' s ▁an nex ation ▁of ▁Austria . ▁While ▁there ▁she ▁received ▁the ▁news ▁that ▁her ▁former ▁colle agues ▁Otto ▁H ahn ▁and ▁Fritz ▁Str ass mann ▁in ▁Berlin ▁had ▁discovered ▁that ▁the ▁collision ▁of ▁a ▁neut ron ▁with ▁a ▁u ran ium ▁nucle us ▁produced ▁b arium ▁as ▁one ▁of ▁its ▁by products . ▁Fr isch ▁and ▁Me it ner ▁hypoth es ized ▁that ▁the ▁u ran ium ▁nucle us ▁had ▁split ▁in ▁two . ▁They ▁estimated ▁the ▁energy ▁released ▁at ▁around ▁ 2 0 0 ▁Me V , ▁and ▁Fr isch ▁appropri ated ▁the ▁term ▁f ission ▁from ▁bi ology ▁to ▁describe ▁it . ▁ ▁H ahn ' s ▁paper ▁described ▁the ▁experiment ▁and ▁the ▁finding ▁of ▁the ▁b arium ▁by product . ▁Me it ner ' s ▁and ▁Fr isch ' s ▁paper ▁explained ▁the ▁physics ▁behind ▁the ▁phenomen on . ▁Fr isch ▁went ▁back ▁to ▁C open hagen , ▁where ▁he ▁was ▁able ▁to ▁isol ate ▁the ▁fragments ▁produced ▁by ▁f ission ▁re actions . ▁Fr isch ▁later ▁re called ▁that : ▁▁ ▁The ▁news ▁of ▁the ▁discovery ▁of ▁f ission ▁was ▁brought ▁to ▁America ▁by ▁Bo hr ▁in ▁January ▁ 1 9 3 9 . ▁Bo hr ▁and ▁John ▁A . ▁Whe eler ▁set ▁to ▁work ▁applying ▁the ▁liquid ▁drop ▁model ▁developed ▁by ▁Bo hr ▁and ▁Fritz ▁Kal ck ar ▁to ▁explain ▁the ▁mechanism ▁of ▁nuclear ▁f ission . ▁George ▁P lac zek , ▁who ▁was ▁ske pt ical ▁about ▁the ▁whole ▁idea ▁of ▁f ission , ▁challeng