mean life

American  

noun

Physics.

1. the average time that an unstable particle or nucleus survives before it decays.

2. decay time.

---

mean life British  

noun

1.  τ.  physics the average time of existence of an unstable or reactive entity, such as a nucleus, elementary particle, charge carrier, etc; lifetime. It is equal to the half-life divided by 0.693 15

---

Example Sentences

One example is extensive, independent testing to ensure the effectiveness and reliability of critical systems, which can mean life or death for servicemembers.

From The Wall Street Journal • Apr. 16, 2026

This does not mean life has been confirmed on Mars.

From Science Daily • Feb. 12, 2026

“It could mean life or death,” McDuffie said.

From Seattle Times • May 19, 2024

For decades, this nonprofit has been at the helm of a process that can mean life or death for many Southern Californians: the recovery of kidneys, livers and other organs from deceased donors for transplants.

From Los Angeles Times • Jul. 20, 2023

That could mean life and death on the upper reaches of the Rhoyne, Yandry claimed.

From "A Dance with Dragons" by George R. R. Martin