US3742366A - Densification of irradiated metal - Google Patents

Densification of irradiated metal Download PDF

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Publication number
US3742366A
US3742366A US00090517A US3742366DA US3742366A US 3742366 A US3742366 A US 3742366A US 00090517 A US00090517 A US 00090517A US 3742366D A US3742366D A US 3742366DA US 3742366 A US3742366 A US 3742366A
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United States
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metal
irradiated
cobalt
radioisotope
irradiated metal
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Expired - Lifetime
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US00090517A
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English (en)
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D France
A Ketcham
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General Electric Co
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General Electric Co
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21G—CONVERSION OF CHEMICAL ELEMENTS; RADIOACTIVE SOURCES
    • G21G4/00—Radioactive sources
    • G21G4/04—Radioactive sources other than neutron sources

Definitions

  • ABSTRACT A method of producing dense bodies of irradiated metal in various geometrical shapes to achieve near theoretical density specimens of such metal is presented. These specimens are excellent radiation sources of high specific activity for medical therapeutic and industrial radiographic applications. The process starts with a target metal which is encapsulated in a metallic jacket and irradiated with a flux sufficient to convert a substantial portion of the target metal to a radioisotope.
  • the irradiated metal is removed from the capsule and a given amount of the irradiated metal sufficient to give a known energy output is segregated and either (a) are melted or (b) inductively cast to achieve a desired configuration as a radiation source.
  • the process gives irradiated metal with a very small focal point and a very high density.
  • Irradiation produces changes in materials that are often impossible to duplicate with other manufacturing methods.
  • energy emitted from radioactive isotopes causes certain effects that are desirable in a variety of manufacturing and processingoperations.
  • ionization kills bacteria and produces chemical changes in many organic substances.
  • irradiation processing can be used for a variety of industrial and other purposes, such as sterilizing medical supplies and foodstuffs, increasing the storage life of fresh foods, improving the physical properties of commercial plastics and efficiently producing bulk chemicals.
  • gamma irradiation One of the most attractive forms of ionizing energy used in large scale production is gamma irradiation. It utilizes gamma rays emitted from a variety of radioactive isotopes. Of these, cobalt-60 seems particularly well suited for industrial and other uses.
  • the cobalt-60 radioisotope is widely used for medical therapy, especially cancer therapy.
  • the cobalt-60 source must have a configuration which furnishes a high intensity output and a small localized focal point. This requires a cobalt-60 source having a small volume with high intensity output per given volume.
  • the cylindrical can is filled with irradiated pellets (right cylinders of 1 mm. in diameter and 1 mm. in height). This gives more flexibility to the configuration of the source and gives good activation capabilities. But the use of pellets introduces the problem of low density of the irradiated metal per given volume due to the uniform shape of the pellets.
  • contamination spread contamination of the irradiated metal
  • Another object of this invention is to achieve irradiated metallic specimens having very small focal points to enable concentration of the radiation intensity.
  • a still further object of this invention is to provide a process for producing a dense cobaltradioisotope in various configurations while minimizing contamination spread and contamination of the cobalt-6O.
  • irradiated metallic specimens having very high density and possessing desirable radiation focal points can be achieved using the process of the present invention.
  • the process starts with particles of the metal in an unirradiated condition (target metal) and encapsulates the particles of target metal in a thin metallic annulus promoting the absorption of neutrons throughout the target metal. During the remainder of the process the target metal is enclosed in shielded zones to confine radioactive energy release.
  • the encapsulated target metal is subjected to irradiation sufficient to enable some of the atoms of the metal to capture neutrons and the irradiated metal is removed from the aluminum encapsulation.
  • a given weight of the irradiated metal sufficient to provide a known irradiation output is measured and the irradiated metal is subjected to sufficient thermal energy to be liquified and then solidified in a desired shape.
  • the irradiated metal thus treated is ready to be positioned in a source holder.
  • the important steps of the process are the liquification and solidification steps which achieve the densification and impart the desired shape to the irradiated metal. It has been found that there are two preferred practices of these steps as follows: (l) are melting the irradiated metal with solidification in a crucible of desired shape or (2) induction casting of the irradiated metal with solidification in a crucible of desired shape. These two preferred practices produce irradiated metal specimens of very high densities.
  • the present invention provides a process for the densification of any metallic radioisotopes with a melting point up to about 2,000C to provide approximately theoretical density specimens of such irradiated metal in various configurations.
  • This process enables an improved radioisotope product for V use in sealed sources having configurations giving very small radiation focal points of very high intensity.
  • the process begins with the unirradiated commercially available metal (target metal) corresponding to the desired metallic radioisotope (e.g., cobalt-59 when cobalt-60 is the desired radioisotope and iron-58 when iron-59 is the desired radioisotope).
  • the target metal may have one or more coatings on the metal especially where it is desirable to prevent oxidation of the metal or possible loss of the metal such as through vaporization. It is preferable to have the metal in the form of dense pellets such as platelets or small cylinders and metals unavailable in this form such as powders are converted to such compacted pellets.
  • the target metal is preferably in the form of pellets having a geometrical configuration of a right cylinder of 1 mm. in diameter by 1 mm. in height.
  • the metal pellets are first encapsulated in a metal jacket such as between two concentric aluminum cylinders to form a capsule with the thickness of the metal pellet annulus being about 0.050 to about 0.100 inches,
  • the aluminum cylinders are joined by welding.
  • the aluminum cylinders enable the metal pellets to absorb neutrons throughout the metal whereas with geometrical configuration of thicker cross sections, the metal pellets would not be uniformly activated (pellets in the center of thick cross sections would not absorb neutrons as readily).
  • the aluminum cylinders be about 0.03 to about 0.04 inches in thickness.
  • the capsule is preferably kept in shielded zones and manipulated by conventional remote control instruments and manipulators.
  • the metallic radioisotope is removed from the capsule by various means such as by cutting through the aluminum jacket and prying open the jacket so that the radioisotope pellets are released (again by use of remote control instruments in a shielded zone due to the radioactive nature of the irradiated metal).
  • irradiated metal MEASURE DESIRED WEIGHT OF RADIOISOTOPE
  • the ultimate use of the irradiated metal will dictate the quantity of metal needed to give a known intensity output.
  • a sealed source which has up to about 4 grams of irradiated metal such as cobalt-60 in a given configuration sealed in a stainless steel holder. Accordingly the desired weight of irradiated metal is measured for liquification and solidification in the desired shape for the sealed source.
  • the desired weight of the irradiated metal pellets is solidified to a given shape by a liquificationsolidification sequence which achieves densification.
  • the radioisotope pellets are subjected to sufficient thermal energy to be liquified and are then solidified in a desired shape.
  • the metal is heated in one practice to a sufficient temperature by arc melting in a metallic or ceramic crucible using a heliarc torch under a controlled atmosphere.
  • the irradiated metal is induction cast at a sufficient temperature in a metallic or ceramic crucible with the heating being done by inductive coils surrounding the crucible under a controlled atmosphere.
  • the liquification and solidification are conducted in hot cells which are highly shielded, controlled atmosphere enclosures with lead glass Windows to enable viewing the process.
  • the hot cells are equipped with externally manipulated mechanical instruments for conducting the process.
  • the incoming atmosphere is controlled for moisture content and the atmosphere withdrawn from the hot cell is run through a high efficiency filter to remove all radioactive particles.
  • the liquification and solidification steps are conducted within controlled temperature ranges generally no higher than about C above the melting point of the metallic radioisotope to avoid vaporization of the radioisotope.
  • An especially preferred process of the present invention is the conversion of cobalt-59 to cobalt-60.
  • the process begins using a metallic coated cobalt-59 such as a nickel coated cobalt59 which is in the form of pellets preferably in the shape of right cylinders having the dimensions of 1 mm. in height and 1 mm. in diameter.
  • the pellets of cobalt-59 are encapsulated between two concentric aluminum cylinders with the thickness of the cobalt annulus being about 0.050 to about 0.100 inches.
  • the encapsulated cobalt-59 is irradiated with a flux of at least about 4 X 10 neutrons per square centimeter per second for a time period of about 1 year to about 3 years.
  • the cobalt is removed from within the aluminum encapsulation.
  • a given weight of irradiated metal sufficient to give a known irradiation intensity output is segregated, liquified and solidified to the configuration desired.
  • the liquification and solidification are accomplished by either (1) arc melting the cobalt-60 in a copper crucible (e.g., a crucible having a spherical shape) using a heliarc torch at a temperature of about l,500 to about 1600 C under a controlled atmosphere (e.g., argon, nitrogen, helium) or (2) induction casting the cobalt-60 in a ceramic (Al- O crucible with heating being done by high frequency inductive coils surrounding the crucible at a temperature of about l,500 to about 1,600 C under a controlled atmosphere (e.g., argon or vacuum).
  • the cobalt radioisotope is then allowed to solidify in the crucible.
  • the liquification and solidification are conducted in a hot cell which is a highly shielded, controlled atmosphere enclosure with a lead glass window to enable viewing the process.
  • the hot cell is equipped with externally manipulated mechanical instruments for conducting the process.
  • the incoming atmosphere is controlled for moisture content and the atmosphere withdrawn from the hot cell is run through a high efficiency filter to remove all radioactive particles.
  • the liquification and solidification steps are conducted within the foregoing temperature range to avoid vaporization of the cobalt-60.
  • the solidified cobalt-60 shape is ready to be placed in a source holder such as a stainless steel source holder.
  • FIG. 2 presents the relationship between the size of the metallic radioisotope body and the weight of the radioisotope in the body for a spherical configuration when the irradiated metal is cobalt.
  • the irradiated metal containing bodies for which this relationship is presented are produced by are melting.
  • the outer aluminum cylinder has an outside diameter of 1.125 inches and an inside diameter of 1.095 inches and the inner aluminum cylinder has an outside diameter of 0.995 inches and an inside diameter of 0.965 inches.
  • the height of the capsule is 4 inches.
  • the capsule was then placed in an irradiation chamber and irradiated with a flux of 4.5 X neutrons per square centimeter of surface area of the metal per second for one year.
  • a method of producing dense specimens of metal lic radioactive bodies from a corresponding target metal comprising the steps of a. encapsulating the target metal in a metallic jacket to form a thin cross section of the target metal,
  • a method according to claim 1 in which the liquification step is performed by are melting the metal in a crucible under a controlled atmosphere.
  • a method of producing dense specimens containing metallic radioisotopes of desired configuration from a given weight of pellets of the irradiated metal comprising the steps of a. liquifying the given weight of pellets of the irradiated metal, and

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Medicines That Contain Protein Lipid Enzymes And Other Medicines (AREA)
  • Sampling And Sample Adjustment (AREA)
  • Particle Accelerators (AREA)
US00090517A 1970-11-18 1970-11-18 Densification of irradiated metal Expired - Lifetime US3742366A (en)

Applications Claiming Priority (1)

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US9051770A 1970-11-18 1970-11-18

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US3742366A true US3742366A (en) 1973-06-26

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US (1) US3742366A (cs)
AU (1) AU463304B2 (cs)
BE (1) BE775456A (cs)
DE (1) DE2156844A1 (cs)
FR (1) FR2115215B1 (cs)
GB (1) GB1323638A (cs)
IT (1) IT955065B (cs)
NL (1) NL7115935A (cs)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5525318A (en) * 1992-09-25 1996-06-11 The United States Of America As Represented By The United States Department Of Energy High specific activity silicon-32
US20150206612A1 (en) * 2014-01-21 2015-07-23 Westinghouse Electric Company Llc Solid state electrical generator

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2120669C1 (ru) * 1997-05-27 1998-10-20 Государственный научный центр РФ Контейнер для облучения делящихся материалов
RU2218621C2 (ru) * 2002-01-17 2003-12-10 Государственное предприятие Ленинградская атомная электростанция им. В.И. Ленина Облучательное устройство ядерного реактора канального типа

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5525318A (en) * 1992-09-25 1996-06-11 The United States Of America As Represented By The United States Department Of Energy High specific activity silicon-32
US20150206612A1 (en) * 2014-01-21 2015-07-23 Westinghouse Electric Company Llc Solid state electrical generator
US9640290B2 (en) * 2014-01-21 2017-05-02 Westinghouse Electric Company Llc Solid state electrical generator

Also Published As

Publication number Publication date
AU463304B2 (en) 1975-07-07
BE775456A (fr) 1972-03-16
AU3576471A (en) 1973-05-24
FR2115215B1 (cs) 1974-06-07
FR2115215A1 (cs) 1972-07-07
DE2156844A1 (de) 1972-05-25
GB1323638A (en) 1973-07-18
IT955065B (it) 1973-09-29
NL7115935A (cs) 1972-05-23

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