MODULE 8 IQ 4

Question 1

radioactive decay definition

Answer 1

natural spontaneous reaction where an unstable nucleus of an atom attempts to become more stable by undergoing a nuclear configuration change

Question 2

alpha decay

Answer 2

excess energy is released in the form of KE in the products
- alpha particle is Helium-4 nucleus
- alpha decay will cause nuclear transmutation –> change composition of nucleus

Question 3

beta minus decay

Answer 3

• neutron inside nucleus is converted into a proton –> ejection of electron
• accompanied by electron antineutrinos

Question 4

beta plus decay

Answer 4

emits a positron (antiparticle of an electron) accompanied by a neutrino

Question 5

gamma decay

Answer 5

• not nuclear transmutation
• release of gamma rays in order to allow daughter nuclides to reach lower energy states

Question 6

the nucleus

Answer 6

• nucleus is a highly dense, concentrated, positive sphere –> nucleus would explode due to electrostatic repulsion (Coulomb’s law)

Question 7

strong nuclear force (SNF)

Answer 7

neutrons within nucleus provide SNF as proton number increases

Question 8

zone of stability

Answer 8

neutron to proton ratio determines the stability of the nucleus

Question 9

SNF properties

Answer 9

• short-range force: attractive, however at extremely small distances it also becomes repulsive
• mediated by gluons
• acts on nucleus regardless of the charge

Question 10

in neutron to proton ratio, when there are more protons…?

Answer 10

electrostatic repulsion > strong force

Question 11

in neutron to proton ratio, when there are more neutrons…?

Answer 11

repulsive strong nuclear force

Question 12

what is a half-life of an isotope

Answer 12

time taken for half of the amount to decay into a daughter nuclide
independent to:
- external factors
- only affected by nuclear interactions involving collisions with the nuclei themselves

Question 13

what is binding energy

Answer 13

the energy input to separate the nucleus into its constituent particles
energy + nucleus –> nucleons
m(nucleus) < m(nucleons)

Question 14

what is mass defect

Answer 14

difference in mass between the nucleus and the nucleons
Binding energy = ∆mc^2
∆m = mass defect

Question 15

stability of the nucleus

Answer 15

• increase of binding energy allows for more stability

Question 16

using Fe-56 to compare stability of the nucleus

Answer 16

fission:
- before Fe-56: exothermic –> spontaneous
- after Fe-56: endothermic –> non-spontaneous

fusion:
- towards Fe-56: exothermic
- past Fe-56: endothermic

Question 17

mass difference equation

Answer 17

∆m = m(reactants) - m(products)

Question 18

nuclear fission definition + important example

Answer 18

• any nuclear transmutation process where larger nuclei split up into lighter, smaller daughter nuclei
  235 1 131 92 1
  92 U + 0 n –> 56 Ba + 36 Kr + 3 0 n

Question 19

critical mass

Answer 19

not all of the neutrons produced in fission reactions induce further fission as they can easily be lost to the environment

Question 20

controlled chain reactions

Answer 20

for every 2 or 3 neutrons released, only 1 must be allowed to strike another uranium nucleus

Question 21

uncontrolled chain reactions

Answer 21

more than one further fission reaction is induced by neutrons emitted from fission

Question 22

nuclear power plant components

Answer 22

fuel rods, moderator, control rods

Question 23

fuel rods function

Answer 23

contain U-235, packaged in zirconium tubes

Question 24

moderator function

Answer 24

slows down neutrons to thermal speed to produce thermal neutrons, increasing percentage of fission, increasing efficiency
- slow neutrons are more likely to interact with the nucleus –> increases matter wavelength, increasing likeliness of interaction

Question 25

control rods function

Answer 25

keep the reaction controlled
- absorb excess neutrons
- generally made of Boron or Cadmium
- operated using gravity not electricity

Question 26

nuclear fusion definition

Answer 26

when 2 or more smaller nuclei combine to form a larger nuclei (occurs in stars)

Question 27

why is nuclear fusion not feasible as an energy source

Answer 27

the cost associated with producing the necessary conditions outweighs the amount of energy produce