12 The Measurement of Nuclear Lifetimes

Abstract

Table of Contents I. Scope and definitions 425 II. Decay constants of "rare" decays 427 A. Very long lifetimes 427 B. Very small activities 428 C. Precision studies of the neutron lifetime 434 III. Direct timing methods (10~6 > τ > 10" 15 s) 437 A. Electronic and pulsed beam timing methods 437 B. Recoil shadow timing methods 445 C. The recoil distance "plunger" method 447 D. The Doppler shift attenuation method 453 E. The GRID method 466 IV. Measurement of very short lifetimes (τ < 10" 15 s) 472 A. X-ray timing 473 B. Crystal blocking 474 C. Nuclear resonance fluorescence 475 D. Determination of narrow resonance widths 478 References 482 I. Scope and definitionsThe decay modes of ground states and the low-lying nuclear states up to about 10 MeV excitation energy via ß-decay, electromagnetic radiations, particle emission and/or fission have been extensively studied for many decades. In all domains of nuclear structure investigations, the measurement of absolute decay probabilities and nuclear lifetimes has given important insight into the facets of nuclear many-body systems and has provided detailed data for in-depth tests of nuclear models. Some of these decay modes involve fundamentally known interactions, e.g. the electro-weak interaction in the case of β-and γ-decay processes, and thus are directly sensitive to the nuclear model wave functions to be tested. Other processes like nucleon emission, α-decay and fission are more difficult to deal with theoretically, as here the wave functions of the nuclear states involved in the transition and the nuclear transition operator, which both determine the decay probabilities, depend on the model used.The experimentally accessible range of nuclear lifetimes covers more than forty-five (!) orders of magnitude. When just considering α-decays, we have, on the one hand, the Unauthenticated Download Date | 6/13/16 9:10 AM

Electromagnetic decay strengths in the isobars89Nb,89Mo and89Tc

“…In the previous experiments, a careful search for Dopplerbroadened line shapes due to short-lived states in 89Mo and SgNb led us to the conclusion that most lifetimes in these two nuclei are in the range accessible to the Recoil Distance Doppler Shift (RDDS) technique [10]. The present experiment was performed at the tandem Van de Graaff accelerator in Cologne, using a plunger apparatus designed by Dewald et al [11].…”