Measurement of Difference in Decay Rate for ⁷Be in Li and ⁷Be in Ta

Abstract

The difference in decay rate for ⁷Be in Ta and ⁷Be in Li was measured and found to be (6.43 ± 0.76) x 10^-4 wk^-1, making the relative difference in decay rate ∆λ/λ = (0.71 ± 0.09)%. The probability of decay by electron capture is proportional to the density of electrons at the ⁷Be nucleus; therefore, ⁷Be nuclei in different chemical environments may decay at measurably different rates. Most previous measurements for different chemical combinations of ⁷Be have found ∆λ/λ to be on the order of 10^-4 to 10^-3. A quasi-differential counting method was used in the current experiment wherein two samples are alternately placed in front of a high-purity germanium detector (HPGe) and the number of counts recorded. A plot of the ratio of counting rates vs. time yielded a straight-line whose slope was proportional to ∆λ. The proportionality constant was determined from the intercept of this plot.

Keywords:

• decay rate
• electron capture
• quasi-differential counting
• differential counting
• beryllium 7
• lithium
• tantalum