Study of radioactive neutral isotopes propagation at ISOLDE: a Monte - PowerPoint PPT Presentation

“Study of radioactive neutral isotopes propagation at ISOLDE: a Monte Carlo and a spectroscopic analysis” Maddalena Maietta Universita` degli Studi di Napoli Federico II TE Vacuum, Surface & Coating, IVM Radioprotection DGS/RP 7 th November 2014 TE/VSC and DGS/RP

Outline of this talk  Introduction: Description of ISOLDE facility Main scopes of the project  Numerical Methods: Simulation theory Practical development Results  Experimental Analysis: Two experiments Description of experimental set up Results  Next steps  Conclusion TE/VSC and DGS/RP

Introduction: ISOLDE BOOSTER ISOLDE LINAC 2 TE/VSC and DGS/RP 3

Introduction: ISOLDE 1.4 GeV Intensity: 3.5 ∗ 10 13 protons/1.2s Energy of products: 60 keV TE/VSC and DGS/RP 4

My project Analysis of the progression of neutral radioactive gas species along the ISOLDE beam line: HRS32 • Monte Carlo simulation • Experimental Analysis HRS31 Tape station HRS25 HRS23 HRS24 HRS22 • Construction of a general tool for RIB vacuum; • Define a zone separation, according to level of contamination TE/VSC and DGS/RP 5

Why contamination study is so important? Isolde vacuum system: The Experimental Hall The separators zone The Front Ends zone RFQ • Venting to atmosphere via Filters and Monitoring TE/VSC and DGS/RP 6

Which species are targeted by the study? Protons Target with high dose rates : Neutrons  U (i.e. UCx) and Th ( α emitters); IONS :  Pb; Transported by the beam optics  Ta. NEUTRALS : Diffusing according to Maxwell- Boltzmann statistics and direction First transfer function (“filter”): distribution Target choice TE/VSC and DGS/RP 7

Which species are targeted by the study? For neutral contamination study Isolde Users 1) Choice of target temperature; Volatility; 2a) Choice of transfer line temperature 1 - Ionization Efficiency (~90%). 2b) Conductance of transfer line; 3) Ionization Efficiency (~10%). Noble gases (few volatile metals e.g. Zn, Cd, Hg ?) Ion species targeted Quartz tube Transfer tube GAS ION TARGET TRANSFE EXTRACTION SOURCE INLET OVEN R LINE ANALYSIS 1 2 3 Tantalum tube with the target material TE/VSC and DGS/RP 8

Numerical Methods : Monte Carlo simulation Pills of Physics of molecules in vacuum : two important equations… Maxwell Boltzmann 1 3/2 2 𝑛𝑤 2 𝑒𝑂/𝑒𝑤 𝑛 = 4π𝑤 2 exp 𝑂 2𝜌𝑙 𝐶 𝑈 𝑙 𝐶 𝑈 8𝑙 𝐶 𝑈 8𝑆𝑈 < 𝑤 > = 𝜌𝑛 = 𝜌𝑛 Lambert’s cosine law d ω 𝑄 𝑒ω = 𝑒ω n 𝜌 𝑑𝑝𝑡𝜄 θ TE/VSC and DGS/RP 9

Numerical Methods : Monte Carlo simulation Pills of Physics of molecules in vacuum : some hypothesis… 𝑸𝑾 = 𝑶𝒍 𝑪 𝑼 Ideal Gas Molecular Flow The molecules in the chamber move independently of each other. P·d < 10 -2 mbar · cm Pumping speed vs sticking factor 𝒘𝒒𝒕 = 𝒈𝒃𝒅𝒇𝒖 𝒃𝒔𝒇𝒃 ∗ 𝒃𝒘𝒇𝒔𝒃𝒉𝒇 𝒏𝒑𝒎𝒇𝒅𝒗𝒎𝒇 𝒕𝒒𝒇𝒇𝒆 ∗ 𝒕𝒖𝒋𝒅𝒍𝒋𝒐𝒉 𝒈𝒃𝒅𝒖𝒑𝒔 𝟓 TE/VSC and DGS/RP 10

Numerical Methods : Monte Carlo simulation Calculation of Pressure Profiles and conductances Analytical Methods Numerical Methods • • No universal formulas No simplification is needed • Only simple geometry MOLFLOW + a Test Particle Monte-Carlo code developed at CERN allows import of stl files From steady state to time-dependent simulation TE/VSC and DGS/RP 11

Numerical Methods : Monte Carlo simulation From official Drawings.. ..to 3D CAD (Inventor…)… ..and STL file for Molflow Simulation Chamber walls are described by planar polygons ( facets ) TE/VSC and DGS/RP 12

Numerical Methods : Molflow+ Desorption value Pumping speed or Sticking factor Time depending pressure profile TE/VSC and DGS/RP 13

Numerical Methods : Monte Carlo simulation -11 x 10 5 Fit He 4.5 Simulated values He 4 3.5 Pressure [mbar] 3 2.5 2 1.5 1 0.5 0 0 1 2 3 4 5 Time [s] TE/VSC and DGS/RP 14

Numerical Methods : Monte Carlo simulation -12 -11 x 10 x 10 3 Kr He Xe Rn Ne 2.5 Ar Kr 2 Xe Pressure [mbar] Rn 3 1.5 Pressure [mbar] 1 2 0.5 0 0 1 2 3 4 5 6 7 8 Time [s] 1 0 0 1 2 3 4 5 6 7 8 Time [s] TE/VSC and DGS/RP 15

Numerical Methods : Monte Carlo simulation 0.30 Equation y =(x)^A Adj. R-Square 0.99719 Value Standard Error T.P. (%) A -0.94306 0.00978 0.25 Transmission Probability [%] 1 𝜏 𝑈.𝑄. = 𝑜 1 − 𝑈. 𝑄. (*) 0.20 *Y.Suetsugu, Application of the Monte Carlo method to pressure calculation 0.15 0.10 0.05 0.00 -0.05 0 50 100 150 200 250 Molecular mass [g/mol] TE/VSC and DGS/RP 16

Numerical Methods : Monte Carlo simulation 3.5 3.0 2.5 Time of flight [s] Equation y =B+(x)^A Adj. R-Square 0.98943 Value Standard Error tof (s) A 0.23961 0.00576 2.0 tof (s) B -0.61299 0.07159 𝜏 𝑢𝑝𝑔. =0.01s 1.5 1.0 0.5 0 50 100 150 200 250 Molecular mass [g/mol] TE/VSC and DGS/RP 17

Experimental Analysis Experiment 1 On-line Sampling : • Realized along the primary pumping system, with active carbon and cellulose filters installed downstream of the turbomolecular pumps; • Spectroscopy Analysis. Filter position TE/VSC and DGS/RP 18

Experimental Analysis Filters positions HRS filters Date of installation: 17 th June 2014 HRS32 Date of removal: 13 th September 2014 Number of target change in this period: 5 HRS31 Type of targets: ZrO, UC 2 -C HRS25 HRS23 HRS24 HRS22 TE/VSC and DGS/RP 19

Experimental Analysis Filters positions in HRS and RFQ HRS 23 HRS 31 HRS24 HRS 32 HRS 42 HRS 43 TE/VSC and DGS/RP 20

Experimental Analysis HPGe detector:  Low relative efficiency;  High energy resolution;  Low work temperature (~77 K).  Resolution (FWHM) of 1.79 keV to 1.33 MeV; and of 0.82 keV to 122 keV  Peak/Compton ratio of 65:1. Analyzed samples : TE/VSC and DGS/RP 21

Some spectroscopy results 1000000 Po-206 Bi-206 100000 Bi-205 Pt-188 Os-185 10000 Log Activity (Bq\unit) Ba-140 I-125 1000 Te- 121 100 10 1 HRS 23 HRS 24 HRS 25 HRS 31 HRS 32 HRS 42 HRS 43 Filter Position Separators zone RFQ TE/VSC and DGS/RP 22

Some spectroscopy results Before He injection After He injection Activités Activités Activités Ech No. Ech No. Ech No. Isotopes (Bq /unit) Incert. Isotopes (Bq /unit) Incert. Isotopes (Bq /unit) Incert. Se-75 3.6E+01 33% Te-121 2.1E+01 20% Te-121 3.1E+00 15% Sb-120 4.4E+01 20% Te-123 1.6E+00 57% I-125 6.9E+00 92% Te-121 3.6E+02 20% I-125 3.3E+01 124% Ba-140 7.8E+00 9% Te-121m 4.4E+01 61% I-131 1.4E+00 171% Ce-141 5.0E-01 29% Te-123 8.9E+01 39% Ba-140 9.2E+00 17% Os-185 5.9E+00 12% TP HRS TP HRS 42 Sb-124 3.1E+02 12% Os-185 4.1E+00 53% Pt-188 1.4E+01 8% Filtre CA 43 Filtre I-125 3.2E+03 76% Pt-188 9.0E+00 19% Ir-189 2.1E+01 13% CA Sb-125 1.8E+02 19% Bi-205 5.1E+01 10% Pt-195 3.7E+01 11% Sb-126 2.0E+02 10% Bi-206 1.9E+02 7% Hg-203 1.6E+01 13% TP HRS 32 I-131 5.0E+01 40% Po-206 9.1E+01 9% Bi-205 1.7E+00 20% Ba-140 5.1E+01 29% Bi-207 9.8E-01 70% Bi-206 8.8E+00 8% Filtre CA Os-185 1.9E+01 100% Po-206 4.5E+00 18% Pt-188 4.7E+01 38% Ir-189 1.4E+02 33% Injection Cooling Au-194 3.1E+02 17% Accumulation stopping Pt-195 3.6E+02 28% extraction Bi-205 9.0E+02 10% Bi-206 9.7E+02 8% Po-206 4.3E+02 17% Bi-207 3.3E+01 33% …Where are the noble gases? TE/VSC and DGS/RP 23

Elements on radioactive decays What Fantasy thinks that radiation can produce: TE/VSC and DGS/RP 24

Elements on radioactive decays What happens in reality: 𝑞 → 𝑜 + 𝛾 + + ν 𝜸 + 𝑜 → 𝑞 + 𝛾 − + ν 𝜸 − 𝐵 𝐵−4 4 𝑄 → 𝐸 + α 𝑎 𝑎−2 2 Beta Alpha Decay Decay ALUMINIUM PAPER LEAD 𝑄 ∗ → 𝐵 𝐵 𝑄 + 𝛿 𝑎 𝑎 Gamma Decay e- p 𝑞 + 𝑓 − → 𝑜 + ν Electron capture TE/VSC and DGS/RP 25

Elements on radioactive decays: Nuclides chart TE/VSC and DGS/RP 26

Elements on radioactive decays: Nuclides chart TE/VSC and DGS/RP 27

Some example 185 Hg β + 205 Rn 185 Au β + β + 140 Xe 121 Xe 205 At 185 Pt 209 Rn β - β + β + β + α 140 Cs 121 I 205 Po 185 Ir β - ε β + β + 140 Ba 121 Te 205 Bi 185 Os TE/VSC and DGS/RP 28

Future step Qualitative to quantitative analysis: • Use of Monte Carlo simulations to evaluate transmission probability in different position (filters); • Comparison with spectroscopic results; • Application of the tool to HRS and GPS filters analysis. Experiment 2 Use of a Tape Station to: • analyze ACTIVITY and evaluate the TIME OF FLIGHT of different gas species (spectroscopy); • TEST the accuracy of Monte Carlo model (time dependent mode). TE/VSC and DGS/RP 29

Future steps Tape station TE/VSC and DGS/RP 30

Future experimental steps -11 70 x 10 5 6 He Fit He 4 He 4.5 60 Simulated values He 4 50 3.5 Pressure [mbar] 3 Beta counts 40 2.5 30 2 1.5 20 1 10 0.5 0 0 0 1 2 3 4 5 1 2 3 4 5 6 7 Time [s] Time after proton impact [s] Courtesy of A. Gottberg TE/VSC and DGS/RP 31