College Chemistry Ch 9

The Nucleus, Radioactivity and Nuclear Medicine

Radioactivity

Process by which atoms emit energetic particles or rays

Radiation

The particles or rays emitted

comes from the nucleus

Nuclear Symbols

Used to designate the nucleus

Atomic symbol, Atomic number, Mass number

Unstable Isotopes

Isotopes that produce radioactivity

Alpha Particle

Slow moving and stopped by small barriers

same He nucleus as (He2+)

2 protons and 2 neutrons

Beta Particle

fast moving electron

more penetrating than alpha particles

emitted from the nucleus as a neutron and converted to a proton

Positron

Has the same mass as an electron or beta particle

has an opposite charge of an electron (+)

Gamma Rays

Pure energy (electromagnetic radiation)

highly energetic

most penetrating form of radiation

Ionizing Radiation

produces a trail of ions throughout the material that it penetrates

Alpha particle< Beta particle< Gamma rays

Nuclear Equation

Used to represent nuclear change

Beta Decay

In ____ ____ one neutron is converted to a proton and the electron, the ____ particle is released

Positron Emission

Unlike beta decay, the product nuclide has the same mass number as the parent BUT the atomic number has decreased by one

Metastable Isotope

The energetically unstable isotope

Gamma Production

Gamma radiation occurs to increase the stability of an isotope

Predicting Products of Nuclear Decay

simply remember that the mass number and atomic number are conserved

Binding Energy

The energy that holds the protons, neutrons, and other particles together in the nucleus

energy is very large

Half Life

The time required for one-half of a given quantity of a substance to undergo change

each radioactive isotope has its own

Radiocarbon Dating

The estimation of the age of objects through measurement of isotopic ratios of carbon

Energy Production

Equation: shows that a very large amount of kinetic energy can be formed from a small amount of matter

Fission

(splitting) occurs when a heavy nuclear particle is split into smaller nuclei by a smaller nuclear particle (like a neutron)

Chain Reaction

The reaction sustains itself by producing more neutrons

Fusion

(to join together) combination of two small nuclei to form a larger nucleus

large amounts of energy are released

Breeder Reactor

Fission reactor that manufactures its own fuel

Nuclear Medicine

The use of radioisotopes in the diagnosis of medical conditions

Tracers

Smaller amounts of radioactive substances used as probes to study internal organs

Nuclear Imaging

Medical techniques involving tracers

Artificial Radioactivity

a normally stable, nonradioactive nucleus is made radioactive

made in core of nuclear reactor or in a particle accelerator

The Magnitude of the Half-Life

Issues may arise when using isotopes with a short half life

Disadvantage: larger amount of radioactivity per unit time

Advantage: if accident occurs, reaches background radiation levels more rapidly

Shielding

Alpha and beta particles need low levels (ex: lab coat and gloves)

Lead and concrete (or both) required for gamma rays

Distance from the Radioactive Source

Doubling the distance from the source decreases the intensity by a factor of 4

Time of Exposure

Effects are cumulative

Types of Radiation Emitted

Alpha and beta emitters are generally less hazardous than gamma emitters

Waste Disposal

Disposal sites are considered temporary

Photographic Imaging

1. isotope is administered

2. isotope begins to concentrate in the organ

3. nuclear images are taken at periodic intervals

4. emission of radiation from the radioactive substance creates the image

The Geiger Counter

Detects ionizing radiation

has largely been replaced by more sophisticated devices

Film Badges

a piece of photographic film that is sensitive to energies corresponding to radioactive emissions

the darker the film when developed, the longer the person has been exposed

Curie

Amount of radioactive material that produces

3.7 × 10^10 atomic disintegrations per second

Becquerel

The amount of radioactive material that produces 1 atomic disintegrations per second

Roentgen

The amount of radiation needed to produce

2 × 10^9 ion pairs when passing through one cm³ of air at 0 C

used for very high energy ionizing radiation only

Rad

Radiation absorbed dosage

2.4 × 10^-3 cal of energy to 1 kg of matter

Gray

absorption of 1 J of energy by 1 kg of matter

REM (Roentgen Equivalent for Man)

obtained by multiplication of the rad by a factor called the relative biological effect (RBE)

RBE = 10 for alpha particles

RBE = 1 for beta particles

Lethal Dose (LD50)

The acute dosage of radiation that would be fatal for 50% of the exposed population

LD50 = 500 rems