atomic structure

Question 1

Atoms

Answer 1

Atoms are very small, having a radius of about 1×10^(−10) metres.

Question 2

basic structure of an atom

Answer 2

The basic structure of an atom is a postively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.

Question 3

basic structure of an atom - nucleus

Answer 3

The radius of a nucleus is less than 1/10 000th of the radius of an atom (A pea compared to a football stadium). Most of the mass of an atom is concentrated in the nucleus.

Question 4

basic structure of an atom - electrons

Answer 4

The electrons are arranged at different distances from the nucleus (different energy levels).

Question 5

basic structure of an atom - electrons - absorption

Answer 5

The electron arrangements may change with the absorption of electromagnetic radiation move further from the nucleus; a higher energy level)

Question 6

basic structure of an atom - electrons - emission

Answer 6

The electron arrangements may change with the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level).

Question 7

electrons in an atom

Answer 7

In an atom the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.

Atoms turn into positive ions if they lose one or more outer
electron(s).

Question 8

atomic no

Answer 8

All atoms of a particular element have the same number of protons.
The number of protons in an atom of an element is called its atomic number.

Question 9

mass number

Answer 9

The total number of protons and neutrons in an atom is called its mass number.

Question 10

isotopes

Answer 10

Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.

Question 11

Type of Radiation - Alpha (α)

Answer 11

What is it? - Helium nucleus - 2 protons + 2 neutrons
Ionising Power? - Strongly ionsing
What material stops it? - Paper
Range in air? - 2-3cm of air
Uses of radiation: smoke detectors
Because…it is highly ionising and cannot penetrate the casing

Question 12

Type of Radiation - Beta (β)

Answer 12

What is it? - A fast moving electron
Ionising Power? - Weakly/moderately ionising
What material stops it? - 3mm aluminium
Range in air? - 1-2m air
Uses of radiation: measuring the thickness of cardboard/foil
Because…Thicker cardboard absorbs more beta radiation, but would not stop gamma and would absorb all alpha

Question 13

Type of Radiation - Gamma (γ)

Answer 13

What is it? - EM radiation - gamma rays
Ionising Power? - Very weakly ionsing
What material stops it? - Many cm of lead
Range in air? - 1 km of air
Uses of radiation: medical tracers
Because…it is the only radiation that will be detected outside the patient (it is the most penetrating) it is also the least ionising

Question 14

radioactive decay

Answer 14

Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process called radioactive decay.

Question 15

Nuclear Activity

Answer 15

Activity is the rate at which a source of unstable nuclei decays.
Activity is measured in: Becquerel (Bq)

Question 16

Count-rate

Answer 16

the number of decays recorded each second by a detector (eg Geiger-Muller tube).

Question 17

The four kinds of nuclear radiation are:

Answer 17

alpha
Beta
Gamma
neutron

Question 18

Alpha Decay

Answer 18

In an alpha decay the nucleus ejects an alpha particle

Note the equation must balance: the mass number and atomic number must be equal on both sides!

Question 19

beta decay

Answer 19

In a beta decay a high speed electron is ejected from the nucleus as a neutron turns into a proton.

Question 20

gamma decay

Answer 20

There is no decay equation for gamma decay as it causes neither the mass number or the proton to change. The nucleus just loses energy.

Question 21

Half Life

Answer 21

Radioactive decay is random

The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve
or
the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.

Question 22

natural sources Background Radiation

Answer 22

rocks
cosmic rays
Radon gas

Question 23

man-made sources Background Radiation

Answer 23

nuclear weapons testing
Nuclear accidents

Question 24

Background Radiation

Answer 24

Background radiation is around us all of the time. It comes from natural & man-made sources.

The level of background radiation and radiation dose may be affected by occupation (e.g. airline pilot) and/or location(e.g. living in Cornwall).

Question 25

Radioactive contamination

Answer 25

Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard. E.g alpha emitters are most dangerous when breathed in or consumed

Question 26

Irradiation

Answer 26

Irradiation is the process of exposing an object to nuclear radiation. The irradiated object does not become radioactive.

Question 27

how to prevent radioactive contamination

Answer 27

To prevent contamination when entering the area around Fukushima people wear… disposable overall, gloves and respirators (gas masks)

Question 28

how to reduce radioactive irradiation

Answer 28

To reduce irradiation from nuclear power plants…
Have limited time on site, monitor their exposure with film badges, have radiation shielding around the reactor.

Question 29

Hazards of Nuclear Radiation

Answer 29

Nuclear radiation is dangerous because it is ionsiing. It can damage DNA which can either kill a cell or mutate a cell (potentially causing cancer).

Question 30

The Sievert

Answer 30

Radiation dose is measured in sieverts (Sv)
1000 millisieverts (mSv) = 1 sievert (Sv)

No-one knows what the maximum safe dose is, so it is important for the findings of studies into the effects of radiation on humans to be published and shared with other scientists so that the findings can be checked by peer review.

Question 31

Nuclear Radiation in Medicine

Answer 31

Nuclear radiations are used in medicine for :
* examination of internal organs
* control or destruction of unwanted tissue.

Question 32

Describe how nuclear radiations is used for the exploration of internal organs (i.e. medical tracers)

Answer 32

A gamma source is injected into the patient where it concentrates in particular regions e.g. where damaged tissue is being repaired. A gamma camera can then be used to detect where the gamma source is concentrated

Question 33

Describe how nuclear radiation is used for the control or destruction of unwanted tissue (i.e. radiotherapy)

Answer 33

Gamma radiation can be used to kill cancer cells as gamma rays are able to penetrate deep inside the body.

A beta source can be placed directly inside a tumour as the radiation will damage the tumour but be unable to penetrate to the surrounding tissue

Question 34

What is the risk of using nuclear radiation for exploration and destruction of tissue?

Answer 34

Ionising radiation can cause cancer. its still used because the risk of developing cancer is less than the risk of not correctly diagnosing a disease

Question 35

what is Nuclear Fission

Answer 35

Nuclear fission is the splitting of a large and unstable nucleus (eg uranium or plutonium).
Spontaneous fission is rare.

Question 36

steps of nuclear fission

Answer 36

for fission to occur the unstable nucleus must first absorb a neutron.
The nucleus undergoing fission splits into two smaller nuclei, roughly equal in size, and emits two or three neutrons plus gamma rays.
Energy is released by the fission reaction as the fission products have less mass than the original nucleus and neutron (E=mc2)
All of the fission products have kinetic energy.

Question 37

nuclear fission - chain reaction

Answer 37

The neutrons may go on to start a chain reaction.
The chain reaction is controlled in a nuclear reactor to control the energy released. The explosion caused by a nuclear weapon is caused by an uncontrolled chain reaction.

Question 38

Nuclear Fusion

Answer 38

Nuclear fusion is the joining of two light nuclei to form a heavier nucleus.

In this process some of the mass may be converted into
the energy of radiation.

Question 39

History of the Atom - 1 - John Dalton

Answer 39

1800’s

John Dalton suggests that each of the elements are made from just one type of atom: tiny spheres that could not be divided

Question 40

History of the Atom - 2 - JJ Thomson

Answer 40

1897

JJ Thomson discovers the electron and proposes the plum pudding model: the atom is a ball of positive charge and the negative charge are embedded in it (like blueberries in a blueberry muffin)

Question 41

History of the Atom - 3 - Ernest Rutherford vs thompson

Answer 41

1911

Ernest Rutherford fired alpha particles at a piece of very thin gold foil(about 10,000 atoms thick).

Thomson’s plum pudding model predicted that…
All alpha particles… passed straight through

However what was observed was:
Most alpha particles… passed straight through
A very few alpha particles… were deflected by more than 90 degrees

Most of the atom is empty space
All the positive charge and most of the mass is concentrated in a small volume (the nucleus)

Question 42

History of the Atom - 4 - Niels Bohr

Answer 42

1913

Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances The theoretical calculations of Bohr agreed with experimental observations.

Question 43

History of the Atom - 5 - James Chadwick & other

Answer 43

1920-1932

Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name protons was given to these particles.
In 1932 James Chadwick discovers the neutrons.

Question 44

The Scientific Model

Answer 44

New experimental evidence may lead to a scientific model being changed or replaced if the existing model cannot explain the observation. E.g. The plum pudding model could not explain why a very few alpha particles were deflected by more than 90 degress so a new model (the nuclear model) came to replace it.

Question 45

Length of half life

Answer 45

Different isotopes have different length half-lives. Isotopes with short lives are initially very active but will not remain active for very long. Isotopes with longer half-lives will remain active for much longer.