Light Output Function and Pulse-Shape Discrimination Capability of p-Terphenyl Organic Scintillator in Wide Neutron Energy Range of 1.1 to 19 MeV

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall:

The paper presents an investigation into the light output function and pulse-

shape discrimination (PSD) capabilities of a p-Terphenyl scintillator over

a wide neutron energy range. The topic is relevant to fast neutron

spectrometry, especially for improving the accuracy of Monte-Carlo

simulations. The study addresses a gap in the literature by extending

the light output function of the p-Terphenyl scintillator beyond

low-energy neutrons.

Strengths:

The paper contributes new data on p-Terphenyl scintillator behaviour at

higher neutron energies, which is important for modelling such scintillator

for different applications. 

 

The experimental design appears sound, with measurements carried out

at reputable facilities such as PTB and CVR.

 

The comparison between p-Terphenyl and NE-213 detectors is very

relevant, highlighting the strengths and limitations of the former,

particularly regarding PSD capability and neutron efficiency.

 

Weaknesses and Recommendations for Improvement:

◦ Figs 6, 7, 8, and 9 are critical to understanding the results, but they

lack detailed captions that explain what readers should observe.

Descriptions should emphasise the key differences or trends seen in

the plots.

◦ In particular, Fig 10, which compares light output functions from

two previous studies, could benefit from more discussion about how

the authors' function differs and why.

◦ The discussion could be expanded to include more implications of

the findings. For example, while it is clear that the p-Terphenyl

scintillator underperforms NE-213 in terms of PSD, it would be

beneficial to discuss scenarios where p-Terphenyl’s performance might

be acceptable or even preferred (e.g., for its solid form over liquids, ease

of use in certain environments, etc.).

◦ Additionally, more elaboration is needed on the Monte Carlo simulations.

It’s mentioned that these simulations support the findings, but readers would

benefit from a deeper dive into how the simulations were structured and

how they corroborate the experimental data.◦ The reference list

is comprehensive, but some citations (e.g., [8], [9]) are referred to

frequently without enough context provided within the text about the

specific insight ts they contribute. More detail on how these studies'

light output functions were calculated would strengthen the paper.

Comments on the Quality of English Language

• L10: First mention to PSD (Pulse Shape Discrimination).

• L12: mm → mm².
• L20-21: “by finding the position of the protons for given neutron energies”. Poor choice of wording, please rephrase.
• L36: “expresses the relation between proton and electron energies”. Poor choice of wording, please rephrase it to something like "It describes the correlation between the light output produced by protons and its electron-equivalent energy."
• L38-L39: The information here is somewhat redundant and could be omitted for clarity, as the key concept is already effectively conveyed earlier in the text.

• L49: mm → mm².

• L65: “The input analog signal from the p-Terphenyl detector”. There is no description of the detector or the photo-sensor used, was that a cluster of SiPMs? A PMT? What? How the scintillator was coupled to the photosensor? What does the assembled detector look like? These details are pretty important.

• L73: “Fig 1.” does not correspond to the text referred to.

• L76: “campaign 2.5 and 19 MeV” → “campaign are 2.5 and 19 MeV”.

• L78: “Targets Ti(T)”, this is one target of titanium tritide.

• L83: “shadow cone”, there is no reference to this. Please either explain or put a reference.
• L127: Switched from PSD to “neutron/gamma separation capabilities”. Please be consistent.

• Fig 6: the x-axis “separation parameter” → PSD.

• L163: “As can be seen in Fig. 7”. This probably refers to Fig 6 not 7.

• L22, L133, L170, and L175: usage of “efficiency”, efficiency of what?it should be accompanied by something like “detection”.

Author Response

For research article

 

 

Response to Reviewer X Comments
1. Summary
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding corrections yellow highlighted in the re-submitted files.
2. Point-by-point response to Comments and Suggestions for Authors
Comments 1: Figs 6, 7, 8, and 9 are critical to understanding the results, but they lack detailed captions that explain what readers should observe. Descriptions should emphasis the key differences or trends seen in the plots. ◦ In particular, Fig 10, which compares light output functions from two previous studies, could benefit from more discussion about how the authors' function differs and why.
Response 1: We agree with these comments. All recommendations were incorporated into the text. Figures have been edited including captions and more information about previous studies has been added.
Comments 2: The discussion could be expanded to include more implications of the findings. For example, while it is clear that the p-Terphenyl scintillator underperforms NE-213 in terms of PSD, it would be beneficial to discuss scenarios where p-Terphenyl’s performance might be acceptable or even preferred (e.g., for its solid form over liquids, ease of use in certain environments, etc.).
Response 2: A description of the advantages of using this detector has been added.
Comments 3: Additionally, more elaboration is needed on the Monte Carlo simulations. It’s mentioned that these simulations support the findings, but readers would benefit from a deeper dive into how the simulations were structured and how they corroborate the experimental data.
Response 3: Agree, the simulation method was described in more detail in the text. Absolute values of the neutron flux are not available, so a comparison with the simulation cannot be done.
Comments 4: The reference list is comprehensive, but some citations (e.g., [8], [9]) are referred to frequently without enough context provided within the text about the specific insight ts they contribute. More detail on how these studies' light output functions were calculated would strengthen the paper.
Response 4: Detailed information on the measurement methods has been added to the manuscript.
3. Response to Comments on the Quality of English Language
Point 1: L10: First mention to PSD (Pulse Shape Discrimination). corrected Point 2: L12: mm → mm2. corrected
Point 3: L20-21: “by finding the position of the protons for given neutron energies”. Poor choice of wording, please rephrase. corrected
Point 4: L36: “expresses the relation between proton and electron energies”. Poor choice of wording, please rephrase it to something like "It describes the correlation between the light output produced by protons and its electron-equivalent energy." corrected
Point 5: L38-L39: The information here is somewhat redundant and could be omitted for clarity, as the key concept is already effectively conveyed earlier in the text. corrected
Point 6: L49: mm → mm2. corrected
Point 7: L65: “The input analog signal from the p-Terphenyl detector”. There is no description of the detector or the photo-sensor used, was that a cluster of SiPMs? A PMT? What? How the scintillator was coupled to the photosensor? What does the assembled detector look like? These details are pretty important. corrected
Point 8: L73: “Fig 1.” does not correspond to the text referred to. corrected
Point 9: L76: “campaign 2.5 and 19 MeV” → “campaign are 2.5 and 19 MeV”. corrected
Point 10: L78: “Targets Ti(T)”, this is one target of titanium tritide. corrected
Point 11: L83: “shadow cone”, there is no reference to this. Please either explain or put a reference. corrected
Point 12: L127: Switched from PSD to “neutron/gamma separation capabilities”. Please be consistent. corrected
Point 13: Fig 6: the x-axis “separation parameter” → PSD. corrected
Point 14: L163: “As can be seen in Fig. 7”. This probably refers to Fig 6 not 7. corrected
Point 15: L22, L133, L170, and L175: usage of “efficiency”, efficiency of what? it should be accompanied by something like “detection”. corrected
5. Additional clarifications
Please note that information from another reviewer is also incorporated in the text to meet your requirements and make good sense.

 

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Review summary:
The manuscript summarises the work of evaluating the neutron light output function for a p-Terphenyl organic scintillator. A cylindrical crystal p-Terphenyl scintillation detector and a NE213 liquid scintillation detector have been irradiated at several neutron facilities and compared. The facilities use mono-energetic neutron sources to aid in the calculation of the light output function for neutrons and pulse shape discrimination methods have been used to separate the neutron data from the gamma interactions in the detector system. The detector was calibrated for gamma response using Cs-137 and Co-60 sources. Due to the interaction mechanisms the neutron spectra have to be unfolded using the light output function from a standard pulse height distribution dataset. The light output function was calculated for the p-Terphenyl scintillation detector. This light output function has been compared to other published results. In addition, the efficiencies of the two scintillation detectors were compared via Monte Carlo analysis.

 

The article is interesting and provides another dataset and function for representing the light output function for neutrons in a p-Terphenyl organic scintillator. The new data has been collected over a larger energy range than previous publications, adding insight into higher-energy neutron response. The current article would benefit from some expansion in places and additional information added to aid the results already presented. Therefore, I suggest this paper goes through a revision process to improve the overall clarity of the manuscript. I have some suggestions and questions as follows:

Comments & suggestions:

General comments: I think the paper would benefit from more citations to previous methods and results using the two scintillators in question. 

 

Title: A revised title is recommended. As the title implies PSD capability is being evaluated when that is not currently couched much upon with the currently presented results. Also adapting the title to make sure that the title includes neutron energies would be advantageous. PSD scintillators are known to have different light output responses to various particle types due to the interaction mechanisms.

 

Abstract:

line 11-12: State scintillator length and diameter separately. At the moment the dimensions read more like a cube scintillator than a cylinder.

 

Section1:

Line 32 - What are the typical particle accelerator energies of interest? An example would be helpful to the reader.

This section could do with a longer introduction on the detector/material including citing recent works that appear to be alluded to in both the introduction and the abstract.

This introduction should be improved and expanded upon.

 

Section 2

Section 2.1

line 49-50: State scintillator length and diameter separately. At the moment the dimensions read more as a cube scintillator than a cylinder.

 

Section 2.2:

How is the light captured out of the scintillator via a SiPM, PMT or a spectrometer? The diagram shows the electrical processing but the text does not allude to how the light was captured. 

How is the light capture device affixed to the scintillator? What is the expected light loss at this interface?

Figure 1 in this section is not referenced.

 

Section 2.3

Line 73: Figure 1 references the spectrometer, yet the text is in reference to the PTB Ion Accelerator

Figure 4 - Labels to describe the highlighted regions would be helpful, so the relevancy of regions is clear.

 

Section 2.4

Line 98: Later in the paper it is revealed that the energy calibration method used is based on the pulse height. However here it is stated the method is the integrated pulse area is used for energy calibration. This needs more detail and correction necessary, removing any ambiguity would help future readers.

Line 99. Details about how the Compton edge was determined from the spectra would be beneficial here or an example spectra here could be useful. Figure 1 from  "Measurement of Compton edge position in low-Z scintillators" https://doi.org/10.1016/j.radmeas.2009.10.015 shows how the maximum cannot be used but rather an offset from this position. Depending on the methodology chosen for this optimisation, errors can be introduced into the analysis.

Line 103: Details on the likely background source would be helpful. Is the background mostly from cosmics or from scattering of the beam from surrounding material/ activated material due to being located at a beamline?

Line 107: The integration method is used which is similar to the common PSD charge comparison method. Additional citations here would be beneficial to the reader.

Line 110: Details on the T_tail and T_end optimisation process would be beneficial to the text here.

 

Section 3

Lines 125 - 128: Additional analysis of the PSD capability of the two detectors would be beneficial here. The 2D PSD plots alone do not provide much insight. Look into the Figure of Merit method of evaluating PSD.

Figure 6: The axis labels are difficult to read and should be improved. Using the same axis limits would aid comparison on both plots shown. A label indicating which "arm" on the plot is gamma and neutrons would be helpful. Label missing from the colour bar - it is assumed it is just counts. Highlighting where the differentiation between neutrons and gamma is made would be beneficial.- is the cut linear or does it change based on energy? Also note, the style and layout are at the author's discretion, but, PSD plots typically are shown with Energy on the x-axis and PSD/separation parameter on the y-axis.

Figure 7. The unit label on the y-axis can come across as confusing. It can be interpreted as counts per cm^{-2} rather than counts per cm^2

Line 133: A basic outline of the simulation performed here would benefit the reader.

Line 135: There is a mention of a 100 keVee threshold. However, there are no details listed in the manuscript stating where this is applied or what it does.

Line 139: The results would benefit from a Chi-square analysis of the appropriateness of using Eq.2. to fit the data. As other papers use different functions, presenting a parameter that represents how well data follows the function would improve the paper.

 

Table 2: Errors are shown but no discussion is added on how these are calculated. Providing a discussion on how these are calculated would be beneficial.

Figure 8. Error bars are not shown on the data. As the neutron spectra is being unfolded this would lead to an uncertainty in the neutron energy due to the spectra lacking full energy peaks.

Lines 145-146 & Figure 9. The text mentions the pulse-height but data is presented as light-yield. Information should be provided in the text to state how the signal pulse height corresponds to light yield.

 

Section 4:

Figure 10: As the L0 and L1 parameters have associated errors, presenting the Fit Eq.2 with an upper and lower bound would aid the plot. Bounds could be 1, 2, and/or 3 sigma. These could then be used to compare to results from the other papers mentioned to improve the comparisons and discussion section.

Line 175. Fig 8 is referenced but I believe that this should be Fig 7. Figure 7 compares the detector efficiencies. 

Line 175. The detector efficiencies are stated to be generated from Monte Carlo. Additional analysis comparing this to the efficiencies calculated from the beamline for each scintillator would improve this section and discussion. At the moment this analysis feels disjointed from the rest of the paper.

Lines 170 - 178: This section feels very different to the rest of the paper and I suggest that this is improved upon and tied into the rest of the paper where possible

Comments on the Quality of English Language

The following comments and suggestions refer to the English and grammar.

 

Line 76. The first sentence does not read well. Consider revision to: "Two neutron energies, 2.5 and 19 MeV, were used in this experimental campaign.

 

Lines 76-79 would benefit from a rewrite to improve reading flow and grammar.

 

Line 88: The sentence is the same as line 79 - adapt the English to be more clear about what each image is showing. i.e. "the experimental arrangement at CVR is shown in Fig. 3", as an example

 

Line 92: The sentence is not clear. Also word choice does not aid reading. "1 m thick" would be a more appropriate description. 

Line 98. The use of "or" implies they are different units but keVee is just another way of wring KeV electron equivalent. Change style to keV electron equivalent (keVee) or similar.

Lines 170 - 178: Consider revision of this paragraph. Some sentences are short and break the flow of the text.

Author Response

For research article

 

 

Response to Reviewer X Comments
1. Summary
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding corrections yellow highlighted in the re-submitted files.
2. Point-by-point response to Comments and Suggestions for Authors
Comments 1: Title: A revised title is recommended. As the title implies PSD capability is being evaluated when that is not currently couched much upon with the currently presented results. Also adapting the title to make sure that the title includes neutron energies would be advantageous. PSD scintillators are known to have different light output responses to various particle types due to the interaction mechanisms.
Response 1: Extension information on the quality of the PSD from the table with calculated FoM parameters has been added.
Comments 2: line 11-12: State scintillator length and diameter separately. At the moment the dimensions read more like a cube scintillator than a cylinder.
Response 2: The dimensions have been specified in the article.
Comments 3: Section1: Line 32 - What are the typical particle accelerator energies of interest? An example would be helpful to the reader. This section could do with a longer introduction on the detector/material including citing recent works that appear to be alluded to in both the introduction and the abstract. This introduction should be improved and expanded upon.
Response 3: Detailed information on neutron energies is given in Table 1. The introduction has been expanded and citations to recent research have been added.
Comments 4: Section 2.1 line 49-50: State scintillator length and diameter separately. At the moment the dimensions read more as a cube scintillator than a cylinder.
Response 4: Corrected
Comments 5: Section 2.2 How is the light captured out of the scintillator via a SiPM, PMT or a spectrometer? The diagram shows the electrical processing but the text does not allude to how the light was captured.  How is the light capture device affixed to the scintillator? What is the expected light loss at this interface? Figure 1 in this section is not referenced.
Response 5: All comments have been incorporated. The figure description has been revised.
Comments 6: Section 2.3 Line 73: Figure 1 references the spectrometer, yet the text is in reference to the PTB Ion Accelerator Figure 4 - Labels to describe the highlighted regions would be helpful, so the relevancy of regions is clear.
Response 6: Figure 1 references has been corrected. Fig. 4 has been modified as requested.
Comments 7: Section 2.4 Line 98: Later in the paper it is revealed that the energy calibration method used is based on the pulse height. However here it is stated the method is the integrated pulse area is used for energy calibration. This needs more detail and correction necessary, removing any ambiguity would help future readers.
Response 7: A clarification has been added.
Comments 8: Section 2.4 Line 99. Details about how the Compton edge was determined from the spectra would be beneficial here or an example spectra here could be useful. Figure 1 from  "Measurement of Compton edge position in low-Z scintillators" https://doi.org/10.1016/j.radmeas.2009.10.015 shows how the maximum cannot be used but rather an offset from this position. Depending on the methodology chosen for this optimization, errors can be introduced into the analysis.
Response 8: The clarification has been incorporated. The citation is given.
Comments 9: Section 2.4 Line 103: Details on the likely background source would be helpful. Is the background mostly from cosmics or from scattering of the beam from surrounding material/ activated material due to being located at a beamline?
Response 9: The background was measured. The background effect was negligible relative to the primary radiation.
Comments 10: Section 2.4 Line 107: The integration method is used which is similar to the common PSD charge comparison method. Additional citations here would be beneficial to the reader.
Response 10: Citations have been added. Note: methods are same.
Comments 11: Section 2.4 Line 110: Details on the T_tail and T_end optimisation process would be beneficial to the text here.
Response 11: Information about the parameters have been added.
Comments 12: Section 3 Lines 125 - 128: Additional analysis of the PSD capability of the two detectors would be beneficial here. The 2D PSD plots alone do not provide much insight. Look into the Figure of Merit method of evaluating PSD.
Response 12: The results of FoM have been included.
Comments 13: Section 3 Figure 6: The axis labels are difficult to read and should be improved. Using the same axis limits would aid comparison on both plots shown. A label indicating which "arm" on the plot is gamma and neutrons would be helpful. Label missing from the colour bar - it is assumed it is just counts. Highlighting where the differentiation between neutrons and gamma is made would be beneficial.- is the cut linear or does it change based on energy? Also note, the style and layout are at the author's discretion, but, PSD plots typically are shown with Energy on the x-axis and PSD/separation parameter on the y-axis.
Response 13: All of recommendations have been incorporated.
Comments 14: Section 3 Figure 7. The unit label on the y-axis can come across as confusing. It can be interpreted as counts per cm^{-2} rather than counts per cm^2
Response 14: Corrected.
Comments 15: Section 3 Line 133: A basic outline of the simulation performed here would benefit the reader.
Response 15: A basic outline of the simulation has been added.
Comments 16: Section 3 Line 135: There is a mention of a 100 keVee threshold. However, there are no details listed in the manuscript stating where this is applied or what it does.
Response 16: This is the simulation parameter that represents the lower discrimination of the spectrum.
Comments 17: Section 3 Line 139: The results would benefit from a Chi-square analysis of the appropriateness of using Eq.2. to fit the data. As other papers use different functions, presenting a parameter that represents how well data follows the function would improve the paper.
Response 17: Statistical characteristics have been added into the text and Fig. 8.
Comments 18: Section 3 Table 2: Errors are shown but no discussion is added on how these are calculated. Providing a discussion on how these are calculated would be beneficial.
Response 18: Added into the text, Matlab SW with fit functions has been used.
Comments 19: Section 3 Figure 8. Error bars are not shown on the data. As the neutron spectra is being unfolded this would lead to an uncertainty in the neutron energy due to the spectra lacking full energy peaks.
Response 19: Statistical characteristics have been added into the text and Fig. 8.
Comments 20: Section 3 Lines 145-146 & Figure 9. The text mentions the pulse-height but data is presented as light-yield. Information should be provided in the text to state how the signal pulse height corresponds to light yield.
Response 20: The information was added into Fig. 9 and table 4.
Comments 21: Section 4 Figure 10: As the L0 and L1 parameters have associated errors, presenting the Fit Eq.2 with an upper and lower bound would aid the plot. Bounds could be 1, 2, and/or 3 sigma. These could then be used to compare to results from the other papers mentioned to improve the comparisons and discussion section.
Response 21:
Comments 22: Section 4 Line 175. Fig 8 is referenced but I believe that this should be Fig 7. Figure 7 compares the detector efficiencies.
Response 22: corrected
Comments 23: Section 4 Line 175. The detector efficiencies are stated to be generated from Monte Carlo. Additional analysis comparing this to the efficiencies calculated from the beamline for each scintillator would improve this section and discussion. At the moment this analysis feels disjointed from the rest of the paper.
Response 23: Additional analysis is not possible because absolute fluence rate was not measured and evaluated.
Comments 24: Section 4 Lines 170 - 178: This section feels very different to the rest of the paper and I suggest that this is improved upon and tied into the rest of the paper where possible
Response 24: removed.
3. Response to Comments on the Quality of English Language
Point 1: Line 76. The first sentence does not read well. Consider revision to: "Two neutron energies, 2.5 and 19 MeV, were used in this experimental campaign. corrected
Point 2: Lines 76-79 would benefit from a rewrite to improve reading flow and grammar. corrected
Point 3: Line 88: The sentence is the same as line 79 - adapt the English to be more clear about what each image is showing. i.e. "the experimental arrangement at CVR is shown in Fig. 3", as an example. corrected
Point 4: Line 92: The sentence is not clear. Also word choice does not aid reading. "1 m thick" would be a more appropriate description. corrected
Point 5: Line 98. The use of "or" implies they are different units but keVee is just another way of wring KeV electron equivalent. Change style to keV electron equivalent (keVee) or similar. corrected
Point 6: Lines 170 - 178: Consider revision of this paragraph. Some sentences are short and break the flow of the text. corrected
5. Additional clarifications
Please note that information from another reviewer is also incorporated in the text to meet your requirements and make good sense.

 

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

L49: (diameter 45 x thickness 45) mm → mm2.

L141: First mention of "FoM" or Figure of Merit. You should also define it somehow, or explain in a few words what it means.

L141-142: The gray fields cover the NE-213 FOM of 1.15. That doesn't exceed 1.27. 

L145: Why do the FOM values in Table 2 not match those on the x-axis in Figure 6? Including a table for FOM values is a great idea, but could you also indicate the corresponding energies from Table 2 in Figure 6 for clarity?

Comments on the Quality of English Language

L24: is lower →  are lower

L34-L41: Rephrase to something like this:  Determining the scintillator's light output function accurately is crucial for Monte Carlo simulations of scintillation detector responses. It is well established that protons and electrons of the same energy produce light pulses of different intensities due to differences in ionisation density. The light output function captures the nonlinear relationship between proton energy (MeV) and the scintillator's light output, typically expressed in terms of electron equivalent energy (MeVee), reflecting the scintillator's response as if the deposited energy were due to electrons.

L45-L46: Rephrase to something like this: Detection efficiency functions for both scintillators were calculated using the Monte Carlo method.

L50-L52: Rephrase to something like this: "The detector was mounted to a Hamamatsu R6231 photomultiplier tube with an effective diameter of 46 mm, using optical silicon rubber."

L80:  remove "The" in this "The two neutron energies".

L161. No need for the second Fig. 8 in "The dotted lines in the Fig. 8"

Reviewer 2 Report

Comments and Suggestions for Authors

The responses to the reviewers' feedback have significantly enhanced the quality of the manuscript. I have no further recommendations for the manuscript related to the science.

Comments on the Quality of English Language

The manuscript reads well, I have only noted one typographical error.

Line 45: "was" should be "were" i.e. "both scintillators were calculated"