DK144020B - METHOD AND APPARATUS FOR PREPARING SOLID SAMPLES FOR USE BY RADIOACTIVE NUCLIDES TESTS - Google Patents

Description

(19) DENMARK \ Ra

| J | (12) PUBLICATION MANUAL OR H4020 B

DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

~ In - I. Il - IIII.I \ | I) "'I'-" >> - (21) Application No. 5181/69 (51) | ntfCI.3 G 01 N 23/00 (22) Filing Date Sep 29 1 969 (24) Race day Sep 29 1969 (41) Aim. available Oct. 50 1970 (44) Presented 16 Nov. 1981 (86) International Application No. - (86) International Filing Day - (85) Continuation Day - (62) Master Application No. -

(30) Priority 29-Apr. 1969, 820269, US

(71) Applicant PACKARD INSTRUMENT COMPANY INC., Downers Grove, US.

(72) NI inventor in lo Hannes Kaartinen, FI.

(74) Clerk of the International Patent Office.

(54) Method and apparatus for producing liquid samples for use in studies with radioactive nuclides.

The invention relates to a process for the preparation of liquid samples for use in studies with radioactive nuclides, which method includes the production of a gaseous oxide which can be liquefied by condensation by combustion of a primary sample containing a radionuclide. adding an oxide of a non-radioactive isotope of the same CO nuclide to the assay gas.

By the addition of the isotopic, non-radioactive oxide to the 0 combustion gases, an increase in the amount of analytical gas available for subsequent analyzes is obtained, thereby making it possible to treat very small primary samples of the magnitude. 100 mg down to less than 1 µg. The uncertainty of □ 2 U4020 is reduced on the analysis result, which is due to the so-called residue, which in the successive treatment of several samples consists in the fact that some of the analyzing gas is adsorbed on walls of the apparatus used and subsequently desorbed during the treatment of a subsequent sample.

From Houben-Weyl, Volume III / 1, Physical Research Forschung Method, Teil 1, 4th Edition, Stuttgart 1955, a process of the kind used is known in which non-radioactive carbon dioxide is produced by combustion of an inactive carbon compound after the previous combustion thereof. primary sample containing radioactive carbon as trace element. By analogy, Analytical Biochemistry 12 (1965) describes a method in which the primary sample is to be analyzed for its content of tritium and, after completion of the combustion of the sample, the combustion chamber is flushed with non-radioactive water vapor.

The process of the present invention is characterized in that the non-radioactive oxide is introduced directly as oxide into the chamber in which the primary sample combustion takes place and during the initial period of the combustion.

Compared to the prior art, which involves the successive flow of the combustion chamber and the adjacent parts of the apparatus used with an active and an inactive substance, the invention achieves a significantly more efficient mixing of the radioactive and non-radioactive gases, which in turn contributes to to increase the quantitative recovery of the radioactive nuclide, even if the primary sample is relatively small, and to reduce the residual phenomenon.

The invention also relates to an apparatus for carrying out the method, which comprises an combustion chamber for receiving a primary sample containing the radioactive nuclide, means for condensing the oxide formed during combustion and means for introducing a gas into the combustion chamber. The above-mentioned advantages are obtained in the apparatus in that the latter means are arranged so that from a supply of an oxide of a non-radioactive isotope of the same nuclide they can supply a certain amount of this oxide to the combustion chamber during combustion.

In one embodiment of the apparatus, the non-radioactive oxide insertion means is a four-way valve whose first port is connected to the oxide supply, whose second port is connected to the combustion chamber, and whose third and fourth ports are interconnected through a conduit extending in a closed loop. predetermined volume, and the valve body has a flow passage connecting in a first position the first and fourth port, in a second position connecting the fourth and third port, and in a third position connecting the third and second port. The embodiment has the advantage that a precisely determined quantity of the non-radioactive oxide can be measured and then introduced into the combustion chamber by successively displacing the valve body from its first position in which the loop conduit is filled with oxide, over the second position in which the line is blocked from the supply. to the third position where the oxide from the loop conduit flows to the combustion chamber.

The invention will be explained in more detail below with reference to the drawing, which schematically shows an embodiment of an apparatus according to the invention.

The apparatus shown can be used in processing samples for studies with radioactive tracers, e.g. studies on the distribution and residue of various chemicals in plant and animal tissues. In the processing of such samples, a sample of the starting material containing the radioactive tracer is burned, for example, a sample of plant or animal tissue, and the radioactive tracer is then recovered from the combustion products. If the radioactive tracer is 1 ° C, this occurs in the combustion products as 1 ° cOa in gaseous form. If the trace element is titanium, ie. 3H, it occurs in the combustion products as 3H20 in the form of condensable vapor. Other radioactive isotopes, e.g. 35S which is converted to SO2 by the combustion.

To obtain samples that can be analyzed for radioactivity, the compounds containing the trace elements must be recovered from the combustion products and separated from other materials which could interfere with the radioactivity measurements. Eg. 3H2O is recovered by cooling the combustion products so that their vapors including 3H2O are condensed, and then the condensed vapors are separated from the remaining gases. can be recovered by condensation or by freezing at very low temperatures, e.g. using liquid nitrogen, but it is more normal to react with a liquid binding agent, such as ethanolamine. The resulting reaction product is then recovered and mixed with a liquid scintillator to give a sample whose radioactivity can be ascertained by examination.

In the apparatus shown in the drawing, a sample to be burned is placed in a crucible 10 which is part of an electric ignition 4AAA020 system and which may be made of platinum or a platinum-rhodium alloy so that it functions both as electrical resistance in the ignition system and as a catalyst for combustion. Two electrical conductors 11 and 12 protrude from a mounting plate 13 and% are connected to the crucible 10, respectively, at the bottom and the top, so that they simultaneously carry the crucible and make its electrical connection with the ignition system. The conductors 11 and 12 are passed vertically down through the plate 13 and terminate in downward contact pin below the plate.

The plate 13 is mounted on a platform 14 screwed on a thread at the end of a piston rod 15, which belongs to a pneumatic working cylinder 16. When a sample is to be placed in the crucible 10, the piston 16 * is withdrawn, whereby the crucible 10 is lowered through an opening 17 at the bottom of a combustion chamber 18. The sample is then placed in the crucible and, by supplying compressed air to the cylinder 16, the piston and piston rod 15 with the crucible 10 are raised through the opening 17 into the chamber 18. When the platform 14 arrives into the aperture 17, a sealing ring 19 arranged in a groove in the circumference of the platform 14 engages the conical walls of the aperture 17 so as to create a gas-tight closure.

The contact pins below the plate 13 fit into contact bushes 20 in the upper side of the platform 14. The bushings 20 are connected to an electrical circuit with a voltage source 21 and a switch 22 which can connect the current through the crucible 10.

At the end of the switch 22, the sample is turned on and when the combustion has begun, the switch can be opened again.

The amount of oxygen required to burn the sample in crucible 10 is supplied as pure oxygen to the chamber 18 through a valve 23, a flow meter 24 and two cooperating channels 25 and 26 in the platform 14 and plate 13 respectively. The velocity of the flowing oxygen is adjusted by the valve. 23 and the meter 24 to a value slightly higher than the amount needed to maintain the combustion of the sample so that there is a small excess of oxygen in the combustion chamber. Therefore, there is generally a relatively thin layer of oxygen-rich atmosphere between the combustion flame and the inner wall of the combustion chamber 18, as indicated by arrows in the drawing. The excess oxygen rises through the combustion chamber and flows out of the chamber together with the combustion products through a lateral outlet 27 at the top of the 54040 chamber.

The combustion chamber, further described in Dapsk Patent No. 128,758, is surrounded by a cylindrical container 30 which defines an annular cavity around the side walls of the chamber 18 and which may contain a preheating fluid.

Before igniting the sample in crucible 10, the fluid in the cavity between the combustion chamber 18 and the container 30 is heated by a heater 32 at the bottom of the cavity such that the chamber walls are uniformly heated to a temperature higher than the condensation temperature of the vapors of the latter. produced combustion products. Condensation in the outlet 27 from the combustion chamber 18 is hindered by the heated fluid in the cavity between the chamber 18 and the container 30, since the fluid also surrounds the outlet 27.

The apparatus contains means for introducing one or more gaseous oxides of a non-radioactive nuclide, which is an isotope of a radioactive nuclide present in the primary sample, into the combustion chamber 18. If the primary sample e.g. containing carbon-14 and tritium, either carbon dioxide or water or both are introduced into the system. Here and hereinafter, the term "water" is used, whether in liquid or gas form, but it will be understood that the water, at the temperature prevailing in the container 30, which may typically be 200 ° C, acts as water vapor.

For introducing water, a pump 101 is provided which contains a manually actuated, spring loaded piston and which sucks water in liquid form through a conduit 102 and a non-return valve 104 from a closed water container 105. The pump 101 delivers the water through a second non-return valve 106 and a conduit 108 to a heater 109 disposed in the container 30, which heats the water to ambient temperature, in the heat exchanger 109, the water is evaporated and the resulting superheated steam is passed through a conduit 110 into the combustion chamber 18 where the conduit opens.

It has been found that a stroke volume of approx. 70 µl is an appropriate capacity of the pump 101. The pump may be activated once or more in connection with each combustion of a primary sample in the combustion chamber 18.

Non-radioactive carbon dioxide can be introduced into the combustion chamber 18 through a counterpart to the water introduction system described above. The drawing shows a four-way valve 111 connected through a line 112 to a carbon dioxide source. Two ports in the valve 111 are interconnected to form a loop 113. Carbon dioxide gas under a pressure exceeding that prevailing in the combustion chamber 18 is collected in the loop 113 when the valve 111's duty is in a position corresponding to 9 o'clock and 12 o'clock When the duty is turned 270 ° clockwise, the enclosed amount of carbon dioxide is delivered to the combustion chamber 18.

Whether water or carbon dioxide is introduced, this occurs during the initial phase of the combustion, preferably at the same time as the end of the electrical circuit supplying the crucible 10, and at least so close to the time of combustion that the non-radioactive gases are thoroughly mixed with the combustion products. when the primary sample ignites.

The amount of water and / or carbon dioxide added to the system either through piston pump 101 or through valve 111 depends on the size of the sample and on the purpose of introducing water and / or carbon dioxide. By introducing water, a significant increase in the recovery of tritium oxide and a significant reduction of the residue by a single injection of 70 mg of water are achieved in a system where the gas flows at a rate of approx. 0.1 to approx.

4 liters per minute. In other words, the total volume of water vapor used to improve the recovery of radioactive nuclides and to reduce the residue is in the range of approx. 1%, preferably 10%, to approx. 50% of the gas volume flowing away from the combustion chamber 18. If a single injection is insufficient to ensure satisfactory separation or reduction of the residue, another simultaneous injection or continuous addition during combustion will usually suffice.

The use of water or other gaseous oxide offers several additional advantages. Although the residue is noticeably diminished by water, it is occasionally the case that an unusually active sample produces a high background count for an extended period of time after the sample burns. In that case, it becomes desirable to determine when the background count is reduced corresponding to a sufficient desorption of the adsorbed radionuclide. In order to check the residue or background count, a simulated combustion is performed without any primary sample in the combustion chamber 18. The only materials recovered in the liquid sample are thus the amount of water introduced from the pump 101 as well as the desorbed contaminants. Counting the sample then gives a measure of the background or residue, and if the count is too high, it can easily be reduced in one or more additional simulated combustions with a few water injections in each combustion.

Injection of water from a pump that delivers a predetermined quantity of water also provides convenient options for preparing a series of so-called quench standards. It is known that water weakens most scintillation fluids, and in order to correct for this weakening, the researcher needs a series of standards, each containing the same amount of a standard activity radionuclide, but with different amounts of water. With the described injection system, a series of standard samples can easily be prepared by conducting a combustion cycle without a primary sample and introducing an increasing number of doses of water, each of 70 mg. Hereby, liquid samples containing a scintillator, a standard radionuclide and various amounts of attenuation factor can be prepared within a few minutes.

Water injection is also advantageous for reconciling quench effects in scintillatlon samples prepared from different sized hydrogen-containing primary samples. For example, one primary sample is large and another is smaller, the efficiency or goodness of the count is different due to the additional weakening or quench due to the higher water content of the larger sample. However, if pump 101 is introduced during the combustion of the smallest of the two samples, an amount of water approximately equal to the additional amount of water produced by the larger primary sample, the total amount of water in each scintillation sample will be approximately the same. , and the weakening and thus the efficiency of the counting will also be substantially the same.

The injected water and / or carbon dioxide are mixed with the combustion products and passed through the recycled portion of the apparatus.

Therefore, no distinction is made between oxides of radioactive and of non-radioactive nuclides.

From the outlet 27, the combustion gases flow into a transfer tube 34 which is insulated to hold the flowing fluids in gaseous form. From the tube 34, the gaseous combustion products flow through a tee 40 into a heat exchanger 41 for cooling the combustion products and condensing their contents of vapors. The heat exchanger 41 includes an internal member 42 which forms a flow channel for the combustion products and an outer housing 43 which forms an annular cavity around the member 42 and is flowed through a coolant. If the radioactive tracer is in the form of condensable steam, e.g. 3H2O, the trace element in the heat exchanger 41 is transferred from vapor to liquid form. If the radioactive tracer is in the form of a gas such as later, to react with a binding agent, the heat exchanger 41 serves to remove condensable vapors from the trace-containing gas before reacting with the binding agent.

Through an elastic connection piece 50 at the bottom of the heat exchanger 41, the outlet of the inner element 42 of the heat exchanger can be connected to a normal sample bottle 51. The bottle 51 stands on a platform 52 which is actuated upwardly against the connector 50 by means of a spring 53 so as to form a tight closure around the top of the bottle. As the combustion products flow out from the lower end of the heat exchanger 41, they flow into the bottle 51 where the liquid components are collected due to gravity while the gases continue through an outlet duct 54 in the connector 50.

When the combustion of a sample is completed, the valve 23 is closed, whereby the oxygen supply to the combustion chamber ceases, and upon opening a valve 60 is opened to supply an inert gas, e.g. nitrogen, to the combustion chamber through meter 24 and ducts 25 and 26. The inert gas supplied under a slight overpressure rises upwardly through the combustion chamber 18 and rinses the chamber clean of any remaining combustion products. The gas then proceeds through the outlet 27, the pipe 34 and the heat exchanger 41.

After the flushing of the combustion chamber and heat exchanger, the inactive rinse gas is shut off by closing valve 60, and the heat exchanger 41's approach can then be successively connected to two liquid delivery systems 61 and 62 for supplying a liquid solvent of the kind normally used in processing, respectively. to be cooled below the freezing point to keep the sample in liquid state and a predetermined quantity of a liquid scintillator for the heat exchanger 41.

For the recovery of tracers by reaction with a binder, the gases separated from the condensed vapors are fed into a reaction column 74 to which a liquid binder can be added and in which the gases can react with this agent during their flow through column. The column is described in more detail in Danish Patent Specification No. 131,746.