Transcript Discovery of Radiation

NUCLEAR CHEMISTRY
Discovery of Radiation
Roentgen (1895)
•Studied fluorescent materials
that glowed when hit with a
beam of electrons.
•Discovered a mysterious form of
radiation was given off even without
electron beam. This radiation could
pass through paper and other
objects but not dense materials
(lead, bone).
•Called them X-rays
Becquerel (1896)
•Studied fluorescent minerals
containing uranium.
•Discovered radioactivity by
accident on a cloudy day:
•Thought that an external
source was needed to
produce the mysterious
radiation.
•Found that uranium emits
radiation without external
source.
Pierre and Marie Curie
Thought radioactivity was a
property of heavy elements.
During study, discovered new
radioactive elements:
Polonium and Radium.
Wondered how small mass
can give off large amount of
energy:
Explained by Einstein with E=mc2.
Rutherford
•Studied radioactivity and named types of nuclear radiation.
•Discovered that elements decay into other elements
after emitting nuclear radiation. Called it Nuclear Decay.
•Gold foil experiment revealed that the mass of an atom
is concentrated in the nucleus (atom is mostly space)
Atomic Structure
Recall:
Atoms – consist of a positively charged nucleus, which has protons and
neutrons.
Isotope – atoms of the same chemical element that have a different
number of neutrons. Each isotope of a given element is designated by
the total number of its protons plus its neutrons.
Isotope
Mo-101
H-2
C-14
U-238
Bi-210
He-4
Symbol
101
42
2
1
14
6
238
92
210
83
4
2
Mo
H
C
U
Bi
He
# protons
# neutrons
Atomic Mass
42
59
101
1
1
2
6
8
14
92
146
238
83
127
210
2
2
4
Nuclear Forces
same
1. Electric repulsion – ________
charge particles
repel each other
2. Strong Nuclear Force – causes protons and
attract each other
neutrons to ________
greater
•Stable Nuclei = strong nuclear force is ________
than repulsion force
•Unstable Nuclei = strong nuclear force is
less
________
than repulsion force
oHave too many or too few neutrons in nucleus
oHave more than 83 protons in nucleus
oWill undergo radioactive decay to form a more
stable nucleus
Nuclear Decay
• Why nuclides decay
– need stable ratio of
neutrons to protons
•Transmutation-One
element becomes another.
238
92
U
234
90
I
131
54
131
53
38
19
106
47
Th  He
4
2
Xe  e
0
-1
K  Ar  e
38
18
Ag  e 
0
-1
0
1
106
46
Pd
More than 83 protons means
that the nuclei is unstable
(radioactive)
Types of Radiation
• Alpha particle ()
– helium nucleus
• Beta particle (-)
– electron
• Positron (+)
– positron
• Gamma ()
– high-energy photon
4
2
Charge Shielding
He
2+
0
-1
1-
e
0
1
0
0
e

paper
lead
1+
0
concrete
Penetrating Ability of Radiation
Alpha Emission
occurs when the nucleus has
too many protons which cause
excessive repulsion.
238
92
parent
nuclide
U
Th  He
234
90
daughter
nuclide
4
2
alpha
particle
Numbers must balance!!
Alpha Emission
Ex. Plutonium-239 undergoes alpha decay
239
94
Atomic Mass:
Atomic #:
235
92
Pu
U
+
4
2
He
239
=
235
+
4
94
=
92
+
2
Masses must be equal = Conservation of mass
Alpha Emission
Ex. Polonium-210 undergoes alpha decay to produce
this daughter nuclide
210
84
Atomic Mass:
Po
210
-
210
Atomic #:
A
Z
4
=
=
2
=
=
84
84
A
Z
-
X
=
+
A
A
+
X
=
206
Z
+
Z
=
206
82
Pb
82
4
2
4
2
He
Beta Emission
occurs when the neutron to proton ratio is too great.
131
53
I
131
54
Xe  e
0
-1
electron
Beta Emission
Ex. Polonium-210 undergoes beta decay to produce
this daughter nuclide
210
84
Atomic Mass:
Po
210
-
210
Atomic #:
A
Z
0
=
=
1
=
=
84
84
A
Z
+
X
=
X
+
A
A
0
+
-1
=
210
Z
+
Z
=
210
85
At
85
0
-1
e
Positron Emission
Occurs when the neutron to proton ratio is too small.
38
19
K  Ar  e
38
18
0
1
positron
Positron Emission
Ex. Polonium-210 undergoes positron emission to produce
this daughter nuclide
210
84
Atomic Mass:
Po
210
-
210
Atomic #:
A
Z
0
=
=
1
=
=
84
84
A
Z
-
X
=
X
+
A
A
0
+
1
=
210
Z
+
Z
=
210
83
Bi
83
0
+1
e
Electron Capture
occurs when the neutron to proton ratio in the nucleus is too small.
106
47
Ag  e 
0
-1
106
46
Pd
electron
Electron Capture
Ex. Polonium-210 captures an electron to produce this
daughter nuclide
210
84
Po
Atomic Mass:
0
+
-1
210
A
Z
e
+
0
A
Atomic #:
84
+
-1
Z
A
Z
X
=
=
=
=
=
A
210
Z
83
210
83
Bi
X
Gamma Emission
occurs when the nucleus is at too high an energy.
– Emission of high energy electromagnetic
wave.
Gamma Emission
Ex. Polonium-210 undergoes gamma decay to produce
this daughter nuclide
210
84
Atomic Mass:
Atomic #:
A
Z
Po
A
=
=
Z
=
=
210
84
A
Z
X
=
X
+
0
0
A
+
0
Z
+
0
210
84
210
84
Po

Write Nuclear Equations!
Write the nuclear equation for the beta
emitter Co-60.