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Brian Keeney, LLU-SCIPP Nanodosimeter
A Silicon Telescope For Nanodosimetry
Santa Cruz Institute for Particle Physics, UC Santa Cruz in collaboration with the
Department of Radiation Medicine at Loma Linda University Medical Center
Brian Keeney, LLU-SCIPP Nanodosimeter
Nanodosimetry for Biomedical Applications - Collaborators
Loma Linda University Medical CenterReinhard Schulte George CoutrakonVladimir Bashkirov Peter Koss
Weizmann Institute of ScienceAmos Breskin Guy GartyRachel Chechik Itzhak OrionSergei Shchemelinin
University of California, San DiegoJohn F. Ward Jamie MilliganJoe Aguilera
Santa Cruz Institute for Particle Physics(University Of California, Santa Cruz)
Abe Seiden Wilko KroegerHartmut Sadrozinski Patrick SpradlinRobert P Johnson Brian Keeney
Brian Keeney, LLU-SCIPP Nanodosimeter
Ionization event (formation of water radicals)
The mean diffusion distance of OH radicals before they react is only 2-3 nm
delta rays
Light damage- reparable
Clustered damage- irreparableWater radicals attack the
DNA
e-
Primary particle track
OH•
Radiation Damage To DNA
Brian Keeney, LLU-SCIPP Nanodosimeter
~1/1.5
MIP
Radmeasure p
Linear Energy Transfer LET:
Radiation damage in DNA occurs within 2-3nm
]2
g[MeV/ )(cm
fdXdE
]2cm
g [ , XXdXdEE
Bethe-Bloch in ND
)@(1
)1@(
)()(
STPpropanembarSTPmbarpropane
DNApropaneDNApropane
)1@(1)(1
)(10001000)1@(
mbarpropanemmDNAnm
DNAmbarpropane
Brian Keeney, LLU-SCIPP Nanodosimeter
1nm solid 1 m @ 1 atm.
Propane
gasLow pressure propane gas
X 1000 X 1000
DNA
1 mm @ .001 atm.
Expanding the DNA
Brian Keeney, LLU-SCIPP Nanodosimeter
Incoming Proton
Ion
Eweak
Estrong
4 Silicon Detectors give position and LET, allow trigger on any combination of planes
Low Pressure Gas
ApertureIon Counter
electron
Vacuum
NOT TO SCALE
X-Y Y-X
1 SSD is 0.4% Xo or 120keV LET at
high energy
Nanodosimetry in Low-Pressure Propane
Brian Keeney, LLU-SCIPP Nanodosimeter
VME CRATE
PC W/ DAQ PCI Card
Localization of Protons
2 Silicon Strip Detector (SSD) Modules
Ion Counter
SSD Readout
Integration of Silicon Modules and Nanodosimeter
Brian Keeney, LLU-SCIPP Nanodosimeter
TOT charge LET!
0
20
40
60
80
100
120
0 50 100 150 200
TOT Measurement vs Charge in MIP'sEffect of Threshold and Voltage
TOT SLACTOT LLUMC
Input Charge [fC]
Time-Over-Threshold (TOT): Digitization of Position and Energy with large Dynamic Range
Brian Keeney, LLU-SCIPP Nanodosimeter
13.5 GeV Spectrum
TOT Spectrum - Effect of Charge Sharing in SMD’s
Brian Keeney, LLU-SCIPP Nanodosimeter
0
50
100
150
200
250
300
0 50 100 150
TOT Spectra for low-energy Protons
250MeV
40MeV
24MeV
17MeV
TOT [us]
TOT Spectra For Protons of Different Energies-An absolute calibration of SSD
Brian Keeney, LLU-SCIPP Nanodosimeter
Results
Proton energy [MeV]
Mean TOT [us]
RMS TOT[us]
Charge Deposition 400um Si
by Bethe-Bloch [fC]
TOT expected
[us]
13,500 7 1.4 5.3 6.5
250 12.3 2.6 13.5 13.7
39 53.4 6.4 54 55
27 70.4 7.5 67.5 69
24 78.3 8.5 76.5 78
22 84.4 9.8 81 82
17.6 105 11.5 99 101
9.5 108 15 189 105
7.4 109 21 243 105
Brian Keeney, LLU-SCIPP Nanodosimeter
10
100
1 10 100 1000 104
TOT vs. Proton EnergyMeasurement vs. Expectation
TOT & Resolution measuredTOT expected
Proton Energy [MeV]
LLUMCSynchrotron P Beam
GLAST SLAC Test Beam
TOT Saturation
TOT and Resolution Measured TOT expected through Bethe-Bloch
Brian Keeney, LLU-SCIPP Nanodosimeter
0.01
0.1
1
10
10 100 1000 104
Resolution of TOT System
LETEnergy
0.01
0.1
1
10
Proton Energy [MeV]
TOT Saturation
Resolution
Energy Resolution = LET Resolution /Slope of TOT(E) Curve
Brian Keeney, LLU-SCIPP Nanodosimeter
1. Silicon detectors provide information on position and energy or LET of primary particles for nanodosimetry
2. Silicon detectors have excellent spatial resolution (60 m)
3. We can measure proton LET to 10-20% in each of 4 planes
4. Given LET, we know energy to 20-25% in each plane through Bethe-Bloch from low energies up to 250 MeV
5. Silicon Detectors allow flexible triggering on primary particles.
Conclusion
