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GSCE Physics > Radioactivity and Particles > Flashcards

Radioactivity and Particles Flashcards

1
Q

what does an atom consist of?

A

a positively charged nucleus made of:
- positive protons
- neutral neutrons
surrounded by negatively charged electrons which orbit the nucleus

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2
Q

what is the relative mass of a proton?

A

1

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3
Q

what is the relative mass of a neutron?

A

1

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4
Q

what is the relative mass of an electron?

A

0.0005

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5
Q

what is the relative charge of a proton?

A

+1

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6
Q

what is the relative charge of a neutron?

A

0

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7
Q

what is the relative charge of an electron?

A

-1

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8
Q

atoms of the same element have the same number of…

A

protons

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9
Q

what are isotopes?

A

forms of an elements atom with the same number of protons but a different number of neutrons

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10
Q

what does the mass number of an element show?

A

the number of neutrons and protons

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11
Q

what does the atomic number of an element show?

A

the number of protons

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12
Q

what is radioactive decay?

A
  • the spontaneous transformation of an unstable nucleus into a more stable one by the release of radiation
  • it is a random process which means one cannot know what nucleus will decay or when it will decay because it is down to chance
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13
Q

alpha decay process

A
  • a heavy nucleus emits an alpha particle (helium nucleus)
  • the nucleus changes to that of a different element
  • they are highly ionising and weakly penetrating
  • they are stopped by a sheet of paper
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14
Q

beta decay process

A
  • a neutron turns into a proton and emits a beta particle (electron)
  • the nucleus changes to that of a different element
  • they are moderately ionising and moderately penetrating
  • they are stopped by a thin sheet of aluminium
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15
Q

gamma decay process

A
  • after a previous decay, a nucleus with excess energy emits a gamma particle
  • gamma particles are a form of electromagnetic radiation
  • they are lowly ionising and highly penetrating
  • they are stopped by many centimetres of lead
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16
Q

neutron radiation decay

A
  • in neutron-rich nuclides, occasionally one or more neutrons are ejected
  • they are also emitted during nuclear fission
  • the nucleus becomes a new isotope of the original element
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17
Q

what are two ways of detecting radiation?

A
  • photographic film
  • GM tube
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18
Q

how does photographic film detect radiation?

A
  • the more radiation absorbed by the film, the darker its gets (the film is initially white)
  • they are worn as badges by people who work with radiation, to check how much exposure they have had
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19
Q

how does a GM tube detect radiation?

A
  • each time it absorbs radiation, it transmits an electrical pulse to the machine, which produces a clicking sound
  • the greater the frequency of clicks, the more radiation present
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20
Q

what is background radiation?

A

weak radiation that can be detected from external sources

21
Q

what are sources of background radiation?

A

from space:
- cosmic rays include high-energy charged particles penetrating the atmosphere

from Earth:
- radioactive rocks which give off radioactive radon gas
- food and drink which contains radioactive iostopes
- fallout from nuclear weapons testing
- medical sources such as x-rays from MRI scanners
- nuclear power plants which produce radioactive waste

22
Q

what is the activity of a radioactive source?

A

the number of decays which occur per unit time

23
Q

what is activity measured in?

A

becquerels (Bq)

24
Q

the activity of a radioactive sources…

A

decreases over a period of time

25
what is the half-life of an isotope?
the time taken for half the nuclei to decay, or the time taken for the activity to halve
26
what must be subtracted before attempting to perform half-life calculations?
background radiation
27
what are two uses of radioactivity in industry?
- smoke detectors - thickness monitoring
28
how is radioactivity used in smoke detectors?
- long half-life alpha emitters are used in smoke detectors - alpha particles cause a current in the alarm - if smoke enters the detector, some of the alpha particles are absorbed and the current drops, triggering the alarm
29
how is radioactivity used in thickness monitoring?
- long half-life beta emitters can be used for thickness monitoring of metal sheets - a source and receiver are placed on either side of the sheet during its production - if there is a drop or rise in the number of beta particles detected, then the thickness of the sheet has changed and needs to be adjusted
30
what are two uses of radioactivity in medicine?
- sterilisation of equipment - diagnosis and treatment
31
how is radioactivity used in sterilisation of equipment?
- gamma emitters are used to kill bacteria or parasites on equipment so it is safe for operations (this means they can be sterilised through their protective packaging to eliminate the risk of contamination)
32
how is radioactivity used in diagnosis and treatment?
- short half-life gamma emitters are used as tracers in medicine as they concentrate in certain parts of the body - the half-life must be long enough for diagnostic procedures to be performed, but short enough to not remain radioactive for too long - other gamma emitters can be used to destroy tumours with a high dose of radiation
33
when does contamination occur?
when a radioactive source has been introduced into or onto an object - the contaminated object will be radioactive for as long as the source is on it
34
what does irradiation occur?
when an object is exposed to a radioactive source which is outside the object - the irradiated object does not become radioactive
35
what happens when something has exposure to radiation?
radiation can destroy all living cell membranes by ionisation, causing the cells to die, or damage DNA which causes mutations that could lead to cancer
36
what are safety measures to take when handling radiation?
- minimising the time of exposure to radiation, keeping as a big distance from the radioactive source as possible, and using shielding against radiation (such as protective clothing made from dense materials such as lead) - radioactive waste from nuclear reactors must be disposed of carefully, usually by burying it in sealed drums deep underground and remotely handling it after it has been thoroughly cooled
37
what is nuclear fission?
the process of splitting a nucleus
38
what happens during nuclear fission?
when a uranium-235 nucleus absorbs a thermal neutron, it splits into two daughter nuclei and 2 or 3 daughter neutrons, releasing energy in the process
39
how is a chain reaction induced in nuclear fission?
the neutrons can induce further fission events by striking other uranium-235 nuclei
40
in a nuclear reactor, what do control rods do?
they are used to absorb neutrons and keep the number of neutrons such that only one fission neutron per event goes on to induce further fission
41
in a nuclear reactor, what are control rods made of usually?
boron
42
in a nuclear reactor, what does the moderator do?
slows down neutrons by collisions so that they are moving slow enough to be absorbed by another uranium-235 nucleus
43
in a nuclear reactor, what is the moderator usually made out of?
water
44
in a nuclear reactor, what does the coolant do?
it is used to prevent the system from overheating
45
in a nuclear reactor, what is the coolant usually made out of?
water
46
in a nuclear reactor, what is the reactor core?
- the reactor core is a thick steel vessel which withstands the high pressures and temperatures and absorbs some of the radiation - the whole core is kept in a building with thick reinforced concrete walls that act as radiation shields to absorb all the radiation that escapes to the reactor core
47
what is nuclear fusion?
- the process of fusing two nuclei to form a larger nucleus - there is a very small loss of mass in the process, accompanied by a release of energy
48
how do the sun and other stars release energy?
nuclear fusion
49
why can nuclear fusion not happen at low temperatures and pressures?
because the electrostatic repulsion of the protons is too great

GSCE Physics (9 decks)

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