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Chapter 10 Nuclear Radiation

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Chapter 10 Nuclear Radiation
10.3 Radiation Measurement
10.4 Half-Life of a Radioisotope
10.5 Medical Applications Using
Radioactivity
Copyright В© 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1
Radiation Measurement
A Geiger counter
• detects beta and gamma radiation.
• uses ions produced by radiation to create an
electrical current.
2
Detecting Radiation
A Geiger-MГјller
counter
3
Geiger-MГјller counter with radioactive
antique orange plate
4
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.
5
Units of Radiation Measurement
6
Exposure to Radiation
Exposure to radiation
occurs from
TABLE 9.6
• naturally occurring
radioisotopes.
• medical and dental
procedures.
• air travel, radon, and
smoking cigarettes.
Copyright В© 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
7
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.
8
Decay Curve
A decay curve shows the decay of radioactive
atoms and the remaining radioactive sample.
Copyright В© 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
9
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
14C
Naturally
Occurring
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
10
Half-Life Calculations
In one half-life, 40 mg of a radioisotope decays to 20 mg.
After two half-lives, 10 mg of radioisotope remain.
40 mg x 1 x 1 = 10 mg
2
2
Initial
40 mg
1 half-life
2 half-lives
20 mg
10 mg
11
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
12
Solution
2) 16 mg
STEP 1 Given 64 g; 26 hr; 13 hr/half-life
STEP 2 Plan
26 hours
Half-life
Number of half-lives
STEP 3 Equalities 1 half-life = 13 hr
STEP 4 Set Up Problem
Number of half-lives = 26 hr x 1 half-life = 2 half-lives
13 hr
13 hr
64 mg
13 hr
32 mg
16 mg
13
Radioactive Decay (cont)
a. Radioactive Dating
1. The radioactive decay of carbon-14 can
be used to estimate the age of organic
materials.
Types of Carbon Isotopes
6C
12
6C
13
6C
14
Mass number = # protons + # neutrons
14
The process of
Carbon-14 Dating
The Shroud of Turin
Reputed as the burial cloth of
Jesus Christ. C-14 dating by 3
independent labs report the Cloth
originated during the Medieval
times, between A.D. 1260-1390.
Credit: The Image Works
16
Mummified remains found frozen in the
Italian Alps
At least 5000 years old
By carbon-14 dating
Credit: Landov
17
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.
Thyroid scan
18
Some Radioisotopes Used in
Nuclear Medicine
19
Learning Check
Which of the following radioisotopes are most likely
to be used in nuclear medicine?
1)
2)
3)
40K
half-life 1.3 x 109 years
42K half-life 12 hours
131I half-life 8 days
20
Solution
Which of the following radioisotopes are most
likely to be used in nuclear medicine?
Radioisotopes with short half-lives are used in
nuclear medicine.
2)
3)
42K
half-life 12 hours
131I half-life 8 days
21
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