Module 6 - 6.4.3 Radioactivity

Question 1

Activity (definition)

Answer 1

Number of nuclear decays per unit time

Question 2

Decay Constant (definition)

Answer 2

Probability of a decay per unit time

Question 3

Unstable nuclei will undergo radioactive decay in order to

Answer 3

become more stable

Question 4

Half Life (definition)

Answer 4

The mean time taken for the activity of a source or the number of undecayed nuclei present to halve

Question 5

Carbon Dating (5)

Answer 5

• whilst a tree is living, it takes in CO2 from the atmosphere
• the vast majority of the carbon is C-12 which is not radioactive but a small fraction is the radioactive isotope C-14
• once the tree dies, no more C-14 will be absorbed and the C-14 in the wood undergoes radioactive decay
• the ratio of C-14 to C-12 in dead organic matter decreases with time
• the ratio of activity in a dead organic sample compared to a living sample can be used for dating

Question 6

Radioactive Penetration: Alpha (3)

Answer 6

• to become an atom, it only needs to add 2 electrons
• electrons are easily attracted to the positive nuclei so easy to become an atom
• highly ionising and so least penetrating

Question 7

Radioactive Penetration: Beta (2)

Answer 7

• to stop being radiation, has to get close to a nucleus to become a part of an atom
• quite ionising and so quite penetrating

Question 8

Radioactive Penetration: Gamma

Answer 8

• to stop being a gamma photon, has to randomly bump into an orbiting electron
• the denser the material, the more likely it will stop a gamma photon
• least ionising and so most penetrating

Question 9

Alpha Particle (definition)

Answer 9

Helium nuclei

Question 10

Beta Particle (definition) (2)

Answer 10

• high speed electron emitted from the nucleus during beta decay
• produced when a neutron changes into a proton

Question 11

Radioactive Decay (definition)

Answer 11

The spontaneous and random decay of an unstable nucleus into a more stable nucleus by the emission of alpha, beta and gamma radiation

Question 12

Spontaneous (definition)

Answer 12

Happens without being affected by any external factors

Question 13

Random (definition)

Answer 13

Not possible to determine exactly how many particles will decay each second, nor which ones will decay

Question 14

After emission of radiation, parent nuclei become

Answer 14

Daughter nuclei

Question 15

Alpha Decay of 238, 92 U

Answer 15

4,2 He + 234,90 Th + 0,0 Gamma

Question 16

Beta Minus Decay

Answer 16

• too many neutrons
• neutron breaks down into a proton under the influence of the weak force
• 14,6 C -> 0,-1 e + 14,7 N + anti electron neutrino
• 1,0 n -> 1,1 p
• d -> u

Question 17

Beta Plus Decay

Answer 17

• too few neutrons
• proton breaks down into a neutron under the influence of the weak force
• can only happen if extra energy is added to the system as a lighter proton decays into a heavier neutron
• 11,6 C -> 0,1 e + 11,5 N + electron neutrino
• 1,1 p -> 1,0 n
• u -> d