Unit 5: Radioactivity

Question 1

What was Rutherford’s experiment?

Answer 1

Directed a narrow beam of a-particles. All of the same kinetic energy. In an evacuated container. At a thin gold film.

Question 2

Why did the a-particles in Rutherford’s experiment need to be of the same KE?

Answer 2

Slower alpha particles would be deflected more than faster ones on the same initial path

Question 3

Why did the container need to be evacuated?

Answer 3

Such that the particles did not colide with air particles

Question 4

What were the observations from rutherford’s experiment?

Answer 4

-Most a-particles passed through -A few a-particles deflected - some more than 90degrees

Question 5

What were the interpretations from Rutherford’s experiment?

Answer 5

mass is concentrated in a small region, the nucleus. Nucleus positively charged because it repels a-particles. Nucleus itself is very small as few a-particles are deflected by a significant angle.

Question 6

3 Type of radiation

Answer 6

Alpha, Beta, Gamma

Question 7

Applications of radiation

Answer 7

a - fire alarms b - thickness of paper y - diagnosstic techniques in medicine

Question 8

Describe alpha radiation

Answer 8

Atom loses 2 protons and 2 neutrons

Question 9

Describe beta(-) radiation

Answer 9

Atom loses one electron, has a neutron turn to a proton and gives off an anti-electron neutrino

Question 10

Describe beta(+) radiation

Answer 10

Atom loses one positron, has a proton turn into a neutron and gives off an electron neutrino

Question 11

Describe electron capture

Answer 11

Atom takes in an electron and results in a proton turning into a neutron and gives off an electron neutrino

Question 12

Why can radiation be damaging

Answer 12

it affects living cells as it can destroy cell membranes and damage DNA

Question 13

States the 4 main properties of the inverse square law for y radiation

Answer 13

1 - Gamma source emits radiation in all directions 2 - Spreads out with distance 3 - Amount of radiation per unit area (Intensity) will decrease with distance 4 - Intensity decreases with the square of the distance

Question 14

What is the equation for intensity and what are the variables

Answer 14

I = kI₀/d²

where I = Intensity, k = constant, d = distance, I₀ = Intensity at source

Question 15

Describe the random nature of radioactive decay

Answer 15

• One can not know exactly when or which particles will decay
• Any sample of particular isotope has the same rate of decay

Question 16

Define activity and the equation giving the variables and the unit used to measure it

Answer 16

• Activity of a sample is the number of atoms that decay each second
• Is proportional to the size of the sample
• A = Lambda*N
• A = Activity, Lambda = Decay constant, N = number of atoms
• Becquerels (Bq) = 1 decay per second

Question 17

What is the half life of an isotope?

Answer 17

Average time taken for the mass of an isotope to decrease by half of its initial mass

Question 18

Draw a diagram representing the principle of half life

Answer 18

standard exponential decay graph with radiative nuclei on the y and time on the x

Question 19

What is the equation for half life and give the variables

Answer 19

• T_1/2 = ln2/lambda
• T_1/2 = Half life, ln2 = the natural log of 2, lambda = decay constant

Question 20

What equation gives the amount of atoms/activity/mass/count rate after an isotope has decay for x amount of time, giving the variables

Answer 20

• N = N₀ e^-lamba*t
• Where N = number of atoms left, N₀ = Inital number of atoms, e = 2.734, lambda = decay constant, t = time

Question 21

Define the decay constant ( lambda) giving its unit

Answer 21

• The probability of an individual nucleus decaying per second.
• Unit is S^-1

Question 22

Explain carbon dating

Answer 22

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