Particles

2.1.1 Some definitions:

Atoms are made of protons, neutrons and electrons. Protons and electrons are in the nucleus of the atom and electrons orbit the nucleus. 

Nucleon: term used for protons and neutrons.

In a neutral atom number of protons equals the number of electrons.

Ion: when an atom loses (positive ion) or gains (negative ion) electrons. 

Isotope: atom of an element with different number of neutrons, but same number of protons.

Specific charge =  ; unit: C/kg

Atomic Mass Unit (u): 1/12 of mass of an atom of carbon-12 (). So “u” of carbon-12 is 12!

Mass of a proton ≈ mass of a neutron ≈ 1 u (≈ : almost equal)

The “atomic mass unit” of all nuclei ≈ nucleon number.

Nuclei: plural of nucleus! 

Fundamental Forces:

1. Electromagnetic force: keeps electrons in orbit, intermolecular bonds, repulsion or attraction between charged particles, friction, drag, tension in a rope are all electromagnetic too, it has infinite range;
2. Gravity: attractive force between all masses, infinite range;
3. Strong nuclear force: holds nucleons in a nucleus together, attractive from 3 fm to 0.5 fm; repulsive below 0.5 fm;
4. Weak nuclear force: affects all particles, range of order 10^-18 m, responsible for nuclear reactions. 

Strong nuclear force: force that holds protons together, otherwise the protons would repel each other because of the electrostatic force.

It is attractive from 3 fm to 0.5 fm

It is repulsive below 0.5 fm. (f: femto = 10^-15), otherwise protons would crush into each other.

Strong nuclear force acts between any two nucleons. 

Electron-volt (eV): small unit of energy used in nuclear physics instead of Jules.

1 eV = energy needed to move an electron in PD of 1 volt.

Radiation:

Elements such as uranium, thorium, and radium have unstable nuclei and emit radiation. 

Radiation:

1. Alpha (α): 2 protons + 2 neutrons short range in air (few of cm), can be stopped with a paper, highly ionising, happens in a nucleus with too many protons & neutrons;
2. Beta minus (β^-): an electron, range of several meters in air, can pass through paper or think plastic, happens when a neutron in the nucleus changes to a proton and electron, then the electron is emitted at high speed; 
3. Beta plus (β⁺): anti particle of electron, called positron. Happens when a proton in the nucleus changes to a neutron and positron, then the positron is emitted at high speed;
4. Gamma (γ): electromagnetic radiation (photon), no charge, no mass, highly penetrative, ionising power less than that of alpha and beta. A photon is produced when a charged particle loses energy such as an electron falling to lower energy orbit (closer to the nucleus).
5. Neutron: itself can be emitted from a neutron rich nucleus. It is highly ionising too!