Nuclear ChangesNuclear Energy – An introduction

Chapter 9

RadioactivityRadioactive materials

have an unstable nucleus that release one or more particles or energy

Nuclear radiation refers to the released energy and matter.

Where does radiation come from?Radiation is generally produced when particles interact

or decayA large contribution of the radiation on the earth is

from the sun (solar) or from radioactive isotopes of the elements (terrestrial)

Radiation is going through you at this very moment!

Isotopes (a review)What’s an isotope?

Two or more varieties of an element having the same number of protons but

different number of neutrons. Certain isotopes are “unstable” and decay to lighter isotopes or elements.

Deuterium and tritium are isotopes of hydrogen. In addition to the 1 proton, they have 1 and 2 additional neutrons in the nucleus respectively*.

Nuclear Radiation As the radioactive nucleus decays, nuclear

radiation leaves the nucleus and interacts with other matter.

Types of nuclear radiation: (4)1. Alpha Particles ()

2. Beta particles ()

3. Gamma rays ()

4. Neutron emission

1. Alpha Particles: a positively charged particle and has a large mass. (consists of 2 protons and 2 neutrons). Do not travel far because of its size. Can barely travel through a piece of paper.

Radium

R226

Radon

Rn222

88 protons138 neutrons

86 protons136 neutrons

2 protons2 neutrons

The alpha-particle is a Helium nucleus.

It’s the same as the element Helium, with the electrons stripped off !

He)

+

2. Beta Particles: negatively charged particle that has little mass Travels much faster than alpha particles Travel through 3mm of aluminum or 10 mm of wood…but are

stopped because they lose energy fairly quickly.

CarbonC14

6 protons8 neutrons

NitrogenN14

7 protons7 neutrons

+ e-

electron(beta-particle)

We see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus.

Gamma Rays: are not made of matter and do not have an electric charge

Gamma Rays consist of electromagnetic energy called PHOTONS

Have very high energy…can travel through 60 cm of aluminum or 7 cm of leadGamma Rays are more dangerous to living things than

alpha or beta particles.

Gamma particles ()In much the same way that electrons in atoms can be in an excited state, so can a nucleus.

NeonNe20

10 protons10 neutrons

(in excited state)

10 protons10 neutrons

(lowest energy state)

+

gamma

NeonNe20

A gamma is a high energy light particle.

It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum.

A gamma is a high energy light particle.

It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum.

Gamma Rays

NeonNe20 +

The gamma from nuclear decayis in the X-ray/ Gamma ray

part of the EM spectrum(very energetic!)

NeonNe20

Nuclear Radiation

Neutron Emission: The release of a neutron from a nucleus…does not have any charge.

Can travel much farther because they do not lose energy very quickly.Can travel through a 15 cm block of lead.

Half-Life The “half-life” (h) is the time it takes for half the atoms of a

radioactive substance to decay.

For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after:

10,000 (50%)

5,000 (25%)

2,500 (12.5%)

1 hour (one lifetime) ?

2 hours (two lifetimes) ?

3 hours (three lifetimes) ?

Time #atoms

remaining% of atomsremaining

Predicting Age Scientists use the Half-Life of an object to

determine its age. For example: Potassium-40 decays to Argon-40,

so the ratio of Potassium-40 to argon-40 is smaller for older rocks than it is for younger rocks.

Scientists use Carbon-14 to date more recent materials like remains of an animal or parts of ancient clothing.

Practicing Half-Life

Radium 226 has a half-life of 1599 years. How long would it take seven-eighths of a radium-226 sample to decay?Given: half-life = 1599 yearsGiven: fraction of sample decayed = 7/8Unknown: fraction of sample remainingUnknown: total time of decay

1. Calculate the fraction of radioactive sample remaining. Fraction of sample remaining = 1 – 7/8 = 1/8

2. Calculate the number of half-lives Amount of sample remaining after one half-life = ½ Amount of sample remaining after 2 half-lives = ¼ Amount of sample remaining after 3 half-lives = 1/8 3 Half-lives are needed for one-eighth of the sample to remain

undecayed.

3. Calculate the total time required for the radioactive decay. Total time of decay = 3 half-lives x 1599 years = 4797 years

Radioactive Dating Game

Sign out a laptop Log in and open the Internet Go to phet.colorado.edu

New Sims - PhET Simulations

Nuclear EnergyBasics of Nuclear Power Video Clip

Brief History Nuclear energy was first discovered in 1934 by Enrico

Fermi The first nuclear bombs were built in 1945 as a result of

the Manhattan Project The first plutonium bomb (Trinity) was detonated on July

16, 1945 The first uranium bomb was detonated over Hiroshima on

August 6th 1945 The second plutonium bomb was dropped on Nagasaki on

August 9th 1945 Electricity was produced with nuclear energy in 1951.

Fission: History and Overview Discovered 1938 by Otto

Hahn and Frittz Strassmann Presented in 1939 by Lise

Meitner and Otto Frisch Research of Nuclear Fission

began U.S. weapons program 1942 first controlled self

sustaining fission reaction by Enrico Fermi

Nuclear fission creates Electricity

Fission Overview Fission is the process of

splitting heavier nuclei into lighter nuclei

Fission releases Energy The mass equivalent of 1kg of

matter is more than the chemical energy of 22 million tons of TNT

Neutrons released by fission can start a chain reaction…a continuous series of nuclear fission reactions.

Fission Today 435 Nuclear Power

plants worldwide 1/6 of the worlds

power is nuclear World Energy

Consumption doubled by 2050

World will turn to fission energy

World Nuclear Power Plants

How Stuff Works - Nuclear Energy

United States Nuclear Power Plants

Nuclear Power in Northeast U.S.

Japan’s Nuclear Power Problems

Japan’s Power Plant Meltdown

Japan’s Nuclear Emergency Efforts to cool down the nuclear reactor Concerns about Proximity to the Power plant

Fusion: Overview and History British Physicists in the 1940’s and 50’s housed ina

hangar at Harwell a device called ZETA-Zero Energy Toroidal Assembly which was the first fusion based operating system

Masked in the secrecy of the Cold War Fusion is the production of a thermonuclear reaction

in a gas discharge Called fusion because it is based on fusing light nuclei

such as hydrogen isotopes to release energy, similar to that which powers the sun and other stars.

Fast Facts A vast, new source of energy Fuels are plentiful Inherently safe since any malfunction results in a

rapid shutdown No atmospheric pollution leading to acid rain or

the greenhouse effect Sunlight is energy released from fusion reactions

in the sun.

The Future is Fusion The sun is our greatest source of energy…the sun

uses fusion. The source of fusion is vastly abundant in our

oceans (an isotope of hydrogen in water) The waste of fusion is helium, and there is no

pollution of long term extent The price of fusion is estimated to be equivalent to

that of fossil fuels Fusion can give us energy for millions of years

Nuclear Waste

Most used Nuclear Waste Sites

Nuclear Waste Nuclear Waste has been accumulating since the

mid-1940’s and is currently in temporary storage at 131 sites in 39 states

Nuclear waste remains highly radioactive for thousands of years.

It will still be potentially harmful to humans long after the manmade containers holding the waste have disintegrated.

Yucca Mountain Will become the nation's first long-

term geologic repository for spent nuclear fuel and high-level radioactive waste that is currently stored at 126 sites around the nation.

Yucca Mountain is located in a remote desert on federally protected land within the secure boundaries of the Nevada Test Site in Nye County, Nevada. It is approximately 100 miles northwest of Las Vegas, Nevada.

Nuclear Radiation Today

Radiation

You are exposed to radiation everyday Background Radiation – nuclear radiation that

arises naturally from cosmic rays and from radioactive isotopes in the soil and air

We are adapted to survive low levels of this natural source of radiation

Radiation is measured in rems or millirems

What are the Possible Effects of Radiation?

Inside Chernobyl - National Geographic Magazine Kasakhstan Fallout Video Clip

Safety VideosDuck and CoverLiving Under the Shadow of the Nuclear Umbrella

Video Clip

Radiation Exposure There are many occupations where people are

exposed to higher levels of radiation.Nuclear radiation, health physics, radiology,

radiochemistry, X-ray technology, MRI It has been decided that these occupations can be

exposed to 5000 millirems annually plus regular background radiation.

Exposure amounts will also depend on where a person lives.

Exposure may increase based on some day-to-day activities as well

Radiation Exposure Average annual radiation dose is 360 millirems per person. 300

from natural sources. Sleeping next to someone for 8 hours: 2 mrems Exposure comes from the naturally radioactive potassium in the

other person's body Coal plant, living within 50 miles: .03 mrem There is much

thorium and uranium in coal. Living within 50 miles of a nuclear power plant adds .009 mrem of

exposure. Both figures are considered extremely low levels. Living in a masonry home: 7 mrems Stone, brick and adobe have

natural radioisotopes in them. Living on the Earth: 200 mrems We are living in a sea of radon. It

is made from the natural decay of uranium and thorium in the soil, left over from the creation of the solar system. Radon is a rare gas that diffuses out of soil and into the air. It contributes more than half of our background

Smoking: up to 16,000 mrems The tobacco leaf acts like the absorbing surface of charcoal in a radon test kit. It collects long-lived isotopes of airborne radon, like lead-210 and polonium. Small portions of the lungs can get relatively whopping doses, compared to background levels.

Porcelain teeth or crowns: tenths of a rem Uranium is often added to these dental products to increase whiteness and florescence.

Air Travel: 1 mrem per 1000 miles 30,000 feet above the ground you're closer to the ionizing radiation (high-energy gammas well as particles) from the sun.

Grand Central Station, NYC: 120 mrem for employees Its granite walls have a high uranium content.

Brazil Nuts: This is the world's most radioactive food due to high radium concentrations 1000-times that of average foods.The US Capitol Building in

Washington DC: This building is so radioactive, due to the high uranium content in its granite walls, it could never be licensed as a nuclear power reactor site.

Radiation Exposure 1500% increase in incidence of testicular and ovarian

cancer in children on Navaho reservation in uranium mining area

500% increase in bone cancer in children affected by uranium

250% increase in leukemia (all ages) in the Navaho population

200% increase in each of the following non-cancer effects: miscarriage, infant death, congenital defects, genetic abnormalities, learning disorders.

400% increase in leukemia incidence in the population living downwind of the Pilgrim nuclear power reactor in Massachusetts in the first 5 years after fuel was know to have leaked excess radioactivity.Baseline: Disease in population before and after Pilgrim radioactive releases and comparison to upwind population.

300—400% increase in lung cancer in the general population within the plume of the Three Mile Island accident releases

600—700% increase in leukemia in the general population within the plume of Three Mile Island accident releases Baseline: Disease in population upwind (out of the radiation plume path) is compared to disease in population downwind (in the pollution plume.)

50% increase in childhood cancer incidence in the Three Mile Island area for each 10 millirem increase in radiation exposure per year.

500% increase in leukemia among Utah nuclear bomb test Downwinders

121% increase in thyroid cancer incidence in the same group

200% increase in breast cancer 700% increase in bone cancer a greater then 120% increase in thyroid cancer in those

who drank milk laced with Iodine-131 from atmospheric nuclear weapons tests

200% increase in lung cancer in women who received radiation treatments for breast cancer

66—96% increase in early cancer deaths due to background radiation

Radiation Exposure in

the U.S.

Benefits of Nuclear Radiation

Nuclear radiation is used in a controlled way Smoke Detectors use nuclear radiation in small

amountsAlpha particles are charged and produce an electric

current Detecting disease

Ultrasound, CT scanning, Radioactive tracers

Benefits in Medicine Radioactive tracers are short-lived isotopes that tend to

accumulate in specfic cells…help to find tumors.

Benefits in Medicine

Radiotherapy is used to treat cancers. Controlled doses of nuclear radiation are used to

kill fast growing cells (also damages healthy cells)

Uses in Agriculture Radioactive tracers are used to identify the flow of water and how it moves

through the crops. Help to identify biochemical processes

NUCLEAR RADIATION: A REVIEW

Risks of Nuclear Radiation Nuclear radiation reacts with living tissue (alpha,

beta, and gamma particles) They change the number of electrons in atoms of

living materials Alpha particles – stopped by layer of clothing Beta particles – travel through a fraction of an inch

in solids and liquids Gamma particles – depends on energy … can

travel through several feet.

Nuclear Radiation

Risk and Amount of Radiation

Small amount of nuclear radiation --- changes cannot be detected.

Relationship with high levels of nuclear radiation and cancerCancers related to radiation levels include: leukemia,

breast cancer, lung cancer, and stomach cancer