Page 300 - 2014 Printable Abstract Book
P. 300
(PS5-23) Development of a track imaging detector for characterization of radiation quality. Margherita
1
2
3
1
Casiraghi ; Vladimir Bashkirov ; and Reinhard Schulte , PSI, Villigen, Switzerland ; Loma Linda University,
Loma Linda, CA ; and Loma Linda University Medical Center, Loma Linda, CA
2
3
For a given absorbed dose, the biological effect of different radiation qualities varies. Monte Carlo
(MC) track structure codes have shown that high LET radiation produces large ionization clusters over
nanometer dimensions with higher frequency than low LET radiation. When overlapping ionization
patterns with models of DNA, a correlation between ionization cluster size and clustered DNA damage is
observed in MC simulations. Experimental characterization of the spatial distribution of radiation induced
ionizations on the nanometric scale would help to benchmark the MC codes and may be used for
monitoring mixed or unknown radiation fields. We are developing a novel instrument for measuring the
spatial distribution of ionizations that is based on the concept of single-ion registration in low-pressure
gas. The small ion diffusion and low momentum transfer preserve the primary ionization pattern,
providing precise spatial information of the initial ionization events. Ions produced by radiation in the gas
volume drift towards a 2D GEM-like well detector, where they are accelerated in a strong electric field
inducing ion impact ionization that develops into a confined electron avalanche. Due to the high gain, the
resulting signal can be read out by standard electronics. Registering the 2D coordinates of the well position
and using the time difference between signals as information on the third dimension, the complete 3D
structure of radiation tracks can be reconstructed. Initial measurements with a detector prototype
showed low ion detection efficiency. More recently, we have successfully started to optimize the detector
working parameters. In particular, detectors with a few wells of different diameters drilled in polystyrene
plates ranging from 3 to 10 mm in thickness and combined with a semiconductor cathode or a high
resistivity cathode were built. Using this simple detector configuration, the response of a single well was
measured as a function of different parameters in order to study the physical properties of the signal
generation process. Preliminary results showed a significant increase of the ion detection efficiency when
increasing the well height. This is ongoing work that may lead to track imaging detectors with namometer-
equivalent resolution.
(PS5-24) Simulations of DSB yields and radiation-induced chromosomal aberrations in human cells
based on the stochastic track structure induced by HZE particles. Artem L. Ponomarev; Ianik Plante; Kerry
George; and Honglu Wu, USRA, Houston, TX
The formation of double-strand breaks (DSBs) and chromosomal aberrations (CAs) is of great
importance in radiation research and, specifically, in space applications. We are presenting a new particle
track and DNA damage model, in which the particle stochastic track structure is combined with the
random walk (RW) structure of chromosomes in a cell nucleus. The motivation for this effort stems from
the fact that the model with the RW chromosomes, NASARTI (NASA radiation track image) previously
relied on amorphous track structure, while the stochastic track structure model RITRACKS (Relativistic Ion
Tracks) was focused on more microscopic targets than the entire genome. We have combined
chromosomes simulated by RWs with stochastic track structure, which uses nanoscopic dose calculations
performed with the Monte-Carlo simulation by RITRACKS in a voxelized space. The new simulations
produce the number of DSBs as function of dose and particle fluence for high-energy particles, including
iron, carbon and protons, using voxels of 20 nm dimension. The combined model also calculates yields of
radiation-induced CAs and unrejoined chromosome breaks in normal and repair deficient cells. The joined
298 | P a g e
1
2
3
1
Casiraghi ; Vladimir Bashkirov ; and Reinhard Schulte , PSI, Villigen, Switzerland ; Loma Linda University,
Loma Linda, CA ; and Loma Linda University Medical Center, Loma Linda, CA
2
3
For a given absorbed dose, the biological effect of different radiation qualities varies. Monte Carlo
(MC) track structure codes have shown that high LET radiation produces large ionization clusters over
nanometer dimensions with higher frequency than low LET radiation. When overlapping ionization
patterns with models of DNA, a correlation between ionization cluster size and clustered DNA damage is
observed in MC simulations. Experimental characterization of the spatial distribution of radiation induced
ionizations on the nanometric scale would help to benchmark the MC codes and may be used for
monitoring mixed or unknown radiation fields. We are developing a novel instrument for measuring the
spatial distribution of ionizations that is based on the concept of single-ion registration in low-pressure
gas. The small ion diffusion and low momentum transfer preserve the primary ionization pattern,
providing precise spatial information of the initial ionization events. Ions produced by radiation in the gas
volume drift towards a 2D GEM-like well detector, where they are accelerated in a strong electric field
inducing ion impact ionization that develops into a confined electron avalanche. Due to the high gain, the
resulting signal can be read out by standard electronics. Registering the 2D coordinates of the well position
and using the time difference between signals as information on the third dimension, the complete 3D
structure of radiation tracks can be reconstructed. Initial measurements with a detector prototype
showed low ion detection efficiency. More recently, we have successfully started to optimize the detector
working parameters. In particular, detectors with a few wells of different diameters drilled in polystyrene
plates ranging from 3 to 10 mm in thickness and combined with a semiconductor cathode or a high
resistivity cathode were built. Using this simple detector configuration, the response of a single well was
measured as a function of different parameters in order to study the physical properties of the signal
generation process. Preliminary results showed a significant increase of the ion detection efficiency when
increasing the well height. This is ongoing work that may lead to track imaging detectors with namometer-
equivalent resolution.
(PS5-24) Simulations of DSB yields and radiation-induced chromosomal aberrations in human cells
based on the stochastic track structure induced by HZE particles. Artem L. Ponomarev; Ianik Plante; Kerry
George; and Honglu Wu, USRA, Houston, TX
The formation of double-strand breaks (DSBs) and chromosomal aberrations (CAs) is of great
importance in radiation research and, specifically, in space applications. We are presenting a new particle
track and DNA damage model, in which the particle stochastic track structure is combined with the
random walk (RW) structure of chromosomes in a cell nucleus. The motivation for this effort stems from
the fact that the model with the RW chromosomes, NASARTI (NASA radiation track image) previously
relied on amorphous track structure, while the stochastic track structure model RITRACKS (Relativistic Ion
Tracks) was focused on more microscopic targets than the entire genome. We have combined
chromosomes simulated by RWs with stochastic track structure, which uses nanoscopic dose calculations
performed with the Monte-Carlo simulation by RITRACKS in a voxelized space. The new simulations
produce the number of DSBs as function of dose and particle fluence for high-energy particles, including
iron, carbon and protons, using voxels of 20 nm dimension. The combined model also calculates yields of
radiation-induced CAs and unrejoined chromosome breaks in normal and repair deficient cells. The joined
298 | P a g e
