Pycnonuclear Reactions Research Articles

Unified formation of astronomical objects up to stellar mass range

In dense interstellar clouds or in the surroundings of just-formed stars, the larger grains form proto-cores by segregating from the gas under the influence of the gravitational field of the cloud during intervals of the order 108 yr. If the mass of the proto-cores is smaller than a certain limit, the object possesses a negligible atmosphere and remains composed mainly of solid grain material. If the mass of the proto-core exceeds the limiting mass, the proto-core can bind around it an atmosphere. When the temperature of the opaque part of the atmosphere is only fractions of a degree above the temperature of the surrounding tenuous gas, gravitational contraction of the opaque part of the atmosphere sets in, forming gaseous objects up to stellar mass range. Binary and multiple systems originate from neighbouring proto-cores, through gravitational contraction of both their separate and common outer atmospheres. Pycnonuclear reactions are not able to prevent a star with mass ≲0.08M ⊙ from cooling to the black dwarf stadium.

Nuclear reactions in superdense magnetized cold hydrogen

The energy yield of nuclear reactions in cold dense hydrogen is shown to be considerably enhanced in the presence of magnetic fields of the order of 1013–1014 G. The energy yield of pycnonuclear reactions is less when the Fermi energy of the degenerate electrons in the magnetic field is too low for the formation of tritium.

Thermonuclear and pycnonuclear reactions

Gaseous fusion reactions are divided into two main classes: e thermonuclear and the pycnonuclear. In a gas of low density and high temperature the Coulomb-barrier penetration probability is only slightly affected by electron screening, and the main contribution to the reaction probability comes from the relatively few fast-moving nuclei at the energy E0 of the Gamow peak. These are the temperature-sensitive thermonuclear reactions. As the density increases and the temperature decreases, the potential barriers are depressed by electron screening and the Gamow peak is increased in height and displaced towards a lower energy. At high densities and low temperatures, when the potential barriers are depressed by an amount larger than E0, the Gamow peak is shifted across the origin and only its tail-end remains. The reaction probability is now density sensitive, and the main contribution comes from the relatively abundant slow-moving nuclei. These reactions are no longer thermonuclear and are more aptly described as `pycnonuclear' (after Cameron). At still higher densities and lower temperatures the nuclear gas becomes degenerate and the reaction probability is independent of the temperature of the gas; these reactions are referred to as `cryonuclear'. The present results for pycnonuclear reactions differ in detail from those obtained by previous authors. Although the results can be readily adapted and extended in the case of astrophysical applications, the main emphasis is on hydrogen-isotope reactions with the possibility in mind of achieving the controlled release of nuclear energy from dense media in the laboratory. For example, in the typical thermonuclear working region of 1014 < n < 1016 cm-3, 108 < T < 109 °K (where n is the ion number density and T is the temperature) the burn-up time of the nuclear fuel is the same as in the cryonuclear working region of 3 × 104 < ρ < 105 g cm-3, T < 105 °K (where ρ is the density of the gas). A proposed classification of the gaseous fusion reactions, based on the form of the reaction probability, is as follows. The first class (a) consists of the thermonuclear or temperature-sensitive reactions, and is subdivided into (i) the araeonuclear reactions which are density independent, and (ii) the pycno-thermonuclear reactions which are density dependent. The second class (b) consists of the pycnonuclear or density-sensitive reactions, and is subdivided into (iii) the thermo-pycnonuclear reactions which are temperature dependent, and (iv) the cryonuclear reactions which are temperature independent and occur only in degenerate nuclear gases.

Energy and Pressure of a Zero-Temperature Plasma.

The equation of state is considered for matter consisting of electrons and nuclei of atomic weight A and charge Z, at zero temperature and at densities much larger than that of the solid at zero pressure. Corrections are evaluated to the energy and pressure of a degenerate Fermi gas of noninteracting electrons, due to the following effectsn classical Coulomb energy of an ion lattice with uniformly distributed electrons (this is the largest correction); Thomas-Fermi deviations from uniform charge distribution of the electrons; and exehange energy and spin-spin interactions between the electrons. The corrections increase with decreasing density, and the approximations break down when the spacing between nuclei is greater than the mean radius of the free Thomas-Fermi atom, and the formulas are not applicable to the interior of planets. At very high densities, where the electrons are extremely relativistic, the correction to the pressure is a multiplying constant factor which is 0.994, 0.986, and 0.960, respectively, for Z = 2, 6, and 26. It is shown that the nuclei form a lattice rather than a gas. At very high densities, restrictions are found on possible values for A and Z due to inverse beta decays and pycnonuclear reactions. For instance,more » C/sup 12/ changes to Ne/sup 24/ at densities above 6 x 10/sup 9/ gm/cc. (auth).« less

Pycnonuclear reactions and nova explosions.

Pycnonuclear reactions and nova explosions.