Nuclear Decay Flashcards
electron
- relative mass
- relative charge
- 1 / 1840
- -1
proton
- relative mass
- relative charge
- 1
- +1
neutron
- relative mass
- relative charge
- 1
- 0
what are isotopes
nuclei with same no. of protons but different no. of neutrons
what is radioactivity
elements that have unstable isotopes disintergrate randomly and spontaneously
what is a becquerel
1Bq = disintegration per second
α-particles radiation
- particles
- ⁴₂He
- +vely charged
- poor penetration powers
- very slow
- highly ionising
β-particle radiation
- particles
- very fast electron
- -vely charged
- average penetration powers
- in between ionising power
- ₋₁⁰e
γ (gamma) rays
- high electromagnetic waves
- great penetrating power
- weakest ionising power
number of unstable nuclei equation
N = N₀e⁻λᵗ
λ = decay constant (e on calculator)
rate of disintegration equation
A = A₀N
A = A₀e⁻λᵗ
A = Bq
what is the decay constant
the fraction of unstable nuclei that decay per second
what is a half life
time taken for:
* half of radioactive nucleipresent to disintegrate
* activity of material to fall to half its value
half life equation
t = 0.693 / λ
0.693 = log2
measuring half life of radioactive substance
apparatus needed for experiment
radon-220
- 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)
rate of decay equation
A = -λN
A ∝ N
*minus sign as as t inc. N decreases
measuring half life of a radioactive substance
describe the steps taken in the experiment to measure half life
radon-220
- adjust the DC amplifier to highest resistance input, usually 10¹¹Ω
- fill ionisation chamber with radon gas; release clips on tubes and sqeeze bottle until reading on milliammeter goes past full scale deflection
- take readings; start clock as current reading falls. record current every 10 seconds for 3mins
*steps in more detail in book
measuring half life of a radioactive substance
what happens when the number of radon gas atoms gets smaller
radon-220
- 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
measuring half life of radioactive substance
how to use results of experiemtn to find half-life
radon-220
- 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)
measuring the half life of a radioactive substance
apparatus needed for experiment
protactinium-234
- Geiger-Muller (GM) tube (acts as -ve electrode)
- central metal rod (acts as +ve electrode)
- counter
- mica window (ensures no leaks of gas)
measuring half life of radioactive substances
how does the counter work
protactinium-234
- electrical discharge is detected and counted
- if connected to internal speaker -> click when radiation enters
measuring half life of radioactive substances
describe steps taken in experiment to measure half life
- measure background radiation: remove known radiation from room and set GM to 0, time for 30mins (divide count by 30)
- set up protactinium source
