²¹²Pa — Unstable · t½ ≈ 5.0 ms · Decay: α → ²⁰⁸Ac · Type: synthetic · Uses: research.
²¹³Pa — Unstable · t½ ≈ 10.0 ms · Decay: α → ²⁰⁹Ac · Type: synthetic · Uses: research.
²¹⁴Pa — Unstable · t½ ≈ 16.0 ms · Decay: α → ²¹⁰Ac · Type: synthetic · Uses: research.
²¹⁵Pa — Unstable · t½ ≈ 36.0 ms · Decay: α → ²¹¹Ac · Type: synthetic · Uses: research.
²¹⁶Pa — Unstable · t½ ≈ 150 ms · Decay: α → ²¹²Ac · Type: synthetic · Uses: research.
²¹⁷Pa — Unstable · t½ ≈ 3.0 ms · Decay: α → ²¹³Ac · Type: synthetic · Uses: research.
²¹⁸Pa — Unstable · t½ ≈ 118 ms · Decay: α → ²¹⁴Ac · Type: synthetic · Uses: research.
²¹⁹Pa — Unstable · t½ ≈ 53.0 ms · Decay: α → ²¹⁵Ac · Type: synthetic · Uses: research.
²²⁰Pa — Unstable · t½ ≈ 22.0 ms · Decay: α → ²¹⁶Ac · Type: synthetic · Uses: research.
²²¹Pa — Unstable · t½ ≈ 36.0 ms · Decay: α → ²¹⁷Ac · Type: synthetic · Uses: research.
²²²Pa — Unstable · t½ ≈ 2.0 ms · Decay: α → ²¹⁸Ac · Type: synthetic · Uses: research.
²²³Pa — Unstable · t½ ≈ 5.1 ms · Decay: α → ²¹⁹Ac · Type: synthetic · Uses: research.
²²⁴Pa — Unstable · t½ ≈ 1.7 s · Decay: α → ²²⁰Ac · Type: synthetic · Uses: research.
²²⁵Pa — Unstable · t½ ≈ 1.7 min · Decay: α → ²²¹Ac · Type: synthetic · Uses: research.
²²⁶Pa — Unstable · t½ ≈ 1.8 min · Decay: α → ²²²Ac · Type: synthetic · Uses: research.
²²⁷Pa — Unstable · t½ ≈ 38.3 min · Decay: α → ²²³Ac · Type: synthetic · Uses: research.
²²⁸Pa — Unstable · t½ ≈ 22.0 h · Decay: β⁻ → ²²⁸U · Type: tracer · Uses: research.
²²⁹Pa — Unstable · t½ ≈ 1.5 d · Decay: β⁻ → ²²⁹U · Type: tracer · Uses: research.
²³⁰Pa — Unstable · t½ ≈ 17.4 d · Decay: α → ²²⁶Ac · Type: tracer · Uses: nuclear physics.
²³¹Pa — Unstable · t½ ≈ 3.28×10⁴ y · Decay: α → ²²⁷Ac · Type: long-lived radionuclide · Uses: geochronology, ocean circulation studies.
²³²Pa — Unstable · t½ ≈ 1.3 d · Decay: β⁻ → ²³²U · Type: tracer · Uses: nuclear physics.
²³³Pa — Unstable · t½ ≈ 27.0 d · Decay: β⁻ → ²³³U · Type: nuclear fuel cycle intermediate · Uses: thorium fuel cycle.
²³⁴Pa — Unstable · t½ ≈ 6.7 h · Decay: β⁻ → ²³⁴U · Type: natural (Uranium series) · Uses: environmental tracer.
²³⁵Pa — Unstable · t½ ≈ 24.5 min · Decay: β⁻ → ²³⁵U · Type: synthetic · Uses: research.
²³⁶Pa — Unstable · t½ ≈ 9.1 ms · Decay: α → ²³²Ac · Type: synthetic · Uses: research.
²³⁷Pa — Unstable · t½ ≈ 8.6 ms · Decay: α → ²³³Ac · Type: synthetic · Uses: research.
²³⁸Pa — Unstable · t½ ≈ 2.3 ms · Decay: α → ²³⁴Ac · Type: synthetic · Uses: research.
²³⁹Pa — Unstable · t½ ≈ 0.6 ms · Decay: α → ²³⁵Ac · Type: synthetic · Uses: research.
Protactinium — isotope count: 28 total · Stable: none · Unstable: 28.
(Data: IAEA LiveChart, NUBASE2020, ENSDF; notable applications: ²³¹Pa in geochronology and ocean circulation, ²³³Pa in thorium fuel cycle, ²³⁴Pa in uranium series as tracer.)