Experiment FindingsPDF Available
International Journal of Archaeology
2021; 9(2): 34-44
http://www.sciencepublishinggroup.com/j/ija
doi: 10.11648/j.ija.20210902.11
ISSN: 2330-7587 (Print); ISSN: 2330-7595 (Online)
On Radiocarbon Dating of the Shroud of Turin
Thomas McAvoy
Institute for Systems Research, Department of Chemical and Biomolecular Engineering, and Bioengineering Department, University of
Maryland, College Park, the United States
Email address:
mcavoy@umd.edu
To cite this article:
Thomas McAvoy. On Radiocarbon Dating of the Shroud of Turin. International Journal of Archaeology. Vol. 9, No. 2, 2021, pp. 34-44.
doi: 10.11648/j.ija.20210902.11
Received: July 2, 2021; Accepted: July 14, 2021; Published: July 23, 2021
Abstract: In the same issue of Nature that the radiocarbon dating results for the Shroud of Turin were published, Phillips
hypothesized that neutron radiation could have altered the reported dates. In addition to making the Shroud appear younger
than its true age, neutron radiation would have produced significant amounts of radioactive chlorine 36Cl in the Shroud. Two
earlier papers showed that ultraviolet (uv) fluorescence intensity is non-uniform over the surface of the Shroud. The right side
of the Shroud fluoresces more than the left side, and the Shroud’s dorsal side fluoresces more than its frontal side. The highest
uv fluorescence occurs in the center of the Shroud’s dorsal side. The shape of the Shroud’s average uv fluorescence intensity
spatial variations very closely matches the shape of the spatial radiocarbon dating variations calculated by Rucker in his
computer simulation of Phillips’ neutron hypothesis. Experimental results given here for neutron irradiated modern linen
demonstrate that such radiation increases the uv fluorescence intensity of linen. Experimental results also show that neutron
radiation greatly increases the 36Cl content of modern linen. Thus, neutron radiation can explain both the Shroud’s anomalous
radiocarbon dating and its unique spatial uv fluorescence properties. In order to test Phillips’ hypothesis additional research on
the Shroud is required, and suggestions for such follow up research are given.
Keywords: Shroud, Radiocarbon, Neutron, Radiation, Ultraviolet, Fluorescence Intensity, Radioactive Chlorine
1. Introduction
The Shroud of Turin which consists of linen approximately
14.25 ft long by 3.58 ft wide is one of the most studied relics
in history. The Shroud has an image of a crucified man on it,
and many believe the image is that of Christ. In 1988 three
laboratories carried out radiocarbon (14C) dating of the
Shroud [1]. The results of this dating gave a range of AD
1260 to 1390 indicating that the Shroud was a medieval
cloth. The statistical analysis of the 14C data given in [1] was
subsequently questioned by van Haelst [2] who showed that
the data contained a systematic bias. The portion of the
Shroud tested was approximately 1.5 inches long by ¾ inch
wide and yet the 14C dates differed by over 200 years from
one end of the test sample to the other. All the 14C dates
should have been close to one another. More recently, a paper
by Schwalbe and Walsh in the International Journal of
Archeaology [3] raised the question of whether the different
cleaning methods used by the three laboratories could be the
cause of the differences in their radiocarbon dating results.
Casabianca et al [4] carried out a thorough statistical analysis
of the raw data that were collected during the 1988 14C dating
study. It took a court order for this data to be released by the
owner of the data, the British Museum. Casabianca et al [4]
conclude that their statistical analysis reinforces the argument
against the goodness of the 14C dating of the Shroud, and
suggests the presence of serious incongruities among the raw
measurements. They further state that the measurements
made by the three laboratories on the Turin Shroud samples
suffer from a lack of precision which seriously affects the
reliability of the 95% AD 1260–1390 interval. All authors
recommend that additional testing be done on the Shroud.
By contrast to the 14C results, essentially all other data on
the Shroud, including floral, numismatic, fabric and historical
data, point to a much earlier origin. Recent research by Fanti
and Malfi using both FT-IR and Raman spectroscopy and
mechanical property testing [5] date the Shroud to Christ’s
time. Fanti and Malfi’s dating results are: FTIR 300 BC ±
400 yrs, Raman 200 BC ± 500 yrs, and mechanical testing
372 AD ± 400 yrs [5]. All three results are compatible with
International Journal of Archaeology 2021; 9(2): 34-44 35
Christ’s time.
Since the publication of the 14C dating results a number of
explanations for the medieval dates based on the idea of
contamination of the sample site have been presented. In
1990 Harry Gove, who pioneered the mass spectrometry
method used for the 14C dating, addressed the contamination
issue [6]. Gove states:
“Even if it did exist in the form of contemporary organic
carbon, which is one way the apparent age can be reduced,
64% of the Shroud sample would have to be such
contamination and only 36% of 2000-year-old carbon to
change the measured date from the first century AD to the
14th century. Visible inspection by the author of the Shroud
sample received by Arizona before it was cleaned made it
clear that no such gross amount of contamination was
present.”
A later paper [7] presented results on an examination on a
piece of the Shroud that was split from one of the Arizona
samples 14C dated in 1988. These authors found “no evidence
of either coatings or dyes and only minor contaminants.”
More recently Rucker [8] has provided a detailed discussion
about why the carbon dating of the Shroud is not explained
by normal contamination. Rucker’s calculations indicate that
anywhere from 60 to 80% of the carbon in the Shroud sample
would have to come from contamination, and such a large
amount would be easily visible. In spite of the statistical
questions raised and considering that contamination can be
ruled out, the fact that the 14C dating would be off by over
1000 years does not seem possible. The very large
discrepancy between the medieval 14C dates and the first
century appears very likely to be due to another cause, and it
does not appear that the 14C dating was significantly affected
by sample contamination.
At present science cannot explain how the image on the
Shroud was formed, and as a result other, alternative
explanations have been put forward. In a 1989
correspondence to the journal Nature [9] Phillips
hypothesized that a neutron flux could have increased the 14C
content in the Shroud thereby affecting its 14C dating. The
neutron radiation would also have produced radioactive
chlorine 36Cl and radioactive calcium 41Ca in the Shroud.
Rinaudo [10, 11] worked on Phillips’ hypothesis and
expanded it to include a radiation mechanism for formation
of the Shroud image itself in addition to the change in the 14C
date. This paper discusses two measureable effects that
would have been produced if Phillips’ hypothesis were true.
These effects are: 1. the spatial uv fluorescence properties
exhibited by the Shroud which could result from fluence
correlation between neutron flux and uv fluorescence
intensity of linen; and 2. the production of 36Cl in neutron
irradiated linen. To test Phillips’ hypothesis additional
experimentation on the Shroud is required.
A very interesting simulation study of Phillips’ hypothesis
was carried out by Rucker [12]. He used a computer software
package, MCNP (Monte Carlo N-Particle [13]), that was
developed at the Los Alamos National Laboratory to
calculate neutron distributions due to neutron emission and
diffusion. Rucker developed a very detailed geometric model
of a tomb that would have existed in the first century AD.
Then he carried out extensive simulations using the MCNP
software. Rucker’s calculations showed that there would be a
very wide range of 14C dates if samples were taken from
various areas of the Shroud. A summary of Rucker’s
simulation results is given below. A very detailed description
of Rucker’s rationale, simulation method, and results is given
in his paper [12].
In two earlier papers twenty two of the uv photos of the
Shroud that Vern Miller took in 1978 as a member of the
Shroud of Turin Research Project (STURP) were analyzed
[14, 15]. The uv photos were cast into the CIE L*a*b color
space [16] to get pixel intensity. It was shown that the Shroud
exhibits very unique spatial average uv fluorescence intensity
characteristics. Its right side fluoresces more than its left side
and where comparisons can be made the fluorescence from
the dorsal side of the Shroud is stronger than fluorescence
from the frontal side. Lastly along the center of the Shroud,
average fluorescence intensity is stronger near the center of
the image on the Shroud than near the image of the head or
feet. Rucker’s MCNP simulation of neutron irradiation of the
Shroud [12] exhibits almost identical properties in terms of
predicted 14C dates. A comparison of the predictions of
Rucker’s MCNP simulation and the average uv fluorescence
properties of the Shroud is given in this paper.
The strong spatial agreement between Rucker’s simulation
results and the average uv fluorescence intensity results
determined from photos of the Shroud, raises the interesting
question of whether neutron radiation and uv fluorescence of
linen can be related to one another. A series of neutron
irradiation experiments on modern linen have been
conducted with the result that neutron flux and uv
fluorescence intensity are indeed correlated. As the neutron
flux to which linen is exposed increases, so does its uv
fluorescence intensity. Experimental results for the neutron
radiation experiments are given in this paper, and they
together with Rucker’s simulation and average uv
fluorescence intensity results support Phillips’ hypothesis that
the Shroud could have been exposed to neutron radiation.
Finally a new experimental result on the production of 36Cl in
neutron irradiated linen that supports Phillips’ hypothesis is
also discussed.
This paper consists of five parts: 1. a review of Rucker’s
simulation of Phillips’ hypothesis; 2. a review of uv
fluorescence intensity results for the Shroud; 3. new
experimental results on the correlation between neutron flux
and uv fluorescence intensity of linen; 4. a new experimental
result on the production of 36Cl in neutron irradiated linen;
and 5. a summary and recommendations for additional
research.
2. Rucker’s MCNP Simulation Results
At the 2014 St. Louis Shroud Conference Robert Rucker
gave a presentation in which he used a computer software
package [13], MCNP (Monte Carlo N-Particle), that was
developed at the Los Alamos National Laboratory to simulate
neutron emissions. Rucker stated that the main assumption in
his simulation is: ‘that the thermal neutrons were emitted
homogeneously (uniformly) from within the body and
36 Thomas McAvoy: On Radiocarbon Dating of the Shroud of Turin
isotropically (uniformly) in all directions.’ The total neutron
fluences simulated by Rucker ranged between ~1.x1014 and
1.25x1015 n/cm2. Experimental results for neutron irradiation
of modern linen in this fluence range are discussed below.
Rucker’s simulation calculated how emitted neutrons would
have affected the 14C dating over the entire Shroud [12].
Figure 1A gives a plot of the predicted 14C dates along the
midline of the body ([12], pg.25).
Figure 1. A. Midline 14C calculated dates [12]. B. Averaged midline 14C
calculated dates [12].
As can be seen the predicted 14C dates go through 2
maxima. The space between the dorsal and frontal arrows is
where the Shroud wraps around the head. It can be noted that
Rucker’s simulation predicts that many areas of the Shroud
would date to the future because of the effects of neutron
radiation. Rucker’s simulation was normalized to the
1260AD 14C date determined in 1988 for the corner of the
Shroud that was 14C dated [1]. His simulation had a slope of
14C dates that matched that of the three laboratories that
carried out the 14C dating. Additional information is given in
[12]. If additional 14C testing of the Shroud is carried out
Rucker’s predictions can be tested. Rucker calculated 32
points along the simulated midline of the Shroud. The x axes
in Figure 1 plot these points from 0 to 22 so that the plots can
be compared to the average uv fluorescence intensity plots
below, which are based on the grid layout used by Vern
Miller for his uv photography.
The following are Rucker’s very interesting key
conclusions about 14C dating of areas of the Shroud [12]:
The values (14C dates) are higher near the elbows than near
the knees because the elbows are closer to the center of the
body mass and so would be closer to where more neutrons
would be emitted.
The values (14C dates) are higher near the back (dorsal)
image than near the front image because neutrons reflected
from the limestone bench below the dorsal half of the cloth
would have caused a higher fraction of the neutrons to pass
through the dorsal half of the cloth multiple times, thus
causing a greater shift in the predicted dates.
The values (14C dates) on the right side of the image are
higher than on the left side of the image because the locations
on the right side of the image would have been closer to the
back wall of the tomb, assuming the head was toward the
right side as the body lay on the back bench in the tomb. This
is because neutron reflection from the limestone wall at the
back of the tomb would have caused a higher fraction of the
neutrons to pass through the right side of the cloth multiple
times, thus causing a greater shift in the predicted dates.
Conclusion 1 is indicated by the fact that there are 2
maxima in Figure 1A at the midsection of the body wrapped
in the Shroud; Conclusion 2 is indicated by the fact that the
frontal maximum shown in Figure 1A is lower than the dorsal
maximum. If neutrons affect the uv fluorescence intensity of
linen then there should be a correlation between the
simulated 14C dates and uv fluorescence intensity. The uv
fluorescence intensity of the Shroud is discussed next.
3. Shroud uv Image Intensity Results
3.1. Images Studied
In 1978 over 30 scientists involved in the Shroud of Turin
Research Project (STURP) carried out an extensive scientific
study in Turin Italy. A technical photography team was
included in the STURP project. Vern Miller was the lead
photographer on the STURP team. Approximately 1000 high
quality images of the Shroud were taken by the STURP
photographers [17]. In April 2019 199 high quality photos
taken by Miller were published on the web
(https://www.shroudphotos.com/). Included in Miller’s
photos were 44 uv images, 22 of which were analyzed in
earlier papers by McAvoy [14, 15].
The uv photos Miller took were induced visible
fluorescence photos in which an exciter filter was used on a
uv source to eliminate visible light and a barrier filter was
used on the camera to eliminate uv reflectance. The uv light
source induces fluorescence in the object being
photographed. With fluorescence, absorbed uv light is re-
emitted at a longer wavelength in the visible light range.
Eight of Miller’s uv photos (E3, E6, E8, E12, E15, E17, E20,
E22) covered the right side of the Shroud and another eight
the left side (B2, B5, B9, B12, B15, B17, B20, B22). Each of
International Journal of Archaeology 2021; 9(2): 34-44 37
these 16 images cover a different region of the Shroud which
is approximately 1.79 ft by 1.85 ft in size. The remaining 6
images (D3, D8, D12, D15, D17, D21) analyzed by McAvoy
were taken down regions in the center of the Shroud and they
are approximately 1.79 ft by 1.85 ft in size. Details of how
these images were produced and transferred to the web are
given by McAvoy [15].
The 22 uv images were downloaded from the web, resized
and converted from the RGB (red, green, blue) color space to
the CIE L*a*b color space [16] in which L gives the image
intensity and color is contained in the a-b plane. It was shown
that Miller’s uv lighting was not uniform [14, 18]. As a result
in order to compare the uv images to one another in terms of
their fluorescence intensity, L, it was necessary to average
the intensity over each image. Recently McAvoy showed that
3 of the center D images analyzed in [14] should have been
different, since they were produced with different camera
parameters and color filters than the other 19 uv images
analyzed [15]. McAvoy also showed how to correct the web
images back toward their original color [15]. In this paper the
3 new images plus the other 19 images, corrected toward
their original color, are analyzed. Color corrected web image
D8 from the center of the Shroud is shown in Figure 2A [15].
Figure 2. A. Color corrected image D8 from web [15]. B. Cluster of image
D8 with highest intensity.
3.2. Uv Fluorescence Intensity Results
When the average fluorescence intensities of Miller’s uv
Shroud images are compared they show some very unique
and interesting spatial properties [15]. A plot of the center
and two side average uv intensities using the 3 new images
plus the other 19 images, corrected for color, is shown in
Figure 3A. The y axis gives the average uv fluorescence
intensity of a region and the x axis is the position along the
Shroud, e.g. for D8 it is 8, and for E17 it is 17, etc.
Note that the Shroud was folded over and the feet are
associated with both positions 2, 3 and 21, 22. The dorsal
side is associated with positions up to and just shy of 12, and
the frontal side with positions just past 12 and up to 22. The
gap near position 12 is where the Shroud was folded over the
top of the head. Points at position 12 are predominately
associated with the dorsal side of the Shroud. The average uv
fluorescence intensity at red point E8 is missing due to the
fact that image E8 was an outlier [14]. Also only 6 center
images were available for analysis since image D6 was an
outlier [14]. As Figure 3A shows the average uv fluorescence
intensity varies over the area of the Shroud. This pattern of
spatial uv intensities is very interesting since one could have
anticipated that there would be only a small variation in
fluorescence intensity over the Shroud. Along the left side of
the Shroud (blue curve) there are 8 points. Frontal and dorsal
points at the same part of the body can be compared for the
blue curve by comparing the following pairs of points along
the x axis: points 2 and 22, points 5 and 20, points 9 and 17
and points 12 and 15. For the right side of the Shroud (red
curve) points 3 and 22, 6 and 20, and 12 and 15 can be
compared. Since red point 8 is missing an 8-17 comparison
cannot be made. For the center of the Shroud (green curve)
points 3 and 21, 8 and 17, and 12 and 15 can be compared.
Figure 3. Average fluorescence intensity at points along Shroud. A entire
image [15], B most intense cluster.
The following is a summary of the unique spatial average
uv fluorescence intensity properties of the Shroud [15]:
Average uv fluorescence is highest in the mid-section of
the dorsal image on the Shroud (green point D8).
Except for the left side blue (B9 B17) comparison the
other nine comparisons show that the dorsal side of the
Shroud fluoresces more (has higher average intensity) than
the frontal side
All of the right side sections of the Shroud (red curve)
fluoresce more (have higher average fluorescence intensity)
than the corresponding left side sections (blue curve).
Along the center D green images average uv fluorescence
38 Thomas McAvoy: On Radiocarbon Dating of the Shroud of Turin
intensity goes through 2 maxima at points 8 and 17.
Along the center D green images average uv fluorescence
intensity drops off sharply toward the feet.
These uv fluorescence patterns are unique and very
interesting. An explanation for them is important in
attempting to understand the Shroud.
To compare the average uv fluorescence intensity
properties of the Shroud to Rucker’s simulation, the results in
Figure 1A were averaged to give Figure 1B. Since 8 uv
images covered the length of the Shroud using Miller’s grid
and there are 32 points in Figure 1A, groups of 4 points along
the Shroud were averaged to generate the 8 averaged points
in Figure 1B. The first point in Figure 1B is the average of
points 1 to 4 in Figure 1A, the second point the average of
points 5 to 8, and so on. The 8 averaged points are evenly
distributed between 2 and 22 on the x axis.
The center images in Figure 3A (green curve) can be
compared to Figure 1B. As can be seen there is a very strong
agreement between the shapes of these 2 curves. If one takes
Rucker’s 3 simulation conclusions discussed above and
substitutes uv fluorescence intensity for 14C dating values, the
uv conclusions and Rucker’s conclusions line up very closely
with one another. Compare uv conclusions 1 to 3 above with
Rucker’s simulation conclusions 1 to 3. Figure 1B shows
double maxima in predicted 14C age, which agrees with uv
conclusion 4. Similarly Figure 1B shows that 14C dates drop
off sharply toward the feet, in agreement with uv conclusion 5.
The fact that the uv fluorescence intensity results and the
results from Rucker’s simulation line up so closely raises the
question of whether there could be a relationship between
neutron radiation and uv fluorescence intensity. As a result,
experimental research on this question was carried out.
4. Experimental Results for Neutron
Irradiation of Modern Linen
4.1. Linen Used and Radiation Facility
The linen used for the neutron experiments was purchased
from Rawganique USA, Inc (https://www.rawganique.com).
The linen was Evening Sand Dunes natural linen. According
to the company the linen is made from 100% organically
grown European flax. The linen is chemical free, unbleached,
undyed and it is woven in house at Rawganique Atelier in
Europe for true purity.
For neutron irradiation the linen was cut into pieces
approximately 4.5 in by 2.75 in. The linen was then rolled up
and placed in semi-clear polypropylene cylindrical vials 2 7/8
inches high and 1 inch in diameter. These vials were placed
in the nuclear reactor used for this study. Neutron irradiation
was carried out at the University of Massachusetts Lowell
Research Reactor
(https://www.uml.edu/Research/RadLab/Neutron-
Facilities.aspx). The reactor has various in-core sample
facilities capable of producing a thermal neutron flux level of
2x1012 n/cm2-s at the maximum operating power of the
reactor. The reactor power can be adjusted to decrease the
thermal neutron flux as needed. The linen samples packaged
in polyethylene vials were inserted into sealed aluminum
tubes. The aluminum tubes were placed into the reactor
sample location for irradiation. The thermal neutron flux and
irradiation time were adjusted to match the desired thermal
neutron dose for each sample and the fast fluence variation
through the sample thickness was minimized via a single
180° rotation of the sample canister at the midpoint of the
irradiation period. Eight linen samples within different
polypropylene containers were irradiated at neutron fluences
(n/cm2) of 2.5x1014, 5x1014, 7.5x1014, 1x1015, 2.5x1015,
5x1015, 7.5x1015, and 1x1016. Lind, et al. [19] presented
experimental results for the production of 14C by neutron
radiation of modern linen. Lind et al. [19] found
experimentally that a neutron fluence of only 1.07×1014
n/cm2 could produce a quantity of 14C that could change the
14C date of the Shroud from 33 to 1260 to 1390. The 14C is
produced primarily by neutron absorption by nitrogen in the
linen.
4.2. Photography Procedure and Computer Processing of
uv Images
In taking the uv photos a chemistry lab stand was used to
support the camera and the uv flashlight employed. The uv
flashlight was held approximately perpendicular to the base
of the lab stand on which the linen was placed and the
camera took images at an angle. The set up used is shown in
Figure 4.
Figure 4. Uv camera set up.
Details on the uv flashlight, camera, and uv filters
employed are given in the Appendix 1.
The height of the flashlight above the linen photographed
was determined by trying to duplicate the power that Miller
used in photographing the Shroud [20]. A discussion of how
the height of the flashlight was calculated is given in the
Appendix 2. The linen samples were placed on the base of
the lab stand for photography. The photos were taken in a
darkened room and 2 replicate photos of each image were
taken. Four different locations on all linen samples were
photographed, giving a total of 8 images for each sample.
Figure 5A shows a photo taken of a sample of non-irradiated
control linen. This photo has a pixel size of 6000x4000 and it
was analyzed using a program written in MATLAB®.
International Journal of Archaeology 2021; 9(2): 34-44 39
Figure 5. A uv photo of modern linen. B to D cluster images.
The following steps were used in the MATLAB® analysis.
The photo was input into MATLAB® and the rgb2lab routine
used to convert it to the CIE L*a*b color space [16]. Next the
MATLAB® imsegkmeans function was used to cluster
images into 3 clusters based on their fluorescence intensity
values, L, in the converted image. Figures 5B to 5D show the
three clusters calculated for the image in Figure 5A. After
clustering the average fluorescence intensity for each of the 3
clusters was calculated. Only the cluster that had the largest
average intensity, cluster 2 in Figure 5C, is used in the
analysis below. This cluster was always the one associated
with the intense circular region generated in the center of a
sample by the uv flashlight. It was also the cluster that had
approximately the same watts/in2 as Miller used for his
photos.
4.3. Comparison with Miller’s Setup
A comparison with the uv filter setup that Miller used can
be made by referring to Figure 1a of his paper with Pellicori
which gives % transmittance [20]. Miller used two xenon uv
light sources that were focused at 45 degrees on the section
of the Shroud being photographed. An exciter filter was used
on the uv source and a barrier filter was used on the camera.
Transmittances for the exciter and barrier filters can be
estimated from Figure 1a in his paper [20]. In [20] it is stated
that “the filters needed to attenuate to a level of 10-4 since
visible light from the xenon tubes would completely swamp
the weak fluorescence signals.” The product of the
transmittances of the exciter and barrier filters gives the
fraction of light from the xenon sources that enters the
camera. Using estimated transmittances it was found that the
filtering Miller used exceeds his specification by a factor of
approximately 2.4 to 2.5 in the 410-415 nm region. The small
amount of non-filtering of light in the 410-415 nm region
could have increased the intensity of Miller’s uv fluorescence
images.
5. Results from Modern Linen
Experiments
A total of 80 uv photos were taken and Figure 6A gives the
results for the mean fluorescence intensity, L, of the most
intense, center cluster of the modern neutron irradiated linen
and two controls (0 fluence). Figure 6A shows that there is a
variation in CIE L*a*b fluorescence intensity, L, with the
four positions photographed on a sample. Figure 6B gives a
plot of the average of the mean CIE L*a*b fluorescence
intensities, L, for the 2 control samples and for the irradiated
samples.
Figure 6. A. Mean uv fluorescence intensity of modern linen versus neutron
fluence for all 80 photos. B. Average sample mean uv fluorescence intensity
of modern linen versus neutron fluence with 2 control samples combined.
In Figure 6B the intensities of the 2 control samples are
averaged and there is only a single point at 0 fluence. As can
be seen there is an increasing trend in average fluorescence
intensity, L, with neutron fluence. Figures 6A and 6B show
that there is a dramatic increase in average fluorescence
intensity that occurs between fluences 1x1015 and 2.5x1015
n/cm2. It is not clear why the average fluorescence intensities
for the 5x1015 and 1x1016 n/cm2 fluences are lower than those
of the preceding fluence in each case. The trend in average
uv intensities is confirmed by the Mann Kendall statistical
test [21, 22] which gives a probability p=.0012 for no trend.
40 Thomas McAvoy: On Radiocarbon Dating of the Shroud of Turin
For the range of neutron fluences used in Rucker’s MCNP
simulation, ~1x1014 to 1.25x1015 n/cm2 the trend in average
uv fluorescence intensities can also be seen, particularly in
the raw data shown in Figure 6A. Since average fluorescence
intensity increases with neutron fluence, neutron radiation is
a potential candidate to explain both the average uv
fluorescence intensity spatial patterns measured in the photos
of the Shroud of Turin as well as its anomalous 14C dating.
Samples of modern linen were artificially aged by heating
to determine if such heat aging affected fluorescence
intensity. The procedure used was the same as that discussed
by Needles and Nowak [23]. These authors heated linen
samples at 180 oC for times ranging up to 10 hours. Results
for heating control linen samples for 1, 3, and 5 hours are
shown in Figure 7. Eight uv photos were taken for each
control sample. As can be seen heating at 180°C results in
very large changes in the linen’s average uv fluorescence
intensity, from approximately 53 to 77. The heated control
samples were noticeably darker compared to the non-heated
control samples.
Figure 7. Mean intensities for heating control linen linen’s average uv
fluorescence intensity, from approximately 53 to 77. The heated control
samples were noticeably darker compared to the non-heated control
samples.
The results for modern linen can be compared to those for
the Shroud images on the web [15]. To do so these images
were clustered using 3 clusters to determine the most intense
cluster, which always occurred in the center of an image.
Then the average uv fluorescence intensity of the most
intense cluster was calculated. Figure 3B gives a plot of the
average uv fluorescence intensity, L, results. As can be seen
from Figure 3B the range for the average uv fluorescence
intensities of the most intense cluster for the Shroud is
roughly 55 to 71. For modern linen Figure 6B shows that the
range is very similar, roughly 53 to 68. For the neutron
fluence range simulated by Rucker, ~1.x1014 and 1.25x1015
n/cm2 [13], Figure 6B shows that the change in average
sample uv intensity of modern linen is much smaller,
approximately 3.5 units, from 53 to 56.5.
There are a number of explanations that can be given for
these differences in the fluence range simulated by Rucker.
First, the Shroud linen is aged and aging could affect its
fluorescence properties. The results obtained by artificially
heat aging linen show that such heating can have a very
strong effect on increasing uv fluorescence intensity. As
Figure 7 shows, only 1 hour of heating raised the uv
fluorescence intensity from approximately 53 to 70. Natural
aging could have a similar effect. Second, as pointed out
above in describing Miller’s setup it is stated that “the filters
needed to attenuate to a level of 10-4 since visible light from
the xenon tubes would completely swamp the weak
fluorescence signals” [20]. However as discussed above, this
level of attenuation was exceeded in the 410 and 415 nm
range. Thus, reflected uv light though small could have
added to the small fluorescence effect that Miller
photographed. Third, camera settings and setup used to
produce the web images and to photograph the modern linen
affect the uv intensity of images. In this study the fstop was
3.5, shutter speed 1/200 sec., and film ISO 400. Increasing
the fstop or decreasing the film ISO or decreasing the shutter
speed results in lower fluorescence intensities for the
irradiated modern linen and vice versa. Images of modern
linen taken with an ISO setting of 200 lowered all intensities
shown in Figures 6 and 7 by approximately 10 units. Also,
the distance between Miller’s camera and the Shroud was
much larger than the distance between the camera used here
and the modern linen. Fourth, the linen used in this study is
different from the Shroud linen. Fifth, the uv source and
camera filters used in this study have different characteristics
than those used by Miller. Sixth, the Shroud sections have
burn marks, patches, and blood marks on them, and the blood
does not fluoresce [20]. The modern linen has none of these
characteristics. All of these factors could contribute to the
difference in fluorescence intensities measured in this study
compared to those measured from Miller’s photos for the
fluence range simulated by Rucker. Ultimately to determine
whether the hypothesis that the Shroud was exposed to
neutron radiation is correct requires additional testing of it.
A possible mechanism for neutron radiation affecting uv
fluorescence properties of linen involves proton recoil
reactions resulting from the radiation. Gilfillan and Linden
[24] studied the effect of neutron radiation on the strength
of yarns. They hypothesized that neutron radiation could
cause proton recoil reactions in the fibers studied and that
these reactions could affect cross linkage in the fibers
which in turn could affect fluorescence. An important
question that needs to be addressed is what physical
mechanism produced the spatial difference in average uv
intensities of the Shroud. Neutron radiation is one potential
answer to this question.
6. Measurement of 36Cl in Neutron
Irradiated Modern Linen and Its
Implication for the Shroud
Lind, et al. [19] presented experimental results for the
International Journal of Archaeology 2021; 9(2): 34-44 41
production of 14C by neutron radiation of modern linen. A
sheet of unbleached modern plain-woven flax linen was used
in their study. Lind et al. [19] found experimentally that a
neutron fluence of only 1.07×1014 n/cm2 could produce a
quantity of 14C that could change the 14C date of the Shroud
from 33 to 1260 to 1390. A piece of irradiated linen from
Lind, et al’s experimental work was obtained by the author. A
small sample of this linen was sent to Lawrence Livermore
Laboratory in California to be tested for 36Cl.
Prior to being neutron irradiated the modern linen was
thoroughly washed to remove any sizing. The washing
should also have removed most inorganic chlorine present in
the linen. After washing, the chlorine content of the modern
linen was measured as 56 ppm. This chlorine was
presumably present primarily as organic chlorocarbons. The
sample sent for analysis weighed. 1509 gms. The lab
measured that the sample contained 1.904x109 atoms of 36Cl
per gm of sample. The weight of 36Cl per gram of sample can
be calculated as (1.904x109)x35.97/6.02x1023 = 1.1377x10- 13
gms 36Cl/gm sample. From this value the ratio of gms 36Cl to
gms Cl can be calculated using the measurement of 56 ppm
Cl in the sample as: 36Cl/Cl ratio = 1.1377x10-13/5.6x10-5 =
2.0316x10-9. This chlorine ratio is significantly higher than
that which naturally would exist in the modern linen or in the
Shroud of Turin. In order to demonstrate this point it is
necessary to estimate a base line value of 36Cl that would
have existed in the Shroud. The same estimate should apply
to both the linen studied by Lind et al [19] and to the
Sudarium of Oviedo [25].
In the Appendix 3 a detailed discussion on estimating a
base line value of 36Cl from the literature is given. It is shown
that a reasonable estimate for an upper limit for 36Cl/Cl ratio
in the Shroud is 10- 12. The laboratory measured value for the
36Cl/Cl ratio in the modern linen studied here is over 2000
times the upper limit estimated for naturally occurring 36Cl in
linen. Thus, if similar levels of 36Cl can be detected in the
Shroud and/or the Sudarium, that detection would be
significant and strongly indicate that these linen cloths had
been exposed to neutron radiation. One potential problem
with testing the Shroud for 36Cl could come from the fire to
which it was exposed in 1532 [26]. The heat from the fire
could have been enough to vaporize 36Cl present in the
Shroud. This problem should not exist for the Sudarium.
7. Conclusions and Recommendations
for Additional Research
This paper has examined Phillips’ hypothesis that the
Shroud of Turin could have been exposed to neutron
radiation. If so, such radiation would have affected the 14C
dating of the Shroud and made it appear younger than it is.
The results presented here show that neutron radiation can
potentially explain the unique spatial uv fluorescence
intensity properties of the Shroud. For neutron irradiation of
modern linen it has been shown that neutron fluence
correlates with the linen’s average uv fluorescence intensity
measured from photos. This result helps strengthen the case
that Phillips hypothesis about neutron radiation affecting the
14C dating of the Shroud is potentially correct.
For the new experimental results modern linen samples
were exposed to neutron fluences in the range 2.5x1014 to
1x1016 n/cm2, and uv fluorescence photos of the samples
taken. It has been shown that for this range of neutron
radiation fluences there is a statistically significant increase
in average uv fluorescence intensity, L, with fluence level.
The average uv fluorescence intensities of modern linen were
compared to those of the Shroud calculated from the
published images of it. For the fluence range simulated by
Rucker, ~1.x1014 and 1.25x1015 n/cm2, the change in uv
fluorescence intensity with neutron fluence is small,
compared to the spatial variation in uv fluorescence intensity
of the Shroud. A number of possible explanations for this
difference are given including: the effect of aging on the
Shroud linen, uv leakage in the original Shroud photos,
different camera parameters, differences between the modern
linen and Shroud linen, and differences between the uv
sources and filters used for the photography.
New experimental results have also been presented that
agree with Phillips’ hypothesis that neutron radiation would
create 36Cl in linen. A linen sample irradiated with a neutron
fluence of 1.07×1014 n/cm2 was tested for its 36Cl
concentration. It was determined that the 36Cl/Cl ratio in the
irradiated line was at least 2000 times greater than the
maximum value which would occur naturally in linen.
If neutron radiation did not cause the unique uv
fluorescence spatial properties of the Shroud an important
question to answer is what was the cause. Several additional
research projects almost all of which would be non-
destructive to the Shroud itself can be suggested to try to
answer this question, and to determine if neutron radiation
was involved. When Miller took his Shroud uv photos his
lighting setup produced uneven illumination [14, 18].
Additional uv photos of the Shroud using even uv
illumination should be taken. Such photos would allow the
calculation of uv fluorescence intensity at every point on the
Shroud so that one would not have to resort to using average
values as was done by McAvoy [14, 15, 18]. These new uv
photos would allow one to determine the exact spatial
variation of the Shroud’s fluorescence intensity. In addition
to using a standard camera hyper-spectral imaging [27]
should be done. Such imaging would help to more clearly
define the important wavelengths where the Shroud
fluoresces. Hyper-spectral imaging could also be applied to
neutron irradiated modern linen to potentially develop a
fingerprint of how neutron radiation affects the fluorescence
of linen. This fingerprint could then be compared to that
42 Thomas McAvoy: On Radiocarbon Dating of the Shroud of Turin
found from the Shroud. Finally, vials containing charred
material from the Shroud that resulted from the fire in 1532
are available. 14C dating of this charred material, or indeed
samples from several different locations on the Shroud could
show whether the Shroud was exposed to neutron radiation.
If the Shroud were exposed to neutron radiation this radiation
would have created very long-lived radioactive isotopes, i.e.
36Cl (half-life 301000 yrs) and 41Ca (half-life 102000 yrs), at
levels well beyond those that occur naturally. It may be
possible to test the charred material from the Shroud or the
Shroud itself for these isotopes. If these isotopes are found at
abnormally large levels in the Shroud that finding would help
support the neutron radiation hypothesis. In summary neutron
radiation has the potential to explain both the Shroud’s
unique fluorescence properties as well as answer the question
about its 14C dating.
Appendix
Appendix 1. Ultraviolet Flashlight, Ultraviolet Filets and
Camera
The flashlight used as a uv source was a Convoy S2 model
(https://www.naturesrainbows.com/single-
post/2017/03/01/365nm-Flashlight-Torch-The-Most-
Significant-Innovation-in-UV-Mineral-Lights-in-Years)
equipped with a 2 mm thick Hoya U-340 bandpass filter
(https://www.ultravioletphotography.com/content/index.php/t
opic/3161-torch-filter-u-340-vs-u-360/). This flashlight uses
an LG 365 nm LED (model - LEUVA33U70RL00) to
produce uv light
(https://www.nichia.co.jp/specification/products/led/NCSU27
6A-E.pdf). This LG uv source outputs a sharp peak in uv
light centered at 365 nm and ranging between 340 and 400
nm. The 2 mm Hoya U-340 filter cuts off essentially all uv
light at and above 400 nm. It does transmit some light above
660 nm. The Hoya filter was the exciter filter. Transmission
characteristics of the U-340 filter were estimated from
published graphs and they are given in Table 1.
The camera used was a Canon EOS Rebel T7 which was
equipped with a Tiffen 52 mm Haze-2A visible and infrared
longpass filter (https://tfma.temple.edu/sites/tfma/files/site-
pdfs/Tiffenfilter-lens.pdf, pg. 6). Transmissions for the Tiffen
Haze-2A filter were estimated from a published graph
(https://tfma.temple.edu/sites/tfma/files/site-pdfs/Tiffenfilter-
lens.pdf, pg. 6) and they are given in Table 1.
The Tiffen-Haze filter was the barrier filter. The Tiffen-
Haze filter transmits an estimated 50% of light at 418 nm and
it peaks out at 90% transmission. The camera was set to
manual mode with the following parameters: fstop = 3.5,
shutter speed (length of time camera shutter is open) 1/200
sec., and ISO 400.
Table 1. Transmission characteristics of camera uv filters used.
Wavelength (nm) Hoya U-340
(estimated)
Tiffen Haze-2A
(estimated)
320 .89 0
340 .91 0
360 .76 0
380 .20 0
400 10-8 0
410 0 .28
415 0 .40
420 0 .54
430 0 .70
440 0 .82
Appendix 2. Calculating the Height of the Flashlight Above
Linen
The height of the flashlight above the linen photographed
was determined by trying to duplicate the power that Miller
used [20]. In his setup two 200 watt lights were used, and
these lights were focused at 45 degrees on the center of a
section of the Shroud being photographed, which can be
designated as the intense region of the section. The Shroud is
14.25 by 3.58 ft2 in area and the 16 photographs taken down
the 2 sides cover the entire Shroud. Thus, each photograph
covered an area of (14.25*3.58)/16 ft2 or 3.19 ft2. The size of
the intense region was estimated by clustering 10 of the web
based Shroud photos [B5 B12 B17 D8 D12 D15 D17 E6 E12
E17] into three clusters based on their image intensity, L, in
the CIE L*a*b space by using the MATLAB® imsegkmeans
function. This function segments image intensity into k
clusters by performing k-means clustering [28] and returns
the segmented labeled output. The cluster with the highest
intensity always occurred near the center of each image.
Figure 2B shows the clustering result for image D8 in Figure
2A. If Figure 2B is compared to Figure 2A it can be seen that
using 3 clusters eliminates fluorescence from most of the
blood marks and the patches.
From the clustering results for the uv web images of the
Shroud, it was determined that the average fraction of an
image covered by the intense region was 0.368. Using this
average the power/in2 that was focused on the intense region
on each of the web based Shroud images can be calculated as
400/(3.19*.368*144) = 2.37 watts/in2. The flashlight used
had an estimated power of 2 watts
(https://www.naturesrainbows.com/single-
post/2015/05/01/Convoy-S2-365nm-False-Power-Claims)
and it generated a circular intense region on the modern linen
tested. Varying the height of the flashlight above the linen
affected the area of this intense circle. The radius of the circle
that matched the power/in2 used by Miller [20] can be
calculated as the square root of 2/(*2.37) or .518 in. The
flashlight height was adjusted until the intense circle had
approximately this radius.
Appendix 3. Estimating a Base Line Level of 36Cl in the
Shroud
In determining how much of a change in the 36Cl/35Cl ratio
resulted from neutron radiation of the Shroud one needs to
have a base line value for the ratio. Wikipedia [29] gives a
36Cl/35Cl ratio value of (7-10) x10-13. This can be converted to
a 36Cl/Cl ratio by multiplying by the mass fraction of 35Cl,
0.7576, to give (5.3-7.6)x10-13. 36Cl is produced naturally in
the upper atmosphere via nuclear reactions and within solid
materials on the earth's surface [30]. The atmospheric 36Cl
then falls down to Earth with rainfall.
The following steps are involved in fabricating linen from
International Journal of Archaeology 2021; 9(2): 34-44 43
flax. First, rainfall brings 36Cl to the Earth’s surface where it
mixes with any 36Cl already present in the soil. Second, water
containing 36Cl is taken up into the flax plant. Third, 36Cl is
washed out of the flax when it is retted prior to producing linen.
Rainfall 36Cl: Numerous papers have been published on the
ratio 36Cl to total Cl in nature (36Cl/Cl). One paper [31] that
measured the ratio in rainwater in Israel gives ratios of .018
to .5 × 10−13. This paper also reported a value of .116 × 10−13
for Jerusalem. Interestingly in this paper sequential testing at
a site showed that the 36Cl/Cl ratio increased during a rainy
period rather than decreasing through wash out as would be
expected. The authors attributed this increase to the rain
stirring up dust that contained 36Cl and adding this 36Cl to the
rainwater sample.
Concentration of Cl by Plants: A number of papers [32-34]
have reported on the uptake of 36Cl by plants. Plants can
significantly concentrate 36Cl and Cl compared to that in the
soil. Sheppard et al [32] used stable Cl as a surrogate for 36Cl
and presented results for plant soil concentration ratios (CR
equals Cl in plant/Cl in soil). In determining CR’s both the
plant and the soil samples were dried. Sheppard et al found
that CR’s in agronomic plants and plant parts sampled at one
site varied between 4 and 120, with a geometric mean value
of 10. In [32] the highest value reported is for winter rye
straw having a CR of 237. Kashparov et al [33, 34] also
published CR values for stable chlorine in agricultural plant
species. Published results show that plants can significantly
concentrate chlorine from the soil into the plants.
Leaching of Cl During Retting: Before using flax to
produce linen, the flax plants are retted. According to
Wikipedia [35] natural water retting employs stagnant or
slow-moving waters, such as ponds, bogs, and slow streams
and rivers. The stalk bundles are weighted down, usually
with stones or wood, for about 8 to 14 days, depending upon
water temperature and mineral content. Kashparov et al [34]
discuss an experiment they carried out with plants that had
acquired 36Cl that had been sprayed onto the soil in which
they were grown. They placed two types of cereal straw in
distilled water and measured how much 36Cl was leached
from each straw. They found that after 4 hours 93-95% of the
36Cl had been leached from the straw. Leaching was complete
after 22 hours. This result strongly suggests that retting flax
for 8 to 14 days will remove a very significant amount of any
36Cl that it contains.
Additional data published in [32, 33] can be compared to
what was determined for the modern linen sample studied
here to help estimate a baseline value for 36Cl in the Shroud
of Turin. Reference [32] gives a value of 3600 ppm for the Cl
concentration of barley stalks. Reference [33] gives a value
of 5330 ppm for the Cl concentration of winter rye straw. Pea
straw had an even higher concentration of 8585 ppm. By
contrast the Cl concentration of the linen sample studied here
was 56 ppm, which is 64 to 153 times lower than the values
in [32, 33]. This relatively low value indicates that retting
probably leached most of the Cl from the flax prior to the
time that the linen was produced.
In section 2 of reference [36] it is stated that the natural
36Cl/Cl ratio varies between 10-12 and 10-15. The upper value is
similar to that in Wikipedia which gives 36Cl/Cl ratios of 5.6-
7.3x10-13. Based on the above discussion it is reasonable to
estimate that an upper limit for 36Cl/Cl ratio in the Shroud is
10-12. The real value is probably smaller. Due to retting this
upper limit should also apply to both the modern linen
studied here and the Sudarium.
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