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-Müller counter

3. Geiger-Müller 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
Exposure to radiation
occurs from
naturally occurring radioisotopes.
medical and dental procedures.
air travel, radon, and smoking cigarettes.
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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 © by Pearson Education, Inc.
Publishing as Benjamin Cummings

9. Half-Lives of Some 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 yr
40K x 109 yr
226Ra yr
238U x 109 yr
51Cr days
131I days
59Fe days
99mTc hr
Naturally Occurring
Medical Uses

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 x 1 = 10 mg
1 half-life 2 half-lives
Initial
40 mg
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) mg

12. Solution 2) 16 mg STEP 1 Given 64 g; 26 hr; 13 hr/half-life
STEP 2 Plan 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 hr
64 mg mg mg
Half-life
13 hr
13 hr

13. Radioactive Decay (cont)
Radioactive Dating
The radioactive decay of carbon-14 can be used to estimate the age of organic materials.
Types of Carbon Isotopes
6C12
6C13
6C14
Mass number = # protons + # neutrons

14. The process of Carbon-14 Dating

15. 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
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 1) 40K half-life 1.3 x 109 years
Which of the following radioisotopes are most likely to be used in nuclear medicine?
1) 40K half-life 1.3 x 109 years
2) 42K half-life 12 hours
3) 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) 42K half-life 12 hours
3) 131I half-life 8 days