Radioisotope heater unit

Matrix context

D = disequilibrium row · C = coupling family column. A cell reads the state of the atlas for that pair.

D.20 × C.27 · Nuclear binding-energy difference × Nuclear heatfamily: Nuclear heat

Measured or reported performance

Summary figures only; no datum-level record yet. Each figure below is a reviewed summary, not a single measurement.

notes

1 W thermal from 2.7 g of Pu-238 oxide; dozens flown on spacecraft to keep instruments warm

Typed bounds on this route

Every limit the atlas holds for this route, as constraint records: reached through bounded_by claims on the route's own entities. Hard bounds (an upper bound or a formula) decide the thermodynamic-bound check above; benchmarks, constitutive relations and resource limits are listed and never decisive. No prose limit exists anywhere (pass 42).

• Carnot limit · formula-bound · hard, filtered out by its applicability
  η ≤ 1 − T_c/T_h for any heat engine between reservoirs at T_h and T_c

Steps

1. 01
   Nuclear binding-energy difference —drives→ Radioactive decayestablishedclaim record

   nuclear → nuclear

   radioisotope required

   refs [1]
2. 02
   Radioactive decay —produces→ Alpha particlesestablishedclaim record

   nuclear → nuclear

   • alpha emitters such as Pu-238, Am-241, Po-210

   refs [1] [2]
3. 03
   Alpha particles —drives→ Radioisotope heatingestablishedclaim record

   nuclear → thermal

   • alpha particles stopped within the source pellet and its cladding (the RTG case)

   radioisotope required

   refs [1]
4. 04
   Radioisotope heating —produces→ Temperature gradientestablishedclaim record

   thermal → thermal

   refs [1]
5. 05
   Temperature gradient —drives→ Heat conductionestablishedclaim record

   thermal → thermal

   q = −κ · ∇T · thermal conductivity κ [W/(m K)]

   refs [3]
6. 06
   Heat conduction —produces→ Heat flowestablishedclaim record

   thermal → thermal

   refs [3]
7. 07
   Heat flow —converts into→ Useful heatestablishedclaim record

   thermal → thermal

   • heat delivered at a temperature above the point of use

   refs [3]

Evidence for the complete composition · 1

1. [1]
   M. A. Prelas, et al.. A review of nuclear batteries (2014)

   Progress in Nuclear Energy 75, 117–148 · doi:10.1016/j.pnucene.2014.04.007 · crossref ✓ 2026-09-19 · record

Evidence for the constituent relations · 3

1. [1]
   M. A. Prelas, et al.. A review of nuclear batteries (2014)

   Progress in Nuclear Energy 75, 117–148 · doi:10.1016/j.pnucene.2014.04.007 · crossref ✓ 2026-09-19 · record
2. [2]
   M. G. Spencer, T. Alam. High power direct energy conversion by nuclear batteries (2019)

   Applied Physics Reviews 6, 031305 · doi:10.1063/1.5123163 · crossref ✓ 2026-09-20 · record
3. [3]
   A. Bejan. Advanced Engineering Thermodynamics (4th ed.) (2016)

   Wiley · doi:10.1002/9781119245964 · crossref ✓ 2026-09-19 · record