Muon Radiography Investigations in Boreholes with a Newly Designed Cylindrical Detector

Round 1

Reviewer 1 Report

The authors present results from a novel borehole-compatible muon tracking detector. The paper has large degree of overlap with a previous publication by the same group (reference [3]). The earlier of the two papers clarifies a number of questions that the present paper alone leaves under-addressed; several others however remain, and some of these are listed below:

- figure 5: how is the "expected" spectrum obtained?

- how do the observed muon rates of figure 5 (0.02 Hz) relate to the observed muon rates of figure 4? Clearly, figure 5 is a differential rate, and figure 4 an integrated one, but do the two agree?

- section 4: regarding over-triggering through presumed gamma rays stemming from Th, Ra, K: while the tracking requirement reduces these (and ensures a cleaner observation), verification of the nature and rate of the background would have been more straightforward through the use of an independent x-ray spectrometer and a concomitant simulation; did the authors attempt such a cross-check?

- captions of figures 6 and 7; it would be good if the caption of figure 7 could indicate more clearly the difference to figure 6, by emphasizing that is has resulted from fig. 6 by removing non-track triggers.

- track rates and trigger rates at the surface and under ground are interesting and puzzling: above ground, trigger (track) rates are 40 (8) Hz; underground, before rejecting low energy hits, these are 80 (0.7) Hz. The claim is that the reduction in the underground data is due to a track energy cut. However, the fraction of low track energy events (below 100 phe) in figure 8 is small, certainly not commensurate with a 100-fold reduction from 80 to 0.7. How then is the reduction factor explained?

- figure 10: the claimed "high similarity" of the two figures does not convince this referee: if one takes the angular resolutions at face value, then the shifts and broadenings of the structures are difficult to reconcile; I would expect the authors to provide a more detailed analysis proving their compatibility. Specifically, taking the MU_RAY structures and smearing them with the worsened spatial pointing accuracy of the boretube tracker should be compared with figure 10b. Elements visible in 10a (i.e. the structure at theta=130, phi=30) are not visible in 10b; is this a question of sensitivity? Finally, given the known topographical structures in the area, it should be possible to identify the claimed voids A, B and C with existing known voids, and to estimate the effect of these on the reconstructed flux maps.

A number of minor omissions and English errors need to be addressed before this paper could be accepted; careful reading by a native English speaker could improve the readability of the paper, while a small number superficial errors should have been caught by the authors (e.g. line 104: "...calculated by integrating Gaisser's modified formula ??.", or "in Figure ??" at line 150).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In general, I thought the article was quite good and the instrument design was well motivated and well explained. I found the performance to be reasonably described, although it was unfortunate that the location chosen for the performance test had such a high level of background radiation. Nevertheless, I feel that the authors showed reasonably well that they could reliably separate the background radiation noise from the muon signal and I don't think it detracts from the overall paper at the level of performance needed to show a proof of principle for the overall design.  

I have a few comments about improving plots and figures and a large number of suggestions for improving the English. For Figure 4 it would be helpful to see some vertical error bars in the trigger rate and muon flux measurements to give the reader some understanding of whether or not the minor fluctuations in flux and trigger rate observed are comparable with the measurement uncertainty. If the vertical error bars are too small to be seen visibly on the plot then that should be noted in the caption. The comment also applies to the underground trigger rate plots in Figure 6. The flux rate plots in Figure 7 appear to have the uncertainties already plotted, so I think it would improve Figures 5 and 6 to do likewise. Finally, on line 150, the authors refer to an unnumbered plot; does that refer to Figure 7, or a plot in a different figure?

For English, I have many suggestions which I will detail line by line.

Abstract:

Line 3 - replace "to exploit them" with "them to be exploited"

Line 5 - replace "of X-rays" with "as X-ray"

Line 7 - replace "to measure" with "for the measurement of"

Line 9 - replace "Mostly" with "Most"

Line 10 - replace "in case possible" with "in case that possible"

Line 13 - replace "borehole typical" with "typical borehole"

Introduction

Line 18 - replace "preserving" with "while preserving them"

Line 20 - replace "to know the topology" with "the topology"

Line 21 - replace "to assume" with "assuming"

Line 22 - replace "than it is expected" with "than is expected"

Line 22 - replace "cosmic muons" with "muons"

Line 24 - replace "manifest" with "manifests"

Line 27 - replace "as instance" with "for instance"

Line 27 - replace "prevent from possible" with "prevent possible"

Line 28 - replace "cavity" with "cavities"

Line 33 - replace "where to install" with "to install"

Line 37 - replace "In the following the detector" with "In the following, the detector"

The detector

Line 42 - replace "allows to maximize the acceptance" with "allows the acceptance to be maximized"

Line 43 - replace "respect to" with "with respect to"

Line 50 - replace "consists in" with "consists of"

Line 53 - replace "produces an" with "produces"

Line 53 - replace "resolutions on" with "resolutions of"

Line 55 - replace "are host in" with "are hosted in"

Line 56 - replace "consists in" with "consists of"

Line 58 - replace "used SiPM" with "SiPMs used"

Line 59 - replace "realized on the base of" with "based on"

Line 60 - replace "the matured experience in" with "experience with"

Line 61 - replace "developed responding" with "developed in response to"

Line 62 - replace "power consumptions." with "power consumption."

Line 68 - replace "watertight" with "watertight shell" 

Line 74 - replace "provided of a" with "provided with a"

DAQ system (the entire paragraph is Line 82 in my manuscript)

Line 82 - replace "muon pass" with "muon passes"

Line 82 - replace "producing light" with "by producing light"

Line 82 - replace "enable or not" with "enable"

Line 82 - replace "compensating fluctuations of" with "compensating for fluctuations in"

Figure 1 caption - replace "Scheme of how" with "Scheme" 

Figure 1 caption - replace "provide" with "providing"

Figure 3 caption - replace "final" with "Final"

Free-Sky data-taking

Line 85 - replace "Performances" with "Performance"

Line 85 - replace "have been tested firstly" with "has been tested first"

Line 87 - replace "absorber" with "absorbing"

Line 94 - replace "anytime" with "when"

Line 102 - replace "simulations have been" with "simulation has been"

Line 104 - There appears to be a reference which is unnumbered at the end of the sentence.

Validation on-site

Line 110 - replace "a little hill" with "a hill"

Line 111 - replace "in the past years" with "in the past"

Line 113 - replace "be moved around" with "move around"

Line 113 - replace "with MU-RAY" with "with the MU-RAY"

Line 115 - replace "allows to easily move it" with "allows for easy relocation"

Line 116 - replace "provides" with "provide"

Line 124 - replace "spotted-out" with "seen"

Figure 7 caption - replace "track" with "Track"

Line 139 - replace "applying" with "by applying"

Line 140 - replace "spotted out" with "seen"

Line 141 - replace "addiction" with "addition"

Line 150 - replace "3%" with "3%,"

Line 153 - replace "have been" with "has been"

Line 154 - replace "test on-field" with "field test" 

Line 155 - replace "have been" with "has been"

Line 156 - replace "have been produced" with "study has been performed"

Line 157 - replace "have been" with "has been"

Line 158 - replace "already obtained" with "was already obtained"

Line 160 - replace "performances" with "performance"

Line 161 - replace "are compatible" with "is compatible"

Line 162 - replace "amount of" with "amounts of"

Figure 8 caption - replace "little" with "small"

Figure 10 caption - replace "muographies" with "relative transmission maps"

Line 166 - replace "in the underground of" with "below"

Line 166 - replace "A strong" with "One major"

Line 171 - replace "described" with "describe"

Line 172 - replace ""to" with "for"

Line 175 - replace "has cylindrical shape" with "has a cylindrical shape"

Line 179 - replace "resulted by" with "were observed in"

Line 180 - replace "application on-field" with "field application"

Author Response

Authors sincerely thanks this referee for her/his effort in reviewing this manuscript. All comment are precious and have been taken seriously in this revision.

Figures 4, 5, 6, have been modified adding error bars on trigger rates. Errors are present in figure 4 bottom but too small to be visible.

All suggestions for English have been appied.

Reviewer 3 Report

This is a very interesting paper, presenting the first field tests of a new muon radiography detector with promising results.

General observations:

1. The title "Muon radiography investigations in boreholes with a newly designed cylindrical detector" suggests that the detector was tested in borehole conditions (as it was designed to do), but it is unclear whether this was actually the case. 

Section 4 (validation on-site) is rather vague about the "many places" in which the detector was installed, apart with a mention of two different chambers, one of which is the Galleria Borbonica (Figures 6 and 7) and comparison with the The MU-RAY experiment (Figure 10) which, according to the reference, was installed near the water cistern.  

If these are in fact the first underground tests of a cylindrical muon radiography detector designed for borehole investigations (but not done in boreholes), this should be clearly stated. 

2. Although the paper is generally well written and understandable, I encountered quite a few spelling and grammatical errors, as well as some words that confused me, including

Line 136 "intercepted": Don't you simply mean that the detector's container "provides adequate shielding against alpha and beta particles"?

Line 148 "significative proof": Maybe this is the first "meaningful demonstration of good performance...."?

I also found missing links "??" in lines 104 and 150.

 

Other comments:

Lines 41-52: The detector geometry description is confusing and difficult to follow, and I had to consult reference [3] to understand it. I suggest starting by saying that the detector's active volume is organized in two semi-cylindrical sections (each with 166 degrees coverage), with the outer layer segmented into 1m scintillator bars parallel with the cylinder axis, and the inner layer segmented axially into 64 layers, each composed of two 83 degree arc-shaped scintillating sensors. You might also mention the two 14-degree "gaps" (shown in Figure 1). I guess that you would orient the detector so that these gaps are outside the desired "field of view"?

Line 63: Low power consumption is clearly important for this detector, but it is unclear what the actual consumption figures are, or how they are achieved. I am guessing that the use of EASIROC helps with this strategy, but it would be nice to add a few words about the low-power features of the design and what the total power consumption is.

Line 76: You have an FPGA interface between the FEE and a RPi computer (for connection to the internet), but how/where are the data stored? What are the connections to the outside world?

Line 82 (DAQ system): Related to the last comment, does the trigger initiate readout of all channels, or just the ones that were fired? It would be nice to know what the typical event size is, and the typical data volumes.

Figures 4, 6, and 7: The horizontal axes are labeled "integrated time (days)". What does "integrated" mean? Was the detector continually active, or does this represent the time that the detector was online?

Line 162: In your comparison of "about 5 and 20 days of data taking", please state explicitly which experiment is which (I assume MU-RAY was the one that took 20 days).

Figure 8: The caption indicates energies around 100 GeV, which seems high for most cosmic rays. What is the scale of these graphs? Does the abbreviation "[phe]" in the horizontal axis labels stand for "photoelectrons"? 

Figure 9: The graph axes are unlabeled.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper has been improved, and most of my concerns addressed adequately. I would agree to publication of the manuscript if the few remaining points are corrected in the paper

minor comments:

Introduction:
- given the fact that a borehole detector is being presented, it would be natural to address the suitability of this detector to real underground borehole use (oil/gas prospecting, geological surveys of e.g. salt domes, etc.), which would require determining a flux of muons at several km underground. The only comment in the introduction regards online monitoring (of what?) with thicknesses of 100 m, which could possibly be probed more easily than via borehole. I would thus encourage the authors to add a corresponding statement on down to which depth such a detector might be envisaged.

- the phrase “with the 85 internet” (page 2) is obscure…

- page 8, line 180: "As Figure 10 clearly shows, the image based on the new detector data is highly similar to the past one, realized with MU-RAY data. “

I have to disagree with the author’s statement that these two figures are highly similar, as already pointed out in my first report. I would encourage the authors to reformulate this statement to tone down the strength of the claim. I would suggest a statement such as: “After accounting for slight differences in the positioning of the two detectors and polar inefficiencies of the borehole detector due to the PD angular gaps, identical structures appear to be identified by the bore-hole detector and the MU-RAY detector (Fig. 10)."

I am also attaching an annotated pdf of v2 of the manuscript in which the remaining English errors / inaccuracies are highlighted in yellow and occasionally corrections are proposed.

Comments for author File: Comments.pdf

Author Response

Dear reviewer  thank you very much for highlighting critical issues of this manuscript. 

Typos and English errors have been corrected.

Regarding your first comment, lines 37-38 have been included to clarify

Regarding your second comment, the text has been modified accordingly.

We thank you again for your effort and we hope we hace adequately answered your question.