Branching ratios in the $\beta$ decay of $^{16}$N

TL;DR

This paper reports high-precision measurements of the branching ratios in the beta decay of nitrogen-16, providing valuable data for nuclear physics research.

Contribution

The study presents new, precise experimental measurements of the branching ratios in $^{16}$N beta decay, improving upon previous data.

Findings

Determined several branching ratios with high precision.

Enhanced accuracy over previous measurements.

Contributes to better understanding of nuclear decay processes.

Abstract

In this brief note, we present the results of an experiment performed at the ISOLDE Decay Station at CERN in which several of the branching ratios in the $\beta$ decay of $^{16}$N were determined with high precision and accuracy.

Tables

Table 1. Table 1: γ 𝛾 \gamma -ray yields relative to the 6.13 → 0 → 6.13 0 6.13\rightarrow 0 transition. The error bars include the systematic uncertainty on the efficiency calibration and statistical uncertainties (combined in quadrature).

Transition	$I_{\gamma }/I_{{\gamma }_{6.13}}$ (%)
$8.87\to 0$	$0.0021\left(10\right)$
$8.87\to 6.05$
$8.87\to 6.13$	$1.52\left(5\right)$
$8.87\to 6.92$	$0.077\left(3\right)$
$8.87\to 7.12$	$0.188\left(7\right)$
$7.12\to 0$	$7.67\left(8\right)$
$7.12\to 6.05$
$7.12\to 6.13$	$0.0081\left(13\right)$
$6.92\to 0$	$0.139\left(3\right)$
$6.92\to 6.05$
$6.92\to 6.13$
$6.13\to 0$	$100$

Table 2. Table 2: β 𝛽 \beta -decay branching ratios, including a 0.9% relative uncertainty on the overall normalisation.

Level	$b_{\beta }$ (%)
8.87	$1.19\left(4\right)$
7.12	$5.02\left(7\right)$
6.92	$0.041\left(14\right)$
6.13	$66.0\left(6\right)$

Table 3. Table 3: γ 𝛾 \gamma -decay branching ratios of the 8.87-MeV level.

Level	${\Gamma }_{{\gamma }_i}/{\Gamma }_{\gamma }$ (%)
0	$0.12\left(6\right)$
6.05
6.13	$85.0\left(4\right)$
6.92	$4.3\left(2\right)$
7.12	$10.6\left(5\right)$

Full text

The $\gamma$-ray spectrum of 16N was measured at ISOLDE using an array of HPGe detectors, as previously reported in Ref. Kirsebom et al. (2018). The $\gamma$-ray peaks were well resolved, allowing the number of counts in each peak to be determined with high precision. Yields of individual $\gamma$-ray transitions were determined by dividing the number of counts with the energy-dependent detection efficiency of the array. Yields were further corrected for summation of $\gamma$ rays emitted in cascade transitions, taking into account the known angular correlations Vermeer and Poletti (1982). Summation was found to be significant only for the 8.87-MeV peak, where it accounts for 90% of the observed yield.

The $\gamma$-ray yields obtained in the present study are given in Table 1. For unobserved transitions we report upper limits at 95% C.L. The $\beta$-decay branching ratios are given in Table 2. Finally, the branching ratios for the de-excitation of the 8.87-MeV level are given in Table 3. The present results generally have better precision than existing literature values Tilley et al. (1993). Where previous data exist, the agreement with the present data is good or fair with one notable exception: The present value for the branching ratio of the $8.87\rightarrow 0$ transition (Table 3) is a factor of $\sim 60$ smaller than the value reported in Ref. Wilkinson et al. (1968). The likely explanation for this discrepancy is that the authors of Ref. Wilkinson et al. (1968) failed to account for the summation of $\gamma$ rays emitted in cascade transitions, thereby incorrectly attributing the entire yield of the 8.87-MeV peak to the $8.87\rightarrow 0$ transition. Given the information provided in Ref. Wilkinson et al. (1968) it is possible to obtain a rough estimate of the summation yield, which in fact is comparable to the observed yield.