We present the first continuous operation in a surface lab of BULLKID, a detector for searches of light Dark Matter and precision measurements of the coherent and elastic neutrino-nucleus scattering. ...The detector consists of an array of 60 cubic silicon particle absorbers of 0.34 g each, sensed by cryogenic kinetic inductance detectors. The data presented focusses on one of the central elements of the array and on its surrounding elements used as veto. The energy spectrum resulting from an exposure of 39 h to ambient backgrounds, obtained without radiation shields, is flat at the level of
(
2.0
±
0.1
stat
.
±
0.2
syst
.
)
×
10
6
counts/keV kg days down to the energy threshold of
160
±
13
eV. The data analysis demonstrates the unique capability of rejecting backgrounds generated from interactions in other sites of the array, stemming from the segmented and monolithic structure of the detector.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
An intense positron sources is a demanding element in the design of future lepton colliders. A crystal-based hybrid positron source could be an alternative to a more conventional scheme based on the ...electron conversion into positron in a thick amorphous target. The conceptual idea of the hybrid source is to have two separate objects, a photon radiator and a photon-to-positron converter target. In such a scheme an electron beam crosses a thin axially oriented crystal with the emission of a channeling radiation, characterized by a considerably larger amount of photons if compared to Bremsstrahlung. The net result is an increase in the number of produced positrons at the converter target. In this paper we present the results of a beam test conducted at the DESY TB 21 with 5.6 GeV electron beam and a crystalline tungsten radiator. Experimental data clearly highlight an increased production of photons and they are critically compared with the outcomes of novel method to simulate the number of radiated photons, showing a very good agreement. Strong of this, the developed simulation tool has been exploited to design a simple scheme for a positron source based on oriented crystal, demonstrating the advantages in terms of reduction of both deposited energy and the peak energy deposition density if compared to conventional sources. The presented work opens the way for a realistic and detailed design of a hybrid crystal-based positron source for future lepton colliders.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A proof-of-principle experimental setup for the extraction of 6 GeV electrons from the DESY II Booster Synchrotron using the channeling effect in a bent crystal is elaborated. Various aspects of the ...experimental setup were investigated in detail, such as the particle beam dynamics during the extraction process, the manufacturing and characterization of bent crystals, and the detection of the extracted beam. In order to optimize the crystal geometry, the overall process of beam extraction was simulated, taking into account the influence of radiation energy losses. As result it is concluded that the multi-turn electron beam extraction efficiency can reach up to 16%. In principle this crystal-based beam extraction technique can be applied at any electron synchrotron in order to provide multi-GeV electron beams in a parasitic mode. This technique will allow to supply fixed-target experiments by intense high-quality monoenergetic electron beams. Furthermore, electron/positron crystal-based extraction from future lepton colliders may provide an access to unique experimental conditions for ultra-high energy fixed-target experiments including searches for new physics beyond the Standard Model.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We observed reduction of multiple Coulomb scattering of 855 MeV electrons within a Si crystalline plate w.r.t. an amorphous plate with the same mass thickness. The reduction owed to complete or ...partial suppression of the coherent part of multiple scattering in a crystal vs crystal orientation with the beam. Experimental data were collected at Mainz Mikrotron and critically compared to theoretical predictions and Monte Carlo simulations. Our results highlighted maximal 7% reduction of the r.m.s. scattering angle at certain beam alignment with the 100 crystal axes. However, partial reduction was recorded over a wide range of alignment of the electron beam with the crystal up to 15
∘
. This evidence may be relevant to refine the modelling of multiple scattering in crystals for currently used software, which is interesting for detectors in nuclear, medical, high energy physics.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present the calibration and data analysis of BULLKID, a cryogenic, low threshold particle detector for searches of low mass dark matter candidates and coherent neutrino on nucleus scattering (CE
ν
...NS) events. The BULLKID detector is an array of 60 cubic particle absorbers made out of 0.34 g of silicon per cube, each one sensed by a kinetic inductance detector (KID). This paper describes the energy calibration of the detector as well as an evaluation of the background rate of the device when operated in an above-ground unshielded environment. By performing coincidence cuts on a cluster of 3x3 dice, the background rejection power of the design is demonstrated, allowing reach to a flat background down to a threshold of 160 eV.
Rare-event search experiments located on-surface, such as short-baseline reactor neutrino experiments, are often limited by muon-induced background events. Highly efficient muon vetos are essential ...to reduce the detector background and to reach the sensitivity goals. We demonstrate the feasibility of deploying organic plastic scintillators at sub-Kelvin temperatures. For the NUCLEUS experiment, we developed a cryogenic muon veto equipped with wavelength shifting fibers and a silicon photo multiplier operating inside a dilution refrigerator. The achievable compactness of cryostat-internal integration is a key factor in keeping the muon rate to a minimum while maximizing coverage. The thermal and light output properties of a plastic scintillation detector were examined. We report first data on the thermal conductivity and heat capacity of the polystyrene-based scintillator UPS-923A over a wide range of temperatures extending below one Kelvin. The light output was measured down to 0.8 K and observed to increase by a factor of 1.61 ± 0.05 compared to 300 K. The development of an organic plastic scintillation muon veto operating in sub-Kelvin temperature environments opens new perspectives for rare-event searches with cryogenic detectors at sites lacking substantial overburden.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•RuN thin films in the zinc-blende structure have been synthesized by rf-magnetron sputtering.•Contribute is given to the understanding of phase-formation mechanisms in systems that under ambient ...conditions present positive enthalpies of formation.•Contribute is given to the understanding of phenomena occurring during reactive sputtering processes.•Nanopillar structure: suitable for application requiring a high effective area, like sensing, catalysis, and electrode material for energy-storage devices.
4d- and 5d-transition metal nitrides are of interest both because of their importance for the understanding of mechanisms of phase formation in systems that under ambient conditions present positive enthalpies of formation and because of their appealing structural and electronic properties. In this study, we report the synthesis of thin films of ruthenium mononitride (RuN) in the zinc-blende structure by radio-frequency-magnetron sputtering. Films present a characteristic structure of packed columns ending with tetrahedral tips. The effect of changing the synthesis parameters was investigated in detail. It was found that RuN can be formed if the nitrogen partial pressure exceeds a minimum value and that the addition of argon has the major effect of increasing the deposition rate because of its higher sputter ability. Temperature plays an important role: if it is too high, decomposition/desorption effects overcome those leading to the formation of the compound. Phenomena resulting in the formation of RuN occur at the surface of the growing films and are related to the interactions of ruthenium with energetic nitrogen ions, or atoms, which can penetrate the first atomic layers by low energy implantation. Because of its properties and structure, this material is a promising candidate for applications like sensing, catalysis, and electrode material for energy-storage devices.
The magnetothermal behavior of antiferromagnetic IrMn layers of different thickness (3, 6, 10 nm) has been studied by exploiting the exchange coupling with a ferromagnetic 5 nm-thick NiFe layer. A ...procedure has been devised for the measurement of the magnetization of the NiFe/IrMn bilayers as a function of temperature and time at different values of an external magnetic field, Hinv, antiparallel to the unidirectional exchange anisotropy. This analysis allows one to probe the effective distribution of anisotropy energy barriers of the antiferromagnetic phase, as sensed by the ferromagnetic layer. Two magnetic regimes have been distinguished. At temperature T < 100 K, the interfacial IrMn spins are frozen in a glassy state and are collectively involved in the exchange coupling with the NiFe spins. At T ∼ 100 K the collective state breaks up; thus, above this temperature, only the interfacial IrMn spins which are tightly polarized by the IrMn nanograins, forming the bulk of the layer, are effectively involved in the exchange coupling mechanism. Due to that, for T > 100 K the exchange coupling is ruled by the anisotropy energy barriers of the bulk IrMn nanograins, namely by the layer thickness. The thermal evolution of the exchange field and of the coercivity in the three samples is coherently explained in the framework of this description of the dynamic magnetic behavior of the IrMn phase.
A link between exchange anisotropy and magnetoresistance has been found to occur in a Ni/NiO sample consisting of Ni nanocrystallites (mean size ∼13nm, Ni content ∼33vol%) dispersed in a NiO matrix. ...This material shows metallic-type electric conduction and isotropic spin-dependent magnetoresistance as well as exchange bias effect. The latter is the outcome of an exchange anisotropy arising from the contact interaction between the Ni phase and the NiO matrix. Combined analysis of magnetization M(H) and magnetoresistance MR(H) loops measured in the 5–250K temperature range after zero-field-cooling (ZFC) and after field-cooling (FC) from 300K reveals that the magnetoresistance is influenced by exchange anisotropy, which is triggered by the FC process and can be modified in strength by varying the temperature. Compared to the ZFC case, the exchange anisotropy produces a horizontal shift of the FC MR(H) loop along with a reduction of the MR response associated to the reorientation of the Ni moments. A strict connection between magnetoresistance and remanent magnetization of FC loops on one side and the exchange field on the other, ruled by exchange anisotropy, is indicated.
•Nanogranular Ni/NiO with giant magnetoresistance (MR) and exchange bias effect.•Exchange anisotropy produces a shift of the field-cooled MR(H) loop and reduces MR.•MR, remanence of field-cooled loops and exchange field are three correlated quantities.•It is possible to control MR of nanogranular systems through the exchange anisotropy.
The magnitude of the exchange bias (EB) effect in nanogranular Ni/NiO samples (with Ni content between about 4 and 69 wt% and mean size of the Ni crystallites of the order of 10 nm) has been found to ...be strictly related to the increase in the remanent magnetization measured after field-cooling, with respect to the value after zero-field-cooling, normalized to the saturation magnetization. This allows describing the EB mechanism in terms of the fraction of the magnetic moments of the Ni nanocrystallites that irreversibly has aligned in the field direction during field-cooling, due to the exchange anisotropy, and that is effectively involved in the loop shift. Hence, the possibility of tuning EB by controlling the field-cooled remanent magnetic state is shown.
► Exchange field Hex related to remanent magnetization state in Ni/NiO samples. ► Drawing of an original picture for the exchange bias EB mechanism in Ni/NiO system. ► EB depends on the fraction of Ni moments that irreversibly aligns with the cooling field. ► Tuning Hex of nanogranular samples by controlling the remanent magnetization state.
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