Radioactive%20Isotope

1
Radioactive Isotope

• Isotope which is unstable. It emits radiation
  changes into another kind of atom.

2
Transmutation Reaction

• When one kind of nucleus changes into another
  kind of nucleus.

3
Stability

• Depends on neutron to proton ratio.

4
Which elements are unstable?

• All the elements with atomic number gt 83 (or
  beyond Bismuth)

5
Types of Radiation

• Alpha, Beta, Gamma
• Separated by electric or magnetic fields.

6
Least penetration power

• Alpha radiation. Shielding can be paper or cloth.

7
Most penetration power

• Gamma radiation. Requires lead/concrete
  shielding.

8
2He or 2?

• Symbol for alpha radiation

4
4
9
2He or 2?

• Same as the nucleus of a helium atom

4
4
10
-1e or -1? or ?- or ?

• Symbol for beta particle

0
0
11
-1e or -1? or ?- or ?

• Fast moving electron originating from nucleus

0
0
12
1e or 1? or ?

• Symbol for positron.

0
0
13
0? or ?

• Symbol for gamma radiation.

0
14
0n or n

• Symbol for neutron

1
15
1H or 1p

• Symbol for proton

1
1
16
Decay Mode

• When radioactive isotopes emit radiation, the
  decay mode is the type of radiation they emit.

17
Alpha Decay

• Unstable nucleus emits an alpha particle. Atomic
  ? by 2. Mass ? by 4.

18
220Fr ? 4? 216At

• Unstable nucleus emits an alpha particle. Atomic
  ? by 2. Mass ? by 4.

2
85
87
19
220Fr ? 4? 216At

• Natural Transmutation.
• 1 term on reactant side.

2
85
87
20
220Fr ? 4? 216At

• Balance nuclear equations using conservation of
  atomic number conservation of mass number.

4 216

220
2
85
87
2 85
87

21
27Al 4He ? 1n X

• Use conservation of atomic number conservation
  of mass number.

So Y 30
1 Y

27 4
Y
0
2
Z
13

13 2
0 Z
So Z 15
Now have 30X. Use PT.
X is P
15
22
Artificial Transmutation

• Particle bullet hits target nucleus new
  isotope is produced.
• 2 terms on reactant side.

23
Artificial Transmutation
bullet
target

• 32S 1n ? 32P 1H

1
16
0
15
24
Artificial Transmutation

• Particle bullet may be proton or alpha
  particle. To react with a nucleus, must overcome
  repulsive forces by accelerating bullet to
  high speeds.
• Particle bullet may be a neutron. Neutrons
  have no charge, so no repulsive forces to
  overcome. No acceleration necessary.

25
Fission

• Fission is division.
• Large nucleus (U-235 or Pu-239) is split into 2
  medium sized nuclei by a neutron bullet. Excess
  neutrons a great deal of energy are also
  produced.

26
239Pu 1n ? 90Sr 147Ba 3 1n

• Fission

94
0
0
38
56
27
Fusion

• Fusion U for unite and U for sun.
• Very small nuclei (H He) are jammed together.
  Huge amounts of energy are released.

28
1H 2H ? 3He

• Fusion

1
1
2
29
Identify each of the rxns
fission

• 1n 235U ? 142Ba 91Kr 3 1n energy
• 59Co 1n ? 60Co
• 3He 1H ? 4He 0e
• 14C ? 14N 0e

0
92
56
36
0
Artificial transmutation
27
0
27
fusion
1
2
2
1
Natural transmutation
6
7
-1
30
Half-Life

• Amount of time required for ½ of a radioactive
  sample to decay.
• Each isotope has its own half-life.
• Not affected by temperature, physical or chemical
  environment, or age of sample.
• The shorter the half-life, the more radioactive.

31
Length of Half-Life
Source http//www.dlt.ncssm.edu/TIGER/chem2.htm
nuclear
32
of Half-Lives

• Time elapsed
• Half-life

33
Half-Life Map
1 ½ ¼ 1/8 1/16 1/32 1/64
Fraction Remaining of Elapsed Half-lives Mass
Remaining
0 1 2 3 4 5 6
? Divide by 2
Minitial
Mfinal
or
? Multiply by 2
This line depends on the information in the
problem.
34

• After 62 hours, 1.0 g remains unchanged from a
  sample of K-42. How much K-42 was in the
  original sample?
• Look up HL of K-42 in table N 12.4 h
• Calculate number of HL
• 62 hours 5 HL
• 12.4 h/HL

35
Half-Life Map
1 ½ ¼ 1/8 1/16 1/32 1/64
Fraction Remaining of Elapsed Half-lives Mass
Remaining
0 1 2 3 4 5 6
? Divide by 2
Minitial
Mfinal
or
? Multiply by 2
1.0 g
2.0
4.0
8.0
16.0
32.0
36
Problem 2

• 80 milligrams of a radioactive substance decays
  to 10 milligrams in 30 minutes.
• Calculate the HL.
• NOTICE They gave BOTH masses.

80 mg ? 40 mg ? 20 mg ? 10 mg
Took 30 min or 3 HL to decay to 10 mg, so 1 HL
10 min.
37
Uses of Radioisotopes

1. C-14 dating of organic material
2. U-238 dating of rocks
3. Chemical tracers
4. Medical use isotopes with short half-lives that
   are quickly eliminated from body. (I-131, Co-60,
   Tc-99)
5. Irradiation of food mail