## Master Isotope Table — NIST SRD-128 Kα₁ (Z = 21–40)
| Z | Elem | Known | Stable | Unstable | Pred. | Gap | Nuclear γ (keV) | NIST Kα₁ (keV) | Context |
|---:|:---:|---:|---:|---:|---:|---:|---:|---:|---|
| 21 | Sc | 25 | 1 | 24 | 59 | 34 | 889.3 / 1120.5 | 4.090 | ⁴⁶Sc tracer γ + XRF |
| 22 | Ti | 26 | 5 | 21 | 62 | 36 | 1157.0 | 4.511 | ⁴⁴Ti (via ⁴⁴Sc γ), XRF |
| 23 | V | 26 | 1 | 25 | 62 | 36 | 983.5 | 4.952 | ⁴⁸V (PET/activation) |
| 24 | Cr | 26 | 4 | 22 | 62 | 36 | 320.1 | 5.415 | ⁵¹Cr tracer |
| 25 | Mn | 26 | 1 | 25 | 62 | 36 | 834.8 | 5.899 | ⁵⁴Mn γ source |
| 26 | Fe | 28 | 4 | 24 | 66 | 38 | — | 6.404 | Fe Kα₁ dominant line |
| 27 | Co | 29 | 1 | 28 | 69 | 40 | 1173.2 / 1332.5 | 6.930 | ⁶⁰Co γ pair |
| 28 | Ni | 31 | 5 | 26 | 74 | 43 | — | 7.478 | Ni Kα₁ (XRF) |
| 29 | Cu | 29 | 2 | 27 | 69 | 40 | — | 8.048 | Cu Kα₁, calibration |
| 30 | Zn | 30 | 5 | 25 | 71 | 41 | 1115.5 | 8.638 | ⁶⁵Zn tracer + XRF |
| 31 | Ga | 31 | 2 | 29 | 74 | 43 | 93.3 / 184.6 / 300.2 | 9.251 | ⁶⁷Ga SPECT |
| 32 | Ge | 32 | 5 | 27 | 76 | 44 | — | 9.886 | Ge XRF line |
| 33 | As | 33 | 1 | 32 | 78 | 45 | 559.1 / 595.9 | 10.543 | ⁷⁴As γ tracer |
| 34 | Se | 30 | 6 | 24 | 71 | 41 | 136 / 265 / 279.5 | 11.222 | ⁷⁵Se tracer |
| 35 | Br | 31 | 2 | 29 | 74 | 43 | 554.3 / 776.5 | 11.924 | ⁸²Br tracer |
| 36 | Kr | 32 | 6 | 26 | 76 | 44 | 514.0 | 12.648 | ⁸⁵Kr noble gas γ |
| 37 | Rb | 32 | 1 | 31 | 76 | 44 | 511 (annih.) | 13.395 | ⁸²Rb PET |
| 38 | Sr | 34 | 4 | 30 | 81 | 47 | 514.0 | 14.165 | ⁸⁵Sr tracer |
| 39 | Y | 32 | 1 | 31 | 76 | 44 | 898.0 / 1836.0 | 14.958 | ⁸⁸Y calibration |
| 40 | Zr | 34 | 5 | 29 | 81 | 47 | 724.2 | 15.775 | ⁹⁵Zr fission product |
✅ That completes Z = 21–40.
Would you like me to continue directly to Z = 41–60 next?