CERN scintillating microfluidics channels

1. CERN scintillating microfluidics channels Hadrotherapy Liquid scintillators Radiation damage Microfluidic technology Davy Brouzet 3rd March 2014

2. CERN scintillating microfluidics channels I-Radiation and damage II-Temperature effect III-Fluidic consideration and pumping IV-Chemical compatibilities V-Cooling VI-Gantt diagram and objectives

3. Radioactivity Theory Equivalent dose: Depends on the radiation type (for biological effect) Absorbed dose: J/kg • Radio or hadrotherapy daily doses about 2Gy (2min duration1) • ATLAS: 100Gy/year dose • When passing through matter, particles lose a certain amount in energy via ionization and molecule excitation to higher energy states. • Cherenkov effect: Photon emission when particle velocity higher than light velocity in a specific medium  Widely used for high energy particle detectors but better to avoid in our case •  278 MeV (EJ-309) and 317MeV (EJ-305) Proton hadrotherapy energies between 30 and 250MeV. How about CERN experiments? 1 proton-cancer-treatment.com

4. Radiation damage in scintillators • Charged particles energy losses (at the ten MeV scale): ≈5% of absorbed energy 2 ≈ 28% of absorbed energy π-electrons Fluorescence Excitation ≈67% of absorbed energy Otherelectrons Thermal dissipation π-electrons Slow scintillation (damage?) • 2 consequences: Diminution of local scintillationand of attenuation length  Light output diminution • Strongly depends on type: Solids  Damaged by low irradiation (50% decrease of light output for anthracene at 10kGy). Sometimes effects at 100-1000Gy. Liquids  60% decrease in scintillation efficiency for BC-505 at 50kGy irradiation. • Energy transfer (and distribution) depends on the nature of the particle (mass, charge and energy)  α-particle>protons>neutrons • No significanteffect of dose rate on radiation damage for the majority of solid and plastic scintillators • Radiation damage of SU-8? Silicon? Ionization Otherelectrons Damage (quenching) 2 See Annex for details

5. Temperature effect Detection efficiency : Fraction of ionizing particle that produce enough scintillation to be detected • In liquids scintillators, an increase in temperature will induce an higher viscosity and higher light output, especially at high temperatures. Maximum 6% gain for toluene solutions between 25°C and 5°C. • Photomultipliers efficiency can also be increased by a lower temperature! • No reasons that radiation damage should depend on temperature •  Important to keep it below room temperature. Tests should be done on the specific scintillator used to quantify the radiation damage and the temperature effect. Absorption efficiency : Fraction of energy that is absorbed by the liquid Scintillation efficiency : Ratio between produced energy as photons and ionizing particle energy

6. Irradiation limit assumed for liquid scintillators: 104 Gy Flow rate estimation • In ATLAS, detectors were irradiated at a maximum 100Gy/year dose  100 years without degradation. No pumping needed? • For hadrotherapy (assuming a 2kg tumor [Reference needed]): How much is really absorbed by the liquid?  Depends on particle and energy • Protons energy loss in toluene: 30MeV  17 MeV/cm  1% losses 250MeV  3.5 MeV/cm  0.03% (*With 200μm-depthchannels  ) • 200 Gy/min  0.12 mL/h 2  Pumpingrecommended * 2 See Annex for details

7. Microfluidic considerations • Pressure difference: • Straight rectangular channel: 3 • Mean fluid velocity: • Flow rate can be multiplied by 2 with 2 liquid entries • If the wanted flow rate is higher (miscalculation or some advantage 4) a geometry change can be considered: Parallel channels would reduce the needed pressure difference by where N is the number of channels. • However, this would require a flow distributor 31.11cP viscosity taken for 1,2,4 trimethylbenzene (different values depending on source) 4 See Annex

8. Pumping technologies • Positive displacement pumps are adapted to low flow applications • Micropumps Adapted to microfluidic application (not so high pressure difference for really small flow rates)

9. Chemical compatibilities • Principal liquid scintillators made of xylene (EJ-301), pseudocumene (EJ-305) and ??? (EJ-309) • Chemical compatibilities: Chemical compatibilities.pdf • EJ-301 quite difficult to find adapted materials, especially for O-rings  FKM or FFKM elastomers. Not compatible with PEXIGLAS. • EJ-305 is less toxic and can for example also be used with Viton. • EJ-309 is made of a particular alkyl-benzene. Which one? However, the fact that it is sold with a ‘low chemical toxicity’’ characteristic indicates that it would be more adapted to a pumping use. Optical properties lower than for the EJ-305 (attenuation length divided by 3, higher refractive index, lower light output) • In all the cases, a sealless pump would avoid leakage and thus toxic damages and problems in void conditions.

10. Cooling • How much energy has to be extracted from liquid: • From radiation thermal excitation (liquid + SU-8 + other materials) • From difference with room temperature (Advection: Not needed if no flow) • Convection process with exterior? Exterior temperature? Void? • From radiation process? • Maximum absorbed dose ~  Taking , and  Doesn’t take into account the heat from the other materials and from the electronic! • Total power to be removed ~ 1W/cm^2 ? 5  Micro-channels cooling has high efficiency and would be perfectly adapted to the microfluidic detectors. Design? 5Micro-channel cooling for HEP particle detectors and electronics

11. Planning and objectives • See Gantt diagram for planning:Organisation\Gantt Diagram.pdf • Objectives: • Finish bibliography review (oxygen quenching, cooling systems, chemical compatibility of EJ-309…) • Deeper investigation on heat exchanges • Viability of the system both in CERN and hadrotherapy application. • Start design of system (pump choice, mechanical integration, define final flow rate, determine if cooling system is needed and if yes which one) • (Numerical simulation?) • Fabrication of prototype • Tests on radiation damage (and temperature effect) on selected scintillator

12. Thank you for your attention

13. References

14. Annex Flow rate calculation: Fluidicconsiderations: • Velocity profile in the channel: • Boundary layer  Slower flow velocity Liquid longer exposure to radiation. A numerical simulation wouldbenecessary to have some quantitative results(an analytic solution onlyexists for a straight channel) • A quicker flow rate wouldreduce the difference in opticalpropertiesbetween the input and the output

15. Annex Energy losses distribution: • Birks (1961) has proposedthat the fracton of energydissipated in the π-electron excitation was: whereis the fraction of π-electrons in the molecule. As usuallyequals 0.15 (close to ), • Thosewereresults for 1MeV electrons. Horrocks (1974) presentedresults relation between pulse height for differentparticles. Protons lead to 50% of the pulse heigthobtainedwithelectrons. Therefore, wecan assume that for protons: Results at higherenergiesare necessary to confirmthisresult. • The energydissipated in otherelectron excitation is: • And the energydissipated in the ionizationprocessisthen:

16. Questions • Energy particle at CERN? Confirm the irradiation found in the CERN report and in Alessandro’s Thesis. • How the total radiation is computed from the light intensity? Is there a calibration to be done? Probably best if the optical properties are the same in all the channels. • Workshop budget? Name of expert for final presentation in September. • Can we organize some meetings every month with Mr. Schiffmann?