Journal of Nuclear and Radiochemical Sciences, Vol. 1, No. 1, pp. 47−50, 2000

47

ArticlesCorrelation of Aluminum Hole Centers with Hydrogen Radicals from γ-Irradiated Quartz
of Different Origins

Tetsuo Hashimoto,*,a Hirotomo Hase,c Duk-Guen Hong,a Hiroki Fujita,b and Hajime KatayamabaDepartment of Chemistry, Faculty of Science, Niigata University, 8050 Ikarashi, Niigata 950-2181, Japan
Graduate School of Science and Technology, Niigata University, 8050 Ikarashi, Niigata 950-2181, Japanc
Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0451, Japanb

Received: February 10, 2000; In Final Form: March 6, 2000
In all quartz samples having different origins, radiation-induced hydrogen radicals (atomic hydrogens) wereobserved in ESR measurement at 77K in addition to intense Al-centers. An obvious positive correlation was recognized between the hydrogen radical intensities and the reduction of the Al-centers after warming up to room
temperature, although there was no clear relationship between hydrogen signals and initial Al-centers at 77K. In
isochronal annealing treatments the hydrogen radicals were gradually decreased with increments of temperatureand completely disappeared after warming up to room temperature. Similar behavior was shown in the Al-centers, but a few percentages of which were still remained at room temperature. The Al-centers remained gave a linear relation to the blue thermoluminescence (BTL) intensity. We concluded that the hydrogen radicals arisingfrom radiolytic products of OH and molecular water impurities could operate as a “killer” of radiation-induced Alcenters related intimately to emission of BTL in natural quartz.

1. Introduction

been further investigated using differently originated quartz
specimens.

Blue-thermoluminescence (BTL) around 470nm wavelengthfrom natural quartz minerals exposed to ionizing radiation has
been attributed to the recombination of Al-hole centers[AlO 4 h + ] 0 with electrons released from trapped sites. 1
However, negative or meaningless correlation between Al
impurity contents and BTL intensities has been often met froma variety of natural quartz of different origins and even fromdifferent segments in a single rock crystal. 2 In the recent
papers, 3,4 the aluminum distributions on the quartz slices,which were visualized by using an EPMA (electron probe
micro-analyzer), have been found to offer somewhat negative
correlation with both the BTL-stripe and the radiation-induced
color center image (CCI) patterns. Some segments from theslice showed the obvious negative-correlation between theradiation-induced phenomena and both Al and OH (probably
due to dangling bonds and molecular water) impurity concentrations, whereas Al-hole centers in the ESR-spectra gave apositive correlation with radiation-induced phenomena.5
Additionally, the formation of Al-hole centers has been also
confirmed to be seldom in Brazilian hydrothermal quartz witha high content of OH and molecular water in the infraredabsorption spectra.6,7 The similar role of OH and molecularwater impurities on radiation-induced phenomena was confirmed on a slice specimen from the Japanese twin quartz,
which showed significantly different behavior between thecore and outer parts; the latter contained large amounts of OH
and molecular water impurities, giving less radiation-induced
phenomena.4
On the basis of these experimental results, a quenchingmechanism of the radiation-induced phenomena for quartz
samples prepared from single Madagascar rock crystal has
been proposed, in which the H0-atoms resulted from a radiolysis product from OH and molecular water impurities can operate as a killer of radiation-induced phenomena derived fromthe Al-hole centers.4,5
In this paper, the quenching model concerning H0 radicals
and Al-centers in electron spin resonance (ESR) spectra has*Corresponding author. E-mail: thashi@sc.niigata-u.ac.jp. FAX:
+81-25-262-6116.

2. Experimental
In the present studies, eight kinds of quartz sample differently originated from Fukushima (Japan), India, Scotland,
Madagascar, Keirin (China), Ottawa, two Brazilian, and Merck(a chemical reagent) were used. Most of the quartz samples
were identified to have a hydrothermal origin and possess theblue-TL (BTL) property. The samples were sieved to adjust
grain sizes ranging from 150 to 250 µm in a diameter for the
ESR measurements.
The Al-impurity contents in the differently originated quartz
samples were nondestructively determined by an instrumental
neutron activation analysis (INAA) using the purest thermal
neutron field as described in the previous publications.8,9 As
mentioned previously,8 the use of the purest thermal neutrons
is essential to determine accurately trace amounts of Al by the
INAA, because the detection criterion of Al in the quartz issignificantly dependent on the interfering reaction of
28
Si(n,p) 28 Al owing to the concomitant fast neutrons andmatrix nuclide 28Si (possessing 92.2% in abundance); even acomplete pure synthetic quartz glass without Al-impurity has
been evaluated to be over 200ppm pseudo Al contents whenusing a normal neutron field of reactor such as in Cd-ratios of
3−4.
The quartz samples of different origins were irradiated at
77K (in liquid nitrogen). The dose rate was about 15kGy/hr at
the central position of 6 0 Co-source in KURRI (Kyoto
University Research Reactor Institute). The total dose appliedat the center position of the source was fixed to 20kGy for the
ESR-measurements. After γ-ray irradiation, the sample wasstored in 77K. The irradiated quartz sample was transferredfrom the glass vial, bearing brown color centers, into a nonirradiated quartz capillary tube for subsequent ESR measurements.
Both hydrogen radicals and Al-centers produced by γ-ray
irradiation of the quartz grains were measured at 77K with an
ESR spectrometer (JEOL Ltd. JES-TE 200) at microwave
power level of 0.03µW and 2mW, respectively. Under these
conditions of the microwave power level, any saturation of the© 2000 The Japan Society of Nuclear and Radiochemical SciencesHashimoto48 J. Nucl. Radiochem. Sci., Vol. 1, No. 1, 2000
signals from all quartz samples was not observed. Resultsfrom the first ESR measurements are called hereafter an initial
Al-center signal because of direct measurement after irradiation at 77K. Subsequently, the sample was warmed up to room
temperature for a few hours and the ESR signals were measured again at 77K. Hereafter, this result is called second Alcenter signal.
Isochronal annealing treatments for irradiated quartz samples were performed by blowing nitrogen gas and holding atconstant temperatures from 77K up to the room temperature.
The quartz grain sample was kept at each annealing temperature for 3 minutes and the ESR spectrometry was repeatedly
conducted at 77K.
The BTL glow curve was measured with a conventional TLmeasuring system by operating the heating rate of 1 ˚C/s.10
The BTL intensities were estimated by integrating the higher
temperature regions of 260−380˚C in glow curve.
3. Results and Discussion
Before γ-ray irradiation, no ESR signal was observed in all
natural quartz because of a simple annealing treatment for a
few minutes at 400˚C. Figure 1 shows typical two ESR spectrafrom the γ-irradiated quartz grains. Two ESR-magnetic fieldregions were employed for the hydrogen radical and respective
Al-center (initial and second) measurements at 77K before andafter warming up to room temperature after irradiation at 77K.
In Figure 1-(a) for an initial spectrum, two typical lines withequal intensity caused by the hydrogen radical appear in a separation of about 52 mT due to the hyperfine splitting of nuclear
magnetic spin (I=1/2). This H0 signal in quartz was in goodconcordant with the previous papers.11,12 Each line has a width
˙ 0.01mT by interpolatingat half maximum amplitude of δH =˙Al-hole centers, which could not be admitted in this figure
owing to delaying saturation feature in comparison with quick
power saturation of H0 signal. A power saturation curve of H0
signals is illustrated in Figure 1-(c), in which square root val(a)0ues of microwave power are plotted against H signal. From
this result the power of 0.03 µW was employed to give a maximum H0 signal.
On the other hand, Figure 1-(b) shows a well-known Alcenter signal due to {[AlO4h+]0}, which is consisting in thehyperfine (hf) structure arising from the interaction of unpaired
hole-like spin with the nuclear spin I=5/2 of the 27Al ion. Fromthe previous experiment,5 the applied power for Al-signal measurements was fixed to be 2mW during the present measurements. Compared with different ESR-saturation behavior
between H0 and Al-center signals, the H0 atoms are considered
to exist in an isolated site, presumably interstitial position,
because H0-property of non-interaction with the surrounding
lattices might cause more rapid power saturation than Al-center signals arising from the substitutional Al.
Initial Al center intensities are plotted against the Al-contents up to 300ppm as presented in Figure 2. There exist
approximately linear relationships with a correlation factor of
0.89. This result should be explained that the Al-center formation at 77K occurs mainly around the substituted Al impurity
sites, of which one bond presumably is consisting of charge
compensator of H ions. If alkaline ions serve for the main
charge compensators, the formation of Al-centers would be
retarded at 77K because of immobilization of alkaline ions as
clarified by Hallibuton et al.13 This result means that the present natural quartz of hydrothermal origin contain prominently
hydrogen charge compensator instead of alkaline ions.14 In
fact, ESR-signal intensities of the hydrogen radicals showed
fairly well proportional relation to that of the initial Al-centers.

(b)

(c)

Figure 1. ESR spectra of hydrogen radicals (a) and Al-hole centers(b) and power saturation curve (c) of hydrogen radicals (H0) fromquartz grains.
Crushed Madagascar quartz grains were irradiated by γ-ray of 20 kGy
at 77K and ESR measurements were carried out at 77K. (a) and (b)were measured with the power level of 0.03mW and 2mW, respectively, after storage for a few hours at 77K. The applied power to thehydrogen radicals was determined from power saturation curve (c).

Figure 2. Dependence of initial Al-hole center signals on the Alimpurity contents.

The changes of H0 and Al-center signals are presented in
Figure 3, in which Keirin and Ottawa quartz samples wereselected as two examples in respect of hydrogen radical intensities. Two hydrogen peaks appear in somewhat different
position estimated about 0.007mT regarding the applied magnetic field. Among 7 kinds of BTL quartz, maximum peakdifference was 0.027mT. This shift might be attributed to thedifference of the Pauli exclusion force causing the increase of
the splitting width between two hydrogen radical peaks.11,15 In
the preliminary experiments, the splitting width in somefeldspars has been broadened to 4mT in comparison with thatof the quartz. These results suggest that the splitting width
presumably contains unknown information related to geologically different origins of quartz.
It was noteworthy that any hydrogen radical signals produced by irradiation at 77K completely disappeared in everyCorrelation of Aluminum Hole Centers with Hydrogen Radicals

J. Nucl. Radiochem. Sci., Vol. 1, No. 1, 2000 49

Figure 4. Correlation of the reducing intensities of Al-centers andhydrogen radicals from quartz samples of different origins.
The difference between initial and second Al-intensities after warming
treatment is corresponding to the reducing intensities of Al-centers.

Figure 3. Two typical hydrogen signals in low magnetic field side (a)and changes of Al-hole center spectra before (b) and after (c) warming
up to room temperature.
The samples were obtained from Keirin and Ottawa quartz and the
ESR-measurements were carried out in the same way as described in
Figure 1, except for warming treatment up to room temperature. Eachsignal intensity is estimated as indicated in the present figures. The
hydrogen radicals from all γ-irradiated natural quartz were completely
disappeared after warming procedure.

sample when the irradiated natural quartz was warmed once up
to room temperature as described in our previous papers.5,16
Similar results from synthetic quartz and glasses have been
already confirmed with incorporation of water component.17,18
On the other hand, the Al center signals maintain more orless characteristic patterns between initial spectrum without
temperature elevation and second spectra after warming once
up to room temperature, as seen in Figures 3-(b) and (c). Both
ESR-intensities due to H0 and Al-centers were indicated in thisfigure. We found meaningless correlation between hydrogensignals and initial Al-centers for natural quartz used in thisstudy. However, when the difference between initial and second Al signals are taken into account by comparison with thehydrogen signals, it appears meaningful relationships fromsample to sample.
With these ESR spectrum changes, the reducing intensities
of Al-centers between initial and second measurements were
examined as a function of the H 0 intensities. The result is
illustrated in Figure 4, in which there certainly exists the positive correlation between them. This result strongly supportsthat mobile hydrogen radicals could react easily with the initial
Al-centers during the elevation of temperature to cause thecorresponding elimination of Al-centers. This mechanism
considered hydrogen radical as a killer of Al-center has been
proposed.4,5Figure 5. Isochronal annealing curves of the hydrogen radical (a) andAl-center intensities (b) from Madagascar quartz. The former signal iscompletely disappeared over 130K, whereas the Al-center signal
remains beyond 140K.

To confirm the present elimination mechanism of Al-centers, an isochronal annealing behavior was studied betweenhydrogen radicals and Al-centers. The results are indicated in
Figure 5. Both curves tend to the similar decreasing trend withincrements of temperature. Prominent decrease of both ESR
signals occurs around 100K, of which temperature agrees wellwith the results by Week and Abraham.17
The similar behavior of both signals with annealing implies
that some portions of Al-centers were disappeared by reactingwith hydrogen radical to form [Al 3+ ]---H + -OSi or Al-OH,
resulting in ESR insensitive sites as described in preceding
publications.5,13 The activation energies were approximately
evaluated as 7.5kJ/mol and 8.5kJ/mol for hydrogen radicals

Hashimoto

50 J. Nucl. Radiochem. Sci., Vol. 1, No. 1, 2000
and Al-centers, respectively, from the Arrhenius analysis oftemperature-dependent curves. This result supports that thehydrogen radicals and the Al-centers could cooperate to
decrease the radiation-induced phenomena, such as color center formation, thermoluminescence, optically stimulated luminescence, ESR radical absorption and so on. Since thehydrothermal quartz is known to contain high quantity of watermolecules, the radiolysis of such water should certainly contribute the formation of hydrogen radicals. In addition to thisreduction process, some OH radicals as a counter part of H0from radiolysis of H2O could be also moved to the interstitialsite adjacent to Al3+ to form ESR-insensitive Al-OH as proposed by Iwasaki and Iwasaki.6
Finally the second Al-hole center intensities, corresponding
to the remained Al-centers, are plotted as a function of BTL, asseen in Figure 6. As expected, there exists excellently positive
correlation between BTL and the second Al-centers even in avariety of differently originated quartz except for two kinds ofquartz (Keirin and Ottawa). As mentioned just above, theKeirin quartz should contain large amounts of molecular water,
followed to much formation of hydrogen radicals to react theAl-centers (cf., Figure 1-(a)). On the other hand, the Ottawa
sample contains extremely small amount -OH and molecularwater, presumably owing to the quartz formation withextremely slow cooling rate. These radiation-induced mechanisms associated with the important role of hydrogen radicals
could be explained well regarding the changeable radiationinduced phenomena showing striped patterns of color center,presumably dependent on the crystal formation conditions
within single crystal rock which have been reported in our laboratory.5 From these results, it is again emphasized that the
OH and water contents in quartz play important roles on thereliable geochronological or archaeological dating using ESR
methods and luminescence techniques, involving TL and optically stimulated luminescence (OSL), because the naturally
accumulated Al-centers are greatly influenced by the quantityof hydrogen radicals formed with radiation.

Figure 6. Dependence of BTL intensities on second Al-center signals.
On the basis of the present results, both ESR and luminescence including BTL and OSL, have been proved to be available to thegeochronology of white minerals, since the second Al-centers should
be correlated closely with the naturally accumulated doses.

4. Conclusions
All of the differently originated quartz showed both thehydrogen radical and the aluminum hole centers in ESR-spectra after irradiation at 77K. The disappearance of hydrogensignals was coincident with the elimination of Al-centers after
elevation of temperature above about 100K. The hydrogenradical signals were positively correlated to the reducing
amounts of Al-center after the temperature elevation up to
room temperature for differently originated quartz. The hydrogen radical formation greatly depends on the amounts of OH
and molecular water in quartz, so that the quartz of different
origins will offer various radiation-induced phenomena influenced by their different OH and water impurity contents.
On the basis of these results, it was concluded that hydrogenradicals from the OH impurities operates as a main "killer" of
all radiation-induced phenomena in natural quartz, such as Alcenters, color centers, luminescence phenomena like radioluminscence (RL), BTL and OSL.
Acknowledgement. This work has been carried out in part
under the Visiting Researchers Program of Kyoto University
Research Reactor Institute. The present study was partly supported by a foundation from Reed Co. Ltd. and a grant-in-aid
for Fundamental Research from the Ministry of Education,
Culture, and Sport, Japan (No. 10480024) and by the REIMEI
Research (No. 2-1999) of Japan Atomic Energy ResearchInstitute.
References(1) S. W. S. McKeever, Nucl. Tracks Radiat. Meas. 18, 5(1991).
(2) T. Hashimoto, S. Sakaue, M. Ichino, and H. Aoki, Nucl.
Tracks Radiat. Meas. 23, 293 (1994).
(3) T. Hashimoto, S. Notoya, T. Arimura, and M. Konishi,
Radiat. Meas. 26, 233 (1996).
(4) T. Hashimoto, K. Yasuda, K. Sato, H. Sakaue, and H.
Katayama, Radiat. Meas. 29, 493 (1998).
(5) T. Hashimoto, H. Katayama, H. Sakaue, H. Hase, T.
Arimura, and T. Ojima, Radiat. Meas. 27, 243 (1997).
(6) F. Iwasaki and H. Iwasaki, Jpn. J. Appl. Phys. 32, 893(1993).
(7) P. L. Guzzo, F. Iwasaki, and H. Iwasaki, Phys. Chem.
Minerals 24, 254 (1997).
(8) T. Hashimoto, S. Sakaue, and H. Ohira, Radioisotopes 41,618 (1992).
(9) T. Hashimoto, T. Ojima, M. Konishi, and M. Kanemaki,
Radioisotopes 44, 379 (1995).
(10) T. Hashimoto, Y. Hayashi, A. Koyanagi, K. Yokosaka,and K. Kimura, Nucl. Tracks Radiat. Meas. 11, 229(1986).
(11) J. A. Weil, Phys. Chem. Minerals 10, 149 (1984).
(12) T. Miyazaki, N. Azuma, and K. Fueki, J. Amer. Ceram.
Soc. 67, 99 (1984).
(13) L. E. Hallibuton, N. Koumvakalis, M. E. Markes, and J. J.
Martin, J. Appl. Phys. 52, 3565 (1981).
(14) J. C. Newton-Howes and R. J. Fleming, Phys. Chem.
Minerals 17, 27 (1990).
(15) F. J. Adrian, J. Chem. Phys. 32, 972 (1960).
(16) H. Fujita, H. Katayam, H. Hase, and T. Hashimoto,
Radiat. Meas. (in press).
(17) R. A. Weeks and M. Abraham, J. Chem. Phys. 42, 68(1965).
(18) N. Azuma, T. Miyazaki, K. Fueki, I. Sakaguchi, and S.
Hirano, J. Am. Chem. Soc. 69, 19 (1960).