"Promethium substitution" is really Pm-147 substitution, because nearly all practical promethium use is tied to that beta-emitting isotope. Most Pm-147 applications have alternatives through either isotope swaps (Sr-90, Kr-85, Ni-63, tritium) or non-nuclear sensor technologies.
Promethium is not substituted like a commodity metal. It's substituted either by another radioisotope source (often Sr-90 or Kr-85 in gauges, tritium in luminous products) or by non-nuclear sensor technologies that avoid sealed sources entirely.
Industry has long used multiple isotopes for beta gauges. The IAEA explicitly lists 85Kr, 90Sr, 147Pm and 204Tl as "most used radioisotopes" for paper thickness measurement in nucleonic gauges.
Sr-90/Y-90: higher beta energy, longer half-life, often used where you need more penetration (but shielding and safety management can be more demanding).
Kr-85: used in some gauging contexts, with its own handling and regulatory profile.
Tl-204: also appears in the standard isotope toolkit for beta gauging.
This is the real structural substitute, and it's accelerating because it removes licensing, disposal, and safety overhead.
A manufacturer whitepaper on web gauging describes how improvements in near-infrared (NIR) sensors are expanding into applications historically served by beta gauges, driven by isotope availability uncertainty and end-user concerns about radioactive sources and disposal.
The trade-off: Beta gauges measure mass-per-area very well. Some non-nuclear methods infer thickness differently and can be sensitive to composition, coatings, moisture, or surface condition.
Pm-147 shows up in the betavoltaic literature, but it's not the only serious option. Reviews and industry analyses consistently point to Nickel-63 and Tritium as leading beta emitters in modern betavoltaic discussions, with Pm-147 present but not dominant.
Nickel-63: very long half-life and widely cited in the literature.
Tritium (H-3): used in specific nuclear battery concepts (often in solid forms like metal tritides).
Carbon-14: showing up more in recent research and prototypes.
Sr-90: can be used in certain nuclear battery concepts, but its higher-energy beta can drive design constraints.
If the "battery" you mean is not betavoltaic micro-power but higher-power radioisotope power: you're typically in Pu-238 RTG territory (a different category than Pm-147 devices).
Bottom line: for nuclear batteries, Pm-147 is usually substitutable by another isotope, but the decision is dominated by half-life, power density, shielding, and regulatory acceptance, not chemistry.
Promethium-147 has been used in self-luminous products, and regulators treat it in the same broad class as tritium and krypton-85 for certain product categories.
The key driver here is that many end users prefer substitutes that avoid sealed-source lifecycle management (licensing, tracking, return/disposal).
For calibration and lab use, substitution usually means:
This is less about "Pm vs X" and more about matching the radiation spectrum and instrument geometry to the measurement requirement.
Niche nuclear battery concepts where the whole value proposition depends on a specific lifetime-power-shielding profile and prior qualification history.
When someone says "Pm-147 can be replaced," ask:
Often Sr-90 or Kr-85, depending on the gauge design and the material being measured. The IAEA lists Pm-147 alongside Kr-85 and Sr-90 as standard isotopes used in nucleonic gauges.
Modern infrared / near-infrared (and other optical) measurement systems are increasingly used to replace beta gauges in web processes, driven by isotope availability concerns and radioactive source lifecycle costs.
Not universally. Analyses of the field often show Ni-63 and tritium as the most commonly discussed beta emitters today, with Pm-147 still used but not the runaway leader.