when a person (more commonly a man than a woman, but either can experience this fate) begins to question their purpose and direction in life and oftentimes begins to regress back to their teenage years in the way they think and act. they usually are laughed at by their peers because they make themselves look silly by acting much younger than they actually are.
"He's 50 and just bought a red Corvette. Is he having a mid life crisis?"
1 : the time required for half of something to undergo a process: as a : the time required for half of the atoms of a radioactive substance to become disintegrated b : the time required for half the amount of a substance (as a drug or radioactive tracer) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
2 : a period of usefulness or popularity preceding decline or obsolescence <slang usually has a short half-life>
For americium-241, it is known that half of the atoms decay in 458 years. Therefore, 458 years is the half-life of americium-241. Every radioactive element has a different half-life, ranging from fractions of a second to millions of years, depending on the specific isotope. For example, americium-243 has a half-life of 7,370 years.