The use of nuclear reactions that do not involve a change in element can be advantageous for radionuclide production because enriched targets are rarely required and the yield of the nuclear reactions is usually adequate. However there is a disadvantage to these reactions for medical imaging because the product radioactivity is of low specific activity. In this report we discuss the application of radiation chemistry and nucleogenic recoil chemistry to two reactions, 16O(3He,4He)15O and 12C(3He,4He)11C, to improve specific activity of the radioactive oxygen and carbon recovered from the target. For both reactions, specific activities were improved, with minimal decrease in recovered radioactivity. For the 16O→15O reaction in water, results demonstrated that the production of [15O]-O2 followed a different reaction mechanism from that for unlabeled O2. The unlabeled yield was quantitatively predicted from classical radiation chemistry G-values for water. The radiochemical product distribution was a consequence of the combined effects of recoil chemistry and radiation chemistry. Studies with thin graphite foils demonstrated that we could irradiate sufficiently thin C foils so that a useful fraction of the recoil nucleogenic 11C atoms escaped the irradiated carbon and reacted with circulating gas to capture an appreciable fraction of the product 11C with an improvement in specific activity. Although we have shown the feasibility of producing GBq quantities of radiopharmaceuticals by recoil techniques, the advantages of even higher specific activity using enriched targets outweigh the cost of using enriched targets.

In-target chemistry during the production of 15 O and 11 C using 3 He reactions

Almost from the beginning of the discovery of radioactivity researchers began looking for ways to create new elements and/or isotopes of those elements. Initially those attempts centred on making use of the alpha particles emitted from natural radioactivity as with Rutherford's demonstration of the 14N(a,p)17O reaction [1]. Soon this escalated to the use of electrostatic devices to impart high energy to protons, deuterons, and alpha particles.

Accelerator Production of Medical Radionuclides: A Review

For several decades, axially symmetric channels with RF focusing by means of nonsynchronous spatial harmonics of the accelerating field are offered as an attractive alternative to proven and reliable RFQ linacs. In a number of works an effectiveness of channels with axially symmetric RF focusing by means of the nonsynchronous harmonics of the field was demonstrated in the proton energy range up to 2 MeV. An effectiveness of discussed channels for protons at energies up to 7 MeV is considered in this paper. Numerical simulation results of proton self-consistent dynamics in a channel with axisymmetric RF focusing are presented and discussed in this article.

https://iopscience.iop.org/article/10.1088/1742-6596/747/1/012071/pdf

Results of using the axisymmetric RF focusing by means of field spatial harmonics at 7 MeV proton linac

During a few decades axisymmetric RF structures with a focusing by means of nonsynchronous spatial harmonics of electromagnetic field are offered instead of proven RFQ. An effectiveness of these structures in the energy range up to 2 MeV was shown in a number of papers. An effectiveness of these structures in the energy range up to 7 MeV is considered in this paper. Results of an analytical investigation and a numerical simulation of selfconsistent proton dynamics are presented and discussed.

Results of the Use of Axisymmetric RF Focusing in Proton Linacs at Energies up to 7 MeV

An RFQ linac has been built that accelerates 3He to 105 MeV for production of C, N, O, F isotopes for PET The accelerator produces 70 μs pulses, at 360 Hz, a 25% duty cycle, with a peak current of ∼6 mAe The RFQ delivers ∼100 μAe A recirculating water target has been evaluated for production of 18F and low specific activity 15O Recoil chemistry within the target has been evaluated to improve 15O specific activity Gas targets have also been tested for production of 15O 13N is made from carbon Several target materials have been evaluated for producing 11C, including C, B and Be The challenges of targetry for this high current, low energy machine led us to evaluate large, high aspect ratio windows and grid supports The 3He RFQ is a useful research machine for testing targets for pulsed, high power density, low LET beams

Jerry T. Bida

Papers

Production of PET radionuclides using a 10.5 MeV {sup 3}He RFQ accelerator