Silicon Detectors and DAQ principles for a physics experiment.
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Transcript of Silicon Detectors and DAQ principles for a physics experiment.
Silicon Detectors and DAQ Silicon Detectors and DAQ principles for a physics principles for a physics
experimentexperiment
Telescopes
Human eyes
Microscope
Accelerators
Detectors
But where does it all start from?
Electronic properties of materials
Atoms are made of proton, neutrons (nucleus) and electrons
Valence and conduction electrons are responsible for the principal characteristics of different atoms
Electronic properties of materials
Everyone wants to be noble !!!
Water is a good example….
Electronic properties of materials
Atomic levels Molecular bands
If some electron is promoted in the conduction band, what may occur?
1) Drift: an external field can move these electrons
2) Multiplication; if the field is strong enough
3) Recombination: if nothing happens, electrons fall back to valence band
What happens then?
How can we describe the situation?
Physicians must be smart and clever….
holes !!!
h+
h+
h+
h+
....and do a smart use of drugs!!!
n doping p dopingWhy ?
p-n Junctions
Fermi level definition
Electrons and holes diffusion
Non equilibrium situation
Donors and acceptors ions field plays against diffusion and equilibrium is reached
Equilibrium !!! … ?
p-n Junctions
Equilibrium is reached when the two Fermi levels are at the same energy
A sort of slope is then created, hard to climb up and easy to roll down!
Equilibrium does not mean immobility!!!
p-n Junctions
Breakdown voltageVbr
Junctions are the basic devices for all semiconductor detectors!
V=RxI
Particles through matter
How can we detect them?
Particles’ measurements
A particle passes through a silicon thickness, generating e-h pairs
e- and h+ are collected by anode and cathode (be aware of recombination…)
An electric field causes electron flow through the device and created charge can be collected (by capacitor for ex.)
SDD, a clever anti-recombination device
An electric field leads electrons, generated by particle flow (x-Rays or ionizing) to a small collector anode. At the same time holes are immediately removed from electron’s path by cathode strips.
Position measurements: strips !
We got the charge...
and now what?
Analog – Digital conversion
Digital signal; signal is a function of discrete numbers, F(N)
Analog signal; signal is a function of continuous numbers, usually time, F(t)
The world is analogic but Pc and analysis software can only work with digital informations…..
Analog signal have to be converted to digital signals!
Analog – Digital conversion
Sampling Quantization
Analog – Digital conversion
channels
Analog – Digital conversion
In this world…..
….this is poker !!!
Analog – Digital conversion
Converting analog signals into digital signals, some information may be lost … but are they really necessary?
From analog signals to files and histograms:
Data AQuisition methods
DAQ
What are we interested in ? Which information can we get?
Charge Timing Rates
DAQ : Discriminators
DAQ : QDC (charge to digital converter)
QDC values(integer numbers)
Histograms
DAQ : TDC (time to digital converter)
DAQ : Scaler
4 events in 10 seconds Rate = 0,4 Hz
A real example!
MPPC (Multi Pixel Photon Counters) detectors
Each pixel acts like a p-n junction
Breakdown current is used
Output signals are summed
MPPC (Multi Pixel Photon Counters) detectors
MPPCSignal coming out from the detecor is then:
QDC spectrum is then composed by several pixes with fixed distance
New physicists?
Questions?
An experience in the lab:
e- charge estimation
areadtiQ
t
Qi
iRV
t
t
tot
1
0
Ohm law
Current definition
Charge definition
b (time)
h (Volt Ω)
2
hbQ
C
sV
R
tVQ
nst
mVV
tot12
92
1051052
1025102
2
)525(
)520(
CAA
AAQQ
preamp
tote
preampetot
195
12
det
det
103,1105105,7
105
Is the result ok?errors…..
st
VV
tR
VV
R
tQ
9
3
22
22
105
105
22
CQ
CQ
e
19
12
103,1
106,1
Huge errors due to the big error estimation on measured values of t and V
Can you do it better ???