Medical Cyclotron Section


Cyclotrons are now one of the most popular commercially available accelerators customized in medical and industrial applications, apart from its use in atomic, nuclear and solid-state physics research. More than hundred cyclotron are engaged worldwide in the production of PET and SPECT isotopes (11C, 13N, 15O, 18F, 123I, 203Tl, 67Ga) used in medical diagnostics, including isotopes for therapeutic applications too, e.g., 64Cu, 103Pd, 186Re etc. In India the reactor produced radio-pharmaceuticals have been routinely used by the nuclear medicine centers for long time. Few low energy cyclotros have also been running for some time in Mumbai, Delhi, Bangalore and Hyderabad, producing PET radioisotope and 18F labeled Fluoro-Deoxy-Glucose (FDG). However, there is increasing demand for SPECT isotopes, 201Tl, 123I, 111In, 67Ga etc., which have advantage of longer half life, hence taking care of the transportation time from the production facilities to the diagnostic centers. All these radioisotopes require higher beam energy and intensity for their profitable production. Therefore, a 30 MeV 500μA proton cyclotron facility is being set up by the Department of Atomic Energy at Kolkata. This high current cyclotron will be used to produce PET (Positron Emission Tomography and SPECT (Single Photon Emission Computed Tomography) isotopes for medical diagnostics purposes. At the same time, there will be provision for front-line research experiments in the fields of material sciences, radiochemistry, liquid metal target development etc.

The facility is based on a high current cyclotron (Cyclone-30) and five beam lines, procured from M/s IBA, Belgium. Two proton beams will be simultaneously extracted from the cyclotron. The beams can be of different energy and intensity. There will be several beam lines for utilization of the beam. Two beam lines are being dedicated for SPECT and one for PET isotope production. In addition, there will be one dedicated beam line for material science and chemistry research. A fifth beam line, which will bend the beam vertically down into a basement cave, will be utilized for dedicated experiments for R&D on windows for high power beams. Several hot cells will be provided for SPECT and PET isotope radiochemistry works. In addition, several hot cells will be provided for research experiments also. This facility will offer unique opportunities for R&D in the area of radiochemistry, material science, isotope production and their applications.

CYCLOTRON SYSTEM LAYOUT

Isotope
(T1/2 hrs)
Nuclear Reaction Proton Energy (MeV) Beam Current (A)
Ga-67
78.3
68Zn(p, 2n) 67Ga 28.5 200*



Tl-201
73.5
203Tl(p,3n)201Pb, (9.4h)
201Pb (EC/+) 201Tl
28.5 200*
In-111
67.9
112Cd(p,2n) 111In 28.5 200*
FDG
1.8
18O(p, n) 18F 18 40
Nuclear reactions responsible for the production of relevant radioisotopes along with the beam energy and current required for these reactions, are listed in Table-1. The required proton beam energy to cover all the reactions varies from 18 MeV up to 28 MeV and beam current varies from 40 up to 200 A. Cyclone-30 is a negative hydrogen ion cyclotron, but positive proton beam is extracted from it. The negative hydrogen ion beam, produced in an external cusp ion source, is axially injected into the cyclotron. Two RF cavities accelerate the negative ions. At extraction radius carbon stripper foils are used to extract two simultaneous proton beams from the machine. The extracted beam energy is adjustable from 15 MeV up to 30 MeV and the beam current is tunable up to 500A. High beam quality is ensured, giving horizontal emittance <10-mm-mrad and vertical emittance <5-mm-mrad.


The facility will have two beam lines on one side and three on the other side, as shown in fig. 2a. Two beam lines will be used for irradiating solid targets (Ga, Tl), one for PET targets and rest of the two beam lines will be used for various R&D experiments. There will be two automated solid target irradiation systems, for the production of 67Ga, 201Tl (optionally 123I, 111In) and one automated gas/liquid target irradiation system for the production of [18F] fluoride, [18F]F2, [11C]CO2, [15O]O2 etc. After irradiation, the solid targets will be transported to the receiving hot-cell via pneumatic transfer system. A fully automated radiochemistry system will be used for the remote production of labelled molecules from the irradiated target

The third beam line will be bifurcated in to two chambers to carry out material science experiments depending on the energies and currents to be utilized for irradiation. The straight beam line will be used for high dose experiments (200uA). There will be a vertical beam line (fig. 2b) to use full beam power (15 kW) on the target, to carry out following experiments: window thermal-cycling studies in LBE target flow conditions, active gas handling techniques, remote handling of irradiated target, radiation damage studies in the materials for target window and other subsystems.


R&D IN MATERIAL SCIENCEHigh intensity proton beams from the Medical Cyclotron Section provide a unique facility for radiation damage studies on reactor materials, as energetic charged particles are useful for simulating the bulk damage induced by fast neutrons. For example, 20 MeV protons with 350 μA current will produce, in stainless steel, a damage of 2x10-5 dpa/sec over a sample thickness of about 0.7 mm. This is higher than the damage rate produced in fast reactors (~10-6 dpa/sec). With this energy, thick samples of the order of 0.5 to 1 mm can be irradiated. This makes the post irradiation investigation of the samples feasible by a variety of bulk techniques like XRD, positron lifetime, mechanical property measurements. The main interest will be in studying the irradiation effects in structural materials like D9, D9I and ferritic steels. Some of the important studies that will be carried out are: ductile to brittle transition in ferritic steels, development of void swelling resistant steels, phase stability under irradiation in advanced austenitic steels etc. Apart from radiation damage studies on nuclear structural materials other areas of experiments in the material science beam line will include induced radioactivity studies, thin layer activation analysis of nano-coatings, production of special isotopes for use as sources in various experiments like PAS, PACS etc., study of mass, charge and angular momentum distribution of fission products in proton induced fission of actinides etc. Studies on basic damage mechanisms are of importance for better understanding of radiation effects in materials will also be carried out using this facility. For example, in the ordered intermetallics, the evolution of disorder and amorphization during irradiation is of fundamental interest. Another class of materials in which defect accumulation and consequent amorphization is of interest is ceramics used for nuclear waste disposal. The availability of high-energy beam will facilitate the study of the damage phenomena in these materials using a wide variety of bulk techniques such as XRD and positron lifetime.

For effective utilization of the proton beam, there will be two beamlines in the Materials science Cave, one for high dose experiments (where high currents for long duration will be used) and another for low dose experiments (where low currents for short duration will be used). The fig. (3) shows the two beamlines inside the cave. The beam will be delivered to either of the beamlines using the switching magnet. The high dose experiments will be carried out in Sub beamline1. Because of the high irradiation dose expected to be produced in the samples, the irradiation facility will be surrounded by a shielding wall (shown in the fig.) and the sample will be removed from the target holder remotely using a Master-Slave manipulator and loaded into a Pb-cask for storage until the activity decreases below the permissible limit of handling. The low dose experiments will be carried out in Sub beamline 2 and the activity will be kept below the permissible limits.

Proper utilization of the beam energy and beam current requires the careful development of irradiation facility including the target chamber, target cooling facility and post-irradiation target handling facilities. The high energy of the proton restricts the use of common materials (usually Fe based), near and around the target. Hence a reasonably large specialized infrastructure has to be designed to enable maximum utilization of the facility. The Materials Science beam line irradiation facility at the DAE Medical Cyclotron Section will include the following special features.

(1) A General purpose target chamber made of Aluminium to reduce the induced activity in the chamber. The chamber will include various facilities such as non-contact temperature monitors (IR Pyrometers), Radiation resistance camera to view the sample, a graphite coated beam dump to collect the beam behind thin samples etc. among others. (The schematic of the target chamber is shown in Fig.
(2) Provision for sample cooling by Helium gas. The arrangement will provide Helium gas in closed loop with heat exchanger facility.
(3) Provision for water cooling arrangement.
(4) Remote sample handling facility including Master Slave manipulators to remove sample from the target holder and transfer into a lead cask.
(5) Monorail arrangement for transferring the lead cask to outside the cave etc.


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