2. Mass Measurements

Question 1

Describe the basics of a deflection spectrometer

Answer 1

Have an acceleration source
Particles pass through a velocity selector
Then go into the mass separation sector where you can calculate the mass dependent on the curvature

Question 2

How can we select the velocity of the particles by using the velocity selector in the deflection spectrometer?

Answer 2

The electric field and magnetic field forces act in opposite directions
F_E - F_B = q(E-vB) = 0
v = E/B from the ratio fo the fields

Question 3

What is the equation to calculate the radius of the curvature of the particles in the mass separation analyser in the deflection spectrometer?

Answer 3

r = mv/qB

Question 4

When are deflection spectrometers not useful/practical?

Answer 4

For short lived nuclei

Question 5

How does kinematic analysis work?

Answer 5

Exploting the energy momentum conservation

Question 6

Explain the general form of a particle equation in kinematic analysis

Answer 6

a + A -> b + B
a - projectile
A - Target nucleus 
b - probe to measure
B - Unknown nucleus

Question 7

What do we define the change in energy to be for kinematic analysis

Answer 7

ΔE = (m_B - m_A)c^2

Question 8

Explain the end result of kinematic anaylsis

Answer 8

Have a quadratic equation in m_B

• Solve via numerical methods and iteration
• Starting initial guess is m_B = A_B * u
• Repeat until convergence

Question 9

Briefly describe how Penning traps work?

Answer 9

Uses electric and magnetic fields to confine a particle

- Moves in a specific motion

Question 10

How does the magnetic field confine a particle in the Penning trap?

Answer 10

Confines its radial direction in an x-y plane

- Charge moves in a circular path

Question 11

How does the electric field confine a particle in the Penning trap?

Answer 11

Confines it in the z direction

Question 12

What three things does the motion of the charge inside the Penning trap depend on

Answer 12

1. Harmonic motion along the direction of the magnetic field
2. Perpendicular to the magnetic field, cyclotron motion
3. Perpendicular to the magnetic field, magnetron motion in and out of the trap

Question 13

How is the mass of a particle determined when using Penning traps?

Answer 13

Via the frequencies, w = qB/m

Question 14

How is the precision of a mass measurement using Penning traps obtained?

Answer 14

By comparing the calculated mass to a known ion to measure the mass difference
Δm/m = 10^-8 -> very precise

Question 15

What do we mean by a non-destructive Penning trap?

Answer 15

When we just have an induced EM field

Question 16

What do we mean by a destructive Penning trap?

Answer 16

Where the trap is opened and ions can escape

- Energy of circular motion is transferred to longitudinal motion (use time of flight)

Question 17

Define Binding energy

Answer 17

The energy needed to take the constituents of a nucleus apart

Question 18

How is the mass defecit of an atom calculated?

Answer 18

Subtract the mass of the nucleus by the mass of the individual protons and neutrons

Question 19

Give the equation for binding energy, and what sign does it have in nuclear physics?

Answer 19

BE = -ΔM(Z,A)c^2

- Mass defecit multiplied by c^2. Positive in nuclear physics