7 Radioactivity and Particles

Question 1

what is a becquerel

Answer 1

the amount of times something decays per second

1 Bq = 1 decay per second

Question 2

what is a nucleon

Answer 2

a particle in the nucleus of a atom

proton and neutrons aka the mass number

Question 3

what does the atomic number refer to

Answer 3

the number of protons an atom has

Question 4

what does the mass number refer to

Answer 4

the weight of a atom

the number of protons and neutrons

Question 5

what is a isotope

Answer 5

a element with the same number of protons (and electrons) but a different number of neutrons

Question 6

how are alpha, beta and gamma particles emitted

Answer 6

from a unstable nucleus in a random process

Question 7

what are alpha, beta and gamma particles

Answer 7

highly ionising radiations

Question 8

what is a alpha radiation particle

Answer 8

a helium nucleus -> 2 protons + 2 neutrons

Question 9

what is a beta particle

Answer 9

an fast moving electron

Question 10

what is a gamma radiation

Answer 10

a gamma ray which is a type of electromagnet wave

Question 11

what is the nature of a alpha particle

Answer 11

highly ionising
low penetration -> stopped by paper or a few cm of air
2+

Question 12

what is the nature of a beta particle

Answer 12

medium ionising
medium penetration -> stopped by a few mm of aluminum + a few meters of air
1-

Question 13

what is the nature of a gamma ray

Answer 13

low ionising
high penetration -> stopped by a few mm of lead

Question 14

practical: investigate the penetration powers of different types of radiation using radioactive souces

Answer 14

Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a one minute period
Repeat this three times, and take an average
Now place a radioactive source a fixed distance of 3 cm away from the tube and take another reading over a one minute interval
Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
Repeat the above experiment for other radioactive sources

analysis of results
if the count over that interval falls to background levels (allow for a little random variation), then the radiation has all been absorbed
Note that some sources will emit more than one type of radiation
If the radiation is stopped by paper, the source will be emitting alpha
If the radiation is stopped by a few mm of aluminium (about 5 or 6) then the source is emitting beta
If some radiation is still able to penetrate a few mm of lead (5 or 6) then the source is emitting gamma

Question 15

what happens to the mass number of an atom if it decays by emitting one alpha particle

Answer 15

mass number decreases by 4
atomic number decreases by 2

Question 16

what happens to the mass number of an atom if it decays by emitting one beta particle

Answer 16

mass number stays the same (a neutron turns into proton)
atomic number increases by one

Question 17

what happens to the mass number of an atom if it decays by emitting a gamma ray

Answer 17

mass number stays the same
atomic number stays the same

Question 18

what happens to the mass number of an atom if it decays by emitting one neutron

Answer 18

mass number decreases by 1
atomic number stays the same

Question 19

what can detect ionising radiation

Answer 19

geiger-muller detector
photographic film

Question 20

what are the backround causes of radiation

Answer 20

radon gas - 50% - natural
rocks and building materials - 15% - natural
medical (xrays…) - 13% - man
food - 11% - natural
cosmic rays - 10% - medical

Question 21

does radioactivity decrease over time

Answer 21

yes

Question 22

what is radioactivity measured in

Answer 22

becquerel

Question 23

what does half life mean

Answer 23

The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half

Question 24

is the half life of every element the same

Answer 24

no

Question 25

uses of radioactivity in industry

Answer 25

sterilizing food
determining the age of ancient artefacts
checking the thickness of materials
smoke alarms

Question 26

uses of radioactivity in medicine

Answer 26

sterilising medical equipment
Diagnosis and Treatment of Cancer

Question 27

what is the difference between contamination and irradiation

Answer 27

contamination is:
The unwanted presence of materials containing radioactive atoms on other materials

irradiation is:
The process of exposing a material to alpha, beta or gamma radiation

Question 28

what are the dangers of ionising radiations

Answer 28

can cause mutations in living organisms - ratiation enters nucleus of cell and destroys DNA and when it reforms it may mutate
can cause damage to cells and tissue
the problens arising from the disposal of radioactive waste and how these risks can be reduced (bury the radioactive material however some of them have long half lives

Question 29

what can nucleur reactions (fusion, fission, radioactive decay) be a source of

Answer 29

energy

Question 30

how can uranium 235 be split

Answer 30

by fission

a neutron is fired at the U235 nucleus which makes it unstable
the nucleus splits (fission)
energy is released as kinetic energy of the fission products

Question 31

what is uranium 235 split into

Answer 31

2 smaller radioactive daughter nuclei (not always identical)
a few neutrons
energy

the combined mass of the 2 daughter nuclei equal the parents

Question 32

how can a chain reaction be set up with U235

Answer 32

Only one extra neutron is required to induce a uranium-235 nucleus to split by fission
so one neutron is fired at the U235 nucleus which then splits into two daughter nuclei which decay and produce more neutrons
During the fission, it produces two or three neutrons which move away at high speed
Each of these new neutrons hits a different U235 nuclues which starts another fission reaction, which again creates further excess neutrons

Question 33

what is a chain reaction

Answer 33

a sequence of reactions where a reactive product or by-product causes additional reactions to take place

Question 34

what is a control rod

Answer 34

absorb excess neutrons which increase or decrease the rate of fission

control rods can be moved in and out of the reacter

Question 35

what is a moderator

Answer 35

slows down high speed neutrons
which increases the rate of reaction and making it more efficient

Question 36

what is the purpose of shielding

Answer 36

The purpose of shielding is to absorb hazardous radiation
The daughter nuclei formed during fission, and the neutrons emitted, are radioactive
The reactor is surrounded by a steel and concrete wall that can be nearly 2 metres thick
This absorbs the emissions from the reactions
It ensures that the environment around the reactor is safe

Question 37

what is the difference between fission and fusion

Answer 37

fission splits a larger nucleus into 2 smaller ones and releasing neutrons
can happen at low temperatures and pressures

fusion is 2 smaller nuclei combining into one larger one
cannot happen at low temperatures and pressures
very difficult to make a practical fusion station

Question 38

what is fusion

Answer 38

2 smaller nuclei joined to form a larger one
this larger one is not as big as the total mass of the 2 smaller nuclei as the missing mass is given off as energy

Question 39

what produces energy for stars

Answer 39

fusion

Question 40

what conditions are needed for nuclear fusion

Answer 40

high temperatures
high pressures
high kinetic energy

these are needed to overcome the electrostatic repulsion of the 2 nuclei