Radioactive element beginning to escape in minutes, I suspect (11)
I believe the answer is:
einsteinium
'radioactive element' is the definition.
'beginning to escape in minutes i suspect' is the wordplay.
'beginning to' indicates taking the first letters.
'suspect' is an anagram indicator.
The initial letter of 'escape' is 'e'.
'minutes'+'i'='minutesi'
'minutesi' is an anagram of 'steinium'.
'e'+'in'+'steinium'='EINSTEINIUM'
(Other definitions for einsteinium that I've seen before include "Metallic element named after famous scientist" , "Synthetic element" , "item on table" , "Radioactive metal" .)