Internal Conversion


Also found in: Wikipedia.

internal conversion

[in′tərn·əl kən′vər·zhən]
(nuclear physics)
A nuclear de-excitation process in which energy is transmitted directly from an excited nucleus to an orbital electron, causing ejection of that electron from the atom.

Conversion, Internal

 

of gamma radiation, a phenomenon observed in the transition of an excited atomic nucleus to a lower energy state when the energy liberated is not radiated as a γ-quantum but is transferred directly to one of the electrons of the same atom, so that a conversion electron is emitted instead.

Conversion electrons may be emitted from the various shells of an atom, and they are correspondingly designated as K, L, M, and so forth. The energy of the electron is equal to the difference between the energy of the converted nuclear transition and the binding energy of the shell from which it is emitted. Measurement of the energy spectra of the conversion electrons makes it possible to determine the energy of the transitions and their multipolarity.

The probability of internal conversion with respect to the probability of a transition with the emission of a γ-quantum is characterized by the internal conversion ratio, which is defined as the ratio of the flux intensity of the conversion electrons (total or for a particular electron shell) to the intensity of the γ-radiation for the given nuclear transition. The internal conversion ratio is calculated according to quantum field theory, allowing for the shielding of the nuclear charge by electrons in the other atomic shells and taking into account the finite dimensions of the nucleus.

The internal conversion ratio varies over a broad range (103 to 10˗4), depending on the energy and multipolarity of the nuclear transition, nuclear charge, and the shell in which the internal conversion takes place. The lower the energy, the higher the multipolarity; and the greater the nuclear charge, the greater will be the ratio.

For transitions between nuclear states with zero spins, the emission of γ-quanta is absolutely forbidden and nuclear transition can only occur by means of internal conversion. Comparison of experimental internal conversion ratios with those computed theoretically is one of the fundamental methods of determining the multipolarities of transitions and the quantum characteristics (spins and parities) of nuclear states.

At nuclear transition energies higher than twice the energy of an electron at rest (Ɛ0 > 2mc2 = 1.022 MeV), internal conversion can occur with the formation of an electron-positron pair (pair conversion), the probability of which increases with the transition energy. The spectra of the electrons and positrons of a conversion pair are continuous, and the total kinetic energy of the electron and positron is equal to Ɛ02mc2. A special case of pair conversion is internal conversion with the emission of monoenergetic positrons. This occurs when an electron of a pair is captured by any shell, of the same atom, that has been cleared as a result of a previous nuclear conversion.

REFERENCES

Groshev, L. V., and I. S. Shapiro. Spektroskopiia atomnykh iader. Moscow, 1952.
Gamma-luchi. Edited by L. A. Sliv. Moscow-Leningrad, 1961.
Al’fa-, beta- i gamma-spektroskopiia, issues 3 and 4. Edited by K. Zigban. Moscow, 1969. (Translated from English.)

T. A. SOROKIN

References in periodicals archive ?
"It allows the neighborhood to continue adding housing through accessory dwelling units, and will also allow internal conversion of larger houses to multiple housing units."
'Should any features of historic significance be uncovered during the internal conversion of the application premises, these shall be exposed and incorporated into the design and layout of the cafe and coffee shop.' Chester's also wish to make the existing signage and colour of the timber frontage frame darker.
But sometimes the internal conversion of a church can disappoint a potential buyer, with original features ripped out and small rooms created to optimise the number of bedrooms and reception rooms.
Internal conversion of agricultural land for 615 households, area of ??87.8ha, conversion of land use purpose from gardens, ponds to land in 22 households with an area of ??0.38ha.
(PKG) should trade at a significant premium as he sees it having multiple internal conversion prospects.
The internal conversion was a huge undertaking but we are extremely pleased with the finished open plan office."
There seems to be more interest in practicing outward traditions than in internal conversion of heart.
The building will undergo a comprehensive internal conversion to create a modern funeral home housing chapels of rest, reception rooms and office accommodation.
For example, a femtosecond laser has been successfully used for efficient ionization before relaxation process of internal conversion and intersystem crossing of some chlorinated, brominated compounds [11,12].
Electronically excited single nucleobases decay to the ground state primarily by ultrafast internal conversion in less than 1 picosecond.
(39-49) Its broad [S.sub.2]([sup.1][B.sub.2u], [pi][[pi].sup.*])-[S.sub.0]([sup.1][A.sub.g]) photoabsorption spectrum suggests that the [S.sub.2] state undergoes ultrafast electronic deactivation (internal conversion) within 30 fs.

Full browser ?