Electron Perturbation Correction Factors - LNHB

1 NACP-02 Perturbation Correction Factors for the NPL primary standard of absorbed dose to water in high energy Electron beamsNACPNACP--02 Perturbation Correction 02 Perturbation Correction Factors for the NPL primary Factors for the NPL primary standard of absorbed dose to water standard of absorbed dose to water in high energy Electron beamsin high energy Electron beamsParis 9 - 11, May 2007 Paris 9 Paris 9 --11, May 200711, May 2007E. Chin1, J. Seuntjens1, H. Palmans2, A. DuSautoy2, D. Shipley2, M. Bailey2, F. Verhaegen1 E.

2 ChinE. Chin11, J. Seuntjens, J. Seuntjens11, H. Palmans, H. Palmans22, A. , A. DuSautoyDuSautoy22, D. Shipley, D. Shipley22, M. Bailey, M. Bailey22, , F. VerhaegenF. Verhaegen1 1 111222 OutlineOutlineOutline1. Calibration procedure at NPL2. Model of ion chamber for MC simulations3. Validation of MC model with backscatter simulations and measurements4. Perturbation Correction Factors in water5. Perturbation Correction Factors in graphite6. Implications for the NPL Electron beam calibration1. Calibration procedure at NPL2.

3 Model of ion chamber for MC simulations3. Validation of MC model with backscatter simulations and measurements4. Perturbation Correction Factors in water5. Perturbation Correction Factors in graphite6. Implications for the NPL Electron beam calibrationNPL Calibration Procedure: high energy electronsNPL Calibration Procedure: high NPL Calibration Procedure: high energy electronsenergy electrons(1) Define reference depth in water(1) Define reference depth in ,50 =(2) Use range scaling to get depth in graphite(2) Use range scaling to get depth in graphite(3) Calibrate chamber against the calorimeter, in graphite, at the NPL(3) Calibrate chamber against the calorimeter, in graphite, at the NPLwgwgRRdd,50,50=grefggrefDMDN,,,=(McEw en et al 1998)(McEwen (McEwen et al et al 1998)1998)

4 Calorimeter for high energy electronsCalorimeter for high energy electronsNPL Calibration Procedure: high energy electronsNPL Calibration Procedure: high NPL Calibration Procedure: high energy electronsenergy electrons(4) Theoretical conversion of graphite to water(4) Theoretical conversion of graphite to waterairgairwgrefwrefgrefDwrefDssppNN,,, ,,,,,=(5) Compare user and reference chambers at dwin water, at NPL(5) Compare user and reference chambers at dwin water, at NPLwuserwrefwrefDwuserDMMNN,,,,,,=NPL Calibration Procedure: high energy electronsNPL Calibration Procedure: high NPL Calibration Procedure.

5 High energy electronsenergy electrons(McEwen et al 1998)(McEwen (McEwen et al et al 1998)1998)wallcavQppp=1=cavp1=wallpA plane parallel chamber with adequately large guard ring can eliminate the in-scattering effectsA plane parallel chamber with adequately A plane parallel chamber with adequately large guard ring can eliminate the inlarge guard ring can eliminate the in--scattering effectsscattering effectsScarce amount of data available at the time and large uncertaintiesScarce amount of data available at the time Scarce amount of data available at the time and large uncertaintiesand large uncertaintiesCurrent

6 Protocols: Electron Perturbation Correction factorsCurrent Protocols: Electron Current Protocols: Electron Perturbation Correction factorsperturbation Correction factorsFor well guarded plane parallel plate ion chambersFor well guarded plane parallel plate ion chambersMonte Carlo model of NACP ion chamberMonte Carlo model of NACP Monte Carlo model of NACP ion chamberion chamberNACP-02 plane parallel ion chamber (NPL report CIRM13)NACPNACP--02 plane parallel ion chamber (NPL report CIRM13)02 plane parallel ion chamber (NPL report CIRM13)

7 Monte Carlo model of NACP ion chamberMonte Carlo model of NACP Monte Carlo model of NACP ion chamberion chamberMonte Carlo model of NACP ion chamberMonte Carlo model of NACP Monte Carlo model of NACP ion chamberion chamberrexoliterexoliterexolitemylarmyla rmylargraphitegraphitegraphiteairairairM C NACP model for DOSRZnrc and CAVRZnrc (not to scale)MC NACP model for DOSRZnrc and CAVRZnrc (not to scale)MC NACP model for DOSRZnrc and CAVRZnrc (not to scale)Primary collimator (CONESTACK)Window (SLABS)Upper foil (SLABS)Lower foil (FLATFILT)Monitor Chamber (SLABS)Mirror (MIRROR)Shield (CONESTACK)Upper and lower jaws (JAWS)Reticle (SLABS)Applicator (APPLICAT)Primary Electron beamMonte Carlo model of linacsMonte Carlo model of linacsMonte Carlo model of linacsScattering foil(SLAB)Monitor ion chamber(CONS3R)Lead and Steel collimator(CIRCAPP)Primary Electron beamNPL Linac (SSD 2m)NPL Linac (SSD 2m)NPL Linac (SSD 2m)Varian Linac (SSD 1m)Varian Linac (SSD 1m)Varian Linac (SSD 1m)a)CL2300 energies 6, 9, 12, 15, 18 MeV (tuned within )b)

8 CL21A energy 4 MeV (buildup tuned within 3%, tail within 2%)c)NPL linac energies 4, 6, 8, 10, 12, 16, 19 MeV (R. Zakikhani)a)a)CL2300 energies 6, 9, 12, 15, 18 MeV (tuned within )CL2300 energies 6, 9, 12, 15, 18 MeV (tuned within )b)b)CL21A energy 4 MeV (buildup tuned within 3%, tail within 2%)CL21A energy 4 MeV (buildup tuned within 3%, tail within 2%)c)c)NPL linac energies 4, 6, 8, 10, 12, 16, 19 MeV (R. Zakikhani)NPL linac energies 4, 6, 8, 10, 12, 16, 19 MeV (R. Zakikhani)Linac Electron energiesLinac Electron energiesLinac Electron energies6 MeV PDD PDD Factors wrt air for NACP-02: Water Graphite Aluminum CopperPhantom material: PMMA (4-12 MeV) Solid water (15 & 18 MeV)Backscatter Factors wrt air Backscatter Factors wrt air for NACPfor NACP--02:02: WaterWater GraphiteGraphite AluminumAluminum CopperCopperPhantom material:Phantom material: PMMA (4 PMMA (4--12 MeV)12 MeV) Solid water (15 & Solid water (15 & 18 MeV)18 MeV)Validation of MC.

9 Backscatter experiments and simulationsValidation of MC: Backscatter Validation of MC: Backscatter experiments and simulationsexperiments and simulationsNACPP hantomBackscatterplatedmaxElectron BeamApplicatortexperimental setupexperimental setupexperimental setupBackscatter Experimental SetupBackscatter Experimental SetupBackscatter Experimental SetupNACPNACP--02 chamber is flush 02 chamber is flush with phantom surfacewith phantom surfaceBackscatter setup with aluminum plate covering NACPB ackscatter setup with aluminum plate covering NACP--0202 Backscatter Experimental SetupBackscatter Experimental

10 SetupBackscatter Experimental SetupBackscatter setup with water phantom on top of NACPB ackscatter setup with water phantom on top of NACP--0202 Backscatter Experimental SetupBackscatter Experimental SetupBackscatter Experimental Setup1. Varied graphite density ( g/cm3)2. All options turned on (bound compton scattering, PE angular sampling, Rayleigh scattering, atomic relaxation)3. Different beam sources (pt src vs. parallel src)4. Varied window graphite density ( Varied graphite density ( g/cm33)) options turned on (bound All options turned on (bound compton scattering, PE angular compton scattering, PE angular sampling, Rayleigh scattering, sampling, Rayleigh scattering, atomic relaxation)atomic relaxation) beam sources (pt src Different beam sources (pt src vs.))