1. Unstable nuclei
Some nuclei are unstable, for example Uranium 235 (it’s to do with the relative numbers of protons and neutrons)
Hi! I’m uranium-235 and I’m unstable. I really need to lose some particles from my nucleus to become more stable.

2. Unstable nuclei To become stable, an unstable nuclei emits a particle
Weeeeeeeeeeeeee!

3. Unstable nuclei
We say the atom has decayed
Weeeeeeeeeeeeee!

4. Unstable nuclei
The decay of an unstable nucleus is random. We know it’s going to happen, but we can’t say when! It is spontaneous. It cannot be affected by temperature/pressure etc.
Weeeeeeeeeeeeee!

5. Becquerels (Bq)
The amount of radioactivity given out by a substance is measured in Becquerels. One becquerel is one particle emitted per second.

6. Detection Particles can be detected by photographic film
Particles can also be detected (and counted) by a Geiger-Müller tube (GM tube) connected to a counter

7. 3 main types of particle
There are 3 main types of particles that can be ejected from an unstable nuclei.

8. Alpha particles
Hi! α

9. He Alpha particles 2+ 4 2 2 protons and 2 neutrons joined together
The same as the nucleus of a helium atom
Stopped by paper or a few cm of air
Highly ionising
Deflected by electric and strong magnetic fields He 2 4 2+

10. Th U He + Alpha Decay 231 235 2+ 4 2 90 92 Atomic mass goes down by 4
Atomic number goes down by 2

11. Beta particles
Yo! β

12. e Beta particles -1 Fast moving electrons
Stopped by about 3 mm of aluminium
Weakly ionising
Deflected by electric and magnetic fields e -1

13. Beta decay
In the nucleus a neutron changes into an electron (the beta particle which is ejected) and a proton (which stays in the nucleus)
During beta decay the mass number stays the same but the proton number goes up by 1.
antineutrino Th 90
231
e + עe Pa 91
231 + -1

14. Gamma rays

15. Gamma rays High frequency electromagnetic radiation
Stopped by several cm of lead
Very weakly ionising
NOT affected by electric or magnetic fields

16. Gamma rays
Associated with alpha decay α Th 90
231 U 92
235 +

17. Alpha, beta and gamma

18. Questions (easy and quick!)
Page 379
Questions 8, 9, 10, 11, 12, 13
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