Radioactivity COPY

Question 1

Give the four points for the random nature of decay

Answer 1

• It cannot be known which unstable nucleus in a group will decay next
• There is an equal probability of each of the unstable nuclei decaying
• I cannot be known when a particular nucleus will decay
• The probability of a nucleus decaying in a certain time period can be known

Question 2

Define the decay constant

Answer 2

It is the proportion of nuclei decaying per unit time OR the probability of decay per unit time

Question 3

What can the decay constant be measured in?

Answer 3

s^-1, hour^-1, day^-1, year^-1

Question 4

What are the equations for the activity of a source?

Answer 4

A = (decay constant) x N

where N it the number of nuclei

A = A₀e^{-t x (decay constant)}

Question 5

What is a Becquerel (Bq)?

Answer 5

1 Bq is one decay per second

Question 6

What must the unit be for the decay constant if the unit for the activity is Bq?

Answer 6

s^-1

Question 7

What is the exponential equation for the number of nuclei?

Answer 7

N = N₀e^{-t x decay constant}

Question 8

What is the number of atoms proportional to?

Answer 8

The mass of the radioactive substance

Question 9

Give the exponential equation for the mass of a radioactive substance

Answer 9

M = M₀e^{-t x decay constant}

Question 10

Define half life

Answer 10

The time taken for half the nuclei initially present to decay OR the time taken for the activity of a radioactive sample to decrease to half its initial value

Question 11

when using the exponential equations (for A, N or M) what must be the case in terms of units?

Answer 11

A & A₀, M & M₀ and N & N₀ must be in the same unit

t and the decay constant must be in the same unit

Question 12

Derive the equation for the half life of a source

Answer 12

Question 13

What is the equation for the half life of a source?

Answer 13

Question 14

what is the fromula for the initial rate of decay?

Answer 14

∆N / ∆t

Question 15

Write A = A₀e^{-t x decay constant} as y = mx + c

Answer 15

Question 16

Why can’t you use carbon dating for things that have been dead a long time?

Answer 16

There would be massive errors as the radiation would become very similar to background radiation

Question 17

Explain carbon dating (4)

Answer 17

• Living things contain many carbon atoms, most are C-12 but some are the unstable C-14
• The unstable C-14 decays into nitrogen, but when the thing is alive, it is replenished by food
• When the thing dies, the C-14 which decays is not replaced so the thign will gradually become less radioactive
• Since the half life of C-14 is known, the time since the thing died can be calculated from taking a measurement of the radioactivity given off

Question 18

What is the equation for the intensity of a gamma source per m²?

Answer 18

I = I₀ / 4πx²

Question 19

What is the most useful version of the equation for the inverse square law for gamma radiation?

Answer 19

I₁X₁² = I₂X₂²

Question 20

Answer 20