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Chapter 9 Nuclear Radiation
9.3 Radiation Measurement9.4 Half-Life of a Radioisotope9.5 Medical Applications Using
Radioactivity
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Radiation Measurement
A Geiger counter • detects beta and gamma radiation.• uses ions produced by radiation to create an
electrical current.
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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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Exposure to Radiation
Exposure to radiation occurs from
• naturally occurring radioisotopes.
• medical and dental procedures.
• air travel, radon, and smoking cigarettes.
TABLE 9.6
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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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.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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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 5730 yr
40K 1.3 x 109 yr226Ra 1600 yr238U 4.5 x 109 yr
51Cr 28 days131I 8 days59Fe 46 days
99mTc 6.0 hr
Naturally Occurring
Medical Uses
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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
1 half-life 2 half-lives
Initial40 mg
20 mg10 mg
Half-Life Calculations
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The half life of 123I is 13 hr. How much of a 64 mg sample of 123I is left after 26 hours?
1) 32 mg2) 16 mg3) 8 mg
Learning Check
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Solution
Half-life
13 hr 13 hr
2) 16 mg
STEP 1 Given 64 g; 26 hr; 13 hr/half-life
STEP 2 Plan 26 hours 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
64 mg 32 mg 16 mg
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Radioactive Decay (cont)
a. Radioactive Dating1. The radioactive decay of carbon-14 can
be used to estimate the age of organic materials.
6C126C13
6C14
Types of Carbon Isotopes
Mass number = # protons + # neutrons
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The Shroud of Turin
Credit: The Image Works
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.
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Mummified remains found frozen in the Italian Alps
Credit: Landov
At least 5000 years oldBy carbon-14 dating
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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. Thyroid scan
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Learning Check
Which of the following radioisotopes are most likely to be used in nuclear medicine?
1) 40K half-life 1.3 x 109 years2) 42K half-life 12 hours3) 131I half-life 8 days
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