SUPERCONDUCTING RF (SRF) SYSTEMS Peter McIntosh (STFC)
Accelerator-driven Production of Medical Isotopes 8 th 9 th
December 2011 1 Slide 2 Outline Medical Isotope Generation The
Photo-Fission Process Accelerators and Isotope Production
Superconducting RF Technology SRF Accelerator Solutions for 99 Mo
Production Conclusions 2 Slide 3 Radioisotopes have become a vital
tool for scientific research and industry: applications in
medicine, biology, physics, chemistry, agriculture, national
security and environmental and materials science. The ability to
attach radionuclide to a pharmaceutical agent for transport to the
desired site is key to its effectiveness for medical applications.
Positron Emission Tomography (PET) scans, produce detailed maps of
active areas in the brain and other organs. Technetium-99m has
become the workhorse of diagnostic nuclear medicine: with over
50,000 procedures performed each day in the U.S. Medical Isotopes 3
Slide 4 99m Tc Production The half-life of an isotope must be long
enough to allow transport from production sites to end-use
locations without excessive loss, and short enough to minimize the
unwanted radiation dose to the patient after the procedure is
complete. The use of generators, involves a longer-lived parent
(2.75-day 99 Mo) that decays to a shorter-lived daughter (6-hour
99m Tc). Specialized reactors produce the 99 Mo as a fission
fragment for transport to end-use sites, where clinicians milk the
99m Tc daughter from the generator as needed. 4 Slide 5 99 Mo
Production (a) Neutron fission of 235 U (present-day reactor
technique). (b) Neutron-capture process on 98 Mo. (c) Photo-neutron
process on 100 Mo. (d) Photo-fission of 238 U. 5 Slide 6
Photo-Fission Process E-Linac Electron Photon Converter 238 U
Target Ion Source Mass Separator RIB Users Photo-fission of 238 U
was proposed by W. T. Diamond (Chalk River) in 1999 as an
alternative production method for RIB. Fission fragments Fission
fragments Neutron High energy photon 6 Slide 7 Isotope sources are
produced using either reactors or accelerators of varying sizes. 99
Mo is a fission fragment that is today typically produced using
Highly Enriched Uranium (HEU) reactors. Specific isotopes from
accelerator induced nuclear reactions, using appropriate beam
species and energies: Typically 10 100s MeV protons Major advances
in high-power particle accelerators and high- power target
technologies offer significant advantages for isotope production
via spallation-induced neutron irradiation. HEU Reactors and
Accelerators 7 Slide 8 SRF Accelerators Superconducting RF (SRF)
accelerator technology is capable of 20x beam power required, which
using rapid-switching techniques could distribute beam
simultaneously to many target stations. Electron beam accelerator
technologies show promise for radionuclide production, either via
photo-nuclear reactions with MW-class beams, or using Compton
backscatter of high-intensity laser beams with high- quality light
source beams. A high-power accelerator facility could provide a
reliable source of neutron produced isotopes such as 99 Mo, and
also have sufficient power and flexibility to supply a steady
stream of research isotopes. 8 Slide 9 Superconductivity Benefits
Both Normal-conducting RF (NRF) and SRF accelerating structures can
produce high gradients (10s of MeV/m), but only SRF technology can
sustain high duty operation. The power dissipated for CW operation
in a NRF structure is potentially enormous, but not so for SRF
cavities. RF power required to generate an accelerating voltage (V
acc ) is defined by: The ratio of shunt resistance to quality
factor (R/Q), which depends on cavity geometry, is not vastly
different between NRF and SRF cases; and so the cavity power (P c )
required is dominated by the bare quality factor Q , which is
typically 10 5 times larger for SRF. Overall, SRF reduces the wall
plug power compared to NRF, by a factor ~200, reducing power
consumption from MWs to kWs. 9 Slide 10 Neutron Amplifier Target
for Isotope Production in a SRF Based Accelerator Facility at ANL
The SRF linac uses energy recovery linac (ERL) technology, whereby
the electron beam is transmitted through the target and is
recollected and re-injected into the accelerating structure. The
recollected beam transfers beam power to the injected electron
beam, and reduces the amount of RF power required to accelerate the
electrons to their final energy. ~10 x less RF power compared to
non-ERL linac technology. The SRF linac is only ~ 2 meters long
making it compact in comparison to existing NC technology. The
energy recovery efficiency is >95%. The depleted beam power is
dumped into a low energy beam stop, which is physically separate
from the target. Courtesy J Nolan, ANL 10 Slide 11 Accelerator
Flexibility The beam energy, target thickness, and recovered power
can be optimized for maximum isotope yield. The target has a vacuum
loadlock, which can be removed from the target chamber and a new
target installed without breaking vacuum or stopping the linac
operation. The activated target requires robotic control, but this
is a well established technology. System has a number of advantages
over conventional linac technology: more compact, higher current
for increased yields, improved thermal management of waste beam
power, a continuous target feed, and multiple target capability.
The linac can also be configured for other isotope production, e.g.
67 Cu, which requires similar energies to 99 Mo. 11 Slide 12 ARIEL
E-Linac at TRIUMF Advanced Rare IsotopE Laboratory as part of the
ISAC facility at TRIUMF. New complementary electron linac (E-linac)
driver for photo-fission. New proton beamline. New target stations
and front end. Staged installation proposed. 12 Slide 13 ARIEL
E-Linac Parameters ParameterValue Bunch Charge16 pC Bunch
Repetition Rate0.650 GHz Frequency1.3 GHz Average Current10 mA
Energy50 MeV Beam Power0.5 MW Duty Factor100 % The requirement: 50
MeV 10 mA = 0.5 MW beam power Bunch PropertiesInjectedEjected
Normalised Emittance (m) -30 -100 Longitudinal Emittance (eV.ns)
-20 -30 Bunch Length (FW), inject (ps)-170-30 Energy Spread
(FW)
