Day 6GHSGT Review

Energy Transformations

Transfer of Energy

Heat is transferred three ways…

Conductionthe movement of heat

energy through a substance by direct contact between the

particlesEx. – a candle heats one end of a metal rod and the other end gets hot because

of the transfer of heat

Convectionthe transfer of heat

energy by the actual movement (or currents)

of heated matterEx. – The water in the

bottom of a teapot becomes hot creating

currents which carry heat upward

Radiationtransfer of heat energy by waves from an area of high temperature to

an area of low temperature

Ex. – Heat from a space heater, fireplace, or the sun

is the spontaneous release of energy and particles from

the nucleus of an atom.

ISOTOPES

Atoms of the same element with a different number of neutrons.

Ex: carbon-12 & carbon-14 Carbon-12

6 protons 6 neutrons 6 electrons

Carbon-14 6 protons 8 neutrons 6 electrons

The nucleus of an atom can be unstable is there are too many

neutrons for the number of protons. An unstable nucleus

will be radioactive.

All elements with an atomic number greater than 83 are radioactive

3 Types of RadioactivityRadioactive Decay

ALPHA PARTICLE (α)

BETA PARTICLE (β)

GAMMA RAYS (γ)

ALPHA PARTICLE2 protons & 2 neutronsnucleus of a helium atomweakest type of radiationcan be stopped by a piece of paper12 inches max. distance travel

What happens to the numbers of particles in the nucleus after alpha decay?

BETA PARTICLE

an electron emitted from the nucleus A neutron splits into a proton & electron The electron is expelled out of the nucleus The proton stays and increases the number of protons

by one. The atomic number of the element increases by one The element changes into the next higher element on

the periodic table. 100x stronger than an alpha particle

What happens to the numbers of particles in the nucleus after beta decay?

Gamma Rays

An electromagnetic waveA packet of energyThe energy readjustment in the nucleusMost powerful form of radiationThe sun is a great source of gamma radiation

Gamma Ray Photography From Space

Antoine Henri Becquerel

In 1896, radioactivity was first discovered.

Used uranium salts = placed them near a photographic film plate.

exposed the film (below)Awarded Nobel Prize in

1903 in Physics

Pierre & Marie Curie (1898)

Discover the radioactive properties of radium & polonium Together awarded the Nobel Prize in 1903 (physics) along

with Henri Becquerel Marie is award a second Nobel Prize in 1911 (chemistry) Pierre is killed in an accident in 1906, Marie continues

working with radioactive substances.

Transmutation

= changes from one element to another element during α and β decay.

Alpha Decay = mass number decreases by 4 and the atomic number decreases by 2

Beta Decay = mass number does not change and the atomic number increases by 1

Alpha Decay

Uranium-238 has 92 protons

After alpha decay (2 protons & 2 neutrons leave the nucleus)

Becomes Thorium-234 and has 90 protons

Beta Decay

Carbon-14 has 6 protons & 8 neutrons

After beta decay (a neutron is split into a proton and electron

& the electron is expelled from the nucleus)

Becomes Nitrogen-14 and has 7 protons and 7 neutrons

Half Life

= the time it takes for one half of the mass of a radioactive substance to decay.Ex: carbon-14 = 5730 years

100 gram sample – In 5730 yrs = 50 grams C-14 & 50 grams N-14– In11,460 yrs = 25 grams C-14 & 75 grams N-14– In 17,190 yrs = 12.5 grams C-14 & 87.5 grams N-14

The Decay of Strontium-90

Number of half-lives

Elapsed Time Amount of strontium-90

present

0 0 10.0 g

1 29 years 5.0 g

2 58 years ?

? ? .625g

Nuclear Reactions

Nuclear Fission

Nuclear Fusion

Nuclear Fission

= the splitting of the nucleus into two smaller nuclei

Neutrons are used to split the nucleusAdditional neutrons are released to continue on

to hit/split other nuclei

Chain Reactions

Critical Mass (required) = concentration of radioactive atoms in a sample.Controlled Chain Reaction = many of the neutrons

that are produced are absorbed in “control rods” prevent excess energy to be released.

Ex. Nuclear Power Plants

Uncontrolled Chain Reaction = all the neutrons are allowed to continue to hit/split other nuclei causing massive amounts of energy to be released all at once.Ex. Atomic Bomb (used on Japan in 1945)

Controlled Chain Reaction

Uncontrolled Chain Reaction

Nuclear Fusion

= the joining of two smaller nuclei into a single larger nucleus

Extremely more powerful release of energy than fission

Requires a temperature of 10 million degrees Celsius

Also known as a thermonuclear reactionex: H-bomb and the sun/stars

Fusion Explosions

World War Breaks out in Europe in 1939

Szilard drafted a letter in consultation with Albert Einstein that was addressed from Einstein to President F.D. Roosevelt and which warned him of the possibility of nuclear weapons (the "Einstein Letter").

This letter was delivered to FDR on October 11, 1939, and ten days later the first meeting of the Advisory Committee on Uranium (the "Briggs Uranium Committee") was held in Washington, DC on Pres. Roosevelt's order.

“The Gadget”

Code Name = Trinity

July 16, 1945 - At 5:29:45 a.m. “The Gadget” was detonated in the first atomic explosion in history. The explosive yield was 20-22 Kt, vaporizing the steel tower.

August 6, 1945

“Little Boy” is used on Hiroshima, Japan

Dropped from the B-29 bomber named “The Enola Gay”

5 mile circle of destructionest. 78,000 killed & 70,000

injured

August 9, 1945

“Fat Man” is used on Nagasaki, Japan

2 mile circle of destruction

40,000 killed & 25,000 injured

Japan unconditionally surrenders a few days later & WWII is officially over

Further Nuclear Developments

August 1949 = Soviet Union tests their first atomic bomb after spies deliver US secret bomb blue-prints

November 1952 = United States the first Hydrogen bomb (H-bomb) 10 MT in strength, USSR tests their first H-bomb in Aug. 1953

Other Atomic weapons countries include Great Britain, China, France, India, Pakistan, and possibly Israel. North Korea and Iran are currently in the news for seeking nuclear capabilities.