

are removed from water molecules, forming highly reactive H2O+

• An H2O+ can react with another water molecule to form H3O+ and a neutral OH

• OH becomes a free radical• A free radical is a substance with one or more unpaired electrons• In cells and tissues, these particles can attack a host of

surrounding biomolecules to produce new free radicals• These new free radicals can initiate a large number of chemical

reactions that are able to disrupt the normal operation of cells• Can contribute to cancer, diabetes, stroke, heart attack, Parkinson's,

Alzheimer's, schizophrenia, and hemochromatosis

Page 11: Energy Changes in Nuclear Reactions

The Damage• Damage depends on the activity and energy of the radiation, the length

of exposure, and whether the source is inside or outside the body• Gamma rays are harmful outside of the body

• They can penetrate human tissue very easily• Can cause organ damage and genetic damage• Dangerous

• Alpha rays are stopped by skin• In the body, alpha rays are particularly dangerous because they transfer their

energy efficiently to the surrounding tissue causing considerable damage• Beta rays can penetrate about a cm beyond the skin• Tissue that shows the greatest damage are those that reproduce at a

rapid rate• Bone marrow, blood-forming tissues, and lymph nodes

Page 12: Energy Changes in Nuclear Reactions

Radiation Doses• Radiation is measured in the gray (Gy) and the rad (radiation absorbed dose)• The gray is equivalent to the absorption of 1 J of energy per kilogram of tissue• The rad is equivalent to the absorption of .01 J of energy per kilogram of tissue• 1 gray= 100 rads

• A rad of alpha radiation causes more damage than a rad of beta radiation• To correct these differences, the radiation dose is multiplied by a factor that

measures the relative biological effectiveness (RBE) of radiation • The exact RBE value varies with dose rate, total dose, and the type of

tissue affected• RBE is approximately 1 for gamma and beta and 10 for alpha

• The product of radiation dose and the RBE gives you the effective dosage in units of rem (roentgen equivalent for man)• Number of rems= (number of rads)(RBE)

• The siervert (Sv) is the unit for effective dosage • 1 Sv= 100 Rem

Page 13: Energy Changes in Nuclear Reactions

Radiation DosesDose (rem) Effect of Short-Term exposures to Radiation

0 to 25 No detectable clinical effects

25 to 50 Slight, temporary decrease in white blood cell counts

100 to 200 Nausea; marked decrease in white blood cells

500 Death of half the exposed population within 30 days after exposure

• 600 rem will cause death• Dental x-rays is .5 mrem• The average exposure for a person in one year due to natural sources of ionizing radiation is about 360

mrem

Page 14: Energy Changes in Nuclear Reactions
Page 15: Energy Changes in Nuclear Reactions

Radiation Therapy• Both healthy and unhealthy cells can be destroyed by radiation

• Can lead to physiological disorders• Cancer is the growth of abnormal cells, that growth produces

malignant tumors• The tumors can be destroyed by exposing them to the same

radiation because rapidly reproducing cells are susceptible to radiation damage • Therefore, cancerous cells are easier to destroy than healthy ones• That’s why radiation is used in cancer treatment

• Side effects• Fatigue, nausea, hair loss, weakened immune system, even death

• Because of these side effects, radiation therapy is a last resort for treatments

Page 16: Energy Changes in Nuclear Reactions

True or False• Radiation in Japan is equal to 38,000 bananas• True• About 1,200 radioactive isotopes have been produced in all the known elements• True• You get little amounts of radiation while on a nuclear submarine• True• Burning coal releases more radiation than a nuclear plant does• True

Page 17: Energy Changes in Nuclear Reactions

Questions• What is ionizing radiation? • Radiation that can ionize water and it can remove an electron from a molecule

• What is a free radical? Why is it so bad?• A substance with one or more unpaired electrons. They disrupt the normal operations of

cells• Which is smaller the rad or the gray and how are they related to eachother?• The rad is smaller than the gray. 1 gray= 100 rads

• What dose of rems cause death?• 500-600 rems

Page 18: Energy Changes in Nuclear Reactions

21.8: Nuclear Fusion

Kyle, Suraj, Brian

Page 19: Energy Changes in Nuclear Reactions

Nuclear Fusion

• Energy is produced when light nuclei fuse into heavier ones– Talked about in 21.6 (don’t write this part

down)– Type of reactions responsible for energy

produced by sun

Equal in hottness (write this equation down)

Nuclear fusionIntense workouts

Page 20: Energy Changes in Nuclear Reactions

Nuclear Fusion

• Several different types of fusion processes:

Page 21: Energy Changes in Nuclear Reactions

Fusion Energy

• Appealing as an energy source– Nonradioactive products– Light isotopes of

hydrogen are easily available

• Currently not used– Extremely high energies

are needed to overcome repulsion of nuclei

Page 22: Energy Changes in Nuclear Reactions

Overcoming Nuclei Repulsion• In order to achieve the

required energies, high temperatures must be maintained– Thus, fusion reactions are

known as thermonuclear reactions

• Lowest temperature required for fusion is 40 million Kelvin

• This temperature has only been achieved by hydrogen bombs– Uncontrolled power generation

-Requires 40,000,000 K to initiate

Page 23: Energy Changes in Nuclear Reactions

Fusion as energy • Numerous problems must

be overcome before fusion becomes a practical source for energy– High Temperatures to start

reaction– Confining the reaction

• No known material is able to withstand the temperature needed for fusion

• Researches try to use tokomaks to achieve fusion

• Also use lasers

Page 25: Energy Changes in Nuclear Reactions

Nuclear Fission

Jake Wiley, James Haeckel, Sergio Machaca

Page 26: Energy Changes in Nuclear Reactions

Fission

• Extremely exothermic• Uranium-233, -235, and Plutonium-239 are

main practical sources• 1 neutron hits a heavy nuclei and causes it to

split• Average of 2.4 neutrons are released• Various and unpredictable products, typically

radioactive

Page 27: Energy Changes in Nuclear Reactions

Chain Reactions• Each neutron released can cause another nucleus to split• Critical Mass

– Enough mass of the material is present to sustain the reaction at a constant rate• Uranium ~ 1kg

• Subcritical Mass– Less than critical mass, neutrons escape without hitting any

nuclei• Supercritical Mass

– More than critical mass, reaction proceeds unchecked, typically with violent results

Page 28: Energy Changes in Nuclear Reactions

Which one is Subcritical? Supercritical?

Page 29: Energy Changes in Nuclear Reactions

Nuclear Arms

• Gun-type– Two subcritical masses

are shot together into a supercritical mass

• Implosion– Subcritical mass of P-239

is compressed by explosives to supercritical mass

Page 30: Energy Changes in Nuclear Reactions

Nuclear Reactors

• Fuel rods typically use 3% U-235– Encased in stainless steel or zirconium tubes

• Control rods regulate amount of neutrons– Typically boron or cadmium

• A moderator is used to slow the neutrons as to be more readily absorbed by fuel

• A cooling liquid is used to carry off excess heat– Often the moderator and cooling liquid are one in

the same

Page 31: Energy Changes in Nuclear Reactions

Nuclear Reactors (Cont.)

• Excess heat is used to turn water to steam– Used to turn a turbine

• Steam is cooled and condensed– Often cooled with water from

a stream or lake• All incased in reinforced

concrete– Prevents radiation leak– Protects reactor from external

forces

Page 32: Energy Changes in Nuclear Reactions

Nuclear Waste

• Estimated at 20 half-lives before safe exposure– Puts used fuel at about 600 years

• Dangerous to handle and transport• Originally stored in pools at reactor and transported to

reprocessing plants– Transportation incredibly unpopular and reprocessing too

hazardous• Spend fuel rods are presently stored on site• Yucca Mountain, Nevada is a possible long term

storage facility

Page 33: Energy Changes in Nuclear Reactions

Thorium• Silvery metal• Topic of energy source discussions• Thorium reactors are considered

safer– No chain reaction– Must be bombarded with neutrons to

drive the fission process– Reactor halts process by itself in case of

overheat• No room for mechanical or electrical failure

• Thorium is as abundant as lead

Page 34: Energy Changes in Nuclear Reactions

Continued

• Thorium poses fewer environmental hazards– Cleaner than uranium or other radioactive materials

used in other reactors– Can burn up plutonium and toxic waste from old

reactors• Saves money– Does not require isotope separation– High neutron yield, better fission rating, longer fuel

cycles– ~100% of recovered thorium is fit for reactors

Page 35: Energy Changes in Nuclear Reactions

Nuclear Reactor Meltdowns

• Three Mile Island, Pennsylvania– Partial Meltdown– March 28, 1979– Fuel rods liquefied

• Chernobyl, Russia– Complete Meltdown– April 26, 1986– Experiment on core failed causing two explosions– Town remains uninhabited

Page 36: Energy Changes in Nuclear Reactions

Questions

1. Is Fission an exothermic or endothermic process?

2. What is critical mass and the two types?3. What do the control rods and the moderator

do in a Nuclear reactor?4. Explain this process:

Page 37: Energy Changes in Nuclear Reactions

Answers

1. Exothermic: the process releases energy2. The amount of fissionable large enough to

maintain a chain reaction, Sub- less than critical mass and Super- more than

3. Control rods regulate neutrons to keep up chain reaction, while preventing overheating; Moderator slows neutrons to be used more readily by fuel

4. 1 Neutron splits an Uranium nucleus into a Krypton and Barium nucleus and 3 Neutrons

Page 38: Energy Changes in Nuclear Reactions
Page 39: Energy Changes in Nuclear Reactions
Page 40: Energy Changes in Nuclear Reactions

Patterns of Nuclear Stability

Melissa Ross, Lexy Smyles, Kevin Miner

Page 41: Energy Changes in Nuclear Reactions

Neutron-to-Proton Ratio

•Strong nuclear force- strong force of attraction that exists between nucleons at close distances• Nucleons= protons and neutrons• Overcomes the repulsive forces of

protons•Nuclei with two or more protons contain neutrons• More protons = more neutrons• Required to bind nucleus together

Page 42: Energy Changes in Nuclear Reactions

Neutron-to-Proton Ratio• Atomic number 20 and lower

– 1:1 ratio of protons and neutrons• Higher atomic number

– More neutrons than protons*Neutron to proton ratio of stable nuclei increases with increasing atomic number*

http://www.youtube.com/watch?v=H8Yd2T9MQBU

Page 43: Energy Changes in Nuclear Reactions

+

Neutron-to-Proton Ratio• In heavier nuclei, the number of protons increases the proton-proton

repulsions which outweighs sum of: – proton-proton attractions– proton-neutron attractions– neutron-neutron attractions

• THEREFORE… number of neutrons must increase at more rapid rate than number of protons

++0

00

0

0

0

0

0

0

DEMO

Page 44: Energy Changes in Nuclear Reactions

Belt of Stability – Area where all stable nuclei lie•Ends at element 83•*All elements with 84 or more protons are radioactive*

Page 45: Energy Changes in Nuclear Reactions

Radioactive Decay• Nuclei above belt of stability– High neutron to proton ratio– Move toward belt by emitting beta particle• Decreases number of neutrons and increases

number of protons

Page 46: Energy Changes in Nuclear Reactions

• Nuclei below belt of stability– Low neutron to proton ratio– Move toward belt by positron emission or

electron capture • Decrease protons and increase

neutrons • Positron emission more common in

lighter elements• Electron capture more common in

heavier elements

Page 47: Energy Changes in Nuclear Reactions

• Nuclei outside belt of stability– Atomic number 84 or higher– Undergo alpha emission

• Decreases both protons and neutrons by two

• Moves diagonally towards belt of stability

http://www.youtube.com/watch?v=VJZuY3_aLnI

Page 48: Energy Changes in Nuclear Reactions

Radioactive Series• Some nuclei can’t gain stability through a single emission, so a series of

successive emissions occur • Radioactive series (nuclear disintegration series) – begins with an

unstable nucleus and ends with a stable one• Three exist:– Uranium 238 – lead 206– Uranium 235 – lead 207– Thorium 232 – lead 208

Page 49: Energy Changes in Nuclear Reactions

Radioactive series example

Net Reaction:

Page 50: Energy Changes in Nuclear Reactions
Page 51: Energy Changes in Nuclear Reactions

Further Observations• Magic Numbers– Nucleus with 2, 8, 20, 28, 50, or 82 protons or neutrons (neutrons

include 126) are more stable than those with other numbers• Even number of both protons and neutrons more stable than odd

numbers• Shell Model of the Nucleus – nucleons reside in shells similar to

electron shells

Page 52: Energy Changes in Nuclear Reactions

Review

• For the first 20 elements, what is the (approximate) proton to neutron ratio?– 2:1– 1:2– 1:1– 1:3

Page 53: Energy Changes in Nuclear Reactions

• Strong nuclear force:– Overcomes the repulsion of protons– Attracts electrons– Charge of neutrons– Repulsive force of protons

Page 54: Energy Changes in Nuclear Reactions

• Neutron to proton ratio of stable nuclei:– Is 1:1 for all elements– Is 1:1 for all elements above atomic number

20– Increases with increasing atomic number

above element 20– Decreases with increasing atomic number

above element 20

Page 55: Energy Changes in Nuclear Reactions

• All elements with 84 or more protons are:– Stable– Radioactive– Highly electronegative– Good electrical conductors

Page 56: Energy Changes in Nuclear Reactions

• Even number of neutrons and protons are:– More stable than odd ones– Less stable than odd ones

Page 57: Energy Changes in Nuclear Reactions

Nuclear Reactors

Danielle Gerstman, Bridget Murray, Rachel Santangelo

Page 58: Energy Changes in Nuclear Reactions

What’s A Nuclear Reactor? • A device that sustains a controlled nuclear chain

reaction• Take place when a nucleus of an atom gets smacked

by either a subatomic particle or another nucleus– Produces atomic and subatomic products– Fission reaction-the nucleus splits apart

Page 59: Energy Changes in Nuclear Reactions

What’s Fission? • The light particle/free neutron collides with the

heavy particle which splits into two or three pieces• Produces energy in the form of both kinetic energy

and electromagnetic radiation• Newly produced free neutrons zoom around and

smack into more uranium or plutonium isotopes • Produces more energy and more free neutrons– Leads to nuclear fission chain reaction

Page 60: Energy Changes in Nuclear Reactions

Main Components • Core: contains nuclear fuel and

generates all heat, low-enriched uranium (<5% U-235), control systems, and structural materials

• Coolant: passes through core and transfers the heat from fuel to turbine

• Turbine: transfers heat from coolant to electricity

• Containment: the structure that separates the reactor from the environment. – Usually dome-shaped, made of high-

density, steel-reinforced concrete• Cooling towers: place where some

plants can dump excess heat that cannot be converted to energy

Page 61: Energy Changes in Nuclear Reactions

Main Components • Control rods: limit rate of

fission inside fuel rods by absorbing some neutrons

• Fuel pins: smallest unit of reactor (usually uranium-oxide) usually surrounded by metal tube called cladding

• Fuel assemblies: bundles of fuel pins that keep pins close, but far enough away so that coolant can fit between them

• Fuel core: several hundred assemblies

Page 62: Energy Changes in Nuclear Reactions

The Pressurized Water Reactor The water is both the coolant and the moderator. Keeps water under pressure so the water heats but does not boil. Heated pressurized water runs through pipes, which heats a separate water line to create steam. The water used to generate steam is never mixed with the pressurized water used to heat it.

Page 63: Energy Changes in Nuclear Reactions

High Temperature, Gas Cooled Reactors• Operate at higher

temperatures• Gas is used as primary

coolant• Mostly moderated by

carbon• Can have higher

efficiencies than PWR’s, but is limited by gas coolant (not as effective)

Page 64: Energy Changes in Nuclear Reactions

Sodium Cooled Fast Reactor• Cooled by liquid sodium metal

(heavier than hydrogen so neutrons move faster)

• Use metal or oxide fuel• Pros:– Breeds own fuel– Burns own waste– Safer- will shut itself down and

cool decay without working backup system

• Unfortunately, coolant (sodium) reacts with water and air, so leads to sodium fires

Page 65: Energy Changes in Nuclear Reactions

Boiling Water ReactorHeats water by generating heat from fission in the reactor vessel to boil water and creates steam, which turns the generator. In both types of plants, the steam is turned back into water and can be used again in the process.

Page 66: Energy Changes in Nuclear Reactions

Boiling Water Reactors• Thousands of fuel rods- twelve feet long, straw-like tubes– Fueled is sealed inside them (ceramic pellets of uranium oxide)– Bundled in core of reactor– Heat up during fission chain reaction, so they are submerged in

the coolant (the water- which is kept pressurized so the boiling point is around 550 degrees Fahrenheit)

– Creates high pressure steam that turns turbines to produce electricity

Page 67: Energy Changes in Nuclear Reactions

What Is A Meltdown? • If the core gets too hot, the fuel rods can crack

and release radioactive gases• Fuel pellets melt and fall to the reactor floor,

where the hot, radioactive material is able to eat through protective barriers and reach the surrounding environment

• Example meltdown: Nuclear reactors in Japan

Page 68: Energy Changes in Nuclear Reactions

What Went Wrong In Japan?

• Nuclear reactors designed to turn off automatically anytime a disaster knocks out the electric grid– The system worked properly

• Even with the plant shutdown, the nuclear fuel still held tremendous heat

• Diesel-powered backup generators are meant to pump water into the plant to cool the fuel,– Systems failed in the tsunami that followed the

earthquake – Emergency batteries provided some power, but not

enough to run the water pumps

Page 69: Energy Changes in Nuclear Reactions

Control Rods• Long, thin rods are bundled together into fuel assemblies

and placed in reactor core• Absorb excess neutrons released in fission process

– Reaction will continue unchecked, since one fission will release multiple neutrons but requires only one to begin

– Control rods prevent this, controlling the chain reactions• Rods are slowly lifted until chain reaction can just be

sustained– As the reactions continue, neutron-absorbing material

builds up– Rods will be withdrawn slowly until reactions can’t be

maintained and the fuel must be replenished• If rods do not function properly, reaction will proceed

uncontrolled

Page 70: Energy Changes in Nuclear Reactions

Questions• What are cooling towers in reactors for?

– Storage of material holding excess heat that cannot be converted into energy

• How do pressurized water reactors generate energy?– Water is heated under high pressure in pipes, boiling a separate line to

produce steam that runs turbines• Although sodium cooled reactors can be beneficial, why are

they more dangerous than other kinds of reactors?– Sodium, the coolant, reacts with water and air, so it can cause fires

• What causes a nuclear meltdown?– If the core overheats, fuel rods crack and release radioactive material

that passes through protective barriers and into the outside environment

Page 71: Energy Changes in Nuclear Reactions

Kwak & Rundle

Radioactivity

Page 72: Energy Changes in Nuclear Reactions

General info

• Inside the nucleus– Protons– Neutrons

• All atoms of the same element have equal protons– Which gives them their atomic number– Can have different amounts of neutrons• Isotopes

– Found in many natural abundances

• Stability of an atom depends on the amount of protons and neutrons in the nucleus

Known as Nucleons – location in nucleus

Page 73: Energy Changes in Nuclear Reactions

Atomic Number/Number of Protons

Mass Number(Neutrons + Protons)

ChemicalSymbol

Page 74: Energy Changes in Nuclear Reactions

• Radioisotopes – atoms containing radioactive nuclei

• Radioactive nuclei are called radionuclides

Radioactive isotopes

Page 75: Energy Changes in Nuclear Reactions

Nuclear equations

• Most of the nuclei in nature are stable\• Radionuclides are unstable and

spontaneously give off particles and electromagnetic radiation– Emitting that radiation is one way to make an

atom/radioactive atom become more stable– Radiation comes off as Alpha particles –

identical to Helium-4 nuclei• Consist of two protons and four neutrons• A stream of particles is called Alpha radiation

Page 76: Energy Changes in Nuclear Reactions

Equations (cont.)

• Spontaneously decomposes – radioactive decay– Sometimes called alpha decay

• Sum of the mass numbers is the same on both sides– Same deal for atomic numbers

• Radioactive properties of a nucleus are independent from the chemical form of the atom– English – It doesn’t matter what phase it is in

when writing the nuclear equation– Doesn’t matter if it is pure element, or element

in compound

Page 77: Energy Changes in Nuclear Reactions

Radioactive Decay• 3 Common Types– Alpha

• Stream of He-4 nuclei– Beta

• Streams of beta particles – high-speed electrons emitted by an unstable nucleus• Causes atomic number to increase

– Converts neutron to a proton

– Gamma• High-energy photons – short length electromagnetic radiation• Does not change atomic number or atomic mass• Almost always accompanies other radioactive emission

– Represents the energy lost when the remaining nucleons reorganize into more stable arrangements

Page 78: Energy Changes in Nuclear Reactions

• Capture by the nucleus of an electron from the electron cloud surrounding the nucleus

• Electron is consumed rather than formed; shown on reactant side– Converts proton to

neutron

• Positron – particle that has the same mass as an electron, but positive charge

• Causes atomic number to decrease– Converts proton to

neutron

Other types

Positron Emission Electron Capture

Page 79: Energy Changes in Nuclear Reactions

Alpha

Gamma

Beta

Page 80: Energy Changes in Nuclear Reactions

Positron Emission

Electron Capture