Cosmic ray detectors for high schools in France

Nicolas Arnauda,∗, Corinne Beratb, Jose Bustoc, Gabriel Chardind, Denis Dumorae, Eric Kajfaszc,Antoine Letessier-Selvonf, Benoit Lotte, Arnaud Marsollierd, Jean-Christophe Pelhateg, Morgan Piezelh,

Gerard Tristramf

aLAL, Univ Paris-Sud, CNRS/IN2P3, Orsay, FrancebLPSC, Universite Grenoble-Alpes, CNRS/IN2P3, France

cCPPM, Aix-Marseille Universite, CNRS/IN2P3, Marseille, FrancedCNRS/IN2P3, 3 rue Michel-Ange, 75016 Paris, France

eCENBG, CNRS/IN2P3 & Univ. Bordeaux, 33170 Gradignan, FrancefLPNHE, UPMC, Universite Paris Diderot, CNRS/IN2P3, France

gProfesseur de physique-chimie, lycee Jean-Pierre Vernant, 92310 Sevres, FrancehProfesseur de physique-chimie, lycee Camille Claudel et Universie de Technologie de Troyes, 10000 Troyes, France

Abstract

In France, the CNRS National Institute for Nuclear Physics and Particle Physics (CNRS/IN2P3) is involved ineducational actions promoting the use of cosmic ray detectors in high schools. These projects are ran in close collabo-ration with teachers to ensure that they match the letter and spirit of the curriculum. These instruments, lent to teachersfor periods ranging from a few weeks to a few years depending on the measurements possible with them, complementnicely the lectures. They allow the students to sense the elementary particles and to understand the problems raised bytheir detection. The well-recognized cosmodetecteur and the new COSMIX detector are described in the following,together with the COSMAX software framework, which gives a direct access to the Fermi satellite data.

Keywords:Cosmic rays, Detectors, Education, Gamma rays, Outreach

1. Introduction

After some years of eclipse, topics related to particlephysics – special relativity, the lifetime of the muon, theradioactive β decay, etc. – are now back in the Frenchhigh school physics curriculum. Introducing these sub-jects at high-school level is a real challenge. In addi-tion to the limited knowledge of students at this level inmathematics and physics, there is no easy window ontothe world of the infinitely small. As radioactive sourcesare now forbidden in schools, cosmic rays remain theonly way to show particles to teachers and students andto study their interactions with matter.

∗Corresponding authorEmail address: narnaud@lal.in2p3.fr (Nicolas Arnaud)

A good detector for an educational experiment basedon cosmic rays should be compact and light enough tobe installed in a classroom, at the same time both effi-cient and robust, and, last but not least, its use shouldbe as straightforward as possible. In France, the Na-tional Institute for Nuclear Physics and Particle Physicsof the CNRS (in short CNRS/IN2P3) is using its highexpertise in particle physics detectors to design, buildand maintain cosmic ray detectors for high schools. Thetwo main such projects, the ”cosmodetecteur” [1] andthe ”COSMIX” detector [2], are described in the fol-lowing. Devices more suited to outreach exhibits, likethe ”Cosmophone” or the ”Cosmic Arch”, exist as well.

As the number of cosmic ray detectors available toteachers is limited, complementary approaches are pur-sued in parallel. Following the successful example

Available online at www.sciencedirect.com

Nuclear and Particle Physics Proceedings 273–275 (2016) 1233–1238

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www.elsevier.com/locate/nppp

http://dx.doi.org/10.1016/j.nuclphysbps.2015.09.196

of the LHC-based International Masterclasses [3], theCOSMAX software framework [4] is being developedto give an easy access to the data of the Fermi satelliteand to the associated analysis tools. This new project isbriefly described at the end of these proceedings.

Figure 1: Poster of the 2012 CNRS/IN2P3 exhibit, called ”The mys-tery of the Cosmic rays”. The exhibit first shows a timeline of thestudy of the cosmic rays, from the first observations of electroscopeself-discharges to the moment, shortly after World War II, when parti-cle accelerators replaced cosmic ray observatories as primary tools tostudy the elementary particles. The second part of the exhibit presentsa panorama of the current experiments and techniques used to studythe energetic particles coming from the cosmos.

Finally, a low-cost and easily transported exhibit [5]has been prepared by the CNRS/IN2P3 in 2012 to cele-brate the 100th anniversary of the cosmic ray discoveryby Viktor Hess – see the exhibit poster in Fig. 1. In-terested teachers can either loan a copy of the exhibithosted by one of the participating CNRS/IN2P3 labo-ratories, or print the panels on their own to get a per-manent copy. The high-definition files of the 16 panelsmaking up the exhibit are available for free on request.

2. The cosmodetecteur

In France, a collaboration started several years agobetween the CNRS/IN2P3 and ”Sciences a l’Ecole” [6],a ministerial plan from the French Education Ministry.Large cosmic ray detectors called cosmodetecteurs are

designed and built in the Marseille CNRS/IN2P3 labo-ratory (the ”Centre de Physique des Particules de Mar-seille”, in short CPPM). A national scientific committeecomposed of researchers, teacher-researchers, inspec-tors and secondary teachers attributes the most appro-priate teaching materials for classroom use.

2.1. The cosmic ray detector

Figure 2: A cosmodetecteur.

A cosmodetecteur consists in three mobile plasticscintillators, each coupled to a photomultiplier (PMT)on top – see Fig. 2. The scintillators can be arrangedin different geometries in order to perform several com-plementary experiments (flux and angular distributionof the cosmic rays, Auger-like [7] and Rossi [8] showerexperiments, etc.). The data acquisition (DAQ) systemis able to trigger on twofold or threefold time coinci-dences between scintillator plates, which efficiently re-moves the background. A Labview interface is used tosteer the detector, to monitor the data taking and recorddata in ASCII format. Two additional elements are in-cluded with the cosmodetecteur – see Fig. 3.

• A Cherenkov radiator coupled to a PMT via a lightguide, which is used to prove that cosmic muonscome from above: students can note that depend-ing on the inclination of the detector, the PMT de-tects photons or not. An explanation of this exper-imental fact can be found knowing that Cherenkovphotons are emitted in a cone along the path of acosmic muon whose speed exceeds the speed oflight in the radiator.

• A thick plastic scintillator tube (2.3 liters) which isused to measure the muon lifetime: when a muonenters in the scintillator and stops, it triggers a firstsignal; later, it decays into an electron or a positron

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No counting

Counting

PMT

Measured � lifetime = 2.26 �s

Cherenkov radiator Thickin a light guide scintillator

Figure 3: Two more experiences possible with the cosmodetecteur. Left: a demonstration that cosmic muons come from above; right: a measure-ment of the muon lifetime.

(and a neutrino-antineutrino pair) which triggersthe second signal. As the timing resolution is atthe level of a few tens of ns, the histogram of thedifference between the two timing signals can be fitby an exponential distribution whose parameter iscompatible with the muon lifetime – about 2.2 μs.

The full price of a cosmodetecteur is about 8,000 e,including a laptop and a transportation box.

2.2. Partnership with Sciences a l’Ecole

Sciences a l’Ecole (”Science at School”) is a Frenchministerial plan created jointly by the National Educa-tion Ministry and the Higher Education and ResearchMinistry in March 2004, which purpose is to renew theteaching of sciences in the French school system, fromsecondary schools to classes preparing for entrance tothe French ”Grandes Ecoles”. It therefore contributes tothe development of scientific vocations among young-sters, as well as promotes sciences as a way for themost part to achieve successful studies. Its action isbased on three main pillars. First, it provides a finan-cial support to projects bringing scientists to classes orcreating educational resources. Then, scientific equip-ments are lent to high schools. The ”Cosmos a l’Ecole”(”Cosmos at School”) program [9] is in charge of thecosmodetecteurs while similar programs exist for otherfields: astronomy, seismology, genetics, meteorology,etc. Each program, called also equipment plan, is basedupon a partnership between ”Sciences a l’Ecole” and the

different research institutes of the particular field. Fi-nally, the plan encourages teams of students to take partin science challenges at the national level and drives theFrench representation to international ones.

2.3. Educational activities based on the cos-modetecteur

The teachers selected by Cosmos a l’Ecole are trainedprior to receiving the cosmodetecteur. They follow aone week-long seminar at CERN – the French part ofthe High School Teacher program [10], sponsored bythe CNRS/IN2P3 and Sciences a l’Ecole and whichinvolves about 35 participants each year – plus a 3-day technical course in CPPM to learn how to use theapparatus. Each teacher which has been lent a cos-modetecteur benefits from an educational leaflet whichincludes an introduction to particle physics, a descrip-tion of the detector, various information about its op-eration and the data analysis methods, such as a list ofsuggested measurements to carry out. They can alsoget advices from a CNRS/IN2P3 physicist who acts as amentor (and not as an operator for the cosmodetecteur),plus some support from the teacher academic author-ity. Meetings are regularly organized to get the teach-ers’ feedback and to allow them to present to colleaguesthe educational activities they have developed based onthe detector.

The cosmodetecteur network is shown in Fig. 4: itcounts 46 high schools (representing more than 1,100students) from 18 out of the 26 education academies.

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� and � : high schoolsequipped before 2013

� : high schoolsequipped in 2014

Figure 4: High schools equiped with a cosmodetecteur.

There are currently 17 such detectors in France and 15more will be released in 2014 thanks to the French ”Pro-gramme d’Investissements d’Avenir” that enables thefunding. These devices are operated over long periodsin order to fully exploit their potential. Therefore, theyremain several months in the same location, under theresponsibility of reference teachers educating their col-leagues about using them. By default, a team of teachersgets a cosmodetecteur for three years and usually makesit available, first in their high school and then locally.

The cosmodetecteur is routinely used by teachers asa part of their pedagogical projects. As an example, inthe framework of the 2010 French Physics Olympiad,a project based on a cosmodetecteur has been awarded.With the new scientific high-school curriculum, the de-tectors are now used during regular teaching hours andnot just for research projects or hands-on activities.In addition to the physics measurements highlightedabove, the cosmodetecteur also brings a true hands-onexperience to teachers. Prior to using the detector, theyhave to calibrate the PMTs by performing the so-called”plateau measurements” (raising in steps the PMT high-voltage until the detection efficiency of the correspond-ing scintillator plates flattens off at a constant level closeto 100%). Moreover, they have to understand signal dis-crimination and coincidence measurements.

2.4. ProspectsIn the medium term, the teacher network will have

to be strengthened. Two initiatives have already beentaken to meet this challenge: first, an online forum

has been created to ease the teacher exchanges; thentwo days of joint data taking have been organized in2014. Other future goals for the program are to or-ganize more formations for teachers and to producenew educational resources related to particle physics.This requires new synergies with other existing edu-cation/outreach projects like the International Master-classes or the ”Passeport pour les deux infinis”. Indeed,all these activities are coordinated by the ”Ecole desdeux infinis” [11] at the CNRS/IN2P3 level.

3. The COSMIX case

Two years ago, the Gradignan CNRS/IN2P3 labora-tory (”Centre Etudes Nucleaires de Bordeaux Gradig-nan”, in short CENBG) started developing a differentcosmic ray detector, called COSMIX. Its main innova-tion is to be highly portable as it fits in a small caseand is plug-and-play. It allows a quick and easy intro-duction to cosmic rays to audiences which do not haveaccess yet to a cosmodetecteur.

3.1. The detector

Display

CsI(Tl) bar

CsI(Tl) bar

Electronics

DAQ• Display• Storage• GPS• Altimeter

Control

Figure 5: COSMIX case prototype.

Figure 5 shows the contents of a COSMIX case. Thedetector uses two scintillator bars made by cutting intwo a spare CsI(Tl) bar from the Fermi-LAT satellite de-tector, connected to Hamamatsu PIN diodes and customelectronics – the DAQ system is based on an Arduinomicro-controller. It includes a GPS, a pressure-meterand a DAQ system allowing data to be stored onto a SDmemory card. It is powered by a simple USB connec-tion, provided for instance by a laptop, and drives about300 mA. The total weight is below 4 kg. The cost of a

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Single rate Coincidences[One bar is movable]

~1 evt/s ~0.4 evt/s

Figure 6: The two measurements possible with the COSMIX case: single or coincidence rates.

COSMIX case is about 1,000 e; a reduction of a factortwo has been achieved by recycling existing detectorsand electronics.

3.2. Measurements

No setting nor calibration is required to take data witha COSMIX case – just to power it. The energy depositedin a bar by a cosmic muon is about 12 MeV, a valuemuch higher than those due to background. Therefore,all analog-triggered signals come from real muons. Twodata taking modes, illustrated in Fig. 6, are possible: thesingle bar rate is about 1 event/second while the coinci-dence rate (one bar is movable and can thus be put ontop of the other) decreases to about 0.4 event/second.Moreover, as all high schools in France have digitalscopes nowadays, they can use them to trigger on thePIN diode outputs to see the signals associated with sin-gle or coincidence detections.

Figure 7 shows an example of a COSMIX measure-ment performed over several hours. The huge rate vari-ation corresponds to a commercial flight, while the de-crease at time ∼24000 s can be traced to a trip in theParis subway. Smaller but clearly visible rate variationshave also been recorded during private plane flights.

Many applications are possible for this detector: shortintroduction to cosmic rays in classrooms, demonstra-tions at the end of a public lecture or during an exhibit,etc. A collaborative website will allow participatingteachers to publish their data while describing how theywere acquired. One example: teachers from everywherein France could be able to study the cosmic ray rates at

Rat

e (p

artic

les/

min

ute)

Time (s)

Figure 7: Example of measurement with the COSMIX case.

the different floors of the Eiffel tower, hence reproduc-ing Theodor Wulf’s experiment from 1909 [12].

3.3. Rolling-out the COSMIX detectors

In 2013, three test cases (among which two werefunded by Sciences a l’Ecole) circulated in the Bor-deaux area: more than 1,000 students from 15 highschools used the COSMIX detector and their feedbackhelped improving its design. One of these prototypes isnow in the Reunion Island (in the Indian Ocean, east ofthe Madagascar island), a place where there are very ac-tive teachers interested in particle physics, but which istoo far from mainland France to get a cosmodetecteur.This example illustrates the complementarity betweenthe two types of detectors.

This year 2014 is the first mass production year forthe COSMIX case: 10 have been produced for the Paris

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area (support of the Ile-de-France region and of the ”Di-agonale Paris Saclay”) and 8 for CNRS/IN2P3 labora-tories. There are enough spare scintillators to produce24 more such cases in the near future.

4. COSMAX

The COSMAX (”COSMic ACCelerators”) project issoftware-based and developed by the same CENBGteam as the COSMIX case. It is based on a suite oftools installed on a ready-to-use linux virtual machine –or directly on linux. It aims at providing access to thevery variable gamma ray sky using the Fermi-LAT data.These data are public, readily available, easy to grasp(photon detection time, measured energy and recon-structed incoming direction on the sky) and all-sky. Thedata analysis tools are the same than those used by thescientific community. They allow the users to producetime-resolved maps or animations and to study manytransient phenomena like blazars, gamma ray bursts orpulsars. Figure 8 shows one example of the sky mapswhich can be produced in the COSMAX framework.

Figure 8: Sky map integrating one week of Fermi data produced withthe COSMAX framework. At coordinates L = 86.1 and B = −38.2one can see the very variable 3C 454.3 blazar (discovered by the Fermisatellite), at that time the brightest gamma source in the sky.

Now that the package is fully-functional, the next stepwill be to improve the user interface to allow users withonly a basic knowledge of computing to use this frame-work and achieve results. Indeed, our experience hasshown that the computing skill of high-school teachersare very variable.

5. Conclusions

The CNRS/IN2P3 and its partners, among which Sci-ences a l’Ecole, are developing educational projectsbased on particles coming from the cosmos: both

(charged) cosmic rays and photons. This is part of anCNRS/IN2P3 global outreach effort targeting teachers,students and the general audience.

The well-recognized cosmodetecteur project starteda decade ago. It combines the CNRS/IN2P3 physicaland technical knowledge with the Sciences a l’Ecoleeducational expertise to produce large cosmic detectorslent to selected teachers which then get some support(resources, advices) to operate these complex devices.Thanks to this project, more and more high-school stu-dents and teachers will discover particle physics throughcosmic rays. The new IN2P3 COSMIX detector, mo-bile and easy to use, is a different tool which offersnew opportunities to provide an introduction to cosmicrays to audiences which do not have access to a cos-modetecteur. Finally, the COSMAX software projectallows to study the gamma rays detected by the Fermisatellite by making use of the fact that these data aresimple to understand and easy to manipulate.

Acknowledgment

The authors would like to thank Sciences a l’Ecolefor its support of CNRS/IN2P3 outreach activities, andin particular Mrs. Solene Chevalier-Thery and ClaireBonnoit-Chevalier.

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