Counting equipment “dead time” independent of net count rate of a radioisotope

Abstract

It has been published that the “dead time” of a G—M counter depends on the measured count rate. In this paper it is shown that the “dead time” is a constant over a limited range from zero to an observed net rate R n . From the fundamental equation τ′, R i R o i o = 1 − τ′R i , we get R i↑q i = ( R q ) o− [τ′( R q ) o]R i , where i = 1 to n, R i and R i o are the observed and true net count rates, q i is a measured physical quantity proportional to the absolute disintegration rate of any radioisotope source S i, ( R q ) o = R i o q i is the true net rate per unit quantity and R i o = q i( R q ) o . The ratio τ′ ∗ = [τ′( R q ) o] ( R q ) o is called the rational overall resolving time per count for a particular counting equipment instead of the “dead time”. At higher net rates R k (> R n ⩾ R i > 0) the parameters, A Δ and B Δ , of R k ↑ q k = B Δ − A Δ R k may be evaluated for various rate intervals ΔR k of the nonlinear ( j = k > n) portion of R j q j vs R j . The values of A Δ B Δ in R k↑q k B Δ = 1 − ( A Δ B Δ )R k have no physical meaning and A Δ B Δ is called the pseudo-resolving time per count. It was found that A Δ B Δ depends on R k lying in various ΔR k rate intervals, R k q k B Δ ≷ 1 − τ′ ∗ R k and ( R q ) o ≷ B Δ . Hence R k q k B Δ ≷ R k R k o , where R k o = q k( R q ) o for any source S k with k = n + 1, n + 2, etc. Raw count-rate data taken from three publications have been used for a comparison of τ′ ∗ with values of A Δ B Δ in the case of G—M, NaI(Tl) scintillation and gas-flow proportional counters.