Transcript Nuclear Radiation

Chapter 9
Nuclear Radiation
Definitions
 Radioactive- any unstable Nucleus that spontaneously
emits energy to become more stable.
 Radiation- any particle or energy that is emitted by a
radioactive nucleus.
 Many Isotopes are radioactive and are called
Radioisotopes
Radioactive Isotopes
A radioactive isotope
• has an unstable nucleus.
• emits radiation to become more stable.
• can be one or more of the isotopes of an element
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Nuclear Radiation
Nuclear radiation
• is the radiation emitted by an unstable atom.
• takes the form of alpha particles, neutrons, beta
particles, positrons, or gamma rays.
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Types of Radiation
Alpha () particle is two protons and two neutrons
Beta () particle is a high-energy electron
0e
-1
Positron (+) is a positive electron 0e
+1
Gamma ray is high-energy released from a nucleus 
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Radiation Protection
Radiation protection requires
• paper and clothing for alpha particles.
• a lab coat or gloves for beta particles.
• a lead shield or a thick concrete wall for
gamma rays.
• limiting the amount of time spent near
a radioactive source .
• increasing the distance from the source.
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Alpha particles: stopped by air, skin and clothes, travel
2-4cm in air. eg. radium-226
Beta particles: stopped by heavy clothes, gloves and
face shields, travel 200-300cm in air. eg. carbon-14
Gamma rays: stopped by lead and concrete type
barriers, travel 500m in air. eg. technectium-99m
Alpha Decay
When a radioactive
nucleus emits an
alpha particle, a new
nucleus forms that has
• a mass number that is
4 less than that of the
initial nucleus.
• an atomic number that
is decreased by 2.
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Balancing Nuclear Equations
In a balanced nuclear equation, the sum of the mass
numbers and the sum of the atomic numbers for the
nuclei of the reactant and the products must be
equal.
MASS NUMBERS
Total =
251
=
251
251Cf
247Cm +
4He
98
Total =
96
2
98
=
98
ATOMIC NUMBERS
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Equation for Alpha Decay
Write an equation for the alpha decay of 222Rn.
STEP 1 Write the incomplete equation
222Rn
?s + 4He
86
2
STEP 2 Determine the mass number
STEP 3 Determine the atomic number
222 – 4 = 218
86 – 2 =
STEP 4 Determine the symbol of element
84
84 = Po
STEP 5 Complete the equation
222Rn
86
218Po
84
+
4He
2
84
Po
85
At
86
Rn
4He
2
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Beta Decay
A beta particle
• is an electron
emitted from the
nucleus.
• forms when a
neutron in the
nucleus breaks
down.
1n
0e + 1H
0
-1
1
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Writing An Equation for a Beta Emitter
STEP 1
Write an equation for the decay of
42Potassium,a beta emitter.
42K
19
new nucleus +
STEP 2
STEP 3
STEP 4
Mass number :
(same)
Atomic number:
19 + 1
Symbol of element 20
STEP 5
42K
42Ca
19
20
+
0e
-1
= 42
= 20
= Ca
0e
-1
0e
-1
19
K
20
Ca
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Learning Check
Write the nuclear equation for the beta decay of 60Co.
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Solution
60Co
60Ni
27
28
+ 0e
1
beta particle
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Positron Emission
In positron emission,
• a proton is converted to a neutron and a positron.
1p
1n + 0e
1
0
+1
• the mass number of the new nucleus is the same, but
the atomic number decreases by 1.
49Mn
25
49Cr
24
+
0e
+1
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Gamma  Radiation
In gamma radiation
• energy is emitted from an unstable nucleus,
indicated by m following the mass number.
• the mass number and the atomic number of the
new nucleus are the same.
99mTc
43
99Tc
43
+ 
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Summary of Changes in Mass and
Atomic Numbers
TABLE 9.4
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Some Radioactive Isotopes are not
naturally produced
Radioactive isotopes are produced
• when a stable nucleus is converted to a radioactive
nucleus by bombarding it with a small particle.
• in a process called transmutation.
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Learning Check
What radioactive isotope is produced when a
neutron bombards 59Co?
59Co
27
+
1n
0
? +
4He
2
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Solution
mass numbers
60
=
60
59Co + 1n
56Mn +
4H e
27
0
27
25
2
=
27
atomic numbers
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Radiation Measurement
A Geiger counter
• detects beta and gamma radiation.
• uses ions produced by radiation to create an
electrical current.
2
Radiation Units
Units of radiation include:
• Curie
- measures activity as the number of atoms that
decay in one second.
• rad (radiation absorbed dose)
- measures the radiation absorbed by the tissues
of the body.
• rem (radiation equivalent)
- measures the biological damage caused by
different types of radiation.
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Units of Radiation Measurement
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Exposure to Radiation
Exposure to radiation
occurs from:
• naturally occurring
radioisotopes.
• medical and dental
procedures.
• air travel, radon, and
smoking cigarettes.
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Biological Damage
-
Exposure to < 25 rem cannot be detected.
-
Exposure to 100 rem will cause temporary depletion of
WBC…….higher than this produces radiation sickness
(vomiting, fatigue, further  WBC)
-
Exposure to about 500 rem is expected to cause death in 50%
of exposed persons.
Measuring the activity of
radioisotopes i.e. Half-Life
The half-life of a radioisotope is the time for the
radiation level to decrease (decay) to one-half
of the original value.
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Decay Curve
A decay curve shows the decay of radioactive
atoms and the remaining radioactive sample.
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Publishing as Benjamin Cummings
7
Half-Lives of Some Radioisotopes
Radioisotopes
• that are naturally occurring tend to have long half-lives.
• used in nuclear medicine have short half-lives.
Half-Lives of Some Radioisotopes
Radioisotope
Half-life
Naturally
Occurring
14C
40K
226Ra
238U
Medical
Uses
51Cr
131I
59Fe
99mTc
5730
yr
1.3 x 109 yr
1600
yr
4.5 x 109 yr
28
8
46
6.0
days
days
days
hr
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Learning Check
The half life of 123I is 13 hr. How much of a 64
mg sample of 123I is left after 26 hours?
1) 32 mg
2) 16 mg
3) 8 mg
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Medical Applications
Radioisotopes with short half-lives are used
in nuclear medicine because:
• they have the same chemistry in the body as
the nonradioactive atoms.
• in the organs of the body, they give off
radiation that exposes a photographic plate
(scan) giving an image of an organ. This is
nuclear medicine.
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 “Scan” eg…………gamma rays from a radioisotope detected
on a photographic plate to give a picture of tumor, blood clot
formation, thyroid function (RAIU or radioactive iodine uptake)
etc.
• Thyroid scan
 “PET scan”……..positron emission topography
- a positron is a particle emitted from the nucleus that has the same
mass as an electron but a positive charge.
 Positron emitters used to diagnose conditions involving blood
flow and brain function are carbon-11, oxygen-15 and nitrogen13.
 Carbon-11 was used to detect Michael J Fox’s Parkinson’s
disease!
Some Radioisotopes Used in
Nuclear Medicine
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RADIATION AND FOOD
Nuclear Fission and Fusion
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Publishing as Benjamin Cummings
1
Nuclear Fission and Fusion
 Fission – the splitting of a nucleus to yield two
smaller nuclei and ENERGY.
 Fusion – the joining of two smaller nuclei to yield a
larger one with the release of ENERGY.
 E = m c2 when the two reactions occur some mass is
‘lost’ that mass difference is converted to ENERGY.
Nuclear Fission
When a neutron bombards 235U,
• an unstable nucleus of 236U undergoes fission (splits).
• smaller nuclei are produced such as Kr-91 and Ba-142.
• neutrons are released to bombard more 235U.
1n
0
+
235U
92
“236U”
92
91Kr
36
+ 142Ba + 3 1n +
56
Energy
0
3
Uranium: An example of Nuclear
Fission
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1n
0
+ 235U
92
“236U”
92
91Kr
36
+ 142Ba + 3 1n + energy
56
0
4
Learning Check
Supply the missing atomic symbol to complete the
equation for the following nuclear fission reaction.
1n
0
+
235U
137Te
92
52
+ ?X + 2 1n + energy
?
0
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Solution
1n
0
+
235U
137Te
92
52
+ 97Zr + 2 1n + energy
40
0
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Chain Reaction
A chain reaction
occurs
• when a critical
mass of uranium
undergoes fission.
• releasing a large
amount of heat
and energy that
produces an
atomic explosion.
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Nuclear Power Plants
In nuclear power plants,
• fission is used to produce energy.
• control rods in the reactor absorb neutrons to
slow and control the chain reactions of fission.
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Nuclear Fusion
Fusion
• occurs at extremely high temperatures (100 000 000°C).
• combines small nuclei into larger nuclei.
• releases large amounts of energy.
• occurs continuously in the sun and stars.
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Learning Check
Indicate if each of the following describes
1) nuclear fission or 2) nuclear fusion.
___ A.
___ B.
___ C.
___ D.
___ E.
a nucleus splits.
large amounts of energy are released.
small nuclei form larger nuclei.
hydrogen nuclei react.
several neutrons are released.
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Solution
Indicate if each of the following is
1) nuclear fission or 2) nuclear fusion.
1
1, 2
2
2
1
A.
B.
C.
D.
E.
a nucleus splits.
large amounts of energy are released.
small nuclei form larger nuclei.
hydrogen nuclei react.
several neutrons are released.
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“The Good, the Bad and the Ugly”
“The Good”:
Fission:
–Efficient & Cheap
Fusion:
–Super Cheap and CLEAN
“The Good, the Bad & the Ugly”
“The Bad”:
 Fission:
– Lots of Radioactive wastes
– Will the Uranium supply last?
– DANGEROUS
 Fusion:
– Almost as Dangerous
“The Good, the Bad & the Ugly”
“The Ugly”:
 Fission:
– Chernobyl; 3 Mile Island
 Fusion:
– Impossible with today’s technology