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Physics > 7 Radioactivity and Particles > Flashcards

7 Radioactivity and Particles Flashcards

1
Q

what is a becquerel

A

the amount of times something decays per second

1 Bq = 1 decay per second

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2
Q

what is a nucleon

A

a particle in the nucleus of a atom

proton and neutrons aka the mass number

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3
Q

what does the atomic number refer to

A

the number of protons an atom has

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4
Q

what does the mass number refer to

A

the weight of a atom

the number of protons and neutrons

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5
Q

what is a isotope

A

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

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6
Q

how are alpha, beta and gamma particles emitted

A

from a unstable nucleus in a random process

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7
Q

what are alpha, beta and gamma particles

A

highly ionising radiations

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8
Q

what is a alpha radiation particle

A

a helium nucleus -> 2 protons + 2 neutrons

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9
Q

what is a beta particle

A

an fast moving electron

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10
Q

what is a gamma radiation

A

a gamma ray which is a type of electromagnet wave

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11
Q

what is the nature of a alpha particle

A

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

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12
Q

what is the nature of a beta particle

A

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

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13
Q

what is the nature of a gamma ray

A

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

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14
Q

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

A

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

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15
Q

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

A

mass number decreases by 4
atomic number decreases by 2

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16
Q

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

A

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

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17
Q

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

A

mass number stays the same
atomic number stays the same

18
Q

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

A

mass number decreases by 1
atomic number stays the same

19
Q

what can detect ionising radiation

A

geiger-muller detector
photographic film

20
Q

what are the backround causes of radiation

A

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

21
Q

does radioactivity decrease over time

A

yes

22
Q

what is radioactivity measured in

A

becquerel

23
Q

what does half life mean

A

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

24
Q

is the half life of every element the same

A

no

25
Q

uses of radioactivity in industry

A

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

26
Q

uses of radioactivity in medicine

A

sterilising medical equipment
Diagnosis and Treatment of Cancer

27
Q

what is the difference between contamination and irradiation

A

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

28
Q

what are the dangers of ionising radiations

A

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

29
Q

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

A

energy

30
Q

how can uranium 235 be split

A

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

31
Q

what is uranium 235 split into

A

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

the combined mass of the 2 daughter nuclei equal the parents

32
Q

how can a chain reaction be set up with U235

A

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

33
Q

what is a chain reaction

A

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

34
Q

what is a control rod

A

absorb excess neutrons which increase or decrease the rate of fission

control rods can be moved in and out of the reacter

35
Q

what is a moderator

A

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

36
Q

what is the purpose of shielding

A

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

37
Q

what is the difference between fission and fusion

A

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

38
Q

what is fusion

A

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

39
Q

what produces energy for stars

A

fusion

40
Q

what conditions are needed for nuclear fusion

A

high temperatures
high pressures
high kinetic energy

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

Physics (9 decks)

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