Radioactivity

Question 1

Explain why a radioactive decay is a random process.

Answer 1

• There is equal probability of any nucleus decaying.
• It cannot be known which particular nucleus will decay next.
• It cannot be known at what time a particular nucleus will decay.
• The rate of decay is unaffected by surrounding conditions.
• It is only possible to estimate the proportion of nuclei decaying in the next time interval.

Question 2

What is half life?

Answer 2

Half-life, T½ , of a radioactive isotope is the time taken for the mass of the isotope to decrease to half the initial mass.

Question 3

What is activity?

Answer 3

• Activity, A, is the number of nuclei of the isotope which disintegrate each second, and is measured in becquerels (Bq).
• 1 becquerel = 1 disintegration per second

Question 4

What is molar mass measured in?

Answer 4

Grams.

Question 5

How many atoms does mass m of an element contain?

Answer 5

mN_A/M

Question 6

What is power of a radioactive source?

Answer 6

The product of activity and the energy of each particle.

Question 7

As radioactive disintegration is a random process:

Answer 7

• ΔN is proportional to:
  
  • N the number of nuclei remaining at time t
  • The duration of the time interval Δt

Question 8

Activty is the rate of change of:

Answer 8

The number of remaining nuclei with respect to time.

ΔN/Δt = -−λN

Question 9

Solved differential equations for nuclear:

Answer 9

• N = Nₒe^-λt
• A = Aₒe^-λt
• C = Cₒe^-λt

Question 10

When graphed as natural logs.

Answer 10

y = c + mx is identical to ln N = ln Nₒ –λt

the gradient = −λ

intercept = lnN₀

Question 11

What is the decay constant?

Answer 11

Decay constant, λ, is the probability of the an individual nucleus decaying per second. = ΔN/NΔt

Question 12

T½ equation

Answer 12

ln2/λ