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