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New eadou scheme o la ge a ea iming & posi ion RPCs
João Sa ai a ∗, Albe o Blanco
LIP, Labo a o y o Ins umen a ion and Expe imen al Pa icle Physics, Po ugal
ARTICLE INFO
Keywo ds:
Gaseous de ec o s
Resis i e Pla e Chambe s
Readou codi ica ion
Muon Sca e ing Tomog aphy
ABSTRACT
A new eadou echnique was de eloped wi h he p ima y aim o keeping he numbe o channels in he
on -end elec onics as low as possible when scaling up he sensi i e a ea o a Resis i e Pla e Chambe (RPC).
The eadou me hod he e p esen ed signi ican ly educes he dependence be ween he de ec o a ea and he
numbe o elec onic channels, wi hou subs an ial educ ion o i s pe o mance: a 30 ×30 cm2double s ack
mul i-gap iming RPC was ope a ed du ing weeks wi h cosmic ays, achie ing a 2D spa ial esolu ion well
below 1 mm and ime esolu ion lowe han 100 ps, while i s e iciency was kep abo e 98%.
1. In oduc ion
Resis i e Pla e Chambe s (RPCs) a e deployed ac oss di e se ields,
o ins ance in High Ene gy Physics (HEP) o pa icle igge ing and
acking o e la ge a eas, bu also o Pa icle Iden i ica ion (PID), i
buil o achie e high iming esolu ions [1]. In ac , wi h he capabili y
o measu ing simul aneously and accu a ely posi ion and ime, RPCs
could ac ually pe o m PID wi hou he need o addi ional de ec o s. In
he ield o he Muon Sca e ing Tomog aphy (MST), RPCs we e i s
employed in 2012 o in e he p esence o a small lead block wi hin a
scanned olume a he cen e o he de ec o [2]. Mo e ecen ly, he
MST echnique was used anew wi h RPCs, showing he p esence o
se e al high-Z ma e ials a e ew minu es o acquisi ion [3]. RPCs a e
indeed well sui ed o muog aphic echniques since hey can be buil
a ela i ely low cos , co e ing la ge a eas wi h high e iciency, spa ial
and ime esolu ions. Howe e , he on -end elec onics (FEE), which
cons i u e he majo expense o he de ec o , can each signi ican
amoun s when co e ing a su ace well abo e 100 m2, he a ea ha
mus be ins umen ed o scan, o example, a shipping con aine . A
no el RPC eadou codi ica ion was he e o e designed and es ed wi h
he main pu pose o add essing he a o emen ioned p oblem, pa ially
decoupling he numbe o FEE channels om he sensi i e a ea o he
de ec o , while keeping high spa ial and iming esolu ions.
2. No el eadou scheme
Wi h his new me hod, he s ips o he eadou elec odes a e
g ouped in pa allel by he Signal Me ging P in ed Ci cui Boa d (SM-
PCB) as shown in Fig. 1. In his way, each FEE channel eads ou se e al
s ips in pa allel, one pe g oup, leading o a signi ican dec ease o he
numbe o p eampli ie s, equi alen o he numbe o g oups c ea ed by
∗Co esponding au ho .
E-mail add ess: [email p o ec ed] (J. Sa ai a).
he SMPCB. Howe e , he ambigui y ha a ises by g ouping oge he
s ips o he hin-s ip eadou boa ds mus be disen angled in o de o
de e mine in which g oup he signal was in ac induced. This is he
ole o he wide-s ip eadou elec ode, which p o ides he 2D aw
posi ion o each e en , allowing he impinged g oup o be iden i ied in
bo h di ec ions.
In his se up, 120 hin s ips we e subdi ided in o 5 g oups, e-
sul ing in he use o only 24 p eampli ie s o ead ou all he s ips.
The educ ion ac o o he numbe o elec onic channels could be
e en highe , by simply adding mo e g oups o s ips in pa allel. In his
way, a la ge de ec o a ea would ha e been co e ed while keeping
he numbe o FEE channels unchanged, decoupling bo h quan i ies, as
p e ended wi h his echnique.
3. Expe imen al se up
Fig. 2 shows he se up, composed o a s ack o wo mul i-gap iming
RPCs and h ee eadou elec odes connec ed o he espec i e FEE.
Wi h an ac i e a ea o 30 ×30 cm2, he RPCs ha e 6 gas gaps each,
300 μm wide, and esis i e elec odes made o loa glass, 1 mm hick
(𝜌≈4×1012 Ωcm a 25 ◦C). The de ec o was ope a ed in open gas
low, wi h a gas mix u e o 95.5% o R-134a and 4.5% o SF6.
Two ypes o pick-up elec odes we e used in he se up:
•wide-s ip eadou PCB: cons i u ed by 5 s ips 5.9 cm wide and
pi ch o 6.1 cm; loca ed be ween he RPCs, i is ead ou by as
h ps://doi.o g/10.1016/j.nima.2024.169803
Recei ed 21 June 2024; Recei ed in e ised o m 3 Augus 2024; Accep ed 24 Augus 2024
Nuclea Ins umen s and Me hods in Physics Resea ch A 1068 (2024) 169803
A ailable online 26 Augus 2024
0168-9002/© 2024 Else ie B.V. All igh s a e ese ed, including hose o ex and da a mining, AI aining, and simila echnologies.
J. Sa ai a and A. Blanco
Fig. 1. P ocess o g ouping in pa allel he hin s ips o wo eadou elec odes
ans e sely o ien ed. A SMPCB is used o each di ec ion. The wide s ips used o
disen anglemen be ween g oups a e ep esen ed in o ange.
Fig. 2. Le : Top iew wi h he de ec o a he cen e and wo SMPCBs g ouping
oge he he hin s ips o he eadou elec odes ans e sely o ien ed; Righ : De ailed
iew o he s ack, om he bo om o he op: (1) hin-s ip PCB, (2) RPC_bo om, (3)
wide-s ip PCB, (4) RPC_ op, (5) ans e sal hin-s ip PCB.
p eamps (based on HADES FEE [4]) in bo h sides o he s ips,
p o iding simul aneously ime and coa se 2D posi ion1o he
in e ac ions occu ing in he sensi i e olume o he de ec o , and
making i possible o iden i y unequi ocally, o each e en , he
g oup o hin s ips whe e he signal induc ion ook place;
• hin-s ip eadou PCB: composed o 120 s ips 1.54 mm wide
and 2.54 mm pi ch; wo o hem we e used, one loca ed a he
bo om o he s ack wi h he s ips o ien ed in he same di ec ion
as he wide ones, and a second boa d a he op o he s ack, wi h
he s ips ans e sely o ien ed wi h espec o he p e ious ones;
bo h pick-up elec odes a e connec ed o a SMPCB, educing he
numbe o channels om 120 o 24 (see Sec ion 2); each o hese
channels (2 ×24) is hen ead ou by slow elec onics2(cus om-
designed), in eg a ing bo h componen s o he induced signals
(elec onic & ionic), allowing, in his way, o submillime ic
p ecision in posi ional measu emen s in bo h dimensions: X & Y.
The de ec o was ope a ed du ing se e al weeks wi h cosmic ays,
using a coincidence igge gene a ed ex e nally by scin illa o s loca ed
1ha ing ime measu emen s om bo h s ip ends ( on ( ) and back (b)),
one can compu e wo quan i ies: he longi udinal posi ion along he s ips
(𝑌= (𝑇𝑓−𝑇𝑏)∕2) and he ime o he e en (𝑇= (𝑇𝑓+𝑇𝑏)∕2). The cha ge is also
measu ed ( ia he Time o e Th eshold (ToT) me hod) and used o de e mine
he ans e se posi ion ela i e o he s ips ( h ough cha ge in e pola ion).
2wi h a cha ge collec ion and in eg a ion p ocess ex ending o e a ew
mic oseconds, he elec onics pe o m well due o he in insically low a e o
he muons a sea le el (∼1μ/cm2/min).
Fig. 3. Le : Time esolu ion o he RPCs, dec easing om 85 o 74 ps (𝜎) a e emo al
o he scin illa o con ibu ion; Righ : On he igh side, he image shows a 2D posi ion
map o he wo g oups o scin illa o s (p ojec ed shadows). A close-up iew is shown
a he bo om side, whe e he loca ion o he nylon mono ilamen space s o he RPCs
is iden i ied by ed a ows. On he le side, he 2D e en maps o he SiPMs and PMTs
a e p ojec ed on o he Y axis, p o iding clea e e idence o he p esence o he 300-μm
gas gap space s.
di ec ly abo e and below he RPCs. Fou plas ic scin illa o s we e used,
wo pa allelepipeds o 8 ×4×1 cm3and wo 8 ×2×3 cm3, coupled
o silicon pho omul iplie s (SiPM) and pho omul iplie ubes (PMT),
espec i ely. The educed elec ic ield was se o app oxima ely 379
Td (a ound 2.75 kV/gap, 92 kV/cm) and he espec i e e iciency was
sligh ly abo e 98%.
4. Resul s
The ime p ecision o he de ec o was de e mined by measu ing
he ime di e ence be ween he RPCs and one o he scin illa o s. A
ime esolu ion o 74 ps (𝜎) was achie ed (see Fig. 3) a e applying
he ime walk co ec ion and emo ing he scin illa o con ibu ion. A
2D posi ion map o he scin illa o e en s is also p o ided in Fig. 3.
In he econs uc ed image o he scin illa o s, i is possible o iden-
i y he p esence o he 300 μm-diame e space lines used be ween
he glass elec odes o he RPCs, p o iding a clea indica ion o he
submillime ic spa ial esolu ion o he de ec o .
5. Applica ion - Muon sca e ing omog aphy
Wi h he p oposed codi ica ion, i is possible o decouple wo quan-
i ies usually di ec ly co ela ed: he de ec o su ace and he numbe
o FEE channels needed o ins umen he espec i e sensi i e a ea. The
decoupling is pa ial since, as seen p e iously, he channels connec ed
o he wide s ips ha e o inc ease p opo ionally wi h he numbe
o g oups o hin s ips added in pa allel. Howe e , due o he la ge
dimensions o he s ips used o disen angling he g oups, he inc ease
o elec onic channels achie ed wi h his echnique is by a lowe han
i each hin s ip would ha e been connec ed o i s own channel.
Conside ing he abo e, and knowing ha he FEE is he d i ing cos
o gaseous de ec o s such as RPCs, he new eadou scheme ou lined in
his documen can be used in any applica ion equi ing la ge sensi i e
a eas. Typical applica ions a e linked o he HEP ield, howe e ano he
s ong candida e is he MST, since:
• he a ea equi ed o he MST o shipping con aine s is a ound
130 m2, on pa wi h he 141 m2co e ed by RPCs in he ALICE
expe imen a CERN [5];
• he spa ial esolu ion equi emen s o a muon acking de ec o
is dic a ed by he p ecision needed o measu e he small sca e -
ing angles be ween he incoming and exi ing muon ajec o ies;
submillime ic spa ial esolu ion allows bo h: (1) keeping he
dis ance be ween de ec o planes, below and abo e he iducial
egion, a ew ens o cen ime e s (maximizing he de ec o accep-
ance and i s compac ness), (2) ha ing he abili y o de ec small
shi s o he muon di ec ion, in he o de o one deg ee (a ound
17 m ad).
Nuclea Ins . and Me hods in Physics Resea ch, A 1068 (2024) 169803
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J. Sa ai a and A. Blanco
Fig. 4. Two s ep simula ion using he FLUKA cosmic ay sou ce and Ea h a mosphe ic
model [6]; geome y: MST acking de ec o o ou 2 m2RPCs, wi h a dis ance o 45 cm
be ween planes and a ungs en block o 10 ×10 ×10 cm3a he cen e ; applied
es ic ions: only sca e s abo e 1.5◦(Le ), emo ing also muons below 500 MeV
(Righ ).
•a ime esolu ion below 100 ps allows, ia he Time O Fligh
(TOF) echnique, o ejec low ene gy muons (a ew hund ed o
MeV) since hey a e highly sca e ed wi hin he ma e ial budge
o he de ec o , esul ing in alse e en s all a ound he iducial
egion. The impac o emo ing low ene gy muons, ob ained ia
Mon e Ca lo calcula ion, is illus a ed in Fig. 4.
6. Conclusion
A new eadou scheme was de eloped o educe he numbe o FEE
channels (d i ing cos o he de ec o ), and es ed wi h a mul i-gap
iming RPC o 30 ×30 cm2. Wi h he p esen ed codi ica ion, 24 +
24 cha ge sensi i e p eamps we e used o ead ou 120 + 120 hin
s ips ans e sely o ien ed, p o iding submillime ic 2D posi ioning.
An addi ional pick-up elec ode was used wi h 5 + 5 cu en sensi i e
as p eamps o ead ou 5 la ge s ips and esol e he ambigui y
in oduced by his echnique. The expe imen al se up made i possible
o achie e a 2D high spa ial esolu ion (<1 mm), along wi h a ime
p ecision o 74 ps (𝜎) enabling PID, and an e iciency abo e 98%. The
nex s ep includes using he same eadou me hod wi h a la ge scale
RPC (120 ×90 cm2), wi hou inc easing he numbe o FEE channels
connec ed o he hin s ips, i.e. keeping he numbe o elec onic
channels independen o he sensi i e a ea o he de ec o , as in ended.
Decla a ion o compe ing in e es
The au ho s decla e ha hey ha e no known compe ing inan-
cial in e es s o pe sonal ela ionships ha could ha e appea ed o
in luence he wo k epo ed in his pape .
Acknowledgmen s
This wo k was suppo ed by he Founda ion o Science and Tech-
nology (Po ugal) (CERN/FIS-INS/0006/2021) and he Eu opean Un-
ion’s Ho izon 2020 Resea ch and Inno a ion p og amme unde G an
Ag eemen AIDAinno a n.◦101004761.
Re e ences
[1] A. Akindino , e al., NIM A 602 (2009) 709–712.
[2] P. Baesso, e al., JINST 7 (2012) P11018.
[3] J. Sa ai a, e al., NIMA 1050 (2023) 168183.
[4] D. Bel e , e al., IEEE T ans. Nucl. Sci. 57 (2010) 2848–2856.
[5] The ALICE Collabo a ion, e al., JINST 3 (2008) S08002.
[6] G. Ba is oni, e al., Ann. Nucl. Ene gy 82 (2015) 10–18.
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