Nuclear Physics

Question 1

What is an Isotope?

Answer 1

Different forms of the same element.
Same number of protons and electrons.
Different number of neutrons.

Question 2

What are three forms of Hydrogen isotope?

Answer 2

1/1 Hydrogen (1 proton, no neutron)
2/1 Deuterium (1 proton, 1 neutron)
3/1 Tritium (1 proton, 2 neutron)

Question 3

What are unstable nuclei?

Answer 3

Stability dependent on relative number proton/neutron
Unstable nucleus decay in several steps (decay chain) creating daughter nucleus.
Can take microseconds -> millions of years!

Question 4

What are unstable isotopes?

Answer 4

They are radioactive radioistopes:

• > Alpha (helium nucleus)
• > Beta minus (high speed electron)
• > Beta plus (high speed positron (positively charged anti-electron)
• > Gamma (electromagnetic wavelength 10X10-14m)

NB. Nucleus excited when particles emitted / decay, releasing gamma (excess energy).

Question 5

What is an N-Z curve?

Answer 5

• Determines how likely decay is
• Stability line: not radioactive / no decay.
• Above: + neutrons, beta minus, neutron ->proton, moves closer to stability.
• Below: + protons ->neutron, emitting positron.
• +82 protons = heavy elements; alpha decay (particle emitted), reduce 2 protons & 2 neutrons.

Question 6

What is alpha decay?

Answer 6

• Usually occurs with +82 protons (heavy elements)
• Unstable nuclide emits alpha particle (He 2p2n)
• Energy (Q) also released, KE of released particle.

Question 7

What is typical alpha decay?

Answer 7

Th 228/90 -> Ra 224/88 + He 4/2 + Q

Question 8

What is the top and bottom number before abbreviation?

Answer 8

Top: Mass. Bottom: Proton.

Question 9

What is beta minus decay?

Answer 9

• neutron-rich nuclei decay by beta minus emission
• high-seed electron ejected from nucleus (not cloud)
• formed by decay of neutrons.
• Proton number +1, new element formed.
• Neutron decays-> proton, emitting W- boson (exchange particle) from the nucleus which decays into ~electron & anti-electron neutrino~
• electron emitted from nucleus, thus is beta particle (b-) distinguishing from orbiting electrons

Question 10

What is a typical beta decay particle?

Answer 10

Al 29/13 -> Si 29/14 + e 0/1 + /ve 0/0 + Q

Question 11

What are neutrinos?

Answer 11

• Conform to conservation of energy principle
• Ghost like particle, difficult to detect.
• electron neutrino & anti-electron neutrino

Question 12

What are the four properties of neutrinos?

Answer 12

1. Interact weakly with other matter (pass through it)
2. No charge
3. Very very small mass
4. Interact via the weak nuclear force (and gravity)

Question 13

What is a Gamma Ray?

Answer 13

Alpha and beta particle emitted, nucleus is excited state, releasing excess energy in the form of a gamma ray.

Question 14

What do exchange particles do?

Answer 14

• transfer force
• transfer charge
• transfer momentum
• transfer energy

Question 15

How do electrons interact?

Answer 15

1. Send out virtual photons, hit and exert force on electrons, then return.
2. Other forces (gravity, strong/weak nuclear) behave similarly by transmitting via emitting virtual exchange particles.

Question 16

What is electron interaction called?

Answer 16

Electron-magnetic force

Question 17

What does a Feynman Diagram look like?

Answer 17

• Vertical direction represents time.
• Horizontal is space.
• Particles solid line in direction of travel
• Virtual particles, wavy and no direction
• Beta -decay emits W-, anti-electron neutrino & electron
• Beta +decay emits W+ (conservation of charge: proton -> neutron).
• W+ change in quark, from proton to neutron (up to down)
• W- change in quark, from neutron to proton (down to up)
• W+/W- are exchange particles, bosons.