Design of Nuclear Batteries for Micro and Nano Scale
Betavoltaic designs and indirect conversion designs appear to overcome many of the problems of the repulsive field effect within a capacitive direct conversion device when the dimensions of the empty gap or stratum of medium of dissipating energy conversion is not much larger than 1/2 of the range of the average beta or alpha particle of the fuel source. This empty gap or stratum of energy conversion surrounds the fuel source. A beta-powered capacitive conversion device is basically a capacitor which functions as a battery in which the fuel source is the beta particle cathode and a cylindrical shell or other sheath remotely surrounds the fuel. for detailed description of a capacitive direct conversion device. The capacitive direct energy conversion device has been discussed here mainly in order to contrast its disadvantage in excessive size to betavoltaic designs and indirect conversion designs, which can be compacted roughly to the scales of range of beta or alpha particles. It is explained that capacitive nuclear batteries need to exceed 1 cm in diameter when using tritium, Ni-63, or any other radioisotopic fuel. Any such battery which is smaller than 1 cm is doomed to electrical efficiency below 1 percent. There are two worthwhile avenues of development of microscopic and submicroscopic configuration of nuclear batteries which we are pursuing: (M1) development of a beta-voltaic cell and (M2) development of tertiary energy conversion devices which include fluorescence or luminescence for the intermediate conversion of the kinetic energy of secondary electrons, β’s, and α’s. Note that tertiary energy conversion and intermediate conversion fall under indirect conversion in accordance of the terminology previously used in previous reports and related presentations. In support of development of (M1), there has been investigation of SiC as a betavoltaic cell with good initial performance. There has been an advocate of SiC for betavoltaic cells in established circles, owing to its initially high performance . However, the efficiency of diodes constituted primarily of SiC does wane with respect to extended dose. Solid-state modified diamond offers even greater potential as betavoltaic device. Diamond has the almost unique property of self-repair crystal structure due to interstitial displacements from radiation. The challenges to developing diamond based transducers hinge around providing both p-type and n-type junctions for such a diode and providing a good conductive contact between the diamond based transducer and the wire conducting electricity to and from the diode.
In support of (M2), there has been a review of and further experimental testing of the Cu+ doped quartz glass. Cu+ doped quartz glass has demonstrated the generation of green photons in response to exposure to beta particles and even X-rays. Lead doped glass also has this property of fluorescence resulting beta (or α) radiation dose . ZnS and Mn and other materials also serve in this way when doped properly with glass. A more exotic configuration of (M2) is to use Krypton or other noble gas which emits UV light in response to irradiation from beta and/or alpha particles. Use of a solid material such Cu+ doped glass in the more standard configuration of (M2) is easier to construct due to its solid nature. Containing a sufficient amount of Krypton fluorescer mixed with or surrounding a radioisotope such as Tritium is an additional burden contingent to use of this exotic configuration with noble gas. This burden makes Kr-84 mixed with Tritium an unlikely candidate for submicroscopic nuclear batteries.
It is illustrative to explain the components of (M2). A nuclear battery of type (M2) consists essentially of: (C1) the radioisotopic fuel; (C2) a material surrounding fuel which undergoes fluorescence or phosphorescence (in range of yellow thru possibly UV) in response to collisions and ionizing irradiation from radiative particles; and (C3) transducers which absorb visible light and efficiently convert it into electrical energy. It is component (C2), the ‘fluorescer’, which makes (M2) type of nuclear battery unique. Immediately below, we shall explain performances and results or (C1), the fuel from various candidates for radioisotopes. Then experimental results for Cu+ doped quartz as (C2) and prior scholarly knowledge of solid materials which can serve as (C2) shall be discussed.