Nuclear Process

Question 1

How does the process of atom splitting ‘fission’ produce energy? (3)

Answer 1

• nuclear fission: the splitting of a large nucleus into smaller ones with the release of energy.
• energy is released because the sum of the masses of these fragments is less than the original mass.
• the missing mass (around 0.1% of the original mass) has been converted to energy.

Question 2

Properties of nucleus (2)

Answer 2

• small size ( r = 1 x 10^-3 cm)
• large density (1.6 x 10^14 g/cm^3)

Question 3

Uranium

Answer 3

draw isotope change

Question 4

only certain atoms can undergo fission reactions, what does this depend on?

Answer 4

a - nucleus size
b - # of protons and neutrons
c - the energy and speed of the neutron used to initiate the fission

• not all isotopes can undergo fission, U-238 cannot

Question 5

Chain reactions (2)

Answer 5

-the produced neutrons can initiate further fission reactions
-nuclear power-plants provide controlled chain reactions

Question 6

energy released formula

Answer 6

E=mc^2

Question 7

Balancing nuclear reactions (2)

Answer 7

• each nuclide should include atomic number (charge) as subscript and mass number (neutrons + protons) as superscript
  -mass number and atomic number on right must = mass and atomic number on left.

Question 8

E=mc^2 (4)

Answer 8

E: equivalence of energy (joules)
m: mass (kg)
c: speed of light. (3.0 x 10^8 m/s)
- large c^2 value means it is possible to obtain a large amount of energy from a small amount of mater.

Question 9

stopping nuclear fission

Answer 9

using a cadmium rods (excellent neutron absorber) placed between fuel rods to redirect neutrons elsewhere and stop the reaction.

Question 10

Radioactivity

Answer 10

• the spontaneous emission of radiation by certain elements.

Question 11

Alpha radiation (3)

Answer 11

• consists of nucleus of helium atom (2 protons, 2 neutrons).
  -no electrons to accompany nucleus so it has a 2+ charge
• heavier than electron

Question 12

Beta radiation (3)

Answer 12

• High speed electron
• (-)ve charge
• mass 1/2000 of proton or neutron

Question 13

Gamma radiation (5)

Answer 13

• accompany emission of alpha and beta particles
• not a particle like alpha and beta but an energy
• high energy, short wavelength photons
• part of electromagnetic spectrum, like UV
• no charge and no mass

Question 14

Radioactive decay (4)

Answer 14

• an atom may emit an alpha or beta particle
• can lead to a change in the atomic/ mass # or both
• this is a change in identity
• sometimes the new atom formed is still radioactive, can emit particles and decay to form another element.

Question 15

Radioactive decay series (2)

Answer 15

• Radioactive isotopes undergo decay until it reaches a stable species
• all isotopes of all elements with atomic number 84 and higher are radioactive.

Question 16

How is an electron (beta particle) emitted from a nucleus? (5)

Answer 16

• no electron exists in the nucleus
• a neutron has no charge, therefore assume that it has a proton and an electron which cancel each-other out and cause the neutral charge.
• If a neutron breaks down into an electron and proton, then a loss of electron (beta particle) can occur.

1 1 0
n —–> p + e
0 1 -1

Question 16

Each radioactive atom / element: (4)

Answer 16

• decay until reaching stable atom
• decay occurs in a specific time period, and is characteristic of the starting atom
• important to know for storage and disposable (dictates how much is still present and poses a hazard)
• whether an atom (isotope) is radioactive or not depends on neutron to proton ratio in the nucleus.

Question 17

Half-life

Answer 17

• time / period of decay, OR time required for level of radioactivity to fall to one half of its value.