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Physics > Atomic Structure > Flashcards

Atomic Structure Flashcards

1
Q

The diameter of an atom is about 0.000 000 000 2 m. What is this distance in standard form?

A

2 x 10 -10 m

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2
Q

What is the nucleus of an atom composed of?

A

Protons and neutrons (except Hydrogen which has no neutrons).

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3
Q

Describe what happens when an electron drops to a lower energy level in an atom.

A

It releases a photon of electromagnetic radiation.

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4
Q

An atom of sodium is represented by:
23 Na 11
Use this information to determine the number of protons, neutrons and electrons in an atom of sodium.

A

Protons = 11 Neutrons = 12 Electrons = 11

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5
Q

What is the electrical charge attached to a neutron?

A

Neutral

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6
Q

What is the electrical charge attached to a electron?

A

Negative

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7
Q

What is the electrical charge attached to a proton?

A

Positive

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8
Q

What is the mass number and the atomic number for fluorine?

19 F 9

A

Mass number = 19; atomic number = 9

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9
Q

What are the two most common isotopes for uranium?

A

236 U 92

239 U 92

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10
Q

Show the number of protons, neutrons and electrons in

236 U 92

A

Protons: 92
Neutrons: 144
Electrons: 92

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11
Q

Show the number of protons, neutrons and electrons in

238 U 92

A

Protons: 92
Neutrons: 146
Electrons: 92

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12
Q

Which scientific discovery resulted in the solid atom theory being adapted into the “plum pudding” model of the atom?

A

Discovery of the electron (in 1897)

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13
Q

Rutherford carried out an experiment to show alpha particles either passing through gold leaf, being scattered off it. Summarise the conclusions he made from this experiment.

A

Most passing through suggests atoms are mostly empty space.
Some being deflected suggests the nucleus has the same charge as the alpha particle (positive).
A few reflected suggests the nucleus is where most of the mass of the atom is

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14
Q

What contribution did Niels Bohr make to the arrangement of electrons in the atomic model?

A

He realised that electrons orbit the nucleus in clearly defined energy levels, at different distances from the nucleus.

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15
Q

Which part of an atom is involved with radioactive decay?

A

The nucleus only.

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16
Q

Explain the meaning of the term activity as applied to

radioactive materials and state the units of activity.

A

The rate at which a source of unstable nuclei decays. Units Bq

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17
Q

What is meant by the term “count rate”?

A

The number of radioactive decays recorded in a given time.

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18
Q

What is the symbol of radiation beta?

A

β

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19
Q

What is the symbol of radiation gamma?

A

γ

20
Q

What is the symbol of radiation alpha?

A

α

21
Q

What is the composition of beta?

A

An electron

22
Q

What is the composition of gamma?

A

Electromagnetic wave

23
Q

What is the composition of alpha?

A

2 protons and 2 neutrons

24
Q

What is the electrical charge of beta?

A

-1

25
Q

What is the electrical charge of gamma?

A

0

26
Q

What is the electrical charge of alpha?

A

+2

27
Q

A piece of radioactive rock shows a reading of 350 counts/min.
When covered in aluminium foil, this drops down to 4 counts/min.
Explain which type of radiation this rock is emitting.

A

Could be alpha or beta as both would be stopped by the foil and gamma would not be stopped by the foil.

28
Q

Radioactive emissions are often described as ionising radiations. What does this mean?

A

The emissions knock off electrons from atoms which then become ions.

29
Q

Smoke detectors use americium-241 which is an alpha emitter. Explain why an alpha source is used in these detectors

A

Alpha particles are easily stopped by smoke.

They do not travel far in air so are safe for the user.

30
Q

Why is an alpha particle often described as a helium nuclei?

A

It contains 2 protons and 2 neutrons, the same as the nucleus of a helium atom

31
Q

When iodine 131 decays, there is no mass change in the nucleus and no new products formed. What type of radioactive emission is this?

A

Gamma emission

32
Q

Explain what is meant by the term “half life”

A

The time it takes a radioactive sample to lose half its radioactivity (as measured by count rate).

33
Q

Explain the difference between radioactive irradiation and radioactive contamination.

A

Irradiation is exposure to emissions from radioactive materials that are not in contact with an object. Contamination is when
radioactive materials are in contact with the object.

34
Q

What is the method of preventing exposure for irradiation?

A

Wear protective clothing, e.g., lead apron, to shield from radiation.
Move away from the radiation.
Shield the radiation with appropriate material.

35
Q

What is the method of preventing exposure for contamination?

A

Avoid contact with radioactive materials.

Prevent radioactive materials being released into the environment.

36
Q

Describe sources of background radiation, clearly identifying which are natural and which are man made.

A

Natural – rocks, cosmic radiation, building materials

Man made – fallout from nuclear weapons testing, nuclear power accidents, industrial and medical waste.

37
Q

Describe two occupations where the radiation dose received by workers is likely to be higher than the background radiation.

A

Working in the nuclear industry, as a radio-medical worker, working with
radioisotopes in industry.

38
Q

Lithium-8 is a beta emitter with a half life of 0.8 s. What precautions would you take when working with this isotope?

A

Take care not to ingest any material or come into contact with it (gloves, safety glasses, lab coat).
Isolate the material for 24 hours to allow it to decay to a safe level.

39
Q

Radium - 226 is an alpha emitter with a half-life of 1600 years. Explain how
the way this material is stored is influenced by these properties.

A

Any sealed container will prevent radiation escaping as alpha particles are not very penetrating. Radioactive material will need to be placed in permanent storage, buried underground, as it will be radioactive for a very long time.

40
Q

The diagram shows how three separate gamma beams are used to treat a cancer tumour.
Why is this preferred to using one powerful
beam?

A

Single beam will damage both healthy or cancer
cells but all three beams are focussed on the tumour so these cells receive a triple dose of radiation to kill them and reduces harm to healthy cells.

41
Q

Alpha emitting radioisotopes cannot be used as tracers in the body to explore injured or diseased organs. Why?

A

Alpha particles are highly ionising so they will cause damage to bodily cells.
They are also easily absorbed by body tissue so they will not escape the body to be detected.

42
Q

Which particle is needed to begin the fission of a large, unstable nuclei?

A

A neutron

43
Q

During the fission of uranium, two smaller nuclei are produced and what else?

A

A number of neutrons and large amounts of energy.

44
Q

Explain what is meant by a controlled chain reaction.

A

Nuclear fission reaction where some of the neutrons produced in the reaction are absorbed to prevent the reaction running out control.

45
Q

What is nuclear fusion?

A

The joining of two small nuclei to form a single larger nucleus.

46
Q

Where does nuclear fusion take place on a large scale?

A

In stars (sun)

Physics (4 decks)

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