Used other than figuratively or idiomatically: see low-background, lead. / Lead with low inherent radiation levels, suitable for instruments and experiments highly sensitive to radiation.

Used other than figuratively or idiomatically: see low-background, steel. / Steel with low inherent radiation levels, suitable for instruments and experiments highly sensitive to radiation.

Ellipsis of cosmic gravitational-wave background.

Alternative form of gravitational wave background

Alternative form of cosmic gravitational-wave background

The stochastic background of gravitational waves produced during the creation of the universe. / The irresolvable diffuse background resulting from the mixture of weak gravitational waves of all sources.