Nuclear and Particles Physics

Name

Definition

Notes

Nucleon/ mass
number

Number of nucleons in the nucleus

Proton/ atomic
number

Number of protons in the nucleus

Thermionic
Emission

A metal is heated
Free electron gain KE
KE > Φ the electron escape from the metal surface
(how charged particles produced for use in particles accelerator)

RUTHERFORD SCATTERING

Rutherford’s
Scattering

Fire a beam of alpha particles at a very thin sheet of gold
Count the number of α particles scattered at different angles

Results

Most go straight through θ ~ 0°
Some α particles will be deflected by large angles (θ ~ 90°)
A few α particles reflected/ go straight back (θ ~ 180°)

Conclusion

The atom is mostly empty
All the positive charges and most of the mass is contained in a very small region

Reasons

Most does not get near enough to any matter to be affected Some came close enough to the charge to be affected A few deflected so nucleus must have mass much greater than the alpha particle mass to cause this deflection

PARTICLE PHYSICS

Particle Physics

Antiparticles

For every particle that is an identical particle with opposite electric charge called its antiparticles When a particle meets its own antiparticle, they annihilate, the energy released makes new particles

Investigate
Nucleons
Structure

De Broglie:

$lambda =frac{h}{p}$

To look at small distance λ must be small
So p must be large
So E must be large $E^{2}=p^{2}c^{2}+m^{2}c^{4}$

If p >> mc

E=pc

FUNDAMENTAL: not made out of other particles

Leptons

Electron	Electron neutrino	1st gen	Have a Leptons
$e^{-}$	$v_{e}$	1st gen
Muon	Muon neutrino	2nd gen
$mu^{-}$	$v_{mu }$	2nd gen
Tau	Tau neutrino	3rd gen
$tau^{-}$	$v_{tau }$	3rd gen

Quarks

Up	Down	1st gen
$u^+{frac{2}{3}}$	$d^-{frac{1}{3}}$	1st gen
Charm	Strange	2nd gen
$c^+{frac{2}{3}}$	$s^-{frac{1}{3}}$	2nd gen
Top	Bottom	3rd gen
$t^+{frac{2}{3}}$	$b^-{frac{1}{3}}$	3rd gen

HADRON

Baryons

Proton	Neutron		Contains 3 quarks Baryon number = +1
$p^{+}$	$Pi ^{o}$		Contains 3 quarks Baryon number = +1

Mesons

Pions			Contain 1 quark + 1antiquark
$Pi ^{+}$	$Pi ^{o}$	$Pi ^{-}$

BOSON

Gauge Bosons

When particles interact, they are affected by one of 4 possible
forces:

Gravity (Graviton): act on energy
Electromagnetism (Photon): charged particles
Strong force (Gluons): quarks
Weak force ( $W^{+},W^{-},Z^{o}$ ) log
In Newtonian physics, we describe these forces using fields
In quantum mechanics, the idea of fields is replaced by the transfer of particles called gauge bosons
We then call these interactions, instead of forces

Name	Definition	Notes
PARTICLES ACCELERATOR
LINACS
	When the next tube is positive the electron accelerates across the gap Inside each tube, the electron has constant v High-frequency supply ensure tube has the correct potential to accelerate the e
	As particles are accelerated by the E field between the tube their speed increase The AC frequency is constant So the time inside each tube must be a constant = ½ period of the AC So the tube must be longer when v↑ The tube will increase in length until the speed reach the speed of light (constant) then the tube lengths become constant
Cyclotron		$Bq=frac{mPi }{t}$ $T=frac{2Pi m}{Bq}$ $f=frac{Bq}{2Pi m}$
	The eaccelerate across the gap end with speed v Inside the dee, the e- move in a semi-circle Time inside the dee $t=frac{Pi r}{v}orfrac{v}{r}=frac{Pi }{t}$ so, $Bq=frac{mPi }{t}$
	E field produce a force Facing dee is always negative (for proton) Increases the KE of the particles across the gap $Delta E_{k}=qV$ B field causes the direction of the particles inside the Dees change
	Limitation: When v→ c, cyclotron stop accelerating particle Newton’s Law of motion don’t apply when v→c Radius of orbit ↑ as energy ↑ but v↓ constant, so time inside dee ↑ so frequency ↓
	Curvature Some particle tracks curve ‘clockwise’ others ‘anticlockwise’ Some have positive charge, some have negative charge Fleming’s left-hand rule tells us the sense of curvature
	Charge particles gain KE so p ↑ ∝ so r↑ The curvature decreases along the length
Synchrotron	Accelerate the particles with an electrical field Particle path is bent with a magnetic field Radius of path is constant As particle E↑, E field get stronger Because the particles are accelerating, they lose E by emitting radiation (synchrotron radiation)	Synchrotron vs Cyclotron The particles move in a circle As KE↑, B↑ to keep r constant
Bubble Chamber	The magnetic field causes the track to bend Uncharged particles leave no track
	Electric field: Accelerate particle Direction of force indicates sign of charge $a=frac{EQ}{m}$ Magnetic field: Circular motion Direction of curvature indicates sign of charge $r=frac{mv}{Bq}$
	Only moving charged particles leave a track Pion are charged so leave a track Pion interact with a stationary charged particle 2 neutral particles created (because no track) to conserve charge Track in different direction so momentum conserved Both particles decayed into opposite charged particle because charge is conserved At all collision momentum and charge are conserved
Fixed target	Ad: lots of collision Dis: There’s momentum before collision so momentum after collision Particles created must have KE So not all KE converted into mass Not many particles are created and their masses are not very big
Colliding beams	Ad: Final = 0 so final KE is small All energy goes into making new particle →can make new massive particles Dis: Not many collisions