Transcript Slides

Development of innovative resistive
GEM alpha detectors for
earthquakes prediction and
homeland security
Participants:
CERN,
INFN Bari, Bari, Italy
UNAM, Mexico
INFN Padova, Padova, Italy
INFN Frascati, Frascati, Italy
Earthquakes are one of the most powerful natural disasters annually taking thousand
of human lives and destroying homes and industrial infrastructures.
Hence the early prediction of earthquakes is a very important task.
Haiti Earthquake building damage
For this reason various scientific
communities (geologists,
seismologists, physicists etc.) try
to find the way of the
earthquake prediction
Rn
It is known that before an earthquake some precursor
phenomena happen: earth surface movements and
stress, changes in radio waves propagation and several
others.
In the last decade, some studies have shown
the possibility to correlate elevated concentrations
in the soil of gas Rn, or rapid changes in soil
or groundwater radon concentration, to
the early prediction of earthquakes
“Yesterday, a magnitude 6.3 earthquake
struck L'Aquila, Italy, killing more than 150
people, injuring some 1,000, and leaving
thousands of people homeless. Soon after
the deadly temblor hit, news outlets
including Time magazine, Reuters, and
The New York Times reported Italian
authorities had previously removed from
the Internet a warning that a big quake was
imminent. The prediction had been posted
weeks earlier by a techician at the Gran
Sasso National Laboratory in Abruzzi, Italy”
“In the geological environment, the radon groundwater
concentration depends on the isotopic abundance of its
parent radionuclides (238U and 226Ra), and on their
geochemical patterns with reference to environmental
redox and pH characteristics”
NASA
data
Time series of daytime anomalous OLR
observed from NOAA/AVHRR
March 1-March12, 2011. Tectonic plate
boundaries are indicated with red lines
and major faults by brown ones and
earthquake location by black stars.
Red circle show the spatial location of
abnormal OLR anomalies within
vicinity of M9.0 Tohoku earthquake.
Infrared emissions above the epicenter increased dramatically in
the days before the devastating earthquake in Japan
These kinds of observations are consistent with an idea called the
Lithosphere-Atmosphere-Ionosphere Coupling mechanism.
The thinking is that in the days before an earthquake, the great stresses
in a fault as it is about to give cause the releases large amounts of radon.
“
“
Normal process of accumulation of Rn in
cavities, cracks and ground water
Crack or cavity
Rn accumulation from rocks
Before the earthquake the soil and rocks
start deforming, cracking and release
Rn accumulated in old cracks, cavities
ground water
a)
Rn
Ground water
Crack or cavity
New cracks
Soil
Rn accumulation from rocks
For reliable prediction of the earthquakes
one has to take into account and analyze all
the precursor phenomena.
INFN Bari and Bari University in close
collaboration with other scientific centers
over the World are deeply involved in
systematic study pre-earthquake
phenomena, for example they have a radio
station
b)
Ground water
New cracks
To the aim of verifying such studies on a
more solid statistical ground one has to
create a wide network of cheap,
compact and high sensitivity Rn
detectors
Hundreds of them should be installed at
different distances and have compact radio
transmitters
How the Rn variations can be monitored in field by our detectors?
They should be installed in wells or in cavities and cracks in rocks
Radio antenna
For sending signals
Drilled well
Crack or cavity
Our Rn detector
for continuous
monitoring the
Rn level
Rn accumulation from rocks
INFN Bari, Bari University and UNAM plan to develop and install a
network of such detectors in the region when weak earthquakes are often happen
There are of course commercial
detectors of Rn operating in on line
mode:
Scintillators based
Solid-state detectors based
Gaseous ionization chambers
However, they are not yet adjusted/ready for this
application (a high degree of robustness is necessary
and capability to operate in harsh conditions) and their
present price is too high for this particular application
*
*There are also accumulative types of Rn detectors which are very cheap, but not suitable for earthquake prediction
Real time detectors
ATMOS, highest
sensitivity
RAD7, medium
sensitivity
In the past we have developed
gaseous detectors of Rn exploiting
two new features:
1) Gas multiplication
2) Drift of negative ions in air and
electron detachment in high electric
field
(See for example: G. Charpak et al., NIM A628,2011,187)
A simple competitor to commercial devices:
Advantages:
simple,
low cost,
robust,
has sufficient sensitivity for
the earthquake application
1) Results obtained with Am:
Typical signals measured with
a single –wire counter (basic lay-out)
operating in air and irradiated by
241Am
Signal amplitude (mV)
10000
height of peaks, mV, 100 µm
height of peaks, mV, 25 µm
height of peaks, mV, 1000 µm
mV
1000
100
10
Ionization chamber signal
1
2
3
4
kV
1000
Alphas
100
10
1
1000
60keV
1500
2000
2500
3000
3500
5
Mean signal amplitude produced by alpha particles vs. the
voltage applied to detectors having a cathode diameter of 60 mm and
different anode wires
10000
Voltage (V)
1
0
source
The pulse amplitudes vs. the voltage measures with
a single-wire counter having
200
Conting rate (Hz)
Counting rate (Hz)
Efficiency of alpha particles detection is ~100%
150
100
Ar
Air
50
0
0
1000
2000
3000
4000
400
300
Alphas
200
60 keV
100
0
1000
1500
Voltage (V)
2000
2500
3000
3500
Voltage (V)
Counting rates vs. the applied voltage measured in
Ar and in air at the same conditions (alpha particles,
Counting rate vs. Vd for alpha particle (blue) and for 60 keV
photons (rose) measured with a basic design of the single
D=60mm, da=100 μm)
wire counter
alphas, 3.15 kV
1000
800
mV
600
Oscillogramm of pulses
produced by 241Am measured
400
in 100% humid air
200
0
0
10
20
30
-200
ms
40
50
60
2) Basic studies with 220Rn (Thoron)
High sensitivity can be achieved only if the noise pulses rate is suppressed almost to zero
a)
b)
Typical shape of pulses produced in the single-wire counter by Thoron: a) smooth pulses, b) pulses containing 1-2 peaks
Typical pulse shape of noise pulses
Counting rate vs. time as measured by the single-wire counter in
which air contaminated with Thoron was injected(T0=56sec).
Noise pulses rejection technique:
Distribution of the noise width
and Thoron induced pulses
(Lab View program)
Pulse height spectrum of Thoron
and noise pulses
(Lab View program)
3) Measurements with 222Rn
6000
Injection of Rn 222
5000
Purging with air
In case of measurements of the
220Rn or 222Rn the air having
traces of these radioactive elements
was introduce in to the detector.
Their concentration was
evaluated from the counting rate
produced by alpha particles.
samples of air containing Rn were
also independently measured by the
experts from the French company
ALGADE
Bq/m3
4000
3000
2000
1000
0
0
10
20
30
40
50
60
70
Counting rate vs. time after injection into the basic design (at t=2min) air
contaminated with 222Rn.
At t=40 min the detector for a few second was flushed with a clean air
80
90
minutes
Comparative measurements with a single-wire counter operating at low voltages
( plateau region):
Counting rate vs. time when the radon contaminated
air was introduces (at t=0sec) into the ionization
chamber and at t=40sec it was flushed with clean air.
The fast decrease of the counting rate is mainly due to
the Po decay
Long-term measurement performed with the ionization chamber:
the counting rate decrease with a good accuracy corresponds to
the decay of the 222Rn (T0=5500min)
However, the most efficient suppression of noise pulses was achieved with MWPC
(a copy of Sauli drift tube)
Anode wires
In this design a large fraction
of primary electrons
escaped attachment
Alpha track
Cathode wires
Standard electronics:
Cathode cylinder
(ss or mesh)
each anode wire was connected to its own amplifier which after the amplitude discrimination produces
a standard square pulse 1μs long. These pulses were sent in parallel to a simple “majority” unit which generate an output
pulse it there was two or more coinciding input signals. These generated pulses were counted by a standard scaller.
In measurements with alpha particlesonly those event were chosen and counted when two or more wires produce signals within
a few μs gate.
R.
Bouclier et al., NIM A2521986,393
The aim of the work, which is currently
carry out at CERN, is to challenge these
wire-type detectors and develop
simpler, cheaper and even more
sensitive Rn detector prototypes based
on new designs of resistive GEMs.
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Potential advantages of GEM
Large volume
Simpler
Lower price
RETGEM-based Rn detectors with large drift region were already preliminary tested
Alpha source
-Vdr
6 cm
Alpha tracks
Ar or air
-V1
-V2
Single or double RETGEMs
Gas vessel
Some preliminary results obtained with a single –step RETGEM
Print of the LabView screen showing
a pulse-height spectrum of alpha
particles measured with a single
stage RETGEM operating in Ar at a
pressure of 1 atm
Pulse-height spectrum of alpha particles
measured with a single stage RETGEM
operating in air. The voltage across the
RETGEM was 3200 V, the thickness of the
drift gap 2 cm.
Raw data:
Signal amplitude
(V)
1mm RETGEM, holes 0.3 mm
100
α
10
Ar+10%CO2
Air
α
1
60 keV
Ar
55
Fe
0.1
0
1000
2000
3000
4000
5000
Voltage (V)
Signal amplitude (V)
RETGEM1 mm thick, holes 0.5mm
100
Air
Fe
10
alphas
1
0
1000
2000
3000
4000
0.1
Voltage (V)
In air the drift voltage was 2.5kV
Counting plateau
Counts (Hz)
Counts vs voltage
150
100
50
0
Ar
0
1000
Air
2000
3000
4000
Voltage (V)
100% efficiency was easily achieved
Operate stably even in humid air
5000
Print of the LabView screen in the case of double
RETGEM operating in air
-6 kV on the divider
+3.6kV on the bottom
Efficiency:
ε=Nair/NAr
Nair=NAr
(practically no spurious
pulses-nair~0)
Efficiency for alphas detection 100%
One of the aims of this work is
TGEM optimization: geometry,
operating voltage etc.
Of course, it is clear in advance
that finally for reliable earthquake prediction
several methods based on precursors should
be combined in one monitoring/analyzing
system and we are in contact with some
groups which are involved in these studies for
a long time
Security
British authorities as well as other
countries are seriously consider
developing a monitoring system capable to
survey large areas-up to 25 km2
See for example: CLASP call for developing a system for:
“rapid detection and assessment of the severity and spatial extend of radiological
contamination (particularly by alpha and beta emitters) over areas of up to 5x 5km2”, 2011
Proposed resistive GEMs can be a good option for this task due to their low
cost, high sensitivity and the possibility to detect alpha particles from the
distance more than 4cm from the examined surface. Moreover, recent test
show that GEM detector operating in ambient air is capable to detect beta
radiation and soft x-ray radiation
Conclusions
1. Preliminary RETGEM looks like an
attractive option for the outdoor application
such as monitoring of Rn or radioactive
contaminations on large areas
2. The aim of the project is to demonstrate
this
3. Industrial/commercial partners are very
welcome
Backup
222Rn (3.8 days
214Po (165μs)
beta
5,5MeV alpha
218Po (3 min)
214Bi (20min)
6MeV alphas
2214Pb (26.8min)
7.7 alphas
210Pb (22.3 years)
beta
beta
2104Pb (5 days))
Task
Starting dateending date
Duration in months
Development special designs
of resistive GEMs capable to
operate in 100 %humid air
January 3-April 30
4
Developing a full prototype
May1-June 30
2
Tests at CERN
July 1-October 30
4
Tests in Bari University and
UNAM
November1_December
30
2
The work plan,
deliverables and the
budged
Table 2
Contribution from collaborating
institutions (kSFr)
Expected contribution from the
RD51 common fund (kSFr)
INFN Bari
1
1
UNAM
3.333
3.333
INFN Padova
2.333
2.333
INFN Frascati
Table 3.
2.333
2.333
Material budged
Amount in kSFr
Notes
Development of new R-TGEMs
capable t operating in 100%
humid air
4
In close collaboration with the TE/MPE
workshop
Production of these R-TGEM
2
TE/MPE workshop
Frontend electronics
2
Modification of existing battery feed
compact amplifiers
Development of a prototype of a
battery feed HV supply
3
Bari-CERN
Equipment rent from CERN
electronic pool
1
Institutions- members of the
RD51collaboration participating
in this project
A set up with the resistive chain divider
Alpha source
1MΩ
-V
55Fe
2-6 cm
10MΩ
Alpha tracks
1MΩ
2-5 mm
15 MΩ
1MΩ
RETGEMs
10MΩ
+V
Commercially available Rn detectors are very expensive ~1000Euro
Atmos 12px