N-Z graphs

Question 1

How can nuclear stability be surveyed?

Answer 1

• graph of neutron number against the proton number

Question 2

Where a stable nuclei found?

Answer 2

lie along a belt curving upwater with an increasing neutron-proton ratio

Question 3

Where are the: alpha emitters, stable nuclei, beta minus emitter, and beta plus emitters found on a N-Z graph?

Answer 3

• stable
  
  • belt curiving upwards
• alpha emitters
  
  • above stable nuclei belt
  • heavy nuclei
• beta minus
  
  • above stable nuclei belt
  • lower in the graph
  • neutron rich nucleus
• beta plus
  
  • below stable nuclei belt
  • proton rich nucleus

Question 4

What happens for light isotopes (Z=0-20)

Answer 4

• nuclei follow straight line
  
  • N=Z
• equal numbers of protons and neutrons

Question 5

What happens as Z increases beyond 20?

Answer 5

• stable nuclei have more neutrons than protons
• the neutron/proton ratio increases

Question 6

Why does the neutron/proton ratio increase?

Answer 6

• extra neutrons help to bind the nucleons together without introducing repulsive electrostatic forces as more protons do

Question 7

Where are alpha emitters found? How do they occur?

Answer 7

• Occur beyond about Z=60
• most have more than 80 protons and 120 neutrons
• they are too large to be stable
  
  • SNF unable to overcome electrostatic repulsion between the protons

Question 8

Where are beta minus emitters found? WHy does this occur?

Answer 8

• left of the stability belt
• isotopes are neutron-rich compared to stable isotopes
• neutron rich isotopes become stable or less unstable by converting a neutron into a proton and emitting a beta minus particle (and an electron antineutrino) at the same time

Question 9

Where are beta plus emitter found? Why does this occur?

Answer 9

• occur to the right of the stability belt where the isotopes are proton-rich compared to stable isotopes
• proton-rich isotopes become less unstable by converting a proton into a neutron and releasing a beta plus particle and an electron neutrino at the same time
• electron capture also takes place in this region

Question 10

How are the different decay represented on a N-Z graph?

Answer 10

• alpha
  
  • loses two protons and two neutrons
  • moves diagnoally downwards to the left across two grid swuared
• beta minus
  
  • loses nuetron and gains a proton
  • moves diagonally downwards to the right across one square
• beta plus or electron captures
  
  • loses a proton and gains a neutron
  • moves diagnoally upwards to the left across one grid square

Question 11

How does alpha decay lead to a more stable nuclei? If the nucleus is unstable when would it release the other types of radiation? (radioactive series)

Answer 11

• when emitted the N-Z plot moves downards parallel to the N=Z line
• greater neutron-proton ratio
• would release another beta minus if its position is left of the stability belt vice versa
  
  • neutron rich nucleus may release beta minus, which will cause it to lie closer to the stability belt