particle

Question 1

rutherfords alpha scattering experiment

- how does it work?

Answer 1

• narrow beam of α particle with same KE
  from a radioactive source
• incident on gold foil (few atomic layers thick)
• α particles scattered by foil
• detected by zinc sulphide screen mounted on a microscope
• microscope was moved around to count no. of α particles scattered at diff angles per minute from 0 to ~ 180

Question 2

alpha scattering experiment

observations

Answer 2

1. Most particles passed straight through golf foil with no scattering
   —> 1/200 particles scattered
2. very few particles were deflected through angles more than 90*

Question 3

alpha scattering experiment

conclusions

Answer 3

1. atoms mostly “empty space” with mass concentrated in the centre (nucleus)
2. nucleus has positive charge —> repelled few +ve α partcles were repelled

Question 4

nucleon number(A) ?

Answer 4

total no. protons + neutrons

Question 5

radius of a nucleus?

Answer 5

R = r₀A^1/3

r₀ has value of about 1.2fm

roughly the radius of a proton

Question 6

what is the average density of a nucleus?

Answer 6

10¹⁷ kg/m³

Question 7

what is tbe average density of an atom?

Answer 7

10³ kg/m³

Question 8

what is the strong nulear force?

Answer 8

holds nuclei together

acts on hadrons

Question 9

why is the strong nuclear force need

Answer 9

using F= Qq / 4πε₀ r²

the electrostatic repulsion between two protons is ≈ 230N

yet, the gravitational attraction is far too small to keep the protons together
(≈ 10^-34)

so another force must be acting

Question 10

what is r₀ ?

Answer 10

roughly the radius of a proton

1.2fm

Question 11

what is the nature of the strong nuclear force?

Answer 11

it is very short ranged

attractive only from 0.3fm to about 3fm
below 0.3 fm it is repulsive

graph to show:

Question 12

what are the 4 fundamental forces

Answer 12

strong nuclear

weak nuclear

gravitational

electromagnetuc

Question 13

what are the relative strengths of the 4 fundamental forces

Answer 13

strong nuclear 1

electromagnetic 10^-3

weak nuclear 10^-6

gravitational 10^-40

Question 14

what are the ranges of the 4 fundamental forces?

Answer 14

strong nuclear ~ 10^-15m

electromagnetic - infinite

weak nuclear ~ 10^-18

gravitational - infinite

Question 15

what are HADRONS

Answer 15

particles/antiparticles that are effected by
- strong nuclear force
AND
- weak nuclear

• if they are charged, the electromagnetic
• decay by the weak nuclear

Question 16

examples of hadrons?

Answer 16

protons

neutrons

mesons

Question 17

what are leptons?

Answer 17

particles/antiparticles
—> NOT AFFECTED by strong nuclear force
—> affected by weak nuclear force

Question 18

examples of leptons

Answer 18

electrons
neutrinos
muons

Question 19

what us an antiparticle

Answer 19

counter part of a particle
with the exact opposite physical properties
(charge…)
exact same rest mass

Question 20

what are mesons?

Answer 20

Hadrons made up of
—>two quarks

•has to be
—>quark + antiquark

Question 21

what are baryons?

Answer 21

hadrons made uo of
—> three quarks

•has to be either
—> three quarks
or
—> three antiquarks

Question 22

what is β- decay

Answer 22

when a neutron in an unstable nucleus decays into a proton electron and electron anti neutrino

Question 23

β- decay equation?

Answer 23

__
¹n —> ¹ p + e- + νe
⁰ ¹

Question 24

what is β+ decay?

Answer 24

a proton decays into:
• neutron
• positron
• electron neutrino

Question 25

β+ decay equation?

Answer 25

p —> n + e+ + νe

Question 26

quark transformation in β- decay?

Answer 26

in a proton the quark configuration if uud
in a neutron it is udd

so, one u quark decays into a d quark