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Show HN: Building a smartphone powered by nuclear decay: the power engineering
Every smartphone built in the last twenty years assumes the same thing: the battery will be charged once a day. Before I get to the math, sit with this for a moment: what would actually change if a phone never needed to be plugged in?<p>That is what I am building. The power source is betavoltaic — electricity generated continuously from the decay of a radioactive isotope, with no moving parts, no combustion, no charging infrastructure.<p>The device I am describing is not a current smartphone with a different power source. It is a device designed from the ground up around a power budget that current betavoltaic technology can sustain. Day One capability is meaningfully more limited than a 2026 flagship phone. That gap closes as the power architecture advances.<p>The source physics:<p>Tritium (H-3) decays by beta emission to helium-3.<p>The emitted electron carries a maximum energy of 18.6 keV, with a mean energy of approximately 5.7 keV. The neutrino carries the rest and is unrecoverable. The beta spectrum is continuous — a statistical distribution of electron energies up to the endpoint — which is why mean energy, not maximum, is the relevant figure for power calculations.<p>Tritium activity for power calculation: 1 Curie of tritium is 3.7 × 10¹⁰ disintegrations per second. At 5.7 keV mean energy per disintegration, 1 Ci of tritium releases approximately 1.6 × 10⁻¹⁹ J/eV × 5,700 eV × 3.7 × 10¹⁰ dis/s = approximately 33.8 mW of total beta energy. This is the upper bound on recoverable power — conversion efficiency determines how much becomes electricity.<p>Tritium's specific activity is 9,650 Ci/g. One gram of tritium therefore releases approximately 33.8 mW/Ci × 9,650 Ci/g = 326 W/g of total beta energy. Commercial betavoltaic cells at 1–4% conversion efficiency yield approximately 3.3–13 W/g electrical output — but tritium gas is diffuse and the actual cell includes a substrate, so power density per unit volume of assembled cell is far lower than per gram of tritium. Practical assembled cell power densities in current commercial products run 1–10 mW/cm².<p>City Labs in Miami produces tritium-on-silicon betavoltaic cells commercially under NRC license. Their current cells produce in the range of 50–300 μW/cm² of active junction area under typical loading. A mid-range figure of 150 μW/cm² is defensible for planning purposes with current commercial cells.<p>A multi-layer stacked cell module with 35 cm² of active junction area per layer and four layers — a total stack volume roughly comparable to a conventional battery pack — yields approximately 35 cm² × 4 layers × 150 μW/cm² = 21 mW total output. Accounting for interconnect losses and cell-to-cell variation, net output at the module terminals: approximately 15–18 mW continuous.<p>The conservative number — fewer layers, lower-yield cells — lands around 5–8 mW. I am designing the Day One architecture around 5 mW continuous as the floor, with 15 mW as the target as cell technology matures.<p>The decay curve is governed by the half-life P(t) = P₀ × (1/2)^(t/12.32)<p>At t = 5 years: P = P₀ × 0.755. At t = 8 years: P = P₀ × 0.629. At t = 12 years: P = P₀ × 0.499. The device at year 12 produces half its launch output. That output is predictable to high precision years in advance. No battery ages on a curve this clean.<p>The decay curve and upgrade cycle:<p>A device launched at 5 mW reaches the Day One capability floor at year 12. No consumer electronics device in history has been designed around a decade of predictable, transparent degradation rather than a two-year replacement cycle driven by software obsolescence. This one is.<p>What I'm looking for:<p>I'm the founder. I'm raising a pre-seed round to sign two co-founders: one with betavoltaic or nuclear battery hardware experience who can lead the prototype program. If you're that person, or you know them, I'd like to talk.<p>For the full essay and technical whitepaper, or to contact me directly, visit shelvin.com.
This is a high-concept 'moonshot' with sound physics but extreme execution and regulatory risks. The 5-15mW power budget is orders of magnitude below what modern mobile OSs require, necessitating a total reinvention of computing that may not meet consumer expectations.