Physics_EnergyLoss.md

@@ -13,7 +13,9 @@ and electronic tables from at http://pdg.lbl.gov/AtomicNuclearProperties, also p
 Shell correction are discussed here: 
 [PhysRevA.46.5761.pdf](uploads/dcdaf0c5f26e0a6df81770028faa36af/PhysRevA.46.5761.pdf)
 
-Heavy particles Z>56 require extra work, e.g. 
+Barkas paper for original shell correction: https://www.nap.edu/read/20066/chapter/8 outdated, but simple to implement. 
+
+Heavy particles Z>56 require extra work, e.g.  ??? 
 
 There is an ICRU Update document from 2014: [newstar.pdf](uploads/96cdd093e48b84427fc78d0630877434/newstar.pdf)