Mass Number - Mass Number Changes in Radioactive Decay

Mass Number Changes in Radioactive Decay

Different types of radioactive decay are characterized by their changes in mass number as well as atomic number, according to the radioactive displacement law of Fajans and Soddy. For example, uranium-238 usually decays by alpha decay, where the nucleus loses two neutrons and two protons in the form of an alpha particle. Thus the atomic number and the number of neutrons each decrease by 2 (Z: 92→90, N: 146→144), so that the mass number decreases by 4 (A = 238→234); the result is an atom of thorium-234 and an alpha particle (4
2He2+):

238
92U
234
90Th
+ 4
2He2+

On the other hand, carbon-14 naturally decays by radioactive beta decay, whereby one neutron is transmuted into a proton with the emission of an electron and an anti-neutrino. Thus the atomic number increases by 1 (Z: 6→7) and the mass number remains the same (A = 14), while the number of neutrons decreases by 1 (N: 8→7). The resulting atom is nitrogen-14, with seven protons and seven neutrons:

14
6C
14
7N
+ e− + ν
e

Another type of radioactive decay without change in mass number is emission of a gamma ray from a nuclear isomer or metastable excited state of an atomic nucleus. Since all the protons and neutrons remain in the nucleus unchanged in this process, the mass number is also unchanged.

Read more about this topic:  Mass Number

Famous quotes containing the words mass, number and/or decay:

    They’re semiotic phantoms, bits of deep cultural imagery that have split off and taken on a life of their own, like those Jules Verne airships that those old Kansas farmers were always seeing.... Semiotic ghosts. Fragments of the Mass Dream, whirling past in the wind of my passage.
    William Gibson (b. 1948)

    If we remembered everything, we should on most occasions be as ill off as if we remembered nothing. It would take us as long to recall a space of time as it took the original time to elapse, and we should never get ahead with our thinking. All recollected times undergo, accordingly, what M. Ribot calls foreshortening; and this foreshortening is due to the omission of an enormous number of facts which filled them.
    William James (1842–1910)

    Now, a corpse, poor thing, is an untouchable and the process of decay is, of all pieces of bad manners, the vulgarest imaginable. For a corpse is, by definition, a person absolutely devoid of savoir vivre.
    Aldous Huxley (1894–1963)