The Structure of the Atom Radioactivity. –Spontaneous emission of radiation by certain atoms...

The Structure of the Atom

Radioactivity

Radioactivity

–Spontaneous emission of radiation by certain atoms

–The structure of atomic nuclei and the changes they undergo

Radioactivity

–Radiation: Rays and particles produced during radioactive decay

–An atom undergoes radioactive decay in order to form a more stable atom by releasing energy.

Types of Radiation

• Alpha Radiation: Deflected towards negatively charged plate, hence alpha particle is positively charged.– Alpha particle – Has +2 charge– Has a mass of 4– Has no electrons– Represented as or

24He2 +

24He

Alpha Radiation

• Example

88226 Ra Rn + He86

22224

HePbPo 42

20682

21084

Beta Radiation

• Fast moving electrons attracted to a positively charged plate.

• Represented as • Has mass of 0• Has a charge of –1

10

Beta Radiation

• Example

614 C N +7

14-10

Gamma rays

• Represented as

• Has mass of 0

• Has a charge of 0

• It is a high energy radiation

• It is usually produced along with

00

22 He and adiation-1

0

Positron Emission

• Same mass as electron but opposite charge

0110

11 np

Positron

Electron Capture

• The nucleus pulls in surrounding electron from the lowest energy level

• The electron combines with a proton to form a neutron.

nep 10

01-

11

Nuclear Stability

– Depends on neutrons to protons ratio (n/p)

– The closer the n/p ratio is to unity (1),

the more stable the atom

– The further below 1 or above 1, the less stable the atom.

Other Terms

– Radioactive Series: A series of reactions that begins with an unstable nucleus and results in the formation of a stable nucleus.

– Transmutation: The conversion of an atom of one element to an atom of another element.

Other Terms

• Induced transmutation: A type of transmutation that involves striking nuclei with high-velocity charged particles

pONHe 11

178

147

42

Other Terms

• Radiochemical Dating: The process of determining the age of an object by measuring the amount of certain radioisotope remaining in the object.

• This is possible because the half-life of radioisotope materials remain constant.

Other Terms

• Nuclear Fusion: The combining of atomic nuclei is called nuclear fusion. This process also produces large amount of energy.

• However, energy must the supplied in order to initiate and sustain nuclear fusion reactions.

• Geiger counter: This is a radiation detection device for ionizing radiation.

Other Terms

• Nuclear Fission: The splitting of a nucleus into fragments is known as nuclear fission.

• This process is usually accompanied by large release of energy.

• Therefore, this is a process used at Nuclear Power Plants to generate energy.

Half-life

• The time required for one half the original amount of a sample to decompose is referred to as the half-life of the reaction.

Half-life

• In general, • If = number of half lives• and t1/2 = half life• Then:1.

OR n = t/Twhere t is the time elasped and T is the duration of the half-life.

elapsed timexlifehalf1

n

21t

Half-life

2. Let original amount = Xo

Let final amount = Xf

Then, Xf = Xo(0.5)n