Development of a Dual-Modality Gamma-ray/Fast Neutron Imaging System for Air Cargo Inspection
, Jungho Mun, Jae Hyun Lee, Yeong-Heum Yeon, Moonsik Chae, Minwoong Lee and Nam-Ho Lee
Richard Kouzes
Round 1
Reviewer 1 Report
This paper discusses a neutron and x-ray system for examination of cargo. It is potentially of interest if corrected. The authors should state why this specific work was undertaken. The topic of neutron and x-ray “imaging” is a well-trodden field. What is unique about their work?
The English grammar of this paper needs to be corrected by a native English speaker.
Everywhere that “organs” appears, it should be “organics”
Figure 2 is not referenced.
The caption for Figure 2 is a copy of that for Figure 1. Needs a correct caption.
Many words have been hyphenated that should not be, including in many places: scintillator, pixel, airports, system, instance, displayed, exposing, background, animal, acquire
There are a number of minor errors:
Line 39: co-60 should be Co-60
Line 42: x-rays should be gamma rays
Line 43: “lighter than other sources” should be “lighter and smaller than electronically generated x-rays
Line 45: “used for a” should be “generated by a”
Line 48: This sentence does not make sense. Just end the sentence where there is a comma.
Line 55-56: “fabricated to produce electric pulsed signals of the photon” should be “used to produce electrical pulses from the photon generated in the scintillator”
Line 70: define R-value here.
Line 78-79: “opposite side of the radiation sources” should be “opposite side of the cargo container from the sources”
Line 141: state that the scintillator was polyvinyl toluene
Line 142: superscript the 3 in mm3
Line 145: superscript the 2 in mm2
Line 158-159: “reflecting” is not the correct term. Use “arising from”
Line 164: define “peak” and “tail” and show an example plot of a pulse
Line 229: superscript the 3 in cm3
Line 237: “carved” should probably be “machined”
Line 246: delete this sentence. It is redundant and out of place.
Line 259: spell out Figure in FOM
Line 264: GFWHM and NFWHM are reversed in order in this sentence
Line 279: “captured or” should eb “captured for” and there should be “,respectively” at the end of this sentence
Author Response
Response to reviewer’ Comments
Comment 1. This paper discusses a neutron and x-ray system for examination of cargo. It is potentially of interest if corrected. The authors should state why this specific work was undertaken. The topic of neutron and x-ray “imaging” is a well-trodden field. What is unique about their work?
Reply) The unique work of this neutron and x-ray imaging system provides the more diverse material discrimination than the radiation imaging using a single radiation source. We have emphasized the ability of this system about the material discrimination at Line 11 in Abstract Section and at Line 36 in 1. Introduction Section.
Comment 1. Everywhere that “organs” appears, it should be “organics”.
Reply) We have changed the word “organs” to “organics” everywhere.
Comment 2. Figure 2 is not referenced.
Reply) Figure 2 is referenced as “High-energy x-ray generator. The x-ray beam is produced from the linear accelerator (LINAC) in the tungsten target by the bremsstrahlung interaction. In front of the LINAC, the reference detector is installed.”.
Comment 3. Many words have been hyphenated that should not be, including in many places: scintillator, pixel, airports, system, instance, displayed, exposing, background, animal, and acquire.
Reply) We have corrected the hyphenated words that you suggested.
Comment 4. Line39: co-60 should be Co-60.
Reply) We have corrected co-60 to Co-60 at Line 42.
Comment 5. Line42: X-rays should be gamma rays.
Reply) We have changed the word “x-rays” to “gamma-rays” in sentences and figures.
Comment 6. Line 43: “lighter than other sources” should be “lighter and smaller than electronically generated x-rays”.
Reply) We have corrected the words “lighter than other sources” to that you suggested at Line 45.
Comment 7. Line 45: “used for a” should be generated by a”.
Reply) We have corrected the words “used for a” to that you suggested at Line 48.
Comment 8. Line 48: This sentence does not make sense. Just end the sentence where there is a comma.
Reply) We have corrected this sentence to end at there is a comma at Line 51.
Comment 9. Line 55-56: “fabricated to produce electric pulsed signals of the photon” should be “used to produce electrical pulses from the photon generated in the scintillator”
Reply) We have corrected the sentences as you were suggested at Line 61.
Comment 10. Line70: define R-value here.
Reply) We write about the R-value definition as “to calculate the R-value, which represented the ratio of neutron and gamma-ray attenuation coefficient” at Line 77. The mathematical definition is in the Line 227.
Comment 11. Line78-79: “opposite side of the radiation sources” should be “opposite side of the cargo container from the source”
Reply) We have corrected the sentences as you were suggested at Line 87.
Comment 12. Line 141: state that the scintillator was polyvinyl toluene
Reply) We have stated polyvinyl toluene at Line 153.
Comment 13. Line 142: superscript the 3 in mm3
Reply) We have revised the superscript at Line 154.
Comment 14. Line 145: superscript the 2 in mm2
Reply) We have revised the superscript at Line 159.
Comment 15. Line 158-159: “reflecting” is not the correct term. Use “arising from”
Reply) We have changed the word as you were suggested at Line 172 and 173.
Comment 16. Line 164: define “peak” and “tail” and show an example plot of a pulse
Reply) We have defined “peak” and “tail” at Line 173 and added the example plot in Figure 5.
Comment 17. Line 229: superscript the 3 in cm3
Reply) We have revised the superscript at Line 257.
Comment 18. Line 237: “carved” should be probably be “machined”
Reply) We have changed the word as you were suggested at Line 264.
Comment 19. Line 246: Delete this sentence. It is redundant and out of place.
Reply) We have deleted this sentence.
Comment 20. Line 259: spell out Figure in FOM
Reply) We have corrected it as you suggested at Line 286.
Comment 21. Line 264: GFWHM and NFWHM are reversed in order in this sentence
Reply) We have revised the end of this sentence at Line 291.
Comment 22. Line 279: “capture or” should be “capture for” and there should be “respectively” at the end of this sentence
Replay) We have revised this sentence as you suggested at Line 305.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Report for paper applsci-1906010
This paper reports about a prototype of an imaging system for air-cargo inspection, based on two complementary radiographic methods, namely high energy gammas and high energy neutrons. High energy gammas are produced by bremsstrahlung induced by a compact electron accelerator with Bremsstrahlung in the MeV region above the energies of Co-60 sources (1.17 and 1.33 MeV). High energy neutrons are produced via a Deuterium-Tritium generator using the well-known fission reaction. These neutrons have a peak energy at 14.1 MeV. Both radiation sources are point like. The imaging is done by separated transmission measurements of the gammas and neutrons. The transmitted radiation is measured by a vertically built-up of a linear detector arrangement, large enough to cover the transmission from the whole cargo-container in one dimension. The 2nd horizontal dimension is achieved by moving the cargo-container horizontally and counting in different time frames.
Having two different radiation sources with considerable different absorption cross-sections for all kind of matter should enable a certain classification of the materials which are in the air cargo. The need for such non-invasive imaging for security reasons is obvious. Therefore, the topic of the paper is interesting and timely and certainly worth be published. However, in its actual form the paper does not yet satisfy a minimum scientific quality to be published.
The detectors technology is described rather precisely. However, one important information is missing, namely the quantum efficiency of these types of detectors. This figure is of importance, because detectors for high energy gammas and neutrons are far from being opaque for the incoming radiation.
It would be interesting to know the energy to which the electrons are irradiated. At least an idea about the energy range of the Bremsstrahlung should be given. This information is important to get an idea about the penetration depth gamma rays. It is only mentioned that energies above the Co-60 energies of 1.17 and 1.33 MeV are produced, this is clearly insufficient information.
The R factor is important for this paper. While there is a texted explanation of the R factor, a clear mathematical definition in the paper would be very helpful and facilitates reading and understanding.
To the reviewer’s opinion having to radiation sources with quite different absorption characteristics for all kind of matter is very helpful in distinguishing the content of the container. Taking high energy neutrons complementary to gamma rays is an obvious choice. However, the shown test measurements show also the limits: material classes could be differentiated, but only for the case of an idealized packing of the container, i.e. each material class was placed at a different locations. The real cargo container might have a very complex composition with different material classes mixed or packed behind (in the direction of the beam) each other. To the reviewer’s opinion tomography, i.e. 3-dimensional imaging is demanded. And if this is done with two complementary radiations then clear materials differentiation the case of a complex packing should be feasible. The paper would profit from a brief discussion of the limitations of the presented radiography and comment on the possibility to go a step further to tomography.
Some further remarks:
Line 42: DT generators work on the basis of the fusion reaction, not fission reaction.
Line 99: “The x-ray beam passes through the collimator in front of the tungsten target …” Isn’t it so, that this collimator is nothing else than an aperture or pin hole? If so, please write accordingly.
Line 272 ff: “The image pixel values are arranged according to the locations of the vertically installed detector modules, that is, the image frame, and are matched to white and black color maps. Radiation images were reconstructed with the accumulation of image frames.” It is really not clear what you mean with “are matched to white and black color maps”. Do you mean the grey tones in fig. 6a and b. I assume the whiter the lower the absorption. Or is it the other way round?
Line 304: “The hollow container frame and back-ground were black 304 because they had the lowest R-value.” Attributing an R value to the empty container makes no sense, because you have subtracted the empty container from your original measurement. So, give what ever color to the frame for orientation, but do not assign an R-value.
Comments for author File: 
Comments.docx
Author Response
Response to reviewer’ Comments
The authors are grateful to the reviewers for their kind and thorough comments as well as their expert opinions, which have greatly helped improve this manuscript.
Comment 1. This paper reports about a prototype of an imaging system for air-cargo inspection, based on two complementary radiographic methods, namely high energy gammas and high energy neutrons. High energy gammas are produced by bremsstrahlung induced by a compact electron accelerator with Bremsstrahlung in the MeV region above the energies of Co-60 sources (1.17 and 1.33 MeV). High energy neutrons are produced via a Deuterium-Tritium generator using the well-known fission reaction. These neutrons have a peak energy at 14.1 MeV. Both radiation sources are point like. The imaging is done by separated transmission measurements of the gammas and neutrons. The transmitted radiation is measured by a vertically built-up of a linear detector arrangement, large enough to cover the transmission from the whole cargo-container in one dimension. The 2nd horizontal dimension is achieved by moving the cargo-container horizontally and counting in different time frames.
Having two different radiation sources with considerable different absorption cross-sections for all kind of matter should enable a certain classification of the materials which are in the air cargo. The need for such non-invasive imaging for security reasons is obvious. Therefore, the topic of the paper is interesting and timely and certainly worth be published. However, in its actual form the paper does not yet satisfy a minimum scientific quality to be published.
The detectors technology is described rather precisely. However, one important information is missing, namely the quantum efficiency of these types of detectors. This figure is of importance, because detectors for high energy gammas and neutrons are far from being opaque for the incoming radiation. It would be interesting to know the energy to which the electrons are irradiated. At least an idea about the energy range of the Bremsstrahlung should be given. This information is important to get an idea about the penetration depth gamma rays. It is only mentioned that energies above the Co-60 energies of 1.17 and 1.33 MeV are produced, this is clearly insufficient information.
The R factor is important for this paper. While there is a texted explanation of the R factor, a clear mathematical definition in the paper would be very helpful and facilitates reading and understanding.
To the reviewer’s opinion having to radiation sources with quite different absorption characteristics for all kind of matter is very helpful in distinguishing the content of the container. Taking high energy neutrons complementary to gamma rays is an obvious choice. However, the shown test measurements show also the limits: material classes could be differentiated, but only for the case of an idealized packing of the container, i.e. each material class was placed at different locations. The real cargo container might have a very complex composition with different material classes mixed or packed behind (in the direction of the beam) each other. To the reviewer’s opinion tomography, i.e. 3-dimensional imaging is demanded. And if this is done with two complementary radiations then clear materials differentiation the case of a complex packing should be feasible. The paper would profit from a brief discussion of the limitations of the presented radiography and comment on the possibility to go a step further to tomography.
Reply) Thank you for your opinion and advice for my manuscript. We recognized the revising points about 1) the explanation of the quantum efficiency of the radiation detectors, 2) the penetration depth of the gamma-ray, 3) the mathematical definition of R-value, and 4) the discussion of this study.
1) We have added the scintillation efficiency and photon detection efficiency for radiation detectors at Line 120, 157 and 159.
2) We have added the penetration length of gamma-ray with examples at Line 57.
3) We have added the mathematical definition of the R-value at Line 229.
4) We have agreed with your opinion on the next step for developing a tomographic inspector that uses gamma-rays and neutrons. We have added the further study on tomography at Line 360.
Comment 2. Line 42: DT generators work on the basis of the fusion reaction, not fission reaction.
Reply) We revised the word as you were suggested at Line 44.
Comment 3. Line 99: “The x-ray beam passes through the collimator in front of the tungsten target …” Isn’t it so, that this collimator is nothing else than an aperture or pin hole? If so, please write accordingly.
Reply) We have changed the words to “slit collimator” at Line 108.
Comment 4. Line 272: “The image pixel values are arranged according to the locations of the vertically installed detector modules, that is, the image frame, and are matched to white and black color maps. Radiation images were reconstructed with the accumulation of image frames.” It is really not clear what you mean with “are matched to white and black color maps”. Do you mean the grey tones in fig. 6a and b. I assume the whiter the lower the absorption. Or is it the other way round?
Reply) The image pixel values are transformed to the gray tone color as you see in figure 6. We have rewritten about the color map at Line 299.
Comment 5. Line 304: “The hollow container frame and background were black because they had the lowest R-value.” Attributing an R value to the empty container makes no sense, because you have subtracted the empty container from your original measurement. So, give what ever color to the frame for orientation, but do not assign an R-value.
Reply) The hollow container frame and background includes almost air in the radiation beam path, so their R-value are very low and their areas are displayed to the black color in the R-value image. We have clarified this sentence at Line 331.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The revised paper is acceptable.
Line 150: gamma-ray is repeated twice
