Paper 1 Development of the atom and radioactivity

Question 1

before the discovery of the atom

Answer 1

some ancient Greek philosophers believed the atom was the smallest building block of everything
they thought it couldn’t be divided into any smaller parts

Question 2

the plum pudding model

Answer 2

when Thompson discovered the the electron he developed plum pudding model in 1897
atom is sphere of positive charge with negative electrons embedded inside

Question 3

rutherford’s experiment

Answer 3

1912. Rutherford’s shot high-speed alpha particles through thin layer of gold. some went straight through some deflected but some bounced back at very large angles
      shows most of the mass of the atom was concentrated in positive nucleus
      electrons orbit around nucleus at different distances

Question 4

Niels Bohr’s model

Answer 4

1913. adapted rutherford’s saying electrons could only orbit nucleus at specific distances
      this agreed with experimental measurements so was accepted as more accurate than rutherford’s

Question 5

the proton 1919

Answer 5

more experiments conducted in 1919 showing charge of nucleus could be divided into protons. every proton had same positive charge
electrons orbited core nucleus at discrete distances

Question 6

chadwick’s discovery

Answer 6

proved existence of neutron in 1932

mass of nucleus too large to be made of just protons so another neutral particle must be responsible for the mass

Question 7

what are radioactive substances

Answer 7

some isotopes have unstable nuclei and will break down.

when this happens they give out radiation and these substances are said to be radioactive

Question 8

alpha particle

Answer 8

consists of 2 neutrons and 2 protons, same as helium nucleus

Question 9

beta particle

Answer 9

a high speed electron ejected from the nucleus as a neutron changes into a proton

Question 10

gamma ray

Answer 10

high energy electromagnetic radiation from the nucleus

Question 11

what do nuclear equations represent

Answer 11

radioactive decay

Question 12

alpha decay

Answer 12

causes both mass and charge of the nucleus to decrease

Question 13

beta decay

Answer 13

doesn’t cause mass of nucleus to change but does cause the charge of the nucleus to increase

Question 14

emission of gamma rays

Answer 14

doesn’t cause the mass or the charge of the nucleus to change

Question 15

what happens when alpha, beta of gamma radiation strike atoms in a substance

Answer 15

they can knock an electron from one atom onto another

Question 16

what is an ion

Answer 16

an atom that’s gained or lost an electron

Question 17

what are alpha particles like

Answer 17

relatively big, heavy and slow moving
large relative charge (+2)
strongly ionising
bash into a lot of atoms and knock electrons off them before they slow down

Question 18

what are beta particles like

Answer 18

quite small and move quite fast

moderately ionising because their relative charge is smaller (-1)

Question 19

what is gamma like

Answer 19

weakly ionising because gamma isn’t charged

Question 20

what is alpha’s range in air and what stops it

Answer 20

few cm

paper, card + skin

Question 21

what is beta’s range in air and what stops it

Answer 21

few metres

aluminium (5mm thick)

Question 22

what is gamma’s range in air and what stops it

Answer 22

infinite

thick shetts of lead or metres of concrete

Question 23

what damage can ionising radiation cause

Answer 23

damages or kills living cells

damage to the genes in a cell can be passed on and lead to cancer

Question 24

from the outside which radiation is the safest and which is the most dangerous

Answer 24

alpha as it’s the least penetrating

gamma because it’s the most penetrating

Question 25

from the inside which radiation is the safest and which is the most dangerous

Answer 25

gamma because it can easily escape

alpha because it can’t escape

Question 26

what is Alpha used for

Answer 26

smoke detectors. ionises air particles, causing current to flow
if smoke in the air, it binds to the ions reducing the number available to carry a current
the current falls and alarm sounds

Question 27

why is alpha used for smoke detectors and why not beta or gamma

Answer 27

small range so safest, only one that can be stopped by smoke, most ionising
aren’t used as won’t be stopped by smoke and and won’t ionise the air enough. bigger range so not safe

Question 28

what is beta used for

Answer 28

test thickness of thin sheets of metal, as particles aren’t immediately absorbed by the material like alpha would be and don’t penetrate as far as gamma

Question 29

gamma tracers in medicine

Answer 29

gamma is used so that it can be detected on the outside of the body
alpha would be too dangerous as highly ionising

Question 30

gamma leak detection in pipes

Answer 30

injected into pipe. outside of pipe is checked with Geiger-moller detector to find areas of high radioactivity. this is where the pipe has a leak
useful for underground pipes that’s hard to get to

Question 31

why would alpha and beta not be used for leak detection in pipes

Answer 31

they would be blocked by the metal and the earth

Question 32

food irradiation

Answer 32

foods like strawberries can be irradiated with gamma radiation, killing any living bacteria or virus meaning less likely to go off

Question 33

What is a half life of a radioactive isotope

Answer 33

It’s the average time it takes for the number of nuclei of the isotope in a sample to half, or the time taken for the count rate of the sample to fall to half its initial rate

Question 34

The more nuclei there are in a sample…

Answer 34

The more a re likely to decay in one half life so the higher the count rate will be

Question 35

What is net decline of a radioactive substance

Answer 35

The fraction of the nuclei that have decayed in a certain time. it’s a fraction, ration or percentage because it doesn’t have a unit

Question 36

What is count rate

Answer 36

The time taken for the count rate from a sample containing the radioactive isotope to fall to half its starting level

Question 37

Radioactive tracers

Answer 37

Tracers used to trace flow of a substance through an organ.
small amount of radioactive material put into patients body (by injection or ingestion)
Tracer given enough time to travel through body before gamma camera is positioned to detect the radiation from outside the body
multiple images takes to show progress of tracer over time by measuring activity over time

Question 38

Gamma cameras

Answer 38

Can be used to image internal organs
as with tracing, a radioactive isotope (gamma emitting) is injected into the patient. The isotope is chosen because it concentrates in the organ

Question 39

How do gamma cameras work

Answer 39

Made of a crystal scintillator (sodium iodide) which produces a burst of light
light picked up by photo multiplier tubes which convert energy into an electrical signal. this fed into computer to get an image
Lead grid acts as collimator which only allows rays aligned with the holes to hit the crystal making the image sharper

Question 40

What does ionising mean

Answer 40

Means atoms are turned into ions by gaining or losing an electron

Question 41

What is ionising radiation

Answer 41

The high frequency end of the electromagnetic spectrum (UV, gamma, x-rays) and gamma and beta radiation

Question 42

What are the dangers of ionising radiation

Answer 42

Can damage living cells if small dose, large dose can kill cells this leads to cancer

Question 43

What is gamma radiotherapy

Answer 43

Gamma radiation is used in narrow beam to destroy cancer cells in a tumour .
the radiation emitted is from the isotope of cobalt

Question 44

How does gamma radiotherapy work

Answer 44

Individual beams that cross over at the target so individual beams less intense and don’t damage healthy cells.
destroys cells by ionising them and gamma because can penetrate further into the body

Question 45

What is that half life of the isotope used in gamma radiotherapy

Answer 45

5 years because it needs to last a long time so that it doesn’t need to be replaced and so the dose the patient receives doesn’t decrease

Question 46

Gamma knife

Answer 46

used to accurately focus many beams of gamma radiation on one or more brain tumours
each beam low intensity but with 200 beams can be accurately concentrated on small volume

Question 47

Radioactive implants

Answer 47

Small seeds or tiny rods used to attack tumour from inside the body. sources place inside tumour or in nearby tissue
with low dose rate the implants can stay in for hours or days

Question 48

What is irradiation

Answer 48

When something has been irradiated, the irradiation stops as soon as the source of radiation has been removed

Question 49

What is contamination

Answer 49

When contamination has occurred the source of ionising radiation itself is transferred such as when radiation isotopes in sold liquid or gas are introduced into the environment

Question 50

What is nuclear fission

Answer 50

Splitting of a large nucleus into 2 smaller nuclei (daughters) releasing energy

Question 51

Which nuclei are usually split in fission reactions

Answer 51

Uranium-235 or plutonium-239

the numbers are the mass number so the number of protons and electrons the element has

Question 52

What is induced fission

Answer 52

When a neutron is fired at the nucleus, causing it to split

Question 53

What is released in nuclear fission and how is it a chain reaction

Answer 53

2 or 3 neutrons released
energy in form of radiation and kinetic energy
Neutrons released may cause further and further fission resulting in a chain reaction

Question 54

What is the energy released in fission used for

Answer 54

Used to heat water, turning the it into steam
steam turns turbine which turns generator which transforms kinetic energy into electrical energy
level of energy produced must remain constant for output of power station to be constant

Question 55

What is nuclear fusion

Answer 55

Happens when 2 nuclei collide and fuse together, forming a larger nucleus releasing energy in the process
the colliding energy need enough kinetic energy otherwise they’ll repel and not fuse

Question 56

How does fusion work in a fusion reactor

Answer 56

Heated by passing and electric current through it
gas becomes so hot it forms a plasma of small nuclei
plasma contained using a magnetic field to prevent it from touching container walls otherwise will cool down and fusion stops
When hydrogen nuclei fuse together helium is formed as one of the products

Question 57

Example of nuclear fusion

Answer 57

process powering the sun and stars
in the core of the sun, hydrogen is converted into helium by fusion providing enough energy to keep sun burning an sustain life on earth

Question 58

Ads of fission

Answer 58

Concentrated source of energy so more J/kg
no polluting gases
supply of uranium for many years
reliable 24/7

Question 59

Disads of fission

Answer 59

Produces radioactive waste
chain reaction to control with severe consequences
expensive

Question 60

Ads of fusion

Answer 60

Produces very little radioactive waste-safer
no chain reaction to control
very concentrated source of energy
fuel readily available (hydrogen in water)
renewable and cheap

Question 61

Disads of fusion

Answer 61

Not yet viable

fusion on earth needs more energy input than the energy output