Chapter 25 Nuclear ChemistryNuclear fusion is the energy source of stars – just like our own Sun....

Chapter 25 Nuclear Chemistry

Radioactivity

• Roentgen was studying fluorescence when he accidentally discovered the X-ray

• Becquerel then discovered the radioactivity

• Marie Curie then continued the research to discover more radioactive elements

Terms you need to know

• Radioactivity: process by which nuclei emit particles and rays

• Radiation: Penetrating rays and particles emitted by radioactive source

• Radioactive decay: atoms with unstable nuclei (radioactive atoms) can change their identity by emitting a particle and energy

Isotopes

• Isotope: Element with the same number of protons but different number of neutrons

• Radioisotopes: an isotope that has an unstable nucleus and undergoes radioactive decay

• An unstable nucleus releases energy by emitting radiation during radioactive decay

3 Types

Of

Radiation

Gamma

Rays

Beta

Particles

Alpha

Particles

Greek Letters:

Alpha Radiation • contains 2 protons and 2 neutrons

• + charged particle

• VERY common in elements with atomic #83 and up

• the largest, slowest, and least penetrating.

• can be blocked by a sheet of

paper.

Alpha Particle Decay

Beta Radiation • the electron resulting from the breaking apart of

a neutron

• Fast moving electrons

• - charged particle

• faster and more penetrating than alpha particles.

•can be blocked by a sheet of

aluminum foil

Beta Particle Decay

Gamma Radiation • a high energy, high frequency photon emitted by

a radioisotope

• No mass, no charge, travel at the speed of light.

• Usually released with alpha/beta particles.

• the most penetrating form of radiation.

• Can penetrate deeply into body, damage to tissues by breaking bonds in molecules

Gamma decay

•Lead and concrete commonly used to block gamma rays.

How do they compare?

Nuclear Stability and Decay • Nuclear Force: attractive force that acts between all nuclear

particles

• 1,500 nuclei only 264 stable, the rest decay or change with time

• Stability depends on neutron-proton ratio

Nuclear Stability and Decay

What do the dots represent?

Stable nuclei

What is the ratio for an element with an atomic number of 60? 1.3

How does the neutron to proton ratio change as the number of protons increases? increases

• The neutron to proton ratio determines the type of decay that occurs

• Positron: particle with the mass of an electron but a positive charge

• All nuclei with an atomic number greater than 83 are radioactive (too many neutrons to protons)

• Mass is not conserved duringradioactive decay, a small amount is converted to energy

Half-Life What percent of the

atoms remain after 1

half-life? 50%

What percent of the

atoms remains after 2

half-lives? 25%

How many half-lives

does it take for 12.5%

of the same to remain?

3 half-lives

Half Life • Each particular isotope has its

own half-life. Time required for one half of the nuclei of a radioisotope sample to decay

• For example, the half-life of 238U is 4.5 billion years.

• In 4.5 billion years, half of the 238U will have decayed into other elements. In another 4.5 billion years, half of the remaining 238U will have decayed.

• One fourth of the original material will remain on Earth after 9 billion years.

Radioactive Dating • All living things have

carbon-14 in them.

• Carbon has a ½ life of 5730 years.

• Scientists measure the amount of carbon-14 left in a body, to determine how old it is.

• This process is called carbon dating.

Example Page 806 Problem 25.1

Example Page 806 Problem 25.1

Example Page 806 Problem 25.1

Your Turn

Practice Problem #7 pg 806

• Manganese-56 is a beta emitter with a half-life of 2.6 hr. What is the mass of Mn-56 in a 1.0 mg sample of the isotope at the end of 10.4 hr?

10.4/2.6 = 4 half lives

1.0 mg/24 = 0.063mg Mn-56

Practice Problem # 8 pg 806

• A sample of thorium-234 has a half-life of 24.1 days. Will all the thorium undergo radioactive decay in 48.2 days? Explain.

• 48.2/24.1 = 2 half lives

• No

• (½)2 = ¼ of the sample will be left

Transmutation • converting an atom of

one element to other element

• Alpha particles cause transmutation because the atoms lose 2 protons.

• Beta particles cause transmutation because the atoms gain a proton.

Exposure to ionizing radiation

• Background radiation: constant level of natural radioactivity always around you

• Background limit: .5rem

• US average: .36 rem

• US Limit in workplace: 5 rem

Radiation units

• Rad – measures the absorbed dose of radiation

• Rem – measures the ionizing effect on living organisms

• Gray (Gy) – measures the quantity of ionizing radiation delivered to a sample

• Sievert (Sv)- expresses the ability of radiation to cause ionization in human tissue

Ionizing Radiation- How much is safe?

• Depends on dose, exposure time, area exposed and tissue type

0-25 rem: no immediate observable effects

25-50 rem: small decreases in white blood cell count

50-100 rem: large decrease in white blood cell count, lesions

100-200 rem: radiation sickness, nausea, vomiting, hair loss, blood cells die

200-300 rem: hemorrhaging, ulcers, deaths

300-500 rem: acute radiation sickness, 50% die in weeks

>700 rem: 100% die

Worksheets….Radiation in your Life

• Video clip --- everyday radiation

Nuclear Energy

•Nuclei combine to produce a nucleus of a

greater mass

•Occurs at very high temperatures

•Example: Sun

•Split a nucleus into smaller fragments

•Releases large amounts of energy

•Ex: Nuclear reactor (controlled fission ) FISSION

FUSION

Nuclear Fission

Nuclear Fission: A Nuclear Power Plant

37

Schematic Diagram of a Nuclear Reactor

U3O8

refueling

• Nuclear Fusion

• Nuclear fission videos / fusion

• Nuclear Fusion How the Sun Shines:

Nuclear fusion is the

energy source of stars –

just like our own Sun.

It has a nuclear fusion

reactor at its core.

The immense pressure

and a temperature of 16

million degrees C force

atomic nuclei to fuse

and liberate energy.

About four million tons

of matter is converted

into sunlight every

second.

Nuclear Weapons: Fission

*August 6, 1945

Enola Gay drops the first nuclear bomb on an occupied location

Schematic of an Atomic Bomb

The Bomb…

• Code Name: Little Boy

February 9, 2011 Smithsonian Institute, Washington DC

Nuclear Weapons: Nagasaki

• August 9, 1945

The Bomb…

• Code Name: Fat Man

Nuclear Weapons: Nagasaki

• August 9, 2011

• National Museum of the Air Force, Dayton, Ohio

• 24 Hours after Hiroshima Video

So, now to you…..

• Was it worth it?

• Is it worth it NOW?