Further measurement of the β-delayed α-particle emission of 16N

We measured the beta-delayed alpha-particle emission spectrum of N-16 with a sensitivity for beta-decay branching ratios of the order of 10(-10). The N-16 nuclei were produced using the d(N-15,N-16)p reaction with 70 MeV N-15 beams and a deuterium gas target 7.5 cm long at a pressure of 1250 torr. The N-16 nuclei were collected (over 10 s) using a thin aluminum foil with an areal density of 180 mu g/cm(2) tilted at 7(degrees) with respect to the beam. The activity was transferred to the counting area by means of a stepping motor in less than 3 s with the counting carried out over 8 s. The beta-delayed alpha-particles were measured using a time-of-flight method to achieve a sufficiently low background. Standard calibration sources (Gd-148, Am-241, Po-208,Po-209, and Ac-227) as well as alpha particles and Li-7 from the B-10(n,alpha)Li-7 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 beta-delayed alpha-particle emission from Li-8 that was produced using the d(Li-7,Li-8)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 beta-delayed alpha-particle emission of N-16 is reported. However, our data (as well as earlier Mainz data and unpublished Seattle data) do not agree with an earlier measurement of the beta-delayed alpha-particle emission of N-16 taken at TRIUMF after averaging over the energy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.