1 / 36

THE STARTRACK EXPERIMENT nanodosimetric ST ructure of h A d R on TRACK s

A really complicated experiment with interesting results . THE STARTRACK EXPERIMENT nanodosimetric ST ructure of h A d R on TRACK s. Valeria Conte. 2 nd Annual Workshop Milano, October 2013. CONTENTS. GENERALITIES OF TRACK STRUCTURE THE EXPERIMENTAL SET UP

noura
Download Presentation

THE STARTRACK EXPERIMENT nanodosimetric ST ructure of h A d R on TRACK s

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A really complicated experiment with interesting results THE STARTRACK EXPERIMENTnanodosimetricSTructureof hAdRon TRACKs Valeria Conte 2nd Annual Workshop Milano, October 2013

  2. CONTENTS • GENERALITIES OF TRACK STRUCTURE • THE EXPERIMENTAL SET UP The rational of the experiment The measuring procedure • DATA ACQUISITION AND DATA ANALYSIS How to handle experimental data • RESULTS Some interesting features of the track structure of light ions

  3. The hypothesis: The damage to segments of the DNA is initiated to a great part by ionizing processes THE TRACK STRUCTURE OF IONIZING PARTICLES 1mm Track structure = detailed description of the interaction pattern of single particles (i) wherethe interaction takes place (spatial distribution of ti) not yet possible experimentally (ii) whichkind of interaction (local energy deposits εi) (iii) whatspecies are possibly formed Effectiveness of radiation strongly depends on the track structure

  4. Characterization of Particle Track Structure by Measuring the frequency distribution of the number of ionizations in nanometre-sized target volumes THE TRACK STRUCTURE OF IONIZING PARTICLES 1mm Track structure = detailed description of the interaction pattern of single particles (i) wherethe interaction takes place (spatial distribution of ti) not yet possible experimentally (ii) whichkind of interaction (local energy deposits εi) (iii) whatspecies are possibly formed Effectiveness of radiation strongly depends on the track structure

  5. the track structure of energetic ions The track component due to primary-particle interactions: Track-coreregion The track component due to secondary-particle interactions: Penumbraregion A detector to measure the track structure characteristics in the core and in the penumbra

  6. 20nm The physics of the interaction at the mmlevel at the nmlevel 1mm 1mm A «picture» of the trackstructure with a pixel of 20 nm

  7. STARTRACK: THE EXPERIMENTAL SET UP

  8. RATIONAL OF THE EXPERIMENT A narrow parallel particle beam is passing a cylindrical target volume of diameter D, at impact parameter r d-electron d-electron primarytrajectory r d-electron D and the number n of ionizations in the volume is counted

  9. RATIONAL OF THE EXPERIMENT A narrow parallel particle beam is passing a cylindrical target volume of diameter D, at impact parameter r d-electron d-electron primarytrajectory r d-electron D 3 mbarpropane, T = 25°C

  10. SINGLE IONIZATION (ELECTRON) COUNTING How to count n ? Counting single electrons single electron gain distribution Peak amplitude h n x G Single electron avalanche variance Because of the small number nof initial electrons, the resolution of measured signal is strongly influenced by gas gain fluctuations. P(G) Small volume small large fluctuations Ionization measurements based on counting of individual electrons

  11. STARTRACK: thedevice MSAC ion track d-electron Drift Column sensitive volume Sensitive Volume r A cylinder 3.7 mm in diameter and height filled with 3 mbar of propane (r= 5.47 mg cm-3at 25°), simulatesa diameter Dr= 2 mg/cm2. At density r = 1 g/cm3: D = 20 nm d-electron

  12. MSAC ZoomedviewSV DRIFT SV

  13. SINGLE IONIZATION (ELECTRON) COUNTING trigger Drift Average arrival time and std of the time distribution controlled by the drift E field sL At low electric fields, the diffusion is symmetric. sT sL =sT diffusion coeff. k : characteristic energy x: drift distance E: electric field E Field SSD Gaining factor: longitudinal diffusion Dispersive factor: transverse diffusion

  14. STARTRACK: DATA ACQUISITION

  15. DATA ACQUISITION AND ANALYSIS Waveformsof 16 mslengtharesampledat a frequencyof1109 s-1by a PCI analogueto digital acquisitioncardandstoredfor off-lineanalysis.

  16. DATA ANALYSIS: 1. CORRELATION OF RAW DATA The correlation method Toincreasethe signal-to-noise ratio, correlationtechniquesareapplied off-linetotheraw pulse trails. In this technique, each digitized primary electron track is correlated with a typical pulse • Pulses above a threshold are counted

  17. DATA ANALYSIS: 2. AMPLITUDE & TIME THRESHOLDS A thresholdisappliedtocorrelatedpulses. x x 1 Vthr = 40 mV A selective time windowisapplied in ordertorejectall the pulse trailsthatare not consistentwiththeexpecteddrift time.

  18. DATA ANALYSIS: 3. BACKGROUND SUBTRACTION The measured cluster distribution is the overlap of primary electron distribution and a background distribution Background distributions are also measured and unfolding procedure is applied Measured distribution background Unfolded

  19. DATA SIMULATIONS • Dedicated Monte Carlo code developed (Grosswendt). • Response function included in the Monte Carlo code. MSAC efficiency P(G) Time resolution

  20. RESULTS OF MEASUREMENTS AND SIMULATIONS

  21. RESULTS OF MEASUREMENTS AND SIMULATIONS probability of n ionizations at impact parameter mean cluster size r Ionization mean free path of the primary ion Mean number of electrons set in motion by the primary ion along a path length D

  22. RESULTS OF MEASUREMENTS AND SIMULATIONS CORE REGION impact parameter r= 0 nm PENUMBRA REGION impact parameter r> 0 nm Ionizations produced by the primary particles + ionizations produced by the secondary electrons (d rays) Ionizations produced only by d-rays

  23. TRACK CORE Symbols: measurementslines: Monte Carlo simulation M1 = 4.6 Sparsely ionizing particles, like 20 MeV protons, and densely ionizing particles, like 26.7 MeV 7Li-ions, show markedly different ionization patterns M1 = 9.2 With decreasing ionization mean free path length of the primary ions the distributions become peaked and shift to larger cluster sizes M1 = 0.55 Pn(Q) M1 = 0.30

  24. TRACK CORE: same velocity, different Z For given velocity and different Z, M1 is approximately proportional to Z2, in accordance with Bethe theory Pn(Q) M1 = 0.55 M1 = 4.6 M1(2H) = 0.55 0.55 x 32=4.95 0.55 x62 = 19.8 M1 = 15 Symbols: measurementslines: Monte Carlo simulation To improve: Efficiency for large cluster sizes.

  25. TRACK CORE: same Z, different velocities Symbols: measurementslines: Monte Carlo simulation 12C, 240 MeV M1= 8.1 lion= 0.57 nm 12C, 96 MeV M1= 15 lion= 0.26 nm Pn Slower particles have more time to interact with the target molecules which results in a larger interaction cross section and hence in a smaller ionization mean free path length of primary particles. With decreasing velocity of the primary ions the distributions shift to larger cluster sizes

  26. AGREEMENT BETWEEN MEASUREMENTS AND SIMULATIONS Does it mean that the experimental results are correct? NO ! Validation of the Monte Carlo simulation code Simulations as a tools to supplement experimental measurements

  27. RESULTS OF MEASUREMENTS AND SIMULATIONS TRACK STRUCTURE in the PENUMBRA impact parameter r > 20 nm Ionizations produced only by the secondary electrons (d rays)

  28. TRACK PENUMBRA: 240 MeV 12C-ions, different r Different impact parameters D = 20 nm r = 22 nm r = 30 nm r = 44 nm Pn(r ) Cluster-size distributions exhibit the same shape, irrespectively of impact parameter multiplying

  29. TRACK PENUMBRA: 240 MeV 12C-ions Different impact parameters D = 20 nm Pnx (r / D)2 r = 22 nm r = 30 nm r = 44 nm From the point of view of a nanometer-sized target site, the radiation quality of secondary electrons seems to be the same, only the probability of being hit decreases with increasing r. When multiplied by the ratio (r / D)2, the distributions form almost a single curve. comparing different ions

  30. TRACK PENUMBRA: different Z and velocities Different Z and velocity ? lion= 0.26 nm 12C, 96 MeV lion= 0.57 nm 12C, 240 MeV lion= 20.5 nm 1H, 20 MeV lion= 0.55 nm 7Li, 26.7 MeV (d=0) Pn Cluster-size distributions in the penumbra region exhibit the same shape, irrespectively of velocity and Z. Dividing

  31. TRACK PENUMBRA after dividing Different Z and velocity lion= 0.26 nm 12C, 96 MeV lion= 0.55 nm 12C, 240 MeV lion= 20.5 nm 1H, 20 MeV lion= 9.41 nm 2H, 16 MeV lion= 0.55 nm 7Li, 27 MeV lion= 1.05 nm 6Li, 48 MeV Pn/ M1 lion= 0.55 nm 4He, 5.4 MeV If divided by M1, the distributions form a single curve, almost independent of radiation quality (charge state and velocity)

  32. CONCLUSIONS The track structure is mainly determined by lion (M1) r The shape of the cluster size distributions is largely independent of r and also of particle type and velocity. Cluster-size distributions in nanometre-sized volumes reflect special properties of particle track structure

  33. 240 MeV 12C-IONS HOMOGENEOUS EXTENDED BEAM Total cluster distributions for beams of different radius Given particles’ flux ~ RV F(1.5 V) the shape is the same

  34. 240 MeV 12C-IONS HOMOGENEOUS EXTENDED BEAM Rfield= 8 mm (45 nm) Which link to radiobiology? In radiotherapy a biological sensitive structure is immersed in a homogeneous broad beam R Measured cluster size distributions can be integrated over the impact parameter to evaluate the track-structure based quality for a nanometer-sized site placed at the centre or at any position of an extended homogeneous beam. Contribution from (1.5 V) only increases the fraction of zeros

  35. Challenges: a practical instrument for track structure measurements. a practical instrument (TEPC) for measurements at the nanometer level.

More Related