Chapter 7: Radiation

Remember from Chemistry:

• Mass numberMass number: the number of protons + number of neutrons

• Atomic numberAtomic number: the number of protons in an atom of an element.

• Isotopes:Isotopes: atoms of the same elements that have a different number of neutrons and therefore a different mass number

There are many isotopes of carbon.

• For example: carbon-12, carbon-13 andcarbon-14

• How many protons in each of these atoms of carbon? – 6

• How many neutrons in each of these atoms of carbon?

• Carbon-12 = ____ neutrons• Carbon-13 = ____ neutrons• Carbon-14 = ____ neutrons

Standard Atomic Notation

• Carbon-12 = 12 C

6

• Carbon-13 = _____

• Carbon-14 = _____

Mass number

Atomic number

Isotopes of Hydrogen

• Hydrogen: 1 proton and 0 neutrons

• Deuterium: 1 proton and 1 neutron

• Tritium: 1 proton and 2 neutrons

Radioactive Decay:

• The nuclei of some isotopes are stable, whereas, others are not.

• In unstable nuclei, the nuclear force is not enough to overcome the repulsive electrical forces with in the nucleus.

• As a result the nuclei are radioactive.

• When an unstable nucleus emits radiation, it undergoes a radioactive decay

Types of radioactive decay

• Alpha Decay:Alpha Decay:• Particle emitted: Helium nucleus• Result: Atom with two fewer protons and

neutrons Sample Equations:Parent isotope Daughter isotope

• U → _____ + He

• U → Th + _____

Types of radioactive decay

• BetaBeta• Particle emitted: Electron• Result: # of neutrons decrease by one and the #

of protons increase by one = new element

Sample Equations:Parent isotope Daughter isotope

• C → ____ + e

• C → N + ____

• GammaGamma• Particle emitted: No particle, but gives off

excess energy• Result: No change to type of nucleus, it just has

less energy. Sample Equations:Parent isotope Daughter isotope

• Ba → _____ + Gamma radiation

• Ba → Ba + ______

Types of radioactive decay

On your data sheets: p12

Radiation

Assignment:• Fill in the 7.1 worksheets p123-5 (all) and

p126 (pick two alpha, two beta and two gamma questions)

• You are going to have to look up some of this information in your textbook

• Quiz next class– Identifying and completing decay equations– Given # of neutrons and number of protons

can you determine, mass #, atomic #, the element, isotope name and isotope symbol.

Half Life

Section 7.2

PLO: Unit 2 #5.2

Half Life:

• Half Life: The time required for half the nuclei of a sample of a radioactive isotope to decay.

• The half life is the same regardless of the starting amount of the isotope.

• Because the amount of all radioactive isotopes decrease by half in each half life, graphs that show the amounts of these isotopes at various times look similar.

• The only difference is the time scale for decrease.

Examples of half life:carbon

020406080

100120

0 20000 40000 60000 80000

Time (Years)

amo

un

t o

f sa

mp

le

left carbon

Uranium

0100200300400500600

0 50000 100000 150000

Time (years)

sam

ple

of

ura

niu

m

Uranium

Half Life Problems

• Figure out what the problem is asking you to find.

• Fill in the table with the information given to you in the problem.

Half Life Table for Solving Word Problems

Time # of Half lives Amount of parent isotope

** optional ** Amount of daughter isotope

0 0 Original Amount 0

1

2

3

4

Homework:

• Fill in the 7.2 worksheets p134 (odd) and 135

• For p 134 you must show the half life tables

Half Life Table for Solving Word Problems

Time # of Half lives Amount of parent isotope

** optional ** Amount of daughter isotope

0 0 Original Amount 0

1

2

3

4