Transcript Radioactivity

Radioactivity
What you don’t see ...
... can hurt you!.

Nuclear Reaction
any change that involves
nucleus
 1896
- Antoine Henri Becquerel
accidently discovered uranium
ores emit invisible rays.
Radioactivity
his 2 students, Marie Curie and
Pierre Curie, isolated several
radioactive elements.
 Marie Curie named the process
by which uranium gives off rays
of radioactivity – radioactive
decay

The Atomic Nucleus
Made of nucleons..
+ proton & neutral - neutron.
held by“strong nuclear force.”
STRONG NUCLEAR FORCE = force
that holds the nucleus together
As size of nucleus increases, a stronger
force needed to hold nucleus
Radioisotope – unstable isotope which
undergoes radioactive decay
Type of
Decay
Particle
emitted
Change in Change in
mass #
atomic #
alpha
decay
4 He
2
beta
decay
0 β
-1
no change increases
by 1
positron
emission
0 β
1
no change decreases
by 1
electron
capture
x-ray
photon
no change decreases
by 1
gamma
emission
0 γ
0
no change no change
decreases
4
decreases
by 2
Radioactive Decay
Nucleus unstable when too many
Protons & undergoes Radioactive decay
Band of Stability

As long as the ratio of neutrons to
protons is between 1.0 and 1.5, the
atom will be stable.
How can these radiation be stopped?
Alpha Radiation
Radium - 226 decays into radon 222 and alpha particles.
 88Ra226 --> 86Rn222 + 24
 24 = 2e4
 Alpha particles - helium nuclei

Use “Radioisotope, Radio Activity &Radioactive
Decay” to describe the above Nuclear Reaction
The Radioisotope, Radium 226, undergoes
radioactive decay to form Radon. The type of
radioactivity emitted is Alpha radiation
Beta Radiation
38
90
Sr
--> 39
90
Y
+ -


 = e0

-
-1
Beta particles - high speed e-
Electron Capture
nucleus catches one close electron which
combines with a proton to form a neutron
Beta Radiation
 38Sr90
 High
--> 39Y90 + -
speed e- from nucleus?
How is mass the same for Y90
but the charge is greater!
Beta Radiation
--> 39Y90 + -
 Consider neutron decay...
1

 0n --> ? + -
1
1

 0n --> 1p + -
 38Sr90
* Isotopes chemically alike
as protons & electrons
determine chemical
properties
Gamma Radiation
 Iron
- 60 decays to Co-60 &
gamma particles.
 26Fe60 --> 27Co60 +  + 
 0 = electromagnetic rad.
 high energy photons.
Where is Radiation in our Life
 Carbon – 14 dating
 Nuclear Waste
 X-rays
 Radiation therapy for cancer
How they discovered Isotopes:
Hydrogen
–Hydrogen has 3 isotopes
• Hydrogen-1 = “Protium” 11H
• Hydrogen-2 = “Deuterium” 21H
• Hydrogen-3 = “Tritium” 31H
Nuclear Fusion
Nuclear fusion - 2 small nuclei COMBINE
 larger element.
Fusion releases more energy than fission
because only @ very high temp 40,000,000oC
fusion of hydrogen into helium
keeps the sun burning.
Fusion

Fusion is how the sun continually
produces energy.
- 4 11H + 2 0-1β 
4 He + a lot of energy
2
Fusion
Fusion – the combining of atomic nuclei
Fission
Fission – the splitting of a large nucleus
Fission (cont.)

Fission is what nuclear power plants
use for energy.

U – 235 + a neutron =
a chain reaction of
neutrons and energy
The Thorium Decay Series Pg 97
& 97 b
--> 24 + 88Ra228
 88Ra228 --> -+ 89Ac228
228

228
 89Ac
--> - + 90Th
228
4
224
 90Th
--> 2 + 88Ra
 88Ra224 --> 24 + 86Rn220
 86Rn220 --> 24+ 84Po216
 90Th232
The Thorium Decay Series
220
4
216
 86Rn
--> 2 + 84Po
 84Po216 --> 24 + 82Pb212
 82Pb212 --> -+ 83Bi212 or
 83Bi212 --> 24 + 81Tl208
 81Tl208 --> -+ 82Pb208
 82Pb208 is stable
Chernobyl
Hurt
Half-life
Pg 96
& 97a
If you have 100 g of Uranium,
How many half lives are
needed to reach ~ 3% of the
original radioactivity.
50 g  25 g 12.5 g 
100 g 
1 ½
st
life
6.25 g 
5th
½ life
2nd ½
life
3.125 g
3rd
½
life
4th
life
Half – Life Problems:
1)
If I have 50g of Pb-208 and it
has decayed during 2 half-lives,
how much is remaining?
2)
If I have 25g of U-235 and it has
a half-life of one day, how much
will be left after a week?
Critical Mass & The Enola Gay
Nuclear Activities
Directions: Each student will hold 3, 6 or 9 ping
pong balls. Divide the room into two sections.
Throw one ping pong ball. The rule is that when a
student is hit by one ping pong ball, three must
be released randomly.
1.
What happened?
Why?
Directions: Now put the entire class within a 3
meter radius and try again.
2.
What happened?
Why?
Transmutation
conversion of an atom of one
element to another
can induce by striking nuclei
with high velocity charged
particles
Example nuclides with magic
Neutron-Proton
Ratio
numbers of nucleons
and
Nuclear
Stability
includes:
These
proton and neutron numbers
are called “Magic Numbers.”
Magic numbers are:
2 8 20 28 50 82 126
4
2
He
2
a doubly
magic
nucleus
a doubly
magic
nucleus
16
8
O8
40
20
Ca
20
a doubly
magic
nucleus
48
20
Ca
28
a doubly
magic
nucleus
120
50
Sn
70
a singly
magic
nucleus
208
82
Pb
126
a doubly
magic
nucleus
38
Half-life
 time
needed for 1/2 of the
particles to decay.
1. 86
3.
Rn217
234
 He + 213____
4
2
84
U  He + Y + ____
gamma
Ba-140 beta
56
Ba-140

o+
b
-1
140
La
57
Radiation Practice
1) *U – 235 +
→ U – 235
2)
Ag – 107 +
→ In – 111
3)
N – 12 +
→ O -12
4)
Fe – 57 +
→ Ni - 61
Pg 108
7. Show the equation for the fission of
Th-232 with one fission product being
Mo-96 plus the release of 2 neutrons
232
90
Th 
96
Mo +
1
0
n+
1
0
n
If I had 20g of U-235 & it decayed over 3
half-lives, how much would I have left?
1) If I have 10g of U-235 and it has
decayed over 7 half-lives, how much
U-235 will I have remaining?
2)
If I have 40g of Pb-208 and it has a
half life of 15 seconds, how much
will remain after 1 minute?
3) If I have 20g of Pt- 144 remaining after
it decayed for a week. Given that it
has a half-life of a day, how much did
I have originally?
Fusion vs. Fission

There are two processes that make
use of the enormous amount of
energy in a nucleus:
Fusion
and
Fission
Ionizing Radiation
 Ionizing
radiation =
radiation with enough
energy to knock an
electron off an atom
and create an ion.
 X-rays and gamma
rays will ionize almost
any molecule or atom
-
-
X-Rays in Medicine
 Transuranium
Elements are all elements
with an
atomic number of 93 or
greater
–all radioactive
–all man-made (SYNTHETIC)
Leptons
+
e νe
+
μ νμ
+
τ ντ
1 u
Up
quarks
Charm
quarks
3|Vud c 3|Vcd
2
2
d
|
d
|
1 u 3|Vus c 3|Vcs
2
2
s
|
s
|
1 u 3|Vub c 3|Vcb
2
2
b
|
b
|
Example 26-1: Calculate the
Nuclear
Stability
and
mass deficiency for 39K. The
Binding
Energy
actual mass of 39K is 39.32197
amu per atom.
sum of masses of protons, neutrons, and electrons
 19  1.0073 amu   20  1.0087 amu   19  0.0005458 amu 
 19.1387 amu  20.1740 amu  0.0104 amu
 39.32307 amu
52
Fission & Fusion Demos
Directions: Blow up a balloon. Pinch and twist in the center.
Nuclear Fission!
Directions: Put 2 drops of water on the overhead projector.
Nuclear Fusion!
Questions:
1.
Why do Doctors use radioactive isotopes which have
short half lives?
2.
What happens to the nucleus during Nuclear Fission?
3.
How many half-lives does Radon need to live out to get
rid of about 87.5% of the radioactivity?
End here