Further measurement of the β-delayed α-particle emission of N16

We measured the β-delayed α-particle emission spectrum of N16 with a sensitivity for β-decay branching ratios of the order of 10^-10. The N16 nuclei were produced using the d(N15,N16)p reaction with 70 MeV N15 beams and a deuterium gas target 7.5 cm long at a pressure of 1250 torr. The N16 nuclei were collected (over 10 s) using a thin aluminum foil with an areal density of 180 μg/cm² tilted at 7^° with respect to the beam. The activity was transferred to the counting area by means of a stepping motor in less than 3s with the counting carried out over 8s. The β-delayed α-particles were measured using a time-of-flight method to achieve a sufficiently low background. Standard calibration sources (Gd148, Am241, Po208,209, and Ac227) as well as α particles and Li7 from the B10(n,α)Li7 reaction were used for an accurate energy calibration. The energy resolution of the catcher foil (180 220 keV) was calculated and the time-of-flight resolution (3 10 nsec) was measured using the β-delayed α-particle emission from Li8 that was produced using the d(Li7,Li8)p reaction with the same setup. The line shape was corrected to account for the variation in the energy and time resolution and a high statistics spectrum of the β-delayed α-particle emission of N16 is reported. However, our data (as well as earlier Mainz data and unpublished Seattle data) do not agree with an earlier measurement of the β-delayed α-particle emission of N16 taken at TRIUMF after averaging over the energy resolution of our collection system. This disagreement, among other issues, prohibits accurate inclusion of the f-wave component in the R-matrix analysis.