Outline Chapter 8a The Nucleus

8-1. Rutherford Model of the Atom 8-2. Nuclear Structure 8-3. Radioactive Decay 8-4. Half-Life 8-5. Radiation Hazards 8-6. Units of Mass and Energy

8 1. J.J. Thompson’s Plum Pudding Model of the Atom

In 1898, British physicist J. J. Thompson described atoms as positively charged lumps of matter with electrons embedded in them.

8-1. Rutherford Model of the Atom

In 1911, an experiment suggested by British physicist Ernest Rutherford shows that alpha particles striking a thin metal foil are deflected by the strong electric fields of the metal atom's nuclei.

8-2. Nuclear Structure

The nucleus of ordinary hydrogen is a single positively charged

proton

; other nuclei contain electrically neutral

neutrons

as well as protons. The number of protons is the atomic number.

8-2. Nuclear Structure

Isotopes

is called a are atoms of the same element that differ in the number of neutrons in their nuclei. A nucleus with a particular composition

nuclide

and is represented by A Z X where

X

= chemical symbol,

mass number

Z

= atomic number, and

A

= or the number of protons and neutrons in the nucleus. A contains.

nucleon

is a neutron or proton; the mass number of a nucleus is the number of nucleons (protons and neutrons) it

Isotope Notation

Protons Neutrons Electrons

6 6 6 6 7 6 6 8 6 How many protons, neutrons and electrons in each of the following:

protons neutrons electrons

23 Na 14 N 38 Ar 35 Cl 36 Cl -1 56 Fe

11 7 12 7 11 7 18 20 18 17 18 17 17 19 18 26 30 26

8-3. Radioactive Decay

In 1896, Henri Becquerel discovered that uranium gives off a penetrating radiation, a property called

radioactivity

. Soon after Becquerel's discovery, Pierre and Marie Curie discovered two more radioactive elements: polonium and radium.

Radioactive decay

waves.

occurs when a nucleus emits particles or high frequency em

Band of Stability

Figure 15.4

The stable nuclides have approximately equal numbers of protons and neutrons (N/Z ratio = 1) in the lighter elements (Z = 1 to 20) and more neutrons than protons in the heavier elements (N/Z ratio > 1).

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8-3. Radioactive Decay

Nuclear Decay

After Decay

• When an atomic nucleus is unstable, decay brings the nucleus to a more stable state • The final product of nuclear decay is a stable element • This may require numerous decay steps – Uranium 238 requires 8 alpha decays and 6 beta decays to eventually become Lead 206, a stable element 238 92 U 206 Pb 82

Discovery of Po and Ra

Marie Sk łodowska Curie (1867-1934)

Marie, and her husband Pierre, analyzed a ton of Uranium ore. After removing the uranium the radioactivity increased. This led to the discovery of Polonium, more radioactive than uranium, named after here home country of Poland. After removing the Polonium the radioactivity increased again. This led to the discovery of a small amount in their hand of Radium, so radioactive that it glowed in the dark.

(1943 Marie Currie Movie 2hrs)

8-4. Half Life

The half-life of a radionuclide (radioactive nuclide) is the time needed for half of an original sample to decay.

http://www.eserc.stonybrook.edu/ProjectJava/Radiation/

http://www.colorado.edu/physics/2000/isotopes/radioactive_decay3.html

8-5. Radiation Hazards

The SI unit of radiation dosage is the

sievert

(Sv); 1 Sv is the amount of radiation having the same biological effects as those produced when 1 kg of body tissue absorbs 1 J of x rays or gamma rays. Maximum dose is 20 mSv per year.

Predicted Indoor Radon Levels

red zones-

greater than 4 pCi/L

orange zones-

between 2 and 4 pCi/L

yellow zones-

less than 2 pCi/L

Santa Barbara/ Ventura Counties highest levels

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Preventing Radon in Homes

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Fig.8.6

A radionuclide tracer can be seen here. The different colors are different amount of tracer absorption. Cancerous bone absorbs more tracer. The white spot indicates a tumor.

8-6. Units of Mass and the Electronvolt

The

atomic mass unit

(u) is the standard unit of atomic mass: 1 atomic mass unit = 1 u = 1.66 x 10 -27 kg The

electronvolt

(eV) is the energy unit used in atomic physics: 1 electronvolt = 1 eV = 1.60 x 10 -19 J The

megaelectronvolt

(MeV) is equal to 1 million eV: 1 megaelectronvolt = 1 MeV = 10 6 eV = 1.60 x 10 -13 J The energy equivalent of a rest mass of 1 u is 931 MeV.

8-7. Binding Energy

All atoms have less mass than the combined masses of the particles of which they are composed. The energy equivalent of the missing mass of a nucleus is called the

binding energy

apart. ; the greater the binding energy of a nucleus, the more the energy is needed to break it

8-8. Binding Energy per Nucleon

The

binding energy per nucleon

is found by dividing the total binding energy of the nucleus by the number of nucleons (protons and neutrons) it contains; the greater the binding energy per nucleon, the more stable the nucleus.

8-9. Nuclear Fission

Lise Meitner (1878-1968) Enrico Fermi (1901-1954)

A

chain reaction

is a series of fission reactions spreading through a mass of an unstable radionuclide such as uranium. When a nucleus undergoes fission, two or three neutrons are released and can cause other nuclei to split and begin a chain reaction. The first chain reaction was demonstrated by the Italian physicist Enrico Fermi in Chicago in 1942.

8-10. How a Nuclear Reactor Works

A nuclear power plant transforms nuclear energy into electricity. The chain reaction within a nuclear reactor is controlled by a

moderator

which slows down neutrons. Reactors use

enriched

uranium as a fuel.

ENCLOSED water circulates around fuel —gets HOT HOT HOT



Super heated water (enclosed) LAST, and VERY IMPORTANT is the COOLING of the whole system. This is the ONLY WATER THAT IS NOT COMPLETELY ENCLOSED. Usually comes from a nearby lake or river, recirculated back into the river… Nuclear fuel More ENCLOSED water is heated to boiling, producing steam, which turns a turbine —causing the coils of an ELECTRIC GENERATOR to rotate-- remember Ampere’s law?

NUCLEAR DECAY PRODUCES HEAT

8-11. Plutonium

When nonfissionable U-238 captures a fast neutron, it eventually forms the fissionable nuclide of plutonium, Pu-239, which can support a chain reaction. Plutonium is a

transuranium element

, meaning that it has an atomic number greater than the 92 of uranium. The fissionable plutonium produced in a uranium-fueled reactor can be used as a fuel or in nuclear weapons.

Little Boy Fat Man

Nuclear Bombs Trinity Bomb Test First nuclear bomb http://www.metacafe.com/watch/400 824/trinity_nuclear_weapon_test/

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Enola Gay

Nuclear Bombs Hiroshima bomb- Little Boy Equivalent to 12-15 kilotons of TNT 70,000 killed immediately and 70,000 died afterward. Half from blast, a third radiation and rest from radioactivity Hiroshima before the bomb.

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Hiroshima after the bomb.

Hiroshima after the blast.

The sky turned pink from gamma rays and abut 15 seconds later the shock wave hit.

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Imprint of sitting person from gamma ray incineration.

Nagasaki-Fatman bomb Equivalent to 20-22 kilotons of TNT. About 20,000 killed immediately and another 20,000 died afterward. A military target that contained a weapons factory.

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A Nuclear World?

Nuclear energy generates about 21 percent of the electricity produced in the United States. Questions of safety, costs, and nuclear waste disposal have halted construction of nuclear reactors in the United States.

http://en.wikipedia.org/wiki/Chernobyl_disaster

A Nuclear World?

Nuclear Power plants locations throughout the world.

Fig. 8.22

Disposal of nuclear wastes is a problem. Here a tunnel is being prepared to store nuclear waste in Yucca Mountain in Nevada.

8-12. Nuclear Fusion.

Here an experimental fusion reactor at Princeton University. This uses powerful magnetic fields to confine the fusion material. This is called a tokamak reactor based on a Soviet reactor.

8-12. Nuclear Fusion.

Nuclear fusion produces tremendous quantities of energy and has the potential of becoming the ultimate source of energy on earth.

Pons and Fleishmann at the University of Utah

8-13. Antiparticles

An

antiparticle

has the same mass and general behavior as its corresponding elementary particle, but has a charge of opposite sign and differs in certain other respects. When an antiparticle and its corresponding elementary particle come together, they undergo

annihilation,

with their masses turning entirely into energy. In the process of

pair production

, a particle-antiparticle pair materializes from energy. Quarks make up protons/neutrons.

8-14. Fundamental Interactions

1. The

strong interaction

, which holds protons and neutrons together to form atomic nuclei.

2. The

electromagnetic interaction

, which gives rise to electric and magnetic forces between charged particles.

3. The

weak interaction

, which, by causing beta decay, helps determine the compositions of atomic nuclei.

4. The

gravitational interaction

another.

, which is responsible for the attractive force one mass exerts on

8-15. Leptons and Hadrons

Leptons

, which are not affected by the strong interaction, have no internal structure. Electrons are leptons.

Neutrinos

are leptons that have no charge and very little mass.

Hadrons

, which are affected by the strong interaction, are composed of quarks; protons and neutrons are hadrons.

8-15. Leptons and Hadrons

Physics is trying to bring all theories together into one

THEORY OF EVERYTHING.

Large Hadron Collider at the CERN laboratory between France and Switzerland, the most powerful particle accelerator in the world.