Radioactivity

John Dalton

Atoms were tiny indivisible spheres

Thomson

Discovered that all matter contains tiny (-) charged particles and it smaller than an atom

with (+) charged .

Thomson’s plum-pudding model

Rutherford

•http://www.youtube.com/watch?v=FfY4R5mkMY8&feature=related

•Solve a sheet

Can we use this model to explain the Alpha-particle scattering?

For more information

•http://olom.info/ib3/ikonboard.cgi?act=ST;f=2;t=26915;&#top

The structure of the atom

ParticleLocation masscharge

ProtonIn the nucleus

1.00728u+

NeutronIn the nucleus 1.00867u0

Electron Orbiting the nucleus

0.00055u-

1 u ( atomic mass unit )= 1.6605X 10 -27 kg

• Proton and the neutron are found in the nucleus .

• All atoms (except for hydrogen atom ) are made up of 3 particles.

What do you notice about the number of protons & electrons in

each atom?

Proton number and nucleon number

Proton number

nucleon number

More info.

• Some terms• There are some terms that you will need to know the meaning of,

they are: • Atomic number - Also called proton number, this is the number of

protons the atom has. This can be looked up on the periodic table Mass number - This basically tells you the number of particles in the nucleus (as the electron has negligible mass).

• These numbers, along with the element symbol are often written together as follows.

• The top number is the mass number and the bottom is the atomic/proton number. If you want to work out the number of neutrons you simply subtract the bottom from the top, leaving you with 30.

Find the:Proton number and nucleon number

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Isotopes

• An isotope is merely where you have different chemicals of the same element, but have different numbers of neutrons.

• the atomic numbers are the same, but the mass numbers are not. On the periodic table, the relative atomic mass is given, this can be thought of as the average mass of the atoms. The example below shows how to calculate this given the relevant data.

Alpha , Beta And Gamma R

Alpha - ray

Beta - ray

Gamma- ray

•Radioactive decay

Strong nuclear force

Electrical repulsion force

Alpha Decay• .Alpha decay usually occurs in heavy nuclei

such as uranium or plutonium, and therefore is a major part of the radioactive fallout from a nuclear explosion. Since an alpha particle is relatively more massive than other forms of radioactive decay, it can be stopped by a sheet of paper and cannot penetrate human skin. A 4 MeV alpha particle can only travel about 1 inch through the air.

•Although the range of an alpha particle is short, if an alpha decaying element is ingested, the alpha particle can do considerable damage to the surrounding tissue. This is why plutonium, with a long half-life, is extremely hazardous if ingested

Beta Decay• Atoms emit beta particles through a process

known as beta decay. Beta decay occurs when an atom has either too many protons or too many neutrons in its nucleus.

• Two types of beta decay can occur:• 1-(positive beta decay) releases a positively

charged beta particle called a positron, and a neutrino;

• 2-(negative beta decay) releases a negatively charged beta particle called an electron, and an antineutrino.

• The neutrino and the antineutrino are high energy elementary particles with little or no mass and are released in order to conserve energy during the decay process. Negative beta decay is far more common than positive beta decay. Beta particles have all the characteristics of electrons. At the time of their emission, they travel at nearly the speed of light. A typical .5 MeV particle will travel about 10 feet through the air, and can be stopped by 1-2 inches of wood.

• Gamma rays are a type of electromagnetic radiation that results from a redistribution of electric charge within a nucleus.

• Gamma rays are essentially very energetic X rays ; the distinction between the two is not based on their intrinsic nature but rather on their origins.

• X rays are emitted during atomic processes involving energetic electrons. Gamma radiation is emitted by excited nuclei or other processes involving subatomic particles; it often accompanies alpha or beta radiation, as a nucleus emitting those particles may be left in an excited (higher-energy) state.

Gamma Rays

• Gamma rays are more penetrating than either alpha or beta radiation, but less ionizing. Gamma rays from nuclear fallout would probably cause the largest number of casualties in the event of the use of nuclear weapons in a nuclear war. They produce damage similar to that caused by X-rays such as burns, cancer, and genetic mutations.

Q1: which types of decay ?