Topic 4 - Atomic structure

Question 1

Explain how the model of an atom has changed through time.

Answer 1

1804, john dalton suggessted that matter was made of tiny spheres that couldn’t be broken up. each element was made up of a different type of atom.
1904- jj thomson discovered electrons . Created the plum pudding model which was a ball of positive matter with negative electrons in it.
1909- rutherford fired a beam of alpha particles at a thin gold foil. some were deflected. doscoverd most of the mass of the atom was concentrated at the centre in a nucleus wtih a positive charge as it reppelled the positive alpha particles. - nuclear model
1913- niels bohr discovered that electrons orbit the nucleus in shells called energy levels.
1932- james chadwick discovered the neutron, which explained isotopes.

Question 2

What is radioactive decay?

Answer 2

When an unstable isotope decays into another element , giving out radiation as they try to become more stable.

Question 3

What is ionising radiation?

Answer 3

radiation that knocks electrons off atoms , creating positive ions .

Question 4

What is an alhpa particle made up of ?
how penetrating is it ?
how ionising is it?

Answer 4

2 neutrons and two protons ( a helium atom)
can be stopped by a sheet of paper, can only travel a few centimeters in air
strongly ionising

Question 5

What is a beta particle made up of ?
How penetrating are they?
How ionising are they?

Answer 5

a fast moving electron released by a nucleus.
moderately penetrating, can travel a few metres in air, are absorbed by a 5mm sheet of alluminium .
moderately ionising

Question 6

What are gamma rays made of ?
How penetrating are they ?
How ionising are they ?

Answer 6

waves of electromagnetic radiation
penetrate far into materials , absorbed by thick sheets of lead, or metres of concrete.
weakly ionsing

Question 7

What is half life ?

Answer 7

time taken for the number of radioactive nuclei in an isotope to halve
time taken for the activity to halve

Question 8

what is the activity of a radioactive substance ?

Answer 8

the rate at which a source decays
measured in becquerels

Question 9

how can we measure the count rate of radiation emiited?

Answer 9

using a geiger muller tube and counter

Question 10

Which is safer , substances with short half life or long half life?

Answer 10

short half life
the release high amounts of radiation at the start , but they quickly become safe whereas long half life releases radiation repeatedly for a very long time.

Question 11

What is background radiation?

Answer 11

low level radiation that all around us

Question 12

Give examples of where bacground radiation can come from.

Answer 12

air, food building materials, rocs, cosmic rays,human activity(nuclear waster) .

Question 13

What is irradiation ?

Answer 13

when omething is exposed to radiation.

Question 14

What is contamination?

Answer 14

when unwanted radioactive atoms get onto or into an object/come in contact with it.

Question 15

How can we prevent irradiation?

Answer 15

keeping radioactive sources in lead lined boxes.
face the radioactive source away from you.

Question 16

How can we prevent contamination?

Answer 16

wear gloves and tongs.
wear protective suits.

Question 17

Explain how dangerous the three types of radiation are inside our bodies and outside our bodies.

Answer 17

outside the body, beta and gamma sources are the most dangerous,
They can penetrate the body and get to organse,
alpha is least dangerous as it is weakly penetrating.

Inside the body, alpha sources are the most dangerous,
because they are strongly ionising,
they can damage cells.
gamma sources are the least dangerous as they pass through without ionising

Question 18

What are the risks of using radiation in the human body?

Answer 18

radiation can enter living cells and ionise atoms and molecules within them,
this can lead to tissue dammage
low doses can cause minor damage without killing th ecell,
this leads to mutant cells dividing uncontrollably (cancer)

high doses kill cells completely causing radiation sickness.

Question 19

What are the symptoms of radiation sickness?

Answer 19

vomiting
tiredness
hair loss

Question 20

What are medical tracers and how do they work ?

Answer 20

radiation is injected or swallowed , their progress araound the body is tracked using an external detector,
a computer converts the reading to a display showing where the strongest reading is coming from.
radiation used is usually gamma so that the radiaiation passes out of the body without causing much ionisation.
they should have a short half life so the radioactivity in the patient wuickly dissapears.

Question 21

How does radiotherapy work and what is it used to treat?
what are the side effects?

Answer 21

used to treat cancer
gamma rays are directed at cancer cells.
radiation emmiting implants (beta emmiters) can also be placed next to the tumors.
can kill normal cells.
leads to radiation sickness

Question 22

What is nuclear fission?

Answer 22

a type of nuclear radiation that is used to release energy ffrom large and unstable atoms by splotting them into smaller atoms.

Question 23

What are the products of nuclear fission?

Answer 23

two daughter nuclei (new lighter elements)
a couple of neutrons.

Question 24

What can the energy produced from nuclear fission be used for?

Answer 24

heat water
make steam to turn turbines and generators.

Question 25

How can we controll the amount of energy produced by fission?

Answer 25

control rods
lowered and raised inside a nuclear reactor to absorb neutrons, slow the chain reation and control the amount of energy released.

Question 26

What is the problem with uncontrolled chain reactions (fission) ?

Answer 26

release a lot of enery as an explosion

Question 27

What is nuclear fusion ?

Answer 27

When two nuclei collide at high speed and fuse to create a larger, heavier nucleus

Question 28

Why are fusion reactors hard and expensive to build?

Answer 28

temperatures and pressures needed for fusion are very high.