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Muon Beam Intensity Monitor Using X-Ray Fluorescence

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Muon Beam Intensity Monitor Using X-Ray Fluorescence InstitutETHZ-IPP-2008-13 fur¨ Elektronik August 2008 Prof. G. Tr¨oster Wintersemester 2005/2006 Diplomarbeit DIPLOMA THESIS Verkehrsmessung mit MuonBildverarbeitung beam intensity monitor using X-ray fluorescence Christian Scheller [email protected] supervised by Prof. Urs Langenegger ETH Zürich Institute for Particle Physics IPP P-R. Kettle Paul Scherrer Institute PSI Laboratory for Particle Physics LTP Verfasser: Betreuer: Remo Huber Bernhard M¨ader, SCS AG Reto B¨attig, SCS AG ETH Zürich, Switzerland Clemens Lombriser, ETH Abstract This report presents a new method of measuring the particle rate of a muon beam using X-ray fluo- rescence. X-ray fluorescence is a common tool for non-destructive trace element analysis. Instead of irradiating a target with radioactive sources in order to induce X-rays, thin foils of Copper, Tantalum and other materials are placed in the muon beam. The X-rays are then measured using a silicon detector and the rate is compared with theoretical predictions. Finally the foil would be mounted permanently in the beam line and by measuring the X-ray rate the muon rate can be continuously monitored. The advantage of this method compared to others is that the muon beam is only affected at a minimum level in terms of energy loss and beam divergence induced by multiple scattering. Measurements using a Cockroft-Walton proton accelerator (at several energies reaching from 250 keV−1 MeV at ≈ 6.25·1012 Hz) as well as measurements using the muon beam (at a muon momentum of 27.75 ± 0.26 MeV/c at 7 + ≈ 3 · 10 Hz) are presented. In case of the proton beam a contamination of ≈ 25% H2 Ions has to be taken into account, whereas in the case of the muon beam the influence of decay positrons, originat- ing from muons stopped in thick targets, must be considered. The method is shown to be viable at the required level of precision (≈ 1%) with modifications to the detector system. Hence with further tests the system can be implemented into one of the world’s most intense surface muon beams as an intensity monitor for the MEG experiment. Contents 1 Introduction 8 1.1 The standard model of particle physics . 8 1.2 Motivation and overview of the MEG experiment . 9 1.3 Diploma thesis in the context of the MEG experiment . 11 2 Theory of X-ray emission 13 3 Comparison of different detectors 16 3.1 XR-123CR Si-detector . 16 3.1.1 Element analysis of a 5SFr coin . 17 3.2 XR-100CR Si-detector . 18 3.2.1 Rate measurement with the XR-100CR detector . 19 3.3 NaI(Tl) crystal detector . 23 3.4 Avalanche Photo Diode and Surface Barrier Detector . 27 4 Calculation of the X-ray emission rate 30 4.1 Ionization and emission cross-section results using ISICS06 . 31 4.2 Energy loss calculations with SRIM 2008 . 35 4.3 Rate calculation including attenuation in the target . 36 4.4 Calculation of the solid angle . 39 4.5 Error calculation . 42 5 Measurements with a proton beam 44 5.1 Cockcroft-Walton proton accelerator . 44 5.2 X-ray rate calculation / measurement . 46 5.3 Rate comparison to predictions . 51 1 6 Measurements with a muon beam 55 6.1 Pion production . 55 6.2 Pion-decay / Muon production . 56 6.2.1 "Surface" / "Sub-surface" muons . 56 6.2.2 "Cloud" Muons . 57 6.3 MEG muon beam line . 57 6.4 Muon induced X-ray rate measurements . 59 6.5 Consideration of the momentum window . 64 6.6 Rate prediction for the large Copper foil . 64 6.7 Rate prediction including positrons . 66 6.8 Comments on the positron induced X-ray rate . 68 6.9 Summary of the muon measurements . 68 7 Conclusion 69 Appendix 81 2 List of Figures 2.1 Schematic drawing of the X-ray emission process . 13 2.2 X-ray emission, Auger electron, Coster-Kronig transition . 14 2.3 Labeling of K-, L- and M-shell X-ray transitions . 14 2.4 Fluorescence yield for K- and L-shell . 15 3.1 Experimental setup for the Copper X-ray measurement . 16 3.2 Element analysis of a 5SFr coin . 17 3.3 XR-100CR Si-detector and PX2CR power supply/amplifier . 18 3.4 Diagram of the readout scheme for the XR-100CR detector . 18 3.5 Copper spectrum with 55F e calibration . 19 3.6 Energy resolution versus X-ray energy of the XR-100CR Si-detector . 19 3.7 XR-100CR trigger check . 20 3.8 XR-100CR dead time . 21 3.9 Comparison of rate measurements: MCA / ICR connected to scaler . 22 3.10 Picture of the NaI(Tl) detector and pre-amplifier . 23 3.11 Schematic drawing of the setup for the NaI(Tl) detector . 23 3.12 241Am spectrum with the NaI(Tl) detector . 24 3.13 P b spectrum with NaI(Tl) detector . 25 3.14 Energy resolution versus X-ray energy of the NaI(Tl) crystal detector. 26 3.15 Comparison of NaI(Tl) signal with and without TFA . 27 3.16 241Am and 109Cd spectrum with APD . 27 3.17 Disturbing signal for measurements with the APD . 28 3.18 109Cd spectrum with the SBD . 29 4.1 Ionization and emission cross-section for protons and muons as a function of the atomic number . 31 4.2 X-ray emission cross-section versus projectile energy . 32 3 4.3 Proton and muon emission and ionization cross-section for Copper versus beta ...................................... 33 4.4 Comparison of ISICS06 calculations to experimental data . 33 4.5 Comparison of ISICS06 calculations to measurements for several elements 34 4.6 Energy loss in Copper calculated with SRIM . 35 4.7 Proton induced X-ray rate . 37 4.8 Muon induced X-ray rate . 38 4.9 Solid angle MC . 40 4.10 Proton beam spot . 41 4.11 Quartz crystal for proton beam spot measurements . 41 5.1 Picture of the C-W proton accelerator . 44 5.2 C-W accelerator column and ion source . 45 5.3 Experimental setup for the C-W measurements . 46 5.4 Proton induced Cu and Ta X-ray spectrum with XR-100CR . 47 5.5 Combined Cu and 55F e spectrum with NaI(Tl) . 47 5.6 Copper spectrum with NaI(Tl) . 48 5.7 Copper spectrum measured with C-W . 49 5.8 Comparison of proton induced X-ray measurements with predictions . 51 5.9 Radiation damage in a Copper target . 52 5.10 Radiation damage simulation with SRIM 2008 . 53 5.11 Measured X-ray rate as a function of the exposure time . 53 6.1 MEG beam momentum spectrum . 56 6.2 Secondary beam lines at PSI and MEG beamline . 57 6.3 Meg muon beam line . 58 6.4 Separation of positrons and muons . 59 6.5 Experimental setup for the muon beam . 60 6.6 Muon beam spot . 60 6.7 Muon induced Ag spectrum . 61 6.8 Comparison of proton and muon induced X-ray spectra . 62 6.9 Comparison of muon and positron induced X-ray spectra . 62 6.10 Rate calculation for the large Copper foil . 65 6.11 Muon measurement results . 67 4 6.12 Spin polarized muon decay . 68 1 Efficiency plot for the different X-ray detectors . 72 2 K- and L- emission line lookup chart . 73 3 Relative abundance of K- and L-shell X-rays . 74 4 Schematic drawing of the C-W X-ray measurement setup . 77 5 Graphical comparison of C-W measurements with predictions . 78 6 Overview of muon induced X-ray measurements using thin foils . 81 5 List of Tables 1.1 Electromagnetic, weak and strong interaction and their respective gauge bosons..................................... 8 1.2 Lepton multiplets . 8 1.3 Lepton numbers for the Michel decay . 10 1.4 Lepton number violating muon decay . 10 1.5 Muon decay channels and probabilities . 11 3.1 Comparison of rate measurements: MCA / ICR and scaler . 22 3.2 Tabulated X-ray energies for the lead spectrum . 25 4.1 Comparison of SRIM 2008 calculations with experimental data . 36 4.2 Comparison of proton and muon induced X-ray production rate . 38 5.1 55F e X-ray lines and emission probabilities . 48 + 5.2 X-ray rate prediction for protons including a H2 contamination . 54 6.1 Delta resonance production . 55 6.2 Decay channels for the delta resonances . 56 6.3 Characteristic properties of the πE5 beam line . 58 6.4 Muon induced X-rays, comparison with predictions . 63 6.5 Labeling of the divisions on the large Copper foil . 65 6.6 X-ray rate prediction for muons including positrons . 67 1 Detector properties (active layer and entrance window) . 72 2 Detector efficiency table . 72 3 Relative abundance of K-shell X-rays . 74 4 Relative abundance of L-shell X-rays . 74 5 Comparison ISICS06 with exp.data from J.Phys.B, Vol.25, Nr.7 . 75 6 Comparison ISICS06 with exp.data from J.Phys.B, Vol.9, Nr.3 . 75 6 7 Comparison ISICS06 with exp.data from J.Phys.B, Vol.14, p.3153 . 76 8 Comparison ISICS06 with exp.data from NIMB, Vol.249, pp.73-76 . 77 9 C-W measurement results . 79 10 Comparison of muon induced X-ray measurements with predictions . 80 11 Measured X-ray energies with muon beam . 81 7 Chapter 1 Introduction 1.1 The standard model of particle physics The standard model of particle physics (SM) includes the combined electroweak interaction, which is a combination of the electromagnetic and weak forces at high energies as well as quantum chromodynamics.
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