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Nuclear Chemistry
By Hao Zhang

Charges of Elemental Components

Of the three elemental components, a proton has a positive charge, a neutron has a neutral charge, and the electron has a negative charge.

Atomic Definitions

The atomic number (designated by the symbol Z) represents the number of protons in the nucleus. In an element, which never has a charge, the number of protons equals the number of electrons. The mass number (A) is the sum of neutrons and protons in the nucleus. Therefore, A - Z equals the number of neutrons in a nucleus.

Typical Nuclide(where X equals any element):

Two Types of Atomic Stability

Kinetic stability- the likelihood of a nucleus to change into a more stable state.

Thermodynamic stability- A comparison of the potential energy of the nucleus to the sum of the potential energy of its protons and neutrons.

A nuclide becomes more stable through radioactive decay.

Alpha particle (a ) decay-emission of helium particle:

Beta particle (b -)decay- emission of an electron:

Positron (b +) emission-a positively charged electron:

Electron capture (b -)-a gaining of electrons:

When a positron and an electron are combined, the result is 2 gamma rays. This process is called annihilation.

Gamma ray (g )-high energy photons that accompany nuclear decays and particle reactions. Since they have neither mass nor charge, they are usually disregarded in equations.

*Gamma rays are only produced in specific reactions.

Some nuclides exhibit a "zone of stability" where radioactive decay does not take place.

  • Light nuclides with proton/neutron ratio of 1 are stable.
  • Even number of protons and neutrons are more stable than odd numbered.
  • Special number of protons and neutrons are more stable. The "magic numbers" are the following: 2, 8, 10, 28, 50, 82, and 126.
  • All nuclides with Z = 84 are unstable.

Rates of Decay

All radioactive decay reactions are 1st order.

For a 1st order reaction:

The half-life equation for a nuclear reaction

Nuclear transformation is the conversion of one element to another.

Two methods of nuclear transformation:

1. Cyclotron - A particle is accelerated through a particle accelerator and is penetrated into the nucleus.
2. Linear Accelerator - particles accelerated by magnetic fields bombards the nucleus.

Fission isthe splitting of a heavy nuclide into two smaller nuclides. Excess neutrons and energy is produced in the reaction. For a chain reaction, the emitted neutrons split nearby nuclides that produce a self-sustaining reaction.

Types of Fission reactions

  • Subcritical: less than one neutron splits one nuclide  (This reaction will not be self-sustaining.In order to be self-sustaining, at least one neutron must go on to split another nuclide)
  • Critical: one neutron splits one nuclide
  • Supercritical: more than one neutrons splits one nuclide

Fusion-combining two smaller nuclides to form one heavy nuclide.

Effects of Radiation

During radioactive decay, the nuclides emit radiation.

  • If the nuclide has a large half-life, the decomposition process is very slow. If a nuclide enter into a human body, it will remain there for a long period of time.
  • If the nuclide has a short half-life, the rapid emission of radiation causes a shorter period of greater damage.

Rads (radiation absorbed dose) -measurement of radiation

1 rad=10-2J / kg tissue

Rem (roentgen equivalent for men)-measures both dosage of radiation and its effectiveness in the environment.

1 rem=#of rads * RBE

RBE-the effectiveness of radiation to cause biological damage.

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