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Thermoluminescence of pyramid stones
Radiat. Phys. Chem.Vol. 19, No. 3. pp. 237-241, 1982 Printed in Great Britain.
0146-5724/82/030237-05503.00/0 PergamonPress Ltd.
THERMOLUMINESCENCE OF PYRAMID STONES M. A. GOMAA and A. M. EID Rad. Prot. Dept., Nuclear Research Centre, Atomic Energy Establishment, Cairo, Egypt (Received 10 December 1980; in revised form 9 April 1981) Abstract--It is the aim of the present study to investigate some thermoluminescence properties of pyramid stones. Using a few grammes of pyramid stones from Pyramids I and II, the TL glow peaks were observed at 250 and 310°C, respectively. The TL glow peaks of samples annealed at 600°C, then, exposed to 6°Co "/-rays were observed at 120, 190 and 3100C, respectively. The accumulated dose of natural samples is estimated to be around 310 Gray (31 krad). By assuming an annual dose is I mGy, the estimated age of pyramid stones is 0.31 M year. INTRODUCTION INTERNATIONAL interest in the field of therm o l u m i n e s c e n c e (TL) of natural materials was shown for the last twenty years. In Egypt, T L studies include the following: 1. T L studies of natural materials. 'l-a) 2. T L dosimetry/5-7> 3. T L / S S n T D c o m b i n e d s y s t e m s ) s) The natural T L materials e x a m i n e d in Egypt were Inshas sand, feldspar and natural quartz. In the present study the natural material under examination is pyramid stones. EXPERIMENTAL The pyramid samples A few broken stones were carefully cut from the interface between two blocks of Pyramids I and II. Historically, the stone pyramid were cut from the Tora quarry on the east bank of the Nile as reported by El-deen et al. (1939). The broken stones were ground and the fine grains were selected for thermoluminescent studies. Samples from the pyramids were subdivided into: 1. Natural (untreated) samples. 2. Annealed samples. For annealing, the pyramid samples were annealed at 600°C for 1 hr.
For TL measurements, the mass of each pyramid sample is 20 mg and in general 5 samples were used for each irradiation condition. Preliminary examination of the pyramid stones showed that it is calcium carbonate (dolomite). Thermoluminescent measurements For TL measurements, the TL read-out system used is the Harshaw 2000 (A + B) equipment. The latter is connected to an X-Y recorder for TL glow curve studies. In general, the read-out conditions were: 1. Condition A, where maximum tray temperature is 250°C, heating time 30 sec and heating rate 8.5°C/sec. 2. Condition B, where maximum tray temperature is 350°C, heating time 60 sec and heating rate 8.5°C/sec. In general, pyramid samples are counted according to condition A before recounting according to condition B. Typical TL measurements for some natural and annealed samples are reported in Table 1. From Table I, it is clear that the natural TL signal is removed by heating. On irradiating the annealed samples with 6°Co y-ray absorbed dose of 302 Gray, the TL signal produced is equivalent to the TL signal of natural samples. Note that natural samples are exposed ~°-m to cosmic rays, and to radioactive isotopes, K-40; U-238 and Th-232 distributed in the soil. For further TL studies, the TL glow peaks are measured. Glow curve of annealed samples For samples annealed at 600°C, then exposed to 6°Co y-rays, the TL glow curve is shown in Fig. 1, where the
TABLE !. TYPICALTL MEASUREMENTFORSOMENATURALANDANNEALED PYRAMIDSTONESSAMPLES Sample No. 1 2 3 4 5 6
Sample type Natural Natural Annealed Annealed Annealed Annealed
Counting condition
TL signal No.
A B A B A B
118.0 84.7 0.9 5.5 127.0 87.0 237
Remarks ----Exposed to 302 Gray Exposed to 302 Gray
238
M.A. GOMAAand A. M. Em
1/,
12
1C
• 8 =or ..s o.-
6
0 0
I tO0
I
1
300
20 0
,1 /.00 "C
Tray T e m p e r a t u r e .
FI6. 1. TL glow curve of annealed pyramid stone sample. maximum tray temperature is 350°C and the heating time is one minute. Careful study of the TL glow curve shows the presence of three TL peaks at 120, 190 and 310°C, noting that the sample was counted half an hour after the end of irradiation. In Fig. 2, the TL glow curve of annealed sample is shown, where the annealed sample was exposed to 6°Co y-rays, then the cleaning method was applied before recounting. Noting that the max. tray temperature for recounting is 350°C. For the cleaning technique, the exposed annealed sample was heated to 250°C in 30 sec twice in order to remove TL signals below 250°C. In Fig. 2, the 310°C peak is seen while the other peaks are removed. RESULTS
Glow curve of natural samples For untreated natural samples, the TL glow curve is shown in Fig. 3, where the maximum tray temperature was 350°C and the heating time lasted 1 min. From Fig. 3 it is clear that natural samples have a TL peak at 250°C and an unresolved peak near 300°C. When the cleaning technique is applied to natural samples, the resultant TL glow curve is shown in Fig. 4, which clearly indicates a TL peak at 310°C. Over the years the fine grain of the pyramid
stones responded to naturally occurring ionizing radiation. The latter causes the formation of trap centres at different activation energies corresponding to TL peak temperatures at 120, 190 and 310°C, respectively. TL glow curves (Figs. 1--4) show the presence of a broad TL peak (150280°C) the latter being superimposed on the 190°C T L peak. Hence, over the years, the low temperature peaks at 120 and 190°C fades (naturally) completely, while a new peak is formed at 250°C (for natural samples, see Fig. 3). From Fig. 3, it seems that the shallow traps are filled, before the deep traps are filled, hence the 250°C peak is superimposed on the 310°C TL peak.
TL Dosimetry The variation of TL signal with 6°C0 y-ray absorbed dose for annealed samples is shown in Fig. 5. Note that for each absorbed dose the TL reading was recorded twice, i.e. according to Condition A, then according to Condition B. In general the variation of TL signal with absorbed dose is found to be linear within the absorbed dose range (1-1000 Gray). The conversion factors were found to be 0.A0 (-+0.01) nC/Gy, according to con-
Thermoluminescence of pyramid stones
239
10-
8
•
j
6
Z,
,
I
,
100
L
,
200 300 Tray Temperature.
I
400 'c
FIG. 2. TL glow curve of annealed samples (Condition B).
lO
$
• s C
I 100
200
I $00
I 400' C
Tray Temperature.
FIG. 3. TL glow curve of natural samples.
dition A and 0.27 (-+0.02) nC/Gy according t o , condition B. From the same figure, it is clear that as the absorbed dose is increased, the TL signal is also increased but non linearly, so that saturation occurs for absorbed doses greater than 5kGy.
Age estimation The age of natural object may be estimated using the following relation "°-12~ Age in Years = Accumulative dose annual dose
240
M.A. GOMAA and A. M. EID
10
_1
I
I
l
200 300 Tr.~yTemperature.
lOO
400 °C
FIG. 4. TL glow curve of natural samples (Condition B).
10-~
-
10 l,
103
10 2
Natural Sampte ~ / ~
,J c
.E
.E NI c
i _J i--
101
10 0 101
// °
.
.
_l
Sampte
,
10 2 Gamma_ray
.
.
.
.
.
.
.
I
101 dose in Grys.
.
10 2
.
.
.
.
.
.
.
I
.......
10 ~
FtG. 5. Variation of TL-signal with absorbed dose: A, max. tray temp. 250°C and B, max. tray temp• 350°C.
10
Thermoluminescence of pyramid stones From the TL results of the natural samples reported in Table l, the accumulated dose is estimated to be (300_ 20) Gray (according to Condition B) and (300 ± 7) Gray according to Condition A. For age determination, the annual dose should be measured at the site. For environmental monitoring using thermoluminescence dosimeters CaSO4; Dy was selected for it is the most sensitive TLD and it exhibits considerably less fading than other TLD. ~3~ Present work experimental results showed that its sensitivity to gamma rays is 6.6 nC per mGy (66 PC per mrad). Where the maximum tray temperature is 240°C, heating time 30 sec and heating rate 8.5°C/sec. Using CaSO4 dosimeter the minimum detectable dose is estimated as less than 4 mrad. The TL output of the unirradiated CaSO4 dosimeters is estimated to be equivalent to 1 mrad and the result are reproducible to within +4%. In an attempt to measure the radioactivity in a room (MAG) the annual absorbed dose rate is estimated to be 0.4mGy. For the pyramid samples, measurements using CaSO4 dosimeters for a period of 87 days only indicated that the absorbed dose is 23.3 ± 4.8 mrad i.e. 0.23 ± 0.05 mGy. Hence, the annual absorbed dose was taken as 97.8( +_20.1) mrad, i.e. 0.98 (±0.20) mGy. Consequently, the age of the pyramid samples is deducted as 3.06( _+0.62) × 105 years. CONCLUSION Although the present work study is a preliminary investigation of the age estimation the TL
241
properties of pyramid stones show the following: 1. TL glow peaks of exposed annealed samples are recorded at 120, 190 and 310°C, respectively. 2. For natural samples the TL glow peaks are recorded at 250 and 310°C, respectively. 3. For dosimetric purposes, the conversion factors are 0.4 nC/Gy (Condition A) and 0.27 nC/Gy (Condition B). Finally, the age of the samples is esimated to be 0.3 M year.
REFERENCES 1. M. A. GOMAAand A. M. LID, ATKE, 1976, 27, 274. 2. M. A. GOMAAand A. M. EID, Int. Appl. Radiat. Isot. 1976, 27, 332. 3. M. M. MORSl and M. A. GOMAA,Central Glass and Ceramic Bulletin, 1977, 24, 43. 4. M. A. GOMAAand A. M. EID, ATKE, 1977, 29, 297. 5. M. A. GOMAA,A. M. SAVED,A. M. LID and M. A. EL-KOLALY,ATKE, 1977, 29, 225. 6. M. A. GOMAA,Radiat. Phys. Chem. 1980, 13, 187. 7. M. A. GOMAA,Health Phys. 1980, 39, 313. 8. M. A. GOMAA,M. A. EL-KOLALYand M. A. EL-FIKI, ATKE 1976, 27, 277. 9. I. N. S. EL-DEEN,Z. ALY, A. N. HASnEM, Egypt in Ancient Ages (in Arabic), p. 40. EI-Maaraf Press, 1939. 10. V. ME.IDAHL,Dosimetry Techniqueces in TL dating, Ris~ Report No. 261, 1972. 11. M. J, AITKEN,D. W. ZIMMERMAN,S. J. FLEMINGand J. HUXTABLE, Proc. 12th Nobel Syrup., p. 129. Sweden 1970. 12. M. J. AITKENand S. J. FLEMIIqG,Topics in Radiation Dosimetry (Supp. 1), p. 1. Academic Press, New York, 1972. 13. K. BECKER,Nucl. Inst. Meth. 1972, 104, 405.
0146-5724/82/030237-05503.00/0 PergamonPress Ltd.
THERMOLUMINESCENCE OF PYRAMID STONES M. A. GOMAA and A. M. EID Rad. Prot. Dept., Nuclear Research Centre, Atomic Energy Establishment, Cairo, Egypt (Received 10 December 1980; in revised form 9 April 1981) Abstract--It is the aim of the present study to investigate some thermoluminescence properties of pyramid stones. Using a few grammes of pyramid stones from Pyramids I and II, the TL glow peaks were observed at 250 and 310°C, respectively. The TL glow peaks of samples annealed at 600°C, then, exposed to 6°Co "/-rays were observed at 120, 190 and 3100C, respectively. The accumulated dose of natural samples is estimated to be around 310 Gray (31 krad). By assuming an annual dose is I mGy, the estimated age of pyramid stones is 0.31 M year. INTRODUCTION INTERNATIONAL interest in the field of therm o l u m i n e s c e n c e (TL) of natural materials was shown for the last twenty years. In Egypt, T L studies include the following: 1. T L studies of natural materials. 'l-a) 2. T L dosimetry/5-7> 3. T L / S S n T D c o m b i n e d s y s t e m s ) s) The natural T L materials e x a m i n e d in Egypt were Inshas sand, feldspar and natural quartz. In the present study the natural material under examination is pyramid stones. EXPERIMENTAL The pyramid samples A few broken stones were carefully cut from the interface between two blocks of Pyramids I and II. Historically, the stone pyramid were cut from the Tora quarry on the east bank of the Nile as reported by El-deen et al. (1939). The broken stones were ground and the fine grains were selected for thermoluminescent studies. Samples from the pyramids were subdivided into: 1. Natural (untreated) samples. 2. Annealed samples. For annealing, the pyramid samples were annealed at 600°C for 1 hr.
For TL measurements, the mass of each pyramid sample is 20 mg and in general 5 samples were used for each irradiation condition. Preliminary examination of the pyramid stones showed that it is calcium carbonate (dolomite). Thermoluminescent measurements For TL measurements, the TL read-out system used is the Harshaw 2000 (A + B) equipment. The latter is connected to an X-Y recorder for TL glow curve studies. In general, the read-out conditions were: 1. Condition A, where maximum tray temperature is 250°C, heating time 30 sec and heating rate 8.5°C/sec. 2. Condition B, where maximum tray temperature is 350°C, heating time 60 sec and heating rate 8.5°C/sec. In general, pyramid samples are counted according to condition A before recounting according to condition B. Typical TL measurements for some natural and annealed samples are reported in Table 1. From Table I, it is clear that the natural TL signal is removed by heating. On irradiating the annealed samples with 6°Co y-ray absorbed dose of 302 Gray, the TL signal produced is equivalent to the TL signal of natural samples. Note that natural samples are exposed ~°-m to cosmic rays, and to radioactive isotopes, K-40; U-238 and Th-232 distributed in the soil. For further TL studies, the TL glow peaks are measured. Glow curve of annealed samples For samples annealed at 600°C, then exposed to 6°Co y-rays, the TL glow curve is shown in Fig. 1, where the
TABLE !. TYPICALTL MEASUREMENTFORSOMENATURALANDANNEALED PYRAMIDSTONESSAMPLES Sample No. 1 2 3 4 5 6
Sample type Natural Natural Annealed Annealed Annealed Annealed
Counting condition
TL signal No.
A B A B A B
118.0 84.7 0.9 5.5 127.0 87.0 237
Remarks ----Exposed to 302 Gray Exposed to 302 Gray
238
M.A. GOMAAand A. M. Em
1/,
12
1C
• 8 =or ..s o.-
6
0 0
I tO0
I
1
300
20 0
,1 /.00 "C
Tray T e m p e r a t u r e .
FI6. 1. TL glow curve of annealed pyramid stone sample. maximum tray temperature is 350°C and the heating time is one minute. Careful study of the TL glow curve shows the presence of three TL peaks at 120, 190 and 310°C, noting that the sample was counted half an hour after the end of irradiation. In Fig. 2, the TL glow curve of annealed sample is shown, where the annealed sample was exposed to 6°Co y-rays, then the cleaning method was applied before recounting. Noting that the max. tray temperature for recounting is 350°C. For the cleaning technique, the exposed annealed sample was heated to 250°C in 30 sec twice in order to remove TL signals below 250°C. In Fig. 2, the 310°C peak is seen while the other peaks are removed. RESULTS
Glow curve of natural samples For untreated natural samples, the TL glow curve is shown in Fig. 3, where the maximum tray temperature was 350°C and the heating time lasted 1 min. From Fig. 3 it is clear that natural samples have a TL peak at 250°C and an unresolved peak near 300°C. When the cleaning technique is applied to natural samples, the resultant TL glow curve is shown in Fig. 4, which clearly indicates a TL peak at 310°C. Over the years the fine grain of the pyramid
stones responded to naturally occurring ionizing radiation. The latter causes the formation of trap centres at different activation energies corresponding to TL peak temperatures at 120, 190 and 310°C, respectively. TL glow curves (Figs. 1--4) show the presence of a broad TL peak (150280°C) the latter being superimposed on the 190°C T L peak. Hence, over the years, the low temperature peaks at 120 and 190°C fades (naturally) completely, while a new peak is formed at 250°C (for natural samples, see Fig. 3). From Fig. 3, it seems that the shallow traps are filled, before the deep traps are filled, hence the 250°C peak is superimposed on the 310°C TL peak.
TL Dosimetry The variation of TL signal with 6°C0 y-ray absorbed dose for annealed samples is shown in Fig. 5. Note that for each absorbed dose the TL reading was recorded twice, i.e. according to Condition A, then according to Condition B. In general the variation of TL signal with absorbed dose is found to be linear within the absorbed dose range (1-1000 Gray). The conversion factors were found to be 0.A0 (-+0.01) nC/Gy, according to con-
Thermoluminescence of pyramid stones
239
10-
8
•
j
6
Z,
,
I
,
100
L
,
200 300 Tray Temperature.
I
400 'c
FIG. 2. TL glow curve of annealed samples (Condition B).
lO
$
• s C
I 100
200
I $00
I 400' C
Tray Temperature.
FIG. 3. TL glow curve of natural samples.
dition A and 0.27 (-+0.02) nC/Gy according t o , condition B. From the same figure, it is clear that as the absorbed dose is increased, the TL signal is also increased but non linearly, so that saturation occurs for absorbed doses greater than 5kGy.
Age estimation The age of natural object may be estimated using the following relation "°-12~ Age in Years = Accumulative dose annual dose
240
M.A. GOMAA and A. M. EID
10
_1
I
I
l
200 300 Tr.~yTemperature.
lOO
400 °C
FIG. 4. TL glow curve of natural samples (Condition B).
10-~
-
10 l,
103
10 2
Natural Sampte ~ / ~
,J c
.E
.E NI c
i _J i--
101
10 0 101
// °
.
.
_l
Sampte
,
10 2 Gamma_ray
.
.
.
.
.
.
.
I
101 dose in Grys.
.
10 2
.
.
.
.
.
.
.
I
.......
10 ~
FtG. 5. Variation of TL-signal with absorbed dose: A, max. tray temp. 250°C and B, max. tray temp• 350°C.
10
Thermoluminescence of pyramid stones From the TL results of the natural samples reported in Table l, the accumulated dose is estimated to be (300_ 20) Gray (according to Condition B) and (300 ± 7) Gray according to Condition A. For age determination, the annual dose should be measured at the site. For environmental monitoring using thermoluminescence dosimeters CaSO4; Dy was selected for it is the most sensitive TLD and it exhibits considerably less fading than other TLD. ~3~ Present work experimental results showed that its sensitivity to gamma rays is 6.6 nC per mGy (66 PC per mrad). Where the maximum tray temperature is 240°C, heating time 30 sec and heating rate 8.5°C/sec. Using CaSO4 dosimeter the minimum detectable dose is estimated as less than 4 mrad. The TL output of the unirradiated CaSO4 dosimeters is estimated to be equivalent to 1 mrad and the result are reproducible to within +4%. In an attempt to measure the radioactivity in a room (MAG) the annual absorbed dose rate is estimated to be 0.4mGy. For the pyramid samples, measurements using CaSO4 dosimeters for a period of 87 days only indicated that the absorbed dose is 23.3 ± 4.8 mrad i.e. 0.23 ± 0.05 mGy. Hence, the annual absorbed dose was taken as 97.8( +_20.1) mrad, i.e. 0.98 (±0.20) mGy. Consequently, the age of the pyramid samples is deducted as 3.06( _+0.62) × 105 years. CONCLUSION Although the present work study is a preliminary investigation of the age estimation the TL
241
properties of pyramid stones show the following: 1. TL glow peaks of exposed annealed samples are recorded at 120, 190 and 310°C, respectively. 2. For natural samples the TL glow peaks are recorded at 250 and 310°C, respectively. 3. For dosimetric purposes, the conversion factors are 0.4 nC/Gy (Condition A) and 0.27 nC/Gy (Condition B). Finally, the age of the samples is esimated to be 0.3 M year.
REFERENCES 1. M. A. GOMAAand A. M. LID, ATKE, 1976, 27, 274. 2. M. A. GOMAAand A. M. EID, Int. Appl. Radiat. Isot. 1976, 27, 332. 3. M. M. MORSl and M. A. GOMAA,Central Glass and Ceramic Bulletin, 1977, 24, 43. 4. M. A. GOMAAand A. M. EID, ATKE, 1977, 29, 297. 5. M. A. GOMAA,A. M. SAVED,A. M. LID and M. A. EL-KOLALY,ATKE, 1977, 29, 225. 6. M. A. GOMAA,Radiat. Phys. Chem. 1980, 13, 187. 7. M. A. GOMAA,Health Phys. 1980, 39, 313. 8. M. A. GOMAA,M. A. EL-KOLALYand M. A. EL-FIKI, ATKE 1976, 27, 277. 9. I. N. S. EL-DEEN,Z. ALY, A. N. HASnEM, Egypt in Ancient Ages (in Arabic), p. 40. EI-Maaraf Press, 1939. 10. V. ME.IDAHL,Dosimetry Techniqueces in TL dating, Ris~ Report No. 261, 1972. 11. M. J, AITKEN,D. W. ZIMMERMAN,S. J. FLEMINGand J. HUXTABLE, Proc. 12th Nobel Syrup., p. 129. Sweden 1970. 12. M. J. AITKENand S. J. FLEMIIqG,Topics in Radiation Dosimetry (Supp. 1), p. 1. Academic Press, New York, 1972. 13. K. BECKER,Nucl. Inst. Meth. 1972, 104, 405.