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

 ZX where X = chemical symbol, Z = atomic number, and A = mass number or the number of protons and neutrons in the nucleus. A nucleon is a neutron or proton; the mass number of a nucleus is the number of nucleons (protons and neutrons) it contains.

A

Isotope Notation

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

protons neutrons electrons23Na14N38Ar35Cl36Cl-156Fe

Protons Neutrons Electrons

6 6 6

6 7 6

6 8 6

11 12 7

1177

18 20 18

17 18 1717 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 occurs when a nucleus emits particles or high frequency em waves.

Band of Stability

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).

15-

Figure 15.4

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

U23892 Pb206

82

Discovery of Po and Ra

Marie Skłodowska 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

15-

red zones-greater than 4 pCi/L orange zones-between 2 and 4 pCi/Lyellow zones-less than 2 pCi/L

Santa Barbara/ Ventura Countieshighest levels

Preventing Radon in Homes

15-

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 = 106 eV = 1.60 x 10-13J

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

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

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.

Lise Meitner (1878-1968) Enrico Fermi

(1901-1954)

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.

Nuclear Nuclear fuelfuel

Nuclear Nuclear fuelfuel

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 DECAY PRODUCES HEAT

ENCLOSED water circulates around fuel—gets HOT HOT HOT

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?

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

25

Nuclear Bombs

Trinity Bomb TestFirst nuclear bomb

http://www.metacafe.com/watch/400824/

trinity_nuclear_weapon_test/

26

Nuclear BombsHiroshima 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. Hiroshima after the bomb.

Enola Gay

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Hiroshima after the blast.

Imprint of sitting person from gamma ray incineration.

The sky turned pink from gamma rays and abut 15 seconds later the

shock wave hit.

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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.

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

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.