Sin título

Página 1

The constituents of the atom are protons, neutrons and electrons. Protons+Neutrons=Nucleons, found in the nucleus of atoms.

The nucleus is surrounded by empty space in which there are electrons.

Specific Charge

SC=Q/M

SC=CKg^-1

Stable and unstable NUclei

4 Fundamental forces:

1.) Gravity

2.) Electromagnetic Force

3.)Strong Nuclear Force

4.) Weak Nuclear Force

The protons in a nucleus are all positively charged so repel each other (electromagnetic force in action). This should push the protons apart, but doesn't, so there must be another force which keeps the nucleus together; the STRONG NUCLEAR FORCE

STRONG NUCLEAR FORCE

Holds nucleons together in the nucleus.

HADRONS experience it, but LEPTONS do not.

Acts over a VERY SHORT RANGE, can be both ATTRACTIVE and REPULSIVE.

Causes a short range ATTRACTION between adjacent nucleons, UP TO A DISTANCE OF 3FEMTOMETERS.

Causes a very short range REPULSION BELOW 0.5 FEMTOMETERS.

STABLE AND UNSTABLE NUCLEI

BISMUTH-Proton Num-83- the stable nuclei with the highest number of protons. All nuclei with proton numbers above 83=unstable=RADIOACTIVE.

Radioactive elements emit:

1.) Alpha Particle-2 protons, 2 neutrons (He Nucleus)

2.) Beta Particle-High speed electron

3.) Gamma Rays- A photon.

Particle interactions!

To explain the forces between particles, we use the concept of exchange particles/Bosons.

Página 2

the protons in a nucleus all have the same positive charge, so repel each other (electromagnetic force). This should push the protons apart, but doesn't. Therefore, there must be another force keeping the NUCLEUS together; THE STRONG NUCLEAR FORCE.

Holds nucleons together in the nucleus.

Hadrons experience it, but not leptons.

V.short range attraction or repulsion.

causes a short range attraction between adjacent nucleons, up to a distance of 3 femtometers.

Causes a v.short range repulsion below 0.5 femtometers.

Página 3

An anti-neutrino is emitted in beta- decay., which is the antiparticle of the neutrino. These particles have no charge, almost zero mass.

Gamma Radiation

When a nuclide emits a photon of electromagnetic radiation, it is called a gamma ray.

Pair production and annihilation

When a particle and its antiparticle meet each other, they annihilate each other. Their mass is converted into energy in the form of photons.

This can also work the other way around, with energy being converted into mass.

High energy photons can produce a [article and its antiparticle; this is called pair production.

E.g. A gamma photon with enough energy can produce an electron and a positron.

Photons

Electromagnetic radiation (Like gamma rays, x-rays, and visible light, etc.) have wave properties and can also behave as particles, which are called photons.