Atom Structure and Decay Equations

Question 1

What is the relative and normal charge and mass of a proton?

Answer 1

• Charge: 1.6x10^-19
• Mass: 1.673x10^-27
• Relative Charge: +1
• Relative Mass: +1

Question 2

What is the relative and normal charge and mass of a neutron?

Answer 2

• Charge: 0
• Mass: 1.675x10^-27
• Relative Charge: 0
• Relative Mass: +1

Question 2

What is the relative and normal charge and mass of an electron?

Answer 2

• Charge: -1.6x10^-19
• Mass: 9.11x10^-31
• Relative Charge: -1
• Relative Mass: 1/2000 (negligible)

Question 3

How do you calculate Specific Charge of an ion and what are its units?

Answer 3

• Equation: Charge/Mass = Total number of electrons added / removed × (1.60 × 10^-19 C) / Total number of nucleons × (1.67 × 10^-27 kg)
• Units: Coulombs per kg (C kg^-1)

Question 3

How do you calculate Specific Charge of a nucleus and what are its units?

Answer 3

• Equation: Charge/Mass = Total charge of protons × (1.60 × 10^-19 C) / Total number of nucleons × (1.67 × 10^-27 kg)
• Units: Coulombs per kg (C kg^-1)

Question 4

What is an isotope?

Answer 4

• An atom (of the same element) that has an equal number of protons but a different number of neutrons

Question 5

Why are isotopes unstable atoms?

Answer 5

• Since isotopes have an imbalance of neutrons and protons, they are unstable (charge isn’t only thing that causes stability/instability in atom, mass does too)
• This means they constantly decay and emit radiation to achieve a more stable form, which can happen from anywhere between a few nanoseconds to 100,000 years

Question 6

What is isotopic data?

Answer 6

• The relative amounts of different isotopes of an element found within a substance
• Isotopic data is often used for determining the age of archaeological findings and is used in radioactive dating

Question 7

What is an example of use of isotopic data?

Answer 7

• Carbon–14 is present in all living beings and undergoes radioactive decay
• When a plant or animal dies, the natural decay of this isotope means the concentration of the carbon–14 in its tissue gradually reduces
• Carbon–14 has a long half-life of around 6000 years, the half-life can be used to determine the age of the plant or animal when it died

Question 8

What is a strong nuclear force?

Answer 8

• Electrostatic repulsion forces protons in nucleus apart
• Gravitational forces due to their mass too weak to keep them together
• Strong nuclear force holds all nucleons together since both protons and neutrons are made up of quarks.

Question 9

What is the range of a strong nuclear force?

Answer 9

• Repulsive below 0.5 fm
• Attractive up till 3.0 fm
• Maximum attraction at 1.0 fm (typical nuclear separation
• Becomes 0 after 3.0 fm
• Has small range compared to other fundamental forces (only up to 3.0 fm)

Question 10

What is alpha decay?

Answer 10

• Common in large, unstable nuclei with too many protons
• Involves nucleus emitting alpha particle (2 protons and 2 neutrons)
• Proton number decreases by 2
• Nucleon number decreases by 4

Question 11

What is beta minus decay?

Answer 11

• β- particle is a high energy electron emitted from the nucleus
• neutron turns into a proton emitting an electron and an anti-neutrino
• Proton number increases by 1
• Nucleon number stays same

Question 12

What is beta plus decay?

Answer 12

• β+ particle is a high energy positron emitted from the nucleus
• Proton turns into a neutron and a positron (anti-electron) and a neutrino
• Proton number decreases by 1
• Nucleon number stays same

Question 13

What is a neutrino?

Answer 13

• Type of subatomic particle with no charge and negligible mass which is also emitted from the nucleus
• its existence was hypothesised to account for the conservation of energy in beta decay

Question 14

What is antimatter?

Answer 14

• Antimatter particles are identical to their matter counterpart but with the opposite charge
• Still have identical mass and rest mass-energy (Rest mass-energy of a particle is the energy equivalent to the mass of the particle at rest)

Question 15

What is annihilation?

Answer 15

• When a particle meets its equivalent anti–particle they both are destroyed and their mass is converted into energy in the form of two gamma ray photons
• The minimum energy of one photon after annihilation is the total rest mass energy of one of the particles
• To conserve momentum photons move in opposite directions
• Mass and energy still conserved (as with all collisions)

Question 16

What is equation in annihilation?

Answer 16

• E (minimum energy of photon) = h (planck’s constant = 6.63x10^-34) x f (frequency)

Question 17

What is pair production?

Answer 17

• When a photon interacts with a nucleus or atom and the energy of the photon is used to create a particle–antiparticle pair (opposite of annihilation)
• Means the energy of the photon must be above a certain value to provide the total rest mass energy of the particle and antiparticle pair
• Minimum energy for a photon to undergo pair production is the total rest mass energy of the particles produced
• To conserve momentum, the particle and anti–particle pair move apart in opposite directions

Question 18

How do you work out frequency?

Answer 18

• Frequency = wave speed / wavelength
• Wave speed is equal to speed of light (3x10^8) for gamma ray photons

Question 19

What does 1 electron volt equal?

Answer 19

• 1.6x10^-19
• So 1 Mev = 1.6x10^-13