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 Center
Reinhard Schulte
Vladimir Bashkirov
George Coutrakon
Peter Koss
Weizmann Institute of Science
Amos Breskin
Rachel Chechik
Sergei Shchemelinin
Guy Garty
Itzhak Orion
University of California, San Diego
John F. Ward
Joe Aguilera
Jamie Milligan
Santa Cruz Institute for Particle Physics
(University Of California, Santa Cruz)
Abe Seiden
Hartmut Sadrozinski
Robert P Johnson
Wilko Kroeger
Patrick Spradlin
Brian Keeney
Brian Keeney, LLU-SCIPP Nanodosimeter
Radiation Damage To DNA
Ionization event (formation of water
radicals)
Light damage- reparable
Primary particle track
delta rays
eOH•
Water radicals attack the
DNA
Clustered damage- irreparable
The mean diffusion distance of OH radicals before they react is only 2-3 nm
Brian Keeney, LLU-SCIPP Nanodosimeter
Bethe-Bloch in ND
Linear Energy Transfer LET:
dE  f (b ) [MeV/ g ]
dX
cm2
E  dE X , X   [ g ]
dX
cm2
~1/b1.5
measure p
MIP
Radiation damage in DNA occurs within 2-3nm

( propane)   DNA  (DNA)
propane

( propane@1mbar)   STP  ( propane@ STP)
1mbar
( propane@1mbar) 10001000 (DNA)
1nm(DNA) 1mm( propane@1mbar)
Rad
Brian Keeney, LLU-SCIPP Nanodosimeter
Expanding the DNA
1nm
solid
1  m @ 1 atm.
X 1000
DNA
1 mm @ .001 atm.
X 1000
Propane
gas
Low pressure propane gas
Brian Keeney, LLU-SCIPP Nanodosimeter
Nanodosimetry in Low-Pressure Propane
4 Silicon Detectors give position and LET, allow trigger on any
combination of planes
Eweak
1 SSD is 0.4% Xo
or 120keV LET at
high energy
electron
Incoming
Proton
Low Pressure
Gas
X-Y
Estrong
NOT TO
SCALE
Vacuum
Ion
Ion
Counter
Aperture
Y-X
Brian Keeney, LLU-SCIPP Nanodosimeter
Integration of Silicon Modules and
Nanodosimeter
VME CRATE
Localization of Protons
2 Silicon Strip Detector
(SSD) Modules
SSD
Readout
PC W/ DAQ
PCI Card
Ion
Counter
Brian Keeney, LLU-SCIPP Nanodosimeter
Time-Over-Threshold (TOT):
Digitization of Position and Energy with large Dynamic Range
TOT  charge  LET!
Brian Keeney, LLU-SCIPP Nanodosimeter
TOT Spectrum - Effect of Charge Sharing in SMD’s
13.5 GeV
Spectrum
Brian Keeney, LLU-SCIPP Nanodosimeter
TOT Spectra For Protons of Different EnergiesAn 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
TOT and Resolution Measured
TOT expected through Bethe-Bloch
Brian Keeney, LLU-SCIPP Nanodosimeter
Resolution
10
10
Resolution of TOT System

LET
Energy
1


1

0.1
0.1
TOT
Saturation
0.01
10
4
0.01
100
1000
10
Proton Energy [MeV]
Energy Resolution = LET Resolution /Slope of TOT(E) Curve
Brian Keeney, LLU-SCIPP Nanodosimeter
Conclusion
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.