radioactive decay

What type of event is radioactive decay?

Random event

Can we predict when an unstable nucleus will decay?

No, it cannot be predicted

Can anything be done to make radioactive decay happen?

No, excluding induced fission

radioactive decay is not affected by

changes in pressure or temperature

decay constant

probability of decay for a specific isotope per unit time

increasing decay constant increases the likelihood that

the nucleus will decay in a given second

higher the activity

shorter the half life

alpha why most ionsing (4 mark q)

1. has the most charge

2. more mass = moves more slowly

3. it produces more ionisations per millimetre

4. loses energy over shorter distance

5. does not go as far/less penetrating ability

alpha atomic number

2

alpha mass num

4

alpha relative charge

+2

alpha speed

0.1c/5-10MeV

alpha ionising ability

high

alpha penetrating power

- few mm in air

- thin card or human hand

beta - charge/atomic num

-1

beta + charge/atomic mass

+1

beta - speed

0.9c/1-5MeV

beta + speed

0.9c/1-5MeV

beta - ionising ability

low

beta - penetrating power

- air 1-2 m

- stopped by aluminium

beta + exists short amount of time because it

positron finds an electron and annihilates itself

gamma atomic number

0

gamma mass number

0

gamma relative charge

0

gamma speed

speed of light, <1MEV

gamma ionising ability

low

gamma penetrating ability

- air unlimited range

- cms of lead

- metres of concrete

speed of light

3.00 x 10^8 m/s

A

mass number

Z

atomic number

decay energy

output of energy from radioactive decay

pure alpha decay energy

kinetic energy of daughter nucleus and alpha particle (shared in a fixed ratio)

monoenergetic

all alpha particles within that specific sample of radioisotope has the same energy

rest energy

energy equivalence of particle mass

in pure alpha decay...

1. no energy is lost as they all go to the kinetic energy of the daughter nucleus and alpha particle

2. this is shared in a fixed ratio

3. alpha particle gets more as it has less mass

alpha decay what conserved

1. nucleon number

2. charge/proton number

3. energy

4. momentum

nucleon

a proton or neutron

Beta - decay

neutron in neutron rich nucleus changes into proton, electron and anti electron neutrino

beta - mass number (A)

stays same

beta - proton number (Z)

+1

eV

electron volts

what is conserved in beta -

1. energy

2. momentum

3. charge

4. baryon number

5. lepton number

baryon

3 quarks joined

Beta + decay

proton in nucleus rich in proton changes into neutron, neutrino and positron

beta + A

same

beta + Z

-1

gamma when

emitted from nucleus if it has too much energy after beta or alpha emission

gamma

emitted from nucleus that is in an excited state

cannot write decay equation for gamma because...

- mass and atomic num stay same because gamma not particle

- gamma has no mass or charge

charge of up quark

+2/3

charge of down quark

-1/3

Beta - energy

the particles have a max energy but have a range of energy because some energy is carried away by the antineutrino

beta + energy

the particles have a max energy but have a range of energy because some energy is carried away by the neutrino

beta + lepton form

uud -> udd + e+ + ve

beta - lepton form

udd -> uud + e- + ν̄e

Activity units

Bq

half life units

seconds

decay constant unit

s^-1

bg rad

1.5 - 2 millisieverts

worldwide average

2.4 mSv

fatal dose

2sV

natural causes of radiation

food and drink, cosmic rays, uranium mines, rocks/soils, radon 220 and 222

artificial sources of radiation

air travel, nuclear industry, medical, burning coal

food and drink

10%

cosmic rays

20%

rocks, soils and building materials

20%

radon 220 and radon 222

35%

air travel

0.5%

nuclear industry

0.5%

medical

10-15%

burning coal

1.5%

BG RAD AFFECTED BY

where they live and occupation affect bg rad dose

absorbed dose

energy deposited in kg of substance by radiation

equivalent dose

absorbed dose weighted for harmful affects of diff radiation