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