Search for X-Ray Induced Acceleration of the Decay of the 31-Yr Isomer ofH178fUsing Synchrotron Radiation

Abstract

Enhanced decay of the 31-yr isomer of (178)Hf induced by x-ray irradiation has been reported previously. Here we describe an attempt to reproduce this result with an intense "white" x-ray beam from the Advanced Photon Source. No induced decay was observed. The upper limits for the energy-integrated cross sections for such a process, over the range of energies of 20--60 keV x rays, are less than 2 x 10(-27) cm(2) keV, below the previously reported values by more than 5 orders of magnitude; at 8 keV the limit is 5 x 10(-26) cm(2) keV.

Nuclear Transitions Induced by Synchrotron X-rays

“…An attempt to confirm this acceleration of the decay rate in 178 m2 Hf was made last year by a collaboration of scientists from Argonne, Los Alamos, and Livermore national laboratories [6]. This group used the APS light source to provide beams of x-rays with intensities that were over 4 orders of magnitude greater than those provided by the dental x-ray machine of Collins et al A "white" beam from a tapered undulator at the SRI-CAT 1-1D beam line was used.…”

“…Here we discuss two processes, which occur with low probability, but which nevertheless are of interest from a fundamental point of view and may have significant potential for various applications. These are 1) NEET (Nuclear Excitation by Electronic Transition), which has only recently, after many erroneous claims by several groups over a period of almost thirty years, been definitively observed in the nucleus 197 Au [1], and 2) the acceleration of the decay of long-lived nuclear isomers by "triggering" with x-ray irradiation, a process that has been claimed [2 -4] to have been observed in the second isomeric state (16 + ) of the nucleus 178 Hf, but that is disputed by other authors [5,6].…”

“…At the APS we have looked for NEET in 189 Os [7,8] and have attempted to verify the x-ray triggering of the decay of 178 m2 Hf [6]. At SPring-8, Kishimoto et al [1] have observed NEET in 197 Au, and other experimenters [4] have reported the observation of triggering in 178 m2 Hf.…”

Study of Triggering of Electromagnetic Pulses From Isomeric Materials

“…Since 1999, there have appeared additional positive reports [15][16][17][18] of triggered gamma emission from '^^"^Hf and a report of a null measurement [25]. Clearly the question remains open whether low-energy triggering (< 100 keV) can be accomplished for '^^-^Hf…”

Radiation Source for the Study of X-Ray Driven Gamma Emission

“…[15][16][17][18][19], and several reports of null measurements in Refs. [20][21][22][23]. Clearly the question remains open whether low-energy triggering (< 100 keV) can be accomphshed for ^^^Hf^.…”