Carbon-14 betavoltaics
Carbon-14 dates the past. We use it to power the future.
DBNS seals carbon-14 recovered from irradiated reactor graphite inside a synthetic diamond that is both the fuel and the semiconductor. The cell is never charged. At the 5,730-year half-life mark it is still at half power.
The case
Two liabilities. One answer.
90,000 t
Irradiated graphite awaiting disposal in the UK alone. Today it is a cost centre with no product attached to it.
5–10 yr
How long a lithium cell lasts inside a sealed device. After that, someone has to physically reach it.
A pacemaker replaced for battery reasons is a surgery. A seabed sensor replaced for battery reasons is a ship.
Process
Waste in. Power out.
Four stages, run end to end. The isotope never leaves the carbon lattice it arrives in.
01
Recover
Irradiated graphite is heated until the carbon-14 concentrated near its surface releases as gas. The bulk graphite left behind drops to a lower waste classification, which is worth something on its own.
02
Grow
That gas feeds a chemical-vapour-deposition reactor. Over several weeks it grows a diamond in which carbon-14 is a structural atom of the lattice, not a passenger inside a container.
03
Convert
Beta particles thrown off by the decay knock electrons across a junction in that same crystal. Fuel and semiconductor are one component, so there is no transfer loss and nothing to wear against.
04
Seal
A second diamond layer, non-radioactive, is grown over the first. Carbon-14's beta emission is stopped by a fraction of a millimetre of solid carbon — the source shields itself.
Spec
What it does, and what it will not do.
This is a trickle source, not a power supply. It suits loads measured in microwatts, or duty-cycled loads sitting behind a capacitor.
| Output, single cell | 15–100 µW configuration dependent |
|---|---|
| Output, 48-cell module | up to 4 mW series-parallel stack |
| Half-life | 5,730 yr carbon-14 |
| Output at 100 years | 98.8 % of day-one output |
| Output at 1,000 years | 88.6 % of day-one output |
| Operating range | −196 °C to +200 °C no derating curve |
| Self-discharge | None no chemistry to relax |
| Charge cycles | Not applicable the cell is never charged |
Fit
Where replacement is the expensive part.
Implantable medical
Cardiac and neurostimulation devices whose battery, not whose electronics, sets the replacement schedule. Removing that schedule removes a surgery.
Subsea and downhole
Sensors on the seabed or several kilometres down a well, where a battery swap means mobilising a vessel or a rig.
Orbital and deep space
Housekeeping loads and beacons that must survive eclipse, cold soak, and mission durations past any solar array's useful life.
Sealed infrastructure
Strain and corrosion gauges cast into a bridge deck at the pour, still reporting when the structure is retired.
Safety
The boring answer is the correct one.
Low-energy emission
Carbon-14 emits beta particles at 156 keV maximum. They travel a fraction of a millimetre in solid carbon and cannot leave the encapsulation.
No dispersal path
The isotope is a covalently bonded atom in a diamond lattice, not a powder or a liquid. There is no leak mode, because there is nothing to leak.
Net waste reduction
Every cell we build removes carbon-14 from a graphite inventory that a government is otherwise paying to store indefinitely.
Licensing status
- Pre-applicationNRC, sealed source and device registration
- In preparationIAEA Category 5 source classification dossier
- PlannedISO 13485 quality system, ahead of medical qualification
DBNS is pre-revenue and pre-licence. Nothing on this page is an offer to sell a licensed device.
Reference
Terms used on this page.
If you would rather read the whole thing without the jargon, there is a plain-language version of this page.
- Betavoltaic
- A cell that turns the beta particles given off by a radioactive material directly into electricity. It is not a reactor and it makes no heat worth speaking of.
- Beta particle
- An electron thrown out of an atom as it decays. The ones carbon-14 emits are weak enough to be stopped by a fraction of a millimetre of solid carbon.
- Half-life
- The time it takes for half of a radioactive material to decay. For carbon-14 that is 5,730 years, so a cell is still at half output after that long.
- Chemical-vapour deposition (CVD)
- A way of growing a crystal by feeding gas into a hot chamber, where it settles atom by atom onto a surface. It is how the diamond in each cell is made.
- Irradiated graphite
- Blocks of carbon used inside some nuclear reactors. Years of use leave them mildly radioactive, and they are currently stored as waste.
- Encapsulation
- The sealed outer layer around the radioactive part of the cell. Here it is a second diamond layer, grown over the first and not radioactive itself.
- Sealed source
- A regulator’s term for radioactive material bonded or enclosed so it cannot escape or be dispersed in normal use, or in an accident.
- Trickle source
- A power source that gives a very small amount of current continuously, rather than a large amount on demand.
- Duty-cycled
- A device that wakes briefly, does its job, then sleeps. It can run on a trickle source by storing charge between wakes.
Abbreviations
- µW
- microwatt — one millionth of a watt
- mW
- milliwatt — one thousandth of a watt
- keV
- kiloelectronvolt — a unit of particle energy
- NRC
- Nuclear Regulatory Commission (United States)
- IAEA
- International Atomic Energy Agency
- ISO
- International Organization for Standardization
- BCE / CE
- Before Common Era / Common Era — calendar eras
- UK
- United Kingdom
- t
- tonne — 1,000 kilograms
We are taking on four design partners.
Bring us a load profile and a duty cycle. We will tell you honestly whether a betavoltaic is the wrong answer for it — usually it is, and the cases where it is not are the ones we want to see.