fission the process whereby certain heavy nuclei (e.g.,23592U) break apart
     into two approximately equal smaller, more stable, nuclei called
     “daughters.” Fission is usually initiated by bombarding heavy nuclei
     with slow moving neutrons. In the process, additional neutrons are
     released, which can cause the fission of yet more nuclei, thus sustaining
     a chain reaction. Fission processes release large quantities of energy.

fusion the process in which two small nuclei (usually H or He) combine to
     form a larger, more stable, nucleus. The heat and light of the sun are
     generated by the fusion of hydrogen isotopes to form helium nuclei.

gamma rays (g) high energy electromagnetic radiation. The wavelength of
     gamma rays is approximately 10–12 m (refer to a standard chemistry
&nstable
     (and therefore undergo nuclear decay), while others may be stable.

moderator a substance that slows down neutrons in a fission reactor.

nuclear decay the general term for any of several processes (alpha
     emission, beta emission, fission, etc.) that an unstable nucleus can undergo
     in order to achieve stability.

nuclear reactor vessel where controlled nuclear fission takes place.

positron (e +, 0+1e ) positively charged particle with the same mass as an
     electron.

radioactivity the generic term for alpha, beta or gamma emission.

transuranium elements the elements heavier than uranium (U), therefore
     those elements with Z > 92.

units of radiation various types of units exist to characterize ionizing
     radiation (alpha, beta, and gamma). Each is a slightly different way to
     measure the radiation.

a. A rad , or radiation absorbed dose, corresponds to 10–5 J of energy
    absorbed per gram of body weight. Not all forms of ionizing radiation
    have the same biological effect, so the RBE, radiation biological
    effectiveness, is a correction factor. For instance, X-rays and gamma
    rays are assigned an RBE of 1, while alpha particles have an RBE of
    10, which means alpha particles can cause more ionization and
    therefore more damage to the body. This term can be misleading
    because alpha particles external to the body are stopped by our skin,
    or even a piece of paper; they have little penetrating power. Gamma
    rays, on the other hand can penetrate soft body parts.

b. The rem , roentgen equivalent man, is calculated by multiplying the
    absorbed dose in rads by the radiation biological effectiveness.
                      rem  =  rad  x  RBE

c. The activity of a radioactive sample is usually measured in
    disintegrations per second, or in curies, where
         1 curie (Ci) = 3.7 x 1010 disintegrations/s
 
 
 

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