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Tracks of heavy charged particles in some natural minerals
0735-245X/90 $3.00 + .00 Pergamon Press plc
Nucl. Tracks Radiat. Meas., Vol. 17, No. 1, pp. 55-57, 1990 Int. 3". Radiat. Appl. Instrum., Part D Printed in Great Britain
TRACKS OF HEAVY C H A R G E D PARTICLES IN SOME N A T U R A L MINERALS B. JAKUPI,*M. BYTYCI,*~.. TODOROVI~,~"R. ANTANASIJEVI(~,~"V. P. PERELYGIN~ and S. G. STETSENKO:~ *Faculty of Science, University of Prigtina, 38000 Pri~tina, Yugoslavia; tlnstitute of Physics, 11001 Beograd, P.O. Box 57, Yugoslavia; and ,Joint Institute for Nuclear Research, Dubna, U.S.S.R.
(Received 31 July 1989) Abstract--We assess the possibilities of registering and analysing heavy charged particles in some naturally occurring minerals from the earth and from meteorites. Using tracks of fission fragments we determine the uranium concentration of the examined minerals, as well as the radiation age in some cases. Based upon the density of the iron-group nuclei of galactic cosmic rays in meteorite minerals, information is obtained concerning their duration in the cosmos and the possible use of these meteorites for analysing the heavy components of galactic cosmic rays. 1. INTRODUCTION IN THElast several years it has been confirmed that the majority of natural minerals are capable of registering heavy charged particles. Tracks of ionizing particles in naturally occurring minerals provide useful information for geology, archaeology, geophysics, astrophysics and various other disciplines. Utilizing minerals as detectors of heavy fragments, one can obtain data concerning the spatial distribution and concentration of fission-activated elements. In addition, on the basis of the density of fossil fission tracks in minerals, the age of the mineral can be determined. In this work we have determined the uranium concentration of several minerals found in Yugoslavia. Geological age is ascertained for some of these analysed minerals. Fossil tracks of galactic cosmic nuclei in meteorite minerals provide useful information about the origin, content and energy of these nuclei. The track density in meteorite minerals falls off exponentially with the depth of the measurement from the outer surface of the meteorite. The majority of nuclei Z ~< 90 are stopped at the outer layer (5 crn thick) of the meteorite. Meteorites with 1& tracks cm-2 iron-group nuclei are the most amenable to analysis of the heavy component of galactic cosmic rays, since this indicates that the minerals are taken from a depth of approximately 5 cm (Bhandari et al., 1973). Here we analyse the minerals from four meteorites which landed in Yugoslavia.
with the samples of the examined minerals, we etched a sample of the same mineral which had been irradiated with xenon and argon ions of an energy of 1-2 MeV u - 1. The conditions during etching of heavy fragment tracks in minerals are described in Table 1. We chose transparent crystals with a dimension greater than 100 # m for etching of tracks in silicate and phosphate minerals. The selected crystals were mounted in epoxy resin and polished. Olivin crystals were etched in WN4 solution at a ph of 7.05 and temperature of 100°C for 8-16 h. Pyroxene crystals were etched in a saturated solution of NaOH at a temperature of 100°C for 0.2-2h. Scanning and measurement of the lengths of the registered tracks were performed using an optical microscope with a magnification of 700-2400 x . The uranium concentration of the examined minerals was measured using the density of the induced fragments registered in the mineral itself, or using an external detector (Abdullaev et al., 1972). Lavsan was used as an external detector. In this case the mineral samples, as a fine powder or thin sheets, depending upon their characteristics, were placed in a vacuum packet of Lavsan. Samples prepared in the described manner, together with the control uranium which was in contact with the Lavsan, were irradiated with thermal neutrons of approximately 1015n cm-2. After exposure, the Lavsan was etched in a 20% solution of NaOH at a temperature of 60°C for 1-3 h. The uranium concentration was determined by the relation:
E C,.NI
2. EXPERIMENTAL M E T H O D S AND RESULTS
C u~ -
We mounted some of the minerals in epoxy resin and then polished them prior to etching, since this facilitated scanning. During defined conditions of fission tracks etching in certain minerals, together
-
N2 Rof
where C., is the concentration of uranium in the target (0.13 10-rgcm-2), N~ is the density of the track in the detector which had been in contact with the sample, N 2 the density of the tracks in the detector 55
56
B. J A K U P I et al. Table 1. Conditions during etching of heavy fragment tracks in minerals
Mineral
Etchant
Concentration (%)
Mica Auripigment
HF NaOH
48 1
Temp. (°C)
Etching time (min)
23 50 100
60-120 2 10-20
23 160 23 100
30 180 1440 180
H20
Calcite
WO4 with additional NaOH to a pH = 12 NaOH HF HNO 3
Quartz Barite
50 48 70
Table 2. Uranium concentration in minerals and their radiation age
Mineral
Site
Mica Mica Auripigrnent Barite Calcite Marmatite Quartz Pyrite
Motajica (Bosanski Kobo~) Bukulja (~utice) Al~,ar Trepta Trepta Trepta Trelx~a Trep~
which had been in contact with the u r a n i u m target, E the efficiency of fission fragment track detection and P~f the thickness of the effective layer of the sample. The thickness of the effective layer of registration was determined by a semiempirical relation (Otgonsuren et al., 1970): P~f = (0.046 =~1a, zi + 0.78 ) where ai is the atomic concentration and z~ is the atomic number of the element in the examined mineral. The geologic age of the mineral was determined by the relation:
Uranium concentration (g g-i)
Age (106yr)
(2.2 -t- 0.18) x 10-s
44
(3.1 -----0.20) × (4.3 + 0.20) x (2.6 _+0.30) x (1.2 +_0.26) x (9.5 _+0.18) × (3.4 +__0.16) x (1.1 -t-0.22) x
19 13 ----
10 -9
10-s 10-s 10-6 I0 -s 10-7 10-7
--
--
age of some of the minerals are given in Table 2. Table 3 displays the u r a n i u m concentrations in the analysed meteorite samples. Geologic age is determined for the mineral mica from the regions of Motajice and Bukulje, and for auripigrnent from the region of AIsar. The values obtained for the geological age of mica are in good agreement with those obtained by the s t r o n t i u m rubidium method (Jakupi et al., 1981). In some of the layers of mica from Motajice, highly dense fission tracks were found along the crack (Fig. 1). U r a n i u m was located in the outer portions of the cracks. This suggests an increased u r a n i u m concentration in the region of Motajice region.
F.~I Np T
~
-
-
2/
• - -
N,
where F is the thermal neutron fluence, tr the effective cross-section for the reaction of 235U ( n , f ) , I is the ratio of the isotopic content of uranium, Np the track density of spontaneous fission, N, the density of the fragment tracks of the induced fission and )./the constant for radioactive decay of u r a n i u m with respect to spontaneous fission. Values for certain concentrations of u r a n i u m in the examined mineral samples and for the radiation
1
Table 3. Uranium concentration in meteorites Meteorite Soko Banja Jelica Milena Zavid
Uranium concentration (g g-~) (3.85 + 0.44) x 10-8 (1.61 _+0.46) x 10-s (2.08 + 0.45) x 10-s (1.80 + 0.46) x 10-8
FIG. I. Spontaneous fission fragment tracks in mica from the region Motajica.
HEAVY C H A R G E D PARTICLE TRACKS
FIG. 2. Spontaneous fission fragment track (centre) and two etch pits due to dislocations in auripigment crystals,
57
FIG.3. Iron-group nuclei tracks from cosmic rays in olivine minerals from meteorite Soko Banja.
Table 4. Mean density and track length of iron group nuclei in olivine and pyroxene Density (Tr cm -2) Mean length (~m) Meteorite olivine pyroxene olivine pyroxene Soko Banja Jelica
4.6 _+ 106 4.6 × 105
8.0 x 106 1.2 xl06
For the mineral auripigment, the radiation age was substantially lower than the age of the site, which is estimated to be 25 million years old. The low radiation age was obtained for two reasons. Firstly, track identification of spontaneous fission in the mineral is difficult. The auripigment tracks have a very pronounced opening (Fig. 2). During prolonged etching the track opening practically covers the length of the track, and this hampers identification. Low thermal stability is the second reason for the low age of auripigment (Todorovi6 et al., 1980). This most likely caused a complete regression of a certain number of spontaneous fission tracks. Fossil tracks of the iron group nuclei were analysed in the meteorite minerals from Soko Banja, Jelica, Zavid and Milena. After etching the olivine and pyroxene in the Soko Banja and Jelica meteorites, the tracks of the iron-group nuclei were identified. The tracks of the iron-group nuclei in olivine meteorite minerals from Soko Banja are shown in Fig. 3. Table 4 displays some of the track density and mean track length values from the iron-group nuclei. We were unable to find crystals with iron-group nuclei in the meteorite samples from Zavid and Milena. The density of the iron-group tracks in olivine mineral from Soko Banja suggests that the analysed samples originate from a depth of approximately 5 cm from the outer surface of the meteorite. In
11 --
15
addition, the mean range of the iron-group nucleus tracks in the olivine mineral from Soko Banja is somewhat less than the mean range of the iron ion tracks (12-14/~ m). This indicates that the Soko Banja meteorite was not exposed to substantial heating during its radioactive age. On the basis of these results, we conclude that the Soko Banja meteorite is suitable for analysis of heavy components of galactic cosmic rays.
REFERENCES Abdullaev H., Kapuscik A., Otgonsuren O., Perelygin V. P. and Chultemm D. (1972) The determination of the concentration of fissionable materials in solid bodies. P T E 2, 78-82. Bhandari N. et al. (1973) Long-term Cosmic ray heavy nuclei fluxes based on observations of meteorites and lunar samples. Astrophys. J. 185, 975-983. Jakupi B., Kosti6 A., Studen M., Perelygin V. P., Stetsenko S. G., Antanasijevi6 R. and Todorovid ~. (1981) La determination de la concentration de l'urane et de la vieillesse g~ologique de certains micas par la m~thode des traces de la fission spontanre. Bull. Mus. Hist. nat. A36, 5-16. Otgonsuren O., Perelygin V. P. and Chulten D. (1970) Build-up of uranium in animal bones. Atomn. Energ. 29, 301-302. Todorovi6 ~., Antanasijevi~ R., Jakupi B., Vukovi~ J. and Mio~inovi6 D. (1980) Fission track annealing of orpiment. Proc. lOth Int. Conf. SSNTD., pp. 805-809.
Nucl. Tracks Radiat. Meas., Vol. 17, No. 1, pp. 55-57, 1990 Int. 3". Radiat. Appl. Instrum., Part D Printed in Great Britain
TRACKS OF HEAVY C H A R G E D PARTICLES IN SOME N A T U R A L MINERALS B. JAKUPI,*M. BYTYCI,*~.. TODOROVI~,~"R. ANTANASIJEVI(~,~"V. P. PERELYGIN~ and S. G. STETSENKO:~ *Faculty of Science, University of Prigtina, 38000 Pri~tina, Yugoslavia; tlnstitute of Physics, 11001 Beograd, P.O. Box 57, Yugoslavia; and ,Joint Institute for Nuclear Research, Dubna, U.S.S.R.
(Received 31 July 1989) Abstract--We assess the possibilities of registering and analysing heavy charged particles in some naturally occurring minerals from the earth and from meteorites. Using tracks of fission fragments we determine the uranium concentration of the examined minerals, as well as the radiation age in some cases. Based upon the density of the iron-group nuclei of galactic cosmic rays in meteorite minerals, information is obtained concerning their duration in the cosmos and the possible use of these meteorites for analysing the heavy components of galactic cosmic rays. 1. INTRODUCTION IN THElast several years it has been confirmed that the majority of natural minerals are capable of registering heavy charged particles. Tracks of ionizing particles in naturally occurring minerals provide useful information for geology, archaeology, geophysics, astrophysics and various other disciplines. Utilizing minerals as detectors of heavy fragments, one can obtain data concerning the spatial distribution and concentration of fission-activated elements. In addition, on the basis of the density of fossil fission tracks in minerals, the age of the mineral can be determined. In this work we have determined the uranium concentration of several minerals found in Yugoslavia. Geological age is ascertained for some of these analysed minerals. Fossil tracks of galactic cosmic nuclei in meteorite minerals provide useful information about the origin, content and energy of these nuclei. The track density in meteorite minerals falls off exponentially with the depth of the measurement from the outer surface of the meteorite. The majority of nuclei Z ~< 90 are stopped at the outer layer (5 crn thick) of the meteorite. Meteorites with 1& tracks cm-2 iron-group nuclei are the most amenable to analysis of the heavy component of galactic cosmic rays, since this indicates that the minerals are taken from a depth of approximately 5 cm (Bhandari et al., 1973). Here we analyse the minerals from four meteorites which landed in Yugoslavia.
with the samples of the examined minerals, we etched a sample of the same mineral which had been irradiated with xenon and argon ions of an energy of 1-2 MeV u - 1. The conditions during etching of heavy fragment tracks in minerals are described in Table 1. We chose transparent crystals with a dimension greater than 100 # m for etching of tracks in silicate and phosphate minerals. The selected crystals were mounted in epoxy resin and polished. Olivin crystals were etched in WN4 solution at a ph of 7.05 and temperature of 100°C for 8-16 h. Pyroxene crystals were etched in a saturated solution of NaOH at a temperature of 100°C for 0.2-2h. Scanning and measurement of the lengths of the registered tracks were performed using an optical microscope with a magnification of 700-2400 x . The uranium concentration of the examined minerals was measured using the density of the induced fragments registered in the mineral itself, or using an external detector (Abdullaev et al., 1972). Lavsan was used as an external detector. In this case the mineral samples, as a fine powder or thin sheets, depending upon their characteristics, were placed in a vacuum packet of Lavsan. Samples prepared in the described manner, together with the control uranium which was in contact with the Lavsan, were irradiated with thermal neutrons of approximately 1015n cm-2. After exposure, the Lavsan was etched in a 20% solution of NaOH at a temperature of 60°C for 1-3 h. The uranium concentration was determined by the relation:
E C,.NI
2. EXPERIMENTAL M E T H O D S AND RESULTS
C u~ -
We mounted some of the minerals in epoxy resin and then polished them prior to etching, since this facilitated scanning. During defined conditions of fission tracks etching in certain minerals, together
-
N2 Rof
where C., is the concentration of uranium in the target (0.13 10-rgcm-2), N~ is the density of the track in the detector which had been in contact with the sample, N 2 the density of the tracks in the detector 55
56
B. J A K U P I et al. Table 1. Conditions during etching of heavy fragment tracks in minerals
Mineral
Etchant
Concentration (%)
Mica Auripigment
HF NaOH
48 1
Temp. (°C)
Etching time (min)
23 50 100
60-120 2 10-20
23 160 23 100
30 180 1440 180
H20
Calcite
WO4 with additional NaOH to a pH = 12 NaOH HF HNO 3
Quartz Barite
50 48 70
Table 2. Uranium concentration in minerals and their radiation age
Mineral
Site
Mica Mica Auripigrnent Barite Calcite Marmatite Quartz Pyrite
Motajica (Bosanski Kobo~) Bukulja (~utice) Al~,ar Trepta Trepta Trepta Trelx~a Trep~
which had been in contact with the u r a n i u m target, E the efficiency of fission fragment track detection and P~f the thickness of the effective layer of the sample. The thickness of the effective layer of registration was determined by a semiempirical relation (Otgonsuren et al., 1970): P~f = (0.046 =~1a, zi + 0.78 ) where ai is the atomic concentration and z~ is the atomic number of the element in the examined mineral. The geologic age of the mineral was determined by the relation:
Uranium concentration (g g-i)
Age (106yr)
(2.2 -t- 0.18) x 10-s
44
(3.1 -----0.20) × (4.3 + 0.20) x (2.6 _+0.30) x (1.2 +_0.26) x (9.5 _+0.18) × (3.4 +__0.16) x (1.1 -t-0.22) x
19 13 ----
10 -9
10-s 10-s 10-6 I0 -s 10-7 10-7
--
--
age of some of the minerals are given in Table 2. Table 3 displays the u r a n i u m concentrations in the analysed meteorite samples. Geologic age is determined for the mineral mica from the regions of Motajice and Bukulje, and for auripigrnent from the region of AIsar. The values obtained for the geological age of mica are in good agreement with those obtained by the s t r o n t i u m rubidium method (Jakupi et al., 1981). In some of the layers of mica from Motajice, highly dense fission tracks were found along the crack (Fig. 1). U r a n i u m was located in the outer portions of the cracks. This suggests an increased u r a n i u m concentration in the region of Motajice region.
F.~I Np T
~
-
-
2/
• - -
N,
where F is the thermal neutron fluence, tr the effective cross-section for the reaction of 235U ( n , f ) , I is the ratio of the isotopic content of uranium, Np the track density of spontaneous fission, N, the density of the fragment tracks of the induced fission and )./the constant for radioactive decay of u r a n i u m with respect to spontaneous fission. Values for certain concentrations of u r a n i u m in the examined mineral samples and for the radiation
1
Table 3. Uranium concentration in meteorites Meteorite Soko Banja Jelica Milena Zavid
Uranium concentration (g g-~) (3.85 + 0.44) x 10-8 (1.61 _+0.46) x 10-s (2.08 + 0.45) x 10-s (1.80 + 0.46) x 10-8
FIG. I. Spontaneous fission fragment tracks in mica from the region Motajica.
HEAVY C H A R G E D PARTICLE TRACKS
FIG. 2. Spontaneous fission fragment track (centre) and two etch pits due to dislocations in auripigment crystals,
57
FIG.3. Iron-group nuclei tracks from cosmic rays in olivine minerals from meteorite Soko Banja.
Table 4. Mean density and track length of iron group nuclei in olivine and pyroxene Density (Tr cm -2) Mean length (~m) Meteorite olivine pyroxene olivine pyroxene Soko Banja Jelica
4.6 _+ 106 4.6 × 105
8.0 x 106 1.2 xl06
For the mineral auripigment, the radiation age was substantially lower than the age of the site, which is estimated to be 25 million years old. The low radiation age was obtained for two reasons. Firstly, track identification of spontaneous fission in the mineral is difficult. The auripigment tracks have a very pronounced opening (Fig. 2). During prolonged etching the track opening practically covers the length of the track, and this hampers identification. Low thermal stability is the second reason for the low age of auripigment (Todorovi6 et al., 1980). This most likely caused a complete regression of a certain number of spontaneous fission tracks. Fossil tracks of the iron group nuclei were analysed in the meteorite minerals from Soko Banja, Jelica, Zavid and Milena. After etching the olivine and pyroxene in the Soko Banja and Jelica meteorites, the tracks of the iron-group nuclei were identified. The tracks of the iron-group nuclei in olivine meteorite minerals from Soko Banja are shown in Fig. 3. Table 4 displays some of the track density and mean track length values from the iron-group nuclei. We were unable to find crystals with iron-group nuclei in the meteorite samples from Zavid and Milena. The density of the iron-group tracks in olivine mineral from Soko Banja suggests that the analysed samples originate from a depth of approximately 5 cm from the outer surface of the meteorite. In
11 --
15
addition, the mean range of the iron-group nucleus tracks in the olivine mineral from Soko Banja is somewhat less than the mean range of the iron ion tracks (12-14/~ m). This indicates that the Soko Banja meteorite was not exposed to substantial heating during its radioactive age. On the basis of these results, we conclude that the Soko Banja meteorite is suitable for analysis of heavy components of galactic cosmic rays.
REFERENCES Abdullaev H., Kapuscik A., Otgonsuren O., Perelygin V. P. and Chultemm D. (1972) The determination of the concentration of fissionable materials in solid bodies. P T E 2, 78-82. Bhandari N. et al. (1973) Long-term Cosmic ray heavy nuclei fluxes based on observations of meteorites and lunar samples. Astrophys. J. 185, 975-983. Jakupi B., Kosti6 A., Studen M., Perelygin V. P., Stetsenko S. G., Antanasijevi6 R. and Todorovid ~. (1981) La determination de la concentration de l'urane et de la vieillesse g~ologique de certains micas par la m~thode des traces de la fission spontanre. Bull. Mus. Hist. nat. A36, 5-16. Otgonsuren O., Perelygin V. P. and Chulten D. (1970) Build-up of uranium in animal bones. Atomn. Energ. 29, 301-302. Todorovi6 ~., Antanasijevi~ R., Jakupi B., Vukovi~ J. and Mio~inovi6 D. (1980) Fission track annealing of orpiment. Proc. lOth Int. Conf. SSNTD., pp. 805-809.