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

We measured the β-delayed α-particle emission spectrum of ¹⁶N with a sensitivity for β-decay branching ratios of the order of 10^-10. The ¹⁶N nuclei were produced using the d(¹⁵N,¹⁶N)p reaction with 70 MeV ¹⁵N beams and a deuterium gas target 7.5 cm long at a pressure of 1250 torr. The ¹⁶N 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 3 s with the counting carried out over 8 s. The β-delayed α-particles were measured using a time-of-flight method to achieve a sufficiently low background. Standard calibration sources (¹⁴⁸Gd, ²⁴¹Am, ^208,209Po, and ²²⁷Ac) as well as α particles and ⁷Li from the ¹⁰B(n,α)⁷Li 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 ⁸Li that was produced using the d(⁷Li,⁸Li)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 ¹⁶N 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 However, our data (as well as earlier Mainz data and unpublished Seattle data) do not agree with an earlier measurement of the β-delayed α-particle emission of ¹⁶N taken at TRIUMF after averaging over the energy resolution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.