26 Radioactivity

Question 1

Rutherford (1911)

Answer 1

-knew that atoms of certain elements are unstable and emit radiation

Question 2

Rutherford experiment

results

Answer 2

• alpha particles directed at a thin piece of metal.
• most alpha particles passed through with little deflection( 1 in 2000 were deflected)
• a small percentage of alpha particles were deflected through angles more than 90 degrees ( 1 in 10000)

Question 3

Rutherford Experiment

explanation

Answer 3

• most of the concentration in the small region (nucleus)

- The nucleus is positively charged because it repels the alpha particle

Question 4

size of the nucleus

Answer 4

-d² =D/10000n

d=nucleus diameter
D=atom diameter
n= number of atoms

Question 5

radiation and radioactive

Answer 5

The source is radioactive not the radiation

Question 6

Radiation

Answer 6

• ionised air so it can conduct electricity

- three different types of radiation

Question 7

radiation and magnetic field

Answer 7

alpha and beta radiation are deflected in opposite ways and has no effect on gamma radiation

Question 8

ionisation experiment

Answer 8

• can be investigated using an ionising chamber and a picammeter
• air at atmospheric pressure
• ions in the chamber are attracted to the oppositely charged electrode where they are discharged
• electrons pass through the picammeter as a result of ionisation in the chamber
• the current is proportional to the number of ions per second

Question 9

ionisation of alpha

Answer 9

strong ionisation but a short range in air (cm)

Question 10

ionisation of beta

Answer 10

weaker than alpha but bigger range than alpha (meters)

Question 11

ionisation of gamma

Answer 11

weaker than alpha and beta but has an infinite range in air

Question 12

cloud chamber

Answer 12

contains saturated air with vapour at a low temperature. alpha and beta radiation leave visible tracks of condensation of water droplets.

Question 13

Cloud chamber alpha

Answer 13

produce straight tracks from the source

all the racks are the same showing that alpha particles have the same range

Question 14

Cloud chamber beta

Answer 14

produce wispy tracks that are easy to deflect. The tracks are less easy to see because beta isn’t as ionising

Question 15

absorption tests

Answer 15

uses a Geiger tube and counter to investigate absorption of different materials. Each particle is one count.

Question 16

count rate

Answer 16

The number of counts per unit time detected by a Geiger Muller tube. Count rates should always be corrected by measuring and subtracting the background count rate

Question 17

Geiger tube

Answer 17

a sealed metal tube that argon gas at low pressure.
ionizing radiation enters the tube, the particle ionising the gas. negative ions are attracted to the rod and the positive ions to the wall. ions accelerate and collide with gas atoms producing more ions. a pulse of charge passes around the circuit through a resistor causing a voltage pulse across the resistor.

Question 18

radiation range in air

Answer 18

alpha - 100mm
beta- 1m
gamma - inserverse square law

Question 19

radiation absorption

Answer 19

alpha - stopped by paper and thin foil
beta - 5mm of aluminium
gamma - several cm of lead

Question 20

radiation ionisation

Answer 20

alpha - produce 104 ions per mm in air at strandard pressure

beta - produces about 100 ions per mm

gamma - very weak ionising effect

Question 21

alpha ( experiment)

Answer 21

alpha particles are collected as a gas in a glass tube fitted with two electrodes. When a voltage was applied to the electrode, the gas conducted electricity and emitted light. using a spectrometer, he proved that the spectrum of light from the tube was the same as from a tube filled with helium gas

Question 22

beta radiation

Answer 22

measuring the deflection of a beam of beta particles using electric and magnetic fields. The measurement was used to work out the specific charge of the particles (specific charge of the electron).

Question 23

beta negative

Answer 23

an electron is created and emitted from a nucleus with too many neutrons as a result of a neutron changing to a proton

Question 24

beta positive (positron)

Answer 24

a nucleus with too many protons, a proton changes to a neutron

Question 25

inverse square law (intensity)

Answer 25

The intensity of gamma radiation from a point source varies with the square of the distance from the source ``` intensity = radiation energy per second/total area. I = nhf/4π² ```

Question 26

hazards of ionising radiation

Answer 26

damages living cells (destroy cell membranes causing cells to die) (damage vital molecules such as DNA) Also as a result of exposure to ionising radiation, living cells die or grow uncontrollably or mutate

Question 27

radiation monitoring

Answer 27

film badge- a strip of photographic film in the light proof wrapper. different areas of the film are covered by absorbers of different materials and different thicknesses. When the film is developed the amount of exposure to each form of ionising radiation can be estimated from the blackening film.

Question 28

background radiation

Answer 28

radiation due to naturally occurring radioactive substances in the environment

Question 29

Radioactive materials

Answer 29

``` air medical ground and buildings food and drink cosmic rays nuclear rays air travel nuclear power ```

Question 30

Half-life

Answer 30

The time is taken for the mass of a radioactive isotope to decrease to half the initial mass or for its activity to halve. this is the same as the time taken for the number of nuclei of the isotope to decrease to half the initial number.

Question 31

nucleus

Answer 31

the relativity small part of the atom where all the positive charge is concentrated

Question 32

atomic number

Answer 32

of an atom of an element is the number of protons in the nucleus of the atom. it is also the order number of the element in the periodic table

Question 33

photon

Answer 33

electromagnetic radiation consists of photons. each photon is a wave packet of electromagnetic radiation. E=hf

Question 34

ionising radiation

Answer 34

radiation that produces ions in the substances it passes through. it destroys cell membranes and damages vital molecules such as DNA directly or indirectly by creating 'free radicals' ions which react with vital molecules

Question 35

proton

Answer 35

particle that has equal and opposite charge to an electron

Question 36

neutron

Answer 36

uncharged particle that has a rest mass of 1.674 x10-27

Question 37

intensity of radiation

Answer 37

at a surface is the radiation energy per second per unit area of normal incidence to the surface

Question 38

x-ray

Answer 38

electromagnetic radiation of wavelength less than 1nm. X-ray are emitted from a X-ray tube as a result of fast-moving electrons from a heated filament as the cathode being stopped on impact with the metal anode. think lead plates are needed to absorb a beam of x-rays

Question 39

dose equivalent

Answer 39

a comparative measure of the effect of each type of ionising radiation, defined as the energy that would need to be absorbed per unit mass of matter from 250 k of x-radaiation to have the same effect as a certain 'dose' of the ionising radiation. the unit of dose equivalent is the sievert (Sv)

Question 40

background radiation

Answer 40

radiation due to naturally occurring radioactive substances in the environment . also can be caused by cosmic radiation

Question 41

decay curve

Answer 41

an exponential decrease curve showing how the mass or activity of a radioactive isotope decrease with time

Question 42

activity

Answer 42

of a radioactive isotope, the number of nuclei of the isotope that disintegrate per second. Bq A = λN

Question 43

decay constant

Answer 43

the probability of an individual nucleus decaying per second

Question 44

excited state

Answer 44

an atom which is not in its ground state

Question 45

de Broglie wavelength

Answer 45

a particle of matter has a wake-like nature which means that is can behave as a wave. λ = h/p = h/mv

Question 46

energy transfer per second from a radioactive source

Answer 46

AE

Question 47

decay constant

Answer 47

ΔN/ Δt = -λN

Question 48

decay of an isotope

Answer 48

A = Are^-λt

Question 49

half-life T 1/2

Answer 49

T 1/2 = In(2) / λ

Question 50

carbon dating

Answer 50

radioactive isotope of carbon-14 n + N --- C +p formed in the atmosphere as a result of cosmic rays knocking out neutrons from the nuclei

Question 51

Argon dating

Answer 51

ancient rock contains trapped Argon gas as a result of the decay of the radioactive isotope of potassium to argon. the age of the rock can be calculated by measuring the proportion of argon of argon-40 to potassium-40

Question 52

radioactive tracers

Answer 52

radioactive tracer is used to follow the path of a substance through a system. have a half-life which is stable enough for the necessary measurements to be made and short enough to decay quickly after use emit B radiation or y radiation so it can be detected outside the flow path

Question 53

detecting underground pipe leaks

Answer 53

radioactive tracer injected into the flow. a pipeline is used to detect leakage B- emitter or gamma emitter

Question 54

modelling oil reservoirs mathematically to improve oil recovery

Answer 54

water contains a radioactive tracer is injected into a oil reservoir at high pressure, forcing some of the oil out. tritiated water HO, B emitter with a half-life for 12 years

Question 55

investigating the uptake of fertilisers by plants

Answer 55

plants watered with a solution containing a fertiliser. by measuring the radioactivity of the leaves, the amount of fertile reaching them can be determined fertiliser = phosphorous

Question 56

monitoring the uptake of iodine by the thyroid gland

Answer 56

patient is given a solution donating sodium iodine which contains a small quantity of radioactive iodine solution of sodium iodide contains iodine B emitter of 8 days

Question 57

thickness monitoring

Answer 57

metal foil is manufactured by using rollers to squeeze plate metal on a continuous production line. a sector measures the amount of radiation passing through the foil. if the foil is too thick, the detector reading drops. a signal is sent if the reading drops which brings the roller together

Question 58

power forces for remote devices

Answer 58

satellites, weather sensors and other remote devices can be powered using radioactive isotopes in thermally insulated sealed container which absorbs all the radiation emitted by the isotope.

Question 59

N-Z graph | light isotopes

Answer 59

stable nuclei flow the straight line N =Z | the nuclei have equal numbers of proton and neutrons

Question 60

N-Z graph | as Z increases beyond 20

Answer 60

stable nuclei have more neutrons than protons. the neutron / proton ratio increases. the extra neutrons help ti blind the nucleons together without introducing repulsive electrostatic forces as more protons would do

Question 61

N-Z graph | α emitter

Answer 61

beyond Z= 60, most of them with more than 80 protons and 120 neutrons. these nuclei have more neutrons than protons but they are too large to be stable. this is because the strong nuclear force of repulsion between the protons

Question 62

B- emitters

Answer 62

occur to the left of the stability belt where the isotopes are neutron rich compared to stable isotopes.

Question 63

B+ emitters

Answer 63

occur to the right of the stability belt where the isotopes are proton-rich compared to stable isotopes

Question 64

technetium generator

Answer 64

used in hospitals to produce a source which emits gamma radiation only. some radioactive isotopes such as the technetium isotope Tc form in the excited state long enough to be separated from the parent state contains an ion exchange column containing ammonium molybdenite exposed to neutron radiation several days to make lots of unstable nuclei. when a solution of sodium chloride is passed through the column, some of the chlorine ions exchange with pertechnate ions but not with molybdenite ion so the solution that emerges contains Tc nuclei

Question 65

diagnostic use of Tc

Answer 65

monitoring blood flow | gamma camera= image internal organs and bones

Question 66

nuclear density

Answer 66

V = 4/3 π ro^3 A

Question 67

inverse square law

Answer 67

I = k / X^2