Nuclear Decay

Question 1

electron

• relative mass
• relative charge

Answer 1

• 1 / 1840
• -1

Question 2

proton

• relative mass
• relative charge

Answer 2

• 1
• +1

Question 3

neutron

• relative mass
• relative charge

Answer 3

• 1
• 0

Question 4

what are isotopes

Answer 4

nuclei with same no. of protons but different no. of neutrons

Question 5

what is radioactivity

Answer 5

elements that have unstable isotopes disintergrate randomly and spontaneously

Question 6

what is a becquerel

Answer 6

1Bq = disintegration per second

Question 7

α-particles radiation

Answer 7

• particles
• ⁴₂He
• +vely charged
• poor penetration powers
• very slow
• highly ionising

Question 8

β-particle radiation

Answer 8

• particles
• very fast electron
• -vely charged
• average penetration powers
• in between ionising power
• ₋₁⁰e

Question 9

γ (gamma) rays

Answer 9

• high electromagnetic waves
• great penetrating power
• weakest ionising power

Question 10

number of unstable nuclei equation

Answer 10

N = N₀e⁻λᵗ

λ = decay constant (e on calculator)

Question 11

rate of disintegration equation

Answer 11

A = A₀N

A = A₀e⁻λᵗ

A = Bq

Question 12

what is the decay constant

Answer 12

the fraction of unstable nuclei that decay per second

Question 13

what is a half life

Answer 13

time taken for:
* half of radioactive nucleipresent to disintegrate
* activity of material to fall to half its value

Question 14

half life equation

Answer 14

t = 0.693 / λ

0.693 = log2

Question 15

measuring half life of radioactive substance

apparatus needed for experiment

radon-220

Answer 15

• ionisation chamber: aluminium can (+ve electrode)
• metal rod centrally in chamber (-ve electrode)
• insulator
• ammeter
• DC amplifier
• stopwatch
• rubber tubes (clips to seal)
• polythene bottle (radon gas generator)

Question 16

rate of decay equation

Answer 16

A = -λN

A ∝ N

*minus sign as as t inc. N decreases

Question 17

measuring half life of a radioactive substance

describe the steps taken in the experiment to measure half life

radon-220

Answer 17

1. adjust the DC amplifier to highest resistance input, usually 10¹¹Ω
2. fill ionisation chamber with radon gas; release clips on tubes and sqeeze bottle until reading on milliammeter goes past full scale deflection
3. take readings; start clock as current reading falls. record current every 10 seconds for 3mins

*steps in more detail in book

Question 18

measuring half life of a radioactive substance

what happens when the number of radon gas atoms gets smaller

radon-220

Answer 18

• fewer α-particles are emitted
• fewer ions are produced so smaller ionisation current flows

★ ionisation current directly proportional to number of radon atoms remaining and hence activity (A ∝ N) ★

∴ half life is time taken for ionisation current to fall to half its original value

Question 19

measuring half life of radioactive substance

how to use results of experiemtn to find half-life

radon-220

Answer 19

• plot a graph of ionisation current againt time and draw smooth curve (read 3 time intervals when current falls 50%)
• plot a linear graph using logs with ln I against time (m = -λ -> use half life equation)

Question 20

measuring the half life of a radioactive substance

apparatus needed for experiment

protactinium-234

Answer 20

• Geiger-Muller (GM) tube (acts as -ve electrode)
• central metal rod (acts as +ve electrode)
• counter
• mica window (ensures no leaks of gas)

Question 21

measuring half life of radioactive substances

how does the counter work

protactinium-234

Answer 21

• electrical discharge is detected and counted
• if connected to internal speaker -> click when radiation enters

Question 22

measuring half life of radioactive substances

describe steps taken in experiment to measure half life

Answer 22

1. measure background radiation: remove known radiation from room and set GM to 0, time for 30mins (divide count by 30)
2. set up protactinium source