half-life vs time period

half-life and time period both are nouns.

Word	Noun	Adjective	Verb	Adverb
half-life	Yes	No	No	No
time period	Yes	No	No	No

As nouns, time period is a hypernym of half-life; that is, time period is a word with a broader meaning than half-life:

half-life: the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
time period: an amount of time

Other hypernyms of half-life include period, period of time.

half-life (noun)	time period (noun)
the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)	an amount of time