Patent Description:
Examples of treatment methods of cancer include resection, administration of anticancer agents, and external radiation exposure. Many lives are still being lost due to cancers which even those techniques are difficult to cure. Accordingly, to develop novel treatment methods is a worldwide urgent problem.

Astatine <NUM> (<NUM>At) is a radioisotope (RI) emitting α-beams which kill cells, and leads to high expectations as next-generation cancer therapy drugs which are administrated into the body. Europe and America are leading studies on <NUM>At into drugs, but in production of <NUM>At which is the backbone of those, do not handle its supply in an amount (tens of gigabecquerels) of radioactivity with which a plurality of hospitals can perform medical treatments.

Conventionally, a radioisotope has been generated in a solid metal by irradiating a radiation on the solid metal as a target, and then, the solid metal after irradiation of the radiation has been taken out to separately collect the RI. It is a relatively unignorable problem in such irradiation with a solid metal being as a target in the field of production of medical RI to secure soundness of the target in irradiation since damage to (melting of) the target in irradiation disturbs efficient generation of an RI, and in addition, causes a concern that the generated RI is released. In addition to this, while medical sites want developments of techniques capable of quickly affording target RIs after irradiation, there has not been a successful example yet in irradiation with a metal being as a target.

The aforementioned problem is significant in production of <NUM>At. <NUM>At is generated by irradiating alpha- (α-) rays on bismuth (Bi), Bi has an especially low melting point as a target, and this limits irradiation power, which problematically disturbs its large-scale production. Accordingly, irradiation schemes have been developed such that Bi does not melt. Moreover, in a conventional dry distillation and separation procedure in which irradiated solid Bi is heated to be separated using the difference in saturated vapor pressure between <NUM>At and Bi, it takes time to take out the solid Bi and separate and purify <NUM>At, which has problematically caused a decay loss of <NUM>At with approximately seven hours of half-life.

As above, in RI production with a solid being as a target, there have had to be taken a series of procedures of irradiation, taking-out of the target, and separation and purification of a target RI from the target.

An object of the present invention is to provide a method of producing a radioisotope with a production time shortened.

In order to solve the aforementioned problem, the following means is employed. Namely, a first aspect is a producing method of a radioisotope according to claim <NUM>.

According to the present invention, there can be provided a method of producing a radioisotope with a production time shortened.

Hereafter, an embodiment is described with reference to the drawings. The configuration of the embodiment is exemplary, and the configuration of the invention is not limited to the specific configuration of the embodiment of the disclosure. When implementing the invention, a specific configuration according to the embodiment may be properly employed.

<FIG> is a diagram illustrating an exemplary configuration of a radioisotope producing apparatus of the present embodiment. A radioisotope producing apparatus <NUM> includes a crucible <NUM>, a heater <NUM>, a jacket <NUM>, a beam port <NUM>, a beam window <NUM>, a beam window <NUM>, an inlet <NUM>, an outlet <NUM> and a trap <NUM>.

The crucible <NUM> is a heat-resistant vessel in which a substance as a target (for example, bismuth) is molten. The crucible <NUM> is a container which houses the substance as the target. As the crucible <NUM>, for example, quartz, china and porcelain, metal, and the like are used. For the crucible <NUM>, it is expected that it is at least durable against the temperature at the melting point of the substance as the target. While the crucible <NUM> is hermetically sealed, gas can pass through the inlet <NUM> and the outlet <NUM> between the inside and the outside. The beam port <NUM> is connected to the crucible <NUM>. The crucible <NUM> is exemplarily a heat-resistant vessel.

The heater <NUM> is heating means for heating the crucible <NUM>. The heater <NUM> heats the crucible <NUM>, and thereby, heats the substance as the target in the crucible <NUM>. Thereby, the target substance can be promoted to be molten. Typically, it melts and liquefies the target substance. As the heater <NUM>, for example, a micro-sheath heater is used. The heater <NUM> is not limited to a micro-sheath heater. All the substance as the target in the crucible <NUM> is not needed to be liquefied. Namely, a part of the substance as the target may be still solid. When the substance as the target is heated by the heater <NUM>, the relevant substance is liquefied. A liquid phase of the liquefied substance and a gas phase of gas introduced from the inlet <NUM> and the like exist in the crucible <NUM>. The heater <NUM> is exemplarily a heating unit.

Notably, while there is herein exemplarily described the case where the heater <NUM> heats the target substance to liquefy the relevant substance, the heating means is not limited to this. For example, temperature increase at a beam irradiated portion at which a radiation beam is irradiated on the target substance (temperature increase originated from heat due to nuclear reaction) may be used. Two or more conventionally known items of heating means may be combined, and, for example, both the aforementioned heating with the heater <NUM> and the temperature increase originated from radiation beam irradiation may be used.

The jacket <NUM> is a cooling space arranged around the crucible <NUM>. An introduction port and a discharge port for a cooling material (for example, air) are provided on the jacket <NUM>, and the cooling material is introduced into the jacket <NUM> from the introduction port to cool the crucible <NUM>. Cooling is also performed by suspending heating of the heater <NUM>, and the cooling is more quickly performed by introducing the cooling material into the jacket <NUM>. The cooling material introduced into the jacket <NUM> is not limited to air (for example, the air at ambient temperature) but may be other gas such as nitrogen or liquid such as water.

While there is herein exemplarily described the case where the cooling material is introduced into the jacket <NUM> to cool the crucible <NUM> as a cooling method of the crucible <NUM>, not limited to this, one or two or more conventionally known items of cooling means can be combined and employed. For example, an element such as a Peltier element may be used.

The beam port <NUM> is a passage for introducing a radiation beam irradiated on the substance as the target in the crucible <NUM>. The interior of the beam port <NUM> is evacuated to a vacuum, or gas (for example, He gas or the like) is introduced thereinto. The beam port <NUM> is tubular, and both ends are closed by the beam window <NUM> and the beam window <NUM>. It connects to a radiation beam generator such as an accelerator with the beam window <NUM>. The beam window <NUM> and the beam window <NUM> are, for example, metal plates. A radiation beam accelerated by an accelerator or the like included in the radiation beam generator enters the beam port <NUM> from the beam window <NUM>, passes through the beam window <NUM>, and is irradiated inside the crucible <NUM>. Namely, it is irradiated on a target (typically, a liquefied liquid target). The beam window <NUM> and the beam window <NUM> are substances which at least part of the radiation beam can pass through. Moreover, the beam window <NUM> is a substance which is not molten even at the temperature of the liquid target in the crucible <NUM>. The beam port <NUM>, the beam window <NUM> and the beam window <NUM> are exemplarily a beam introducing portion.

The inlet <NUM> is an introduction port for introducing gas into the crucible <NUM>. The inlet <NUM> is, for example, a tubular pipe. The inlet <NUM> connects the inside and the outside of the crucible <NUM> such that gas can pass through therebetween. Gas for collecting a radioisotope is introduced from the inlet <NUM>. As such gas, gas that is not liquefied or solidified by cooling with the trap <NUM> mentioned later is preferably employed. The relevant gas is, for example, He gas. Gas is introduced from the inlet <NUM>, and thereby, the gas is discharged from the outlet <NUM>. As a result, in the gas phase inside the crucible <NUM>, a flow of the gas from the inlet <NUM> toward the outlet <NUM> arises. Such flow of the gas can carry the radioisotope transferred to the gas phase in the outlet direction. The amount of gas discharged from the outlet <NUM> can be regulated by regulating the amount of the gas introduced from the inlet <NUM>. Moreover, the pressure of the gas phase in the crucible <NUM> can be controlled by regulating the amount of the introduced gas by regulating the amount of the gas discharged from the outlet <NUM> (for example, decreasing the flow rate, typically, closing the outlet <NUM>) or by closing the discharge side of the trap <NUM> or by the similar manner. The pressure of the gas phase in the crucible <NUM> can be more accurately controlled by combining regulating the gas amount discharged from the outlet <NUM> or regulating the gas amount discharged from the discharge side of the trap <NUM> to regulating the gas amount introduced from the inlet <NUM>.

The outlet <NUM> is a discharge port for discharging gas from the crucible <NUM>. The outlet <NUM> is, for example, a tubular pipe. The outlet <NUM> connects the inside of the crucible <NUM> and the trap <NUM> such that gas can pass through therebetween. The gas introduced from the inlet <NUM> and a gasified radioisotope and the like are discharged from the outlet <NUM>. The radioisotope is a substance generated by irradiating the radiation beam on the liquid target.

The trap <NUM> is a device that separates and extracts the radioisotope from the gas introduced from the crucible <NUM>. The trap <NUM> is hermetically connected to the crucible <NUM> such that gas containing the radioisotope can pass through. For example, the trap <NUM> cools gas introduced from the crucible <NUM>. Thereby, it can liquefy or solidify the radioisotope to separate the radioisotope from the gas containing the radioisotope (typically, mixture gas with He). The aforementioned cooling is not specially limited as long as the radioisotope can be separated from the mixture gas, but may be performed, for example, at a temperature not more than the boiling point of the radioisotope, preferably at a temperature not more than the melting point of the radioisotope or at a temperature not more than the freezing point thereof. It is still preferably set to be a temperature lower than the melting point and the freezing point of the radioisotope. For example, it can be <NUM> (<NUM>) or less, typically -<NUM> (<NUM>) or less, preferably -<NUM> (<NUM>) or less, still preferably -<NUM> (<NUM>) or less. As cooling means, for example, cooling water, acetone-dry ice, liquid nitrogen, or the like can be used. At that time, since He gas is not liquefied or solidified at the liquid nitrogen temperature (<NUM>), the radioisotope can be separated. Moreover, gas that is discharged from the trap <NUM> after the separation (for example, He gas) may be reintroduced into the crucible <NUM> from the inlet <NUM>. In the trap <NUM>, the radioisotope can be separated by a similar method to known dry distillation and separation. The trap <NUM> is exemplarily an extracting unit.

One or more items of temperature measuring means such as thermocouples may be installed in the crucible <NUM>. With the temperature measuring means, the temperature at a liquid phase position and the temperature at a gas phase position in the crucible <NUM> can be measured. For example, it can be determined whether or not the substance as the target is liquefied by measuring the temperature at the liquid phase position.

<FIG> is a diagram exemplarily illustrating an operation flow of a radioisotope producing apparatus. It is herein supposed that the substance as the target has been already put in the crucible <NUM>. Moreover, it is supposed that He gas is being introduced from the inlet <NUM> at a predetermined amount per unit time.

In S101, the heater <NUM> of the radioisotope producing apparatus <NUM> heats the crucible <NUM>. The heater <NUM> may be controlled, for example, by a control device such as a computer or the like. The crucible <NUM> is heated, and thereby, the substance as the target in the crucible <NUM> is heated (typically, to be molten into liquid). The crucible <NUM> is preferably heated at a temperature not less than the melting point of the substance as the target. The liquefied substance as the target is also called liquid target. The substance as the target is herein supposed to be bismuth (Bi). The substance as the target substance includes Bi or Pb. Since the melting point of bismuth is <NUM>, the crucible <NUM> may be heated at <NUM> or more. The crucible <NUM> is herein supposed to be heated at <NUM> by the heater <NUM>. The temperature of the target (liquid target) is preferably a temperature at which a ratio of the saturated vapor pressure of the generated radioisotope relative to the saturated vapor pressure of the liquid target is higher. Moreover, in order to efficiently obtain the target radioisotope, a target element is preferably selected with which a ratio of the saturated vapor pressure of the generated radioisotope relative to the saturated vapor pressure of the liquid target is higher. In this stage, the type of a irradiated radiation beam is selected as follows.

In S102, a radiation beam irradiates on the liquid target in the crucible <NUM> via the beam port <NUM>. The radiation of the radiation beam is, for example, α-beams (<NUM>He<NUM>+), <NUM>He<NUM>+, <NUM>H+, <NUM>H+, <NUM>Li<NUM>+, or the like. The radiation beam is herein supposed to be α-beams.

In S103, the radioisotope is generated through nuclear reaction between the substance as the target and the radiation beam. When the substance as the target is Bi and the radiation beam is α-beams, a mainly generated radioisotope is <NUM>At. Moreover, in the liquid phase of the crucible <NUM>, Bi heated with heat due to the nuclear reaction rises, Bi cooled with gas in the gas phase and air or the like via the wall of the crucible <NUM> falls, and thereby, a convection current of Bi arises. Therefore, the temperature of Bi in the liquid phase can be held to be constant.

In S104, the radioisotope generated by irradiating the radiation beam is vaporized. For example, the saturated vapor pressure at the melting point (<NUM>) of At is <NUM>×<NUM><NUM> Pa. Generated At is vaporized until a partial pressure of At in the crucible <NUM> becomes the saturated vapor pressure. Moreover, the saturated vapor pressure at the melting point (<NUM>) of Bi is <NUM>×<NUM>-<NUM> Pa. Bi is also vaporized until a partial pressure of Bi in the crucible <NUM> becomes the saturated vapor pressure. When it is supposed that the saturated vapor pressure of At at the melting point (<NUM>) of Bi is approximately the same as the saturated vapor pressure of At at its melting point (<NUM>), the saturated vapor pressure of At is <NUM><NUM> times or more higher than the saturated vapor pressure of Bi. Accordingly, even when the ratio of At relative to Bi is very low in the liquid phase of the crucible <NUM>, most of elements vaporized from the liquid surface (elements transferred from the liquid phase to the gas phase) is At since the partial pressure of Bi immediately reaches its saturated vapor pressure in the gas phase. For example, when the temperature of the liquid target is <NUM>, a ratio of At out of the elements vaporized from the liquid surface is <NUM>% or more if the volume of Bi is appropriately set. Namely, the elements vaporized from the liquid surface is almost At. The amount of At existing in the gas phase is much larger than the amount of Bi existing in the gas phase. Therefore, At is separated from Bi.

Namely, when the saturated vapor pressure of the element generated by irradiation is higher than the saturated vapor pressure of the element as the target, most of elements vaporized from the liquid surface of the liquid phase are to be the generated element (radioisotope). By irradiating the radiation beam on an element as the target, the radioisotope is generated and transferred to the gas phase (gas).

<FIG> is a table exemplarily presenting relation between saturated vapor pressures and temperatures of group <NUM>, group <NUM>, group <NUM> and group <NUM> elements. For example, the saturated vapor pressure of group <NUM> Ge at <NUM> is <NUM><NUM> Pa. It is known in principle that the saturated vapor pressure of an element monotonically increases with respect to its temperature. Herein, saturated vapor pressures are compared between elements in the same period. In the table of <FIG>, as to the same saturated vapor pressure, the temperatures of group <NUM>, group <NUM> and group <NUM> elements are higher than the temperature of group <NUM> one. Namely, in comparison for the same temperatures, the saturated vapor pressures of the group <NUM>, group <NUM> and group <NUM> elements are lower than the saturated vapor pressure of the group <NUM> element. Moreover, the boiling point of a group <NUM> element is generally much lower than the boiling points of the other elements. Therefore, in comparison for the same temperatures, the saturated vapor pressures of the group <NUM>, group <NUM> and group <NUM> elements are lower than the saturated vapor pressure of the group <NUM> element. Namely, the saturated vapor pressures of the group <NUM>, group <NUM> and group <NUM> elements at the melting points of the group <NUM>, group <NUM> and group <NUM> elements are lower than the saturated vapor pressures of the group <NUM> and group <NUM> elements at the melting points of the group <NUM>, group <NUM> and group <NUM> elements. Otherwise, the group <NUM> and group <NUM> elements are gas at the melting points of the group <NUM>, group <NUM> and group <NUM> elements. Accordingly, a ratio of the radioisotope elements vaporized from the liquid surface is made high by setting the liquid target to be a group <NUM>, group <NUM> or group <NUM> element and setting the generated element (radioisotope) to be a group <NUM> or group <NUM> element.

In S105, the radioisotope (for example, <NUM>At) vaporized into the gas phase from the liquid surface of the liquid phase reaches the trap <NUM> via the outlet <NUM> along with He gas and the like in the gas phase. The trap <NUM> extracts the radioisotope by being cooled with liquid nitrogen or the like or by the similar manner. By cooling with liquid nitrogen, He gas is still gas in the trap <NUM> and passes therethrough, while the radioisotope remains in the trap <NUM> due to its solidification or the like. Thereby, the radioisotope can be separated and extracted.

With the radioisotope producing apparatus <NUM>, separation and extraction of the radioisotope in the trap <NUM> can be performed while irradiation of the radiation beam being continued. Namely, with the radioisotope producing apparatus <NUM>, irradiation of the radiation beam and extraction of the radioisotope can be performed in parallel. When irradiation of the radiation beam and extraction of the radioisotope are performed in parallel, any one process of irradiation of the radiation beam and extraction of the radioisotope may be suspended. The target element does not have to be taken out of the crucible <NUM> in extraction of the radioisotope. Therefore, the radioisotope producing apparatus <NUM> can efficiently generate the radioisotope.

<FIG> is a diagram illustrating an exemplary configuration of a radioisotope producing apparatus of a modification of the present embodiment. A radioisotope producing apparatus <NUM> in <FIG> includes a crucible <NUM>, a heater <NUM>, a nozzle <NUM>, a beam port <NUM>, a beam window <NUM>, a beam window <NUM>, an inlet <NUM>, an outlet <NUM>, a trap <NUM>, a pump <NUM> and a heat exchanger <NUM>. The radioisotope producing apparatus <NUM> may include a jacket which cools the crucible <NUM> similarly to the radioisotope producing apparatus <NUM> in <FIG>.

The crucible <NUM>, the heater <NUM>, the beam port <NUM>, the beam window <NUM>, the beam window <NUM>, the inlet <NUM>, the outlet <NUM> and the trap <NUM> have the same configurations as those of the corresponding members in the radioisotope producing apparatus <NUM>.

A passage for discharging the liquid target is provided in a lower portion of the liquid phase of the crucible <NUM>, and the liquid target is discharged from the crucible <NUM> by the pump <NUM>. The discharged liquid target is cooled by the heat exchanger <NUM>. The cooled liquid target is introduced into the nozzle <NUM> disposed in an upper portion of the crucible <NUM>. The liquid target introduced into the nozzle <NUM> flows like a waterfall from a lower portion of the nozzle <NUM>, and reaches the liquid phase of the crucible <NUM>. The beam port <NUM> is installed such that the radiation beam is irradiated on the liquid target that flows out of the nozzle <NUM>. By forcibly circulating the liquid target, heat generated through nuclear reaction can be efficiently removed, and temperature increase in the crucible <NUM> can be suppressed.

The radioisotope producing apparatus <NUM> operates similarly to the radioisotope producing apparatus <NUM> except the portion which forcibly circulates the liquid target.

Conventionally, a radiation beam has been irradiated on a solid target put in an apparatus to generate a radioisotope in the solid target. Therefore, the solid target put in the apparatus has been taken out after the irradiation to extract the radioisotope by dry distillation and separation of heating, melting and other processing of the solid target. A time loss has arisen during the process from taking-out of the solid target to completion of the dry distillation and separation. Moreover, irradiation power has been wanted to be suppressed such that the solid target does not melt in irradiation on the solid target. Suppression of the power causes the amount of the generated radioisotope to decrease.

On the contrary, with the apparatus of the present embodiment, a radiation beam is irradiated on a liquid target to generate a radioisotope in the liquid target. By regulating the temperature and the pressure near the liquid surface of the liquid target, a ratio of the generated and vaporized radioisotope relative to the elements vaporized from the liquid phase can be made high. Since in the aforementioned example, the saturated vapor pressure of <NUM>At is much higher than the saturated vapor pressure of Bi, most of elements vaporized from the liquid phase is <NUM>At. Therefore, collecting the vaporized elements is to purify the radioisotope. The process of generation, separation and purification of the radioisotope spontaneously proceeds until the partial pressure of <NUM>At near the liquid surface of the liquid target becomes the saturated vapor pressure to reach the equilibrium state. Accordingly, when At is being extracted continuously or in appropriate timing, <NUM>At can continue to be produced continuously or intermittently. Moreover, with the apparatus of the present embodiment, since the radioisotope can be extracted without suspending irradiation of the radiation beam on the liquid target to take out the liquid target, production of the radioisotope from generation to extraction of the radioisotope can be performed in a short time. Namely, according to the apparatus of the present embodiment, the radioisotope can be extracted from gas containing the radioisotope generated and vaporized by irradiating the radiation beam.

Moreover, with the apparatus of the present embodiment, irradiation power is not wanted to be suppressed such that the target does not melt since the target is liquid, and the irradiation power of the radiation beam can be made high without increasing the temperature of the liquid target by a convection current, a forcible circulation and the like of the liquid target for cooling it. Such higher irradiation power can produce larger amount of radioisotopes.

Notably, while in the aforementioned embodiment and its modification, there are exemplarily described cases where the target substance is bismuth (Bi), the radiation beam irradiated on the target substance is α-beams, and thereby, <NUM>At is generated as the radioisotope, in the aforementioned embodiment and its modification, the target substance may be lead (Pb) rather than bismuth (Bi), a radiation beam other than α-beams may be irradiated on the target substance, and an astatine isotope other than <NUM>At may be generated.

The following tables are tables presenting combination patterns of target substances, radiation beams and radioisotopes which can be generated by various nuclear reactions.

In each of the aforementioned tables, the description at the column labeled as "target" presents elements which can be employed as target substances. In the aforementioned embodiment and its modification, examples of those include lead (Pb) and bismuth (Bi).

Moreover, in each of the aforementioned tables, the description at the column labeled as "nuclear reaction" presents types of nuclear reactions with radiation beams irradiated on target substances and as described in the tables, examples of those include α-reaction using α-particles, p-reaction using protons, and nuclear reaction using lithium. At the column of the nuclear reaction, the left side of commas (,) represents ones which enter target substances, and the right side of the commas (,) represents ones which are emitted from the target substances.

Moreover, in each of the aforementioned tables, the description at the column labeled as "descendant nuclide(s)" exemplarily presents nuclide(s) generated through radioactive decay of products. As presented in each of the aforementioned tables, germanium (Ge), bromine (Br) and the like are presented as the descendant nuclide(s), and asterisks (*) are displayed for ones in which various kinds of descendant nuclides are generated not to be contained in the description column of the table.

Moreover, in each of the aforementioned tables, the description at the "target" column and at the "product" column in the column labeled as "heating temperature" presents the states of the substances, "Sol" represents being solid, "Liq" represents being liquid, and "Gas" represents being gas.

By applying the combinations of the targets and the nuclear reactions presented in the aforementioned tables various radioisotopes can be generated. Further, in each of the aforementioned tables, a target is a substance having a higher temperature at which it is gasified under a pressure in irradiating a radiation beam than a temperature at which a radioisotope as the product is gasified under the same pressure. Therefore, in the aforementioned embodiment and its modification, by adjusting the temperature of the target substance so as to be within a temperature range not less than the temperature at which the radioisotope is gasified under the same pressure and less than the temperature at which the target substance is gasified under the same pressure, the target substance is not gasified but the radioisotope is gasified, and the radioisotope can be extracted from the gas in the trap <NUM>. Notably, "gasification" stated in this application is that a substance is in the state of gas, and, for example, is a concept including the state where it is transferred to the gas phase by exceeding its boiling point or its sublimation point. Therefore, the "temperature at which the target substance is gasified under the same pressure" mentioned above can be replaced by the "boiling point or the sublimation point at which the target substance is vaporized under the same pressure".

For example, with the combination of No. <NUM> in the table, while the boiling point of sulfur (S) as a target substance at ambient pressure is approximately <NUM>, the boiling point of chlorine (Cl) as the product at ambient pressure is approximately -<NUM>, which is lower than that of sulfur (S), therefore, as presented at the "heating temperature" column in the table, when the radiation beam is irradiated on the target in the state where the temperature in the crucible <NUM> is <NUM>, chlorine (Cl) as the product is exclusively vaporized in the crucible <NUM> while sulfur (S) as the target substance maintains the state of liquid, and chlorine (Cl) vaporized in the crucible <NUM> is extracted through its condensation in the trap <NUM>.

Moreover, for example, with the combination of No. <NUM> or No. <NUM> in the table, while the boiling point of gallium (Ga) as a target substance at ambient pressure is approximately <NUM>, the boiling point of arsenic (As) as the product at ambient pressure is approximately <NUM>, which is lower than that of gallium (Ga), therefore, as presented at the "heating temperature" column in the table, when the radiation beam is irradiated on the target in the state where the temperature in the crucible <NUM> is <NUM>, arsenic (As) as the product is exclusively vaporized in the crucible <NUM> while gallium (Ga) as the target substance maintains the state of liquid, and arsenic (As) vaporized in the crucible <NUM> is extracted through its condensation in the trap <NUM>.

Moreover, for example, with the combination of No. <NUM>, No. <NUM> or No. <NUM> in the table, while the boiling point of selenium (Se) as a target substance at ambient pressure is approximately <NUM>, the boiling point of bromine (Br) as the product at ambient pressure is approximately <NUM>, which is lower than that of selenium (Se), therefore, as presented at the "heating temperature" column in the table, when the radiation beam is irradiated on the target in the state where the temperature in the crucible <NUM> is <NUM> or <NUM>, bromine (Br) as the product is exclusively vaporized in the crucible <NUM> while selenium (Se) as the target substance maintains the state of liquid, and bromine (Br) vaporized in the crucible <NUM> is extracted through its condensation in the trap <NUM>.

Moreover, for example, with the combination of No. <NUM> or No. <NUM> in the table, while the boiling point of antimony (Sb) as a target substance at ambient pressure is approximately <NUM>, the boiling point of iodine (I) at the product at ambient pressure is approximately <NUM>, which is lower than that of antimony (Sb), therefore, as presented at the "heating temperature" column in the table, when the radiation beam is irradiated on the target in the state where the temperature in the crucible <NUM> is <NUM> or <NUM>, iodine (I) as the product is exclusively vaporized in the crucible <NUM> while antimony (Sb) as the target substance maintains the state of solid or liquid, and iodine (I) vaporized in the crucible <NUM> is extracted through its condensation in the trap <NUM>.

Moreover, for example, with the combination of No. <NUM> in the table, while the boiling point of bismuth (Bi) as a target substance at ambient pressure is approximately <NUM>, the boiling point of radon (Rn) as the product at ambient pressure is approximately -<NUM>, which is lower than that of bismuth (Bi), therefore, as presented at the "heating temperature" column in the table, when the radiation beam is irradiated on the target in the state where the temperature in the crucible <NUM> is <NUM> or <NUM>, radon (Rn) as the product is exclusively vaporized in the crucible <NUM> while bismuth (Bi) as the target substance maintains the state of solid or liquid, and radon (Rn) vaporized in the crucible <NUM> is extracted through its condensation in the trap <NUM>.

Notably, while at the "heating temperature" column in each of the aforementioned tables, the two cases of temperatures of <NUM> and <NUM> are exemplarily presented, there is not limited to any of <NUM> and <NUM> the temperature in the crucible <NUM> in the case where the combinations of the targets and the nuclear reactions presented in the aforementioned tables are to be implemented in the aforementioned embodiment and its modification. Namely, the temperature of the target substance in the crucible <NUM> in the case where the combinations of the targets and the nuclear reactions presented in the aforementioned tables are to be implemented can be any temperature within a temperature range not less than a temperature at which the product is gasified under a pressure in the crucible <NUM> and less than a temperature at which the target substance is gasified under the same pressure. For example, with the combination of No. <NUM> in the table, while the boiling point of sulfur (S) as a target substance at ambient pressure is approximately <NUM>, the boiling point of chlorine (Cl) as the product at ambient pressure is approximately -<NUM>, which is lower than that of sulfur (S). Therefore, assuming that the interior of the crucible <NUM> is at ambient pressure, when the temperature of sulfur (S) in the crucible <NUM> is within a range from approximately -<NUM> to approximately <NUM>, chlorine (Cl) as the product can be exclusively vaporized in the crucible <NUM> without sulfur (S) as the target substance gasified to extract chlorine (Cl) vaporized in the crucible <NUM> through its condensation in the trap <NUM>.

Moreover, while there are described, at the "target" column in each of the aforementioned tables, the names of elements as the targets alone, the crucible <NUM> is sufficient to contain a substance as a target as presented at the "target" column in each of the tables, there may be employed the state where two or more kinds of target substances are put therein, or there may be employed the state where a substance other than the target is put therein along with the target substance.

Notably, when two or more kinds of substances are put in the crucible <NUM> together to form an alloy, the melting point thereof is different from that in the case where each substance exists as a simple substance. For example, the melting point of an alloy prepared from bismuth (Bi) and tin (Sn) in the ratio of <NUM>:<NUM> is <NUM>, at ambient pressure, which is lower than <NUM> as the melting point of bismuth (Bi) and <NUM> as the melting point of tin (Sn). Nevertheless, the boiling point of a product obtained by irradiating a radiation beam on bismuth (Bi) and the boiling point of a product obtained by irradiating the radiation beam on tin (Sn) themselves are not relevant to whether or not they are in the state of an alloy, and hence, each product can be selectively extracted with the trap <NUM> by adjusting the temperature in the crucible <NUM> to be appropriate.

Claim 1:
A producing method of a radioisotope, the method comprising:
irradiating a radiation beam on a target substance; and
extracting the radioisotope which is generated by irradiating the radiation beam and transferred to gas from the gas at an extracting unit,
wherein at least part of the target substance is liquid during the irradiation of the radiation beam,
characterized in that the target substance includes Bi or Pb in a container,
in that the radioisotope includes At, and
in that the extracting unit is directly and hermetically connected to the container.