Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F1/00—Shielding characterised by the composition of the materials
  • G21F1/02—Selection of uniform shielding materials
  • G21F1/10—Organic substances; Dispersions in organic carriers
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F1/00—General methods for the manufacture of artificial filaments or the like
  • D01F1/02—Addition of substances to the spinning solution or to the melt
  • D01F1/10—Other agents for modifying properties
  • D01F1/106—Radiation shielding agents, e.g. absorbing, reflecting agents
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F8/00—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof
  • D01F8/04—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers
  • D01F8/06—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers with at least one polyolefin as constituent

Definitions

• the present invention relates to the field of neutron-shielding materials, and in particular to fibers effectively protecting humans and neutron-sensitive objects from thermal neutrons, said fibers showing low emission of secondary radiation while being at the same time highly flexible.
• the invention further relates to a method of manufacturing said neutron-shielding fibers.
• neutron capture therapy consists of irradiating cerebral tumors with a definite quantity of neutrons so that only the tumor will be destroyed.
• neutron-shielding material of sufficient flexibility is urgently required, which does not yield any high secondary radioactivity and/or radioactive rays as a result of neutron absorption.
• neutron-shielding materials exist in the form of boards or plates comprising cadmium and boron compounds.
• such neutron-shielding boards of said materials are physically rigid and do not show any flexibility.
• cadmium is known to yield a considerable quantity of secondary gamma rays as a result of neutron absorptibn, this chemical element cannot be used to protect the human body against neutron radiation.
• the Japanese Laid-Open Patent Applications Nos. 52-127597 and 52-131097 disclose neutron-shielding materials which can be formed into sheets and are made on the basis of various kinds of plastics and boron and/or lithium compounds, which in case of neutron absorption yield only small quantities of secondary gamma rays.
• the Japanese Laid-Open Patent Application No. 53-21398 discloses a method of manufacturing neutron-shielding fibers consisting of ion exchange fibers which have adsorbed ionized compounds of boron and lithium, or of staple-fiber-like polymers containing boron and/or lithium compounds.
• the finished products do not show the desired effective shielding due to incomplete adsorption and fixation of the neutron-shielding ionized compounds within the ion exchange fibers or due to the fact that the ionized compounds which have been fixed may be released from said fibers during washing and rinsing operations.
• the staple-fiber-like polymers which are obtained by jet-spinning a mixture of neutron-shielding inorganic compounds and fiber-forming polymers can physically retain their fibrous structure.
• said staple fibers cannot be processed with any known yarn-spinning and knitting or texturizing machine due to their insufficient tensile strength, elongation and fiber configuration (textured styles).
• said staple fibers usually carry the neutron-shielding compounds exposed on their surface so that the latter may easily be rubbed or stripped off this surface, whereby the shielding properties inevitably deteriorate.
• any protective clothing made of fibers of the known type showed a loss of neutron-shielding compounds during and after washing operations and as a result of frictional forces between the clothing and various objects during its practical use. It was also found that the finished products made from prior art neutron-shielding fibers, when exposed to neutron rays, yielded significant quantities of secondary radioactive radiation and/or materials due to various nuclear reactions. For example, when lithium (Li) was used as a neutron-shielding element the lithium compounds present on the fiber surface, when exposed to thermal neutron rays, generated a significant quantity of tritium ( 3 H) which spread by diffusion into the atmosphere.
• Li lithium
• the neutron-shielding composite fiber according to the present invention containing neutron-absorbing particles of about 25 pm maximum in diameter and characterised in that said fiber is a bicomponent fiber having a core and sheath structure comprising a fiber-forming polymer (A) as the core component, which contains at least 5% by weight of said particles of at least one neutron-absorbing compound, and at least one kind of a fiber-forming polymer (B) as the sheath component.
• A fiber-forming polymer
• B fiber-forming polymer
• the fiber-forming polymer (B) must be compatible with the fiber-forming polymer (A), that is, it should bond to the core component.
• the present invention further includes a method of producing said composite neutron-shielding fiber or neutron-shielding bicomponent fiber.
• the core component should contain from 10 to 60% by weight of said neutron-absorbing compound, the particles of which should most preferably have a diameter of 15 11m or less.
• the polymer (A) of the core component and the polymer (B) of the sheath component should be selected so that the ratio of the viscosity of the sheath component to the viscosity of the core component at the temperature at which the composite or bicomponent fiber or yarn is spun falls in the range of 0.2 to'0.9.
• the present invention makes it possible for the first time to manufacture neutron-shielding fibers that satisfactorily meet the practical requirements for neutron-shielding clothing materials in that the generation of secondary radiation is minimized whilst at the same time the new fibers show satisfactory mechanical properties or can be manufactured into clothing without losing any of the neutron-shielding components of the fibers, so that the neutron-shielding effect will remain stable throughout manufacturing and use of the corresponding clothing.
• the textile materials made from the fibers in accordance with the present invention show sufficient flexibility to be manufactured into comparatively comfortable protective clothing.
• Neutron-absorbing compounds which can preferably be used as particles in the core component of the fibers according to the present invention should be chemically stable and physically capable of effectively absorbing thermal neutrons and minimizing or eliminating the occurrence of secondary radioactive radiation such as secondary gamma rays.
• Such compounds are in particular compounds containing isotopes such as 6 Li and/or 1 °B.
• lithium compounds and/or boron compounds containing said isotopes in the normal natural ratio may be used, e.g. compounds such as lithium carbonate, lithium fluoride, boric acid, boron carbide, boron nitride, etc. It is more preferable, however, to use compounds constituted from artificially separated and enriched isotopes.
• the mixed compounds are difficult to spin into fibers, leading to poor mechanical properties of the fibers eventually obtained.
• said neutron-shielding compounds When mixing said neutron-shielding compounds with the core-forming component polymer (A), it is also an important factor that said neutron-shielding compounds are mixed into said core component polymer (A) at a rate of at least 5% by weight, preferably at a rate within the range of 10 and 60% by weight. If the content of the neutron-shielding compound in the core material is below 5% by weight, the neutron-shielding finally obtained will be lower than desired and necessary. Conversely, if the content of the neutral-shielding component in the core compound is more than 60% by weight, the spinning process wilt be very difficult, leading to poor mechanical properties of the fibers themselves, even though their neutron-shielding properties are improved.
• the core-forming component polymer (A) the essential component of the bicomponent fiber
• a variety of widely used fiber-forming raw materials can be used, such as polyesters, polyamides, polyolefins, etc.
• polyethylene and various kinds of copolymers of polyethylene are copolymers containing polyethylene as their main constituent, especially copolymers consisting of polyethylene and less than 10 mol % of a second monomer, e.g. vinyl acetate, propylene, another alpha-olefin such as 1-butene, 1-hexene or N-vinyl carbazol.
• a second monomer e.g. vinyl acetate, propylene, another alpha-olefin such as 1-butene, 1-hexene or N-vinyl carbazol.
• the present invention is not restricted to the use of any specific sheath-forming polymer (B) forming the sheath of the bicomponent fiber according to the present invention, provided that the polymer used as polymer (B) is compatible with the polymer (A) used, that is, it must be properly bonded to the core-forming polymer (A). In this connection, however, it is preferred to use a sheath-forming polymer (B) which falls under the same category of polymers as the core-forming polymer (A).
• the composite ratio of the core component to the sheath component fall within a range of 0.5 to 10. That is to say, if the actual composite ratio does not meet the indicated range, e.g. if the core-versus-sheath ratio exceeds a maximum of 10, the capability of the sheath-forming polymer to cover the core will become unstable so that the core component may be bared, becoming part of the surface of the obtained fiber, which will result in very critical problems. In this case part of the neutron-absorbing compounds can get lost or rubbed off in the spinning process and radioactive material secondarily generated by a nuclear reaction with absorbed neutrons can diffuse out of the fiber finally obtained.
• the core-versus-sheath composite ratio is below 0.5, the originally intended effective neutron-shielding properties of the final product cannot be obtained since the amount of the core component containing the neutron-shielding compounds will become too low, with respect to the sectional areas of the composite fibers.
• said core-versus-sheath composite ratio should preferably fair within a range of 1 to 4, thus enabling the sheath-forming polymer to cover sufficiently the neutron-shielding compounds of the core without any drop out at all, and thus sealing even the smallest quantity of radioactive materials generated by the neutron rays inside the core component polymer without any possibility of these materials escaping into the atmosphere.
• the diameter of the filaments obtained preferably is in the range of 5 to 200 ⁇ m, most preferably of 10 to 100 ⁇ m.
• the fibers according to the present invention as disclosed above are composite or bicomponent fibers showing a. marked and sufficient shielding effect in shielding humans and/or objects from neutron rays, especially from thermal neutrons.
• the present invention relates to a process of manufacturing the core-and-sheath composite or bicomponent fibers according to the invention. It was found that, when using conventional equipment for spinning bicomponent yarns which are built up from composite or bicomponent fibers of the core-and-sheath type, said conventional equipment comprising a known spinneret for spinning conventional synthetic bicomponent fibers, the ratio of the melt viscosity X of the core-forming component polymer (A) containing the particulate neutron-shielding compounds to the melt viscosity Y of the sheath-forming component polymer (B) plays a very important role.
• melt viscosity ratio is not in the recommended range as referred to above, it is very difficult to spin the composite fibers stably according to the present invention, since the spun yarn will often be cut during the spinning process, thus disenabling the operators to perform the spinning operation satisfactorily.
• the composite fibers produced in accordance with the present invention and their secondary products show very excellent neutron-shielding properties, especially with respect to shielding against thermal neutrons, without causing any intense radiation of secondary radioactive rays.
• the fabrics obtained do not lose any of the fixed neutron-shielding compounds by friction or during washing, and they are not only highly effective with respect to their neutron-shielding effects, they can also be easily manufactured into protective clothing for protecting humans against an attack of neutrons. Said positive characteristics are not a consequence of any secondary treatment of the fabrics obtained, but are due to the fibers themselves.
• the clothing obtained shows the mechanical properties common to any conventional fibers, also with respect to the high flexibility of the fabrics.
• protective clothing for shielding humans against neutron rays made of the composite fibers in accordance with the present invention, satisfies a long felt need with respect to the performance of protective clothing of the present kind and is of high value in any field of the nuclear industries.
• high-density polyethylene powder typically "HIZEX" 2100 GP, a product of Mitsui Petrochemical Company, Japan
• the mixed materials were then kneaded three times by means of an extruder (having a cylindrical diameter of 30 mm and a screw length of 500 mm) employing a screw revolution of 60 rpm and temperatures in the range of 250° to 280°C.
• the mixture obtained consisted of polyethylene chips containing fine 6 LiF powder, the net contents of said 6 LiF being measured as 38.5% by weight.
• the melt viscosity of said polyethylene chips was measured at 260°C by means of the "KOKA” type flow tester, manufactured by Shimazu Seishakusho, Ltd., Japan, and the determined melt viscosity was 2520 poise.
• the mono-filament section of the spun yarn obtained was investigated using an optical microscope with light penetration. It was found that the spun yarn obtained had evenly concentric core-and-sheath bicomponent fibers, the core component of which contained a specific amount of said fine LiF particles.
• the fibers obtained were elongated at a draw ratio of 5.0 on a plate heated to 95°C.
• the desired continuous filaments made of core-and-sheath bicomponent fibers were successfully obtained.
• the continuous filaments obtained by the preceding procedure were combined so that each of the yarns obtained contained 60 filaments, which were then processed by a knitting machine in order to make tubular knitted fabrics for testing purposes.
• the knitted fabric obtained showed a thickness of 1.30 mm and the area density was 490 g per square meter.
• the shielding properties against thermal neutrons of this knitted fabric were evaluated.
• the tests were carried out in the thermal neutron standard field based on the Maxwellian distribution by means of the KUR heavy water facilities, where the shielding effect of the evaluated knitted fabrics against the broad thermal neutron rays was measured by activated gold (Au) foils.
• the results obtained for the neutron-shielding properties are shown in Table 1 below.
• Example 2 Analogous to the procedure of Example 1, a total amount of 750 g of fine B 4 C particles (typically "DENKA BORON" No. 1200, a product of Denki Kagaku Kogyo K.K., Japan) graded on the dry basis, having a diameter of 10 pm maximum and an average cubic diameter of 3.2 pm, was mixed with a total amount of 1000 g high-density polyethylene powder (typically "HIZEX" 2100 GP, a product of Mitsui Petrochemical Company, Japan). The mixture obtained was kneaded by means of an extruder, and polyethylene chips containing uniformly distributed and dispersed fine B 4 C powder were obtained. Upon analysis it was confirmed that the polyethylene chips showed a content of said B 4 C powder of 42% by weight. Following the procedure of Example 1 the melt viscosity of the mixture obtained was measured as being 2690 poise at. 260°C.
• the spinning of core-and-sheath composite fibers was carried out, employing concentric composite spinnerets each having 12 holes with a diameter of 0.50 mm.
• the spinning operation was stably performed under the given operative-conditions so that an output of 10 g per minute of the core component and of 4.5 g per minute of the sheath component was obtained at 260°C.
• the take-up speed was 400 m per minute.
• the mono-filament sections of the spun yarns were investigated by means of an optical microscope using light penetration. The results confirmed that the spun yarns obtained consist of evenly concentric core-and-sheath composite or bicomponent fibers, the core component of which contain a specific amount of said fine B 4 C particles.
• the composite fibers obtained were elongated at a draw ratio of 5.5 on a plate heated to 95°C. Continuous filaments made of core-and-sheath bicomponent fibers were successfully obtained.
• the filaments obtained showed a tensile strength of 2.3 g per denier and 21 % elongation so that they were found to show satisfactory mechanical characteristics.
• the continuous filaments obtained by the preceding procedure were combined so that the integrated yarn contained 48 filaments, and the yarn obtained was then processed by a knitting machine in order to make tubular knitted fabrics for testing purposes.
• the knitted fabric obtained had a thickness of 1.25 mm and an area density of 430 g per square meter.
• Example 2 Analogous to the procedure of Example 1, a fine boron nitride powder (typically a product of Denki Kagaku Kogyo K.K., Japan) was mixed and kneaded with the respective amount of high-density polyethylene powder (typically "HIZEX" 1300 J, a product of Mitsui Petrochemical Company, Japan) by means of a Henschermixer, and thus a corresponding amount of polyethylene chips containing 55% by weight of boron nitride was obtained, the melt viscosity at 250°C of the chips obtained being 2900 poise.
• high-density polyethylene powder typically "HIZEX" 1300 J, a product of Mitsui Petrochemical Company, Japan
• the filaments obtained were then processed into a taffeta having a thickness of 0.50 mm and an area density of 250 g per square meter. Using the same equipment and methods as in Example 1, the thermal neutron-shielding properties of the taffeta obtained were tested. When 10 pieces of said taffeta were piled up to form a layer with a total thickness of 5 mm, the amount of thermal neutrons actually penetrating was determined as being 2.0x10-2.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Textile Engineering (AREA)
• Dispersion Chemistry (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Manufacturing & Machinery (AREA)
• Multicomponent Fibers (AREA)

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• 1981
  • 1981-08-14 JP JP12669481A patent/JPS5831117A/ja active Granted
• 1982
  • 1982-08-13 CA CA000409361A patent/CA1186465A/en not_active Expired
  • 1982-08-13 DE DE8282107384T patent/DE3269630D1/de not_active Expired
  • 1982-08-13 EP EP82107384A patent/EP0072550B1/en not_active Expired

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