Comment on:"The interaction of neutrons with 7Be at BBN temperatures: Lack of Standard Nuclear Solution to the Primordial $^7$Li Problem"by M. Gai et al

The Authors of this Comment were integral part of the design and execution of the experiments reported by M. Gai et al. in the Conference Proceedings entitled"The interaction of neutrons with $^7$Be at BBN temperatures: Lack of Standard Nuclear Solution to the"Primordial $^7$Li Problem". They reject the interpretation of the experiments presented by M. Gai et al. and disavow the extraction of any physical quantity from its results owing to inadequate calibration of tracks formed in CR-39 detectors and to uncontrolled background.

1 arXiv:2008.06049v1 [nucl-ex] 13 Aug 2020 The article by M. Gai et al. [1] is the publication of a preprint posted earlier [2]. It has now been published with an author list representing only a minority of the actual collaboration with no new experimental data or further improvement in data evaluation or method development. This article, which we show below is void of valid physical content, was followed by another publication by E. E. Kading et al. [3] equally inappropriate that we quote below and have also addressed separately. All Authors of this Comment are collaborators or PI (MP) of the reported experiment, holding the original logbooks and disavow the conclusions of [1].
A long list of shortcomings of the experiment and its interpretation by M. Gai et al. was addressed in [4]. We address here first an assignment reported in [1] for the important cross section of the 7 Be(n, α) reaction that we consider unfounded and misleading to the nuclear physics and nuclear astrophysics community. The reported assignment is based on a selective presentation of calibration data for α-particles and on their misleading interpretation. The alleged data result from irradiated CR-39 detectors that were subsequently scanned and interpreted in various ways. Figure 1 shows some of the curves used for calibration at different times. Based on their internal inconsistency and contradictory trends, the data are incompatible with the extraction of a quantitative cross section value. Following up the comments in [4], we focus here on the analysis of excess pits analyzed in a CR39 track detector in the radii region of interest (RRI) between 0.8 µm and 1.4 µm claimed by M.
Gai et al. to be assigned to protons created in the 7 Be(n, p) reaction ( Fig. 3 in [1]). We show in Figure 2 the calibration curve reported in a previous publication of the Authors [5]. The curve is a steeply sloping curve making the Authors definition of the proton signal, indicated by two red lines, purely arbitrary. It is revealing that in their later publication [3] the Authors of [1] justify this illegitimate RRI assignment for protons by showing (Fig. 3 (bottom) in [3]) an artificial peak created by an arbitrary cut-off at radii smaller than 0.8

µm.
A detector efficiency for protons of 8.7% is deduced, quoted as 8.7±3% in [1] and as 8.7±1.3% in [3], based on the same experimental data set. In fact, neither of the two quoted uncertainties (34% and 15% relative uncertainty) is realistic because of the large systematic uncertainty, as explained below.
E. E. Kading et al. [3] report an uncertainty of 0.2 µm for the pit radii determination caused by temperature variations during the etching procedure. Figure 2 clearly shows that 2 taking this uncertainty into account, the number of pits within the RRI changes dramatically by shifting the RRI on the steep calibration curve by the radius uncertainty. The resulting spread of the detector efficiency varies from 2.2% (RRI 0.6-1.2 µm) to 22.6% (RRI 1.0-1.6 µm), when using the data from Figure 2. Consequently, the cross section deduced from the described experiment is uncertain within one order of magnitude or more. It must be added