Betavoltaics
Betavoltaics obtains electric current from beta decay. A radioactive preparation emits electrons; these strike a semiconductor and create charge carrier pairs there, which flow off as current.
The principle resembles photovoltaics — except that what arrives is not light but beta radiation. And it is the best counterpart to neutrinovoltaic technology, because both promise the same thing while going about it in entirely different ways.
How a betavoltaic cell is built
Three parts suffice: a source, a semiconductor and contacts.
The sources are nuclides that are pure or nearly pure beta emitters and whose radiation is easily shielded:
| Nuclide | Half-life | Note |
|---|---|---|
| Tritium (³H) | 12.32 years | very soft radiation, easily managed |
| Nickel-63 | 100.1 years | long running time, common in today's cells |
| Promethium-147 | 2.62 years | used in early applications |
The electrons carry energies in the range of a few kiloelectronvolts. That is low enough for a thin casing or the housing itself to hold the radiation back — unlike gamma emitters, which require heavy shielding.
With tritium a sheet of paper is enough. Such a cell is harmless from the outside; only ingestion of the material into the body would be dangerous.
What it achieves — and what it does not
The decisive quantity is the power density, and it is small. A betavoltaic cell typically delivers microwatts to milliwatts. The efficiency is usually in the low single-digit percent range.
The reason is fundamental: a preparation gives off only as much energy as its decay provides, and the longer the half-life, the less per unit time. Long running time and high power exclude one another.
The field of use is thereby clearly circumscribed. A betavoltaic cell runs no motor and charges no telephone. It supplies things that need very little and must last very long:
- memory devices meant to retain their contents over decades
- sensors in places nobody visits again
- pacemakers — in the 1970s cells with promethium-147 were actually implanted, before the lithium battery displaced them
- spaceflight and military technology with very long service life
The advantage is duration. A cell with nickel-63 still has half its output after a hundred years. No chemical battery comes close.
History and present
The first cells appeared in the 1950s. In the 1970s the Betacel brought to market a pacemaker that ran for years without replacement — until the lithium battery became cheaper and simpler.
Today there are commercial tritium cells for niche applications. In 2024 a Chinese company announced a coin-sized nickel-63 cell said to deliver microwatts over decades. Such announcements are to be read with the usual reserve — the physics behind them is established, and the power class does not change because of them.
Distinction from neutrinovoltaic technology
The difference is fundamental.
Betavoltaics carries its fuel with it. Inside the device sits a radioactive preparation that is consumed, that has to be licensed and disposed of, and whose quantity limits the output.
Neutrinovoltaic technology, in the account of the Neutrino® Energy Group, contains no radioactive material. It seeks to obtain energy from fluxes that pass through every object anyway — neutrinos, cosmic muons, electromagnetic fluctuations, thermal fluctuations. In this picture the component is not consumed, because it brings nothing with it that could be consumed.
The orders of magnitude differ considerably too. Betavoltaics is an established, commercially available technology with very small output. For neutrinovoltaic technology the group names distinctly larger targets — around 1 to 1.5 kilowatts for the Life Cube — and describes these values expressly as design targets in development.
What connects the two
Both begin where sun and wind do not reach: in darkness, underground, inside devices, in places without maintenance. And both build on the same basic thought — that energy which is present anyway need not go unused.
Related
- Neutrinovoltaic technology — the approach without a preparation
- Energy harvesting — the wider field
- Thermoelectrics — the third route to maintenance-free power
Sources
- Particle Data Group and IAEA nuclide chart: half-lives and decay energies.
- Neutrino® Energy Group: Energy Harvesting, neutrino-energy.com.