7. Nuclear Properties Flashcards
Who invented the Plum Pudding Model?
JJ Thompson
Describe the plum pudding model
Tiny negatively charged electrons are spread through the atom, which must be positively charged since overall the atom is neutral. The atom is seen as a positively charged diffuse sphere of matter with electrons embedded in it.
Who first carried out Rutherford scattering?
Geiger and Marsden under Rutherford
Describe the process of Rutherford scattering
Alpha particles were fired at gold film. It was found that a small number of particles underwent large scattering angles (which is very unlikely in the plum pudding model).
What did Rutherford propose for the structure of the atom?
The planetary model of the atom. He proposed that atoms have a small positively charged core which contain most of the atomic mass.
Rutherford scattering is often regarded as the _____ __ ________ ________.
Birth of nuclear physics.
What assumptions are required to calculate the Rutherford cross section?
- There is a Coulomb interaction between the alpha particle and the nucleus.
- Scattering is elastic.
- The target is thin enough to only consider single scattering.
What is the electric charge of a proton?
+1e
What is the mass of a proton?
1.6726 x 10^-27 kg (0.9383 GeV/c^2)
What is the spin of a proton?
1/2
What is the electric charge of a neutron?
0
What is the mass of a neutron?
1.6749 x 10^-27 kg (0.9383 GeV/c^2)
What is the spin of a neutron?
1/2
What is the parity operation?
An operator that reflects all spatial coordinates through the origin.
A physical property has _____ parity if it is invariant under the parity operation.
Even
A physical property has ____ parity if it changes sign under the parity operation.
Odd
Does a scalar property like temperature have odd or even parity?
Even: scalar quantities have no direction so are not impacted by the parity operation.
Does a vector property like velocity have odd or even parity?
Odd
Describe the signs of a wave function with even parity
Describe the signs of a wave function with odd parity
What determines whether or not a wavefunction has odd or even parity?
Whether or not it is symmetric
State the parity operator
Parity is ______ for particles because they are said to have ‘__________’ parity, so are either odd (-) or even (+).
Fixed
Intrinsic
Particles with half-integer spins (fermions) have ________ parity to their anti-particles.
Opposite
Particles with integer spins (bosons) have ___ _____ parity to their anti-particles.
The same
The parity of two or more particles (a composite system) is given by the algebraic product of the ___________ _________ and an __________ _________ _____.
Individual parities
Angular momentum term
Give the equation for the parity of 2 or more particles
P1, P2 = intrinsic parities
l = angular momentum
Which two forces do not violate parity?
- Strong nuclear force
- Electromagnetic interactions
Which force does violate parity?
- Weak nuclear force (which involves beta decay)
Why does beta emission violate parity?
Because a beta emission is preferentially in the direction opposite the nuclear spin.
Give the classical equation for magnetic moment
µ = magnetic moment
e = electron charge
r = radius
v = speed
m = electron mass
l = angular momentum
Give the quantum equation for magnetic moment
µ = magnetic moment
e = electron charge
m = electron mass
l = angular momentum
What is the Bohr magneton?
µ_B = Bohr magneton
e = electron charge
m_e = electron mass
What is the nuclear magneton?
µ_N = nuclear magneton
e = electron charge
m_p = proton mass
What is the magnetic moment for protons and neutrons? (In terms of angular momentum)
µ = magnetic moment
g_l = orbital angular momentum g-factor (=1 for protons and =0 for neutrons)
l = angular momentum
µ_N = nuclear magneton
Protons and neutrons have _________ _____ which also includes a magnetic moment.
Intrinsic spin
What is the magnetic moment for protons and neutrons? (In terms of spin)
µ = magnetic moment
g_s = spin g-factor
s = spin (=1/2 for protons and neutrons)
µ_N = nuclear magneton
What is the EXPECTED spin g-factor for protons and neutrons?
Neutrons: zero
Protons (and other spin 1/2 point particles): 2
What is the spin g-factor for electrons?
-2.0023193043
What is the spin g-factor for protons?
5.5856912
What is the spin g-factor for neutrons?
-3.8260837
What parity do protons have?
Even
What parity do neutrons have?
Even
Is a proton stable or unstable?
Very stable
Is a free neutron stable or unstable?
Unstable
Is the observed g-factor the same as expected for point particles?
No
