Transcript Cathode Ray Oscilloscope

Radiation Detector
Gold Leaf electroscope
Geiger Muller Tube
3
Radiation Detector
Diffusion Cloud Chamber
4
Characteristics of α, β, and γ
Radiations
• Ionizing Power
• Penetrating Power
• Deflection by Electric and
Magnetic Fields
5
Ionizing Power
6
Penetrating Power
7
Deflection of α, β, and γ Rays
Type of Radiations
• Alpha (α) particles
> Helium Nucleus ( 42He)
> Positive Charge
> high mass
> a few centimeters range in air
> slight deflection in electric/magnetic fields.
> strong ionization
> can be stopped by thin paper
> Pure source: Americium (Am-241)
Type of Radiations
• Beta (β) particles
> High-energy electron (0-1e)
> Negative Charge
> low mass
> a few meters range in air
> great deflection in electric/magnetic f.
> weak ionization
> can be stopped by aluminium (5mm)
> Pure source: Strontium (Sr-90)
Type of Radiations
• Gamma (γ) rays
> High-energy electromagnetic radiation
> un-charge
> zero mass
> a few hundred meters range in air
> none deflection in electric/magnetic field.
> very weak ionization
> can be stopped by thick lead or concrete
> source: Cobalt (Co-60) covered by
aluminium
Radioactive Decay
• After ejecting particles, a nucleus becomes
the nucleus of a different element. It’s called
radioactive decay.
• If the new element is also unstable, the
process of decay will continue until there are
atoms with stable nuclei.
242
94
Pu
238
92
U
234
90
Th
Radioactive Decay
• Alpha Decay.
A
Z
X
A-4
Z- 2
X
+
4
2
He
Parent
nuclide
Daughter Alpha particle
nuclide (helium nucleus)
226
88
222
86
Ra
Rn
+
4
2
He
Radioactive Decay
• Beta Decay.
A
Z
X
Parent
nuclide
90
38
Sr
A
Z1
X
Daughter
nuclide
90
39
Y
+
0
-1
e
Beta particle
(electron)
+
0
-1
e
Radioactive Decay
• Gamma Rays are usually given off during both
Alpha decay and Beta decay.
226
88
90
38
Ra
Sr
222
86
Rn
90
39
Y
+
+
4
2
He
+ 
0
-1
+ 
e
Half Life
16
Half Life
17
Plutonium-238 (plutonium oxide). The plutonium
glows in the dark as a result of nuclear fission
reactions which release enough energy to increase
the metal's temperature to red-heat. The heat
produced by plutonium has been used as an energy
source on spacecraft.
18
Sample Problems
1.
A radioactive source has a half-life of 10
minutes. What fraction is left in 1 hour?
2.
Carbon-14 has a half-life of 5700 years. A 10 g
sample of wood cut recently from a living tree
has an activity of 160 counts/minute.
A piece of charcoal taken from a prehistoric
campsite also weight 10 g but has an activity of
40 counts/minute. Estimate the age of the
charcoal.
19
Sample Problems
3.
The ratio of the number of atoms of argon-40
to potassium-40 in a sample of radioactive rock
is 1 : 3.
Assuming that there was no potassium in the
rock originally and that argon-40 decays to
potassium-40 with a half life of 1500 million
years, estimate the age of the rock.
4.
Radioactive Uranium-238 (U, proton number
92) decays to thorium (Th), emitting an alpha
particle and gamma rays. Show this decay
reaction as a nuclide equation
20