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:
“For half a mile from the shore it was one mass of white breakers, which, with the wind, made such a din that we could hardly hear ourselves speak.... This was the stormiest sea that we witnessed,more tumultuous, my companion affirmed, than the rapids of Niagara, and, of course, on a far greater scale. It was the ocean in a gale, a clear, cold day, with only one sail in sight, which labored much, as if it were anxiously seeking a harbor.... It was the roaring sea, thalassa exeessa.”
—Henry David Thoreau (18171862)
“Take away from the courts, if it could be taken away, the power to issue injunctions in labor disputes, and it would create a privileged class among the laborers and save the lawless among their number from a most needful remedy available to all men for the protection of their business interests against unlawful invasion.... The secondary boycott is an instrument of tyranny, and ought not to be made legitimate.”
—William Howard Taft (18571930)
“The goal of every culture is to decay through over-civilization; the factors of decadence,luxury, scepticism, weariness and superstition,are constant. The civilization of one epoch becomes the manure of the next.”
—Cyril Connolly (19031974)