Low Energy Electron Beam
Goal of This Presentation • Review a R&D case study of low energy electrons • Dosimetry issues associated with low energy electrons • Evaluation of dose measurements SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 3
Scenario The Ask: Dosimetry for absorbed dose measurements for a low energy electron beam irradiation of a thin product Dose map to evaluate single and double sided processing Process Optimization: Energy, Air Gap SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 4
Preliminary Evaluation Preliminary evaluation consisted of Monte Carlo modeling: a. Air gap b. Energy c. Dose depth profile for dosimetry assessments d. Dose delivery as a double sided process simulated as the summation of two single sided irradiations SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 5
Air Gap Models In low energy electron beam applications energy losses are heavily influenced by the air gap; energy losses in air Two energy models were constructed to evaluate the energy losses at several air gaps Initial Energy Air Gap 240 keV 10mm 15mm 20mm 25mm 300 keV 10mm 15mm 20mm 25mm SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 6
Air Gap Models Initial Energy Air Gap 240 keV 10mm 15mm 20mm 25mm 220.4 keV 219.2 keV 217.8 keV 215.8 kEv 300 keV 10mm 15mm 20mm 25mm 290.2 keV 289.1 keV 287.4 keV 286.3 keV SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 7
Air Gap Models Conclusions: a. As the air gap is increased a corresponding increase in the energy loss over the air gap occurs b. Energy losses were larger for lower initial energy primarily due to energy loss in window c. Air gap variation due to product conveyance was known to be ± 5mm ; a 15mm air gap was selected SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 8
Energy Dose depth profiles were modeled to provide insight: a. Expected penetration of the thin product b. Estimate dose gradients for dosimetry assessment c. Three energies were initially evaluated 220 keV 250 keV SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 275 keV Confidential | 9
Dose Depth Profiles Monte Carlo Simulation 15mm air gap in 1.12 g/cm 3 absorber 6E‐12 5E‐12 4E‐12 220 keV Relative Dose 3E‐12 250 keV 2E‐12 275 keV 1E‐12 0 0 50 100 150 200 250 300 350 SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, ‐1E‐12 0000 μ m Confidential | 10
Dose Depth Profiles Conclusions: a. Higher energies provided larger penetration b. Higher energies provided smaller dose gradients* *smaller dose gradients were a consideration for dosimetry SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 11
Dose Depth Profiles SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 12
Dosimetry The thinner the dosimeter the smaller the dose gradient Significant when determining the absorbed dose measurement with dosimetry, i.e. average dose vs. apparent dose Large dose gradients over the thickness of the dosimeter would cause differences between average dose and apparent dose SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 13
Dose Depth Profiles SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 14
Dosimetry Dose gradients over 18 um increments were evaluated using dose depth profiles SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 A low energy provided the most significant challenge with respect to dose gradients Confidential | 15
Dosimetry The 220 keV dose depth profile data was used to estimate the residuals of the actual dose depth profile and the estimate assuming constant gradient slope through the 18 um thickness of the B3 dosimeter SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 16
Dosimetry 220 keV 37 to 54 um 220 keV 0 to 18 um 1.15 1.08 1.07 1.06 1.14 1.05 1.04 1.03 total res 0.002 total res 7E‐07 1.13 1.02 0‐9 0.000365 0‐9 0.000719 1.01 10‐18 0.002554 10‐18 0.000757 1 0.99 1.12 0 5 10 15 20 0 5 10 15 20 220 keV 19 to 36 um 220 keV 55 to 72 um 1.13 1.15 1.12 1.14 1.11 1.14 1.1 total res 2E‐07 1.13 1.09 0‐9 0.00057 total res ‐1.9E‐06 10‐18 0.000713 0‐9 0.000759 1.13 1.08 10‐18 0.000719 SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 1.07 1.12 0 5 10 15 20 0 5 10 15 20 Confidential | 17
Dosimetry Dose Depth 220keV 1.400 e f g j k b c d h i a 1.300 1.200 1.100 1.000 0.900 0.800 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 segment sum res. 1‐9 10‐18 a 2.000E‐03 0.000365 0.002554 b 2.000E‐07 0.000570 0.000713 c 7.000E‐07 0.000719 0.000757 d ‐1.900E‐06 0.000759 0.000719 e 5.000E‐07 0.000720 ‐0.000719 f 8.000E‐07 0.000681 ‐0.000680 g 0.000E+00 0.000833 ‐0.000833 h 1.600E‐06 0.001256 ‐0.001255 SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, i ‐1.000E‐07 0.001388 ‐0.001388 0000 j 7.000E‐07 ‐0.000375 0.000375 k 2.000E‐07 ‐0.002309 0.002309 Confidential | 18
Dosimetry No significant difference: apparent dose vs. average dose 220 keV 55 to 72 um 1.145 1.14 1.135 1.13 1.125 1.12 0 5 10 15 20 total res ‐ 1.9E ‐ 06 Uniform vs. Gradient 220 keV 'd' 1.145 1.14 -0.000002 = 0.00017% 1.132 1.135 1.13 1.125 SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 1.12 0 5 10 15 20 Confidential | 19
Dosimetry Calibration irradiation of the B3 can be done either with low energy or high energy (in ‐ situ) If low, Alanine film would need to be corrected (apparent dose ≠ average dose) If high, Alanine film apparent dose = average dose B3 in either low or high, apparent dose = average dose SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 20
Dose Mapping Simulations Dose mapping simulations using Monte Carlo Simulate 2 ‐ sided irradiation with sum of 2 single ‐ sided models location 18 28 48 58 88 98 118 128 148 158 178 188 208 SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 218 238 0000 248 Confidential | 21
Dose Mapping Simulations Dose mapping simulations using Monte Carlo 1.60E ‐ 05 1.40E ‐ 05 1.20E ‐ 05 1.00E ‐ 05 1st pass 8.00E ‐ 06 2nd pass 6.00E ‐ 06 1 ‐ 2 pass 4.00E ‐ 06 2.00E ‐ 06 0.00E+00 0 50 100 150 200 250 300 SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 22
Dose Mapping Simulations Dose Map vs. Monte Carlo 240 keV Model Prediction Dose Map Data SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 23
Low Energy Electron Beam Conclusions: a. Low energy electron beam was viable for thin product processing b. At energies of 220 keV the difference of average dose and apparent dose are negligible in an 18 um thick dosimeter that is optically assayed c. Execution of dose mapping proves a challenge as physical placement of a dosimeter influences the absorbed dose measurement SUBGROUP NAME: REGION AND/OR PROJRCT | Confidential | Month 00, 0000 Confidential | 24
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