Reminder: The difference between the mass number and the atomic number gives you the number of neutrons.

RADIATIONRADIATIONPenetrating rays and particles emitted by Penetrating rays and particles emitted by a radioactive source.a radioactive source.

An unstable nucleus loses energy by emitting radiation during the process of radioactive decay.

TYPES OF RADIATIONTYPES OF RADIATION

ALPHAALPHA -- -- helium nuclei that are emitted from a radioactive source.

BETABETA – fast-moving electrons formed by decomposition of a neutron

GAMMA – high energy electromagnetic radiation given off by a radioisotope.

Contain two protons and two neutrons and have a positive two charge.

Symbol = He+242

Stopped by a sheet of paper.

Fast moving electrons released by a nucleus.

•No mass and a negative charge.

•More penetrating than alpha particles

•stopped by aluminum

foil or thin pieces of wood.

e0-1

High-energy electromagnetic radiation often emitted with alpha or beta radiation.

• No mass or charge.

• stopped by lead or several meters of concrete.

A particle with the mass of an electron but a positive charge.

e0+1

When a proton is converted to a neutron, the atomic number decreases by 1 and the number of neutrons increases by 1.

Protons and neutrons in the nucleus Protons and neutrons in the nucleus are held together by nuclear are held together by nuclear forces forces that overcome the electromagnetic that overcome the electromagnetic repulsion between the protonsrepulsion between the protons..

However, the nucleus can be However, the nucleus can be unstable and undergo decay based unstable and undergo decay based on the proton to neutron ratio.on the proton to neutron ratio.

What Causes a Nucleus to be What Causes a Nucleus to be Unstable?Unstable?

                                                                                                                

All nuclei with an atomic number greater than 83 are radioactive.

They have too many neutrons and too many protons to be stable , therefore, they undergo decay.

Most undergo alpha decay or

Beta decay. How does alpha and

Beta decay effect the mass # and atomic # ?

Remembering IsotopesRemembering Isotopes

Isotopes = atoms of the same Isotopes = atoms of the same element that have the same number element that have the same number of protons, but a different number of of protons, but a different number of neutrons.neutrons.

Ex: Ex:

Carbon – 12; Carbon – 13; Carbon - 14Carbon – 12; Carbon – 13; Carbon - 14

The time required for one-half of the nuclei of a radioisotope sample to decay to products.

Half-lives may be a fraction of a second or billions of years.

Carbon-14, which has a half-life of 5730 years, is used extensively to date artifacts that are made of organic material.

After an organism dies, the ratio of carbon-12 to carbon-14 changes as the carbon-14 changes to nitrogen-14.

Carbon-14 dating can be used to determine the ages of objects between 200 and 50000 years old.

Nitrogen-13 emits beta radiation and decays to carbon-13 with a half life (t1/2) of 10 min. Assume a starting mass of 2.00 g of nitrogen –13.

a) How long is three half-lives?3 x 10min = 30 min

b) How many grams of the isotope will still be present at the end of three half-lives? 2.00 g x ½ x ½ x ½ = 0.250 g

What are nuclear Reactions?What are nuclear Reactions?

nuclei of unstable isotopes, nuclei of unstable isotopes, radioisotopesradioisotopes, gain stability by , gain stability by undergoing changes. undergoing changes.

An unstable nucleus releases An unstable nucleus releases energy by emitting radiation energy by emitting radiation during the process of radioactive during the process of radioactive decay.decay.

Nuclear Reactions…Nuclear Reactions…

produceproduce LARGE LARGE amounts of amounts of energyenergy

Reactions are not affected by Reactions are not affected by changes in temperature, pressure, or changes in temperature, pressure, or presence of catalysts.presence of catalysts.

Nuclear Reactions cannot be sped Nuclear Reactions cannot be sped up, slowed down, or turned off.up, slowed down, or turned off.

How Nuclear Reactions Differ from How Nuclear Reactions Differ from Chemical Reactions:Chemical Reactions:

When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments.

Atomic bombs are devices that start uncontrolled nuclear chain reactions.

Nuclear reactors , use controlled fission to produce useful energy.

The energy released from the sun, is the result of nuclear fusion. Fusion occurs when nuclei combine to produce a nucleus of greater mass.

Fusion releases much more energy than fission.

Fusion reactions take place at very high temperatures – in excess of 40,000,000 oC.

The reaction requires two beta particles.

2 1 H + 2-1e 1 0 4 2 He + energy

Observers watch an atomic nuclear blast in this March 23, 1955 file photo.

Image 151 HARRY, part of Operation Upshot/Knothole, was a 32 kiloton weapons related device fired from a tower May 19, 1953 at the Nevada Test Site.

Image 154 HOOD, conducted at the Nevada Test Site on July 5, 1957 was a 74 kiloton device exploded from a balloon.

Yucca Flat Nevada -- This photo was taken November 1, 1951 at Yucca Flat, the Nevada Test Site. Note: The soldiers were provided no protection from the harmful radiation, however, the 'Top Brass' viewed the shot from high atop Lookout Mountain in concrete reinforced bunkers.