diff --git a/activation/index.html b/activation/index.html
index 0a1bfea..c8ad686 100644
--- a/activation/index.html
+++ b/activation/index.html
@@ -1031,6 +1031,7 @@ <h3>Thermal flux</h3>
     handbook (<a class="cite" href="#ref_IAEA">IAEA 1987</a>), and the
     scattering calculator uses the IUPAC 2021 atomic weights and isotope composition
     database (<a class="cite" href="#ref_CIAAW">CIAAW 2021</a>).
+    Half-life values come from NUBASE2020 (<a class="cite" href="#ref_Kondev2021">Kondev 2021</a>).
 </p>
 <p>
     For very high fluences, e.g., more than 10<sup>16</sup> n/cm2, the activation
@@ -1392,12 +1393,23 @@ <h3>References</h3>
         Williams & Wilkins, Baltimore.
         [<a href="https://github.com/python-periodictable/periodictable/blob/master/periodictable/activation.dat">activation data</a>]
     </li>
+    <li id="ref_Kondev2021">
+        Kondev, F.G.; Wang, M.; Huang, W.J.; Naimi, S. and Audi, G. (2021).
+        <em>The NUBASE2020 evaluation of nuclear physics properties.</em>
+        Chin. Phys. C45, 030001.
+        doi:10.1088/1674-1137/abddae
+        [<a href="https://www.anl.gov/phy/reference/nubase-2020-nubase4mas20">half-life data</a>]
+    </li>
     </ol>
 </div>
 
 <div id="help_history" class="help">
     <h3>History</h3>
     <dl class="inline">
+    <dt>2026-01-xx v2.1.0</dt>
+        <dd>Use half-life from NUBASE2020. The following isomers change by 20% or more:
+            <br />32Si, 38Clm, 41Ca, 79Se, 97Tc, 108Ag, 121Snm, 126Sn, 135Cs, 157Tb, 177Lum
+        </dd>
     <dt>2025-04-23 v2.0.0</dt>
         <dd>Fix sort by half-life with units of ky, My, Gy.</dd>
     <dt>2025-02-28 v2.0.0</dt>