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Dokumentenidentifikation EP1173855 05.04.2007
EP-Veröffentlichungsnummer 0001173855
Titel GAMMA-STRAHLUNGSQUELLE
Anmelder QSA UK Ltd., Didcot, Oxfordshire, GB
Erfinder SHILTON, Mark Golder, Aston Clinton, Buckinghamshire HP22 5JF, GB
Vertreter Pürckhauer, R., Dipl.-Ing., Pat.-Anw., 57234 Wilnsdorf
DE-Aktenzeichen 60033511
Vertragsstaaten AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LI, LU, MC, NL, PT, SE
Sprache des Dokument EN
EP-Anmeldetag 20.04.2000
EP-Aktenzeichen 009209115
WO-Anmeldetag 20.04.2000
PCT-Aktenzeichen PCT/GB00/01549
WO-Veröffentlichungsnummer 2000065608
WO-Veröffentlichungsdatum 02.11.2000
EP-Offenlegungsdatum 23.01.2002
EP date of grant 21.02.2007
Veröffentlichungstag im Patentblatt 05.04.2007
IPC-Hauptklasse G21G 4/04(2006.01)A, F, I, 20051017, B, H, EP
IPC-Nebenklasse G21G 4/06(2006.01)A, L, I, 20051017, B, H, EP   

Beschreibung[en]

The present invention relates to a gamma radiation source containing 75Se, and in particular to a source for use in gamma radiography. Such a source has application, for example, in nondestructive testing, industrial gauging, densitometry and materials analysis in industry, research and medicine.

In the past, 75Se sources have been made by encapsulating elemental 74Se target material inside a welded metal target capsule. This is irradiated in a high flux reactor to convert - some of the 74Se to 75Se. Typically, target capsules are made of low-activating metals, such as aluminium, titanium, vanadium and their alloys. Other expensive metals and alloys are also possible. The use of these metals ensures that impurity gamma rays arising from the activation of the target capsule are minimised. The 75Se is typically located within a cylindrical cavity inside the target capsule in the form of a pressed pellet or cast bead. To achieve good performance in radiography applications it is necessary for the focal spot size to be as small as possible and the activity to be as high as possible. This is achieved by irradiating in a very high neutron flux and by using very highly isotopically enriched 74Se target material, typically >95% enrichment.

After the irradiation, the activated target capsule is welded into one or more outer metal capsules to provide a leak-free source, which is free from external radioactive contamination.

An article by Weeks K.J. et al "Selenium-75:a potential source for high-activity brachytherapy irradiators" published in Medical Physics, Sept-Oct 1986 USA Vol.13 No.5 pp 728-731(XP000896098 ISSN:0094-2405) discloses a gamma radiation source comprising elemental selenium-75.

The general features and benefits of these sources and their performance relative to other sources are discussed in, for example, "Gammagrafie mit Selen-75", C Sauerwein, et al, Deutsche Gesellschaft für Zerstörungsfreie Prüfüng, Jahrestagung 9.-11 Mai 1994 in Timmendorfer Strand, also "Gamma radiography utilising selenium-75", R Grimm et al, Insight, Vol 38 no 9 September 1996. "Selenium and Selenides", D M Chizhikov et al, translated by E. M. Elkin, Pub, Collets, London & Wellingborough 1968, provides additional background information.

Elemental selenium is chemically and physically volatile. It melts at 220°C and boils at 680°C. It reacts with many metals, which might be suitable as low-activating capsule materials at temperatures above about 400°C, this includes titanium, vanadium and aluminium and their alloys. Selenium may react explosively with aluminium. This means that careful choice of target capsule material is required and the temperature of the target capsule during irradiation must be kept below about 400°C to prevent the selenium reacting with, and corroding the target capsule wall. If this occurred, it would increase the focal spot size, distort the focal spot shape and reduce the wall thickness and strength of the target capsule.

An object of the present invention is to provide a source having a selenium target composition, which overcomes or ameliorates one or more of the problems associated with the use of elemental selenium, specifically the problems of achieving a thermally stable, non-volatile, non-reactive, high density, stable selenium target which nevertheless contains a very high density of selenium, comparable with the elemental form of the material.

The invention provides, in one of its aspects, a gamma radiation source comprising selenium-75 which is combined with an acceptable metal or metals in the form of a stable compound, alloy, or mixed metal phase, the said acceptable metal or metals being a metal or metals the neutron irradiation of which does not produce products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of selenium-75, the said acceptable metal or metals being from the group comprising vanadium, molybdenum, rhodium, niobium, thorium, titanium, nickel, lead, bismuth, platinum, palladium, aluminium, or mixtures thereof.

Thus, for example, an acceptable metal, such as vanadium or rhodium, is activated but has no interfering gamma radiation. Molybdenum produces molybdenum-99 which does have interfering gamma radiation, but is very short lived and is therefore also an acceptable metal. Again, thorium produces palladium-233 having a 27 day half life, but the gamma radiation of palladium-233 is 300 - 340 keV which is very similar to selenium-75 and therefore acceptable.

The invention also provides a precursor for a gamma radiation source comprising encapsulated selenium-74 which is combined with an acceptable metal or metals in the form of a stable alloy, compound, or mixed metal phase, the encapsulation and its contents being adapted for irradiation with neutrons to convert at least some of the selenium-74 to selenium-75 whilst not at the same time producing any products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of selenium-75, the said acceptable metal being as specified above.

Preferably, the selenium is provided in the form of a pellet or bead of a compound of formula MxSey where y/x is in the range 1-3 and M is one or a mixture of two or more of the said acceptable metals.

The preferred range for y/x is 1.5-2.5. More preferably, y/x is 2.

Preferably, the pellet or bead comprises VSe2 or MoSe2 or Rh2Se5.

Conveniently, elemental selenium is included in intimate admixture with the said compound, alloy or mixed metal phase to act as a binder therefor, in particular to facilitate formation of a dense, pore free pellet or bead.

For the safe containment of the active constituents, the pellet or bead is contained within a sealed, welded, metal capsule.

Preferably, the pellet or bead is formed to have a spherical or pseudo-spherical focal spot geometry.

The invention provides, in another of its aspects, a method of manufacturing a gamma radiation source comprising mixing selenium-74 and one or a mixture of metals from the group comprising vanadium, molybdenum, rhodium, niobium, thorium, titanium, nickel, lead, bismuth, platinum, palladium, aluminium, in appropriate proportions for the desired product compound, and heating the mixture to cause the constituents to inter-react and subsequently subjecting the reaction product to irradiation to convert at least a proportion of the selenium-74 to selenium-75.

A specific method and construction of a gamma radiation source embodying the invention will now be described by way of example with reference to the drawings filed herewith, in which:

  • Figure 1 is a sectional view of an irradiation capsule assembly,
  • Figure 2 is an exploded view of the components shown in Figure 1,
  • Figure 3 is a sectional view of a modified irradiation capsule assembly, and
  • Figure 4 is a side elevation of a component of the assembly shown in Figure 3.

Referring to Figures 1 and 2 of the drawings, a pellet 11 incorporating selenium-75 is hermetically sealed in the capsule comprising a cylindrical body 12, a cylindrical plug 13 and a cylindrical lid component 14 one end of which is of slightly increased diameter. Lid component 13 is wholly received within the body 12 and welded to the body 12 around that part which is of increased diameter. The pellet 11 is held within the capsule clamped between the plug 13 and lid component 14.

The modified assembly shown in Figures 3 and 4 is generally similar, but involves a reduced number of components. The capsule comprises a cylindrical body 12a and a cylindrical lid component 14a received in a correspondingly shaped recess in the body 12a. The lid 14a and body 12a are shaped internally to receive a pellet incorporating selenium-75 which is formed in two halves 11a and 11b, one of which, 11a, is shown in side elevation in Figure 4. The pellet halves 11a and 11b also have a cylindrical geometry so that, whilst in the section shown the shape of the two halves put together forms an octagon, the shape in section at right angles to that shown is circular. After assembly the lid 14a is welded at 15 to the body 12a.

The pellet composition is a metal selenide compound (in which part or all may be regarded as an intimate mixture of metal particles and elemental selenium) having the composition MxSey in which M is an acceptable metal, which minimizes unwanted impurity gamma rays. Examples of suitable acceptable metals include, but are not limited to vanadium, molybdenum, rhodium, niobium, thorium, titanium, nickel, lead, bismuth, platinum, palladium, aluminium. The most preferred metals are molybdenum, vanadium and rhodium which produce especially dense metal-selenium phases, which are rich in selenium. "x" and "y" in the chemical formula can have any values depending on the valence state of the metal, but the highest selenium density is achieved when the ratio of y/x is in the range 1-3, more preferably 1.5-2.5, most preferably 2. Examples of suitable metal-selenium target materials are as follows: Valence Examples 2 VSe, TiSe, PbSe, NiSe, BiSe 2&3 Bi3Se4 3 Bi2Se3, Al2Se3 4 RhSe2, VSe2, TiSe2 MoSe2, PtSe2 PdSe2, NbSe2 NiSe2 5 Rh2Se5, Th2Se5 6 MoSe3

Metal-selenium pellet compositions can be prepared by a variety of methods. The method found to be most convenient, which gives rise to minimal process losses is to weigh out and mix a known quantity of enriched 74Se powder with a calculated quantity of powdered metal, and to heat the mixture in an inert, sealed container, such as a flame sealed glass ampoule, gradually increasing the temperature over several hours to the reaction temperature and then holding that temperature for several more hours. For example, the reaction temperature for the reaction between 74Se powder and vanadium powder is in the range 450°C - 550°C. In a specific example, a mixture of vanadium and selenium powders in the ratio one part vanadium to 1.9 parts enriched selenium-74 was heated in an evacuated flame sealed quartz ampoule, first at 550C for 4 hours and then at 800C for 100 hours. The product VSe1.9 was pressed into half octagonal section pellets 11a and 11b of the form shown in Figure 4.

Cylindrical pellets or beads can be prepared by several methods. For example, powder can be cold-pressed, hot-pressed or sintered to form cylindrical, spherical or pseudo-spherical geometries. These can be inserted into the target capsule, or cast or pressed in-situ. The capsule is then welded and leak tested prior to irradiation. Metal-selenium pellet compositions may consist of a pure metal selenide compound such as VSe2, or a mixture of compounds such as VSe2, MoSe2, MoSe3, or more complex phases obtained by reacting such mixtures together at high temperature. The composition may contain some metal powder and elemental selenium. Excess elemental selenium may be purposefully added as a bonding agent to bond metal selenide particles together to form pore free, high density pellets or beads. Pellets, which are made of mixtures, such as VSe2+VSe+Se, or MoSe2+MoSe3+Se may react or sinter together within the target capsule, either during a special annealing process prior to irradiation, or during the irradiation itself, as follows: VSe + Se = VSe 2 and MoSe 2 + Se = MoSe 3

One advantage of using metal selenide phases is that the thermal and physical stability of the materials enables unencapsulated pellets and beads to be irradiated, in-principle. This can provide significant cost advantages by reducing the amount of reactor space, which is wasted by the presence of the low activating target capsules.


Anspruch[de]
Gamma-Strahlungsquelle mit Selen-75, das kombiniert ist mit einem akzeptablen Metall oder mit Metallen in Form einer stabilen Verbindung, Legierung oder gemischten Metallphase, wobei dieses akzeptable Metall oder diese akzeptablen Metalle ein Metall ist oder Metalle sind, dessen bzw. deren Neutronenbestrahlung keine Produkte erzeugt, die zur ungedämpften Emission von Strahlung in der Lage sind, die unakzeptabel mit der Gammastrahlung von Selen-75 interferieren würde, wobei dieses akzeptable Metall oder diese akzeptablen Metalle aus der Gruppe stammt bzw. stammen, die Vanadium, Molybdän, Rhodium, Niob, Thorium, Titan, Nickel, Blei, Wismut, Platin, Palladium, Aluminium oder Gemische derselben einschließt. Vorläufer für eine Gamma-Strahlungsquelle nach Anspruch 1, mit eingekapseltem Selen-74, das mit einem akzeptablen Metall oder Metallen in Form einer stabilen Legierung, Verbindung oder gemischten Metallphase kombiniert ist, wobei die Einkapselung und deren Inhalt für eine Bestrahlung mit Neutronen geeignet sind, um zumindest einiges von dem Selen-74 in Selen-75 umzuwandeln, während es zur gleichen Zeit keinerlei Produkte erzeugt, die zur ungedämpften Emission von Strahlung in der Lage sind, die unannehmbar mit der Gammastrahlung von Selen-75 interferieren würde, wobei dieses akzeptable Metall oder diese akzeptablen Metalle aus der Gruppe stammt bzw. stammen, die Vanadium, Molybdän, Rhodium, Niob, Thorium, Titan, Nickel, Blei, Wismut, Platin, Palladium, Aluminium oder Gemische derselben umfasst. Vorläufer nach Anspruch 2, bei dem das Selen-74 isotopisch angereichertes Selen-74 enthält. Quelle oder Vorläufer dafür, wie in jedem der vorangehenden Ansprüche beansprucht, wobei dieses akzeptable Metall oder diese akzeptablen Metalle eines oder ein Gemisch von Vanadium oder Molybdän oder Rhodium aufweist bzw. aufweisen. Quelle oder Vorläufer dafür, wie in jedem der vorangehenden Ansprüche beansprucht, wobei das Selen in Form eines Pellets oder einer Perle einer Verbindung der Formel MxSey vorgesehen ist, wobei y/x im Bereich 1-3 liegt und M eines oder ein Gemisch von zwei oder mehr der genannten akzeptablen Metalle ist. Quelle oder Vorläufer dafür nach Anspruch 5, wobei y/x im Bereich 1,5-2,5 liegt. Quelle oder Vorläufer dafür nach Anspruch 6, wobei y/x 2 ist. Quelle oder Vorläufer dafür nach Anspruch 5, wobei das Pellet oder die Perle VSe2 oder MoSe2 oder Rh2Se5 aufweist. Quelle oder Vorläufer dafür nach einem der vorangehenden Ansprüche, wobei elementares Selen in inniger Beimischung zu der genannten Verbindung, Legierung oder gemischten Metallphase enthalten ist, um als ein Bindemittel dafür zu agieren. Quelle oder Vorläufer dafür nach einem der vorangehenden Ansprüche, wobei die genannte Verbindung, Legierung oder gemischte Metallphase in Form eines dichten, porenfreien Pellets oder einer dichten, porenfreien Perle vorliegt. Quelle oder Vorläufer dafür nach Anspruch 10, wobei das Pellet oder die Perle in einer abgedichteten, verschweißten Metallkapsel enthalten ist. Quelle oder Vorläufer dafür nach Anspruch 10 oder 11, wobei das Pellet oder die Perle zu einer sphärischen oder pseudosphärischen Brennpunkt-Geometrie geformt ist. Quelle oder Vorläufer dafür nach Anspruch 12, wobei das Pellet oder die Perle zu einer Geometrie geformt ist, die achteckig in dem einen Abschnitt und kreisförmig in dem quer zu dem achteckigen Abschnitt verlaufenden Abschnitt ist. Verfahren zur Herstellung einer Gamma-Strahlungsquelle, gekennzeichnet durch das Mischen von Selen-74 und eines Metalls oder Gemisches von Metallen aus der Gruppe, die Vanadium, Molybdän, Rhodium, Niob, Thorium, Titan, Nickel, Blei, Wismut, Platin, Palladium, Aluminium in angemessenen Proportionen für die gewünschte Produktverbindung umfasst, und Erhitzen des Gemisches, um die Bestandteile interagieren zu lassen, und durch das anschließende Aussetzen des Reaktionsproduktes einer Strahlung, um zumindest einen Teil des Selen-74 zu Selen-75 umzuwandeln.
Anspruch[en]
A gamma radiation source comprising selenium-75 which is combined with an acceptable metal or metals in the form of a stable compound, alloy, or mixed metal phase, the said acceptable metal or metals being a metal or metals the neutron irradiation of which does not produce products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of selenium-75, the said acceptable metal or metals being from the group comprising vanadium, molybdenum, rhodium, niobium, thorium, titanium, nickel, lead, bismuth, platinum, palladium, aluminium, or mixtures thereof. A precursor for a gamma radiation source as claimed in claim 1, comprising encapsulated selenium-74 which is combined with an acceptable metal or metals in the form of a stable alloy, compound, or mixed metal phase, the encapsulation and its contents being adapted for irradiation with neutrons to convert at least some of the selenium-74 to selenium-75 whilst not at the same time producing any products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of selenium-75, the said acceptable metal or metals being from the group comprising vanadium, molybdenum, rhodium, niobium, thorium, titanium, nickel, lead, bismuth, platinum, palladium, aluminium, or mixtures thereof. A precursor as claimed in claim 2, wherein the selenium-74 comprises isotopically enriched selenium-74. A source or precursor therefor as claimed in any one of the preceding claims, wherein the said acceptable metal or metals comprises one or a mixture of vanadium or molybdenum or rhodium. A source or precursor therefor as claimed in any one of the preceding claims, wherein the selenium is provided in the form of a pellet or bead of a compound of formula MxSey where y/x is in the range 1-3 and M is one or a mixture of two or more of the said acceptable metals. A source or precursor therefor as claimed in claim 5, wherein y/x is in the range 1.5-2.5. A source or precursor therefor as claimed in claim 6, wherein y/x is 2. A source or precursor therefor as claimed in claim 5, wherein the pellet or bead comprises VSe2 or MoSe2 or Rh2Se5. A source or precursor therefor as claimed in any one of the preceding claims, wherein there is included elemental selenium in intimate admixture with the said compound, alloy or mixed metal phase to act as a binder therefor. A source or precursor therefor as claimed in any one of the preceding claims, wherein the said compound, alloy or mixed metal phase is in the form of a dense, pore free pellet or bead. A source or precursor therefor as claimed in claim 10, wherein the pellet or bead is contained within a sealed, welded, metal capsule. A source or precursor therefor as claimed in claim 10 or claim 11, wherein the pellet or bead is formed to have a spherical or pseudo-spherical focal spot geometry. A source or precursor therefor as claimed in claim 12, wherein the pellet or bead is formed to have a geometry which is octagonal in one section and circular in the transverse section. A method of manufacturing a gamma radiation source comprising mixing selenium-74 and one or a mixture of metals from the group comprising vanadium, molybdenum, rhodium, niobium, thorium, titanium, nickel, lead, bismuth, platinum, palladium, aluminium, in appropriate proportions for the desired product compound, and heating the mixture to cause the constituents to inter-react and subsequently subjecting the reaction product to irradiation to convert at least a proportion of the selenium-74 to selenium-75.
Anspruch[fr]
Source de radiations gamma comprenant du sélénium 75 qui est combiné à un ou plusieurs métaux acceptables sous la forme d'un composé stable, d'un alliage stable ou d'une phase métallique mixte stable, le ou lesdits métaux acceptables étant un ou plusieurs métaux dont l'irradiation par des neutrons ne donne pas de produits capables d'émission prolongée de radiations qui interféreraient de façon inacceptable avec les radiations gamma du sélénium 75, le ou lesdits métaux acceptables faisant partie du groupe comprenant le vanadium, le molybdène, le rhodium, le niobium, le thorium, le titane, le nickel, le plomb, le bismuth, le platine, le palladium, l'aluminium ou leurs mélanges. Précurseur pour une source de radiations gamma selon la revendication 1 comprenant du sélénium 74 encapsulé qui est combiné à un ou plusieurs métaux acceptables sous la forme d'un composé stable, d'un alliage stable ou d'une phase métallique mixte stable, l'encapsulation et son contenu étant adaptés pour une irradiation par des neutrons pour convertir au moins certains des noyaux de sélénium 74 en sélénium 75 tout en ne produisant pas en même temps de produits capables d'émission prolongée de radiations qui interféreraient de façon inacceptable avec les radiations gamma du sélénium 75, le ou lesdits métaux acceptables faisant partie du groupe comprenant le vanadium, le molybdène, le rhodium, le niobium, le thorium, le titane, le nickel, le plomb, le bismuth, le platine, le palladium, l'aluminium ou leurs mélanges. Précurseur selon la revendication 2 dans lequel le sélénium 74 comprend du sélénium 74 enrichi isotopiquement. Source ou précurseur de source selon l'une quelconque des revendications précédentes dans lequel le ou lesdits métaux acceptables comprennent le vanadium, le molybdène, le rhodium ou un de leurs mélanges. Source ou précurseur de source selon l'une quelconque des revendications précédentes dans lequel le sélénium est fourni sous la forme d'un comprimé ou d'une bille d'un composé de formule MxSey, où y/x se situe dans le domaine de 1 à 3 et M est un desdits métaux acceptables ou un mélange de deux ou plus de ceux-ci. Source ou précurseur de source selon la revendication 5 où y/x se situe dans le domaine de 1,5 à 2,5. Source ou précurseur de source selon la revendication 6 où y/x = 2. Source ou précurseur de source selon la revendication 5 où le comprimé ou la bille comprend VSe2 ou MoSe2 ou Rh2Se5. Source ou précurseur de source selon l'une quelconque des revendications précédentes dans lequel est inclus du sélénium élémentaire en mélange intime avec ledit composé, alliage ou ladite phase métallique mixte pour agir comme liant. Source ou précurseur de source selon l'une quelconque des revendications précédentes dans lequel ledit composé, alliage ou phase métallique mixte est sous la forme d'un comprimé ou d'une bille dense et non poreux. Source ou précurseur de source selon la revendication 10 dans lequel le comprimé ou la bille est contenu dans une capsule métallique scellée et soudée. Source ou précurseur de source selon la revendication 10 ou 11 dans lequel le comprimé ou la bille est mis en forme pour avoir une géométrie sphérique ou pseudo-sphérique à point focal. Source ou précurseur de source selon la revendication 12 dans lequel le comprimé ou la bille est mis en forme pour avoir une géométrie qui est octogonale dans une section et circulaire dans la section transversale. Procédé de fabrication d'une source de radiations gamma comprenant le mélange du sélénium 74 et d'un ou d'un mélange de composés issus du groupe comprenant le vanadium, le molybdène, le rhodium, le niobium, le thorium, le titane, le nickel, le plomb, le bismuth, le platine, le palladium, l'aluminium en proportions appropriées pour le composé produit désiré, et le chauffage du mélange pour faire interagir les constituants et ensuite soumettre le produit de la réaction à une irradiation pour convertir au moins une proportion du sélénium 74 en sélénium 75.






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