14. GM tube
Radiation
Enters through
mica window
240 V
Ionizes
argon gas
Pulse of
current
produced
Pulse of current
counted using
ratemeter/scaler
Number of
counts
period of time
15.
16. spark counter
Suitable for alpha rays
ionizes
the air
between the
gauze and the
wire
radioactive
source is
brought near
sparks
are produced
17. radioactive decay
• Nuclei that have too
few or too many neutrons are
unstable.
the process of a nucleus changing to a
more stable nucleus while emitting
most likely to be
•
radiation.
• Nucleus before the decay = parent
product of the decay
•
•
nuclide
= daughter nuclide.
The daughter nuclide may still be unstable and will eventually decay into another
nuclide.
This process continues until a stable nuclide is reached.
18. Alpha decay
-This type of decay usually
happens to the heavier
unstable nuclei.
-The proton number is reduced by
2 while the nucleon number is
reduced by 4 and emit αparticles
238
92
U
238 – 4 = 234
92 – 2 = 90
Th +
4
2 He
19. 14
6C
14 - 0 = 14
N
6 - (-1) = 7
+
0
-1
e
Beta decay
-Beta decay usually occurs
for nuclei that have
an
excess of
neutrons.
- There is no change in
the nucleon number but the
proton number increases by 1
and emit β-particles
20. Gamma decay
-occurs when an unstable nucleus
releases its excess energy [ high
frequency electromagnetic
waves ] called γ-rays.
-no change in proton number and
nucleon number but emit γ-rays
-A nucleus that undergoes alpha or beta
decay may
60
Co
27
also emit γ-rays.
60
27
Co +
γ
21. half-life
• Time taken for undecayed nuclei to be
reduced to half of its original number
• The number of unstable nuclei have not
decayed decreases with time.
• The half-life constant ~ the decay process
is random and large.
22. 128
64
Original number of
undecayed nuclei
= 256
Half of original number = 128
It takes 3 hours for the
undecayed nuclei to be reduced
to half of original number.
∴ 1 half-life = 3 hours
