ⓉⓄⓅⒾⒸ 5 Flashcards

1
Q

An atom consists of:

A

● A positively charged nucleus made of:
○ Positive protons
○ Neutral neutrons
● Surrounded by negatively charged electrons which orbit the nucleus
The radius of the nucleus is a lot smaller than the radius of the entire atom. Almost all the mass of
the atoms lies in the nucleus.

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2
Q

PROTON

A

Particle Proton

Relative Mass 1 Relative Charge+1

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3
Q

NEUTRON

A

Particle neutron
Relative Mass 1
Relative Charge 0

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4
Q

ELECTRON

A

Particle electron
Relative Mass 0.0005
Relative Charge-1

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5
Q

Alpha particle scattering:

A

alpha particle scattering:
● An early model of the atom proposed by JJ Thomson
was the plum pudding model - that the atom consisted
of a cloud of positive charge with negatively charged
electrons dotted around inside it

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6
Q

Rutherford’s scattering experiment

A

he aimed a beam
of alpha particles at a thin gold foil. He concluded that:
○ The atom was composed primarily of empty space
because most alpha particles passed straight through.
○ It had a nucleus which was massive and contained most
of the mass of the atom because it deflected some alpha
particles straight back.
○ The nucleus was positively charged because it repelled
the positively charged alpha particles.

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7
Q

Nuclear fission:

A

● The process of splitting a nucleus is called nuclear fission
● Uranium-235 is a commonly used isotope as the fuel in nuclear reactors
● When a Uranium-235 nucleus absorbs a neutron, it splits into two daughter nuclei
and 2 or 3 neutrons, releasing energy in the process
● The neutrons then can induce further fission events in a chain reaction

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8
Q

Nuclear fusion:

A

● The process of fusing two nuclei to form a larger nucleus is called nuclear fusion
● Energy is released during this process
● Nuclear fusion is how the sun and other stars release energy

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9
Q

Radioactive decay

A

is 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 and when it will decay because it is down to chance.

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10
Q

Decay processes:

A

● Alpha:
● Beta:
● Gamma:

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11
Q

● Gamma:

A

○ After a previous decay, a nuclei 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.
○ They are not deflected by electric and magnetic fields

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12
Q

● Beta:

A

○ A neutron turns into a proton and emits a beta particle (electron)
○ The nucleus changes to that of a different element according to the following
equation: a/z 𝑋 → a/z+1 𝑌 + 0/−1E-
○ They are moderately ionising and moderately penetrating. They are stopped by a
thin sheet of aluminium.
○ They are greatly deflected by electric and magnetic fields

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13
Q

Some ways of detecting radiation

A

● Photographic film:
● Geiger-Muller tube:
● Cloud chamber:

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14
Q

● Cloud chamber:

A

○ A cloud chamber is a small container full of water vapour.
○ Alpha particles create short, broad tracks while beta particles produce long, wispy
tracks

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15
Q

● Geiger-Muller tube:

A

○ A Geiger-Muller tube is a tube which can detect radiation.
○ 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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16
Q

● Photographic film:

A

○ The more radiation absorbed by the film, the darker it 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.

17
Q

Weak radiation that can be detected from external sources is called background radiation

A

● Cosmic rays
● Radiation from underground rocks
● Nuclear fallout
● Medical rays

18
Q

Uses of radioactivity:

A

● Smoke detectors
● Thickness monitoring
● Sterilisation of equipment
● Diagnosis and treatment

19
Q

● Diagnosis and treatment

A

○ Short half life gamma emitters such as technetium-99m 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 such as cobalt-60 can be used to destroy tumours with
a high dose of radiation.

20
Q

● Sterilisation of equipment

A

○ Gamma emitters are used to kill bacteria or parasites on equipment so it is
safe for operations.

21
Q

● Thickness monitoring

A

○ 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.

22
Q

● Smoke detectors

A

○ 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.

23
Q

effects of radioisotopes on cells and safety precautions

A

●Exposure to radiation can destroy living cell membranes by ionisation, causing the cells to die, or
damage DNA which causes mutations that could lead to cancer.

Safety measures include:
● Minimising the time of exposure to radiation. For example, radioactive tracers with a short
half life should be used.
● Keeping as big a distance from the radioactive source as possible. They should be handled
using tongs and held far away from people.
● Using shielding against radiation, such as the concrete shielding around a nuclear reactor.
Radioactive sources must also be kept in a lead-lined box.

24
Q

Half life calculations

A

if element H has an activity of 240Bq, its half life = 3 years, what will its activity be after 12 years

12years divided by 3 = 4 half lifes

-divide 240 by 2, then 2 again, than 2 again, the 2 again

=15Bq