Looking Inside The Atom Flashcards
Rutherford scattering experiment?
- alpha particle fired amd thin gold foil
- most went straight through so atom is mostly empty space
- some were deflected through large angles so centre must be positive to repel them
- very few scattered more than 90 degrees so nucleus must be tiny but more massive than the alpha particle
- most of mass must be in nucleus as fast particle still deflected
How to calculate distance of closest approach?
-refelcts when epe is equal to ke so
Initial K.E=electrical potential energy=kq(alpha)Q(gold)/r
-r is distance of closest approach ie distance from nucleus
How to find charge of nucleus
-proton has same charge as e
-So no of protons x charge of e
-
What is the charge of an alpha particle?
+2e
What is a hadron?
- Particles that have strong interactions
- reason protons and neutrons are held when they repel
- made up of quarks
What are two hadrons and how do they differ?
- Proton a stable hadron
- neutron is a unstable hadrom that decays into a proton caused by the weak interaction when not in the nucleus
- reaction is n ~> proton + electrom +antineutrino
- neutrons not in the nucleus have a half life of 15 mins
Whats a lepton
-Particle that interact via the weak interactions and gravity
What 2 leptons od we need to know?
- electrons (-1 charge)
- neutrinos (0 charge 0 mass) symbol of v (but curvy), neutrinos only experience the weak interaction
What is lepton number?
-number of leptons, electrosn and neutrinos is 1
Always conserved
What is an antiparticle?
A corresponding particle w same mass but opposite charge
What happens when energy is converted to mass
- equal amounts of matter and anti matter
- this is called pair production
- draw diagrams and check them in book
When does pair production happen?
- when one photon has enough energy to produce that mass
- near a nucleus to ocnserve moentum
- usually get low mass particle
- calculate minimum energy using Erest=mc^2
- draw squiggly line into two curved lines of opposite particle
What is annihilation?
- particle and antiparticle meet
- total mass converted to energy forming pair of identical photons
- use Ephoton=mc^2 to calculate the min energy of photons
What are we assuming as negligible in annihilation?
Kinetic energy
How long do amtiparticles exist for?
Fraction of a secomd so quickly anihilate after pai creation
What are fundamental particles?
Quarks
What quarks do we need to know?
- Up quark, symbol u, charge +2/3
- down quark,symbol d, charge -1/3
- also there anti quarks
What quarks make a proton?
uud
=+2/3 +2/3 -1/3
What quarks make a neutron?
udd
= +2/3 -1/3 -1/3
What happens when u try sepertae quarks with lots of energy?
Energy transfeered to mass so pair production
Each one of the 4 fundamental forces in nature has its own….
Gauge bosons (exchange particles when they interact)
What is the gauge boson that causes the strong interaction and how does it cause pair creation?
Gluon
Causes strong foce in hadrons (protons and neutrons)
-when quarks in hadrons are pulled apart the energy in gluon field increases until a quark + anti quark pair is produced
How does a linear particle accelerator work?
- long straight tube of electrodes
- connected to alternating pd supply so charge of electrode keeps changes from + to -
- timed so particles always attracted to the next electrode and reppeled from current ome
- speed increases each time so can approach speed of light
- collide w fixed target at end of tube
Whats a synchrotrons?
-circular accelerator w two beams in opposite directions so can produce very high energy collisions
