Journal of Nuclear and Radiochemical Sciences, Vol. 17, pp. 1-7, 2017

ArticlesMössbauer Spectroscopic Characterization of Iron in Ashes Made from the Ancient Woods
Excavated in the Foothills of Mt. Chokai
Shigeru Yamauchi,a,* Yasuji Kurimotoa and Yoichi SakaibabInstitute of Wood Technology, Akita Prefectural University, Noshiro, Akita 016-0876, Japan
Department of Chemistry, Daido University, Nagoya, Aichi 457-8530, Japan

Received November 12, 2016; Accepted January 10, 2017, Published online
The chemical states of iron in ashes made from umoregi woods excavated in the foothills of Mt. Chokai in 2015,
were characterized by using 57Fe-Mössbauer spectroscopy and complementary analytical techniques. Four kindsof ancient trees, Japanese oak, Japanese chestnut, Japanese cedar, and Japanese zelkova were burned at 650-710°C. The ashes showed brown, reddish brown, or yellowish brown colors. Elements (> Na) in the ashes were
determined by X-ray fluorescence spectrometry using a compact spectrometer. 57Fe-Mössbauer spectra of theashes and soil from the excavation site were recorded at 293 and 78 K. Raman scattering of the ashes was measured in the 1200-900 cm-1 range. It was confirmed that calcium ferrite, Ca2Fe2O5, was formed in the three ashes
and its formation rate depended on the Fe/Ca ratio. Mössbauer spectra suggested that CaFe2O4 and/or similar ironoxides were contained in the two ashes. In the case of Fe/Ca > 2, sextet components assigned to α-Fe2O3 werealso detected in the Mössbauer spectra. It was proposed that the color tone of the ashes was affected by Fe oxides.
Mössbauer spectra suggested that some parts of Ca2Fe2O5 formed in the ashes were such a fine particle that superparamagnetic phenomena were observable.

1. Introduction
The Japanese terms “umoregi” and “jindai-boku” refer toancient trees that are buried or submerged. More specifically,
these terms imply that the ancient trees were buried or submerged by natural phenomena such as a landslide or groundsubsidence more than several hundred years ago, after which
they have not completely decomposed because they have beenin anoxic conditions. However, these Japanese terms do notbelong to the scientific vocabulary and possess a degree of
ambiguity. Although ancient buried trees are generally classified as “umoregi” or “jindai-boku” even if it is partiallydecomposed with slight carbonization, we defined “umoregi
wood” here as the stem of an ancient buried tree that contains
neither carbonized nor petrified components.
Most umoregi woods maintain enough strength to be used
as construction materials, and they exhibit dark brown or
black colors depending on the chemical reactions of their components. Thus, in Japan, umoregi wood is much more expensive than ordinary wood because of its dignified hue and woodgrain pattern. It is recognized that the hue is due to the compounds consisting of polyphenols and Fe accumulated inumoregi wood. It is also known that ash made from umoregi
wood, showing brown, reddish brown, or deep yellow colors,
is regarded as top-quality incense burner ash for the Japanese
tea ceremony (Sado) since at least the 15th century.1
Few scientific reports, however, have been available onumoregi wood until recently. In the last decade, Narita andYatagai have published several studies focusing on the organic
components contained in umoregi woods excavated in Japan.2-6
Fe is enriched, to varying degrees, in umoregi wood,6 but nostudies are available on the chemical state of Fe in umoregi
wood except for two reports using 57Fe-Mössbauer spectroscopy.7, 8 In addition, there is little scientific information about
the ash made from umoregi wood.
*Corresponding author. E-mail: sigeru@iwt.akita-pu.ac.jp, Fax:
+81-185-52-6924

The aim of our study is to obtain the sufficient information
on Fe in umoregi wood ash to be able to discuss its chemical
states because enrichment of Fe is a common feature in umoregi wood. In this st udy, we explored the ashes using
57
Fe-Mössbauer spectroscopy and complementary analyticaltechniques, and investigated the relevance of Fe species tophysical properties such as color and particle size.
2. Experimental
2.1. Umoregi wood and soil samples. The sample ashes
were made from umoregi woods excavated from Nikaho Cityin Akita Prefecture, Japan, located to the north-west of Mt.
Chokai (Figure 1) in 2015. Umoregi woods were the stems oftrees buried by large-scale landslides from Mt. Chokai ca.
2500 years ago.9, 10 The material umoregi woods were Japaneseoak (Quercus serrata or Quercus crispula), Japanese chestnut(Castanea crenata), Japanese cedar (Cryptomeria japonica),
and Japanese zelkova (Zelkova serrata). “Japanese” is hereinafter abbreviated as “Jpn.” such as Jpn. cedar. These umoregi
woods were divided into two groups based on their color. One
group looked brown or dark green, and the other group
showed black. The former contained Jpn. cedar and Jpn. zelkova umoregi woods, and the latter, Jpn. chestnut and Jpn. oakumoregi woods.
After removing soil and bark, the umoregi woods weredried indoors at ambient temperature for several months, andthen cut into ca. 5 cm square blocks. Soil was collected at the
excavation site of a Jpn. zelkova umoregi tree. The soil was
ground in a mortar after air-drying.
2.2. Aqueous solution including Fe2+ and Fe3+. Aqueous
Fe2+ and Fe3+ solution was prepared using Fe(NH4)2(SO 4)2 ∙6H 2O and FeNH4(SO 4)2 ∙ 12H 2O. Fe2+/Fe3+ ratio and total Fe
concentration in this solution were 3/7 and 2 w/w%, respectively. Special-grade Fe compounds were purchased from
Wako Pure Chemical Industries, Ltd. and used without further
purification.

© 2017 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 01/23/2017

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J. Nucl. Radiochem. Sci., Vol. 17, 2017

Yamauchiand 50 kV (1000 s). Relative mass percentages of elements tototal elements detected were calculated using a standardlessfundamental parameter method11, 12 from characteristic X-ray
intensities.

Aomori Prefecture

Akita Prefecture

Excavation site ofumoregi wood in
Nikaho City

Iwate Prefecture

Mt. Chokai (2,236 m)
Yamagata Prefecture

Miyagi Prefecture

Figure 1. The locations of excavation sites of the umoregi trees inthis study and the summit of Mt. Chokai.

2.3. Fe-impregnated raw wood samples. Raw woods ofJpn. oak (Quercus crispula), Jpn. chestnut, Jpn. cedar, and Jpn.
zelkova were cut into ca. 5 cm square blocks and dried at 105°C for 24 hours in an electric oven. After overall immersionof the blocks in the aqueous Fe2+ and Fe3+ solution, the vessel
holding the solution and blocks was placed in a vacuum desiccator. The internal pressure was reduced using a water-jetpump until it was held constant. The desiccator was sealed for
24 hours. The blocks were taken out from the solution andsubsequently dried in air for more than 3 days.
2.4. Ashing method. The blocks of umoregi woods andFe-impregnated raw woods were dried at 105 °C for 24 hours.
Ashes were obtained by firing the dried blocks in an opentype electric furnace maintained at 600 °C for 24 hours. Theinternal temperature of the block was recorded using a thermocouple every 20 seconds until the internal temperature of
the furnace reached to 50 °C. The ashes obtained by heat
treatment were subjected to analytical techniques without
grinding. Ash content was calculated by dividing the mass of
the ash by the mass of the oven-dried wood before heat treatment.
2.5. X-ray fluorescence spectrometry. Metal elementswith atomic numbers greater than 11 in the ash and soil samples were detected by X-ray fluorescence spectrometry using aspectrometer (MESA-500, Horiba, Ltd.). Ash (0.06-0.11 g)
and soil (~2.3 g) powder were placed in a cylindrical Teflon
cell with a diameter of 20 mm. A sample chamber was held ina vacuum during a measurement. X-ray irradiation was performed at ambient temperature and the total measurement
time was 2000 s. The X-ray tube voltages were 15 kV (1000 s)

2.6. Mössbauer spectroscopy. 57Fe-Mössbauer measurements were performed in a conventional transmission mode ona Mössbauer spectrometer (Topologic System Inc. Model-222)
with a 57Co(Rh) source (925 MBq). Measurement temperatures were 78 and 293 K regulated using an Oxford cryostat
DN-1726 with a temperature controller ITC-601. Curve fittingof the Mössbauer spectra was performed by a nonlinear leastsquares method using the MossWinn 4.0Pre program, assuming that all spectra were composed of Lorentzian-shaped
peaks. The isomer shift and Doppler velocity scale were calibrated with respect to the sextet of α-Fe at room temperature.
The sample thicknesses of the umoregi ashes, the ash of
Fe-impregnated Jpn. cedar wood and soil powder were ca. 15
mg/cm2, ca. 15 mg/cm2, and ca. 30 mg/cm2, respectively.
2.7. Raman spectroscopy. Raman scattering by umoregi
wood ashes was recorded at room temperature using a
Renishaw Raman Imaging Microscope System 1000 connected to an air-cooled CCD detector. A He-Ne laser (632.8nm) was used as an excitation source at a power of ca. 20 mW.
Back-scattered Raman signals were collected through a microscope and edge filters in the range of 1200-900 cm-1 with aspectral resolution of about 2 cm-1. The sample powder was
spread thinly on a slide glass. The Raman measurements werere peated at more t ha n ten poi nt s for each sa mple.
Wavenumber calibration was carried out using the 520 cm-1
line of a silicon wafer and the 1332 cm-1 line of diamond.
3. Results and Discussion
3.1. Ashing of the ancient woods. Figure 2 shows photographs of the ashes made from four kinds of umoregi woodand Fe-impregnated Jpn. cedar wood. Fe-impregnated Jpn.
cedar wood ash exhibits a vivid red color. Its appearance
allows us to predict that it contains substantial amounts of
α-Fe2O3. Other three ashes prepared from Jpn. oak, Jpn. chestnut, and Jpn. zelkova wood impregnated with Fe also showed a
red color, although their shades were subtly different to one
another. On the contrary, the umoregi wood ashes show yellowish brown or brown tones although Jpn. oak umoregi woodash has a faintly reddish tone.
A plot of internal temperature of Jpn. zelkova umoregi
wood against time during the heat treatment is demonstrated
in Fig. 3. It is known that the ignition temperature range ofwood is relatively wide (350-490 °C), and the ignition temperatures of four umoregi wood species are within the range of
430-480 °C.13 Thus, the temperature curve indicates that theinternal temperature of Jpn. zelkova umoregi wood exceeded
600 °C and reached ~700 °C by combustion of itself. Similar

Figure 2. Four kinds of umoregi wood ashes and Fe-impregnatedJpn. cedar wood ash. a: Jpn. oak umoregi wood ash, b: Jpn. chestnut
umoregi wood ash, c: Jpn. cedar umoregi wood ash, d: Jpn. zelkova
umoregi wood ash, e: Fe-impregnated Jpn. cedar wood ash.

J. Nucl. Radiochem. Sci., Vol. 17, 2017

Mössbauer Spectroscopic Characterization of Iron in Ashes Made from

3

102

800
700

Relative intensity / %Temperature /°C

600
500
400
300
200

100

98

100
0
0

50

100

150

200

96

250

Time /min

10

0

10

Doppler shift / mm s -1

Figure 3. Internal temperature curve of a Jpn. zelkova wood block.
Figure 4. Mössbauer spectrum at 293 K of soil collected at the excavation site of a Jpn. zelkova umoregi tree. Blue and red doublet
curves indicate Fe2+ and Fe3+ components, respectively.

temperature curves were obtained with respect to the otherumoregi woods. The maximum temperatures during the heat
treatment of Jpn. oak, Jpn. chestnut, Jpn. cedar, and Jpn. zelkova were 707 °C, 653 °C, 676 °C, and 697 °C, respectively.
As listed in Table 1, the ash content in the umoregi woods
were in the range from 0.6% to 2.8%. This indicates that theorganic components of umoregi wood were decomposed completely and the chemical states of Fe changed drastically byashing.

elemental compositions of the soil at the excavation point andthe raw wood before burial around 2500 years ago. In addition, the molar ratios Fe/K and Fe/Al in umoregi wood ashes
were much larger than those in the soil whereas molar ratios
Fe/Si with umoregi wood ashes were significantly smaller
compared with the soil, suggesting that inorganic elements
exhibit different behaviors in their transfer from the soil to thewood and vice versa.

3.2. Elements in ashes and ash contents. Table 1 contains
a summary of the relative mass percentages of Mg to Fe inumoregi wood ashes, Fe-impregnated Jpn. cedar wood ash,and the soil. Several elements heavier than Fe such as Ni, Cu,
Zn, and Sr, were detected in a few samples, but their mass percentages were lower than 0.2%. The molar ratio of Fe/Ca andash content are listed in Table 1 together.
For all the umoregi wood ashes, the primary and secondary
elements were Fe and Ca, respectively, and the total mass percentages of them were over 80%. Other major elements
included Mg and Si. It should be noted that the amount of sulfur in Jpn. oak umoregi wood ash was much larger than that ofother umoregi wood ashes. Japanese raw wood contains Ca
and K as major inorganic elements regardless of tree species,
whereas Fe is a trace element and its amount is less than thoseof Mn and Cu.14 Therefore, it appears that the elemental composition of umoregi wood ashes was predominantly due to the3.3. Mössbauer spectra. Figure 4 depicts a 57Fe-Mössbauer
spectrum at 293 K of the soil collected at the excavation site of
Jpn. zelkova umoregi tree. The gray soil was a clay-like substance and included a considerable amount of water when it
was sampled, but its viscosity disappeared completely upondrying in air. The spectrum was only composed of two symmetrical doublets, and their Mössbauer parameters are summarized in Table 2. It was concluded that doublets 1 (bluecurve) and 2 (red curve) were assigned to high-spin Fe2+ andhigh-spin Fe3+, respectively. The area ratio of Fe2+/Fe3+ wasapproximately 3/7. The IS value of doublet 1 indicated that theatoms in the primary coordination sphere of Fe2+ formed anoctahedron, whereas it was difficult to determine based on the
IS and QS values of doublet 2 whether Fe3+ was placed at thecenter of tetrahedral or octahedral structures. However, it wasreported that Fe3+ in silicate or aluminate glass species forms a

TABLE 1: Relative mass percentage of elements in ashes and soil
Element wt%

SampleJpn. oak umoregi wood ash
Jpn. chestnut umoregi wood ash
Jpn. cedar umoregi wood ash
Jpn. zelkova umoregi wood ash
Fe-impregnated Jpn. cedar wood ash
Soil*

Mg
3.6
5.3
8.9
9.9
2.2

Al
1.1
0.3
0.6
1.6
0.7
11.6

Si
1.8
3.5
1.7
4.8
0.4
61.5

*gray soil at the excavation point of Jpn. zelkova umoregi

P
0.1
0.1
-

S
8.0
0.2
0.4
0.8
3.2
1.2

K
0.4
1.2
1.0
0.8
1.5
4.5

Ca
19.5
30.9
44.5
46.0
2.9
4.2

Mn
2.0
0.4
1.2
0.3
0.2

Fe
63.3
57.5
41.6
35.6
91.1
13.3

Molar
ratio,
Fe/Ca

Ashcontent,
%

2.3
1.3
0.7
0.6
15
2.3

1.31
2.73
0.62
1.38
3.24
-

J. Nucl. Radiochem. Sci., Vol. 17, 20174

YamauchiTABLE 2: Mössbauer parameters of soil sampled at excavation point of Jpn. zelkova umoregi tree
QS, mm s-1

LW, mm s-1

Doublet 1

1.13(1)2.59(1)0.41(2)

Doublet 20.34(1)0.63(1)0.51(2)100
Relative intensity / %ab

Relative intensity / a.u.

IS, mm s-1

90

c

d

80

10

0

10

Doppler shift / mm s-1
Figure 5. Mössbauer spectrum at 293 K of Fe-impregnated Jpn.
cedar wood ash.

tetrahedral structure.15, 16 The soil contained Al and Si as
major elements as shown in Table 1. Therefore, Fe3+ in the soil
was likely to be located at the center of tetrahedral structures.
The Mössbauer spectrum at 293 K of Fe-impregnated Jpn.
cedar wood ash is displayed in Figure 5 and was composed ofa sextet (IS: 0.372(1) mm/s, QS: -0.207(1) mm/s, H: 51.535(3)T, LW: 0.292(1) mm/s). These parameters were completely
identical with those of α-Fe2O3.17 If Mg or Ca included in
Fe-impregnated woods is comparable to Fe, it can be expectedthat the Mössbauer absorptions attributed to magnesium ferrites or calcium ferrites are observed. However, such ferrites
were not observable in the Mössbauer spectrum because Mg
was negligible and Fe/Ca ratio was substantially large. The
Mössbauer spectra at 293 K of the other three Fe-impregnatedwood ashes also showed only a sextet whose parameters had
no significant differences from those of α-Fe2O3. Thus, almost
all of the Fe species produced by ashing of Fe-impregnatedwoods were found to be α-Fe2O3, which exhibits no characteristics of nanoparticles. This suggested that Fe compounds precipitated as microcrystals in the woods by drying.
Figure 6 illustrates the Mössbauer spectra at 293 K of umoregi wood ashes. All the spectra showed an apparent doublet
whose center was placed in the range of 0.3-0.4 mm/s. Except
for Jpn. cedar umoregi wood ash, the Mössbauer spectra ofother umoregi wood ashes exhibited obvious magnetic hyperfine structures. One and two sextets were observed in the
spectra of Jpn. oak and Jpn. zelkova umoregi wood ashes,
respectively and their Mössbauer parameters were determinedbased on curve-fitting analysis.
The parameters of umoregi wood ashes are given in Table 3.
It was expected that calcium ferrites would have formed,
because umoregi wood ashes were enriched with Fe and Ca as
described above. Thus, the Mössbauer parameters of CaFe2O4
and Ca 2Fe2O5 reported previously18, 19 are shown together for100
Doppler shift / mm s

10-1

Figure 6. Mössbauer spectra at 293 K of umoregi wood ashes, a:
Jpn. oak umoregi wood ash, b: Jpn. chestnut umoregi wood ash, c:
Jpn. cedar umoregi wood ash, d: Jpn. zelkova umoregi wood ash.
Orange and green straight lines indicate Fe3+ in Oh and Td sites of
Ca2Fe2O5, respectively (cf. TABLE 3).

comparison. Brownmillerite type calcium ferrite, Ca 2Fe2O5,
has a tetrahedral and octahedral site in terms of Fe3+.
It was concluded that the sextet observed in the spectrum of
Jpn. oak umoregi wood ash was attributed to bulky particles of
α-Fe2O3 because its Mössbauer parameters agree well withthose of Fe-impregnated Jpn. cedar wood ash described above.
The parameters of sextets 1 and 2 in the spectrum of Jpn. zelkova umoregi wood ash are close to those of Fe3+ (Oh) and Fe3+
(Td) in Ca 2Fe2O5, respectively, suggesting the formation ofbrownmillerite type calcium ferrite by ashing of Jpn. zelkova
umoregi wood. Line widths of the two sextets were muchlarger than that of the sextet of Jpn. oak umoregi wood ash.
This broadening was possibly caused by structural distortiondue to the influence of Al, Mg, and K impurities.
The positions of the two sextets reported by Randhawa andSweety18 are shown in Fig. 6 using colored lines, with orange
and green straight lines corresponding to Fe3+ (Oh) and Fe3+
(Td), respectively. Thus, these lines indicated that the considerable yield of Fe was distributed as brownmillerite type calcium ferrite (Ca 2Fe2O5) in Jpn. chestnut umoregi wood ash.
Furthermore, it seemed likely that weak absorptions assigned
to Ca2Fe2O5 appeared in the Mössbauer spectrum of Jpn. cedar
umoregi wood ash.
Hirabayashi et al. reported that the yields of Ca2Fe2O5 and
CaFe2O 4 depended upon the Fe/Ca ratio in synthesis using
Fe2O3 and CaO at 1000 °C.19 According to their study, most of
Fe species are Ca2Fe2O5 when the Fe/Ca ratio is less than 1.0,
and the two calcium ferrites have the almost same production
rate when the Fe/Ca ratio is about 1.3. Moreover, more than 85% of iron forms CaFe2O4 when the Fe/Ca ratio exceeds 2.0.
It was expected that the major Fe species contained in Jpn.
cedar, and Jpn. zelkova umoregi wood ash would be Ca2Fe2O5

J. Nucl. Radiochem. Sci., Vol. 17, 2017

Mössbauer Spectroscopic Characterization of Iron in Ashes Made from5

TABLE 3: Mössbauer parameters of iron species in umoregi wood ashes and calcium ferrites
SampleChemicalsate of ironType ofline-shape

Temp.,K

IS,
mm s-1QS,
mm s-1

H,
T

LW,
mm s-1

Ref.

Jpn. oakumoregi wood ash-

Sextet*293

0.372(5)-0.22(1)51.41(4)0.27(1)

-

Fe3+
Fe3+
Fe3+ (Oh)Fe3+ (Td)
Fe3+ (Oh)Fe3+ (Td)
Fe3+ (Oh)Fe3+ (Td)

DoubletSextet**Sextet***DoubletSextetSextetSextetSextetSextetSextetSextet

293
293
293
293
78
300
300
77
77
293
293

0.317(5)0.35(1)0.16(1)
0.37
0.48
0.37
0.18
0.46
0.27
0.35
0.18

0.798(9)-0.44(3)0.66(2)0.52-0.031
-0.52
0.72
-0.52
0.71
-0.52
0.72

49.5(1)41.5(9)
46
50.4
42.9
54.0
47.5
50.7
43.2

0.82(2)0.72(3)0.72(3)
-

19
19
18
18
18
18
19
19

Jpn. zelkova
umoregi wood ash
CaFe2O4

Ca2Fe2O5-*red curve, **orange curve (sextet 1), ***green curve (sextet 2)ab

Relative intensity / a.u.

assuming that the yields of Ca2Fe2O5 and CaFe2O4 reported byHirabayashi et al. were applicable to the umoregi wood ashes,
because the Fe/Ca ratios of Jpn. cedar, and Jpn. zelkova umoregi wood ash were 0.7, and 0.6, respectively. In addition, it canbe presumed that Jpn. chestnut umoregi wood ash (Fe/Ca =1.3) contained CaFe2O4 as well as Ca2Fe2O5, and CaFe2O4 wasincluded in Jpn. oak umoregi wood ash (Fe/Ca = 2.3) as amajor Fe species. Magnetic hyperfine structures will notappear in Mössbauer absorptions due to CaFe2O 4 at 293 K
because the Néel temperature of CaFe2O 4 is around 190 K,19
and the absorptions are likely to appear as a doublet.
Figure 7 shows the Mössbauer spectra at 78 K of the fourkinds of umoregi wood ashes. In the figure, the positions of a
sextet assigned to CaFe2O4 19 were marked with blue straightlines in addition to those of the sextets at 77 K of Ca2Fe2O5.18
Drastic changes because of cooling down to 78 K wereobserved in the Mössbauer spectra of Jpn. oak and Jpn. chestnut umoregi wood ashes. For Jpn. oak umoregi wood ash, thedoublet disappeared almost entirely, and the asymmetric andbroad sextet absorptions appeared dramatically. Although thisapparent sextet was likely to correspond to more than one Fe
species, it would not substantially contain absorptions attributed to Ca2Fe2O5. In addition, there was incomplete agreement
between the six blue lines and sextet absorption bottom positions. However, these differences would not be negative evidence for the formation of CaFe2O 4. The asymmetric line
shape of Mössbauer absorptions allowed us to speculate thatCaFe2O4 and the ferrites having similar structures to CaFe2O4,
such as MgFe2O 4 and Mg1-xCa x Fe2O 4, 20 are contained in theash, because Mg is a major element in all ashes as shown in
Table 1. Besides, the magnetic hyperfine structures (redstraight line) assigned to α-Fe2O3 were also observed obviously.
The Mössbauer spectrum of Jpn. chestnut umoregi woodash was likely to have magnetic hyperfine structures otherthan those assigned to Ca2Fe2O5. On the basis of the line shapeof absorptions, it may be expected that the considerable
amounts of CaFe2O 4 and similar ferrites showing magnetic
hyperfine structures at 78 K are included as well as Jpn. oakumoregi wood ash.
On the contrary, no sextet components other than those due
to Ca2Fe2O5 were confirmed in the Mössbauer spectra of Jpn.
cedar and Jpn. zelkova umoregi wood ashes, although the sextets due to Ca2Fe2O5 increased relative to the doublet. A possible explanation for the increase in intensity of the sextets at 78
K in the spectra of Jpn. cedar and Jpn. zelkova umoregi wood

c
d

10

0

10

Doppler shift / mm s-1
Figure 7. Mössbauer spectra at 78 K of umoregi wood ashes. a: Jpn.
oak umoregi wood ash, b: Jpn. chestnut umoregi wood ash, c: Jpn.
cedar umoregi wood ash, d: Jpn. zelkova umoregi wood ash. Orange
and green straight lines indicate Fe3+ in Oh and Td sites of Ca2Fe2O5,
respectively (cf. TABLE 3). Red and blue straight lines indicate Fe3+
in α-Fe2O3 and CaFe2O4, respectively (cf. TABLE 3).

ashes was nanoparticles having a magnetic transition point in
the temperature range from 78 K to 293 K. Moreover, Jpn.
cedar umoregi wood ash maintained the high intensity doublet
even at 78 K, suggesting that its particle size was significantly
smaller than that of Jpn. zelkova umoregi wood ash. However,further experimental data, such as TEM imaging, will be necessary to confirm this explanation.

J. Nucl. Radiochem. Sci., Vol. 17, 2017

These results indicated that the reddish tone observed overJpn. oak umoregi wood ash was due to α-Fe2O3 and the yellowish brown tones of other umoregi wood ashes were mainly due
to the calcium ferrite Ca 2Fe2O5. Furthermore, it is generally
believed that umoregi wood ash has qualities of fineness andsmoothness. The doublet observed in the Mössbauer spectra
at 78 K could be scientific evidence of these characteristics ofumoregi wood ash, if it corresponds to superparamagnetic
components, suggesting that Fe dispersed homogeneously in
the Jpn. cedar and Jpn. zelkova umoregi woods. Mössbauer
measurements at lower temperatures may be required to discuss the ferrites in the umoregi wood ashes in more detail.
3.4. Raman spectra. Figure 8 shows Raman spectra ofumoregi wood ashes in the range from 1200 to 900 cm-1. For
Jpn. oak umoregi wood ash, a Raman band was detected at1085 cm-1 on some measuring points (Fig. 8a), whereas most of
the spectra had a band at 1015 cm-1 (Fig. 8b). Typical Raman
spectra of Jpn. chestnut umoregi wood ash exhibited nothing
in this region but a weak band was observed rarely at 1085
cm-1 as shown in Fig. 8c. Raman spectra of Jpn. cedar and
Jpn. zelkova umoregi wood ashes always showed a bandclearly at 1085 cm-1.
Hirabayashi et al. reported that the Raman spectra of calcium ferrites synthesized from Fe2O3 and CaO (Fe/Ca=1 and 2)
at 1000 °C showed a band at 1093 cm-1 assigned to a stretchingmode of a superoxide radical O2- and another band was foundat 1022 cm-1 in the case of Fe/Ca=2.21 The frequency of thesebands seemed to be readily variable over a relatively wide
range.22-25 The Fe/Ca ratio is 2.3 for Jpn. oak umoregi woodash showing the two Raman bands. Assuming that the Raman
bands at 1085 and 1015 cm-1 correspond to those at 1093 and1022 cm-1 reported by Hirabayashi,21 the Raman spectra were
further evidence for the formation of Ca 2Fe2O5 by ashing ofumoregi woods.
4. Conclusions.
In the present study of the chemical states of iron in ashes
made from umoregi woods excavated in the foothills of Mt.
Chokai, the important findings were obtained from Mössbauer
spectroscopy and complementary analytical techniques. It
was confirmed that α-Fe2O3 was included in Jpn. oak umoregi
wood ash (Fe/Ca = 2.3). Moreover, it was revealed that Jpn.
chestnut (Fe/Ca = 1.3), J. cedar (Fe/Ca = 0.7) and Jpn. zelkova(Fe/Ca = 0.6) umoregi wood ashes contained Ca 2Fe2O5. Our
Mössbauer data proposed that CaFe2O4 and/or similar ferrites
were made by ashing of Jpn. oak and Jpn. chestnut umoregi
wood. The formation rate of these Fe oxides mainly depends
on Fe/Ca ratio in ashes. It was proposed that the Fe oxides significantly affected the color tone of umoregi wood ash.
Furthermore, the Mössbauer spectra suggested that the ashes
contained some parts of Ca2Fe2O5 as such fine particles that asuperparamagnetic effect appears.
We hope that our analytical method described here isapplicable to other umoregi wood ashes.
Acknowledgement
The authors are grateful to the Nikaho City Board of
Education for the donation of valuable umoregi woods.
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Figure 8. Raman spectra at room temperature of umoregi woodashes. a: Jpn. oak umoregi wood ash, b: Jpn. oak umoregi wood ash,c: Jpn. chestnut umoregi wood ash, d: Jpn. cedar umoregi wood ash,
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