RADIATION AND RADIOACTIVITY Pages 98 - 117
Radiation is the process taking place in the atom’s nucleus which allows unstable elements to become stable. Unstable elements give off radiation.
TYPES OF RADIATION
Type of Nuclear Particle Particle Particle
Decay Change Mass (amu) Charge Description
Alpha Emission of 4 +2 Helium nucleus
4
a
2
Electron Emission of 0 -1 Electron
0
b
-1
Capture of 0 -1 Electron
0
b
-1
Positron Emission of 0 +1 Positron
0
b
+1
Gamma
Emission of rays no no
High-energy
g
particle particle radiation
HALF-LIFE
Def: Time that it takes for one-half the radioactive atoms to go to a stable form. It ranges from nanoseconds to millions of years. Uranium 238 has a half-life of 4.5 billion years.
Biological Half-Life Time it takes an organism to metabolize and get rid of the compound. If you had radioactive carbon, it would take 5723 years for its chemical half-life. If the carbon was in ethanol (booze), most of the carbon would be gone as carbon dioxide within 24 hours.
Nuclear Reactions
226
222
4 0 Ra = radium Rn = radon
Ra ---------à
Rn + a
+ g
88
86
2 0
211
4
Bi=bismuth
Bi
-----------à a
+ ______________
83
2
Beta Emission
0
Electron
b
-1
70
0 70 Ga =
gallium Ge = germanium
Ga
--------à
b + Ge
31 -1
32
113
0
Ag=silver
Ag
------à
b
+ _____________
47
-1
0
b
+1
30
0 30 P = phosphorus Si = silicon
P --------à
b + Si
15
+1 14
23
0 Mg = magnesium
Mg --------à
b + _________
12
+1
What would happen if a proton (p) gave off a positron?
1 0
p
------à
b
+ ________
+1 +1
An electron is captured on the left side of the equation. In the previous cases, the electrons were given off or emitted on the right side of the equation..
0
b
-1
87 0
87 Rb = rubidium Kr = krpton
Rb
+ b
---------> Kr
37 -1 36
73 0
As = arsenic
As
+ b
---------> ______
33 -1
Emission means a particle is given off. The radioactive particle is on the right side of the equation
Capture means a particle is added. The radioactive particle is on the left side of the equation.
1
A heavy nucleus is
bombarded with neutrons. n
0
U = uranium I = iodine Y = ytterbium
235 1 135
97 1
U
+ n ------> I + Y + 4
n + energy
92 0 53
39 0
Ba = barium
235 1
139 1
U
+ n -------> Ba + ______ + 3 n
+ energy
92 0
56 0
Sn = tin Mo = molybdenum
235 1 131
103 1
U
+ n --------> Sn + Mo + _____
n + energy
92
0 50 42
We use neutrons to bombard the nucleus and we get more neutrons as products along with a new element. These neutrons can then bombard new nuclei and get more neutrons and radioactive elements. This is a chain reaction.
Two nuclei combine to form a new nucleus.
2 1 3
H
+ H -------> He
1 1 2
Problems:
Tell whether the new element has a higher or lower atomic number than the starting element for the following cases.
a) alpha decay
b) electron capture
c) electron emission
d) positron emission
e) nuclear fission
f) nuclear fusion
USES OF RADIOISOTOPES Pages 98 - 102
A) Tracers - study where the compound or element goes. The original amount is
in too small a
concentration to measure. By using a radioactive element
in the compound, the
compound can be 'seen' by the radioactivity coming off,
by using a counter or
a radiograph.
B) Irradiation of foods It kills microorganisms responsible for spoilage.
C) Radiation therapy Used in the treatment of cancer. Radiation can kill
cells. The rapidly
dividing cells, like cancer cells, are more susceptible
to being killed. Getting
the dosage correct is important, since normal cells
will also be killed in the
process.
D) Diagnostic uses
1. Iodine-131 in KI. Used for hyperthyroid and
thyroid cancer. The thyroid produces
a hormone, thyroxin, which has iodine as part of the molecule. The
radioactive
iodine will concentrate in the thyroid. The
radiation given off will kill the rapidly
dividing cells. The half-life of Iodine-131 is
8.1 days. Beta and gamma rays are
given off.
2. Gadolinium-153 Used to measure bone
demineralization. It gives off gamma and x-rays.
Scanning the bone and measurement of the bone
densities are determined.
3. Technetium-99m The 'm' means
metastable. It will give off radiation and go to being
a more stable element.
99m 99
Tc ----------> Tc +
g
43 43
It has a half life of 6 hours. Technetium-99 is formed from Molybdenum-99.
4. Positron Emission Tomography - PET scans
Use positron emitting isotopes. The positron
reacts with an electron and two gamma rays are formed.
The gamma rays are given
off in opposite directions. The gamma rays are measured. The instrument
looks like a big donut. The patient's head or body is passed into this hole and the
radiation recorded.
The computer part of the instrument can 'see' where the
positron and electron collided
11
11 0
C ----------->
B + e (aka
b
)
6
5 +1
0 0
e + e -------> 2
g
+1 -1
E) Carbon dating
Carbon-14 is formed by the bombardment of Nitrogen-14 with neutrons
14
1 14 1
N + n
---------> C + H
7 0
6 1
Carbon-14 has a half life of 5730 years. If an old dead plant had one half the C-14 which is found in the earth's CO2, that means the plant was alive one half-life ago or 5730 years.
The shroud of Turin was found to be from the time period of 1260 to 1390 A.D. So it is not the shroud used to wrap Christ.
Chapter 4 Questions 19, 27,37, 39, 43,59