Radiant energy – Ionic separation or analysis – With sample supply means
Patent
1989-06-27
1992-02-04
Anderson, Bruce C.
Radiant energy
Ionic separation or analysis
With sample supply means
250281, 250283, B01D 5944, H01J 4900
Patent
active
050862251
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
This invention will separate and enrich a single isotope such as iodine-123, to very high purity, from a polyisotopic mixture produced by a conventional small cyclotron. This invention will also greatly increase the recovery rate of the selected isotope, thus lowering the cost of pure isotopes, and making feasible their use in nuclear medicine.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
BACKGROUND OF THE INVENTION
Many elements have chemically identical isotopes, which vary only in the number of their neutrons. These isotopes of a single element are often co-produced in a single reaction. The isotopes of a single element do vary, particularly in their radioactivity, and therefore purification or separtion of the isotopes leads to an improved product. However, these isotopes, being chemically identical, are difficult to separate.
By way of example, iodine-123 is a close-to-ideal radioactive isotope used in nuclear medicine. It permits diagnostic tomography of a patient's brain to allow a physician to distinguish between multiple infarct dementia, associated with a series of strokes, and Alzheimer's Disease. These two diseases, requiring quite different treatment, have, prior to diagnostic tomography, given only obscure and conflicting symptoms.
Pure iodine-123 is close-to-ideal because it has a 13 hour half life allowing shipment nationwide and yet decaying sufficiently rapidly so that the patient does not receive an excessive dosage of radiation. Pure iodine-123 emits a single characteristic energy, 159 keV, and practically no other radiation. Pure iodine-123 is well tolerated by the human organism and is readily compounded as a label into many biochemical agents without disrupting their action.
The principal drawback to the use of pure iodine-123 in nuclear medicine is that pure iodine-123 is expensive to produce. Most of the iodine-123 which is available is not pure. It is produced by a 20 to 40 MeV cyclotron or linear accelerator. The high energy protons from the cyclotron bombard a target enriched in tellurium-124, whose atomic number is 52 compared with iodine, whose atomic number is 53. The high energy proton principally dislodges two neutrons to produce iodine-123 in the reaction:
Some of the bombarding protons dislodge only one neutron. In addition, the target contains residual amounts of tellurium-125 and tellurium-126. The result is that about 3% of iodine-124 and iodine-125 is coproduced in the side reactions:
These two isotopes of iodine, even a few percent, are each unwatned in nuclear medicine for different reasons. Iodine-124 emits other radiation which degrades the output of diagnostic tomography, making it a less precise test. The radiation from iodine-125 is soft, i.e., X-rays which are absorbed within the patient, and therefore does not degrade the output of diagnostic tomography. However, iodine-125 has a half life of 60 days, thus substantially increasing the internal radiation dosage to the patient.
Two alternative processes exist to produce pure iodine-123. The first one uses a 20-40 MeV cyclotron in which the high energy proton bombards a target of xenon-124 and dislodges two neutrons to produce cesium-123. This then decays in 8 minutes to xenon-123, which decays in 2 hours to iodine-123, according to the reaction:
This reaction produces high purity iodine-123, but does so very expensively because xenon-124 is a very rare isotope. The process was, until recently, therefore limited to research applications.
The second process uses a 70 MeV cyclotron with an iodine 127 target the high energy proton can dislodge 5 neutrons to produce xenon-123, which decays in 2 hours to a solid iodine-123 according to th
REFERENCES:
patent: 2533966 (1950-12-01), Simmons
patent: 3758777 (1973-09-01), Brunnee et al.
patent: 4737638 (1988-04-01), Hill
patent: 4758721 (1988-07-01), Hill
Anderson Bruce C.
KPG Associates, Inc.
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