Note: Descriptions are shown in the official language in which they were submitted.
200A079
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STRUCTURE FOR SHIELDING RADIOACTIVE RADIATION
FIELD OF THE INVENTION -
The present invention refers to the field of the pro~
tection against radioactivity and offers a structure for
shielding radioactive radiation especially under very speci-
fic conditions, e.g. in the cosmic space. Hence, the object ``~
of the present invention is a structure for shielding radio-
active radiation, having first and second sides, the radio-
active radiation striking the structure from first side, the
structure comprising at least three structural layers and
each of the first two structural layers, taken in sequence
15 from the first side, comprises an element which converts at ; ~ -`
least a part of a first kind of radioactive radiation into a
second kind thereof. ;
BACKGROUND OF THE INVENTION
The protection of the human beings and goods against
radioactive radiation is generally secured by specific ma~
terials described in detail in the literature of the art.
The protection systems are realized by the use of specified
material structures offering security in the presence of a
source of a well-defined kind of radiation. In the normal
conditions, all nuclear and X-ray sources applied in proces-
ses controlled by the society are well-defined and therefore
the existing methods of protecting the environment against
30 the possible damages caused by this kinds of sources are sa- i`
tisfactory. ~ m
Frcm the related art, see e.g. in US-PS 2 580 360
(granted in 1945 to Ph. Morrison), US-PS 4 081 689 (granted
A4580-5903/NE-KO - ~
,. " .",~
i ~
2004079
-2-
'`"`'' :'`,`~,'
in 1978 to Reiss) or GB-PS 2 117 964 (granted in 1982 to
Amershem Int. plc) follows that the philosophy of protection
against radioactive radiation has been long time based on
systems consisting heavy metals, especially uranium and/or
lead. The proposed shield structures are expensive and dif~
ficult to move because of the weight. Therefore an important
task should be seen in reducing the thickness and weight of
such kinds of shields.
A new approach to the problem of the structures for
shielding radioactive radiation can be found in the US-PS
4 795 654 (granted in January 1989 to P. Teleki). The pro-
posed structure secures shielding X-ray and gamma-radiation.
It comprises a three layer system composed of different ele-
ments, which converts the X-ray and gamma-radiation into an-
other kind of radiation, on absorbing energy of the radia-
tion. The first layer forming the first side of the struc-
ture for receiving the radiation - the radioactive radiation
strikes it - consists of uranium, gold, lead, osmium, rhe-
nium, tungsten and/or tantalum. The second layer arranged
behind the first is consisted of tin, indium, palladium,
rhodium, ruthenium, molybdenum, and/or niobium. The third,
i.e. the rear layer may be made of zinc, copper, nickel, co-
balt, iron, manganese, chromium, vanadium and/or titanium.
Each of the layers can be consisted of one element or a mix-
ture (alloy) including at least two of the materials listedup above. The structure proposed by the US-PS 4 795 654 is
made of relatively heavy metals and offers no protection
against neutrons and alpha-particles. The problem of safety
under conditions of intensive neutrbn radiation follows from
the fact that the high energy neutron flux impacting the
plurality of materials results in generating high-energy
gamma radiation causing also difficulties in securing the
protection. The plurality of metals listed up in the speci-
fication creates the possibility of realizing effective pro-
tective structures in environment comprising defined, i.e.
'',"'''''''`~
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ZoO4079
-3-
known and localised sources of X-ray and gamma-radiation up
to a middle energy level.
The known radioactive shield structures described in
the art offer no satisfactory solution when high security .
protection is to be ensured in a radioactive environment ge-
nerated by sources difficult to identify. The situation of
such kind can occur especially in the space technology. In -~ `
the cosmic space uncontrolled radiation sources act having
sometimes intensity changing in wide range which may cause ~ ~ i
10 heavy damages to the apparatuses applied in the cosmic ve- ~;
hicles and laboratories. In war and catastrophic situations
the same problem may arise also on the Earth.
In the environment of the cosmic space the most dan-
gereous are the particle showers comprising neutral and .
15 charged particles together with the high energy X-ray and `~.
gamma-radiation. The high energy elementary and charged par-
ticles and radiation are capable of inducing different kinds
of atomic reactions in the materials of the apparatuses app- ;~
lied and in the shield structures prepared generally in form
of plate like elements (armour plates). The existing power
limitations of the rocket vehicles in the space technology !'~''~'.. ',`~,''`
do not allow to apply heavy and thick shields and therefore ~`
it is practically impossible to avoid many damages caused to
the means of this technology applied for exploring the cos~
-25 mic space and/or realizing specific technologies in the con-
ditions of the weightlessness. ;~
. ,, .. ~,; ~
SUMMARY OF THE INVENTION
Hence, the object of the present invention is to
create a relatively light but effective shield structure ~ 5
applicable on aeroplanes and in aerospace engineering means !,
securing high safety level protection against different ,
kinds of the radioactive radiation and capable of securing
the required safety up to the energy range 50 MeV character-
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..-.......
Z004079
-4-
izing the most intensive particle showers.
The invention is based on the following considera- ~ ;~
tions.
The high energy radiation is always capable of acti-
vating the elements forming any shield. In this activationprocess often occurs that the basic material becomes also
radioactive. The activation process can not be avoided at ~ `
all and therefore the solution should be found in the appro-
priate material structure of a shield.
10The strongest influence can obviously be experienced
on the first side of the shield which receives the radio~
active radiation. This side subject also to optical and inf-
rared radiation - the last can generally be compensated
without dificculties by the known means. Of course, when se-
lecting the thickness of the layer on the first side, it is
important to take into account that a vaporization process
can take place under influence of the kinds of radiation
differing from the radioactive ones.
The electrones falling into the first side can
20 generate bremsstrahlung in the X-ray range. The alpha-par- - `;
ticles can cause nuclear reactions only in the light ele-
ments, having atomic number above 20. The slowing down pro-
cess of the electrones results in the requirement that the ;
first side shouldn't include elements having atomic numbers p~r~
exceeding 60. This is the range of the elements with middle
atomic numbers. As for protecting against proton showers it
is also advantageous to apply even this atomic number range.
In the first side neither the very light nor the heavy ele- -~`.a~ ~`
ments are advantageous. The measurements and analysis show
that the maximal energy of the gamma- and neutron radiation
to be expected in normal conditions doesn't exceed 2û MeV.
In specific conditions 50 MeV can be expected also. This is,
however, the maximal range to be taken into account because
over 50 MeV another mechanisms play role. In the shield the ~ ~ ;
reaction (gamma, n) should be realised under influence of
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2004079 - ~ ~
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the gamma-radiation and the neutron radiation has to cause a
change in the atomic number +1. 0f course, other reactions
can take place, too. Here it is important to select the re-
actions according to their probability and effective cross- ~ -~
-section.
On the basis of the above consideration a material ~ r
structure should be realised wherein the elements resulting
from the transformation reactions of atomic nuclei form also - ~,`'`!`;~`'',
a metal which can coexist with the basic material and gives ~ `
sufficient mechanical strength. Therefore it is important to
select the structure according to the long term changes of
the nuclei, i.e. to make a choice on the basis of the worst
expected characteristics. The investigations show that no
element can bear longer series of loss or capture of neut-
rons and the only one element resulting in another elements
of sufficient strength after the loss of one neutron or a `
series of captures of neutrons is the titanium, 22Ti.
According to the recognition recapitulated above thetitanium as structural layer is also very effective in com-
20 bination with a light metal, especially magnesium and beryl- " i
lium when protection should be given against showers of
charged particles, especially alpha-particles.
Thus, the present invention proposes a structure for
shielding radioactive radiation, the structure having first `~
and second sides, the radioactive radiation striking the
structure on the first side, the structure comprising at
least three structural layers, wherein each of the first two :
structural layers, taken in sequence from the first side to- ~i
ward the second side, comprises an element which converts at
30 least a part of a first kind of radioactive radiation into a ;:
second kind thereof. The structure comprises at least two ;`.. : ~
titanium structural layers and a middle part arranged be- ` ~ :
tween the titanium structural layers, wherein one of the ti- ,
tanium structural layers constitutes the first side and the ~:
middle part includes at least one intermediate structural
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2004079
layer made of beryllium and/or magnesium.
It is advantageous to apply in the proposed structure
the intermediate structural layer comprising beryllium and
separated from the titanium structural layers by shield
structural layers prepared with boron for slowing down neut~
rons.
In another advantageous embodiment of the proposed
structure the intermediate structural layer is made of be-
ryllium dispergated in form of beryllium oxide in magnesium
and/or copper.
In a preferred e.mbodiment~ of the structure proposed
by the invention the shield structural layers consist of
boron dispergated in magnesium.
According to another possibility the shield struc~
tural layers consist of filaments made of a boron or gra-
phite, the filaments are covered with a layer made respec-
tively of graphite or boron.
In a further preferred embodiment of the proposed
structure the structural layers are separated by a layer
including at least one oxide, nitride or carbide of boron or
titanium.
It is also preferred if the proposed structure com-
prises an outer covering layer consisted of titanium-nitride
and/or rhodium, wherein the outer covering layer is prepared
on the first side.
The protection safety is especially high when the
structure realised according to the invention comprises at
least thirty-two structural layers of preferred thicknesses
not exceeding 0.01 mm, the structural layers forming a body
of thickness at least about 0.3 mm, wherein the structural
layers are separated by compound layers of thicknesses at
most 0.001 mm. The compound layers generally consist of at
least one oxide, nitride or carbide of at least one metal
selected from boron, magnesium and titanium.
The protection safety offered by the structure pro-
2004079
:~ ....
,
-7-
posed by the invention can be further improved by applying -~`
a graphite sheet covering the first side.
The structure according to the invention secures pro~
tection against showers of neutral and charged particles, ~ .
and gamma- and X-ray radiation, as well. Of course, the me-
tal layers are capable of capturing beta-radiation without
any damage. :~
BRIEF DESCRIPTION OF THE DRAWINGS
, ~
The shield structure proposed by the invention will
be further shown in more detail with reference to the at-
tached drawings and several embodiments described by way of
example only. In the drawings ~ -
FIG. 1 illustrates a cross-section of an eight-layer ~ -
structure with some separating compound la-
yers, ;; .
FIG. 2 shows a cross-section of a structure compris-
ing a high number of, e.g. thirty-two layers, .
and
FIG. 3 is the cross-section of a relatively simple
preferred embodiment of the structure const- -~
ructed according to the invention.
.'''..:, ;,.~:''.;
OESCRIPTIûN OF THE PREFERRED EMPODIMENTS
The structure proposed by the invention (Fig. 1) con- ;~
sists of at least two titanium structural layers 1 and a
middle part therebetween. The middle part is consisted of .~
either an intermediate structural layer 5 limited by two ..
shield structural layers 3 lying at the titanium structural :
layers 1 or a magnesium intermediate structural layer 11.
The structural layers form a body with preferred thickness
at least û.3 mm. ` ` ~- .
The structure is arranged in the way of propagation
1,
' ' ' ....
Z004079
-8-
of a kind of radioactive radiation R, impacting a first side
of the structure, and this side is equipped with an outer
covering layer 7 made of titanium-nitride, rhodium (45Rh)
or graphite. The shield structural layers 3 are made of bor-
on (5B) and the intermediate structural layer 5 consists ofberyllium (48e). The structural layers 1, 3, 5 and 11 are
separated by compound layers 9, 12 comprising at least one
nitride, oxide or carbide of boron, magnesium or titanium.
The compound layer 12 is preferably thin layer. The first
side of the structure can be covered by a graphite sheet 13
of appropriate thickness (Fig. 2 and 3). Graphite is a well-
-known moderator substance.
As it is shown in Fig. 3 it is advantageous to pre-
pare combined structures comprising pairs of titanium
structural layers 1, the pairs being divided by an inter~
mediate covering layer 17 made of at least one nitride,
oxide or carbide of boron, magnesium or titanium. The com-
pound layers 9 divide the structure into parts comprising
the pairs of the titanium structural layers 1. Each pair of
the titanium structural layers 1 delimitates a system ar-
ranged in its middle part and including either two shield
structural layers 3 made of boron and between the last the
intermediate structural layer 5 of beryllium or the magne-
sium intermediate structural layer 11 in a space sequence as
required by the given conditions, e.g. alternatively.
A preferred embodiment of the structure of the inven~
tion comprises advantageously at least thirty-two structural
layers 1, 3, 5, 11. These thin layer have thicknesses in the
range from 0.0001 to 0.01 mm, e.g. in the sequence shown in
Fig. 2. They are separated by compound layers 9 and 12 hav-
ing thicknesses at most 0.0001 mm. This structure is prefer-
ably at most 0.3 mm thick.
Of course, the structure as proposed by the invention
may include structural layers of thicknesses higher than
0.01 mm. In some applications the layers are preferably se-
', ,' ~ ' '.i'.
2004079
. ~ '.
_9_
. . .
lected to have thickness exceeding 0.01 mm, advantagQusly of
about 0.1 mm. The choice of the dimensions depends on the :
task of realizing the structure, on the field of the appli~
cation.
The basis of the structure proposed by the invention
is the titanium. This is a metal having seven isotopes
whereamong five are stables. The average cross-section of
the titanium (22Ti) is 5.8 barn for the thermal neutrons and
this average value refers generally to the isotopes, too.
The cross-section for reactor and fast neutrons is much
smaller than the value mentioned. The titanium has the fol- ;
lowing scheme of transformation (the percentage values given -. :
hereunder represent the natural isotopic composition of ti~
tanium)~
;~
2452Ti* (half-period 3.û9 h) ~ 2462Ti (7.99 %) - ; - .
~ 2427Ti (7.32 %) ~ 4282Ti (73.98 %) - 292Ti (5.46 %) -
- 202Ti (5.25 %) ~ 22Ti* (half-period 5.80 h) `;i
. i"':-'.. '.;- '
(* - transformation with beta-decay and emission of gamma-
-radiation.)
It can be seen, that the first neutron captured by
the titanium causes a (n, gamma) reaction. In the first cap- ~ `
ture reactions 94.75 % of the titanium atoms are not subject :~ i:
to the change of the atomic number. This means that under
influence of the neutrons only about 5.25 % of the titanium
will be converted into vanadium in the first stage of the
process. It is very advantageous that in the second stage of ; `
this process about 89.29 % of the titanium applied at the
beginning take part yet. The titanium isotope with mass num-
ber 52 converts into vanadium with the half-period of this -
converting process less than 6 minutes. In the scheme men-
tioned above the instable isotopes of the titanium (with
mass numbers 45 and 51) are subject to beta-decay with gam-
35 ma-emission. -
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2004079
. ~ -
-10- ,". ~ ~
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The vanadium shows the following scheme of transfor-
mation (the percentage values given hereunder represent the
natural isotopic composition of vanadium):
23V (half-period 330 days) - 23V (0.25 %, half-
-period 5.1014 years) - 21V (99.75 %) - 23V ~ ~ `
The last isotope shows half-period 3.75 min. and transforms ;~ ~ -
by beta-decay with gamma-radiation. It can be seen that in
this way the generation of the rather not desired isotope of
vanadium with mass number 50 is practically avoided. The
next stage of the transformation process provides chromium
from vanadium, then the process results from chromium in
manganum and the activation process ends on iron. The res-
pective transformation data can be found in many different
handbooks, so there is no need to recite them. Therefore the
schemes of transformation are not shown further here. It is
to noted, however, that the rather dangerous chromium iso- - -
tope having mass number 51 (24Cr) is present only in small~ ~ .
amounts (the respective half-period makes out about 27.8 ~:
days). ~ ~
The transformation scheme can be continued by cobalt, ~ -
nickel and copper having respective atomic numbers 27, 28 ~
and 29. The probability of reaching the cobalt and further . `.
25 stages from titanium is very low. It should be mentioned the
full scheme beginning from the titanium up to copper results
always in metals of relatively high mechanical strength. The
conclusion is that different products applied in radioactive -
environment, e.g. the containers, vessels, etc. can be made
30 on the basis of pure titanium and applied long time in the
conditions of the very intensive neutron and gamma-particle
showers. --
The elements of this transformation scheme have crys-
talline lattice of cubic and orthorombic systems. . ~
As for the titanium it should be mentioned that in a . .
;,,~: ,.., "~
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200A079
-` : .,'.
.
(n,2n) reaction it can be converted into scandium (2415Sc).
This reaction has relatively low probability and therefore
the transformation scheme in this direction leading to a
stable calcium isotope (2404Ca) is not dangerous.
According to the investigations the neutron capture
processes result in the following change of the composition ; `
of a material initially composed of titanium~
1. After the capture of the first neutron: 94.75 % Ti ,,`,,",.,`.~!",',,,,',,
and 5.25 % V. ~:
2. After the capture of the second neutron: 89.29 %
Ti, 5.46 % V and 5.25 % Cr.
3. After the capture of the third neutron: 15.31 %
Ti, 73.98 % V, 5.46 % Cr and 5.25 % Mn. ;:
4. After the capture of the fourth neutron: 7.99 %
Ti, 7.32 % V, 73.98 % Cr, 5.46 % Mn and 5.25 % Fe.
5. After the capture of the fifth neutron: titanium :
vanishes, 7.99 % V, 7.32 % Cr, 73.98 % Mn, 5.46 % Fe and ...
5.25 % Co. " `
6. After the capture of the sixth neutron: titanium
and vanadium vanish, 7.99 % Cr, 7.32 % Mn, 73.98 % Fe, ; `^~
5.46 % Co and 5.25 % Ni.
The process can be continued, however, the probabili-
ty of lasting up to vanishing iron is rather low.
According to the invention between the titanium
25 structural layers 1 can form a sandwich structure together ~ /,
with a magnesium intermediate structural layer 11. The mag- ^~
nesium is advantageous because of forming aluminium by a
transformation process~
24 - 25 - 26 - 217*2Mg _ 27 2183Al -
_ 28 - 29 ~ 30 ~ 314Si - 131P
(* - transformation with beta-decay and emission of gamma- ',"~3'~
-radiation.) :-~
The magnesium takes part with isotopes having mass
2004079 ~
-12-
numbers 24, 25, 26 and 27. The last isotope has half-period ~ -~
9.5 min., it transforms by beta-decay with gamma-radiation.
The same transformation characterises the instable isotope
of aluminium with mass number 28. It is obvious that alumi-
nium and magnesium can be used in structural applications
requriring high mechanical strength. The data evidence that
a magnesium layer retains the mechanical strength during two
neutron capture processes, and the resulting aluminium will
survive a capture process more. The magnesium structure is,
however, advantageous because of low capture cross-section,
i.e. the probability of a capture process is relatively low.
Therefore magnesium with a neutron shield can long live in
the environment of intensive neutron radiation.
The structure proposed by the invention includes the :
titanium structural layers 1 as an outer protective cover
The cover receives the shower of the charged particles, too. ~ `
As secondary structural substance magnesium can be applied.
The outer surface of the titanium structural layer 1 limit- ~-~
ing the structure from the first side is preferably covered ~;
by titanium nitride.
The three-layer structure of the invention compris~
ing two titanium structural layers 1 and a magnesium inter- ;~ -
mediate structural layer 11 therebetween is not applicable ~;; `
against neutron and gamma-radiation without further means :; .?
25 and shielding layers. , ' . ,' ~ ' ,. ', ;'i,r
The neutron radiation generally comprises reactor and
fast neutrons which require slowing down when securing ef- ..
fective protection. This process is desired because of con- `;;
siderable increase in the cross-section for a neutron cap-
30 ture process. The problem is that the excellent neutron ab- ; . .~.-
sorbents as cadmium or gadolinium emit very intensive gamma-
-radiation having energy range from 1 to 10 MeV. This gamma- . -. .
-radiation emitted under influence of an intensive neutron -
shower can destroy any structural material except concrete
or lead used in thick shields. The last materials are prac-
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2004079
..
-13- ~
.. ~ , ~... ...
tially not applicable in the space technology. Therefore it
is necessary to slow down the neutrons and this should be ~ `
done by a process not based on the (n, gamma) reaction. It ~ -
is also a novel feature of the invention that for slowing
down the neutrons the reaction (n, alpha) is preferably app-
licable. This recognition results in the selection of the
intermediate structural layer 5 to be covered by a shield n~ ::
structural layer 3 made of boron or lithium for slowing down - `
the neutrons, transforming thereby the reactor and fast
neutrons into thermal neutrons absorbed by the intermediate
structural layer 5. The features of the boron are more ad-
vantageous than that of the lithium. The cross-section of -
the boron for the (n, alpha) reaction is 4000 barn. Under
influence of the neutron shower the following process takes
place~
,: :
. .
loB (n, alpha) 7Li
In this process energy Q = 2.8 MeV becomes free and will
result in heating up the material. A low intensity charac-
teristic radiation is emitted also. The lithium is a stable
element but the chemical features are not acceptable for a .`.~ `.~ "'`~.'t,'.
mechanical system. The boron acts therefore as a moderator
emitting gamma-radiation which should be absorbed by a be~
ryllium layer forming the material of the intermediate ~
structural layer 5. The alpha-particles emitted in the reac- ~ xtion recited above have energy about 1.5 MeV and they take `
up respective electrons from the atoms of the environment ;-
transforming thereby into helium. In a relatively low proba-
30 bility reaction the tritium (31H) can be deliberated, too. ` ;
These processes mentioned form the disadvantage of the
structure proposed by the invention.
The disadvantage is not so important. The advantage
of the structure is that boron is applied which is a low ~.~;`
density material with relatively high strength and its melt-
- ~ ' ~`''''~
~,, '.. .. ,~ ,1 '
- 200407~
-14- --
ing point is also high (2030 C). Therefore the armour plate
comprising a boron layer is applicable in the space techno-
logy.
The boron structural layer 3 secures thereby protec-
tion against the neutron showers entering from the environ~ment. This protection is, however, not effective against the
neutrons generated by the gamma-radiation impacting the `
boron layer and in the other layers of the structure. -
Therefore is a rear boron layer necessary, as shown in the
Fig. 1, 2 and 3.
The beryllium layer as intermediate structural layer
5 is also a very important feature of the present invention,
because beryllium is an especially light metal having den-
sity about 1.85 kg/dam3. The advantage of applying beryl-
15 lium is even the (gamma, n) reaction taking place therein ~ "
according to the following scheme~
4Be (gamma, n) 4He
The prncess results in deliberating energy Q = 1.65 MeV. Thereaction takes place under the condition of impacting gamma-
-radiation having energy at least 1.7 MeV. The neutrons have "
energy 110 keV. The last particles will be absorbed by the ~c
second shield structural layer 3 made of - as mentioned - ~: e
25 boron. ~ ~:
The effective cross-section of beryllium for the
process of capturing neutrons is low, about 0.01 barn but : -
the scattering effect is relatively strong therefore beryl-
lium is rather a neutron reflector than moderator. A thin
layer of a heavy metal can improve the shielding effect of
the structure built up as proposed.
The structure according to the invention comprises a `~
titanium structural layer 1 on the first side where the ra- , . .
dioactive radiation strikes the body. It is preferred to'.~'','',J,.~'"''`~''`~',~
prepare here an outer covering layer 7 of titanium-nitride.
Z0040~79
-15-
A thick layer made of e.g. rhodium can be also advantageous
if applied together with the titanium-nitride layer or sepa-
rately. The rhodium layer gives protection against strong
optical radiation and it is capable of surviving one activa-
5 tion process. ~`
The titanium elements can show disadvantageous mecha~nical features in the high temperature range. The vanadium +
+ titanium alloy is free of this drawback. Therefore the -~
alloy is also applicable, especially because of comprising ~ -
the vanadium component forming the second stage of the
process of activating titanium. The shield structural layer
3 should be made rather of pure boron associated, when ne~
cessary with graphite. It is proposed to apply boron on gra- `~ ;~
phite filaments - if the mechanical strength requirements
allow to do so. The combined filament structure can be com-
pacted by pressing the filaments together. This solution is , `
advantageous because of ensuring place for helium deliberat-
ing in the transformation process of the nuclei. Of course,
boron can be sintered or compacted by other technologies, '`",'" ~!`'.$`
too. Another preferred possibility is to apply boron fila-
ments covered with graphite and this structure can also be
compacted by known methods.
In the intermediate structural layer 5 beryllium can ` ~ -
be dispergated in magnesium. The first material is present i/ '.','":.!:,',
in form of an oxide (Be~) and magnesium constitutes a plate.
(Pure boron or boron in form of carbide or nitride can be
dispergated also in the magnesium plate.) The shield struc-
ture built up from the materials mentioned above should have
thickness at least 0.3 mm. The thickness of the layers is ~p
30 not restricted, it depends on the circumstances of applying `
the protective shield structure proposed and can vary in the
range from 0.0001 up to 0.1 mm.
The basic element of the structure proposed by the
present invention can be recapitulated as follows:
2004079
--1 6--
1. layer: 22Ti comprising, when necessary 23V and covered ~
from the outer side by TiN and/or 45Rh; -
2. layer: 5B in pure form or dispergated in magnesium plate -~
or in form of a cover prepared on graphite fila- -
ments or of a core of filaments covered with gra-
phite; ~ ~M
3. layer: 4Be in pure form or dispergated in a magnesium or
copper plate;
4. layer: similar to the 2. layer; ~
5. layer: 22Ti comprising, when necessary 23V. ~ ~p` -
The layers described above are generally separeted by
compound layers, made of oxide, nitride or carbide of boron,
magnesium and/or titanium. Of course, a mixed compound layer
may be also applied. The layers can be united by mechanical
means, if required or by appropriate adhesive substance. The
basic structure as shown above is a low density body. The
mechanical strength is high, the radiation up to very high
energy range can not cause heavy damage to it. The layers ;~
slow down and absorbe practically all kinds of neutral and `` ~ ;`;
20 charged particles. The activation process lasts short time, ~, ;
generally some minutes. The isotopes characterised by longer
half-period are present only in very small, trace amounts.
The protection against gamma-radiation is very effective for
the energy range exceeding 1.7 MeV. If the effectiveness for i
the lower energy range should be improved a thin layer of a
heavy metal would be required, however, the structure itself
secures protection also in this energy range.
The construction as proposed can be strengthened by
the other sandwich structure described. The last comprises a
magnesium layer connected with respective titanium layers on
each side. The magnesium layer can be applied together with :
and behind the five-layer structure shown above as the sixth ;~
layer followed by a further titanium layer, if necessary. `
The magnesium layer is prepared generally for improving the ` -
mechanical features under the conditions when intensive sho-
:', ."~
. ~, ,....~....
Z004079
-17-
wers of neutral and charged elementary particles, nuclear
fragments attack the shield structure proposed by the inven-
tion.
The sandwich structures specified above can be appli-
ed in a body comprising a plurality of these structures. Theminimal thickness of the body should generally be 0.3 mm. It
is advantageous to prepare at least one of the structures
with structural layers in form of thin layers of thickness ~ -
in the range from about 0.0001 mm to 0.01 mm, preferably
10 about 0.001 mm. The thin layer structure is advantageous be- ~ - ~s
cause of the backscatter phenomenon caused by the gamma-ra- M -~
diation on impacting. As example, construction units with `~ `
the following sequence of the structural layers 1, 3, 5, 11
can be prepared (the chemical elements are here shown with-
out respective atomic numbers)~
Ti - B - Be - B - Ti -; Mg -; Ti - B - Be - B - Ti `~ ` .
Ti - B - Be - B - Ti -; Mg -; Ti
Ti - B - Be - B - Ti
Ti - B - Be - B - Ti -; Mg -; Ti - B - Be - B - Ti -; Mg
Ti - B - Be - B - Ti; followed by any one of the ^
above structures
The titanium structural layers 1 can form together
with the magnesium intermediate layers 11 a structure where- ;~
in at least one pair of layers Ti + Mg is present and the
structure is closed by a TiN layer. Magnesium can be mixed
(alloyd) with copper, the other additives are rather to be
avoided.
The structure of the invention can be completed with
further protecting means. As a very effective protecting ..
element the application of a graphite plate of thickness ex-
ceeding 0.5 mm is especially advantageous.
As mentioned above, it is especially preferred to
build up the structure of the invention with at least thir-
ty-two structural layers wherein at least one of the basic
35 construction units defined` above is made of thin titanium, -
,....~ ,.,.", ,..,.; ,.
~:'"" '' . '" ~,
Z004079
-18-
boron and beryllium layers having thickness in the range
from û.OOûl to 0.01 mm, preferably about 0.001 mm. The gene~
ral thickness of this system should be however higher than
û.3 mm (of course, a thicker construction can be built up,
wherein more layers have thickness exceeding û.l mm and the
summarized thickness is at least 0.5 mm).
The structures proposed by the present invention can
be produced without technological difficulties. They are not
too expensive, they ensure high level safety for long terms.
lû The density is relatively low, which is of outraging impor~
tance in the space technology. The structure shows high re-
sistance against chemical substance and it can be applied in
preparing containers receiving nuclear waste, shields to be
used on aeroplanes or in space technology means for ensur-
ing protection against different kinds of radioactive radia-
tion.
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