## Physics > Radioactivity > Flashcards

1
Q

Carbon dating

A

Living plants contain a small percentage of radioactive C-14

Negligible decay throughout the lifetime of the plant - half life of 5570 years

Once dead no further carbon is taken in so the proportion of C-14 begins to fall

Calculate age of sample using n = Ne^-lambda x t

2
Q

Argon dating

A

Ancient rocks contain trapped argon gas as a result of the decay of K-40 to Ar-40

Half life of K-40 is 1250 million

Age can be calculated by measuring the proportion of Ar-40 to K-40

For every N K-40 atoms if there is 1 Ar-40 then there must of been N+9 K-40 atoms originally

3
Q

A

Should have a half life long enough for necessary measurements to be taken but short enough to reduce damage caused

Emit beta or gamma radiation so the radiation is able to be detected outside

4
Q

Engine wear -> piston ring

A

Rate of wear of a piston ring can be measured by fitting a radioactive ring

Radioactive atoms transfer from the ring to the oil

By measuring the radioactivity of the oil the mass transferred from the ring can be determined and the rate of wear calculated

5
Q

Detecting underground pipe leaks

A

Beta or gamma emitter injected injected into the flow (depending on depth, soil density etc)

A detector on the surface above the pipeline is used to detect leakage

6
Q

Modelling oil reservoirs mathematically to improve oil recovery

A

Water containing a tracer is injected into an oil reservoir at higher pressure, forcing some of the oil out

Detection at the production wells monitor the presence of the radioactive isotope to see how much oil is being lost

The tracer is tritaited water, a beta emitter with a half life of 12 years

7
Q

Investigating the uptake of fertilisers by plants

A

Plant watered with a solution containing a fertiliser which contains P-32, a beta emitter with a half life of 14 days

By measuring the radioactivity of the leaves, the amount of fertiliser reaching them can be determined

8
Q

Monitoring the uptake of iodine by the thyroid gland

A

Patient is given a solution containing sodium iodide which contains a small quantity of radioactive I-133 (beta emitter with a half-life of 8 days)

The activity of the patient’s thyroid and the activity of an identical smaller prepared at the same time is measured 24 hours later

9
Q

Thickness monitoring

A

Detector measures the amount of radiation passing through the foil

If the foil is too thick, the detector reading drops and the rollers move closer together to make the foil thinner
and vice versa

The source is a beta emitter with a long half-life

10
Q

Power sources for remote devices

A

Satellites, weather sensors etc

Radioactive isotope in a sealed container which absorbs all the radiation emitted by the isotope

Thermocouple attached to container produces electricity through the heat from the absorption of the radiation

11
Q

Reasons for nuclear instability

A

Too many neutrons

Too few neutrons

Too many nucleons - too heavy

Too much energy

12
Q

When does alpha emission occur?

A

Occurs when nuclei are too massive to be stable - the strong nuclear force doesn’t have the range to hold large nuclei together

13
Q

When does beta-minus occur?

A

Beta minus decay occurs in nuclei that are ‘neutron rich’ - have more neutrons than protons

14
Q

When are gamma rays produced?

A

After decays the nucleus is often still excited - this energy is released as gamma rays

No change in nuclear constituents but a loss in energy

Also produced when the nucleus captures one of its own orbiting electrons

15
Q

Energy of emitted radiation and half-life

A

There is an inverse relationship between half life and energy of emitted particles

So the lower the energy the longer the half life

16
Q

Conclusions from Rutherford scattering

A

Most of the atom is empty space - most alpha particles pass straight through

Nucleus has a large positive charge as some alpha particles were deflected by a large angle

Nucleus must be small as few alpha particles were deflected

Most of the mass must be in the nucleus - alpha particles with high momentum are deflected

17
Q

Experimental conditions for Rutherford scattering

A

Very thin gold foil - as otherwise the alpha particles would be absorbed

Narrow beam - as otherwise it would be difficult to tell if the alpha particles had been scattered or passed through

Alpha particles must all be travelling at the same speed - otherwise slower alpha particles would be deflected more than faster particles on the same path

Apparatus in an evacuated chamber - otherwise alpha particles would be stopped by air molecules

Source of alpha particles must have a long half life - otherwise later readings would be lower than earlier readings

18
Q

Ionisation and living cells

A

Can destroy cell membranes causing cells to die

Can damage vital molecules directly such as DNA or indirectly by creating free radicals

Damages nuclei

Damaged DNA may cause cells to divide and grow uncontrollably - causing a tumour

Damaged DNA may be passed onto future generations as a mutation in the egg or sperm

19
Q

Using gamma rays for cancer treatment

A

Rotating beam is used to lessen the damage to the surrounding tissue whilst giving a high dose to the tumour at the centre of rotation

Treatment causes side effects:

Tiredness
Reddening or soreness or skin
Infertility

20
Q

A

Use long handling tongs

Store in a lead-lined box when not in use

Reduce exposure time by only using the source for as long as is necessary

Wear a film badge - has 3 areas which darken depending on the radiation type

21
Q

A

Cosmic rays

Medical practice and industry

Food and drink

Nuclear power

Ground and buildings

Living things

22
Q

Metastable state

A

An excited state of the nuclei of an isotope that lasts long enough for the isotope to be separated from the parent isotope

Usually occurs after alpha or beta emission

23
Q

Metastable technetium formation

A

Molybdenum isotope 99-Mo has a half life of 67 hours and decays by beta minus emission to form metastable 99-Technetium

Ground state technetium is a beta minus emitter with a half life of 500000 years

Hence a sample of metastable technetium effectively only emits gamma rays

24
Q

Uses of metastable technetium - monitoring blood flow through the brain

A

external detectors are used to analyse the activity of the brain’s blood vessels after sodium pertechnate is administered intravenously

25
Q

Uses of metastable technetium - the gamma camera

A

A lead shielded detector is used to build up an image of internal organs and structures from emitted gamma rays

For example bone deposits can be located using a phosphate tracer labelled with metastable technetium

26
Q

A

Impossible to predict which one of the large number of nuclei in a sample will decay

Impossible to predict when a nucleus will decay

27
Q

When can background count be ignored in experiments?

A

When background count is negligible compared to the count rate

When fluctuations in count rate are greater than the background count

28
Q

Curve of stability

A

Graph of N against Z

Where N is number of neutrons

Z is number of protons

Starts curving upwards when N = 20

Alpha emitters to the top right of the curve

Beta minus emitters to the middle left of the curve

Beta plus emitters to the middle right of the curve

29
Q

Limitations of carbon dating

A

Measures the ratio of carbon 12 to 14 - contamination may result in a variation in sample age

Very old samples can’t be dated as their activity will be negligible or similar to the background count

30
Q

The smallest nucleus

An atom

A

1 x 10^-15 m (1 fm)

5 x 10^-11 (0.05nm)

31
Q

What does the significant difference in nuclear density and atomic density suggest?

A

Density of nucleus - 1.45 x10^17 kgm^-3
Density of an atom - between 10^3 and 10^5 kgm^3

Most of the atom’s mass is in its nucleus
The nucleus is small compared to the atom
An atom is mostly empty space

32
Q

A

Test what the radiation is absorbed by using a count rate and paper, aluminium and lead

Use magnetic fields - charged particles (alpha and beta) will be deflected in a circular path, direction and radius depends on charge and mass

33
Q

Decay constant

Half life

A

The probability of a give nucleus decaying per unit time

The time it takes for the number of unstable nuclei in a sample of an isotope to halve
OR
The time taken for the activity of a sample of a radioactive isotope to halve

34
Q

Equation for calculations involving mol

A

N = nNa

N is number of atoms
n is number of moles