only certain combinations or ratios of neutrons and protons are stable such that the repulsive force is balanced by the attractive forces.

If the combination and arrangement of neutrons and protons does not fall within a stable “range,” the nucleus is unstable.

An unstable nucleus attempts to achieve stability by changing its nuclear configuration.

This will be accomplished by nuclear transformations which eliminate surplus nucleons so as to balance nuclear forces.

When a proton or neutron is eliminated from the nucleus the ratio of neutrons and protons is

thereby changed.

- at the high atomic number part of the Periodic Table, above 2Bi, there are no completely stable nuclei. 

This emission of particles or energy from the nucleus is called radiation.

 >Each step in the series of transformations will mean a distinct reduction in total mass-energy of the nucleus. As the energy of the nucleus is reduced, the nucleus is said to disintegrate or decay.

>The process by which a nucleus spontaneously disintegrates (or is transformed) by one or

more discrete energy steps until a stable state is reached is called radioactive decay.

A nucleus emitting an alpha particle decays to a daughter element, reduced in atomic number (Z) by 2 and reduced in mass number (A) by 4. The standard notation for alpha decay is:

Alpha particles are the least penetrating of the three types of radiation. They can be absorbed or stopped by a few centimeters of air or a sheet of paper.

>Because a neutron has been replaced by a proton, the atomic number increases by one, but the mass number is unchanged.

> emission of an antineutrino,

> Neutrinos  and anti-neutrinos are neutral (uncharged) particles account for energy transfer in positrons and beta particles

4a.alpha decay

A nucleus emitting an alpha particle decays to a daughter element, reduced in atomic number (Z) by 2 and reduced in mass number (A) by 4. The standard notation for alpha decay is:

4b. beta decay

In beta-minus emitters, the nucleus of the parent gives off a negatively charged particle, resulting in a daughter more positive by one unit of charge. Because a neutron has been replaced by a proton, the atomic number increases by one, but the mass number is unchanged. There is also the emission of an antineutrino, symbolized by the Greek letter nu with a bar

above it .

With positron emitters, the parent nucleus changes a proton into a neutron and gives off a positively charged particle. This results in a daughter less positive by one unit of charge.  Because a proton has been replaced by a neutron, the atomic number decreases by one and the mass number remains unchanged. The emission of a neutrino (symbolized by (v)) also occurs in conjunction with the positron emission.

Electron Capture

For radionuclides having a low n:p ratio, another mode of decay can occur known as orbital electron capture (EC). In this radioactive decay process the nucleus captures an electron from an orbital shell of the atom, usually the K shell, since the electrons in that shell are closest to the nucleus. The nucleus might conceivably capture an L-shell electron, but K-electron capture is much more probable. This mode of decay is frequently referred to as K-capture. The transmutation resembles that of positron emission, as follows:

5 radioactive nuclide decay

two aspects

• Modes of decay

• Types of emissions

• Energies of the emissions involved

• Rate of decay

6a. natural .

man-made--

are a type of electromagnetic radiation, higher energy (MeV), emitted from the nucleus of unstable atoms, no gain or loss of protons of neutrons,

6b. 

artificial radioactivity

result of various man-made reactions.

. Over 1,000 unstable nuclear species are listed in the Chart of the Nuclides. (boron, magnesium, aluminum),

man-made--lighter artificially-produced radionuclides generally revert to stability in only a few decay steps

artificial radionuclides

Heavy radionuclides (natural, and artificial) generally decay by a long series of alpha and beta

emissions. Lighter, artificial radionuclides, such as activation and fission products, usually

decay by beta or positron emission or by orbital electron capture.

too large a proportion of neutrons to protons for stability

the fission products in the above equation have too many neutrons.

Nuclides above the line of stability will usually undergo positron decay or electron capture.

nuclides below the line of stability will usually undergo beta-minus decay.

Uranium series: Uranium-238, 206 82Pb

Thorium series: Thorium-232, 208 82Pb

Actinium series: Uranium-235, 207 82Pb

9a. nuclide, locate its block on

Chart of tha. e Nuclides

atomic number

a. atomic number : (N) is plotted horizontally on the x-axis neutrons (N) are found along the bottom N=240

9b. nuclide, locate its block on

Chart of tha. e Nuclides

atomic mass

b. atomic mass : ( Z) on the y-axis;

24 0.053807

for Pu 240

9c. nuclide, locate its block on

Chart of tha. e Nuclides

natural percent abundance

Na 23 Percent Abundance: - 100%

9d. nuclide, locate its block on

Chart of tha. e Nuclides

stability :