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

TE/VSC and DGS/RP

“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

7th November 2014

TE/VSC and DGS/RP

• 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

Outline of this talk

TE/VSC and DGS/RP

LINAC 2 BOOSTER ISOLDE

Introduction: ISOLDE

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Introduction: ISOLDE

1.4 GeV

Intensity: 3.5 ∗ 1013 protons/1.2s Energy of products: 60 keV

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HRS31 HRS23 HRS25 HRS22 HRS24 HRS32

My project

Analysis of the progression of neutral radioactive gas species along the ISOLDE beam line:

• Monte Carlo simulation
• Experimental Analysis

Tape station

• Construction of a general tool for RIB

vacuum;

• Define a zone separation, according to level
• f contamination

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Why contamination study is so important?

Isolde vacuum system:

The Front Ends zone

The separators zone The Experimental Hall

• Venting to atmosphere

via Filters and Monitoring RFQ

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Which species are targeted by the study?

Target with high dose rates:  U (i.e. UCx) and Th (α emitters);  Pb;  Ta. First transfer function (“filter”): Target choice IONS: Transported by the beam optics NEUTRALS: Diffusing according to Maxwell- Boltzmann statistics and direction distribution

Neutrons Protons

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For neutral contamination study Isolde Users

1) Choice of target temperature; 2a) Choice of transfer line temperature 2b) Conductance of transfer line; 3) Ionization Efficiency (~10%).

Volatility; 1 - Ionization Efficiency (~90%).

Which species are targeted by the study?

Noble gases (few volatile metals e.g. Zn, Cd, Hg ?)

TARGET OVEN

1

TRANSFE R LINE

2

ION SOURCE

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EXTRACTION ANALYSIS GAS INLET Quartz tube Transfer tube Tantalum tube with the target material

Ion species targeted

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Numerical Methods : Monte Carlo simulation

Pills of Physics of molecules in vacuum : two important equations… Maxwell Boltzmann Lambert’s cosine law

𝑒𝑂/𝑒𝑤 𝑂 = 4π𝑤2 𝑛 2𝜌𝑙𝐶𝑈

3/2

exp 1 2 𝑛𝑤2 𝑙𝐶𝑈 < 𝑤 > = 8𝑙𝐶𝑈 𝜌𝑛 = 8𝑆𝑈 𝜌𝑛 𝑄 𝑒ω = 𝑒ω 𝜌 𝑑𝑝𝑡𝜄

n dω θ

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Numerical Methods : Monte Carlo simulation

Pills of Physics of molecules in vacuum : some hypothesis… Ideal Gas Molecular Flow 𝑸𝑾 = 𝑶𝒍𝑪𝑼 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

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Calculation of Pressure Profiles and conductances Analytical Methods Numerical Methods

• No universal formulas
• Only simple geometry
• No simplification is needed

Numerical Methods : Monte Carlo simulation

MOLFLOW + a Test Particle Monte-Carlo code developed at CERN allows import of stl files From steady state to time-dependent simulation

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From official Drawings.. ..to 3D CAD (Inventor…)… ..and STL file for Molflow Simulation

Numerical Methods : Monte Carlo simulation

Chamber walls are described by planar polygons (facets)

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Numerical Methods : Molflow+

Pumping speed or Sticking factor Desorption value Time depending pressure profile

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1 2 3 4 5 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 x 10

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Time [s] Pressure [mbar] Fit He Simulated values He

Numerical Methods : Monte Carlo simulation

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1 2 3 4 5 6 7 8 1 2 3 x 10

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Time [s] Pressure [mbar] He Ne Ar Kr Xe Rn

Numerical Methods : Monte Carlo simulation

1 2 3 4 5 6 7 8 0.5 1 1.5 2 2.5 3 x 10

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Time [s] Pressure [mbar] Kr Xe Rn

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50 100 150 200 250

• 0.05

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Transmission Probability [%] Molecular mass [g/mol]

Equation y =(x)^A

• Adj. R-Square 0.99719

Value Standard Error T.P. (%) A

• 0.94306

0.00978

Numerical Methods : Monte Carlo simulation

𝜏𝑈.𝑄. =

1 𝑜 1 − 𝑈. 𝑄. (*)

*Y.Suetsugu, Application of the Monte Carlo method to pressure calculation

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50 100 150 200 250 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Time of flight [s] Molecular mass [g/mol]

Equation y =B+(x)^A

• Adj. R-Square

0.98943 Value Standard Error tof (s) A 0.23961 0.00576 tof (s) B

• 0.61299

0.07159

Numerical Methods : Monte Carlo simulation

𝜏𝑢𝑝𝑔.=0.01s

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On-line Sampling :

• Realized along the primary pumping system, with active carbon and

cellulose filters installed downstream of the turbomolecular pumps;

• Spectroscopy Analysis.

Experimental Analysis

Experiment 1

Filter position

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HRS31 HRS23 HRS25 HRS22 HRS24 HRS32

Filters positions

Experimental Analysis

HRS filters Date of installation: 17th June 2014 Date of removal: 13th September 2014 Number of target change in this period: 5 Type of targets: ZrO, UC2-C

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HRS 31 HRS 23

Filters positions in HRS and RFQ

HRS 32 HRS 43 HRS 42 HRS24

Experimental Analysis

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Experimental Analysis

HPGe detector:

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

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1 10 100 1000 10000 100000 1000000 HRS 23 HRS 24 HRS 25 HRS 31 HRS 32 HRS 42 HRS 43

Log Activity (Bq\unit) Filter Position

Po-206

Bi-206 Bi-205 Pt-188 Os-185 Ba-140 I-125 Te- 121

Some spectroscopy results

Separators zone RFQ

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Some spectroscopy results

Ech No. Activités Isotopes (Bq /unit) Incert. TP HRS 32 Filtre CA Se-75 3.6E+01 33% Sb-120 4.4E+01 20% Te-121 3.6E+02 20% Te-121m 4.4E+01 61% Te-123 8.9E+01 39% Sb-124 3.1E+02 12% I-125 3.2E+03 76% Sb-125 1.8E+02 19% Sb-126 2.0E+02 10% I-131 5.0E+01 40% Ba-140 5.1E+01 29% Os-185 1.9E+01 100% Pt-188 4.7E+01 38% Ir-189 1.4E+02 33% Au-194 3.1E+02 17% Pt-195 3.6E+02 28% Bi-205 9.0E+02 10% Bi-206 9.7E+02 8% Po-206 4.3E+02 17% Bi-207 3.3E+01 33% Ech No. Activités Isotopes (Bq /unit) Incert. TP HRS 42 Filtre CA Te-121 2.1E+01 20% Te-123 1.6E+00 57% I-125 3.3E+01 124% I-131 1.4E+00 171% Ba-140 9.2E+00 17% Os-185 4.1E+00 53% Pt-188 9.0E+00 19% Bi-205 5.1E+01 10% Bi-206 1.9E+02 7% Po-206 9.1E+01 9% Bi-207 9.8E-01 70% Ech No. Activités Isotopes (Bq /unit) Incert. TP HRS

43 Filtre

CA Te-121 3.1E+00 15% I-125 6.9E+00 92% Ba-140 7.8E+00 9% Ce-141 5.0E-01 29% Os-185 5.9E+00 12% Pt-188 1.4E+01 8% Ir-189 2.1E+01 13% Pt-195 3.7E+01 11% Hg-203 1.6E+01 13% Bi-205 1.7E+00 20% Bi-206 8.8E+00 8% Po-206 4.5E+00 18%

Before He injection After He injection

Injection stopping Cooling Accumulation extraction

…Where are the noble gases?

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What Fantasy thinks that radiation can produce:

Elements on radioactive decays

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Elements on radioactive decays

What happens in reality: e- p 𝑄∗ → 𝑄 + 𝛿

𝑎 𝐵 𝑎 𝐵

𝑄 → 𝐸 + α

2 4 𝑎−2 𝐵−4 𝑎 𝐵

𝑞 → 𝑜 + 𝛾+ + ν 𝑜 → 𝑞 + 𝛾− + ν 𝜸+ 𝜸−

Alpha Decay Gamma Decay Beta Decay Electron capture

𝑞 + 𝑓− → 𝑜 + ν

PAPER ALUMINIUM LEAD 25

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Elements on radioactive decays: Nuclides chart

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Elements on radioactive decays: Nuclides chart

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Some example

121I 205Bi 121Te 185Os

ε

121Xe

β+

205Po

β+

205At

β+ β+

205Rn

α

209Rn 185Ir

β+

185Pt

β+ β+

185Hg

β+

185Au 140Cs 140Ba

β-

140Xe

β-

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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.

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).

Experiment 2

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Future steps

Tape station

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1 2 3 4 5 6 7 10 20 30 40 50 60 70

Beta counts Time after proton impact [s]

1 2 3 4 5 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 x 10

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Time [s] Pressure [mbar] Fit He Simulated values He

Future experimental steps

6He 4He

Courtesy of A. Gottberg

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Conclusions

This work open different ways to be explored: Monte Carlo Analysis:  Molflow+ simulation of Noble gases behavior in GPS and evaluation of transmission probability and time of arrival;  Use of time-dependent mode;  Tool application to HRS and experimental benchmarking (next step);  Try to take the RFQ into account (next tech. student?). Spectroscopic analysis:  HRS: Activity decrease from frontend to main switchyard;  Analysis of GPS and hall filters (next step);

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Special thanks to:

• Giovanna Vandoni (TE/VSC-IVM)
• J. Vollaire, A. Dorsival, N. Riggaz, S. Castelli, (DGS/RP-AS)
• R. Kersevan and M. Ady (TE/VSC-IVM)
• A. Gottberg , T. Stora (EN/STI-RBS Isolde Target Group)
• J.A. Ferreira Somoza, H. Rambeau, P. Chiggiato, R. Catherall, M. Lozano,
• S. Marzari, V. Barozier, H. Montano.
• Friederike, Ida, Maria (Girls open space support group!)

Acknowledgments

TE/VSC and DGS/RP