WO2008147239A1

WO2008147239A1 - Lithium container

Info

Publication number: WO2008147239A1
Application number: PCT/RU2007/000276
Authority: WO
Inventors: Boris Fedorovich Bayanov; Sergei Yuryevich Taskaev
Original assignee: Budker Institute Of Nuclear Physics Sibirskogo Otdeleniya Rossiiskoi Akademii Nauk
Priority date: 2007-05-28
Filing date: 2007-05-28
Publication date: 2008-12-04

Abstract

The invention can be used mainly in neutron and neutron capturing therapy. The inventive container is used for evaporating a lithium layer on the neutron-generating target of an accelerator-based neutron source. Said lithium container is designed in the form of a closed hollow metal (for example aluminium) thin-walled body which is completely filled with pure solid-state lithium. The lithium container makes it possible to store metallic lithium in a standard atmosphere. Said property substantially simplifies the transportation of the container and the process for loading lithium in an evaporator unit, since the inert atmosphere is not required. The lithium container, which is made of a thin-walled aluminium sheet, enables the pure lithium, heated to a temperature lower than the aluminium melt point, to be evaporated on the target substrate. Said property substantially reduces loads and simplifies the structural design for the evaporating system. The aim of the invention is to simplify a lithium layer evaporation process.

Description

LITHIUM CONTAINER

The invention relates to nuclear physics and medicine and can be used in neutron sources based on charged particle accelerators. Such sources are intended for use mainly in medical equipment used in neutron therapy, mainly in neutron capture therapy (NRT). The concept of neutron capture therapy in oncology was proposed in

1936, four years after the discovery of the neutron. Its physical principle is as follows. A solution containing the stable boron-10 isotope is introduced into human blood, and after some time, boron is sorbed mainly in tumor cells. Then the tumor is irradiated with a stream of epithermal (from 1 eV to 1 keV) neutrons. As a result of neutron absorption by the stable ¹⁰ B isotope, a nuclear reaction occurs, and the resulting energetic α-particle and ⁷ Li ion are rapidly inhibited along the cell size and release energy ~ 2.3 MeV within the cell that contained the boron nucleus, which leads to her defeat. Thus, boron neutron capture therapy (BNCT) allows the selective destruction of malignant tumor cells.

In the early 1950s, it was first demonstrated that certain boron compounds provide a higher concentration of boron in cancer cells compared to a healthy one. Since the mid-1950s, the methodology has been tested with varying success at nuclear reactors in a number of countries. The main achievements were associated with the name of the Japanese neurosurgeon Hatanaki, who irradiated more than 200 patients with very encouraging results, and with the progress in the synthesis of drugs containing the isotope 'B. Thus, drugs were obtained that create a concentration of the isotope' B in tumor tissue up to 40 mcg / g, which is 3.5 times more than in healthy tissue. Such concentration and contrast make it possible to make the contribution of background radiation reasonably small, and indeed provide the possibility of selective damage to tumor cells. The feasibility of developing neutron capture therapy technology is due to its focus on the treatment of such types of malignant tumors that are practically not amenable to any other methods, such as brain glioblastomas and melanoma metastases. In the 1990s, simultaneously with work on reactors, intensive discussions began on the development and creation of a neutron source based on a compact and inexpensive accelerator, which could be equipped with almost every oncology clinic. Various principles have been proposed for constructing NCT systems based on an accelerator with a particle beam interacting with a neutron generation target. Basically, four reactions are considered [T. Blue and J. Yaps. Asselegatór-based érétgmöl sörgös source för börop bört sartuge théraru of baip tumors. Jörpal of Neuro-opsologo 62 (2003) 19-31; S. Lee, X. Zhou. Thiсk tagget paths fors ⁷ Li (p, p) ⁷ Be rаstiop peag thеşоld. NIM B 152 (1999) 1-1 L]: ⁷ Li (p, p), ⁹ Be (p, p), ⁹ Be (d, p) and ¹³ C (d, p). The best reaction for generating epithermal neutrons is the proton bombardment of lithium: the neutron flux is large and the energy spectrum is relatively soft. Thus, a proton beam of 10 mA 2.5 MeV leads to a neutron flux of 8.9 x 10 ¹² s ^-1 at an average neutron energy of 0.55 MeV. The therapeutic beam of epithermal neutrons is formed by a system consisting of a moderator, a reflector and a collimator. Since reaction ⁷ Li (p, n) ⁷ Be is a threshold and is characterized by an unusually rapid increase in the reaction cross section near the threshold, this property allows us to consider the additional possibility of working in a threshold mode, when the proton energy exceeds the reaction threshold of 1.882 MeV by 30–40 keV, in this case kinematically ollimirovanny forward neutron beam with an average energy of 30 keV can be directly used for neutron capture therapy.

The concept of a proton beam — a lithium target — has been developed in Russia, including the use of a tandem accelerator to expose a lithium target to protons with energies exceeding the production threshold of 1.882 MeV in the ⁷ Li (p, n) ⁷ Be reaction, similar to that described in Pat. US 5976066, A61N5 / 10, 02.1 1.1999. Preliminary studies have shown that obtaining a proton beam of 10 mA will provide the desired treatment time in tens of minutes.

At the same time, the accelerator-based lithium target concept has a number of critical problems, mainly related to the poor mechanical, chemical, and thermal properties of lithium.

An important aspect of the target is its significant beam heating. So, for static targets, the specific heat flux can reach 1 kW / cm ² . As an example of a static target for a relatively small specific heat flux, we can cite neutron-producing targets described by Pat. US 4,666,651, A61N5 / 10, 05/19/1987; Rat. US 5920601, A61N5 / 10, 07/06/1999. When using a lithium target, it is necessary not only to remove such a high specific load, but also to maintain the lithium layer in a solid state (below 180 ° C) to limit the propagation of the radioactive isotope of beryllium-7 that is constantly formed as a result of the ⁷ Li (p, n) ⁷ Be reaction. Although lithium compounds have a significantly higher melting point, the neutron yield from lithium hydride is 30% less, and from lithium oxide 2 times less.

The next important aspect of the lithium target is its thickness, since inelastic proton scattering on lithium nuclei leads to a significant flux of γ-quanta with an energy of 0.477 MeV. The optimal thickness of lithium is such a thickness at which the proton is inhibited to 1.882 MeV - the energy of the threshold of the neutron generation reaction. At an initial proton energy of 2.5 MeV, this size is 88 μm, and at 1.915 MeV it is 4.3 μm [H. Andersen (Ed.). Well gogep storripg rovers apd rappes ip all elepts, Regamop Press Ips, 1977]. Further absorption of protons should be carried out in tungsten, molybdenum, or any other substance in which, unlike lithium, proton scattering does not lead to the emission of gamma rays.

Another important aspect of the target is its limited lifetime due to induced activity and surface layer modification during proton implantation, up to the formation of blisters and flaking of flakes. When working in a clinic, it will be advisable to change the target at least once a week. Thus, the optimal neutron-generating layer is a layer of pure lithium metal with a thickness of 10 to 100 microns. Currently, accelerators existing in a number of countries are being adapted for conducting experiments on the production of epithermal neutron beams. In Birmingham (England) [A. Wowp, C. Forseu, and M. Sott. The desigp apd testigp high rover lithium tagget fog asseleretog-based bogop suture sarte teraru. Reseagsh apd Develmept ip Neutro Sarture Théraru, Ed .: W. Sauerweip, R. Moss, apd A. Wittig. Mopduzzi Editoge, 2002, p.277-282] and in Obninsk (Russia) [O. Kopopov, et al. Ortimizatiof оf ap asselératog-based erithermal path sourse fog path sarture teraru. Arrliéd Radiátiop apd Isotores 61 (2004) 1009-1013] lithium targets are used. Since these works are not yet aimed at treatment and are of a research nature, a number of target parameters are not optimal. So, in Birmingham, the thickness of lithium is 1 mm. A lithium layer about 1 mm thick is usually obtained by melting lithium in an inert atmosphere. The need to work in an inert atmosphere is due to the fact that when lithium is placed in the air, its compounds (nitride, hydride and lithium oxide) are instantly formed. Therefore, lithium is stored, as a rule, in sealed vessels, either in kerosene or in mineral oil with paraffin, and any operations with lithium are carried out in an inert atmosphere.

Another way to obtain a lithium layer is to heat lithium compounds. So, lithium chromate tablets are commonly used, which can be used in a normal atmosphere. For lithium reduction, titanium or zirconium powders are used, which, together with lithium chromate, are heated to a temperature of about 600 ° C. To obtain a lithium layer of the required thickness, a significant amount of material and heating to a high temperature are required. Since zirconium powder ignites in a normal atmosphere, working with it requires special precautions.

The objective of the invention is to simplify the creation of a lithium layer of a neutron-generating target of a neutron source based on an accelerator.

To solve this problem, a lithium container is made, which is a closed hollow metal (for example, aluminum) thin-walled body, completely filled with pure lithium in the solid state.

Thin-walled housing can be made in the form of a cylinder. The metal case may be prefabricated and then filled with lithium.

The metal case can be made parallel to the lithium filling process. So, if lithium is stored in a bellows and squeezed out under pressure in the form of a rod, then a thin-walled aluminum tube enveloping lithium can be squeezed out in parallel. Thin-walled metal housing can be made in the form of a thin plate, which is wrapped with lithium.

The lithium container allows you to save lithium in a metallic state, as it prevents the interaction of lithium with the surrounding air. A lithium container allows you to transport and perform any other operations with it in a normal atmosphere, rather than inert, typical for working with pure lithium.

A lithium container made of aluminum allows the deposition of lithium at a temperature below the melting point of aluminum (660 C). The lithium container was installed in the developed lithium deposition system, consisting of a heater and a system of holes for the formation of a uniform stream of lithium vapor. It was experimentally determined that heating a lithium container to a temperature of 450 ° C, which is 210 ° C lower than the melting temperature of aluminum, leads to the deposition of a dense clean lithium layer of controlled thickness from 10 to 100 μm on the target substrate. Most likely, when the lithium container is heated, an alloy is formed whose melting point is lower than the melting temperature of aluminum. Since at a temperature of 450 ° C the vapor pressure of aluminum is of the order of 10 ^{~ 12} Torr, and lithium 10 ^{^} Torr, only lithium evaporates. The possibility of deposition of lithium when heated to a temperature of the order of

450 ° C greatly simplifies the spraying system compared with the case of heating lithium compounds or alloys, when not only a higher heating temperature is required, but also heating a larger volume of material.

Claims

CLAIM

The use of a sealed container with lithium for use in an accelerator-based neutron source.