Physics Particles

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1 Matter And Radiation

1.1-Inside The Atom

1.2-Stable And Unstable Nuclei


1.4-Particles And Antiparticles

1.5-How Particles Interact

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1.1 Inside the atom

Positively charged nucleus made from protons and neutrons (nucleon/mass number)

Electrons surround nucleus

electrons held near nucleus by electrostatic force

Electron mass: 9.11x10^-31kg,  proton mass: 1.67x10^-27kg,  neutron mass: 1.67x10^-27kg

Electron charge: -1.6x10^-19c, proton charge: 1.6x10^-19c, neutron charge: 0c

Isotopes: same number of protons, diffrent number of neutrons

Specific charge=Charge of nucleus/mass of nucleus

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1.2 Stable and Unstable Nuclei

Strong Nuclear Force is the force that holds stable nuclei together

SNF has a very short range: 3-4fm

SNF keeps nucleons together but separate

Radioactive Decay

there are three types of radioactive decay:Alpha, Beta,Gamma

Alpha is 2 protons and 2 neutrons and is a particle

Beta is an electron or positron being emitted due to a proton changing into a neutron or vice versa.

gamma is electromagnetic radiation. it has no mass or charge. it is emitted following alpha or beta emission.

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1.3 Photons

Travel at speed of light (3x10^8ms-1)

Wavelength=Speed of light/frequency (λ=c/f)

Electromagnetic waves emitted when electron stops or moves to different atom energy level

Emitted as short bursts called photons

Energy of a photon=Planck constant x frequency


Planck Constant= 6.63x10^-34Js

Power of laser beam=NHF

N= number of photons passing a fixed point per second

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1.4 Particles and antiparticles


When a particle and its corresponding antiparticle meet they annihilate each other and produce 2 gamma ray photons.

The particle and the antiparticle have the same rest mass but opposite charges

Pair production= photon>>>particle and antiparticle (which then separate)



Rest energy (E)= Mass of (anti)particle (M) x Speed of light^2 (c^2)      E=MC^2

Minimum energy of each photon produced in annihilation (hfmin) = Rest energy (E0)

Minimum energy of photon needed during pair production (hfmin) =2xRest Energy (2E0)

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1.5 How particles Interact

Weak nuclear force is responsible for beta decay.

Neutron > Proton + Beta- + Anti-Neutrino        (W- boson exchanged)

Proton > Neutron + Beta+ + Neutrino               (W+ boson exchanged)

Neutrino + Neutron > Proton + Beta-                (W- boson exchanged)

Anti-neutrino + Proton > Neutron + Beta+        (W+ boson exchanged)

Proton + electron > Neutron + Neutrino           (W+ boson exchanged)

W boson Exchanged

W boson has non-zero rest mass, very short range, positively or negatively charged

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