Cjapter 25 Radioactivity

Question 1

What are three types of radiation and info about them

Answer 1

Alpha radiation = is a helium nucleus, two protons and two. Dutton’s , hence 4/2, and has a charge of +2

Beta radiation = consists of either fast moving electrons B- or positrons which are B+

Gamma radiation is just EM radiating

Question 2

What are all these three type of raids it on referred to as ionising?

Answer 2

Energy enough to cause an electron to be kicked of atoms, making them POSITIVE IONS

Question 3

Beta radiation, what is positrons?

Answer 3

This is thr ANTIMATTER PART OF AN ELECTRON

Question 4

How will all 4 types of radiosonde (b- and b+) interact in the presence of a UNIFROM ELECTRIC FIELD
Supplied by two parallel charged plates

Answer 4

1) gamma = will just go through, because uncharged
2) b+ will deflect towards the negative , and B- towards positive plate, both in exact mirror opposite trajectories, as everything else is same (mass etc)
3) the alpha will also deflect towards negative, but because more MASS, will deflect less (even tho charge is twice, mass is 4, so )

Question 5

Remember when using a GM tube ti measure radiation, WHAT MUST ALWAYS DO TI GET PROPER RESDINGS

Answer 5

Measure the BACKGROUND RADIATION count rate first, and subtract from measured count rate in edperiemnt

Question 6

IONISING POWER vs RANGE IN AIR for each 3

Answer 6

Alpha has highest mass charge so HIGHEST IONISING POWER
- but the lowest range in air thus (as ionises quick)

BETA has less mass so Less ionising power
- thus better range in air than alpha

Gamma has no charge so even LESS IONISING than beta
- range is longggg

Question 7

What stops each radiation in air (materials’

Answer 7

Alpha stopped COMPLETELY by a thin sheet of PAPER, or few cm of air
- BETA stopped by a few mm of ALUMINIUM
- Gamma must need LEAD, few cm

Question 8

How to be safe with radioactive sources, what are they usually stored in

Why they dangerous?

Answer 8

Ionising can cause damage ti cells, so always stored in LEAD,
# should wear tongs and gloves keep far away as possible

Question 9

Hat is charge of position.

Answer 9

+e

Question 10

What happens in an ALPHA emission (change in mass charge what emitted)

Answer 10

Alpha nucleus emitted that’s it

Mass number decrease by 4, and proton by 2

Question 11

What happens in a BETA - EMISSION

Answer 11

HERE too many NEUTRONs so unstable
= a NEUTRON converts into a proton, and releases an electron and an ELECTRON ANTI NEUTRINO

Thus mass decreases but increases so nothing happens to mass

Charge on proptin increases so +1

New element formed

Question 12

What happens in BETA + EMISSION

Answer 12

here too many protons so unstable
= a proton changed into a neutron and releases a position, and electron anti neutrino

Thus mass stays the same again

Proton number DECREASES , so new element

And positron and anti neutrino rrlease

Question 13

What happens with GAMMA emission

Answer 13

No charge or mass , as it’s just em wave

Energy is given off as gamma, and new nucleus stabke

Question 14

Remember what happens as soon as the Proton number changes

Answer 14

Here the ELEMENT WILL CHANGE

Question 15

Will an unstable nucleus keep decaying forever? What normally happens

Answer 15

It will decay a few times, and of different decays, until it’s finally stable

Question 16

How ti describe the decay of a radioactive source as spontaneous and random

Answer 16

Decay is random bevause
- can’t predict which nucleus will decay
- each nucleus has the SAME chance of decaying p

It’s spontaneous bevause
- not affected by presence of other nuclei
- or external factors like pressure

Question 17

What is half life

What kinda decay does this show

Answer 17

The average time taken for half of the active nuclei remaining to decay

Exponential decay

Question 18

What is ACTIVITY A
Units

What does it depend on

Answer 18

This is the rate at which nuclei are decayed per second

This is bq, 10 bq means 10 per second

Depends on number left snd half life, csn model using exp decay

Question 19

Explain A = decay constant x N formula

Answer 19

Basicslly the rate of decay of nuclei is proprtinsl to the number there is left
So chnage propritnsk to - N, because the N is decreasing

If we put a constsnt in to make it an equation, we know chnage is just the activity

A = kN

Where K is the decay constsnt

Question 20

What definition can we give to the decay constsnt

Units?

Answer 20

This is DIFFERENT FOR each isotope, so unique

Thus it’s the PROBABILITY of decay of any nucleus per unit time , units 1/s

Question 21

As N decreases exponentially, and as A proprtinsl to N , what two equations can we write to model their decrease

Answer 21

N = N0 e ^-Kt
A= A0 e^-kt

Question 22

What is equatuin fir half life (how to derrive)

Answer 22

Ln2 / k = half life

Derrive by trying to find the time taken for half N using an equatuin

Question 23

How to do questions to calculate change in activities

Answer 23

Use info you have to find the decay constant

Now use activity equation

Question 24

What 2 things yiu need to measure half life then

And how

Answer 24

Just the number of. H lei usign mass spec

And activity which can be measured using detectors

Question 25

How does CARBIN dating work

Answer 25

Here the ratio of CARBIN 14 which is unstable to Carbon 12 in thr atmosphere and LIVING ORGANISMs is said ti be constsnt

Thus if you measure some dead organic matter, and compare the nuclei of carbon 14 or the ratios of activities (because activity is oroeotinsl to N), you can work out the time taken presuming you know the half life of carbon 14 , then you can work out time

Question 26

How is CARBON 14 which is used for dating formed in the earths atmospher

Answer 26

1) high speed protons from cosmic rays collide with atoms to produce neutrons
2) these collide with nitrogen 14 nuclei to form carbon 14 nuclei

Question 27

How does carbon 14 decay

Answer 27

It decays by beta - and become nitrogen again

(Yiu saying it will decay until you find material again, less nuclei means less activity, compare activity or nuckeinetc

Question 28

What are TWO LIMITSTIONS TO CARBON DATING

Answer 28

1) make the assumption the ratio of cabrinn14 to cabrinn12 in living matter has REMAINED CONSTANT since you were dating it (it might have changed now)

2) the activists of CARBIN 14 in organic matter is similar to the background rate so hard to tell

Question 29

Why can’t we use CARBIN 14 to date ROCKS

What material is needed instead

Answer 29

rocks are much older than life and so CARBIN 14s half life is TOO SMALL to have been in the rocks

Need a material whose half life is big enough to have been able to decayed and still be in the source