Cross section, fusion

The confinement region in which nuclear fusion proceeds is surrounded by a blanket in which the neutrons produced by the fusion reaction are captured to produce tritium. Because of its favorable cross section for neutron capture, lithium is the favored blanket material. Various lithium blanket... 

Figure 15.9 Cross section of stainless steel weld showing crevice corrosion along a site of incomplete fusion. (Magnification 15x.)...

Separation of 6Li from natural abundance (7.4%) feed to synthesize 6LiD (an important component of the fuel used in hydrogen fusion weapons (hydrogen bombs)). This, because the (n,T) cross section for 6Li is much larger than that of 7Li, so production of tritium is much enhanced in the triggering explosion. 

Hard silvery-white metal hexagonal close-packed crystal structure density 12.41 g/cm3 at 20°C melts at 2,334°C vaporizes at 4,150°C electrical resistivity 7.1 microhm-cm at 0°C hardness (annealed) 200-350 Vickers units Young s modulus 3.0x10 tons/in magnetic susceptibility 0.427 cm /g thermal neutron absorption cross section 2.6 barns insoluble in water, cold or hot acids, and aqua regia can be brought into aqueous phase by fusion of finely divided metal with alkaline hydroxides, peroxides, carbonates and cyanides. 

Grayish-white metal hody-centered cubic crystalline structure density 19.3 g/cm3 melts at 3,422°C vaporizes at 5,555°C vapor pressure 1 torr at 3,990°C electrical resistivity 5.5 microhm-cm at 20°C modulus of elasticity about 50 to 57 x lO psi (single crystal) Poisson s ratio 0.17 magnetic sus-ceptibilty +59 x 10-6 thermal neutron absorption cross section 19.2 + 1.0 barns (2,200m/sec) velocity of sound, about 13,000 ft/sec insoluble in water practically insoluble in most acids and alkabes dissolves slowly in hot concentrated nitric acid dissolves in saturated aqueous solution of sodium chlorate and basic solution of potassium ferricyanide also solubibzed by fusion with sodium hydroxide or sodium carbonate in the presence of potassium nitrate followed by treatment with water... 

The cross-section of a fusion reaction, as well as the rate constant of a-decay, decreases exponentially with decreasing kinetic energy of the nuclei relative motion. This strong dependence of the reaction cross-section on the energy leads to an unusual (from the point of view of the classic physical and chemical kinetics) dependence of the reaction rate constant on temperature... 

The probability of fusion is a sensitive function of the product of the atomic numbers of the colliding ions. The abrupt decline of the fusion cross section as the Coulomb force between the ions increases is due to the emergence of the deep inelastic reaction mechanism. This decline and other features of the fusion cross section can be explained in terms of the potential between the colliding ions. This potential consists of three contributions, the Coulomb potential, the nuclear potential, and the centrifugal potential. The variation of this potential as a function of the angular momentum l and radial separation is shown as Figure 10.26. 

The cross section for production of a heavy evaporation residue, ctEVr, by a complete fusion reaction can be written as ... 

In Figure 15.4, we show current measurements (filled squares) of the cross sections for cold fusion reactions as a function of the atomic number Z of the completely fused system. (The cold fusion point at Z = 118 is an upper limit.) Also shown (as open circles) are the cross sections for hot fusion reactions. Clearly, future efforts will have to focus on experiments at the 0.1- to 1.0-pb cross-section level or lower. Current technology for cold fusion reaction studies would require 12 days to observe one event at a cross-section level of 1 pb. Similarly, a cross section of 1 pb in a hot fusion reaction would require 6—19 days to observe one event. From examining the data in Figure 15.4, it would also appear that hot fusion reactions might be the reactions of choice in pursuing future research in this area. 

Figure 15.4 Plot of the observed cross sections for the production of heavy elements by cold and hot fusion reactions.

Figure 15.5 Plot of the contours of log10 o-fus (where ct,ms is the. v-wave fusion cross section at the interaction barrier).

From Figure 15.5, one predicts the fusion cross section to be 10-32 cm2, while Figure 15.6 would suggest an excitation energy of 20 MeV. Thus, one would roughly estimate the overall cross section for producing 265Hs to be... 

Hopefully, our results (some of which have been presented previously [KUM83]) for the superheavy nuclei will also stimulate other theorists to recalculate fission lifetimes, and, especially, fusion cross-sections for the suggested target-projectile combinations. These cross-sections are expected to be small and the corresponding experiments are expected to be quite difficult. 

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