Transcript Radioactivity - MrSimonPorter

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.
Unstable nuclei
To become stable, an unstable nuclei
emits a particle
Weeeeeeeeeeeeee!
Unstable nuclei
We say the atom has decayed
Weeeeeeeeeeeeee!
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!
Becquerels (Bq)
• The amount of radioactivity given out by a
substance is measured in Becquerels.
One becquerel is one particle emitted per
second.
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
3 main types of
particle
There are 3 main
types of particles
that can be
ejected from an
unstable nuclei.
Alpha particles
Hi!
α
Alpha particles
•
•
•
•
•
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
2+
4
2
He
Alpha Decay
Atomic mass goes down by 4
235
231
4
92
90
2
U
2+
He
+
Th
Atomic number goes down by 2
Beta particles
Yo!
β
Beta particles
•
•
•
•
Fast moving electrons
Stopped by about 3 mm of aluminium
Weakly ionising
Deflected by electric and magnetic fields
0
e
-1
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. http://www.youtube.com/watch?v=lAAmAbJvvJg&feature=related
231
Th
90
antineutrino
Pa + -1e + ‫ע‬e
231
91
0
0
0
Gamma rays
Gamma rays
•
•
•
•
High frequency electromagnetic radiation
Stopped by several cm of lead
Very weakly ionising
NOT affected by electric or magnetic fields
Gamma rays
Associated with alpha decay
235
231
92
90
U
Th +
α
Alpha, beta and gamma
• http://www.youtube.com/watch?v=wsspFQ
n0mWM
Questions (easy and quick!)
• Page 379
• Questions 8, 9, 10, 11, 12, 13
• Use page 778-779 to help