Colloque café - scientifique

Animé par Dominique Thers

jeudi 20 juin 2019 à 13:30


Brief History of Hadron Accelerators and the Next Generation of Hadron Therapy

Ken Takayama

High Energy Accelerator Research Organization (KEK), Accelerator Laboratory

It took about 160 years for particle accelerators to evolve from Cathode tube to LHC via the invention of Electrostatic Accelerator, Betatron, Cyclotron, and Synchrotron. It is well known that their acceleration principles are governed by Gauss law, Gauss law/Faraday law, and a full-set of Maxwell equation, respectively. Accelerator performing on a simple operating principle is generic beyond all doubt. Electrostatic accelerator such as Cockcroft-Walton or Van de Graaff is almighty and never chooses ion species or their charge-state. Their invention and development had been quite early and so quick. In the next place, induction accelerator such as Betatron or Linear Induction Accelerator (Linear Betatron) is generic and should have evolved much faster than Cyclotron or Synchrotron. However, it was not true in history. Technology for microwave or RF acceleration dramatically advanced through and just after World War II, where about 150 B US$ in currency value had been invested to develop Radar weapons and to deploy them in UA/Great Britain (major), Germany, and Japan. If this cost is regarded as R&D cost for RF and microwave accelerators having made their appearance after WW-II, we will be surprised at their quick evolution.

In 1990’s a low-loss magnetic core material such as nanocrystalline alloy and fast high-power solid-state switching device such as Si-MOSFET have been developed to become commercially available. Those devices allow to realize an induction synchrotron, where a 1-to-1 pulse transformer called the induction cell driven by the switching power supply is employed as an acceleration device instead of a usual RF cavity and a large freedom of beam handling in the moving direction is promised. At KEK the slow cycling/fast cycling induction synchrotron were demonstrated in 2006 [1] and 2013 [2].     

Recently a novel concept of hadron therapy [3] allowing tracking irradiation on a moving and deformed tumor target has been proposed under the international collaboration, based on the fast cycling induction synchrotron. It is named Energy Sweep Compact Rapid Cycling Therapy (ESCORT). Its concept is characterized as follows;

a) Its beam driver is a fast cycling induction synchrotron (10-20 Hz), where a fully stripped heavy ion beam is delivered from the laser ablation ion source, the injected ion beam is captured in the barrier bucket and accelerated with the induction step voltage, a beam spill is continuously extracted by the energy sweep extraction method.

b) A combination of beam profile monitors and the full-body Liq. Xe 3g camera being developed by D.Thers et al. is used to obtain the dose profile/position in depth by detecting prompt gs. The accompanied X-ray camera also catches the position/profile of the tumor target. Signals are quickly processed in computers and the irradiation errors are found at 20 Hz.

The ESCORT in India is seriously under consideration now. At the seminar, History of hadron accelerators and the latest topic in their medical applications will be discussed.

[1] K.Takayama et al., Experimental Demonstration of the Induction Synchrotron”, Phys. Rev. Lett. 98, 054801 (2007).

[2] K.Takayama et al., Induction acceleration of heavy ions in the KEK digital accelerator: Demonstration of a fast-cycling induction synchrotron”, Phys. Rev. ST-AB 17, 010101 (2014).

[3] Leo Kwee Wah, K.Takayama et al., “Compact hadron driver for cancer therapies using continuous energy sweep scanning”, Phys. Rev. AB 19, 042802 (2016).


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Beta decay of neutron-rich nuclei with isomeric states: TAGS measurements for reactor calculations

Victor Guadilla-Gomez

Subatech (équipe SEN)

The study of the beta decay of neutron rich niobium isotopes is a rather complicated problem due to the existence, in many cases, of isomeric states close in energy to the ground states. The disentanglement of the beta decays of these levels requires a good separation technique and a well-controlled detection set-up. Many of these niobium isotopes are fission products contributing significantly to the reactor antineutrino spectrum and to the reactor decay heat. Using summation calculations, some of them have been identified as high priority cases to be measured. The reason is that their beta-intensity distributions, ingredients of these summation calculations, are missing or seem affected by a systematic error, the so-called Pandemonium effect, in the evaluated databases. The improvement of these decay data will allow a better understanding of the reactor antineutrino spectrum with the summation method, as well as a more accurate prediction of the reactor decay heat. Total Absorption Gamma-ray Spectroscopy (TAGS) has proven to be a suitable technique to measure beta-intensity distributions without Pandemonium.

A campaign of measurements was carried out in Jyvaskyla with beams provided by the mass separator of the IGISOL IV facility. A precision trap-assisted separation was used, with the JYFLTRAP double Penning trap system. The beta decay of the nuclei extracted from the trap was measured with the Decay Total Absorption gamma-ray Spectrometer (DTAS) in coincidence with a plastic beta detector. In this talk we will present the results for 100Nb and 102Nb, each with an isomeric state 313 keV and 94 keV, respectively. The experimental strategies followed to disentangle the decays of each ground state and isomeric state will be presented, as well as the impact of these results on decay heat and antineutrino spectrum summation calculations.

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