Molybdenum-converter based electron linear accelerator and method for producing radioisotopes

Abstract

The present invention provides a method for producing molybdenum-99 comprising: i) providing an electron accelerator; ii) providing a molybdenum converter/target unit (Mo-CTU) comprising one or more metallic components, wherein each one of said metallic components is made of a material selected from the group consisting of natural molybdenum, molybdenum-100, molybdenum-98, and mixtures thereof; iii) directing an electron beam generated via said electron accelerator onto said Mo-CTU to produce a braking radiation (bremsstrahlung); iv) employing said bremsstrahlung onto said Mo-CTU to produce molybdenum-99 and neutrons via a photo-neutron reaction; v) slowing down the neutrons produced in step iv) with a low atomic liquid, e.g. distilled water; and optionally vi) employing the neutrons produced in step iv) to produce a complementary amount of molybdenum-99 via a neutron capture reaction on said Mo-CTU. The invention further provides an apparatus for producing molybdenum-99.

Claims

1. An electron accelerator based method for producing molybdenum-99 (Mo-99) comprising: i) providing an electron accelerator producing a high energy electron beam; ii) providing one molybdenum converter/target unit (Mo-unit) comprising molybdenum-100 (Mo-100) wherein said Mo-unit simultaneously serves both as a braking radiation (bremsstrahlung) converter and a radioisotope production target; and iii) directing said electron beam onto said Mo-unit, thereby producing braking radiation (bremsstrahlung) which subsequently reacts in the same Mo-unit with said Mo-100 via the (γ,n) reaction to produce Mo-99 in said Mo-unit, in which the Mo-99 product accumulates; wherein said Mo-unit further comprises molybdenum-98 (Mo-98), the method further comprising slowing down the neutrons produced in step iii) with a low atomic number liquid and reacting them with said Mo-98 via the (n,γ) reaction to produce additional Mo-99 in said Mo-unit, thereby maximizing the efficiency in the production of Mo-99.

2. The electron accelerator based method of claim 1 for producing Mo-99 and other radioisotopes, further comprising the step of placing one or more external target materials outside the Mo-unit and adjacent to it so that said bremsstrahlung photons and neutrons around said Mo-unit generate further radioactive isotopes via (γ,n) and (n,γ) reactions on said one or more external target materials.

3. The method of claim 2, wherein said external target materials comprise Xe-124, and wherein said further radioactive isotopes are I-123 and I-125.

4. The method of claim 2, wherein said external target materials are selected from F-19, O-16, N-14 and C-12, and wherein said further radioactive isotopes are F-18, O-15, N-13 and C-11, respectively.

5. The method of claim 2, wherein said external target materials comprise low enriched uranium (LEU) which is used in a photo-fission (γ,f) reaction.

6. An electron accelerator based apparatus for producing molybdenum-99 (Mo-99), comprising: a) an electron accelerator producing a high energy electron beam; b) one converter/target unit made from molybdenum (Mo-unit) comprising molybdenum-100 (Mo-100) wherein said Mo-unit serves both as a braking radiation (bremsstrahlung) source and as a radioisotope production target; and c) means for directing said electron beam onto said Mo-unit to produce braking radiation (bremsstrahlung) which subsequently reacts with said Mo-100 via the (γ,n) reaction to produce and accumulate Mo-99 in said Mo-unit; wherein said Mo-unit further comprises molybdenum-98 (Mo-98), the apparatus further comprising a low atomic number liquid which slows down said neutrons produced in the (γ,n) reaction, the neutrons subsequently reacting with said Mo-98 via the (n,γ) reaction to maximize the efficiency in the production of Mo-99.

7. The apparatus of claim 6, wherein the low atomic number liquid is distilled water.

8. The method of claim 1, wherein said Mo-unit comprises natural molybdenum.

9. The method of claim 1, wherein said low atomic number liquid is water.

10. The apparatus of claim 6, wherein said Mo-unit comprises natural molybdenum.

11. The apparatus of claim 6, wherein said low atomic number liquid is water, which serves both for cooling the Mo-100 unit and for slowing down the neutrons.

Description

BRIEF DESCRIPTION OF THE FIGURE

(1) FIG. 1 schematically illustrates an electron linear accelerator according to one embodiment of the invention.

DETAILED DESCRIPTION

(2) Reference is made to FIG. 1. To overcome the drawbacks of the prior art, the present invention employs a bremsstrahlung producing converter/target unit made from molybdenum (Mo-CTU). In this way, the molybdenum target to be irradiated with the bremsstrahlung is ideally located in the bremsstrahlung radiation focus, thus maximizing the production of Mo-99 via the (γ,n) reaction. In addition, the use of molybdenum directly as a bremsstrahlung converter/target unit enables using the neutrons produced by the reactions (γ,n), (γ,2n), (γ, pn), and so on, for the complementary production of Mo-99 via the (n,γ) reaction on the isotope Mo-98 (when present in the Mo-CTU, for instance in natural molybdenum or in pure form Mo-98):
Mo-98+n=Mo-99+γ  (Eq. 4)

(3) Isotopic abundance of the isotope Mo-98 in natural molybdenum is 2.5 times higher than that of Mo-100 and amounts to 24.13%. It means that in such a case, Mo-99 will be produced simultaneously from the two stable isotopes of molybdenum: both from Mo-100 (9.63%) via the (γ,n) reaction and from Mo-98 (24.13%) via the (n,γ) reaction. It should be pointed out that in order to maximize the second channel for the Mo-99 production via the (n,γ) reaction, the neutrons from the first (neutron producing) channel should be slowed down to the epithermal/thermal energy interval. For this purpose, a low atomic number liquid, e.g. distilled water, which was intended primarily for cooling down of the target assembly of the electron linear accelerator can be used for neutron slowing down too.

(4) In the method of the invention, production and accumulation of the isotope Mo-99 has been carried out in the Mo-CTU itself located inside the target assembly of the linear accelerator. Therefore, high fluxes of high energy bremsstrahlung photons and neutrons (many MeV's energy range) are found around the target assembly outside the accelerator. These high energy bremsstrahlung photons can be used to produce some other very important radioactive isotopes via the (γ,n) reaction on the appropriate target materials placed outside the accelerator target assembly and adjacent to it. For example, placing an external target of the stable isotope Xe-124, enables the simultaneous production of the primary radioisotope Mo-99 (inside the accelerator Mo-CTU) and of two important radioisotopes of iodine: I-123 via the (γ,n) reaction and I-125 via the (n,γ) reaction.

(5) Moreover, short-lived radioisotopes like F-18, O-15, N-13, and C-11 for use in Positron Emission Tomography (PET) can be also produced in this way by placing an external target from an appropriate stable isotope adjacent to the accelerator target assembly. All this occurs simultaneously with the production and accumulation of the primary radioisotope Mo-99 in the Mo-CTU inside the linear accelerator. In addition, the high flux of high energy bremsstrahlung photons exiting the accelerator target assembly can be used for photo- fission (γ,f) of LEU samples placed outside the accelerator target assembly and adjacent to it.

(6) It should be pointed out that the photonuclear accelerator-based technique in general has several advantages: 1) natural or depleted uranium (U-238) target can be used, thereby obviating problems of security and NPT; 2) the electron accelerator can be turned on and off at will; 3) an electron accelerator is inexpensive to decommission at end-of-life; 4) the electron accelerator-based technology promises to be scalable.

(7) All the above description has been provided for the purpose of illustration and is not intended to limit the invention in any way. As will be apparent to the skilled person the invention allows exploiting different products of the reaction, and to use different targets, all of which results in a flexible, safe and economic method and system.