The Mechanism of Nuclear Evaporation Produced by High-Energy Pi Mesons; EL MECHANISMO DE LAS EVAPORACIONES NUCLEARES PRODUCIDAS POR MESONES PI DE ALTA ENERGIA

Thesis/Dissertation · Wed Oct 31 04:00:00 EST 1962

OSTI ID:4823939

Bravo, O R

A systematic analysis of the kinematic characteristics of the nuclear fragments emitted in a high-energy disintegration permits the determination of the mechanism which governs the nuclear evaporation. The only detection instrument which permits the exact identification and measurement of heavy fragments is the nuclear photographic emulsion. Nuclear disintegration products were analyzed in a block of Ilford G5 emulsion 600-microns thick, exposed to a 4.15-Bev pi -meson beam. Determinations were made of the spectral length and angular distribution of the particle tracks, as well as the angular distribution of the other evaporated particles. The spectral length of the particles reveals that in the evaporation of heavy nuclei (Br and Ag), only fragments of 2- to 3- micron range are emitted. The light nuclei (C, N, and O), on the other hand, contribute fragments with a 12-micron range. From the angalar distribution, it was deduced that the nuclear evaporation occurs by means of a kinematic mechanism similar to the formation of a compound nucleus in nuclear reactions of low energy; the evaporation nuclei, extremely excited by the effects of the nuclear cascade, receives a transfer of impulse in the direction of the incident pion. The evaporation of the nucleus takes place in flight, altering the angular distribution of the particles and nucleons evaporated through the effects of the Lorentz transforrmation. Also, it was established that the fragment is a genuine recoil colliraated in a direction opposite to the evaporated particles. In the case of heavy nuclei, the center-of-mass velocity of evaporating nuclei is negligible; the angular distribution does not suffer much from appreciable modifications in the transformation to the laboratory system. The slight anisotropy of the light particles evaporated from the heavy nuclei is explained considering the contribution of the remainder of the low-energy nuclear cascade. (tr-auth)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-16-004881
• OSTI ID: 4823939
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

COMPOUND NUCLEI
EVAPORATION MODEL
EXCITATION
LORENTZ TRANSFORMATIONS
NUCLEI
PHYSICS
RELATIVITY THEORY