Search for D-D Fusion initiated by Nuclear Hotspots in Boranes

. In the group of boron hydrogen compounds, decaborane and aminoborane belong to those with a particularly high hydrogen density in the molecular volume. Almost 100% of the protons in the molecule can be replaced by deuterons. In the element boron, the isotope 10 B is 19.9% naturally present. By capturing thermal neutrons in this isotope, the high-energy reaction products 4 He and 7 Li are formed. It thus forms a hotspot in a spatially stable cloud of deuterium nuclei, which can be triggered by external action and whose energy could be transferred to deuterium in a similar way to neutral beam injection, a successful method to heat a fusion plasma.


Introduction
The molecules of certain boranes have a very high hydrogen density.These densities exist without externally acting forces and are stable.The hydrogen nuclei may be replaced by deuterium.Decaborane molecules contain two atoms of 10 B on the average.The reaction B 5 10 (n,α) L 3 7 i produces two energetic ions and might serve as a "hotspot" within a dense cloud of deuterons, triggered by thermal neutron capture.The effect of such "hotspot" energy release is comparable to neutral gas injection, an effectively used method of injecting deuterons or tritons with energies of 50 keV to 130 keV into a fusion plasma that is held together magnetically.The fast ions lose energy through coulomb collisions with electrons and ions in the plasma and thus act as a heat source [1].In our case, just Coulomb interactions must be considered.
According to classical collision laws, the supplied energy could be sufficient to initiate D-D fusion.An experiment to show whether this energy can be transferred to deuterium nuclei, is proposed in this paper.

Decaborane
Decaborane has a history as an admixture to solid rocket fuel and recently for hydrogen storage.Deuterated decaborane has also found application in fusion research [2].This shows that the use of decaborane is also possible for producing nuclear environments.* Corresponding author: priesmeyer@physik.uni-kiel.deKasper et al. [3] have determined the unitcell parameters of decaborane to: a0 = 1.445 nm, b0 = 2.088 nm, c0 = 0.568 nm.Therefore the unitcell volume is 1.714 x 10 -27 m 3 .Since there are 8 molecules per unitcell and 14 deuterons per molecule, the deuteron density in decaborane is nD = 6.54 x 10 28 /m 3 .For Aminoborane the deuteron density amounts to n D = 9.15 x 10 28 /m 3 .

Properties of Decaborane
Typically about 98% deuteration of boranes can be achieved.

Uncertainties in the experimental procedure
A number of open questions exists: How does the time of molecular disintegration compare to the velocity of the ions created?Will the deuteron density remain high for the duration needed for an interaction?What is the probability of electric charges coming into the required proximity to each other?Can the same probability be assumed for the required energy transfer to initiate fusion or will it be lower?These questions led us to approach the task empirically.It has to be expected that the planned experiment has particularly high requirements with respect to a high flux of incident thermal neutrons, a very low background of fast neutrons, efficient fast neutron detectors with a high solid angle range.The detection of fast neutrons (both 2.45 MeV and 14 MeV) in time coincidence with the 480 keV γ -ray from the 7 Li* decay proves the initiation D-D fusion.
As an estimate for the conversion factor of a nuclear "hotspot" -reaction we consider the early developments to produce 14.1 MeV neutrons from thermal neutrons using converters based on lithium deuteride compounds and the reaction 6 LiD(n,α)T, which showed that about one fast neutron is produced per 10 4 thermal neutrons [4].
If we assume a factor of 10 -4 for the probability to transfer energy from a primary deuteron to the next, it becomes clear that the energy transfer to initiate fusion has low probability.An estimate for the ratio of the number of 10 B(n,α)Li reactions to the number of deuterons accelerated by α particles or Lithium ions could be of the same order of magnitude.This would yield a reaction rate of one D-D fusion per 10 8 thermal neutrons captured.Such a probability is, however, subject to uncertainties in both directions, but it shows clearly that very great effort will be experimentally required to demonstrate this fusion.In any case, the experiment must be sensitive enough to detect the 2.45 MeV neutrons that are produced.+ 480 keV -ray If the energy transfer from fast 7 Li and 4 He ions allow the initiation of D-D fusion, this will occur in two branches with an almost equal likelihood: The detection of the 480 keV gamma ray from the excited 7 Li* nucleus defines the time of the energy release within the borane molecule.Contrasting to this, D-D fusion in about a half of the cases will produce a 2.45 MeV neutron.The detection of these neutrons in coincidence with the 480 keV gamma rays proves D-D fusion.The other half of the reactions will produce 1.01 MeV tritons.Due to the higher cross-section of D-T fusion, 14 MeV neutrons might be generated by this fusion type.Therefore, both branches of D-D fusion may serve as evidence of its initiation.
These reactions could in principle contribute to the energy inventory within the reaction volume.