Abstract   Neutron emission during the development of hadronic showers can be used to discriminate between electromagnetic and hadronic interacting particles impinging a calorimeter. A neutron detector based on a high efficiency 'active moderator' is presented and its performance is evaluated with the aid of Monte Carlo simulation

A. Viciani

E. Vannuccini

G. Castellini

G. Sorichetti

Giacomo Sguazzoni

Lorenzo Bonechi

M. Bongi

O. Adriani

P. Papini

P. Sona

P. Spillantini

Raffaello D'Alessandro

S. B. Ricciarini

S. Bottai

English

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ARTICLE IN PRESSNuclear Instruments and Methods in Physics Research A 617 (2010) 464–466Contents lists available at ScienceDirectNuclear Instruments and Methods inPhysics Research A0168-90doi:10.1 CorrE-mjournal homepage: www.elsevier.com/locate/nimaAn innovative approach to compact calorimetry in space, NEUCALS. Bottai a,, G. Castellini a, P. Papini a, G. Sguazzoni a, E. Vannuccini a, O. Adriani b, L. Bonechi b, M. Bongi a,R. D’Alessandro b, S. Ricciarini a, G. Sorichetti b, P. Sona b, P. Spillantini b, A. Viciani ba INFN Sezione di Firenze, via Sansone, 1-I-50019 Sesto F. no (FI), Italyb University of Florence, via Sansone, 1-I-50019 Sesto F. no (FI), Italya r t i c l e i n f oAvailable online 27 October 2009Keywords:Neutron detectorsImaging calorimeterHadron rejection02/$ - see front matter & 2009 Elsevier B.V. A016/j.nima.2009.10.089esponding author.ail address: bottai@fi.infn.it (S. Bottai).a b s t r a c tNeutron emission during the development of hadronic showers can be used to discriminate betweenelectromagnetic and hadronic interacting particles impinging a calorimeter. A neutron detector basedon a high efficiency ‘active moderator’ is presented and its performance is evaluated with the aid ofMonte Carlo simulation.& 2009 Elsevier B.V. All rights reserved.1. IntroductionThe development of techniques for the detection of neutrons inconnection with the use of compact calorimeters (that may not beable to completely absorb the incident hadron), has become veryimportant with the new generation of astroparticle spaceexperiments, since these types of calorimeters must still dis-criminate, with a high rejection power, between electromagneticand hadron showers.2. Simulation of neutron emissionThe idea of enhancing calorimeter discrimination by measur-ing the neutron component of the showers, was first tried withthe PAMELA [1] experiment on satellite. There an ‘old’ styleneutron detector was placed at the back-end of the calorimeter.Unfortunately, traditional neutron detectors are sensitive mainlyto the low energy component of the neutrons produced in thecalorimeters, the one that has been moderated by, for example,polyethylene and have very low efficiency. NEUCAL instead, willdetect signals coming from the actual neutron moderationprocess (using a de facto active moderator), so as to significantlyincrease the performance of the detector. The detector itself willbe a composite structure where various techniques are combinedto produce an optimized detector for space applications. Duringthe development of hadronic showers inside calorimeters,neutrons are expected to be produced both by nuclear excitationsand by hadronic interactions. Electromagnetic showers can alsoproduce neutrons via the giant resonance mechanism and viaphoto-nuclear interactions in general. In order to preciselycharacterize the neutron component associated with the differentll rights reserved.types of showers a detailed Monte Carlo simulation has beenperformed using the FLUKA simulation package [3]. As a ‘testdetector’ the CALET [2] BGO homogeneous calorimeter, consistingof a BGO tower (60 cm 60 cm 30 cm height) with a verticaldepth of approximately 30 0 has been simulated. For eachsimulated event the produced neutrons have been propagated tillthey reached the outside of the calorimeter. The energy, directionand arrival time of each neutron exiting the calorimeter from thebottom side where the NEUCAL moderator is placed are loggedfor further use. In Fig. 1 the number of neutrons exiting fromthe calorimeter is shown for 1 TeV interacting protons and for400 GeV electrons (1 TeV proton showers on average give thesame calorimetric signal as 400 GeV electrons in BGO). Therejection factor achievable for hadronic showers can be as highas  103 just considering the neutron counting. The bulk ofneutrons originate from the excitation and de-excitation ofnuclei and exhibit a maximum in the MeV energy region(Fig. 2). Many neutrons undergo moderation before escapingand their energy is consequently degraded down to the eV energyregion. Some neutrons can also be produced promptly in thehadronic interactions along the shower core, with an energythat can reach that of the primary proton. The highest energyneutrons (E410 MeV) arrive close in time with respect to thecharged component of the shower, while the low energy andmore abundant component arrives in the neutron detector with adelay which ranges from 10 to 1000 ns and thus can be easilyidentified. The figure for electromagnetic showers is similar butwith a much reduced contribution for the prompt neutronemission.3. NEUCAL neutron detectorThe NEUCAL neutron detector concept is presented in Fig. 3and is based on the use of two active detectors: layers of plasticscintillators and arrays of 3He proportional counter tubes.ARTICLE IN PRESS2502001501005000 200 400 600 800 1000 1200 1400 1600 1800 2000Number of outgoing neutrons per even1 TeV protons400 GeV electrons3025201510500 10 20 30 40 50 60 70 80 90 100Number of outgoing neutrons per eventFig. 1. Neutron yield outside the CALET calorimeter for 1 TeV interacting protons and 400 GeV electrons.Fig. 2. Energy distribution of neutrons exiting from the CALET calorimeter in caseof 1 TeV interacting protons.Fig. 3. A scheme of the proposed NEUCAL neutron detector.RESPONSE TO SINGLE NEUTRONS (1000 EVENTS)60050040030020010000 2 4 6 8 10 12TOTAL ENERGY RELEASED IN SCINTILLATORS (MEV)IDEntriesMeanRMSIDEntriesMeanRMS2410000.97500.62592310003.7053.8543503002502001501005000 2 4 6 8 10 12TOTAL ENERGY RELEASED IN SCINTILLATORS (MEV)Fig. 4. Response of 12 scintillator layers to single neutron. The figure on top showsthe energy released in all the scintillators by 1 MeV neutrons. The figure on thebottom refers to the response in case of 10 MeV neutrons.S. Bottai et al. / Nuclear Instruments and Methods in Physics Research A 617 (2010) 464–466 465Neutron–proton elastic scattering in the plastic scintillatorsprovide the active neutron moderation. Scattered protonsrelease their energy inside the scintillators and hence providethe signal associated with the neutron moderation process. Themoderated neutrons can be detected by means of nuclear capturefollowed by 0.765 MeV proton emission in the 3He counters.The response to single neutron has been simulated for neutrondetector composed of 12 scintillators layers. As can be seen inFig. 4 neutrons with energy up to few MeV are fully moderatedand detected with high efficiency. In case of 10 MeV neutrons adetectable signal in the scintillators appear for 70% of the eventsbut only 10% of them are fully moderated and detectable by the3He tubes.ARTICLE IN PRESSS. Bottai et al. / Nuclear Instruments and Methods in Physics Research A 617 (2010) 464–466466A prototype of NEUCAL composed of eight scintillators layers andfive 3He tubes is under construction and is expected to be tested atCERN at the end of summer 2009. The test will be performed using acalorimeter in front of the neutron detector in such a way the wholeprocess of neutron emission, transport and detection can be verifiedagainst the simulations that have already been performed.References[1] P. Picozza, et al., Astropart. Phys. 27 (2007) 296.[2] T. Shoji, et al., J. Phys. Conf. Ser. 120 (2008) 062020.[3] B. Giuseppe, et al., AIP Conf. Proc. 896 (2007) 31 /http://www.fluka.org/fluka.phpS.

An innovative approach to compact calorimetry in space, NEUCAL

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An innovative approach to compact calorimetry in space, NEUCAL

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