EP1536732B1 - Light radiation protection material for a large energy application field - Google Patents

Description

The invention relates to a lead replacement material for radiation protection purposes in the energy range of an X-ray tube with a voltage of 60-140 kV.

Conventional radiation protection clothing for use in X-ray diagnostics usually contains lead or lead oxide as protective material.

Substitution of this protective material for other materials is desirable, in particular, for the following reasons:

On the one hand leads lead and its processing due to its toxicity to a high environmental impact, on the other hand leads lead due to its very high weight necessarily to a very high weight of the protective clothing and thus to a strong physical burden on the user. When wearing protective clothing, for example during medical operations, the weight is of great importance for the wearing comfort and the physical stress of the physician and the assistant personnel.

Therefore, for years, a replacement lead material has been sought in radiation protection. Here, the use of chemical elements or their compounds with the atomic number of 50 to 76 is mainly proposed.

The DE 199 55 192 A1 describes a method for producing a radiation protection material from a polymer as matrix material and the powder of a metal of high atomic number.

The DE 201 00 267 U1 describes a highly elastic, lightweight, flexible, rubbery radiation protection material wherein additions of chemical elements and their oxides having an atomic number greater than or equal to 50 are added to a specific polymer.

To reduce weight compared to conventional lead aprons is in the EP 0 371 699 A1 proposed a material which also has elements of higher atomic number in addition to a polymer as a matrix. This is called a large number of metals.

The DE 102 34 159.1 describes a lead substitute material for radiation protection purposes in the energy range of an x-ray tube with a voltage of 60-125 kV.

The FR-A-2741472 describes metal alloys used in the field of radiation protection. The alloys preferably contain lead or, if no lead is included, they do not have tungsten.

Out US-A-5,360,666 For example, materials for protective shields are known for use during radiotherapy. The materials are alloys that consist of two elements, none of which is tungsten.

Depending on the elements used, the degree of attenuation or the lead equivalent (International Standard IEC 61331-1, Protective devices against diagnostic medical radiation x-radiation) of the respective material shows a partially very pronounced dependence on the beam energy, which is a function of the voltage of the X-ray tube.

Lead-free materials have lead behavior that differs greatly from that of lead, depending on the X-ray energy. Therefore, for simulating the absorption behavior of lead while maximizing weight savings, an advantageous combination of different elements is required.

Thus, the known radiation protective clothing made of lead-free material compared to lead a more or less severe drop in absorption below 70 kV and above 110 kV, especially about 125 kV. That is, to achieve the same shielding effect as with leaded material, a higher basis weight of protective clothing is required for this range of tube tension.

Therefore, the scope of commercial lead-free radiation protection clothing is usually limited.

In order to substitute lead for radiation protection purposes, an absorption behavior which is as similar as possible to lead is required over a relatively large energy range, since radiation protection agents are usually classified according to the lead equivalent and the radiation protection calculations are often based on lead equivalents.

Total lead equivalent in a protective-layer-shaped construction of a lead substitute material is understood to be the lead equivalent of the sum of all protective layers. The total nominal equivalent value is understood to mean the lead equivalent value specified by the manufacturer of personal protective equipment according to DIN EN 61331-3.

Matrix material is understood as meaning the carrier layer for the protective materials, which may consist of rubber, latex, flexible or solid polymers, for example.

X-ray voltages of up to 140 kV occur in certain X-ray applications, such as computed tomography and bone density measurements, as well as in luggage inspection equipment.

The object of the present invention is to replace lead as a radiation protection material in terms of its shielding properties over a wide energy range of an X-ray tube, so over a large energy range and at the same time to achieve the largest possible weight reduction. In this case, only environmentally friendly materials should be used compared to lead.

The object of the invention is a lead substitute material for radiation protection purposes in the energy sector an X-ray tube with a voltage of 60-140 kV, wherein the lead substitute material 12-22 wt .-% matrix material, 0-75 wt .-% tin or tin compounds, 0-73 wt .-% tungsten or tungsten compounds, 0- 80 wt .-% bismuth or bismuth compounds and wherein at most one of the components is 0 wt .-%, wherein this component is not tungsten or the tungsten compound. The mixture detects nominal total lead values of 0.25-2.0 mm.

To solve the problem, it was therefore necessary to find a selection of materials and their quantity selection, which can shield the X-ray radiation well effective even in the high energy range.

Surprisingly, it has been found that the absorption effect at high energies by high proportions of tungsten and / or bismuth, wherein tungsten is always present, significantly improved in the lead replacement material.

In a preferred embodiment of the invention, the lead substitute material is characterized by having 12-22 wt% matrix material, 0-39 wt% Sn or Sn compounds, 0-60 wt% W or W compounds and 0-60% by weight of Bi or Bi compounds, and wherein at most one of the components is 0% by weight, which component is not tungsten or the tungsten compound.

In a particularly preferred embodiment of the invention, the lead substitute material is characterized in that it contains 12-22% by weight of matrix material, 0-39% by weight of Sn or Sn compounds, 16-60% by weight of W or W Compounds and 16-60 wt .-% Bi or Bi compounds.

In a further preferred embodiment of the invention, the lead substitute material is characterized in that it comprises 12-22% by weight matrix material, 40-60% by weight Sn or Sn compounds, 7-15% by weight W or W Compounds and 7-15 wt .-% Bi or Bi compounds.

In a further particularly preferred embodiment of the invention, the lead substitute material is characterized in that it additionally contains up to 40% by weight of one or more of Er, Ho, Dy, Tb, Gd, Eu, Sm, La, Ce, Nd , Cs, Ba, I and / or their compounds and / or CsI.

Table 1 below shows the mass attenuation coefficients of lead-free protective substances outside the absorption edges at different photon energies. The advantageous elements to be used for the respective energy are underlined. Table 1 Energy (keV) sn Gd He W Bi 40 19.42 6.92 8.31 10.67 14.95 50 10.70 3.86 4.63 5.94 8.38 60 6.56 11.75 13.62 3.71 5.23 80 3.03 5.57 6.48 7.81 2.52 100 1.67 3.11 3.63 4.43 5.74 150 0.61 1.10 1.28 1.58 2:08

By the lead substitute material additionally comprising one or more elements Er, Ho, Dy, Tb, Gd, Eu, Sm, La, Ce, Nd, Cs, Ba, I and / or their compounds and / or CsI is a reached a particularly strong increase in the absorption effect. In this way, the weight of the protective clothing can be significantly reduced.

To achieve the described properties, according to Table 1, the individual elements can be assembled so that a certain energy range is covered or that the most uniform course of the weakening results over a larger energy range.

Surprisingly, it has been found that when using the above-mentioned additional elements of their compounds in the lead substitute material, a disproportionate increase in the protective effect occurs, preferably when their weight fraction of the lead substitute material is between 20% and 40%.

In a further preferred embodiment of the invention, the lead substitute material is characterized in that it additionally comprises up to 40% by weight of one or more of the following elements Ta, Hf, Lu, Yb, Tm, Th, U and / or their compounds.

In addition, in the lead substitute materials usable metals Er, Ho, Dy, Tb, Gd, Eu, Sm, La, Ce, Nd, Ba, I, Ta, Hf, Lu, Yb, Tm, Th, U can also metals and / or their compounds and / or CsI be used with a relatively low degree of purity, as they arise as waste products.

In DIN EN 61331-3 a deviation from the nominal lead equivalent value downwards is not permitted. Only the German version of the standard allows one exception, namely a deviation of 10% from the nominal lead equivalent. For these reasons, it is desirable to have as flat a lead as possible over the energy of a lead substitute material.

A fall in the lead equivalent below the nominal lead equivalent or below the lower tolerance limit means that the radiation protection material can not be used at the relevant tube voltages, since the shielding effect is too low. In this case, alternatively, the basis weight of the lead substitute material must be increased to the extent that the permissible tolerances of DIN EN 61331-3 are met. However, an increase in basis weight is considered disadvantageous.

Another possibility is the limitation of the field of application with regard to the energy or the tube voltage.

It was therefore a further object of the present invention to select elements or their compounds in such a way that the lowest possible drop in the lead equivalent in the desired energy utilization range takes place, taking into account the accessibility of the respective elements or their compounds.

The relative strength N _rei as an increase in the lead equivalent (PbGW) relative to a normalized mass coverage of 0.1 kg / m ² was determined in a series of materials in test series and summarized in Table 2 below. It reproduces the weakening properties of the individual elements even more clearly than the mass attenuation coefficients described above, since here the absorption is included in the immediate area of the respective absorption edges. Table 2 material N _rei Mean growth PbGW based on 0.1 kg / m ² (rel. Pb) PbGW increase from 60 to 80 kV based on 0.1 kg / m ² group 60-90 kV 60-125 kV 100-125 kV 125-150 kV sn 1.64 1.30 0.96 0.80 -0,005 A Bi 1.41 1.27 1.13 1.17 -0,005 A W 0.91 1.07 1.25 1.07 + -0.000 A Gd 1.85 2.05 2.27 1.56 +0.007 B He 1.20 1.45 1.70 1.36 +0.009 B

Surprisingly, this shows that the elements or their compounds can be classified as follows: Group A: Relatively low efficiency materials with values of N _rei <1.2 - 1-6 mm PbGW per 0.1 kg / m ² and a small or negative increase of 60-80 kV. These elements or their compounds include Sn, Bi and W. Group B: Relatively high efficiency materials with N _rei ≥ 1.3 mm PbGW per 0.1 kg / m ² and a high rise of 60-80 kV.

In a particularly preferred embodiment of the invention, therefore, the energy range 60-140 kV is divided into several, partly overlapping, regions corresponding to the most common applications of the x-ray radiation:

1. Energy range 60-90 kV

In this field of energy predominantly dental applications of the single-shot technique and the panoramic layer technique take place.

2. Energy range 60-125 kV

This area of energy includes the most common X-ray examinations and X-ray interventions, such as angiography, computed tomography, cardiac catheter examinations, interventional radiology, thorax hard-beam technique.

3. Energy range 100-125 kV

Most computer tomographs fall into this energy range.

4. Energy range 125-150 kV

This is an energy range for specific applications such as special computed tomography, bone density measurements, special thorax hard-jet technology and nuclear medicine diagnostics.

Lead-free protective clothing that can only be used in a certain energy range must be marked accordingly by the manufacturer.

In one embodiment of the lead replacement material for radiation protection purposes in the energy range of an x-ray tube having a voltage of 60-90 kV, the lead substitute for nominal total lead equivalent of 0.25-0.6 mm is characterized by having 12-22 wt. % Matrix material, 49-65 wt% Sn or Sn compounds, 0-20 wt% W or W compounds, 0-20 wt% Bi or Bi compounds, and 2-35 wt% of one or more of the elements Gd, Eu, Sm, La, Ce, Nd, Cs, Ba, I, Pr and / or their compounds and / or CsI, wherein W or the W compound is not O. The energy range is preferably that of an X-ray tube of a dental X-ray machine.

In a particular embodiment of the present invention, the lead substitute material comprises 2-25% by weight of I, Cs, Ba, La, Ce, Pr and / or Nd and / or their compounds and / or CsI.

In the relatively narrow energy range, it was shown from Table 2 that of the group A elements Sn is the most effective. From Group B Gd is preferred, but CsI also resulted in a lead substitute with very good properties.

Energy range 60-125 kV (general X-ray range):

From Table 2, for example, elements with low and high rise of the lead equivalent in be advantageously selected in such a way that the curves of the lead equivalent remain as flat as possible over the entire range. A certain elevation at 80 and 100 kV is physically impossible to avoid.

Thus, one or more elements or their compounds of group A can be optimally combined with one or more elements or their compounds of group B, the choice being made according to the efficiency of the shield, the accessibility of the element or its compound and As constant as possible of the lead equivalent takes place.

Here, a dependence of the proportion of the A elements or their compounds is given by those of the B elements or their compounds. Thus, when increasing the content of a B-element, the relative weight fraction of an A-element with opposite energy behavior must also be significantly increased in order to keep the course of the lead equivalent above the energy as flat as possible.

For example, if more than 20% by weight of B-elements or their compounds, the proportion of Sn or Bi should exceed 40% by weight to ensure low energy dependence.

Energy range 100-140 kV:

This is the energy range for most recent computer tomographs.

In a particularly preferred embodiment of the invention, the lead replacement material for radiation protection purposes in the energy range of an X-ray tube with a voltage of 100-140 kV is characterized in that the lead replacement material for nominal total lead equivalent values of 0.2 5-0.6 mm 12- 12. 22 wt .-% matrix material, 40-73 wt .-% Bi and / or W or their compounds (where W is always answesend), and 5-38 wt .-% of one or more of comprises the following elements Gd, Eu, Er, Hf and / or their compounds.

High protective effects or low basis weights can be achieved by using the elements or their compounds, which have their highest shielding effect especially in this small energy range. For reasons of accessibility, a greater proportion of the elements or their group A compounds should be combined with a smaller proportion of the elements or their group B compounds, in which case a flat energy balance of the lead equivalent will not be so important because of the relatively small energy window is.

Energy range 125-150 kV:

This area concerns special applications in radiology and nuclear medicine. The weight per unit area of the radiation protection apron is not in the foreground of the optimization in this area since the protective clothing is generally worn here only for a short time or stationary radiation protection screens are used.

The selection of the elements or their connections is done according to the above criteria. Gd and Er provide very good results in combination with Bi. The effect of W is too low in this area.

In summary, it can thus be stated that the composition of protective substances for individual energy ranges can be expediently optimized by splitting according to the most frequently occurring X-ray applications.

In a further preferred embodiment of the invention, the lead substitute material has a structure of at least two separate or interconnected protective layers of different composition, wherein at least one layer at least 50% of the Total weight consists of only one element from the group Sn, W and Bi or their compounds.

In particular, the lead substitute material has a structure of at least two separate or interconnected protective layers of different composition, wherein at least one layer at least 50% of the total weight only of at least 40 wt .-% Sn or its compounds and at least 10 wt .-% I. , Cs, Ba, La, Ce, Pr and / or Nd and / or their compounds and / or CsI. Particularly advantageous is a layer comprising 40 to 50 wt .-% Sn and 10 to 20 wt .-% cerium.

In a further preferred embodiment of the invention, the lead substitute material is characterized in that it comprises a construction of at least two separate or interconnected protective layers of different composition, wherein the protective layer (s) removed from the body predominantly the elements or their compounds with higher X-ray fluorescence yield and the body-near protective layer (s) comprise the elements or their compounds with lower X-ray fluorescence yield.

In the irradiation of materials with X-rays, characteristic X-radiation is excited as fluorescence radiation. The fluorescence yield depends on the atomic number. This fluorescence content leads to an additional radiation exposure of the skin and the organs immediately below it. From measurements on protective clothing it was determined that in particular elements with smaller atomic numbers, in the present case in particular Sn, fluoresce particularly strongly. In the case of a layered structure of the radiation protection material, stratification according to elements can advantageously take place such that the elements lie on the skin side with the lowest possible fluorescence yield.

The fluorescence component, also referred to as build-up factor, is represented by commercially available lead-free protective materials (material B) in the following Table 3 in comparison with a material constructed in layers according to the principle described here (material A). As can be seen, the build-up factor can reach values up to 1.42. That is, the skin is burdened in this case by the fluorescent component by 42% more. Table 3 kV Material A Material B 80 1.15 1.42 90 1.14 1.35 100 1.14 1.32 110 1.16 1.36

In a further particularly preferred embodiment of the invention, the lead substitute material is characterized in that it has a structure of protective layers of different composition.

The lead substitute material may comprise a construction of at least two separate or interconnected protective layers of different composition, with the body-removed protective layer (s) predominantly comprising the lower atomic number elements or their compounds and the proximal protective layer (s) comprise the elements of higher atomic number or their compounds.

The lead substitute material may also have a construction of at least three separate or interconnected protective layers of different composition, the more remote from the body protective layer (s) and the near-main (s) protective layer (s) predominantly the elements of higher atomic numbers or their compounds include and in the middle at least one Protection with predominantly elements of low atomic numbers is arranged.

Thus, for example, on both sides outside a barrier layer of a material of higher atomic numbers, such as bismuth or tungsten. In between lies a layer or layers of a material with a lower atomic number. The resulting fluorescence radiation is thus effectively shielded on both sides and can not penetrate to the outside.

Alternatively, a layer structure of at least one highly concentric, compacting powder layer of a mixture of the abovementioned protective substances and at least two carrier layers can be provided on both sides of the powder layer. The powder layer contains as little matrix material as possible. The carrier layers may be composed of matrix material. Suitable materials include polymers such as latex or elastomers. The carrier layers increase the mechanical stability, while the concentrated filling improves the radiation-shielding effect. FIG. 4 shows this layer structure with a highly compressed protective material layer 2 as the core and the outer carrier layers 1.

The lead substitute material may also be characterized in that a weakly radioactive layer is embedded between two separate or nonradioactive protective layers connected to the radioactive layer.

It can be used as elements or their compounds of group B to shield high energy radiation and the actinides thorium or uranium, the latter z. B. as depleted uranium, are used. They have a high shielding effect in the energy range of 125-150 kV, but are themselves weakly radioactive.

The effect of self-radiation can be mitigated by embedding the radioactive layer between two non-active layers of Bi. The proportion of self-exposure by thorium or uranium should be low in most cases and therefore negligible. There is a trade-off here, which contrasts the benefits of lead elimination and higher protection with low intrinsic exposure.

aufweisen, worin D ₅₀ die 50er-Perzentile der Korngrößenverteilung, d die Schichtdicke in mm und p den Gewichtsanteil der jeweiligen Materialkomponente am Gesamtgewicht bedeuten und die 90er Perzentile der Korngrößenverteilung D₉₀ ≤ 2 · D₅₀ ist.In a further preferred embodiment of the invention, the lead substitute material is characterized in that the metals or metal compounds are grained and their grain sizes a 50th percentile according to the following formula $$D_{50}=\frac{d\cdot p}{10}\mathit{mm}$$

where D _{50 is} the 50th percentile of the particle size distribution, d is the layer thickness in mm and p is the weight fraction of the respective material component in the total weight and the 90th percentile of the particle size distribution D ₉₀ ≦ 2 * D ₅₀ .

In the measurements of the lead equivalents on protective layers, which consist of metal powders or powders of metal compounds, it surprisingly turned out that the radiation permeability of the layer consisting of granular substances is higher compared to a film layer with the same mass coverage. This mainly affects the lower energy range of 60-80 kV. At higher energies, the local transmission differences, i. the X-ray contrast, increasingly lower.

For example, with an Sn content of 30% = 0.3 and a layer thickness of 0.4 mm $$D_{50}=0.4\mathit{mm}\cdot 0.3=0.012\mathit{mm}=12\mathit{microns}\mathrm{,}$$

In addition, the 90th percentile of the particle size distribution should not be greater than 2 · D ₅₀ = 24 μm.

Therefore, low weight materials must also have a small grain size, i. be very finely distributed to develop an optimal protective effect.

By taking advantage of this effect, the weight of a radiation protection apron can be further reduced.

The material of the invention can be used advantageously for example in protective gloves, patient covers, gonadal protection, ovarian protection, dental shields, fixed lower body protection, table tops, stationary or portable radiation protection walls or radiation curtains.

In the following, the invention will be explained in more detail by way of examples.

example 1

FIG. 1 shows the lead replacement material according to the invention with 22% by weight of tin, 27% by weight of tungsten, 4% by weight of erbium and 15% by weight of matrix material. This lead substitute material is designated 2 in FIG. 1. 1 denotes a commercially available material of the composition 65% by weight of antimony, 20% by weight of tungsten and 15% by weight of matrix material.

Fig. 1 shows a weight comparison of lead substitutes with a nominal lead equivalent of 0.5 mm.

From Fig. 1 it can be seen that the required to achieve a nominal lead equivalent of 0.5 mm basis weight between 100 and 140 kV in the material according to the invention increases only by about 7%, while the increase in the comparison material is considerably greater.

Example 2

FIG. 2 shows the lead replacement material according to the invention with 20% by weight of tin, 36% by weight of tungsten, 29% by weight of bismuth and 15% by weight of matrix material. This lead substitute material is designated 2 in FIG. 1 denotes a commercially available material of the composition 70% by weight of tin, 10% by weight of barium and 20% by weight of matrix material.

Fig. 2 shows a weight comparison of lead substitutes with a nominal lead equivalent of 0.5 mm.

From Fig. 2 it can be seen that the required to achieve a nominal lead equivalent of 0.5 mm basis weight between 100 and 140 kV for a material according to the invention increases only by about 9%, while the increase in the comparison material is about 60% ,

Example 3

Lead-free, light radiation protection apron for the dental sector of 60-90 kV Pb nominal lead equivalent 0.5 mm.

A lead-free radiation protection apron was produced from 59% by weight Sn, 24% by weight Gd, 1% by weight W and 16% by weight matrix material.

The radiation protection effect corresponded to that of a corresponding lead apron with a reduced basis weight of only 4.4 kg / m ² by about 35%.

Example 4

Lead-free lightweight radiation protection apron for the application range 60-125 kV.

A radiation protection apron was made from 50% by weight Sn, 11% by weight W, 23% by weight Gd and 16% by weight matrix material.

This resulted in a basis weight of 4.5 kg / m ² for a nominal lead equivalent of 0.5 mm lead, and a basis weight of 3.3 kg / m ² for a nominal lead equivalent of 0.35 mm lead, and a nominal Lead equivalent of 0.25 mm lead a basis weight of 2.4 kg / m ² .

Example 5

Lead-free lightweight radiation apron for computer tomography.

A radiation protection apron was produced from 40% by weight of Bi, 10% by weight of W, 34% by weight of Gd and 16% by weight of matrix material.

The result was a surprisingly low basis weight of 0.5 mm nominal lead equivalent of only 4.6 kg / m ² .

Example 6

FIG. 3 shows the calculated relative basis weights of the protective clothing according to the invention with nominal lead equivalents of 0.5 mm according to Examples 3, 4 and 5 in comparison with a lead apron with 0.5 mm lead equivalent. From the illustration it can be seen that the protective aprons for dental application, general X-ray and computer tomography (CT) each have the lowest basis weight in the envisaged energy ranges.

In addition, if the user is working with tube voltages of 80-100 kV, the lead equivalent value is approximately 20% higher than the nominal value of 0.5 mm Pb of a corresponding bleaching apron. This means an additional increased radiation protection.

Example 7

Lead-free lightweight apron in the energy range from 60 to 120 kV with two-layer construction.

The matrix content is 15% by weight.

The following composition of protective material layers was chosen: layer Element / compound Material weight (kg / m ² ) Fluorescent layer (outside) sn 1.20 Gd (oxide) 0.72 Cerium (oxide) 0.48 Barrier layer (inside) Bi 1.44 W 0.48 Gd (oxide) 0.48

The result was a low basis weight of only 4.8 kg / m ² for a lead equivalent of 0.5 mm.

Claims (22)

1. Lead substitute material for radiation protection purposes in the energy range of an X-ray tube having a voltage of from 60 to 140 kV, wherein for nominal overall lead equivalents of from 0.25 to 2.0 mm the lead substitute material comprises
   from 12 to 22 wt.% matrix material,
   from 0 to 75 wt.% Sn or Sn compounds,
   from 0 to 73 wt.% W or W compounds,
   from 0 to 80 wt.% Bi or Bi compounds, and
   wherein not more than one of the constituents is 0 wt.%,
   wherein that constituent is not W or the W compound.
2. Lead substitute material according to claim 1,
   characterised in that
   the lead substitute material comprises
   from 12 to 22 wt.% matrix material,
   from 0 to 39 wt.% Sn or Sn compounds,
   from 0 to 60 wt.% W or W compounds and
   from 0 to 60 wt.% Bi or Bi compounds, and
   wherein not more than one of the constituents is 0 wt.%.
3. Lead substitute material according to claim 2,
   characterised in that
   the lead substitute material comprises
   from 12 to 22 wt.% matrix material,
   from 0 to 39 wt.% Sn or Sn compounds,
   from 16 to 60 wt.% W or W compounds and
   from 16 to 60 wt.% Bi or Bi compounds.
4. Lead substitute material according to claim 1,
   characterised in that
   the lead substitute material comprises
   from 12 to 22 wt.% matrix material,
   from 40 to 60 wt.% Sn or Sn compounds,
   from 7 to 15 wt.% W or W compounds and
   from 7 to 15 wt.% Bi or Bi compounds.
5. Lead substitute material according to any one of claims 1 to 4,
   characterised in that
   the lead substitute material additionally comprises up to 40 wt.% of one or more of the following elements: Er, Ho, Dy, Tb, Gd, Eu, Sm, La, Ce, Nd, Cs, Ba, I, Pr and/or their compounds and/or CsI.
6. Lead substitute material according to claim 5,
   characterised in that
   the lead substitute material additionally comprises up to 20 wt.% of one or more of the following elements: Er, Ho, Dy, Tb, Gd, Eu, Sm, La, Ce, Nd, Cs, Ba, I, Pr and/or their compounds and/or CsI.
7. Lead substitute material according to claim 6,
   characterised in that
   the lead substitute material additionally comprises up to 8 wt.% of one or more of the following elements: Er, Ho, Dy, Tb, Gd, Eu, Sm, La, Ce, Nd, Cs, Ba, I, Pr and/or their compounds and/or CsI.
8. Lead substitute material according to any one of claims 1 to 7,
   characterised in that
   the lead substitute material additionally comprises up to 40 wt.% of one or more of the following elements: Ta, Hf, Lu, Yb, Tm, Th, U and/or their compounds.
9. Lead substitute material according to claim 8,
   characterised in that
   the lead substitute material additionally comprises up to 20 wt.% of one or more of the following elements: Ta, Hf, Lu, Yb, Tm, Th, U and/or their compounds.
10. Lead substitute material according to claim 9,
    characterised in that
    the lead substitute material additionally comprises up to 8 wt.% of one or more of the following elements: Ta, Hf, Lu, Yb, Tm, Th, U and/or their compounds.
11. Lead substitute material for radiation protection purposes in the energy range of an X-ray tube having a voltage of from 60 to 90 kV according to any one of claims 5 to 10,
    characterised in that
    for nominal overall lead equivalents of from 0.25 to 0.6 mm the lead substitute material comprises
    from 12 to 22 wt.% matrix material,
    from 49 to 65 wt.% Sn or Sn compounds,
    from 0 to 20 wt.% W or W compounds,
    from 0 to 20 wt.% Bi or Bi compounds and
    from 2 to 35 wt.% of one or more of the elements Gd, Eu, Sm, La, Ce, Nd, Cs, Ba, I, Pr and/or their compounds and/or CsI.
12. Lead substitute material according to claim 11,
    characterised in that
    the lead substitute material comprises from 2 to 25 wt.% I, Cs, Ba, La, Ce, Pr and/or Nd and/or their compounds and/or CsI.
13. Lead substitute material for radiation protection purposes in the energy range of an X-ray tube having a voltage of from 100 to 140 kV according to any one of claims 5 to 10,
    characterised in that
    for nominal overall lead equivalents of from 0.25 to 0.6 mm the lead substitute material comprises
    from 12 to 22 wt.% matrix material,
    from 40 to 73 wt.% Bi and/or W or their compounds and
    from 5 to 38 wt.% of one of more of the following elements: Gd, Eu, Er, Hf and/or their compounds.
14. Lead substitute material according to any one of claims 1 to 13,
    characterised in that
    it comprises a structure of protective layers of different compositions.
15. Lead substitute material according to claim 14,
    characterised in that
    it comprises a structure of at least two protective layers of different compositions which are separate or joined together, wherein the protective layer(s) more remote from the body comprise(s) predominantly the elements having a lower atomic number, or their compounds, and the protective layer(s) close to the body comprise(s) predominantly the elements having a higher atomic number, or their compounds.
16. Lead substitute material according to claim 14 or 15,
    characterised in that
    it comprises a structure of at least two protective layers of different compositions which are separate or joined together, wherein at least in one layer at least 50% of the total weight consists of only one element from the group Sn, W and Bi or their compounds.
17. Lead substitute material according to claim 14 or 15,
    characterised in that
    it comprises a structure of at least two protective layers of different compositions which are separate or joined together, wherein at least in one layer at least 50% of the total weight consists only of at least 40 wt.% Sn or its compounds and at least 10 wt.% I, Cs, Ba, La, Ce, Pr and/or Nd and/or their compounds and/or CsI.
18. Lead substitute material according to claim 14,
    characterised in that
    it comprises a structure of at least two protective layers of different compositions which are separate or joined together, wherein the protective layer(s) more remote from the body comprise(s) predominantly the elements or their compounds having a higher X-ray fluorescent yield, and the protective layer(s) close to the body comprise(s) the elements or their compounds having a lower X-ray fluorescent yield.
19. Lead substitute material according to any one of claims 14 to 18,
    characterised in that
    it comprises a structure of at least three protective layers of different compositions which are separate or joined together, wherein the protective layer(s) more remote from the body and the protective layer(s) close to the body comprise predominantly the elements having a higher atomic number or their compounds, and there is arranged in the middle at least one protective layer comprising predominantly elements having a lower atomic number.
20. Lead substitute material according to any one of claims 14 to 20,
    characterised in that
    a weakly radioactive layer is embedded between two nonradioactive protective layers which are separate from or joined to the radioactive layer.
21. Lead substitute material according to any one of claims 1 to 20,
    characterised in that
    the metals or metal compounds are granular and their particle sizes exhibit a 50th percentile according to the following formula $$D_{50}=\frac{d\cdot p}{10}\mathit{mm}$$

    

    
    wherein

    D₅₀ represents the 50th percentile of the particle size distribution,

    d represents the layer thickness in mm and

    p represents the proportion by weight of the particular material component in the total weight,

    and the 90th percentile of the particle size distribution D ₉₀ ≤ 2 · D ₅₀.
22. Radiation protection apron of lead substitute material according to any one of claims 1 to 21.

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