Scintillating substance and scintillating wave-guide element

The invention is related to nuclear physics, medicine and oil industry, namely to the measurement of x-ray, gamma and alpha radiation; control for trans uranium nuclides in the habitat of a man; non destructive control for the structure of heavy bodies; three dimensional positron-electron computer tomography, etc. The essence of the invention is in additional ingredients in a chemical composition of a scintillating material based on crystals of oxyorthosilicates, including cerium Ce and crystallized in a structural type Lu.sub.2 SiO.sub.5. The result of the invention is the increase of the light output of the luminescence, decrease of the time of luminescence of the ions Ce.sup.3+, increase of the reproducibility of grown crystals properties, decrease of the cost of the source melting stock for growing scintillator crystals, containing a large amount of Lu.sub.2 O.sub.3, the raise of the effectiveness of the introduction of SCintillating crystal luminescent radiation into a glass waveguide fibre, prevention of cracking of crystals during the production of elements, creation of waveguide properties in scintillating elements, exclusion of expensive mechanical polishing of their lateral surface.

FIELD OF INVENTION
 The invention is related to nuclear physics, medicine and oil industry,
 namely to scintillating materials, and is meant for: registration and
 measurement of an x-ray, gamma and alpha radiation; control for trans
 uranium radio nuclides in the habitat of a man (in particular, in the
 zones of Chernobyl catastrophe); sparing (non-destructive) control of the
 structure of hard bodies; three dimensional positron-electron computer
 tomography and x-ray computer fluorography without the use of photo films;
 as well as for the control of the level of liquid in oil reservoirs.
 DESCRIPTION OF RELATED ART
 Known is the material of lutetium oxyorthosilicate with cerium
 LU.sub.2(1-x) Ce.sub.2x SiO.sub.5 where x is varying in the range from
 2.times.10.sup.-4 to 3.times.10.sup.-2 (U.S. Pat. No. 4,958,080: date of
 Patent Sept. 18, 1990, "Lutetium orthosilicate single crystal Scintillator
 detector", Inventor C. I. Melcher, W. Redding Assignee: Schlumberger
 Technology Corp., as well as Victorov L. V., Skorikov V. M., Zhukov V. M.,
 Shulgin B. V. "Inorganic scintillating materials", Published by the
 Academy of Sciences of the USSR, series Inorganic materials, volume 27, N
 10, pages 2005-2029, 1991). These scintillating crystals Lu.sub.2(1-x)
 Ce.sub.2x SiO.sub.5 have a number of advantages compared to other
 crystals: bigger density, high atomic number, relatively low refractive
 index, high light output, short time for scintillations decay. The
 drawback of the known scintillating material is a big scattering of the
 most important scintillating parameters:
 the value of a light output, the position of a luminescence maximum and
 time of luminescence. This is explicitly demonstrated by experimental
 results (J. D. Naud, T. A. Tombrello, C. I. Melcher, J. S. Schweizer "The
 role of cerium sites in the scintillation mechanism of LSO" IEEE
 transactions on nuclear science, vol. 43, N 3, (1996), p. 1324-1328.)
 The scattering of scintillating elements patameters of lutetium
 oxyorthosilicate with cerium is the result of a small coefficient of
 cerium ions distribution between a growing crystal and melt (Kc.sub.e
 =0.25), as a result of which a boule, grown by Czochralski method, has a
 concentration of cerium which is several times higher in the lower part
 than in the upper one. This brings about the fact that the light output of
 samples luminescence is 2-5 times lower in the lower part than in the top
 part, and the decay time is increased from 41 ns to 50 ns. Such scattering
 of parameters allows to use only a small part of a crystal boule for the
 production of scintillating elements.
 As a prototype for the proposed invention it is possible to select
 scintillating crystals of the company Hitachi Chemical Co. Ltd. (Tokyo,
 Japan), having the composition, represented by the following chemical
 formula Gd.sub.2-(x+e) Ln.sub.x Ce.sub.y SiO.sub.5, where Ln=Sc, Tb, Dy,
 Ho, Er, Tm, Yb and 0.03.ltoreq.x.ltoreq.1.9, 0.00.ltoreq.y.ltoreq.0.2
 (European patent ER 0456 002B1: Date of publication Jun. 11, 1996 "Single
 crystal scintillator and apparatus for prospecting underground strata
 using same". Inventor S. Akiyama, T. Utsu, H. Ishibashi, C. I. Melcher, J.
 S. Schweizer, Assignee: Hitachi Chemical Ltd., as well as U.S. Pat. No.
 5,264,154: date of Patent Mar. 11, 1996, "Single crystal scintillator",
 Inventor S. Akiyama, H. Ishibashi, T. Utsu, C. I. Melcher, J. S.
 Schweizer, Assignee: Hitachi Chemical Co. Ltd).
 In prototype crystals it is possible to substitute a Gd.sup.3+ ion with a
 big radius for an ion with a small radius, for example, for Lu.sup.3+ ion.
 This allows to control some scintillation parameters, in particular, to
 shift a maximum peak of luminescence from 430 nm up to 416 nm--in the
 field of a greater sensitivity of photoelectronic multipliers. The change
 of prototype crystals composition also allows to smoothly change their
 density and to decrease the time of luminescence for Ce.sup.3+ ions up to
 30 ns. Even with a non-significant content of Gd in melt .about.20 mol %,
 it is possible to increase the homogeneity of the crystals grown, because
 of the increase of cerium ions distribution coefficient.
 The drawbacks of the prototype are the decrease of the light output of
 luminescence and of effective atomic number, compared to known crystals of
 lutetium oxyorthosilicate. Comparison of the light output of the prototype
 with the known crystals of Ce.sub.2-x Lu.sub.2(1-x) SiO.sub.5 are made by
 the authors of the given invention and are summed up in table 1 (G. B.
 Loutts, A. I. Zagumennyi, S. V. Lavrishchev, Yu. D. Zavartsev, and P. A.
 Studenikin "Czochralski growth and characteristics of (Lu.sub.1x
 Gd.sub.x).sub.2 SiO.sub.5 single crystals for scintillators". J. Crystal
 Growth, Vol. 174 (1997), p. 331-336).
 To the drawbacks of the prototype can also be referred that with the
 content of Gd of more than 50 at. % in the melt, these materials are
 crystalized in a monoclinic syngony with the spatial group P2.sub.1 /c,
 Z=4.
 In crystals with such a spatial group, deterioration of scintillation
 characteristics of ion Ce.sup.3+ is observed, compared to known crystals
 of Ce.sub.2-x Lu.sub.2(1-x) SiO.sub.5, which are crystallized in a
 structural type with a spatial group B2/b, Z=8. So, for example, in
 crystals with a spatial group P2.sub.1 /c observed are: the increase of a
 constant for the time of scintillations decay .tau. up to 50-60 ns; the
 displacement of the peak of luminescence up to 430-440 nm, where the
 sensitivity of electronic photomultipliers is less. One more essential
 drawback of crystals with a spatial group P2.sub.1 /c is a strong cracking
 during crystal boule cutting and their polishing, which sharply increase
 the cost of manufacturing elements of the size 2 mm.times.2 mm.times.15 mm
 for three dimensional positron-electron tomography with the resolution of
 8 mm.sup.3.
 The essential technical drawback of known scintillating crystals Ce.sub.2-x
 Lu.sub.2(1-x) SiO.sub.5 and crystals of the prototype is the growing of
 crystals from melting stock, containing an extremely expensive reagent
 Lu.sub.2 O.sub.3 with the chemical purity of not less than 99.99%. The
 common drawback of these materials is also the impossibility of creating
 scintillating waveguide elements at the expense of refractive index
 gradient along the waveguide cross section.
 SUMMARY OF INVENTION
 The technical task of the invention is the increase of the light output of
 luminescence, decrease of the time of luminescence of ions Ce.sup.3+,
 increase of the reproducibility of properties of grown single crystals,
 decrease of the cost of source melting stock for growing crystals
 scintillators, contained in great amount of Lu.sub.2 O.sub.3, the
 extension of the arsenal of technical facilities, implementing
 scintillating properties, the increase of effectiveness of the
 introduction of scintillating crystal luminescent radiation into glass
 waveguide fibre. In specific forms of implementation the task of the
 invention is also the prevention of crystals cracking during cutting and
 manufacturing scintillation elements, creation of waveguide properties in
 scintillation elements at the expense of refractice index gradient along
 its cross section, exclusion of expensive mechanical polishing of the
 lateral surface of scintillating crystals at the stage of their growth.
 The technical result is achieved due to the growing of crystals in a
 structural type Lu.sub.2 SiO.sub.5 with a spatial group B2/b (Z=8), as
 well as at the expense of an advantageous content of Ce.sup.3+ ions in a
 crystal. As our research has shown, oxyorthosilicates are crystallized
 with a spatial group B2/b only in the case if the content of lutetium in a
 crystal is not less than 50 at. % and/or the parameter of a scintillating
 material lattice does not exceed the following maximum values: a=1.456 nm;
 b=1/051 nm; c=0.679 nm; .beta.=122.4.degree..
 In crystals with a spatial group B2/b (Z=8) an anomaly high scintillating
 light output for ions Ce.sup.3+ is observed, compared to all other known
 compositions of silicates, which as a rule have 2-5 times less light
 output during gamma excitation.
 The share of x-ray radiation, transformed into the energy of primary
 electrons, and especially the effectiveness of interaction of
 gamma--quantum with the material of a scintillator, approximately depends
 in proportion to the cube of effective atomic number. For .gamma.--quanta
 with the energy of E.sub..gamma..ltoreq.1.022 MeV, interaction of .gamma.
 quanta with the material of a scintillating crystal takes place due to the
 process of photo effect, non coherent and coherent scattering. With the
 energies exceeding a doubled energy of electrons state of rest
 (E.gamma.&gt;1.022 MeV), a process of formation of electron--positron pairs
 is also added. It is supposed that in the formation of a pair each of
 interacted primary .gamma. quanta gives birth to at least three secondary
 scattered .gamma. quanta. Two of which having an energy of 0.511 MeV each,
 and represent radiation, appearing in electron and positron annihilation.
 It is obvious from that that in a three dimensional positron-electron
 tomography it is preferable to use scintillating crystals with a greater
 effective atomic number. In the process of crystal growth heavy ions of
 Lu.sup.3+ which are replaced by lighter admixture ions Me.sup.1+,
 Me.sup.2+, Me.sup.3+, Me.sup.4+, Me.sup.5+, Me.sup.6+, can cause the
 growth of a crystal with a smaller density of 7.2-7.4 g/cm.sup.3, and
 atomic number Z=58-63. In growing large crystal boules by the method of
 Czochralski for compensating the charge and for the correction of
 effective atomic number, it is preferable to use heavy ions Hf.sup.4+,
 Ta.sup.5+ and W.sup.6+, which prevents the changing of physical parameters
 (density, refractive index) along the diameter of large crystals (40-80
 mm) and additionally allows to receive crystals with identical
 scintillation parameters, i.e. to increase the reproducibility of
 properties of scintillating elements, which are manufactured from grown
 single crystals.
 The spatial group B2/b (z=8) contains 64 ions in an elemental unit, in
 particular 8 ions of lutetium of the first type (Lu.sub.1) and eight ions
 of lutetium of the second type (Lu.sub.2). The energy of substitution
 Ce.sup.3+ {character pullout}Lu.sub.1 is equal to +6.90 eV, and the energy
 of substitution of Ce.sup.3+ {character pullout}Lu.sub.2 is equal to +7.25
 eV. In both the cases the energy of substitution is positive, as ion
 radius Ce.sup.3+ is greater than the ion radius Lu.sup.3+. Different
 displacement of oxygen ions after the substitution of Ce.sup.3+ {character
 pullout}Lu.sub.1, Lu.sub.2 in coordination polyhedron LuO.sub.7 and
 LuO.sub.6 determine principally different scintillation characteristics of
 the material. The light output, the position of the luminescence maximum
 and the constant of time for scintillations decay (time of luminescence)
 depend on the number of Ce.sup.3+, which substituted ions Lu.sub.1 and/or
 ions Lu.sub.2. So, in gamma excitation both centres of luminescence are
 always excited and luminescence simultaneously, and the constant of time
 for scintillations decay will depend both on the duration of luminescence
 of the first and second centres, and on the relationship of the
 concentration of ions of Ce.sup.3+ in coordination polyhedrons LuO.sub.7
 and LuO.sub.6. The centre of luminescence Ce.sub.1 (polyhedron LuO.sub.7)
 has the time of luminescence of 30-38 ns and the position of the
 luminescence maximum 410-418 um. The centre of luminescence Ce.sub.2
 (polyhedron LuO.sub.6) has the time of luminescence of 50-60 ns and the
 position of maximum luminescence of 450-520 nm. The maximum technical
 result is observed in scintillating crystals containing ions Ce.sup.3+
 only in coordination polyhedrons LuO.sub.7. The simultaneous presence of
 Ce.sup.3+ ions in Lu.sub.7 and LuO.sub.6 decreases the light output 3-10
 times, increasing the time of luminescence up to 40-50 ns and shifts the
 luminescence maximum into the area of less sensitivity of photo electron
 multipliers. The crystals containing ions of Ce.sup.3+ advantageously in
 coordination polyhedrons Lu.sub.7 are received from the melt additionally
 doped with ions of the following elements: Zr, Sn, Hf, As, V, Nb, Sb, Ta,
 Mo, W. By that, ions Ti, Zr, Sn, Hf, Nb, Sb, Ta occupy in the crystal
 lattice the position with octahedral coordination (polyhedron LuO.sub.6)
 due to higher bond energies of these ions. For example, ions As, V, Mo, W,
 occupy tetrahedral positions, however with that the octahedral positions
 are strongly distorted.
 Additional technical result is achieved by the use as a source reagent of
 Lu.sub.2 O.sub.3 with the purity of 99.9% (or less) instead of reagent
 Lu.sub.2 O.sub.3 with a purity of 99.99% and purity of 99.999% used in the
 prototype, which allows to decrease the cost of a melting stock for
 growing crystals 2.5-3 times. Some admixtures in the source reagent
 Lu.sub.2 O.sub.3 with the purity of 99.9% (or less) can decrease the light
 output of luminescence 2-10 times. The decrease of the light output occurs
 due to the formation of Ce.sup.4+ ions in heterovalent substitution which
 takes place during the growth of crystal on the background of
 crystallization. Below listed are the simplest schemes of substitution:
 (1) Lu.sup.3+ +Si.sup.4+ {character pullout}Ce.sup.3+ +Si.sup.4+ --optimal
 substitution of lutetium ions by cerium ions.
 (2) Lu.sup.3+ +Si.sup.4+ {character pullout}Ce.sup.+4 +Me.sup.3+ --highly
 probable, harmful and undesirable heterovalent substitution with the
 compensation of charge for admixtures Me.sup.3+.ltoreq.Be, B, Al, Cr, Mn,
 Fe, Co, Ga, In.
 (3) 2Lu.sup.3+ {character pullout}Ce.sup.4+ +Me.sup.2+ --highly probable,
 harmful and undesirable heterovalent substitution with the compensation of
 charges for admixtures Me.sup.2+ =Mg, Ca, Mn, Co, Fe, Zn, Sr, Cd, Ba, Hg,
 Pb.
 (4) 3Lu.sup.3+ {character pullout}Ce.sup.+4 +Ce.sup.+4 +Me.sup.1+
 --probable harmful and undesirable heterovalent substitution with the
 compensation of charge at big concentrations of cerium ions for admixtures
 Me.sup.+ =Li, Na, K, Cu, Rb, Cs, Tl.
 However, the additional introduction into the melt of at least one of
 chemical compounds (for example, oxide) of the elements of the group Zr,
 Sn, Hf, As, V, Nb, Sb, Ta, Mo, W in the amount 2-3 times greater than the
 summary concentration in atomic percent of admixture ions (Me.sup.+
 +Me.sup.3+ +Me.sup.3+) eliminated the formation of Ce.sup.+4 ions in the
 process of the crystal growth. This related to the fact that at the
 background of crystallization there takes place a heterovalent
 substitution according to energetically more beneficial schemes with the
 compensation of charge
 (5) Lu.sup.3+ +Si.sup.4+ {character pullout}Me.sup.2+ +Me.sup.5+
 (6) Lu.sup.3+ +Si.sup.4+ {character pullout}Me.sup.+ +Me.sup.6+
 (7) Lu.sup.3+ +Si.sup.4+ {character pullout}Me.sup.4+ +Me.sup.3+
 In the specific form of invention implementation the technical result,
 expressed in the prevention of crystals cracking during cutting and
 manufacturing of scintillating elements is achieved by way of additional
 introduction into the material of at least one of the elements of the
 group H, F, Li, Be, B, Na, Mg, Al, K, Ca, Ti, V, Cr, n, Fe, Co, Ni, Cu,
 Zn, Ga, Ge, As, Rb, Sr, Zr, Nb, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, Hf, Ta, W,
 Hg, Tl, Pb, Bi.
 Crystalline boules, containing heterovalent micro admixtures with a non
 compensated charge, are responsible for cracking in the process of growth
 of a crystal and its cutting. That is why, for example, the addition into
 a scintillating material of a necessary quantity of ions, having the
 degree of oxidation of +4, +5, +6 (for example, Zr, Sn, Hf. As, V, Nb, Sb,
 Ta, Mo, W, Th) allows to prevent the cracking of crystals in the process
 of growth, as well as during cutting single crystal boules and
 manufacturing elements. The above ions in an optimal concentration provide
 for the heterovalent substitution with the compensation of charge
 according to equation (5), (6), (7).
 Independent technical result--the creation of waveguide properties in a
 waveguide element along its cross section is achieved irrespective of
 spatial structure of oxyorthosilicate being crystallized, i.e.
 independently of the content of lutetium in a crystal because of the
 additional, compared to the prototype, content in a scintillating material
 of at least one elements of the group: H, F, Li, Be, B, C, N, Na, Mg, Al,
 P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb,
 Sr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, Hf, Ta, W, Re, Os,
 Ir, Pt, Au, Hg, Ti, Pb, Bi, U, Th. While the availability in the central
 part of a scintillating element of ions F and/or H, Li, Be, B, C, N, Na,
 Mg, Al, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As,
 Se, Rb, Sr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, Sc, Y, La,
 Ce, Pr, Nd, Sm, Eu, Th, Dy, Ho, Er, Tm, Yb, Lu in a lesser concentration,
 and heavy ions of Hf, Ta, W, Re, Os, Ir, Au, Hg, Tl, Pb, Bi, U, Th in a
 greater concentration than in the peripheral zone of the volume-causes
 wave guide properties of this element.
 The specific case of the offered invention is the growing of the described
 above crystals in inert, restoring or weakly oxidising environments. Under
 these conditions the vacancies in oxygen sub--lattice are formed in
 crystals and the composition of crystal is described by the formula:
 Lu.sub.1 A.sub.1-x, Ce.sub.x SiO.sub.5-z, where A--Lu and at least one of
 the elements of the group Gd, Sc, Y, La, Pr, Nd, Sm, Eu, Th, Dy, Ho, Er,
 Tm, Yb, x--the concentration of cerium ions, z--concentration of oxygen
 vacancies. With the small concentration of vacancies in the oxygen
 sub--lattice, vacancies weakly influence upon the times of luminescence of
 ions Ce.sup.3+ and the light output of scintillating materials, however
 the increase of concentration brings about the sharp decrease of the light
 output. In this connection the proposed scintillating material with oxygen
 vacancies has to be considered as an individual case of the present
 invention. The presence in the source reagents or the addition in
 necessary quantity into the scintillating material of ions, having the
 degree of oxidation of +4, +5, +6 (for example, Zr, Sn, Hf, As, V, Nb, Sb,
 Ta, Mo, W, Th) interferes with the formation of vacancies in an oxygen
 sub--lattice.
 Raising the efficiency of introducing radiation from scintillating crystal
 into the glass waveguide fibre, is an independent technical task. This
 technical result is achieved by way of using waveguide scintillating
 element, i.e. creating waveguide properties in the scintillating element
 itself at the expense of the refractive index gradient along its cross
 section. The refractive index gradient appears in crystal because of the
 difference of the chemical composition of its central part from the
 chemical composition of its lateral part, similar to glass optical
 waveguides, used for the optical transmission of information ["Reference
 book on laser technology". Translation from German by V. N. Belousov,
 Moscow, "Energoizdat", 1991, page 395// WISSENSSPREICHER LASERTXCHNIK/
 Witolf Brunner, Klaus Junge./ VEB Fachbucherverlag Leipzig, 1987]. The
 refractive index of the central part of the scintillating waveguide
 element should be grater than that of the peripheral part. In this case a
 scintillation element acquires an additional property: it focuses
 radiation along the axis of an element, as a result of which the radiation
 goes out of the scintillating element with a smaller divergence than from
 usual scintillating elements. This allows to decrease the divergence and,
 as a consequence, decrease the losses of radiation during its introduction
 into a glass fibre. Decease of the refractive index of the peripheral part
 of the scintillating element due to the change of the crystal composition
 can be achieved by any of the known methods or their combination:
 growing of a profiled crystal, which allows to immediately receive
 crystals, the composition of the peripheral part of which is different
 from their central part.
 diffusion of light atoms from the melt,
 diffusion from hard phase or gas phase into the surface layer of the
 scintillation element.
 Additionally, for strengthening the waveguide effect, after growth and/or
 non polished surfaces of scintillating elements can be polished
 chemically. Bt that all lateral surfaces can be polished simultaneously at
 scintillating elements in the amount 2-100 pieces (or more), for example,
 with the size 2.times.2.times.15 mm or 3.times.3.times.15 mm. For etching
 it is possible to use any polishing mixtures of acids, based on H.sub.3
 PO.sub.4 with the addition of any acids, for example, HNO.sub.3, H.sub.2
 SO.sub.4, HCl, HF. For improvement of polishing properties any organic or
 inorganic salts containing ions H, Li, Be, B, C, N, F, Na, Mg, Al, Si, P,
 S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb,
 Sr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Cs, Ba, Sc, Y, La,
 Ce, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir,
 Pt, Au, Hg, Ti, Pb, Bi, U can be added to the mixture of acids. Comparison
 of scintillating elements with mechanically polished surfaces and
 chemically polished elements has shown that chemical polishing provides
 for the increase of the refractive capacity of the surface of any
 scintillating element, including a waveguide element.
 Both the growing of profiled scintillating crystals, and the additional
 chemical polishing of scintillating element surfaces, allows to achieve a
 positive technical result--the exclusion of expensive mechanical polishing
 of lateral surfaces of scintillating crystals, including that at the stage
 of their growth. It is necessary to point out that growing of profiled
 scintillating crystals allows to avoid an expensive polishing of lateral
 surfaces due to the introduction into the material of the above
 admixtures. These admixtures, at certain concentrations, allow to suppress
 the evaporation of easily volatile components from the surface of the
 growing crystal. As a result the surface of blanks for scintillation
 elements is smooth, does not require further mechanical polishing. In
 separate cases an additional chemical polishing of the lateral surfaces of
 scintillating elements is required.
 Waveguide scintillating elements with the refractive index gradient along
 its cross section allow for almost two times increase the effectiveness of
 the introduction of radiation into a glass waveguide fibre (with the
 length of 4-5 meters), which transmits radiation from a scintillation
 crystal to the photo electronic multiplier. The presence of a glass
 waveguide fibre is principle and obligatory design element in a new type
 of medical three dimensional tomographs, in which simultaneously used are
 two different physical methods of obtaining image of a man's brain:
 electron--positron tomography for metabolic process in the brain and
 magnetic resonance tomography for the creation of the map of the anatomic
 composition of the brain. Magnetic resonance tomography requires the
 placement of metal containing components of photo electronic multipliers
 at certain distance, and because of that the use of a glass waveguide
 fibre is the only possibility to combine electron-positron tomography with
 magnetic resonance tomography in one device. That is why the use of a
 waveguide scintillating element which can be manufactured from any
 scintillating material (Ce: Gd.sub.2 SiO.sub.5, Ce:Lu.sub.3 Al.sub.5
 O.sub.12, Ce:YAlO.sub.3, Bi.sub.4 Ge.sub.3 O.sub.12 and others), can be
 considered as an application for new purpose of the material, having a
 waveguide properties, at the expense of the refractive index gradient
 along its cross section.
 1. Scintillating material based on known crystals of oxyorthosilicates,
 including cerium Ce and crystallized in a structural type of LU.sub.2
 SiO.sub.5 with a spatial group B2/b, Z=8, the composition of which is
 represented by the chemical formula
EQU Lu.sub.1 A.sub.1-x Ce.sub.x SiO.sub.5
 where A--Lu and at least one of the elements of the group Gd, Sc, Y, La,
 Pr, Nd, Sm, Eu, Th, Dy, Ho, Er, Tm, Yb,
EQU x--from 1.times.10.sup.-4 f. units up to 0.2 f. units
 wherein it contains at least one element of the group Zr, Sn, Hf, As, V,
 Nb, Sb, Ta, Mo, W in the range from 1.times.10.sup.17 atom/cm.sup.3 up to
 5.times.10.sup.20 atom/cm.sup.3.
 The lower limit of these elements is determined by the fact that at
 concentrations lower than the above limit of the technical result, the
 increase of the light output of luminescence, decrease of the time of
 luminescence for ions Ce.sup.3+, increase of the reproducibility of the
 properties of grown single crystals, decrease of the cost of source
 melting stock for growing crystals of scintillators, containing in great
 amount of LU.sub.2 O.sub.3 --are not observed. With the concentrations of
 the above elements lower that the above limit, the implementation of the
 technical task in individual forms of execution is also not achieved,
 namely it is not possible to prevent the cracking of crystals during
 cutting and manufacturing of scintillating elements, if as a source
 reagent used is LU.sub.2 O.sub.3 with the purity of 99,9% (or less).
 The upper limit of these elements is determined by their maximum possible
 content in crystals, which are crystallized in a structural type LU.sub.2
 SiO.sub.5 with a spatial group b2/b (Z=8). When their content is above the
 indicated limit, the destruction of the structural type LU.sub.2 SiO.sub.5
 takes place and the formation of inclusions of other phases, which
 determine the scattering of light and the decrease of transparency of a
 scintillating crystal.
 2. Scintillating material based on known crystals of oxyorthosilicate,
 including cerium Ce, the composition of which is represented by the
 chemical formula
EQU A.sub.2-x Ce.sub.x SiO.sub.5
 where A--is at least one of the elements of the group Lu, Gd, Sc, Y, La,
 Pr, Nd, Sm, Eu, Th, Dy, Ho, Er, Tm, Yb,
EQU x--from 1.times.10.sup.-4 f. units up to 0.2 f. units
 wherein it contains fluorine F in the range from 1.times.10.sup.-4 f. units
 up to 0.2 f. units and/or at least one of the elements of group H, Li, Be,
 B, C, N, Na, Mg, Al, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,
 Ga, Ge, As, Se, Rb, Sr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs,
 Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, U, Th in the range from
 1.times.10.sup.17 atom/cm.sup.3 up to 5.times.10.sup.20 atom/cm.sup.3.
 The lower limit of these elements is determined by the fact that at
 concentrations lower than the indicated limit of a technical result, lying
 in creating waveguide properties in scintillating elements at the expense
 of a refractive index gradient along the cross section, cannot be reached.
 The upper limit for these elements is determined by their maximum possible
 content in crystals with the structure of orthosilicate. When their
 content is higher than the above limit the destruction of oxyorthosilicate
 structure takes place.
 3. An individual case of the proposed inventions is a scintillating
 material, wherein it additionally contains oxygen vacancies in the amount
 of not more than 0.2 f. units. This scintillating material, crystallized
 at the structural type LU.sub.2 SiO.sub.5 with a spatial group B2/b, Z=8,
 the composition of which is represented by the chemical formula
EQU Lu.sub.1 A.sub.1-x Ce.sub.x SiO.sub.5-z
 where A--Lu and at least one of the elements of the group Gd, Sc, Y, La,
 Pr, Nd, Sm, Eu, Th, Dy, Ho, Er, Tm, Yb,
EQU x--from 1.times.10.sup.-4 f. units to 0.2 f. units.
EQU z--from 1.times.10.sup.-5 f. units to 0.2 f. units.
 While growing the above new scintillating materials in an inert, restoring
 or weakly oxidising environments, oxygen vacancies are formed in crystals,
 which in small concentrations weakly affect the achievement of the
 positive result of the invention. It is practically impossible to
 establish the lower limit for the content of oxygen vacancies in a
 scintillating material because of the lack of valid methodologies for
 determining low concentrations of vacancies for oxygen, that is why the
 lower limit is equal to 1.times.10.sup.-5 f units, which corresponds to
 the minimal concentration of heterovalent admixtures Me.sup.2+, the
 presence of which in a crystal of a scintillator causes the appearance of
 vacancies in an oxygen sub--lattice.
 The upper limit of the content of oxygen vacancies is determined by the
 fact that scintillating materials with the content of oxygen vacancies in
 the material in the unity greater than 0.2 f. units is not applicable for
 utilization for its direct purpose--for the registration of x-ray, gamma
 and alpha radiation.
 4. The other individual case of the proposed inventions is a scintillating
 material wherein it contains ions Ce.sup.3+ in the range from
 5.times.10.sup.-5 f. units up to 0.1 f. units.
 The lower limit for the ions of cerium is determined by the fact that with
 the content of Ce.sup.3+ in the quantity of less than 5.times.10.sup.-5 f.
 units, the effectiveness of a scintillation luminescence of Ce.sup.3+
 becomes insignificant because of the small concentration. It is necessary
 to point out that the limit of concentration interval for the content of
 cerium in a crystal is decreased two times. This is related to the fact
 that due to the use of the proposed scintillating matter a possibility of
 receiving scintillating materials-oxyorthosilicates with a maximum
 possible contents of ions of Ce.sup.+3 appears only in a coordination
 polyhedron LuO.sub.7.
 The upper limit of the content of Ce.sup.3+ in a crystal is determined
 based on the fact that with the content of Ce.sup.3+ greater than 0.1 f.
 units, it is impossible to optically receive a high quality crystal. This
 is related to the high content of additional elements in a crystal,
 necessary for obtaining a maximum possible content of ions of cerium +3 in
 coordination polyhedrons LuO.sub.7.
 5. The other individual case of the proposed inventions is a scintillating
 material, wherein its surfaces are additionally polished by way of a
 chemical etching.
 Additional chemical polishing allows to increase the effects, reached
 during the solution of technical tasks in the process of manufacturing
 scintillating elements from the proposed new materials.
 6. For the solution of the technical task of raising the effectiveness of
 the introduction of irradiation into the glass waveguide fibre, it is
 offered got the first time to use the known waveguide effect, created at
 the expense of the gradient of concentrations, directly in a scintillating
 element. Thus, a waveguide scintillating element allows to use the known
 waveguide effect for a new purpose, namely for the increase of the light
 output of irradiation, appearing in a scintillating element during the
 registration of x-ray, gamma and alpha radiation-by focusing the radiation
 of luminescence along the axis of a scintillating element. The features of
 invention relating to a waveguide scintillating element bear a general
 character, i.e. they are related to any scintillating material (glass,
 oxide and fluorine crystals, composite materials and other materials) for:
 registration and measurement of x-ray, gamma and alpha radiation, protons,
 neutrons and other heavy particles.

DETAILED DESCRIPTION OF THE INVENTION
 Table 1 shows a comparison of the light output and effective atomic number
 of crystals of the prototype depending on the composition of a
 scintillating material. Table 2 shows the constant of the scintillations
 decay time (.tau., ns) and the light output (%) and provides examples of
 specific compositions of crystals and the prototype, grown by Czochralski
 method,
 TABLE 1
 Comparison of the light output and the effective atomic number of
 prototype crystals depending on the composition of a
 scintillating material
 Effective
 Light atomic
 Crystal Crystal composition output number
 Ce:LSO C. L. Melcher, 0.94 63.7
 Schlumberger-Doll Research
 Ce:LSO Lu.sub.1.974 Ce.sub.0.0046 SiO.sub.5 1.00 63.71
 0.8LSO/0.2GSO Lu.sub.1.672 Gd.sub.0.298 Ce.sub.0.0036 SiO.sub.5 0.77
 62.82
 0.5LSO/0.5GSO Lu.sub.1.136 Gd.sub.0.847 Ce.sub.0.0072 SiO.sub.5 0.43
 61.12
 0.1LSO/0.9GSO Lu.sub.0.173 Gd.sub.1.830 Ce.sub.0.0127 SiO.sub.5 0.29
 57.66
 Ce:GSO Commercial sample of Hitachi 0.41 56.94
 Chemical Co.
 TABLE 2
 Constant of scintillations decay time (.tau., ns) and light output (%)
 Con-
 stant
 of the Light
 The composition of decay out-
 the melting stock Size of time put,
 and purity of source reagents the sample .tau., ns %
 Lu.sub.1.98 Ce.sub.0.02 SiO.sub.5 *) 10 .times. 10 .times. 2 mm 42.3
 100
 Lu.sub.2 O.sub.3, CeO.sub.2, SiO.sub.2 purity 99.995% ***)
 Lu.sub.1.98 Ce.sub.0.003 SiO.sub.5 *) 10 .times. 10 .times. 2 mm 44.1
 98
 Lu.sub.2 O.sub.3, CeO.sub.2, SiO.sub.2 purity 99.995% ***)
 Lu.sub.0.99 Gd.sub.0.99 Ce.sub.0.002 SiO.sub.5 **)
 Lu.sub.2 O.sub.3, CeO.sub.2, SiO.sub.2, Gd.sub.2 O.sub.3 5 .times. 5
 .times. 5 mm 33.9 43
 purity 99.995% ****)
 Lu.sub.1.98 Ce.sub.0.003 SiO.sub.5 *)
 Lu.sub.2 O.sub.3, purity 99.8% 10 .times. 10 .times. 2 mm 43.8 31
 CeO.sub.2, SiO.sub.2, purity 99.995% ***)
 Lu.sub.1.975 Ce.sub.0.02 Ta.sub.0.005 SiO.sub.5.002
 Lu.sub.2 O.sub.3 purity 99.8% 10 .times. 10 .times. 2 mm 38.3 100
 CeO.sub.2, SiO.sub.2 Ta.sub.2 O.sub.5, purity 99.995% ***)
 Lu.sub.1.977 Ce.sub.0.02 W.sub.0.003 SiO.sub.5.002
 Lu.sub.2 O.sub.3 with the purity 99.8% 10 .times. 10 .times. 2 mm 39.2
 100
 CeO.sub.2, SiO.sub.2, WO.sub.3, purity 99.995% ***)
 Lu.sub.1.974 Ce.sub.0.02 Ca.sub.0.001 Ta.sub.0.05 SiO.sub.4 F.sub.0.06
 Lu.sub.2 O.sub.3 with the purity 99.8% 10 .times. 10 .times. 2 mm 32.1
 102
 CeO.sub.2, SiO.sub.2, Ta.sub.2 O.sub.5, purity 99.995% ***)
 CaO, CeF.sub.3, purity 99%
 Lu.sub.1.975 Ce.sub.0.00025 Ta.sub.0.005 SiO.sub.5.002
 Lu.sub.2 O.sub.3, CeO.sub.2, SiO.sub.2 Ta.sub.2 O.sub.5 with 10 .times. 10
 .times. 2 mm 38.0 6
 the purity of 99.995% ***)
 Notes:
 *) the known scintillating crystal is indicated
 **) prototype crystal is indicated
 ***) two surfaces 10 .times. 10 mm are mechanically polished
 ****) all surfaces 5 .times. 5 mm are mechanically polished
 EXAMPLE 1
 Growing of crystals with a structural type LU.sub.2 SiO.sub.5 and a spatial
 group B2/b (Z=8), additionally containing at least one element of the
 group Ti, Zr, Sn, Hf. As, V, Nb, Sb, Ta, Mo, W.
 Growing of these crystals was conducted according to the general scheme--by
 way of extruding from melt by any method, in particular by Czochralski
 method (described in detail below in example 2).
 A scintillating crystal, grown of a melting stock Lu.sub.1.977 Ce.sub.0.02
 W.sub.0.003 SiO.sub.5,002 on the basis of LU.sub.2 O.sub.3 (purity 99.8%),
 additionally containing the ions of tungsten in the range of
 1.2.times.10.sup.19 atom/cm.sup.3, has a position of a maximum of
 luminescence about 418 nm and the time of luminescence (decay of
 scintillations) .tau.=39 ns, compared with .tau.=42 ns for crystal, grown
 from the melt with the composition of Lu.sub.1.98 Ce.sub.0.02 SiO.sub.5
 (table 2).
 These data confirm the possibility of growing crystals, containing ions of
 Ce.sup.3+ advantageously in coordination polyhedrons LuO.sub.7, if the
 melt is additionally doped with ions of the following elements: Ti, Zr,
 Sn, Hf; As, V, Nb, Sb, Ta, Mo, W, which occupy in a crystal an octahedral
 polyhedron LUO.sub.6 or tetrahedral positions. All these admixtures ions
 have an increased concentration in the diffused layer at the
 crystallisation front, as their coefficients of distribution are small
 (K&lt;0.2). An increased concentration of admixtures with the charge 4+, 5+,
 6+ in a diffused layer interferes with the incorporation into the crystal
 of cerium atoms in the form of Ce.sup.4+, and does not affect the
 competing process of the substitution of Ce.sup.3+ {character
 pullout}Lu.sub.1, when it becomes the main one.
 EXAMPLE 2
 Obtaining a scintillation material on the basis of oxyortho silicate
 crystal, including cerium Ce, the composition of which is expressed by the
 chemical formula A.sub.2-x Ce.sub.x SiO.sub.5, wherein A is at least one
 element of the group Lu, Gd, Sc, Y, La, Pr, Nd, Sm, Eu, Th, Dy, Ho, Er,
 Tm, Yb, as well it contains fluorine F and/or at lest one of the elements
 of the group H, Li, Be, B, C, N, Na, Mg, Al, P, S, Cl, K, Ca, Ti, V, Cr,
 Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Zr, Nb, Mo, Ru, Rh, Pd,
 Ag, Cd, In, Sn, Sb, Cs, Ba, Hf; Ta, W, Re, Os, fr, Pt, Au, Hg, Tl, Pb, Bi,
 U, Th.
 The data of table 2 demonstrate the possibility of using reagent Lu.sub.2
 O.sub.3 with the purity of 99.8% instead of a more expensive Lu.sub.2
 O.sub.3 with the purity of 99.995%. The introduction of additional
 compensating ions while using reagent Lu.sub.2 O.sub.3 with the purity of
 99.8% eliminates the possibility of deterioration of the most important
 parameter--the constant of time of scintillations decay .tau., for
 example, for crystals grown of the melting stock of the composition
 Lu.sub.1.974 Ce.sub.0.002 Ca.sub.0.001 Ta.sub.0.05 SiO.sub.4.94 F.sub.0.06
 and Lu.sub.1.975 Ce.sub.0.02 Ta.sub.0.05 SiO.sub.5.002.
 For growing the crystal of lutetium--cerium--tantalum orthosilicate by the
 method of Czochralski the melting stock of the composition of Lu.sub.1.975
 Ce.sub.0.02 Ta.sub.0.05 SiO.sub.5.002 was used, which contained micro
 admixtures of Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Co, Ni, Cu, Zn, Mo, Ba, Sc,
 Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, W, Pb, Th--which
 were present in the source reagent Lu.sub.2 O.sub.3 (99.8%) in the range
 from 1.times.10.sup.17 atom/cm.sup.3 up to 1.times.10.sup.19
 atom/cm.sup.3. By that, the following method of receiving samples was
 used: source reagents lutetium oxide and silicon oxide were thoroughly
 mixed, pressed in tablets and synthesised in a platinum crucible during 10
 hours at 1200.degree. C. Then by means of induction heating the tablets
 were melted in an iridium crucible in a sealed chamber in the atmosphere
 of nitrogen (100 volumetric % of N.sub.2). Before growing, a cerium and
 tantalum oxide were added into the melt. A crystal was grown out of
 iridium crucible with the diameter of 80 mm with the volume of the melt of
 330 cm.sup.3. At a speed of crystal pulling of 3 mm/hour and the frequency
 of crystal rotation of 20 rounds per minute. After detachment of the grown
 crystal from the melt, the crystal was gradually cooled down to a room
 temperature during 40 hours.
 Experimental research of the relationship of the constant of the time of
 decay of scintillations (.tau., ns) and the light output in the area of
 400-430 nm, depending on the chemical composition of crystals, was carried
 oufusing the radiation of radio nuclide .sup.60 Co, similar to the
 methodology of
 E. G. Devitsin, V. A. Kozlov, S. Yu. Potashov, P. A. Studenikin, A. I.
 Zagumennyi, Yu. D. Zavartsev "Luminescent properties of Lu.sub.3 Al.sub.5
 O.sub.12 crystal, doped with Ce". Proceedings of the International
 Conference "Inorganic scintillators and their applications" (SCINT' 95),
 Delft, the Netherlands, Aug. 20-Sept. 1, 1995. The results of measurements
 are shown in table 2.
 EXAMPLE 3
 Scintillating material based on the crystal of orthosilicate additional
 containing oxygen vacancies. For creating oxygen vacancies in crystalline
 samples, obtained by the method of Czochralski, their heating in vacuum
 during 2 hours at the temperature in the interval of 1200.degree.
 C.-1620.degree. was used.
 The formation of oxygen vacancies insignificantly affects the scintillation
 parameters of crystals, grown from reagents with the purity of 99.995%. On
 the contrary, oxygen vacancies bring about the decrease by 20% -70% of the
 light output of crystals, additionally doped, for example, by ions of Mo,
 W, Ta, due to the formation of dying centres.
 The presence of oxygen vacancies completely suppresses the luminescence of
 admixture rare earth ions Pr, Sm, Tb, Ho, Er, Tm, and does not affect the
 luminescence properties of ions of Ce.sup.3+. In crystals of
 oxyorthosilicate additionally containing oxygen vacancies completely
 suppressed and absent is the luminescence of ions of Tm.sup.3+ at 452 ran,
 ions Pr.sup.3+ at 470-480 nm and 520-530 nm, ions Tb.sup.3+ at 544 nm,
 ions Ho.sup.3+ at 550 nm, ions Er.sup.3+ at 560 nm, ions 593 um. The time
 of luminescence (decay of scintillations) of ions Pr, Sm, Tb, Ho, Er, Tm,
 is for several orders of magnitude longer than for ion of Ce.sup.3+, that
 is why the suppression of luminescence of admixture rare earth ions in the
 visible and infrared area of the spectrum is necessary for the
 preservation of quick operation of elements based on Ce.sup.3+ ion, which
 is experimentally observed in silicates crystals, additionally containing
 oxygen vacancies.
 EXAMPLE 4
 Scintillating material on the basis of oxyorthosilicate crystal, which
 contains Ce.sup.3+ ions in the quantity of 5.times.10.sup.-5 f., units up
 to 0.1 f. units. For growing by Czochralski method of
 lutetium--cerium--tantalum orthosilicate crystal, containing Ce.sup.3+
 ions in the range of 5.times.10.sup.-5 f. units, the melting stock was
 used with the chemical composition of Lu.sub.1.975 Ce.sub.0.0025
 Ta.sub.0.005 SiO.sub.5.002 on the basis of source reagents (Lu.sub.2
 O.sub.3, CeO.sub.2, Sio.sub.2, Ta.sub.2 O.sub.5) with the purity of
 99.995%. The crystal was grown out of the iridium crucible with the
 diameter of 60 mm at a speed of pulling of 3 mm/hour and frequency of
 rotation of 20 rounds per minute.
 At a contents of Ce.sup.3+ in a crystal in the amount of less than
 5.times.10.sup.-5 f. units, the effectiveness of the scintillation
 luminescence of Ce.sup.3+ becomes insignificant due to a small
 concentration, as a result of which the light output (table 2) does not
 exceed 6% for samples, made of the top and bottom part of the crystalline
 boule with the weight of 1040 g.
 The important technical advantage of scintillation crystals of
 oxyorthosilicates, containing small quantities of Ce.sup.3+ ions
 (5.times.10.sup.-4 -5.times.10.sup.-5 f. units), is the possibility to use
 100% of the me the process of crystal growth, which considerably increases
 the time of operation of iridium, crucibles, and, consequently, decreases
 the cost of scintillating elements.
 EXAMPLE 5
 Chemical polishing of the lateral surface of a scintillating element.
 Stepanov's method or any other similar method allows to grow scintillation
 crystals with a necessary cross section (2.times.2 min or 3.times.3 mm),
 which allows to eliminated the operation of cutting a large boule, and
 chemical polishing permits to polish all lateral surfaces simultaneously
 at scintillating elements in the quantity of 2-100 pieces (or more), for
 example, with the size of 2.times.2.times.15 mm or 3.times.3.times.15 mm.
 By that the lateral surface can have any form: cylindrical, conical,
 rectangular, polygonal or random. Cheap chemical polishing allows to
 exclude and expensive mechanical polishing of the lateral surface of
 scintillating elements in the process of their manufacturing.
 The crystal Lu.sub.1.997 Ce.sub.0.002 Ta.sub.0.001 SiO.sub.5.0004 was grown
 by the method of Czochralski according to the methodology, described in
 example 2. 40 scintillating elements were cut out of a crystalline boule
 (10 elements of the size 2.times.2.times.15 mm, 10 elements of the size
 2.times.2.times.12 mm, 10 elements of the size 3.times.3.times.15 min, 10
 elements of the size 3.times.3.times.20 mm). All 40 elements were
 simultaneously subjected to chemical polishing at temperature of
 260.degree. C. in the mixture of the following composition: H.sub.3
 PO.sub.4 (30%)+H.sub.2 SO.sub.4 (61%)+NaF (4%0+NaCl (5%). The
 concentration is indicated in weight percent. Optimal time of chemical
 etching is 30 minutes. As a result of chemical polishing an optically
 smooth lateral surface was obtained at which there are no pyramids of
 growth and etching pits.
 The light output of a scintillating element Lu.sub.1.997 Ce.sub.0.002
 Ta.sub.0.001 SiO.sub.5.0004 after chemical polishing is more than 5 times
 higher than with the standard one used in electron--positron tomography
 Bi.sub.4 Ge.sub.3 O.sub.12 with mechanically polished lateral surfaces
 (FIG. 3).
 EXAMPLE 6
 The creation of waveguide properties in scintillating elements at the
 expense of the refractive index gradient along its cross section.
 In the process of growth of a profiled crystal from melt, its cross section
 is determined by the form of a melt column. Different physical effects are
 used for the shaping of the melt. The creation of the melt column of a
 certain form with a help of a shaper is known as Stepanov's method for
 growing profiled crystals [Antonov P. I., Zatulovskiy L. M., Kostygov A.
 S. and others "Obtaining profiled single crystals and articles by
 Stepanov's method", L., "Nauka", 1981, page 280].
 The application of Stepanov's method opens the possibility of growing
 scintillating crystals of the size of 3.times.3.times.200 mm with the
 formation of a waveguide nucleus in the crystal in the process of growth.
 The waveguide nucleus appears if there are admixtures in the melt, which
 depending on the coefficient of distribution are concentrated in the
 central part (K&gt;1) or in the peripheral part (K&lt;1) of the growing crystal.
 FIG. 2 shows non uniform distribution of admixture along the crystal cross
 section (n.sub.1, refractive index in the centre of a crystal and n.sub.2
 --refractive index at the periphery of the crystal). Non uniform
 distribution of admixture ions along the cross section (3.times.3 mm) of
 the crystal brings about the refractive index gradient along its cross
 section, while if n.sub.1 &gt;n.sub.2, a waveguide effect takes place. The
 waveguide effect brings about focusing of a light flow along the axis of
 an element and increases the amount of light, leaving the end plane of the
 scintillating element, which in the long run determines the effectiveness
 of an actual gamma ray detector. The increase of the light flow from the
 end plane of the scintillating element occurs due to the decrease of the
 summary losses of scintillating radiation during reflection from a lateral
 surface.
 The second important advantage of scintillating elements (size
 3.times.3.times.15 mm after cutting of a crystal rod into several
 elements) with a waveguide effect compared to the elements
 3.times.3.times.15 mm, manufactured from a large crystalline boule, is
 1.5-1.6 times greater effectiveness of the input of light beams into a
 glass light guide, which is responsible for the transfer of scintillating
 radiation from a scintillating element to the photoelectronic multiplier
 in a new type of medical 3-dimensional tomographs, in which simultaneously
 two different physical methods of obtaining brain image of a man are used:
 electron-positron tomography and magnetic resonant tomography.
 The growing of a profiled crystal by Stepanov's method was conducted using
 an iridium crucible with an iridium former, having a cross section of the
 outer edge of 3.times.3 mm, which was assigning the cross section of the
 growing crystal. Transportation of melt out of crucible took place along a
 central capillary with the diameter of 0.9 mm due to capillary effect. For
 example, for obtaining a lutetium--gadolinium--cerium orthosilicate
 crystal with a focusing waveguide effect a melting stock with the
 composition Lu.sub.1.672 Gd.sub.0.298 Ce.sub.0.0036 SiO.sub.5 was used,
 using the following methodology. Source reagents: lutetium oxide,
 gadolinium oxide and silicon oxide were thoroughly mixed, pressed in
 tablets and synthesised in a platinum crucible during 10 hours at
 1200.degree. C. Then, by means of induction heating the tablets were
 melted in an iridium crucible in a sealed chamber in the atmosphere of
 nitrogen (100 volumetric % N.sub.2). Cerium oxide was added to the melt
 before growing. The former allowed to grow from one to four profiled
 crystals simultaneously. Etching was performed to the crystal Lu.sub.2
 SiO.sub.5, cut in a crystallographic direction (001), i.e. along the axis
 of optical indicatrix, having the greatest refractive index n.sub.g.
 Profiled crystals were pulled out of melt at a speed of 4-15 mm/hour
 without rotation. growing a profiled crystal at a speed of higher than 20
 nun/hour brings about the growth of crystal of a permanent composition
 along the rod cross section. Upon the crystals reaching the length of
 50-90 mm they were torn from the shaper by a sharp increase of the speed
 of pulling. The grown profiled crystals were cooled to a room temperature
 during 12 hours.
 Profiled crystalline rods were cut into several scintillating elements of
 the size of 3.times.3.times.15. One sample with mechanically polished 6
 surfaces was used for the determination of composition with a help of
 electronic micro analysis (Cameca Camebax SX-50, operating at 20 kV, 50
 .mu.A and diameter of the beam of 10 microns). For a profiled crystal,
 grown at a speed of pulling of 4 mm/hour, a crystalline rod in the centre
 had a composition Lu.sub.1.78 Gd.sub.0.202 Ce.sub.0.0015 SiO.sub.5 and
 lateral surfaces had a composition in the range LU.sub.1.57-1.60
 Gd.sub.0.30-0.0045 SiO.sub.5. Gradient of the refractive index along a
 crystal cross section was determined from the interference picture:
 n.sub.1 -n.sub.2 =0.006, where n.sub.1 is a refractive index at the centre
 of a crystal and n.sub.2 is a refractive index at the periphery of a
 crystal. The presence of a refractive index gradient causes focusing along
 the axis of a waveguide scintillation element of all beams of
 scintillating radiation thanks to a complete internal reflection, if an
 angle between an optical axis and the direction of scintillation radiation
 is less than the angle .alpha..sub.max., calculated according to the
 formula ["Reference boor on laser technique". Translation from German B.
 N. Belousov, Moscow, Energoizdat", 1991, page 395// WISSENSSPREICHER
 LASERTECHNIK/Witolf Brunner, Klaus Junge./ VEB Fachbucherverlag Leipzig,
 1987]:
EQU sin.alpha..sub.max. =n.sup.2 K-n.sup.2 m (8)
 where n.sub.m the refractive index of the coating (periphery) of a light
 guide and n.sub.k is a refractive index of the core of the optical
 waveguide.
 For a scintillating element with the value of a refractive index gradient
 along the crystal cross section equal to n.sub.1 -n.sub.2 =0.006 a
 complete internal reflection of all scintillating beams will take place if
 the angle of their spread is less than angle .alpha..sub.max. =8.4
 degrees. It is necessary to point out that a complete internal reflection
 of scintillation beams, having the direction of .alpha.&lt;.alpha..sub.max.,
 takes place irrespective of the fact if the lateral surface of a
 scintillating element is polished or not. For scintillating elements
 widely used in computer tomography with a cross section of 2.times.2 mm or
 3.times.3 mm and length of 15-20 mm with the angle of complete internal
 reflection .alpha..sub.max. =8.4 degrees there will take place 2-3
 complete internal reflections of scintillating beams before their leaving,
 the element (FIG. 2).