Author's Accepted Manuscript Application of Neutron Tomography in Cul- ture Heritage Research T. Mongy PII: S0969-8043(13)00448-X DOI: http://dx.doi.org/10.1016/j.apradiso.2013.11.028 Reference: ARI6411 To appear in: Applied Radiation and Isotopes Received date: 31 July 2013 Revised date: 2 October 2013 Accepted date: 12 November 2013 Cite this article as: T. Mongy, Application of Neutron Tomography in Culture Heritage Research, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j. apradiso.2013.11.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. www.elsevier.com/locate/apradiso
Transcript
Author's Accepted Manuscript
Application of Neutron Tomography in Cul-ture Heritage Research
Received date: 31 July 2013Revised date: 2 October 2013Accepted date: 12 November 2013
Cite this article as: T. Mongy, Application of Neutron Tomography in CultureHeritage Research, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2013.11.028
This is a PDF file of an unedited manuscript that has been accepted forpublication. As a service to our customers we are providing this early version ofthe manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting galley proof before it is published in its final citable form.Please note that during the production process errors may be discovered whichcould affect the content, and all legal disclaimers that apply to the journalpertain.
Neutron Tomography (NT) investigation of Culture Heritages (CH) is an efficient tool for understanding the culture of ancient civilizations. Neutron Imaging (NI) is a‐stat‐of‐the‐art non‐destructive tool in the area of CH and plays an important role in the modern archeology. NI technology can be widely utilized in the field of elemental analysis.
At Egypt Second Research Reactor (ETRR‐2), a collimated Neutron Radiography (NR) beam is employed for neutron imaging purposes. A digital CCD camera is utilized for recording the beam attenuation in the sample. This helps for detection of hidden objects and characterization of material properties. Research activity can be extended to use computer software for quantitative neutron measurement. Development of image processing algorithms can be used to obtain high quality images.
In this work, full description of ETRR‐2 was introduced with up to date neutron imaging system as well. Tomographic investigation of a clay forged artifact represents CH object was studied by neutron imaging methods in order to obtain some hidden information and highlight some attractive quantitative measurements. Computer software was used for imaging processing and enhancement. Also Astra image 3.0 Pro software was employed for high precise measurements and imaging enhancement using advanced algorithms.
This work increased effective utilization of ETRR‐2 Neutron Radiography/Tomography (NR/T) technique in culture heritages activities.
ERRR‐2 Neutron Radiography (NR) facility was commissioned in 1999. The first experiments carried out were determination of characterization parameters, such as, flux map, n/γ ratio, Cd ratio and spatial resolution. The results were compared with MCNP calculations. Internal details were detected for different samples using nitrocellulose film. Photographic film was replaced by nitrocellulose film to get high quality image formation. A lot of experiments were performed toward scientific research and quality assurance as well. Welding inspection, measuring water permeability in building materials and imaging enhancement by scattered neutron deblurring were the major experiments achieved in the past.
Fast Neutron Resonance Radiography (FNRR) was also introduced using portable neutron source. The characterization parameters were determined for the neutron source. Detection of hydrogenous components was implemented to study water permeability in building materials using quantitative FNRR (T. Mongy, 2011). Capabilities of underground water migration in soil were also investigated and implemented to preserve cultural heritage monuments.
2
Gamma ray radiography (γR) technique was used to inspect welding materials. NR technique was compared with γR in 2011. Dynamic System Neutron Radiography (DSNR) was pre‐commissioned using DELCam camera. High definitions, high resolution and high quality images were obtained using imaging processing technique.
2. Description of ETRR‐2:
ETRR‐2 is an open pool‐type research reactor with variable core arrangement (F. Esposto, 1999). The core power is 22 MWth cooled by light water, moderated by water and with beryllium reflectors. The design concept is based on versatile utilizations, It has been mainly designed for:
1‐ Basic and applied research in reactor physics and nuclear engineering, 2‐ Neutron radiography for research and industrial purpose, 3‐ Radioisotope production for medical and industrial purposes, 4‐ Beam holes experimentation for neutron scattering experiments and neutron radiography, 5‐ Material testing, 6‐ Material irradiation, 7‐ Activation analysis, 8‐ Training of scientific and technical personnel.
ETRR‐2 has four neutron beams and a thermal column as the main experimental devices allow neutron sources outside the reactor core. The four neutron beams tubes are:
1‐ The Neutron Radiography Facility, 2‐ The Radial Beam Tube, 3‐ The Tangential Beam Tube, 4‐ The Underwater Neutron Radiography Facility.
Figure 1 represents the reactor tank with its internals. The Figure shows: � passing mechanism, � pool cooling pipe, � thermal column, � beryllium block, � tangential tube, � guide box, � control rods, � chimney, � core cooling system pipe, � pool cooling system diffuser, � fuel elements, � reflectors, � irradiation grid, � irradiation chamber shield, � suction box, � radial tube and � Under Water Neutron Radiography (UWNR) tube.
3. State of the Art Neutron Imaging Facility at ETRR‐2:
The commissioning of state of the art new Neutron Imaging (NI) system is started at the end of March 2012 under the frame work of TC communication between AEA and IAEA. The lay out of the system is shown in Figure 2. The NI system was installed to replace static based film neutron radiography.
3
Figure 1. ETRR‐2 tank with its internals.
Figure 2. Layout for neutron radioscopy system with a scintillation screen and cooled CCD camera as used in ETRR‐2.
4
For NI, the neutrons are attenuated and a sufficient amount of light is produced by a scintillation screen that detected with a CCD camera. The scintillation screen used had a composition of LiF:ZnS:Cu (L.G.I. Bennett, et al., 2001). The neutrons interact with lithium due its large cross section to produce an alpha particle (4He++) and tritium (3H) daughter products. The energy from alpha particle is deposited into zinc sulfide (ZnS) and efficient phosphor producing visible light. The copper element acts as a wave length shifter to produce light in the yellow‐green region, which has an average wavelength of 525 nm.
The use of CCD camera system has an advantage of tomography experiments possibility. The CCD camera with its lenses, mirror and integrated cooling unit are housed in a shielded light tight aluminum box. Table 1 summarizes the CCD camera system with technical specifications.
Camware program was employed for camera control and image acquisition. Image acquisition and image processing was accomplished by using ImageJ. VGStudioMAX software from Volume Graphics was used for data processing, visualization and animation of image capturing. For image reconstruction, Octopus software was also applied.
Table 2 summarizes the used software for data reconstruction with specific technical functions.
Table 1 Equipment used for NT in ETRR‐2 with specifications
Equipment Technical specifications PCO2000 CCD thermo‐electrical cooling camera system compact with power supply Lenses Mirror Scintillator Light tight box
‐ High resolution (2048 x 2048 pixel), ‐ 14bit dynamic range, ‐ Image rate of 14.7 fps @ full
resolution, ‐ Low noise, ‐ Low dark current, ‐ Pixel size (hor. x ver.) is 7.4 x 7.4
μm2, ‐ 4GB camera memory.
Nikon, 50 mm focal length.
‐ 45 degree, ‐ high reflectivity polished silicon.
6LiF+ZnS. Aluminum.
Table 2 Software for data reconstruction with specific functions.
Software FunctionsCamware ImageJ
‐ Camera control, ‐ Image acquisition and archiving in
various file format.
‐ Display. Edit, analyze, process, save, print 8bit color and gray scale,
formatting. ‐ 3D image processing and animation, ‐ Volumetric Data analysis and
measurement, ‐ High quality inner structure
visualization, ‐ Volume element characterization.
4. Application of NT in Culture Heritage Research:
The experiment was carried out at ETRR‐2 Neutron Radiography/Tomography Facility (NR/TF). The facility characterization parameters are summarized in table 3 (M. A. Abou Mandour et al., 2007).
Table 3. Characterization parameters of ETRR‐2 NR/TF
Parameters Characterizations Inlet aperture (D) of the collimator Outlet aperture of the collimator (beam opening at sample position) Source to object distance (L) L/D (resolution parameter) Thermal flux at sample position (nth) (nth /γ) ratio Cd ratio(a)
3 cm 22 cm 351.8 cm 117.3 1.5 * 107 neutrons/cm2s 105 n.cm‐2.mR‐1 10
a Ratio between total and fast fluxes.
Figure 3 illustrates scheme diagram of neutron radiography beam tube showing collimator inlet aperture (D) and source to object distance (L).
Figure 3. Scheme diagram of neutron radiography beam tube
6
A simulated forged pottery Peruvian artifact, shown in Figure 4, provided by IAEA was scanned to enhance reconstructed image formation resulting from Octopus reconstruction software. For a three dimensional tomographic reconstruction, transmission images of the artifact were taken from different view angles (1.2 degree per projection). A rotational table is driven by a stepper motor connected to a computerized motion control system, was installed at the sample position. The number of projections to full scan the artifact with 360 degree were 300 projections. To synchronize the Camware software (CCD camera software) and the rotational table; a new software based on Copley Controls macro language was designed and used.
Reasonable exposure time was adjusted at 10 Sec. per projection with 10 Mwatt reactor power operation, it means about one hour was sufficient to full scan the object including image processing correction (dark current and flat field correction).
Dark current images are offset images taken at the same irradiation time (10 sec.) averaged over 10 images, in this experiment. Flat field images are open beam images taken at the same irradiation time (10 sec.) averaged over 10 images.
To correct recorded beam intensity inhomogeneities, image normalization was calculated, by Octopus software, according to equation (1):
Normalized image = (Tomography image – Average dark current images)/ (Flat field image – Average dark current images) (1) For dark and flat field (open beam) images, the correction was done by applying a median filter over 10 images by Octopus software. For each pixel the median pixel value (within the 10 values of the 10 images) was taken to obtain the resulting dark current and flat field (open beam) images.
Figure 4. The Peruvian forged pottery artifact on its scanning position at the beam opening. The
artifact has 26 cm height, 12 cm width and 9 cm side.
As chargeless particles, neutrons can deeply penetrate objects and non‐destructively provide information about the inner structure and composition of materials (Chadwick, 1932). The resultant 3D images reconstructions of the artifact after applying imaging processing enhancement by Octopus are shown in Figure 5.
7
Figure 5. Image reconstruction and enhancement using Octopus software.
For imaging enhancement resulting from Octopus, Astra Image 3.0 Pro was used. Astra is image processing software used for, debluring, sharpening and analyzing 3D image formation.
To extract features from the scanned article, Astra Image Pro was used by implementing Point Spread Function (PSF), Cauchy type, with 2.0 PSF size and 20 iterations, high quality results were provided. Figure 6 shows 3D image reconstruction and enhancement by Octopus software (left). Right one represents Imaging enhancement of the article by Maximum Entropy Dconvolution tool in Astra image Pro.
Figure 6. Imaging enhancement using Astra Image Pro.
8
From the figure, enhanced, sharp and high quality image we obtained by Astra Image Pro. A lot of protrusions have appeared, i.e., the article is full of unlimited protrusions.
Astra Image 3.0 Pro is powerful software to calculate line profile and image statistics. The scanned line profile (AA), in Figure 7, was plotted for the 3D image formation resulting from Octopus reconstruction software. The enhancement was carried out by the former mentioned tool using Astra Image Pro (right image in Figure 7). The line profile is shown in Figure 8.
Astra Image pro has function of calculating image statistics, such as the minimum (minimum pixel value in the image) and maximum (maximum pixel value in the image), the mean (the mean of all pixels in the image) and the standard deviation (Std. Dev.). From the definition, the standard deviation of all pixels in the image measures how much variation or dispersion from the mean. A low standard deviation indicates that the data points tend to be very close to the mean; and hence high quality image formation is obtain with noise suppression (Ian T. Young et al., 2007), on the other hand, high standard deviation indicates that the data points are spread out over a large range of values, and hence weak image formation is obtained with presence of noise.
The Std. Dev. of the red (R), green (G) and blue (B) colors are tabulated in table 4. There is no image degradation from Std. Dev. view point.
Figure 7. Comparison of enhanced Image reconstruction by Octopus (left) and imaging enhancement technique by Astra Image Pro (right).
9
Figure 8. Line profile of the scanned line AA of Figure 7 (the conversion factor is 0.28 mm/pixel).
Table 4 Std. Dev. of enhanced image reconstruction by Octopus and Astra Image pro.
Software Color Std. Dev. Octopus R 39.330 G 59.090
B 72.877Astra Image pro R 39.330 G 59.090 B 72.877
From Figure 7, the article side measured value (9 Cm) represents by pixel number from 125 to 450. i.e., each pixel represents 0.28 mm. Table 5 represents actual, experimental values and percentage of error for different dimensions of article side view that shown in Figure 9.
Figure 9. Different locations of actual and experimental values of article side view.
10
Table 5 Actual, experimental values and percentage of error for side view locations of Figure 8.
3D surface plot was created by the software to find out some detail hidden information. To measure the depth of the two porosities 1 and 2 of the enhanced image formation of the article, the rectangular selection tool is used to draw surface plot of the selected surface. The surface plot gray level ranges from 64.67 to 255, this gray level profile represents 0.5 cm depth (measured value). Thus the conversion factor is 0.002 cm/ gray level. Figure 10 shows the selected rectangular surface to obtain 3D surface plot.
Figure 10 3D surface plot of the rectangular selected surface.
The distinction of NT for detection of presence of air voids inside material (porosities) is pronounced, as clearly shown in Figure 9. Surface plots tool was employed for the two porosities 1 and 2 to investigate the porosities shapes. Figure 11 shows 3D surface plot of porosities 1 (upper) and 2 (down). Referring to the porosity 1, the deepest depth was found to be 2.66 mm and for the porosity 2 it is 2.12 mm.
11
From Figure 11, valuable notifications must be mentioned. First, the porosity 1 is not a normal void; it has a prominence of height 0.665 mm. Second, the porosity 2 is differing from porosity 1 and it has an egg‐shaped with concave depth.
The same tool was used to explore features of grit 1 and 2 of Figure 9. The surface plots were drawn showing 1.2 mm and 0.86 mm heights for the grits 1 and 2 respectively. Also, the line profiles were drawn to find out grits radius (the conversion factor is 0.28 mm/pixel), it was found to be 0.28 and 0.84 mm respectively.
Figure 11 3D surface plot of porosities 1 (upper) and 2 (down)
For high quality 3D animation and visualization, VGStudioMax software was used for the creation of impressive animation of the article from volumetric data set imported from Octopus software. Videos from the slice image stacks are created providing another possibility to easily display and share analysis results. Figure 12 shows VGStudioMax
12
providing high accuracy determination features on the basis of voxels data set from Octopus software.
The functionality of VGStudio MAX for volumetric data analysis and animation was implemented. For back void investigation, 3D surface plot tool was used again to explore the void shape of the selected area in Figure 12. The intensity of each pixel determines its height in three‐dimensional space. Figure 12 shows the 3D surface plots. The void extends through the article thickness.
Figure 12 Back void surface plots of the article.
5. Conclusions:
Neutron Tomography (NT) has been developed as a mature scientific method in ETRR‐2. Non‐destructive investigation of Culture Heritages (CH) is important for understanding the culture of ancient civilizations. Neutron Tomography (NT) is a‐stat‐of‐the‐art non‐destructive tool in the area of CH, and plays an important role in the modern archeology.
6. Acknowledgements:
The author would like to express his deep thanks to Nikolay Kardjilov, Helmholz Institute, Germany, for his assistance and advices. Also, a great thanks from deep heart to D. Ridikas, IAEA, for facilitating all difficulties in financial supports.
13
References:
F. Esposto, 1999. Characterization of the neutron beam facilities, 0767‐1330‐3TABL‐702‐1O. Ian T. Young, et al., 2007. Fundamentals of Image Processing Handbook. Delft University of Technology. L.G.I. Bennett, et al., 2001. Neutron Radioscopy Inspection of Composite Flight Control Surfaces. 10th Asia‐Pacific Conference on Non‐Destructive Testing. M. A. Abou Mandour, et al., 2007. Characterization and Application of the Thermal Neutron Radiography Beam in the Egyptian Second Experimental and Training Research Reactor (ETRR‐2). Hindawi Publishing Corporation, Science and Technology of Nuclear Installations Vol. 1. T. Mongy and Mohamed A. Gaheen, 2011. Development of Neutron Radiography Facility for Detection of Hydrogenous Components Using Recoil Proton Technique. Arab Journal of Nuclear Sciences and Applications, 44 (1), 322‐329.
Research Highlights This manuscript highlighted the following:
1- Neutron tomography is an efficient tool in the field of cultural heritage research,
2- The full description of the ETRR-2 and state-of-the- art neutron tomography system,
3- Implementation of using computer software package in image reconstruction and imaging processing,
4- Precise measurements that was impossible by traditional methods,
5- The manuscript opens the door to investigate ancient Egyptian treasures.
