1

Ch 9 - Nuclear RadiationCh 9 - Nuclear Radiation1. Nuclear Emissions

2. Nuclear Equations

3. Producing Radioactive Isotopes

4. Half-Life

5. Nuclear Fission and Fusion

6. Uses & Effects

2

ReviewRemember• Protons: + charge• Neutrons: neutral • Electrons: - charge

B115 atomic symbol

atomic number number of protons

mass number number of

protons and neutrons

Nuclear SymbolsNuclear Symbols – notice mass number is on top

3

1. Nuclear Emissions

• Radiation comes from the nucleus of an atom.• Unstable nucleus emits a particle or energy

alpha

beta

gamma

• non-radioactive particle = neutron n10

4

Alpha Particle

Same as a helium nucleus

(He)

4

2 He or

Two protons

Two neutrons

5

Beta Particle

An electron emitted from the nucleus

0

e or 1

A neutron in the nucleus breaks down1 1 0

n H + e 0 1 -1

6

Gamma Radiation

• Pure radiation

• Like an X-ray but comes from the nucleus

7

Radiation Protection

• Shielding

alpha – paper, clothing

beta – lab coat, gloves

gamma- lead, thick concrete

• Limit time exposed

• Keep distance from source

8

Radiation Protection

9

2. Nuclear Equations2. Nuclear Equations

In the reactants and products

Atomic numbers must balance

and

Mass numbers must balance

10

Alpha decay

11

Beta decay

234Th 234Pa + 0e 90 91 1

beta particle

12

Gamma radiation

No change in atomic or mass number

11B 11B + 0

5 5 0

boron atom in a

high-energy state

13

Learning CheckLearning Check• To predict the product, simply remember that

the mass number and atomic number are conserved

• What is the identity of X?

e01-23992 XU

14

Learning CheckLearning Check

Write the nuclear equation for the beta emitter Co-60.

15

SolutionsSolutions

60Co 60Ni + 0 e

27 28 -1

93

239Npe01-23992 XU

16

3. Producing Radioactive Isotopes3. Producing Radioactive Isotopes

Bombardment of atoms produces radioisotopes = 60 = 60

59Co + 1n 56Mn + 4H e

27 0 25 2

= 27 = 27

cobalt neutron manganese alpha

atom radioisotope particle

17

Learning Check

What radioactive isotope is produced in the following bombardment of boron?

10B + 4He ? + 1n

5 2 0

18

Solution

What radioactive isotope is produced in the following bombardment of boron?

10B + 4He 13N + 1n

5 2 7 0

nitrogen

radioisotope

19

4. Half-Life of a Radioisotope4. Half-Life of a RadioisotopeThe time for the radiation level to fall (decay) to one-half its initial value

20

Examples of Half-Life

Isotope Half life

C-15 2.4 sec

Ra-224 3.6 days

Ra-223 12 days

I-125 60 days

C-14 5700 years

U-235 710 000 000 years

21

Learning Check

The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours?

22

Solution

t1/2 = 13 hrs

26 hours = 2 x t1/2

Amount initial = 64mg

Amount remaining = 64 mg x ½ x ½

= 16 mg

23

5. Fission VS Fusion5. Fission VS Fusion

Fission

large nuclei break up

235U + 1n 139Ba + 94Kr + 3 1n +

92 0 56 36 0

Energy

24

Fission of Uranium-235• Chain reaction – the reaction sustains itself

by producing more neutrons

25

Nuclear FusionNuclear Fusion

Fusion

small nuclei combine

2H + 3H 4He + 1n +

1 1 2 0

Occurs in the sun and other stars

Energy

• Excessive heat can not be contained

• Attempts at “cold” fusion have FAILED.

• “Hot” fusion is difficult to contain

26

Learning CheckLearning Check

Indicate if each of the following are

(1) Fission (2) fusion

A. Nucleus splits

B. Large amounts of energy released

C. Small nuclei form larger nuclei

D. Hydrogen nuclei react

Energy

27

SolutionSolution

Indicate if each of the following are

(1) Fission (2) fusion

A. 1 Nucleus splits

B. 1 + 2 Large amounts of energy released

C. 2 Small nuclei form larger nuclei

D. 2 Hydrogen nuclei react

28

6. Uses & Effects6. Uses & Effects• Radiation - treatment of cancer• Nuclear medicine - use of radioisotopes in diagnosis

– Tracers – small amounts of radioactive substances used as probes to study internal organs

– Nuclear imaging – medical techniques involving tracers

• Food Irradiation– Food - irradiated with g rays from 60Co or 137Cs.– Irradiated milk - shelf life of 3 mo. w/o cooling.– USDA - approved irradiation of meats and eggs

29

30

Exposure Sources