Hypernucleus


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hypernucleus

[¦hī·pər′nü·klē·əs]
(nuclear physics)
A nucleus that consists of protons, neutrons, and one or more strange particles, such as lambda particles.

Hypernucleus

 

(also called hyperfragment), an atomic nucleus made up of a hyperon in addition to nucleons. A hypernucleus is formed during the interaction of high-energy particles with nucleons of the nucleus or when a slow K- meson is captured by the nucleus. As a result of this a slow Λ0 hyperon that forms a bound system with the nucleus appears. The lifetime of a hypernucleus is determined by the lifetime of the Λ0 hyperon (~10-10 sec).

The first hypernucleus was detected in 1952 by the Polish physicists M. Danysz and J. Pniewski, who used nuclear emulsions exposed to a cosmic-ray flux. All known hyper-nuclei are lambda hypernuclei, that is, nuclei containing a Λ0 hyperon. This is because all other hyperons enter into fast reactions with nuclear particles, but for the Λ0 hyperon such reactions are forbidden by the selection rules. A hypernucleus is designated by the chemical symbol of the element with the subscript A at left. For example, the nucleus of hyperhelium, whose structure is 2p + 2n + Λ0, is designated by the symbol Λ5 He.

Hypernuclei are studied by means of nuclear photoemulsions and bubble chambers. The characteristics of more than ten types of light hypernuclei are known. Upon the interaction of high-energy particles with the heavy nuclei of the photoemulsion, the formation of heavy hypernuclei with mass number A of up to 100 is observed. The existence of hypernuclei attests to the fact that an attractive force exists between hyperons and nucleons. The first double hypernucleus, ΛΛ10Be (4p + 4n + 2Λ°) was detected in 1963, and in 1966ΛΛ6He (2p + 2n + 2Λ°) was observed. The study of the properties of double hypernuclei makes it possible to determine the nature of the forces acting between the two hyperons.

REFERENCES

Telegdi, V. L. “Giperiadra.” In Fizika atomnogo iadra. Moscow, 1965. (Nad chem dumaiut fiziki, issue 4.)
Filimonov, V. A. “Obnaruzhenie vtorogo sluchaia dvoinogo giperiadra.” Uspekhifiziche skikh nauk, 1967, vol. 92, issue 3, p. 535.

V. S. EVSEEV

References in periodicals archive ?
These, in turn, impinged on a beryllium target, which, on occasion, released a hypernucleus containing a proton, a neutron, and two lambdas.
The experiment, dubbed EPOS, originally sought to create positrons out of the vacuum by the strong electric forces that are generated when two heavy nuclei come together to form a kind of hypernucleus with 500 or more neutrons and protons.