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Enrichment of quartz fine grains for TL and ESR dating
Nuc/. Tracks, Vol. 10. Nos 4-6, pp. 609-612, 1985 Printed in Great Britain
0191-278X/8553.00+0.00 Pergamon Press Ltd.
ENRICHMENT OF QUARTZ FINE GRAINS FOR TL A N D ESR DATING G. KJTIS and S. CHARALAMBOUS Department of Nuclear Physics, University of Thessaloniki, Thessaloniki, Greece (Receired 5 Norember 1984; in ret,ised form 16 January 1985)
Abstraet--A simple magnetohydrostatic method is applied to enrich quartz grains from pottery and clay samples. In the paper the method is described. TL spectra and factors of enrichment are presented. It is found that for carefully controlled conditions there are consistent results. The enrichment factor depends on the type of sample. For a cycle of enrichment, factors up to 10 were measured.
The equations of motion for the same size particles (radius r) of quartz and of pottery matrix, that govern separation are:
1. I N T R O D U C T I O N As POINTED Out by Fleming (1966) and now is well known, the thermoluminescence from pottery sherds is mainly due to quartz grains. Thus to increase the sensitivity of TL or ESR dating several methods are proposed in order to enrich the quartz proportion. The methods are based on the differences of physical properties between quartz and pottery matrix. Among the applied methods are flotation and magnetic separation. The liquid method generally requires the use of toxic and expensive liquids. The "Franz magnetic separator" is well known and largely used. Several modifications on its principle are reported (Greene and Cornitius, 1970; Berger et al., 1980). A method of enrichment of quartz grains is the magnetohydrostatic method (Andres, 1975). Several versions of the magnetohydrostatic method have been reported (Gaulin and Hedgcock, 1981: Jan6r and Jungner. 1982). The present paper describes a version of the magnetohydrostatic apparatus and the results of enrichment of quartz under various conditions.
Vertical m o t i o n :
(la)
~ r 3 ( p c -- Pm)g = 6~zrnV~
(lb)
Horizontal motion: ~rrr3(kq - k~) H OH = 6nrn V~q
(2a)
4 3 (kc - k m) H -OH grrr ~ = 6rrrnV~ ~
(2b)
g-h
2. A P P A R A T U S AND BASIC IDEA The apparatus is shown schematically The basic idea is that grains falling in medium situated between the poles of (non-homogeneous magnetic field) can be by their magnetic susceptibility.
~4 r 3(pq -- p~)g = 6nrn V~ q
in Fig. 1. a viscous a magnet separated 609
where p = density; m -- medium; q = quartz; c = pottery matrix; n = viscosity; g = gravitational acceleration; V~q, V~~ = vertical components of terminal velocities for quartz and pottery matrix; V0hq, V0h~= horizontal components of terminal velocities for quartz and pottery matrix; kin, kq, k c = volume magnetic susceptibilities of medium, quartz and pottery matrix; H = magnetic field strength, OH~OH = magnetic field gradient in the horizontal axis; in a non-homogeneous magnetic field with horizontal field gradient. In the vertical direction the gravity and the viscosity forces and in the horizontal direction, the magnetic force and the viscosity, act on the grains. The forces and velocity diagrams are shown in Fig. 2. Depending on the Size and the magnetic susceptibility of the grains, the intensity and the
610
G. KITIS and S. C H A R A L A M B O U S Obviot]sty other liquids (or solutions) could be used, water among them; however, after evaporation, they might leave undesirable materials on the grains. Acetone was found to be the most convenient liquid for two other important reasons: its low viscosity allows the quick settling of grains into the removable chamber. Also due to its relatively low boiling point ( - 5 8 ° C ) the collected grains can be easily dried, in a few minutes, and at reasonably low temperature
(< 50°C).
FIG. 1. Schematic diagram of the apparatus used. gradient of the magnetic field and the vertical length of the magnetic field, the matrix grains approach the wall of the glass tube and become attached there. Under controlled experimental conditions the quartz grains fall directly in the lower removable chamber. When the quartz grains have fallen in the removable chamber then by slowly moving the glasstube upwards the attached grains can be gathered in the "collector", part A, of the tube. After that the liquid is gently removed with a siphon. 3. RESULTS A strong electromagnet capable of providing a wide range of field intensities (0-5 kG) and gradient (up to 3 kG cm-t), was used. Various shapes of poles can be adapted on it. Finally we decided that the poles should be as shown in Fig. 1. The liquids used were acetone and water. We performed experiments with various combinations of pure quartz (blank experiment) with bulk powder from crushed pottery with several sizes of powder and with various intensities of magnetic fields and magnetic gradient.
For the enrichment experiments, the pottery was crushed as usual and the grains were selected following their size, using differential sieves or for small grains (2-8 #m) by the Zimmerman method (1971). In the following the grains are separated using the proposed method, then the powders from: "bulk", "separated" and "rest" are annealed for 1 h, at 500°C. Afterwards, the powders are irradiated by the same dose, usually a few grays. Finally, samples with the same weight are prepared and their TL is measured, 3 days after irradiation. Typical glow-curves are presented in Fig. 3. The curve (a) corresponds to the bulk powder, while curve (b) to the enriched one. The enrichment factor was obtained as the ratio of the height (or integral) at a given temperature (or between two temperatures) of TL of separated samples, to TL of bulk samples. Under carefully controlled conditions there are consistent results. To check this, the initial powder of a ceramic was divided into three parts. For each part of powder the full enrichment procedure was performed. Between each procedure a day elapsed. The results are shown in Fig. 4. However, the general results are not as good as in the case of Fig. 4. Large discrepancies were generally found. But this does not introduce implications in the case that the enriched product is used for dating, since one should be working the whole cycle of a dating procedure either Foroul VII
H
I 0 Q I I; i l l l l l
8H elX
i ~Fgr
FIG. 2. Force and velocity diagrams in the process of magnetohydrostatic enrichment.
ENRICHMENT
OF QUARTZ
FINE GRAINS
FOR DATING
¢ .q
bulc
-
•
"
-
+
- - -
'
"
'~
p
-
"
'
"'
Iu
200
400
" T(°C)
FIG. 3. Typical glow-curves showing the quartz enrichment. Grains' size 100-140gin.
°g=
,.d I-
1
a
o
2~o
I
400
T(oc)
FIG. 4. Under carefully controlled conditions, in a complete cycle of enrichment the consistency of the results is excellent. The three curves (b) show the natural TL of enriched samples from the same ceramic in three separate cycles of enrichment. Curves (a) show the TL of the bulk powder of the same ceramic. Grains' size 2-8 gin. .+
611
612
G. K I T I S and S." C H A R A L A M B O U S
with the a m o u n t of one single cycle of enrichment or with the homogeneous mixture of the products of two or more cycles o f enrichment. It was found that the enrichment factor depends on the type of ceramics and on the experimental conditions. The factors found were generally around two. However, cases were found where the enrichment factor was close to one, as well as a case where it was ten. In conclusion, the proposed enrichment procedure can be introduced in the cycle of pottery dating (or ESR) of fine grains to increase the sensitivity by a factor of about two.
Acknowledgements--The authors wish to thank Maria Tsakiri for her assistance. Financial support for this work was partially provided by Stiftung Volkswagenwerk.
REFERENCES Andres U. (1975) Magnetohydrodynamic and magnetohydrostatic separation--a new prospect for mineral separation in the magnetic field. Miner. Sci. Engng 7, 99-109. Berger G. W., Mulhern P. J. and Huntley D. J. (1980) Isolation of silt-sized quartz from sediments. Ancient TL 11, 8-9. Gaulin B. and Hedgcock F. (1981) An inexpensive method for separating quartz from pottery. Ancient TL 15, 2-5. Greene G. M. and Cornitius L. E. (1970) A technique for magnetically separating minerals in a liquid mode. J. Sediment. Petrol. 41, 310-312. Fleming S. (1966) Study of thermoluminescence of crystalline extracts from pottery. Archaeometry 9, 170-173. Janrr J. and Jungner H. (1982) A simple method tbr separation of quartz in TL dating. In Proceedings ~/' the 2nd Specialist Seminar on TL Dating, Vol, 6, Oxford, 1980, pp. 214-215. Zimmerman D. (1971) Thermoluminescent dating using fine grains from pottery. Archaeomet O' 13, 29 52.
0191-278X/8553.00+0.00 Pergamon Press Ltd.
ENRICHMENT OF QUARTZ FINE GRAINS FOR TL A N D ESR DATING G. KJTIS and S. CHARALAMBOUS Department of Nuclear Physics, University of Thessaloniki, Thessaloniki, Greece (Receired 5 Norember 1984; in ret,ised form 16 January 1985)
Abstraet--A simple magnetohydrostatic method is applied to enrich quartz grains from pottery and clay samples. In the paper the method is described. TL spectra and factors of enrichment are presented. It is found that for carefully controlled conditions there are consistent results. The enrichment factor depends on the type of sample. For a cycle of enrichment, factors up to 10 were measured.
The equations of motion for the same size particles (radius r) of quartz and of pottery matrix, that govern separation are:
1. I N T R O D U C T I O N As POINTED Out by Fleming (1966) and now is well known, the thermoluminescence from pottery sherds is mainly due to quartz grains. Thus to increase the sensitivity of TL or ESR dating several methods are proposed in order to enrich the quartz proportion. The methods are based on the differences of physical properties between quartz and pottery matrix. Among the applied methods are flotation and magnetic separation. The liquid method generally requires the use of toxic and expensive liquids. The "Franz magnetic separator" is well known and largely used. Several modifications on its principle are reported (Greene and Cornitius, 1970; Berger et al., 1980). A method of enrichment of quartz grains is the magnetohydrostatic method (Andres, 1975). Several versions of the magnetohydrostatic method have been reported (Gaulin and Hedgcock, 1981: Jan6r and Jungner. 1982). The present paper describes a version of the magnetohydrostatic apparatus and the results of enrichment of quartz under various conditions.
Vertical m o t i o n :
(la)
~ r 3 ( p c -- Pm)g = 6~zrnV~
(lb)
Horizontal motion: ~rrr3(kq - k~) H OH = 6nrn V~q
(2a)
4 3 (kc - k m) H -OH grrr ~ = 6rrrnV~ ~
(2b)
g-h
2. A P P A R A T U S AND BASIC IDEA The apparatus is shown schematically The basic idea is that grains falling in medium situated between the poles of (non-homogeneous magnetic field) can be by their magnetic susceptibility.
~4 r 3(pq -- p~)g = 6nrn V~ q
in Fig. 1. a viscous a magnet separated 609
where p = density; m -- medium; q = quartz; c = pottery matrix; n = viscosity; g = gravitational acceleration; V~q, V~~ = vertical components of terminal velocities for quartz and pottery matrix; V0hq, V0h~= horizontal components of terminal velocities for quartz and pottery matrix; kin, kq, k c = volume magnetic susceptibilities of medium, quartz and pottery matrix; H = magnetic field strength, OH~OH = magnetic field gradient in the horizontal axis; in a non-homogeneous magnetic field with horizontal field gradient. In the vertical direction the gravity and the viscosity forces and in the horizontal direction, the magnetic force and the viscosity, act on the grains. The forces and velocity diagrams are shown in Fig. 2. Depending on the Size and the magnetic susceptibility of the grains, the intensity and the
610
G. KITIS and S. C H A R A L A M B O U S Obviot]sty other liquids (or solutions) could be used, water among them; however, after evaporation, they might leave undesirable materials on the grains. Acetone was found to be the most convenient liquid for two other important reasons: its low viscosity allows the quick settling of grains into the removable chamber. Also due to its relatively low boiling point ( - 5 8 ° C ) the collected grains can be easily dried, in a few minutes, and at reasonably low temperature
(< 50°C).
FIG. 1. Schematic diagram of the apparatus used. gradient of the magnetic field and the vertical length of the magnetic field, the matrix grains approach the wall of the glass tube and become attached there. Under controlled experimental conditions the quartz grains fall directly in the lower removable chamber. When the quartz grains have fallen in the removable chamber then by slowly moving the glasstube upwards the attached grains can be gathered in the "collector", part A, of the tube. After that the liquid is gently removed with a siphon. 3. RESULTS A strong electromagnet capable of providing a wide range of field intensities (0-5 kG) and gradient (up to 3 kG cm-t), was used. Various shapes of poles can be adapted on it. Finally we decided that the poles should be as shown in Fig. 1. The liquids used were acetone and water. We performed experiments with various combinations of pure quartz (blank experiment) with bulk powder from crushed pottery with several sizes of powder and with various intensities of magnetic fields and magnetic gradient.
For the enrichment experiments, the pottery was crushed as usual and the grains were selected following their size, using differential sieves or for small grains (2-8 #m) by the Zimmerman method (1971). In the following the grains are separated using the proposed method, then the powders from: "bulk", "separated" and "rest" are annealed for 1 h, at 500°C. Afterwards, the powders are irradiated by the same dose, usually a few grays. Finally, samples with the same weight are prepared and their TL is measured, 3 days after irradiation. Typical glow-curves are presented in Fig. 3. The curve (a) corresponds to the bulk powder, while curve (b) to the enriched one. The enrichment factor was obtained as the ratio of the height (or integral) at a given temperature (or between two temperatures) of TL of separated samples, to TL of bulk samples. Under carefully controlled conditions there are consistent results. To check this, the initial powder of a ceramic was divided into three parts. For each part of powder the full enrichment procedure was performed. Between each procedure a day elapsed. The results are shown in Fig. 4. However, the general results are not as good as in the case of Fig. 4. Large discrepancies were generally found. But this does not introduce implications in the case that the enriched product is used for dating, since one should be working the whole cycle of a dating procedure either Foroul VII
H
I 0 Q I I; i l l l l l
8H elX
i ~Fgr
FIG. 2. Force and velocity diagrams in the process of magnetohydrostatic enrichment.
ENRICHMENT
OF QUARTZ
FINE GRAINS
FOR DATING
¢ .q
bulc
-
•
"
-
+
- - -
'
"
'~
p
-
"
'
"'
Iu
200
400
" T(°C)
FIG. 3. Typical glow-curves showing the quartz enrichment. Grains' size 100-140gin.
°g=
,.d I-
1
a
o
2~o
I
400
T(oc)
FIG. 4. Under carefully controlled conditions, in a complete cycle of enrichment the consistency of the results is excellent. The three curves (b) show the natural TL of enriched samples from the same ceramic in three separate cycles of enrichment. Curves (a) show the TL of the bulk powder of the same ceramic. Grains' size 2-8 gin. .+
611
612
G. K I T I S and S." C H A R A L A M B O U S
with the a m o u n t of one single cycle of enrichment or with the homogeneous mixture of the products of two or more cycles o f enrichment. It was found that the enrichment factor depends on the type of ceramics and on the experimental conditions. The factors found were generally around two. However, cases were found where the enrichment factor was close to one, as well as a case where it was ten. In conclusion, the proposed enrichment procedure can be introduced in the cycle of pottery dating (or ESR) of fine grains to increase the sensitivity by a factor of about two.
Acknowledgements--The authors wish to thank Maria Tsakiri for her assistance. Financial support for this work was partially provided by Stiftung Volkswagenwerk.
REFERENCES Andres U. (1975) Magnetohydrodynamic and magnetohydrostatic separation--a new prospect for mineral separation in the magnetic field. Miner. Sci. Engng 7, 99-109. Berger G. W., Mulhern P. J. and Huntley D. J. (1980) Isolation of silt-sized quartz from sediments. Ancient TL 11, 8-9. Gaulin B. and Hedgcock F. (1981) An inexpensive method for separating quartz from pottery. Ancient TL 15, 2-5. Greene G. M. and Cornitius L. E. (1970) A technique for magnetically separating minerals in a liquid mode. J. Sediment. Petrol. 41, 310-312. Fleming S. (1966) Study of thermoluminescence of crystalline extracts from pottery. Archaeometry 9, 170-173. Janrr J. and Jungner H. (1982) A simple method tbr separation of quartz in TL dating. In Proceedings ~/' the 2nd Specialist Seminar on TL Dating, Vol, 6, Oxford, 1980, pp. 214-215. Zimmerman D. (1971) Thermoluminescent dating using fine grains from pottery. Archaeomet O' 13, 29 52.