**LAYER OF HALF EASING (LHE)** — thickness of a layer of the substance weakening the directed ionizing radiation twice. Distinguish SPO of flux density of energy (intensity) of ionizing radiation, power of an air dose, etc.

Size SPO is used for bystry assessment of necessary thickness of protection against ionizing radiation. In radiodiagnosis and radiation therapy of SPO use for the characteristic of effective energy of a continuous spectrum of x-ray emission and, therefore, its penetration. Definition of SPO is applied also to calculation of antiactinic protection against beta radiation and in certain cases to approximate definition of energy of beta particles.

For the photon radiation

of SPO = ln2/μ = 0,693/μ,

where μ — a linear extinction coefficient of a narrow monoenergetic bunch of radiation. E.g., to weaken a flow of ionizing radiation in To time, the number of layers of half weakening of n shall be such that 2^{ n } = K. Tak, if To = 8, then n = 3, or if To = 1024, then n = 10, since 2^{ 10 } = 1024.

In practice of antiactinic protection use also the concept «layer of tenfold easing» — thickness of a layer of the substance weakening the directed photon radiation by 10 times.

See also Antiactinic protection .

*U. Ya. Margulies.*