Radioactivity Flashcards
Only one or two of an elements isotopes are stable. What happens if they are unstable ? This is radioactive decay
They can decay into other elements by emitting radiation like alpha beta or gamma
Ionisation
Radioactivity can cause ionisation in atoms. The high energy radiation strikes the atom making it able to knocks off an electron. This will give it a net positive charge. This free electron may then attach itself to another atom giving this one a net negative charge. In this way a radioactive source can produce a number of positive and negative ions.
How can ionisation be detected?
using a photographic film or a Geiger-Muller tube.
Alpha radiation
-10% speed of light
-Most ionising
-2 protons and 2 neutrons (same as helium nucleus)
-Penetrate a few cm of air
-Stopped by paper
Alpha particles hit another particle with enough energy so an electron can be knocked off.
Beta particles
-90% speed of light
- An electron
-Penetrate paper
-Stopped by a few mm of aluminium
Gama rays
- Speed of light
- Least ionising
- An electromagnetic wave
- Penetrate a few cm of lead
ALPHA
𝛼
-Atomic number decreases by 2.
-Mass number decreases by 4.
-Can also be represented as Helium, He
BETA
β
-One of the neutrons in the nucleus turns into a proton and an electron (beta particle).
- Atomic number increases by 1.
Mass number stays the same because even though it lost a neutron it gained a proton.
-write the beta particle with the beta symbol or with and e for electron. Both need to have a 0 on top (as mass is pretty much zero) and -1 at the bottom (charge of -1)
GAMMA
𝛾
-Atomic number stays the same.
-Mass number stays the same.
(don’t change because they don’t have mass or change)
-represented as the gamma symbol
Half life definitions
-Half-Life is defined as the amount of time required for the number of radioactive nuclei in a sample to half.
-Half-Life is defined as the amount of time required for the Radioactivity of a sample to half
Why and when do particles decay?
When an unstable radioactive nucleus decays it emits radiation (alpha, gamma, beta) and change into a new element. It is impossible to know when each particle will decay as it is random.
How to find half life?
Plot graph of time against activity. See the time it takes for activity to half. That is your half life (In hours)
The half-life of source is 40 hours. There are initially 3 000 000 radioactive nuclei in the sample.
How many nuclei will remain after 5 days.
1) discover how many half-lives
2) half the number of initial radioactive nuclei that many times
24x5= 120h
120/40= 3 half-lives
3 000 000/ 2= 1 500 000
1 500 000/ 2= 750 000
750 000/ 2= 375 000
Let us imagine that a doctor has choice of three radioactive substances with different half lives: 2 minutes, 12 hours and 4 years. Which one would be best to use. Explain why.
You should try to use the smallest half lives but still long enough to be able to do the experiment. For to long periods of time can be harmful specially alpha because it is the most ionising therefore can cause most harm.
Contamination
when radioactive particles get on to other objects
