Calcium-48
Encyclopedia
Calcium-48 is a rare isotope of calcium
containing 20 proton
s and 28 neutron
s. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, the only radioactive decay
pathway open to it is the extremely rare process of double beta decay
. Its half-life
is about 4.3×1019 years, so for all practical purposes it can be treated as stable. One factor contributing to this unusual stability is that 20 and 28 are both magic numbers
, making 48Ca a "doubly magic" nucleus.
Since 48Ca is both stable and neutron-rich, it is a valuable starting material for the production of new nuclei in particle accelerator
s, both by fragmentation and by fusion reactions with other nuclei, for example in the recent production of ununoctium
. Heavier nuclei generally require a greater fraction of neutrons for maximum stability, so neutron-rich starting materials are necessary.
48Ca is the lightest nucleus known to undergo double beta decay
and the only one simple enough to be analyzed with the sd nuclear shell model. It also releases more energy (4.27 MeV
) than any other double beta decay candidate. These properties make it an interesting probe of nuclear structure models and a promising candidate in the ongoing search for neutrinoless double beta decay.
Isotopes of calcium
Calcium has a total of 24 isotopes, from 34Ca to 57Ca. There are five observationally stable isotopes , plus one isotope with such a long half-life that for all practical purposes it can be considered stable...
containing 20 proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s and 28 neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, the only radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
pathway open to it is the extremely rare process of double beta decay
Double beta decay
Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...
. Its half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
is about 4.3×1019 years, so for all practical purposes it can be treated as stable. One factor contributing to this unusual stability is that 20 and 28 are both magic numbers
Magic number (physics)
In nuclear physics, a magic number is a number of nucleons such that they are arranged into complete shells within the atomic nucleus...
, making 48Ca a "doubly magic" nucleus.
Since 48Ca is both stable and neutron-rich, it is a valuable starting material for the production of new nuclei in particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
s, both by fragmentation and by fusion reactions with other nuclei, for example in the recent production of ununoctium
Ununoctium
Ununoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is...
. Heavier nuclei generally require a greater fraction of neutrons for maximum stability, so neutron-rich starting materials are necessary.
48Ca is the lightest nucleus known to undergo double beta decay
Double beta decay
Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...
and the only one simple enough to be analyzed with the sd nuclear shell model. It also releases more energy (4.27 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...
) than any other double beta decay candidate. These properties make it an interesting probe of nuclear structure models and a promising candidate in the ongoing search for neutrinoless double beta decay.