Passive magnetic cylindrical shielding at gauss-range static fields

A study has been performed in order to find the optimal solution for the magnetic shielding of the 10 in. photomultipliers which will be used in the Double Chooz neutrino experiment under a very low magnetic field (less than 2 G). The results obtained with analytical and numerical calculations are compared with measurements made using test prototypes of several magnetic materials, with different dimensions and from different manufacturers. An exhaustive analysis of the magnetic materials was needed to understand the observed disagreement between calculations and test results obtained at low field values.     

The extended-track event reconstruction for MiniBooNE

The Booster Neutrino Experiment (MiniBooNE) searches for ν_μ→ν_e oscillations using the neutrino beam produced by the FNAL Booster synchrotron. The array of photomultiplier tubes (PMTs) lining the MiniBooNE detector records Cherenkov and scintillation photons from the charged particles produced in neutrino interactions. We describe a maximum likelihood fitting algorithm used to reconstruct the basic properties (position, direction, energy) of these particles from the charges and times measured by the PMTs. The likelihoods returned from fitting an event to different particle hypotheses are used to categorize it as a signal ν_e event or as one of the background ν_μ processes, in particular charged current quasi-elastic scattering and neutral current π⁰ production. The reconstruction and event selection techniques described here can be applied to current and future neutrino experiments using similar Cherenkov-based detection.     

A detector system for the study of intermediate energy neutrino interactions

A 15 t fine-grained neutrino detector and high efficiency anticoincidence system are in operation at the LAMPF beam stop, an intense source of neutrinos with a maximum energy of 53 MeV. The primary use of this equipment is in an experiment which is directed towards the observation and cross section measurement of the ν_ee⁻ elastic scattering reaction. The design, operation, and performance of the apparatus is reported.     

MARE-1 in Milan: Status and Perspectives

The international project MARE (Microcalorimeter Array for a Rhenium Experiment) aims at the direct and calorimetric measurement of the electron neutrino mass with sub-eV sensitivity. Although the baseline of the MARE project consists in a large array of rhenium based thermal detectors, a different option for the isotope is also being considered. The different option is ¹⁶³Ho. The potential of using ¹⁸⁷Re for a calorimetric neutrino mass experiment has been already demonstrated. On the contrary, no calorimetric spectrum of ¹⁶³Ho has been so far measured with the precision required to set a useful limit on the neutrino mass. The first phase of the project (MARE-1) is a collection of activities with the aim of sorting out both the best isotope and the most suited detector technology to be used for the final experiment. One of the MARE-1 activities is carried out in Milan by the group of Milano–Bicocca in collaboration with NASA/GSFC and Wisconsin groups. The Milan MARE-1 arrays are based on semiconductor thermistors, provided by the NASA/GSFC group, with dielectric silver perrhenate absorbers, AgReO₄. The experiment, which is presently being assembled, is designed to host up to 8 arrays. With 288 detectors, a sensitivity of 3 eV at 90% CL on the neutrino mass can be reached within 3 years. This contribution gives an outlook for the MARE activities for the active isotope selection. In this contribution the status and the perspectives of the MARE-1 in Milan are also reported.     

A study of reactor neutrino monitoring at the experimental fast reactor JOYO

We carried out a study of neutrino detection at the experimental fast reactor JOYO using a 0.76 tons gadolinium loaded liquid scintillator detector. The detector was set up on the ground level at 24.3 m from the JOYO reactor core of 140 MW thermal power. The measured neutrino event rate from reactor on-off comparison was 1.11±1.24(stat.)±0.46(syst.) events/day. Although the statistical significance of the measurement was not enough, backgrounds in such a compact detector at the ground level were studied in detail and MC simulations were found to describe the data well. A study for improvement of the detector for future such experiments is also shown.     

Cryogenic design and operation of liquid helium in an electron bubble chamber towards low energy solar neutrino detectors

We are developing a new cryogenic neutrino detector: electron bubble chamber, using liquid helium as the detecting medium, for the detection of low energy p-p reaction neutrinos (<420 keV), from the Sun. The program focuses in particular on the interactions of neutrinos scattering off atomic electrons in the detecting medium of liquid helium, resulting in recoil electrons which can be measured. We designed and constructed a small test chamber with 1.5 L active volume to start the detector R&D, and performed experimental proofs of the operation principle. The test chamber is a stainless steel cylinder equipped with five optical windows and ten high voltage cables. To shield the liquid helium chamber against the external heat loads, the chamber is made of double-walled jacket cooled by a pumped helium bath and is built into a LN₂/LHe cryostat, equipped with 80 K and 4 K radiation shields. A needle valve for vapor helium cooling was used to provide a 1.7-4.5 K low temperature environments. The cryogenic test chamber has been successfully operated to test the performance of Gas Electron Multipliers (GEMs) in He and He + H₂ at temperatures in the range of 3-293 K. This paper will give an introduction on the cryogenic solar neutrino detector using electron bubbles in liquid helium, then present the cryogenic design and operation of liquid helium in the small test chamber. The general principles of a full-scale electron bubble detector for the detection of low energy solar neutrinos are also proposed.     

Influence of specimen size and microstructure on the fracture toughness of a martensitic stainless steel

The fracture toughness of alloy HT-9,² a martensitic stainless steel under consideration for fast reactor and fusion reactor applications, was determined from circular compact tension specimens using the multi-specimen R-curve method. Specimens with thicknesses of 11.94, 7.62 and 2.54mm and widths of 23.88 and 11.94 mm were tested to investigate the effects of specimen size on fracture toughness. The test results obtained from all specimens are in good agreement and thickness requirements for a valid J_1c test are satisfied. The experiment indicates that small specimens of HT-9 may be used for post-irradiation fracture toughness testing.Fractographic examination of the fracture surfaces reveals that fracture in HT-9 is significantly influenced by delta ferrite stringers present in the material. The fracture surface examination and crack opening displacement measurements for specimens tested at various temperatures are consistent with the temperature dependence of the J_1c results.     

Solar neutrino results from Borexino and main future perspectives

Borexino is a solar neutrino experiment running at the Laboratori Nazionali del Gran Sasso, Italy. The radioactive background levels in the liquid scintillator target meet or even exceed design goals, opening unanticipated opportunities. The main results, so far, are the measurement of the ⁷Be solar neutrino flux (the first ever done) and the measurement of the ⁸B neutrino flux performed with electron energy threshold of 2.8 MeV. The short and medium term perspectives are summarized in the conclusions.     

Silicon photomultipliers characterization for the EMR prototype of the MICE experiment

The SiPMs are excellent candidates for the replacement of PMTs in many experimental situations. In this article we describe the performances of different types of SiPMs from Hamamatsu and FBK-IRST before and after irradiation with photons and neutrons in terms of signal to noise ratio, time resolution and efficiency. The SiPMs are connected to a scintillation tracker/calorimeter, composed of eight layers (4x and 4y) of 10 scintillating bars each and have been tested at the CERN PS T9 beamline. The tracker/calorimeter is a small-size prototype of a bigger detector called EMR (Electron Muon Ranger), a particle identification system developed for the MICE experiment.     

A proposal on cryogenic detection of neutrino magnetic moment at a level better than 10−11 µB (Bohr magneton)

A thermal detection of recoil electrons caused by (anti)neutrino scattering is considered in viewpoint of non-zero neutrino magnetic moment. A compact, low-background tritium-based antineutrino source providing a flux of 2.10¹⁵cm^–2s^–1 is proposed. An upper limit of 2.10^–12 µ_B is expected for germanium 1L volume calorimetric detector.     

On the possibility of experimentally confirming the hypothesis of reactor antineutrino passage into a sterile state

The “Neutrino-4” experiment for the 100-MW SM-3 reactor has been developed with the aim of testing the reactor antineutrino anomaly at Petersburg Nuclear Physics Institute. The advantages of this reactor for studying the antineutrino anomaly are (i) a low background level and (ii) small dimensions (35 × 42 × 42 cm) of the active zone. Operation of a position-sensitive antineutrino detector comprising five working sections and moving so as to cover a region of distances within 6–13 m from the active zone has been simulated by the Monte-Carlo method. The range of experimental sensitivity with respect to the oscillation parameters Δm ² and sin²2θ is determined, which will make it possible to confirm the hypothesis of antineutrino oscillations into a sterile state.     

Trigger electronics of the new Fluorescence Detectors of the Telescope Array Experiment

The Telescope Array Project is an experiment designed to observe Ultra High Energy Cosmic Rays via a “hybrid” detection technique utilizing both fluorescence light detectors (FDs) and scintillator surface particle detectors (SDs). We have installed three FD stations and 507 SDs in the Utah desert, and initiated observations from March 2008. The northern FD station reuses 14 telescopes from the High Resolution Fly's Eye, HiRes-I station. Each of the two southern FD stations contains 12 new telescopes utilizing new FADC electronics. Each telescope is instrumented with a camera composed of 256 PMTs. Since the detectors are composed of many PMTs and each PMT detects fluorescence photons together with the vast amount of night sky background, a sophisticated triggering system is required. In this paper, we describe the trigger electronics of these new FD stations. We also discuss performance of the FDs with this triggering system, in terms of efficiencies and apertures for various detector configurations.     

Pulse Shape Analysis with Scintillating Bolometers

Among the detectors used for rare event searches, such as neutrinoless Double Beta Decay (0νDBD) and Dark Matter experiments, bolometers are very promising because of their favorable properties (excellent energy resolution, high detector efficiency, a wide choice of different materials used as absorber, …). However, up to now, the actual interesting possibility to identify the interacting particle, and thus to greatly reduce the background, can be fulfilled only with a double read-out (i.e. the simultaneous and independent read out of heat and scintillation light or heat and ionization). This double read-out could greatly complicate the assembly of a huge, multi-detector array, such as CUORE and EURECA. The possibility to recognize the interacting particle through the shape of the thermal pulse is then clearly a very interesting opportunity. While detailed analyses of the signal time development in purely thermal detectors have not produced so far interesting results, similar analyses on macro-bolometers (～10–500 g) built with scintillating crystals showed that it is possible to distinguish between an electron or γ-ray and an α particle interaction (i.e. the main source of background for 0νDBD experiments based on the bolometric technique). Results on pulse shape analysis of a CaMoO₄ crystal operated as bolometer are reported as an example. An explanation of this behavior, based on the energy partition in the heat and scintillation channels, is also presented.     

Hadron shower punchthrough for incident hadrons of momentum 15, 25, 50, 100, 200 and 300 GeV/c

We present data on the punchthrough probability for showers of positively charged hadrons with momenta 15, 25, 50, 100, 200, and 300 GeV/c. Data were taken using the CCFR neutrino detector (the Lab E detector), an iron calorimeter instrumented with counters every 10 cm of iron, and drift chambers every 20 cm of iron.     

Enhancement of mechanical strength by shape memory effect in TiNi fiber-reinforced composites

Since there are strong demands for materials that have the high mechanical properties, the authors developed the new design concept that improve the material strength. It uses SMA to actively control the material strength. Using the TiNi shape memory fiber-reinforced epoxy matrix composite as the test specimen, the experiment was conducted to analyze the effectiveness of the new design concept. The test was conducted by the photoelastic method. The photoelastic fringe patterns and the behavior of K-value at the crack tip clearly support the effectiveness of the new design concept. Then, an analytical model based on Eshelby’s model is developed in order to compute the average matrix compressive stress. The experimental trend that |ΔK₁| increases with prestrain ϵ_T was in good agreement with the predictions based on the present model.     

A neutron Albedo system with time rejection for landmine and IED detection

A neutron Albedo system has been developed for imaging of buried landmines and improvised explosive devices (IEDs). It involves irradiating the ground with fast neutrons and subsequently detecting the thermalized neutrons that return. A scintillating ⁶Li loaded ZnS(Ag) screen with a sensitive area of 40 cm×40 cm is used as a thermal neutron detector. Scintillation light is captured by orthogonal arrays of wavelength-shifting fibers placed on either side of the scintillator surface and then transferred to X and Y multi-pixel PMTs. A timing circuit, used with pulsed neutron sources, records the time when a neutron detection takes place relative to an external synchronization pulse from the pulsed source. Experimental tests of the Albedo system performance have been done in a sand box with a ²⁵²Cf neutron source (no time gating) and with pulsed D-D (2.6 MeV) neutrons from the Defense R&D Ottawa Van de Graaff accelerator (with time gating). Information contained in the time evolution of the thermal neutron field provided improved detection capability and image reconstruction. The detector design is described and experimental results are discussed.     

A multiplexed optical-fiber system for the PMT calibration of the Borexino experiment

A multiplexed system of optical fibers has been designed for the photomultiplier calibration of the Borexino experiment at Gran Sasso. Both time and energy calibration are of paramount importance in Borexino for the measurement of the solar ⁷Be neutrino flux. Equalization of photomultipliers within 1 ns is required to define a Fiducial Volume to isolate a very pure internal region of observation, and accurate energy determination and resolution are crucial for the spectral shape recognition of the neutrino signal. The size of the detector, its tightness and radiopurity constraints require special care in the material selection and mechanical handling of the system. The solution of multiplexed fiber chains has been realized for the first time in a large underground detector. In this paper we illustrate the PMT calibration system design and the results of various feasibility tests performed.     

Cryogenic Design of the Setup for MARE-1 in Milan

A large worldwide collaboration is growing around the project of Micro-calorimeter Arrays for a Rhenium Experiment (MARE) for a direct calorimetric measurement of the neutrino mass. To validate the use of cryogenic detectors by checking the presence of unexpected systematic errors, two first experiments are planned using the available techniques composed of arrays of 300 detectors to measure 10¹⁰ events in a reasonable time of 3 years (step MARE-1) to reach a sensitivity on the neutrino mass of ∼2 eV/c². Our experiment in Milan is based on compensated doped silicon implanted thermistor arrays made in NASA/GSFC and on AgReO₄ crystals. We present here the design of the cryogenic system that integrates all the requirements for such experiment (electronics for high impedances, low parasitic capacitances, low micro-phonic noise).     

Developments of Microresonators Detectors for Neutrino Physics in Milan

Superconducting microwave microresonators are low temperature detectors which are compatible with large-scale multiplexed frequency domain readout. We aim to adapt and further advance the technology of microresonator detectors to develop new devices applied to the problem of measuring the neutrino mass. More specifically, we aim to develop detector arrays for calorimetric measurement of the energy spectra of ¹⁶³Ho EC decay (Q～2–3 keV) for a direct measurement of the neutrino mass. In order to achieve these goal, we need to find the best design and materials for the detectors. A recent advance in microwave microresonator technology was the discovery that some metal nitrides, such as TiN, possess properties consistent with very high detector sensitivity. We plan to investigate nitrides of higher-Z materials, for example TaN and HfN, that are appropriate for containing the energy of keV decay events, exploring the properties relevant to our detectors, such as quality factor, penetration depth and recombination time.