FISSION ASYMMETRY

Journal Article · Wed Oct 01 00:00:00 EDT 1958 · Annals of Physics (New York) (U.S.)

DOI:https://doi.org/10.1016/0003-4916(58)90046-0· OSTI ID:4295714

Inglis, D R

Part I is a simplified treatment of the droplet model. To bring the common fissionable nuclei to the region of the "saddle" in the energy surface, It is necessary to have deformations very far from the spherical shape. To study this region without expanding about a spherical shape, and to clarify some aspects of the process that might otherwise be hidden in large machine calculations, a simplified model of a nucleus near the saddle shape is introduced consisting of a cylinder with hemispherical ends. Relatively simple methode are used for estimating the change in electrostatic self-energy for small changes from this shape, and this is compared with the change of surface energy. A long charged cylinder of this sort does not expand indefinitely in length, and for the empirical values of the constants it always tends to contract. Above a certain minimum length, a neck may develop leading toward fission. The initial instability of the neck is considered under various conditions leading toward either symmetric or asymmetric fission. It is made clear that the neck has a strong tendency to start at the symmetric position, but if started asymmetrically it has a tendency to grow faster because of smaller reduced mass of the system. The droplet model alone does not provide an adequate explanation of the asymmetry of low-energy fission. Part II is a discussion of the origin of fission asymmetry as related to other phenomena, particularly the observed angular anisotropies of fission and the low odd states of even nuclei. It is considered likely that specific nucleon effects may make the nucleus "pear-shaped" in the region of the saddle and beyond. Such effects may be related to, but not nearly as extreme as, the picture of two clusters, one with 50 and the other with 82 neutrons, and perhaps better calculated in terms of a small asymmetric deviation from spheroidal shape. It seems theoretically likely that such a mechanism is effective in some states and not others, and various experimental results on fragment mass distribution and angular anisotropy are interpreted most simply if the ground state and its rotational neighbors have saddles favoring asymmetry but some inportant excited states do not. (auth)

• Research Organization: CERN, Geneva; Argonne National Lab., Lemont, Ill.
• NSA Number: NSA-13-002429
• OSTI ID: 4295714
• Journal Information: Annals of Physics (New York) (U.S.), Vol. Vol: 5; Other Information: Orig. Receipt Date: 31-DEC-59
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

PHYSICS AND MATHEMATICS
ANGULAR DISTRIBUTION- ANISOTROPY- CONFIGURATION- DISTRIBUTION- ENERGY LEVELS- FISSION- FISSION PRODUCTS- MAGIC NUMBERS- MASS- NEUTRONS- NUCLEAR MODELS- NUCLEI- ROTATION
CONFIGURATION- DEFORMATION- ELECTRIC POTENTIAL- ELECTROSTATICS- ENERGY- ENERGY RANGE- FISSION- LIQUID DROP MODEL- MASS- NUCLEAR MODELS- NUCLEAR THEORY- NUCLEI- OSCILLATIONS- SURFACES