Fission and Fusion Farley Visitors Center 1 Cancer

Fission and Fusion Farley Visitors Center 1

Cancer Risks ã Increased risk of cancer mortality from 1 m. Sv of radiation (average annual background): – Solid tumor cancer risk is about one chance out of 25, 000 (1: 25, 000) – Leukemia risk is about one chance out of 125, 000 (1: 125, 000) – Total risk is about one chance out of 20, 000 (1: 20, 000)

Comparative Risks ã “Normal” risks we face: – Smoking (lifetime): 1: 4 – Police officer: 1: 2500 – Agriculture industry (per year): 1: 2600 – Vehicle accident (per year): 1: 6000 – Falls (per year): 1: 20, 000 – Home fire (per year): 1: 50, 000 – Airplane crash (one trip): 1: 1, 000

What is Safe? ã Driving a car is “safe” – (1: 6, 000) ã Living at home is “safe” – (Falls: 1: 20, 000, Fires: 1: 50, 000, Poisoning: 1: 40, 000; total: 1: 10, 000) ã Radiation (1 m. Sv) is safe – (1: 20, 000)

Years of Life Lost

Hours of Life Lost

Measurement of Radioactivity

Radiation from a radioactive source is so energetic that it is called ionizing radiation. When it strikes an atom or a molecule, one or more electrons are knocked off, and an ion is created. – Geiger counters – film badges – scintillation counters

Geiger Counter ã The detector tube is a pair of oppositely charged electrodes in an argon gas-filled chamber fitted with a thin window. ã When radiation, such as a beta particle, passes through the window into the tube, some argon is ionized, and a momentary pulse of current (discharge) flows between the electrodes. ã These current pulses are electronically amplified in the counter and appear as signals in the form of audible clicks, flashing lights, or numeric readouts.

Film Badges ã The badge contains a piece of photographic film in a light-proof holder and is worn in areas where radiation might be encountered. ã The silver grains in the film will darken when exposed to radiation. ã The badges are processed after a predetermined time interval to determine the amount of radiation the wearer has been exposed to.

Scintillation Counter ã Used for Biomedical applications. ã Composed of molecules that emit light when exposed to ionizing radiation. ã A light-sensitive detector counts the flashes and converts them to a numerical readout.

Ionizing Radiation ã Radiation where energy dislocates bonding electrons and creates ions when passing through matter. ã Radiation can damage or kill living cells and can strike the cell nuclei and affects molecules involved in cell production

Acute Radiation Damage ã High levels of radiation, especially from gamma rays or X-rays, produce nausea, vomiting, and diarrhea. ã The effect has been likened to a sunburn throughout the body. ã If dosage is high enough, death will occur in a few days. ã For this reason that cancers are often treated with gamma radiation from a Co-60 source. Cancerous cells multiply rapidly and are destroyed by a level of radiation that does not seriously damage normal cells.

Long-Term Radiation Damage ã Exposure to low levels of any form of ionizing radiation can weaken an organism and lead to the onset of malignant tumors, even after fairly long time delays. ã Largest exposure is due to X-rays. Evidence suggest that the lives of early workers in radioactvity and X-ray technology may have been shortened by long-term radiation damage.

Strontium-90 Isotopes ã Sr-90 isotopes are present in the fallout from atmospheric testing of nuclear weapons. Sr is in the same column as Ca and therefore has similar behavior. ã Hence when food contaminated with Sr-90 are eaten, the ions are laid down in bone tissue along with ordinary Ca ions. ã Sr-90 is a beta emitter with a half-life of 28 years. Blood cells manufactured in bone marrow are affected by the radiation from Sr-90. hence there is concern that Sr-90 accumulation in the environment may cause an increase in the incidence of leukemia and bone cancers.

Genetic Effects ã Radiation can damage DNA molecules. ã If the damage is not severe enough to prevent the individual from reproducing, a mutation may result. ã In other words the genetic effects of increased radiation exposure are found in future generations, not in the present generation.

Fission and Fusion

E = mc 2 ã Matter can be changed into Energy ã Einstein’s formula above tells us how the change occurs ã In the equation above: E = Energy m = Mass c = Speed of Light (Universal Constant) Energy Mass Light Speed

E = mc 2 ã The equation may be read as follows: Energy (E) is equal to Mass (m) multiplied the Speed of Light (c) squared ã by This tells us that a small amount of mass can be converted into a very large amount of energy because the speed of light (c) is an extremely large number

Fission In nuclear fission, a heavy nuclide splits As the atom splits, it releases energy and into two or more intermediate sized two or three other neutrons, each of fragments when struck in a particular which can cause another nuclear fission. way by a neutron Farley Visitors Center 20

Characteristics of Nuclear Fission • Large quantities of energy are produced as a result of the conversion of a small amount of mass into energy. • Many nuclides produced are radioactive and continue to decay until they reach a stable nucleus.

Fission of 235 U Each time fission occurs three neutrons and two nuclei are produced. 18. 5

ã • In a chain reaction the products cause the reaction to continue or magnify. For a chain reaction to continue, enough fissionable material must be present so that each atomic fission causes, on average, at least one additional fission.

ã The minimum quantity of an element needed to support a self-sustaining chain reaction is called the critical mass. • Since energy is released in each atomic fission, chain reactions provide a steady supply of energy.

Nuclear Fission

Fission and chain reaction of 235 U. 18. 6

Nuclear Power

ã A nuclear power plant is a thermal power plant in which heat is produced by a nuclear reactor instead of by combustion of fossil fuel. The major components of a nuclear reactor are – an arrangement of nuclear fuel, called the reactor core. – a control system, which regulates the rate of fission and thereby the rate of heat generation.

ã In the United States breeder reactors are used to generate nuclear power. • Breeder reactors use U 3 O 8 that is enriched with scarce fissionable U-235. • In a breeder reactor, excess neutrons convert nonfissionable isotopes, such as U-238 or Th-232, to fissionable isotopes, Pu-239 or U-233.

The Atomic Bomb

ã The atomic bomb is a fission bomb. • “Wild” or uncontrolled fission occurs in an atom bomb, whereas in a nuclear reactor the fission is carefully controlled. • A minimum critical mass of fissionable material is required for a bomb.

ã When a quantity of fissionable material smaller than the critical mass is used, too many neutrons escape and a chain reaction does not occur. • The fissionable material of an atomic bomb is stored as two or more subcritical masses and are then brought together to achieve a nuclear detonation.

ã Uranium-235 and plutonium-239 are the nuclides used to construct an atomic bomb. • 99. 3% of uranium is nonfissionable uranium-238. Uranium-238 can be transmuted to fissionable plutonium 239.

Nuclear Fusion

Fusion ã Fusion is a nuclear reaction whereby two light atomic nuclei fuse or combine to form a single larger, heavier nucleus ã The fusion process generates tremendous amounts of energy; refer back to Einstein’s equation ã For fusion to occur, a large amount of energy is needed to overcome the electrical charges of the nuclei and fuse them together

The masses of the two nuclei that fuse into a single nucleus are greater than the mass of the nucleus formed by their fusion. tritium deuterium 3. 0150 1. 0079 amu Thedifference in mass is released as energy. 4. 0026 amu 4. 0229 amu – 4. 0026 amu = 0. 0203 amu

Nobody has put the technology into practice yet, but working reactors aren't actually that far off. Fusion reactors are now in experimental stages at several laboratories in the United States and around the world. Photo courtesy ITER Proposed construction site of ITER fusion reactor plant at Cadarache, France. See more fusion reactor pictures. A consortium from the United States, Russia, Europe and Japan has proposed to build a fusion reactor called the International Thermonuclear Experimental Reactor (ITER) in Cadarache, France, to demonstrate the feasibility of using sustained fusion reactions for making electricity

ã NASA is currently looking into developing small -scale fusion reactors for powering deep-space rockets. Fusion propulsion would boast an unlimited fuel supply (hydrogen), would be more efficient and would ultimately lead to faster rockets.

Fusion ã Fusion reactions do not occur naturally on our planet but are the principal type of reaction found in stars ã The large masses, densities, and high temperatures of stars provide the initial energies needed to fuel fusion reactions ã The sun fuses hydrogen atoms to produce helium, subatomic particles, and vast amounts of energy

Fusion power will be far more superior to fission power because – Virtually infinite amounts of energy are possible from fusion power. – While uranium supplies are limited, deuterium supplies are abundant. – It is estimated that the deuterium present in a cubic mile of seawater used as fusion fuel can provide more energy than the petroleum reserves of the entire world.

Fusion power will be far more superior to fission power because – Fusion power is much “cleaner” that fission power. – Fusion reactions (unlike uranium and plutonium fission reactions) do not produce large amounts of long-lived and dangerously radioactive isotopes.

Nuclear Fusion Sun + + + Four hydrogen nuclei (protons) Two beta particles (electrons) One helium nucleus Energy

Conservation of Mass …mass is converted into energy Hydrogen (H 2) Helium (He) H = 1. 008 amu He = 4. 004 amu FUSION 2 H 2 1 He + ENERGY 1. 008 amu x 4 4. 0032 amu = 4. 004 amu + 0. 028 amu This relationship was discovered by Albert Einstein E = mc 2 Energy= (mass) (speed of light)2

Review ã Mass and Energy are two forms of the same thing; neither can be created nor destroyed but mass can be converted into energy (E = mc 2) ã Fission is a nuclear reaction in which a heavy atomic nucleus is split into lighter atomic nuclei ã Fusion is a nuclear reaction in which 2 light atomic nuclei are combined into a single, heavier atomic nucleus

Which nuclear process produces large amounts of energy? 1. 2. 3. 4. Fission Fusion Both 1 and 2 Neither 1 nor 2

Fission is the process that atomic nuclei. 1. 2. 3. 4. Combines Burns up Stores Splits

Mass may be converted into energy. 1. 2. True False

The fission process requires heavy nuclei. 1. 2. True False

Quiz ã Name a nuclear reaction that occurs within the sun:

Quiz ã Fission is a natural process that occurs the planet Earth. A. True B. False on

Quiz ã Explain this equation: E = mc 2