Measurements of precise internal conversion coefficients with an in-beam spectrometer

Abstract

A technique is described in which the NPG method is applied to the measurement of internal conversion coefficients of prompt transitions following nuclear reactions. An intermediate-image electron spectrometer and a Ge(Li) detector were used to observe simultaneously internal conversion electrons and gamma-rays produced during proton bombardment of thin targets placed at the source position of the spectrometer. With the value α T=(9.1±0.2)×10 −2 for the 662 keV transition in 137Ba accepted as a standard, the total internal conversion coefficient of the 843 keV ( 1 2 + → 5 2 + ) ground-state transition of 27Al, populated through the (p,p′) reaction, was found to be α T=(4.6±0.3)×10 −5. This value is in excellent agreement with the theoretical E2 value. The total internal conversion coefficient of the 413 keV ( 1 2 −→ 3 2 − ground-state transition in 55Fe, populated through the 55Mn(p,n) 55Fe reaction, was measured to be α T=(9.4±0.8)×10 −4. This value implies a nearly pure M1 character for the 413 keV transition. The technique described can readily be extended to other transitions populated in nuclear reactions.