Radioactivity

Question 1

Describe JJ Thomposons model of the atom

Answer 1

The plum pudding model, with the atom being spheres of positive charge with tiny electrons stuck inside them

Question 2

Describe Rutherfords model of the atom

Answer 2

Rutherford believed that the atom was mainly empty space, and proved this with the gold foil experiment. Alpha particles (Helium Nuclei) deflected off the centre of the atom (Nuclei) but most just passed through empty space.

Question 3

Describe the modern day atom

Answer 3

A nucleus made of protons and neutrons with electrons orbiting at set distances. Most of the mass is in the nucleus. Protons have +1 Charge, Neutrons have 0 and Electrons have a -1 charge.

Question 4

Whats the overall charge of an atom?

Answer 4

0, they are neutral

Question 5

What happens if an electron absorbs EM Radiation and has the right amount of energy?

Answer 5

The electron will move up an energy level into the next shell. Eventually with enough EM Radiation the electron will fire off out of the atom.

Question 6

What happens if material changes in the nucleus?

Answer 6

It produces gamma rays.

Question 7

Define ionisation

Answer 7

If an atom loses an electron its ionised

Question 8

What ionises atoms?

Answer 8

Nuclear radiation.

Question 9

Define Isotopes

Answer 9

An element that has a different number of protons to its standard form. If a atom is not stable it will radioactively decay until it is.

Question 10

Alpha particles

Answer 10

Helium Nuclei - emitted from the nucleus of an atom. Strong ionising power, Low penetration Eg: will be stopped by paper.

Question 11

Beta (-/+) particles

Answer 11

Fast moving - emitted from the nucleus. Virtually no mass and a relative charge of -1 (B-). Moderately ionising.
B+ particles are electrons but with a +1 charge. They can both penetrate a few metres in air and will be absorbed by a sheet of aluminium about 5mm thick.

Question 12

Gamma Rays

Answer 12

Short wavelength - Penetrates deep into materials, will travel a long way in air. Weakly ionising as they tend to pass through rather than collide. When they do hit something they do Damage. They can be absorbed by lead or metres of concrete.

Question 13

Alpha decay Equation

Answer 13

DECREASES CHARGE AND MASS OF THE NUCLEUS

DECREASES BY 4 MASS
DECREASES BY 2 ATOMIC NUMBER

Question 14

Beta decay Equation

Answer 14

Mass number stays the same

Atomic number +1 (Neutron into a proton)

Question 15

Positron emission

Answer 15

Decreases charge of the nucleus (beta plus)

Mass number decreases.

Question 16

Half life definition.

Answer 16

Time taken for number of radioactive nuclei in a substance to halve.

Question 17

How can radiation damage cells by ionisation?

Answer 17

Radiation can enter living cells and damage them. Lower doses tend to not kill the cell but just damage it - this results in a mutant cell and this is what causes diseases like cancer

Question 18

Irradiation

Answer 18

Exposing objects to beams of radiation is called irradiation. Irradiation from radioactive decay can damage living cells.

Irradiation can be used to preserve fruit and sterilise objects. Gamma rays can be used to kill cancerous tumors deep inside the body.

Question 19

Advantages/disadvantages of irratiaton

Answer 19

+ it can be used to kill bacteria on things that would melt
+ can be done without high temps.

• May not kill all bacteria on an object
• can be very harmful to people.

Question 20

Nuclear fission

Answer 20

Splitting of large atomic nucleus into smaller nuclei.

Nucleus splits into 2 large fragments called daughter nuclei.

Question 21

Fission reactors.

Answer 21

Contains Nuclear fuel, A moderator (Graphite core for example), Control rods, coolant, and a concrete shield.

Many features are designed to control the speed of the reaction and the temp. inside the shielding. Uncontrolled fission is the basis of an atomic bomb.

Question 22

Advantages/Disadvantages of nuclear power stations.

Answer 22

+ clean energy, no polluting gasses
+ doesnt contribute to global warming
+ high research benefits other industries
+ power station has a very long lifetime.

• Waste is radioactive and difficult to dispose of safely
• Local thermal pollution affects marine life
• Public perception of nuclear power is negative
• costs are very high.

Question 23

Nuclear Fusion

Answer 23

2 small light nuclei join together to make one heavier nucleus. This process is what happens in the sun. The fusion has to happen under immense pressure and very high temperatures to overcome the electrostatic repulsion