ETCHING EFFICIENCY OF THE TRACKS UNDER THEIR DIFFER ORIENTATION RELATIVELY TO THE CRYSTAL

LATTICE SYMMETRICAL AXIS IN THE OLIVINE MONOCRYSTALS

A.B.Alexandrov, A.V.Bagulya, L.A., Goncharova, A.I. Ivliev, G.V. Kalinina, L.L. Kashkarov, N.S.Konovalova, N.G. Poluhina, A.S.Rusetskii, N.I. Starkov

Lebedev Physical Institute, Russian Academy of Sciences, Moscow.

Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow.

cosmo@geokhi.ru ugeochem@geochem.home.chg.ru

Annotation

- Olivine mineral from the meteorites of the type pallasite is one of the best natural track detectors for registration of super heavy (Z ≥ 50) nuclei in the composition of the galactic cosmic rays.

- The method being developed for the nuclei charge identification must consider the possible relationship between the parameters of the chemically etched tracks and their orientation to the olivine crystal lattice symmetrical axis.

- In work there are presented the measurement results for major parameters (etching rate VTR, length L, and diameter D) of tracks formed by the accelerated nuclei 131Хе (Е=1.5 GeV) in ten individual olivine grains with different crystal structure characteristics from the Marjalahti pallasite.

Passing of the high-energy accelerated Xe and U nuclei through olivine matter, composition of the Marjalahti pallasite

• Profile of energy loss for Xe131 and U238 beams passing through olivine of composition (Mg 0.88 Fe 0.12 )2 SiO4

• Critical energy losses (dE/dx)el,cr for the olivine crystal and energy dependence value for the chemically etched 131Xe nuclei tracks at energy E=11.4 MeV/nuclon

E m ax

E st

E fin

E m in

Track length (L) distribution in olivine crystals irradiated by the accelerated nuclei of Xe (a, b) and U (c, d), Emax = 11.4 MeV/nucl.

a

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100

Nb

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100

c

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100

N d

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100R, мкм

X-ray analysis of individual olivine grains from the Marjalahti pallasite

Noolivinegrain

Radiation Orientation Deviationangle

=| - |

Observed reflex

Intensity(%)

(∆/) Monocrystaldegree

1

MoK (020) ~0.7

(020)(040)(080)

(0.10.0)

1002

0.81.5

3·10-2 Low

2 MoK (134) ~0.13 (134) 100 8·10-3 Middle

3

MoK (020) ~0.2

(020)(040)(080)

((0.10.0)(0.12.0)

10056

1711

4·10-3 High

4CuK (131) <0.1

(131)(262)

1002.5

1·10-3 High

5CuK (101) ~3.6

(101)(202)

1006

1·10-3 High

6 CuK (021) ~0.5 (021) 100 2·10-3 Middle

7CuK (002) ~3.1

(002)(004)(006)

111003

1.3·10-3 Highqualitytextura

8 CuK (041) ~3.8 (041) 100 1·10-3 High

9 CuK (112) ~13 (112) 100 6·10-3 Middle

10 CuK - - - - - Policrystal

Microphotographs of the entrance track holes, etched on surface of irradiated by accelerated (Emax=11.4 MeV/nucleon) 131Xe nuclei olivine

dc

ab

Etching conditions

Etching time: 12, 24, 36 and 48 hours (a-d).

Track etching was doing in the modified solution (pH=8.60.2) at 110oC in a hermetically closed vessel

[Petrova, Perelygin et al.,Radiat. Meas. (1995) v.25, nos 1-4, p. 329] .

The size of an each field of vision ~3050 µm.

Distribution of diameters D (in un.0.384 μm) and lengths L (in un.1.70 μm) for the tracks of 131Хе ions with Emax = 1.50 GeV in the olivine crystals

from the Marjalahti pallasite. Etching time 12 h.

2.0 2.5 3.0 3.5 4.0 4.5 5.00

2

4

6

8

10

12

14

N№1

40 42 44 46 48 50 520

2

4

6

8

10

12

N

2.0 2.5 3.0 3.5 4.0 4.5 5.00

2

4

6

8

10

12

№2N

40 42 44 46 48 50 520

2

4

6

8

10

12

N

Continuous

2.0 2.5 3.0 3.5 4.0 4.5 5.00

2

4

6

8

10

12

14

N №3

D42 44 46 48 50 52

0

2

4

6

8

10

12

N

L

Conclusion

• - Configuration and dimension of the track entry oval holes on the crystal etching surface (as a rule, they are irregular-shaped) differ what can be explained by dependence of the etching rate for undisturbed crystal matter (VB) from the track angles with the symmetrical axis of its undisordered lattice;

• - There is no dependence between the entry hole geometry form and the form of the near-surface section of track that is observable as round, normal section;

• - No interdependence in full etched track-length and their etching rate due to orientation concerning the basic planes (axes) of olivine crystal symmetry have been detected. That is connected with:

• - "island" structure of an olivine crystal lattice;• - relation of the cross-section sizes of a zone of radiation

disordering of an olivine crystal lattice ~(30-60 Å) and the sizes of elementary olivine crystal cells ~3 Å.