WHAT YOU ARE RESPONSIBLE FOR Quia – PARTS OF NUCLEAR REACTOR –

Vocab from game SAT REVIEW BOOK: P. 336 Methods of Detection P. 335 Nature of Radioactive Emissions Writing Nuclear Equations Solving Half Life problems Differentiating between Decay, fission

and fusion Benefits and Harm of using

Radioactive Isotopes

NUCLEAR CHEMISTRY OVERVIEW Nuclear Chemistry is the study of reactions

which alter the NUCLEUS of an atom. Reactions involving changes to the

nucleus also involve Radioactivity: spontaneous emission of particles and/or energy from the nucleus of an atom

Emissions are referred to as radiation.

NUCLEAR REACTIONS HAPPEN IN TWO WAYS NATURALLY and ARTIFICIALLY

1)Natural Transmutation – Alpha, Beta and Positron Decay - also FUSION Isotopes of elements that have unstable

nuclei, (a ratio of neutron to protons that causes instability), will undergo decay. This causes them to be transformed into another element. The time it takes for half a sample of this isotope to decay and be transformed into another element is called half life.

NUCLEAR REACTIONS HAPPEN IN TWO WAYS

Fusion as natural transmutation:

In stars, the nuclear reaction fusion results in the combination of lighter nuclei to form larger elements.

In most cases fusion cannot occur on earth, the temperature and pressures required are too extreme to allow for fusion without it becoming too destructive.

UNSTABLE ATOMS

If # of neutrons is too high or too low, the nucleus becomes unstable and emits energy.

Above atomic #83 there are no stable nuclides.

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WHAT HAPPENS TO ELEMENTS WHEN THEY DECAY??

A isotope undergoes transmutation when it decays. So the portion of the sample that has decayed, will turn into another element.

If a sample of N-16 will decay to produce another gas. If the half life of N-16 is 7.13s, and there are 45 grams present, what other element will be present after decay occurs for 35.65 seconds? How much of it will be present?

PARTICLE EMISSION & ENERGY Each particle leaves the nucleus,

traveling through other materials. This is radiation.

YOU MUST KNOW, the penetrating power of different particles.

Some reactions generate gamma radiation- this is a very high energy emission with no mass or charge. As a result it has the greatest penetrating power.

PENETRATING POWER

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THESE ARE IN YOUR REGENTS and SAT REVIEW BOOKS

NUCLEAR REACTIONS HAPPEN IN TWO WAYS

2) Artificial Transmutation- Fission and Nuclear Bombardment

These are manmade reactions in which the nucleus of an atom is forced to collide with a smaller particle.

WE STARTED WITH Types of nuclear equations which

include:

1) Alpha decay, beta decay and positron decay

2) Fission3) Fusion

WHAT ABOUT EMISSIONS? Particles given off by reactions are

somewhat similar to subatomic particles or elements you already know.

Alpha particles = the nucleus of a helium atom. Since they have 2 protons and NO electrons, they have a net positive charge of +2

WHAT ABOUT EMISSIONS? Beta Particles – Are high energy electrons

ejected from the nucleus when a neutron decays into a proton. They have negligible mass and a charge of -1.

Positrons – An anti-particle, basically the opposite of a beta particle. It also has negligible mass but the opposite +1 charge.

Neutrons can be emitted by reactions, neutron notation will show it has a mass of 1, and the zero subscript, shows it is alone and has no protons.

WHAT ABOUT EMISSIONS? Gamma Radiation- when gamma

radiation is emitted, it does not necessarily mean that transmutation has occurred. It does often occur after natural decay. It may also accompany fission and fusion reactions. It has no charge and no mass, so balance accordingly.

BALANCING NUCLEAR REACTIONS

•In the reactants and products

Atomic numbers must balanceand

Mass numbers must balance and Charge Must Balance

•Use a particle or isotope to fill in the missing protons and neutrons

ALPHA DECAY:MASS DECREASES BY FOUR, ATOMIC NUMBER DECREASES BY TWO.

238U undergoes alpha decay238U 4He + 234Th

The total mass on the left must equal the total mass on the right (238 = 4 + 234)

The total charge on the left must equal the total charge on the right (92 = 2 + 90)

92 2 90

ALPHA DECAY

16

U236

92 + He4

2Pu240

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BETA (MINUS) DECAY:MASS REMAINS THE SAME, ATOMIC NUMBER INCREASES BY ONE.

234Th undergoes beta decay234Th 0e + 234Pa

The total mass on the left must equal the total mass on the right (234 = 0 + 234)

The total charge on the left must equal the total charge on the right (90 = -1 + 91)

90 -1 91

BETA DECAY

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Ba137

56 + e0

-1Cs137

55

p 1

1 + e0

-1n 1

0

(One of Cs’s neutrons converts to a proton and electron.)

POSITRON (BETA PLUS) DECAY:MASS REMAINS THE SAME, ATOMIC NUMBER DECREASES BY ONE.

37K undergoes positron decay37K 0e + 37Ar

The total of the mass numbers on the left must equal the total on the right (37 = 0 + 37)

The total charge on the left must equal the total charge on the right (19 = 1 + 18)

19 +1 18

POSITRON DECAY

20

Mn 53

25 + e0

+1Fe53

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FISSION & TRANSMUTATION Fission converts a larger element into

several atoms of elements with smaller atomic numbers.

Therefore, this is a form of TRANSMUTATION, however, since it is initiated by people…IT IS

ARTIFICIAL TRANSMUTATION

PATTERN Fission Reactions: A Large nuclei will be

shown, colliding with/absorbing a neutron or small particle. The product will be several smaller elements and emissions.

Nuclear Bombardment, a smaller particle is shown colliding with an element.

Fusion Reactions: Smaller elements, (such as hydrogen), will be shown combining to form larger elements. Other particles and emissions may be present.

FISSION PRACTICE Complete the fission equation and account

for the missing particle:

Use table O for help with particle symbols

3

FUSION PRACTICE

Complete the following equation by finding the missing particle.

3 H + 2 H + 1 n1 1 04 He 2

THE HALF-LIFE OF A RADIOACTIVE NUCLIDE IS THE AMOUNT OF TIME IT TAKES FOR HALF OF THAT NUCLIDE TO DECAY INTO A STABLE NUCLIDE.

The half-life of a radioactive nuclide cannot be changed.

HALF LIFE The principle behind half life allows

radioactive isotopes to be used to:

1) Determine the age of organic and inorganic material. 2) Use selected isotopes for medical treatment and imaging

PROBLEM If a sample of Radon – 222 is allowed to

decay for 15.28 days…

If the amount left is 5 grams, how much was present in the original sample?

How many half lives did the sample undergo?

PROBLEM

How much of a 20.g sample of 131I remains unchanged after 24 days?

PROBLEM What is the half life of an isotope that

has decayed for 120 hours, if the original sample was 40 grams and the sample left weighs 1.25 grams.

DISINTEGRATION SERIES

“Heavy” atoms (greater than Bismuth, #83) naturally decay to smaller atoms along a consistent path, or series, of decays.

Radioactive U-238 → Th-234 + aTh-234 → Pa-234 + bPa-234 → U-234 + bU-234 → Th-230 + aTh-230 → Ra-226 + aRa-226 → Rn-222 + aRn-222 → Po-218 + aPo-218 → Pb-214 + aPb-214 → Bi-214 + bBi-214 → Po-214 + bPo-214 → Pb-210 + aPb-210 → Bi-210 + bBi-210 → Po-210 + bPo-210 → Stable Pb-206 + a

Mas

s Num

ber

Atomic Number & Symbol

Source: http://www.frontiernet.net/~jlkeefer/uranium.html

ENERGY RELEASED DURING NUCLEAR REACTIONS IS MUCH GREATER THAN THE ENERGY RELEASED DURING CHEMICAL

REACTIONS.

Fission – used in nuclear reactors and atomic bombs

Fusion – used in hydrogen bombs and the energy that powers the sun.

ENERGY RELEASED IN A NUCLEAR REACTION (FISSION OR FUSION) COMES FROM THE FRACTIONAL AMOUNT OF MASS CONVERTED

INTO ENERGY. NUCLEAR CHANGES CONVERT MATTER INTO ENERGY.

E=mc2

The energy released is equal to the mass lost (m) times the speed of light (c) squared. A small amount of mass lost converts to a very large amount of energy.

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NUCLEAR FISSION Fission: process in which the nucleus of a large,

radioactive atom splits into 2 or more smaller nuclei Caused by a collision with an energetic neutron.

• *A neutron is absorbed by a U-235 nucleus. The nucleus is now less stable than before. It then splits into 2 parts and energy is released. Several neutrons are also produced; they may go on to strike the nuclei of other atoms causing further fissions in a process called supercriticality.

Ba +13956

Kr +9436

3 n + energy10 U235

92n + 10

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*The process of neutron capture and nucleus splitting happens very quickly (takes about 1 x 10-12

seconds).

An incredible amount of energy is released: As heat and gamma radiation Because the product atoms and neutrons weigh less than the original U-235 atom; the “missing mass“ has been converted to energy by E=mc2

*A FISSION CHAIN REACTION

QUESTION??? Why are neutrons used in this

process and not protons?

Since neutrons are not charged, they can approach the nucleus. Using a proton would mean having to overcome the repulsive force of the other positive protons present in the nuclei.

Additionally, Particle accelerators often manipulate protons and electrons using enormous magnets. Due to a neutrons lack of charge, this is not possible.

Basic Tour of

a Nuclea

r Power Plant

THE REACTOR

The reactor contains what are known as fuel rods. Fuel rods contain about 3% of the isotope U-235, (Uranium).

The Fission reaction, is a chain reaction.

The reactor employs what are known as Control Rods to help slow the reaction down if necessary. Control Rods are made of Boron and Cadmium, (other elements) and these absorb some of the neutrons.

The reaction produces a lot of

heat, and water is circulated around it

to transfer that heat to a place

where it can produce steam.

Water that Circulates around

the reactor is heated to

temperatures of 320 degrees

CelsiusThat is a temp of 608 degrees Fahrenheit. Water Boils at 212 degrees Fahrenheit. www.howstuffworks.com

PRODUCING STEAM This super heated water is piped

through a separate tank where the heat transfers to water that is heated to produce steam.

The steam produced then turns the turbine of an electrical generator.

www.HowStuffWorks.com

www.HowStuffWorks.com

These structures we all associate with Nuclear Power Plants are actually the cooling towers. They help cool water down so it can either be

re-circulated into the system, or moved to cooling reservoirs to be returned to a body of

water.

If technicians are able to drop the control rods into the reactor, they can stop the fission

reaction…

However a meltdown can still occur since so much heat collects in

the reactor. This is also a reason why shutting a reactor down, even for temporary service, is a tricky maneuver.

NUCLEAR POWER The United States currently imports over 58%

of its oil supply. There is a need to develop alternative energy sources, such as nuclear, wind, geothermal, solar, …

By 2020 it is expected to be 67%.

At present about 20% of the electrical energy used in the U.S. is generated from power plants using uranium. In France the percentage is 75% .

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THE ATOMIC BOMB Uses an unregulated fission reaction in a very

fast chain reaction that releases a tremendous amount of energy.

*Critical mass: the minimum amount of radioactive, fissionable material needed to create a sustainable fission chain reaction

* Site of fission reaches temperatures believed to be about 10,000,000°C.

Produces shock waves and a, b, g, x-rays, and UV radiation.

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*US Army aerial photograph from 80 km away, taken about 1 hour after detonation over Nagasaki, Japan,

August 9, 1945.

*The classic “mushroom cloud” is a result of dust and debris lifted into the air as a result of the

detonation.

NUCLEAR FUSIONFusion: process in which 2 nuclei of small elements are united to

form one heavier nucleus * Requires temperatures on the order of tens of millions of

degrees for initiation. * The mass difference between the small atoms and the

heavier product atom is liberated in the form of energy. Responsible for the tremendous energy output of stars (like

our sun) and the devastating power of the hydrogen bomb.

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H + 31

H 21

He +42

n10

+ energy

STARS & THE HYDROGEN BOMB The first thermonuclear bomb was exploded in 1952

in the Marshall islands by the United States; the second was exploded by Russia (then the USSR) in 1953.

“H bombs” utilize a fission bomb to ignite a fusion reaction.

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ISOTOPES &USES U-238 and Pb-206 are used to date rocks

and inorganic material – C-14 used for organic material

I-131 is used to take images of and to treat thyroid cancer

Cobalt-60 and Tc-99 are used in radiation treatments to destroy cancerous tumors.

Gamma radiation is used to irradiate food and kill pathogens. (source Cs-137&Co-60)

*RADIOCARBON (C-14) DATING

Basic assumptions: CO2 in the atmosphere contains about

0.00000000010% C-14; this level is held constant through the decay of N-14 to form C-14 which happens in the upper atmosphere.

Plants consume CO2 during photosynthesis and animals eat plants, so they contain C-14:C-12 in the atmoshperic ratio as long as they are alive.

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• Discovered at University of Chicago in 1949 by Dr. W.F. Libby and his colleagues.

Limitations: C-14 dating has a limit of about 70,000 years. Beyond that, the %

of C-14 remaining is too small to accurately calculate the age.

Sources: http://www.geology.sdsu.edu/visualgeology/geology101/lab6time.htmhttp://www.dc.peachnet.edu/~pgore/geology/geo102/radio.htmhttp://superstringtheory.com/cosmo/cosmo1.html

- When an organism dies, the amount of C-12 does not change, but the C-14 content diminishes as it decays. The half-life of C-14 is 5730 years.

- By comparing the C-14:C-12 ratio in an artifact to the same ratio in living plants, the age of the artifact can be estimated.

NUCLEAR MEDICINE: IMAGING

Thyroid imaging using Tc-99m

FOOD IRRADIATION

•Food can be irradiated with g rays from 60Co or 137Cs.•Irradiated milk has a shelf life of 3 mo. without refrigeration.•USDA has approved irradiation of meats and eggs.

DANGERS OF RADIATION

Marvel Comics’ “The Incredible Hulk” was created in 1962 by Stan Lee and artist Jack

Kirby. The Hulk’s powers began when nuclear scientist Dr. Bruce Banner was accidentally

bombarded with gamma rays from a "gamma bomb" he had invented.

Remember that isotopes will have different masses, but that chemically they will be the same as other stable forms of the element.

For example Sr-90 can be taken up in bone because it is chemically similar to Calcium. The half life of Sr-90 is 28 years. Before nuclear weapons and power plants it was not found in the Environment.

BIOLOGICAL EFFECTS OF RADIATIONAcute: High level radiation (gamma ray & x–ray) can cause death. Damage is centered in nuclei of cells; cells undergoing rapid

cell division are most susceptible. Gamma rays from a Co-60 source are often used to treat

cancer (since cancer cells multiply rapidly).

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Long term:• Can weaken organism and lead to onset of malignant tumors,

even after fairly long time delays.• Largest source: X–rays• Sr-90 isotopes are present in fallout from atmospheric testing of

nuclear weapons.• Contaminated foods can increase incidence of leukemia and bone

cancers.