Cosmic-ray Induced Background Research Articles

Zenith angle dependence on cosmic-ray background in HPGe gamma spectrometers by using GEANT4 simulation

In this study, we investigate the impact of zenith angle variations on cosmic-ray induced background in High-Purity Germanium (HPGe) gamma spectrometers using a coincidence technique based on plastic scintillator-Germanium detectors. We utilize an HPGe detector (Model GC2018 Mirion Ge Detector) enclosed within a low-activity cylindrical lead shield (Model 747E Mirion Lead Shield). For cosmic ray detection, a coincidence detection system with plastic scintillator detectors was positioned on top of the lead shielding. The zenith angle at the Germanium detector is computed using the dimensions of the square plastic scintillator and its distance from the Germanium detector center. We carried out measurements of cosmic-ray induced background in an HPGe gamma spectrometer with a square plastic configuration (80cm x 80cm), equivalent to a 45° zenith angle. The experimental measurements were compared with GEANT4 simulation data. The results demonstrate a good agreement between the measured energy spectrum and the simulated data across the energy range of 0.05 to 47 MeV. Further investigations into the effects of varying zenith angles provide valuable insights for optimizing HPGe spectrometer setups with minimized background interference.

Study of a possible silicon photomultiplier based readout of the large plastic scintillator neutron detector NeuLAND

The NeuLAND (New Large-Area Neutron Detector) plastic-scintillator-based time-of-flight detector for 0.1–1.6GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3,000 2.7m × 5 cm × 5 cm big plastic scintillator bars that are read out on each end by fast timing photomultipliers.Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a NeuLAND bar was instrumented on each end with a SiPM-based prototype of the same geometry as a 1” photomultiplier tube, including four 6 × 6mm2 SiPMs, amplifiers, high voltage supply, and microcontroller.Tests were carried out using the 35MeV electron beam from the superconducting Electron Linac for beams with high Brilliance and low Emittance (ELBE) with its picosecond-level time jitter in two different modes of operation, namely parasitic mode with one electron per bunch and single-user mode with 1–60 electrons per bunch. Acqiris fast digitisers were used for data acquisition. In addition, off-beam tests using cosmic rays and the NeuLAND data acquisition scheme have been carried out.Typical time resolutions of σ≤ 120ps were found for ≥95% efficiency for minimum ionising particles, improving on previous work at ELBE and exceeding the NeuLAND timing goal of σ< 150ps. Over a range of 10–300MeV deposited energy in the NeuLAND bar, the gain was found to deviate by ≤10% (≤20%) from linearity for 35μm (75μm) SiPM pitch, respectively, satisfactory for calorimetric use of the full NeuLAND detector. The dark rate of the prototype studied was found to be lower than the expected cosmic-ray induced background in NeuLAND.

Direct measurement of the 19F(p, αγ)16O reaction in JUNA

The 19F(p, αγ)16O reaction is of crucial importance for Galactic 19F abundances and CNO cycle loss in first generation Population III stars. Due to its extremely small cross sections, the 19F(p, αγ)16O reaction has not been measured in the low energy part of the Gamow window(70-200 keV). As a day-one campaign, the experiment was performed under the extremely low cosmicray-induced background environment of the China JinPing Underground Laboratory(CJPL), one of the deepest underground laboratories in the world. The γ-ray yields were measured over Ec.m. =72.4–344 keV, covering the full Gamow window for the first time. The direct experimental data will help people to expound the fluorine over-abundances, energy generation, as well as heavy-element nuclosynthesis scenario in asymptotic giant branch (AGB) stars, with the astrophysical model on the firm ground.

Nuclear astrophysics in underground laboratories

Nuclear processes are responsible for energy generation that makes stars shine, for the synthesis of the elements in stars and also play a decisive role in explaining the chemical composition of the interstellar medium. The experimental determination of the reaction cross section at the astrophysical relevant energies is extremely difficult due to the Coulomb repulsion between the interacting nuclei which turns out in cross section values down to the fbar level. As a result, these cross sections are often too small to be measured in laboratories on the Earth’s surface, where the signal would be overwhelmed by the cosmic-ray induced background. An effective way to suppress the comic-ray induced background is to perform experiments in underground laboratories. LUNA is an experimental approach for the study of nuclear fusion reactions based on an underground accelerator laboratory. Aim of the experiment is the direct measurement of the cross section of nuclear reactions relevant for stellar and primordial nucleosynthesis. In the following the latest results and the future goals will be presented.

Background in γ-ray detectors and carbon beam tests in the Felsenkeller shallow-underground accelerator laboratory

The relevant interaction energies for astrophysical radiative capture reactions are very low, much below the repulsive Coulomb barrier. This leads to low cross sections, low counting rates in $\gamma$-ray detectors, and therefore the need to perform such experiments at ion accelerators placed in underground settings, shielded from cosmic rays. Here, the feasibility of such experiments in the new shallow-underground accelerator laboratory in tunnels VIII and IX of the Felsenkeller site in Dresden, Germany, is evaluated. To this end, the no-beam background in three different types of germanium detectors, i.e. a Euroball/Miniball triple cluster and two large monolithic detectors, is measured over periods of 26-66 days. The cosmic-ray induced background is found to be reduced by a factor of 500-2400, by the combined effects of, first, the 140 meters water equivalent overburden attenuating the cosmic muon flux by a factor of 40, and second, scintillation veto detectors gating out most of the remaining muon-induced effects. The new background data are compared to spectra taken with the same detectors at the Earth's surface and at other underground sites. Subsequently, the beam intensity from the cesium sputter ion source installed in Felsenkeller has been studied over periods of several hours. Based on the background and beam intensity data reported here, for the example of the $^{12}$C($\alpha$,$\gamma$)$^{16}$O reaction it is shown that highly sensitive experiments will be possible.

Nuclear Astrophysics deep underground and the LUNA experiment

The cross sections of nuclear reactions relevant for astrophysics are crucial ingredients to understand the energy generation inside stars and the synthesis of the elements. In stars, nuclear reactions take place at energies well below the Coulomb barrier. As a result, their cross sections are often too small to be measured in laboratories on the Earth’s surface, where the signal would be overwhelmed by the cosmic-ray induced background. An effective way to suppress the cosmic-ray induced background is to perform experiments in underground laboratories. LUNA is a unique facility located at Gran Sasso National Laboratories (Italy) and devoted to Nuclear Astrophysics. The extremely low background achieved at LUNA allows to measure nuclear cross sections directly at the energies of astrophysical interest. Over the years, many crucial reactions involved in stellar hydrogen burning as well as Big Bang Nucleosynthesis have been measured at LUNA. This paper provides a short overview on underground Nuclear Astrophysics and discusses the latest results and future perspectives of the LUNA experiment.

A high-efficiency gas target setup for underground experiments, and redetermination of the branching ratio of the 189.5 keV 22Ne(p, $\gamma$ γ )23Na resonance

The experimental study of nuclear reactions of astrophysical interest is greatly facilitated by a low-background, high-luminosity setup. The Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator offers ultra-low cosmic-ray induced background due to its location deep underground in the Gran Sasso National Laboratory (INFN-LNGS), Italy, and high intensity, 250-500 $\mu$A, proton and $\alpha$ ion beams. In order to fully exploit these features, a high-purity, recirculating gas target system for isotopically enriched gases is coupled to a high-efficiency, six-fold optically segmented bismuth germanate (BGO) $\gamma$-ray detector. The beam intensity is measured with a beam calorimeter with constant temperature gradient. Pressure and temperature measurements have been carried out at several positions along the beam path, and the resultant gas density profile has been determined. Calibrated $\gamma$-intensity standards and the well-known $E_p$ = 278 keV $\mathrm{^{14}N(p,\gamma)^{15}O}$ resonance were used to determine the $\gamma$-ray detection efficiency and to validate the simulation of the target and detector setup. As an example, the recently measured resonance at $E_p$ = 189.5 keV in the $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction has been investigated with high statistics, and the $\gamma$-decay branching ratios of the resonance have been determined.

Nuclear Astrophysics Deep Underground

Cross sections of nuclear reactions relevant for astrophysics are crucial ingredients to understand the energy generation inside stars and the synthesis of the elements. At astrophysical energies, nuclear cross sections are often too small to be measured in laboratories on the Earth surface, where the signal would be overwhelmed by the cosmic-ray induced background. LUNA is a unique Nuclear Astrophysics experiment located at Gran Sasso National Laboratories. The extremely low background achieved at LUNA allows to measure nuclear cross sections directly at the energies of astrophysical interest. Over the years, many crucial reactions involved in stellar hydrogen burning as well as Big Bang nucleosynthesis have been measured at LUNA. The present contribution provides an overview on underground Nuclear Astrophysics as well as the latest results and future perspectives of the LUNA experiment.

Monte Carlo simulation of background characteristics of a HPGe detector operating underground in the Gran Sasso National Laboratory

Monte Carlo (MC) simulation of background components of an ultra-low background high purity germanium (HPGe) detector operating in a deep underground laboratory was carried out. The results show that the background of the HPGe detector is about two orders of magnitude higher than the MC prediction when accounting only for cosmic-ray induced background. The difference is due to natural radioactivity in the parts surrounding the Ge detector. To get reasonable agreement between MC simulations and the experiment, a contamination in the parts surrounding the Ge crystal from 40K, 208Tl and 214Bi of 0.1mBqkg−1 was required to include in the simulations.

Investigation of cosmic-ray induced background of Germanium gamma spectrometer using GEANT4 simulation

In this article, a GEANT4 Monte Carlo simulation toolkit was used to study the response of the cosmic-ray induced background on a High-Purity Germanium (HPGe) gamma spectrometer in the wide energy range, up to 100MeV. The natural radiation background measurements of the spectrometer were carried out in the energy region from 0.04 to 50MeV. The simulated cosmic-ray induced background of the Ge detector was evaluated in comparison with the measured data. The contribution of various cosmic-ray components including muons, neutrons, protons, electrons, positrons and photons was investigated. We also analyzed secondary particle showers induced by the muonic component.

Neutron triples counting data for uranium

Correlated neutron counting using multiplicity shift register logic extracts the first three factorial moments from the detected neutron pulse train. The descriptive properties of the measurement item (mass, the ratio of (α,n) to spontaneous fission neutron production, and leakage self-multiplication) are related to the observed singles (S), doubles (D) and triples (T) rates, and this is the basis of the widely used multiplicity counting assay method. The factorial moments required to interpret and invert the measurement data in the framework of the point kinetics model may be calculated from the spontaneous fission prompt neutron multiplicity distribution P(ν). In the case of 238U very few measurements of P(ν) are available and the derived values, especially for the higher factorial moments, are not known with high accuracy.In this work, we report the measurement of the triples rate per gram of 238U based on the analysis of a set of measurements in which a collection of 10 cylinders of UO2F2, each containing about 230g of compound, were measured individually and in groups. Special care was taken to understand and compensate the recorded multiplicity histograms for the effect of random cosmic-ray induced background neutrons, which, because they also come in bursts and mimic fissions but with a different and harder multiplicity distribution. We compare our fully corrected (deadtime, background, efficiency, multiplication) experimental results with first principles expectations based on evaluated nuclear data. Based on our results we suspect that the current evaluated nuclear data is biased, which points to a need to undertake new basic measurements of the 238U prompt neutron multiplicity distribution.

Status and New Data of the Geochemical Determination of the pp-Neutrino Flux by LOREX

LOREX (LORandite EXperiment) addresses the determination of the solar (pp) neutrino flux during the last four million years by exploiting the reaction 205Tl+νe→ 205Pb+e-with an incomparably low-energy threshold of 50 keV for the capture of solar neutrinos. The ratio of205Pb/205Tl atoms in the Tl-bearing mineral lorandite provides, if corrected for the cosmic-ray induced background, the product of the flux of solar neutrinos and their capture probability by205Tl, averaged over the age of lorandite. To get the mean solar neutrino flux itself, four problems have to be addressed: (1) the geological age of lorandite, (2) the amount of background cosmic-ray-induced205Pb atoms which strongly depends on the erosion rate of the lorandite-bearing rocks, (3) the capture probability of solar neutrinos by205Tl and (4) the extraction of lorandite and the appropriate technique to “count” the small number of205Pb atoms in relation to the number of205Tl atoms. This paper summarizes the status of items 1 (age) and 3 (neutrino capture probability) and presents in detail the progress achieved most recently concerning the items 2 (background/erosion) and 4 (“counting” of205Pb atoms in lorandite).

Muon-induced backgrounds in the CUORICINO experiment

To better understand the contribution of cosmic ray muons to the CUORICINO background, 10 plastic scintillator detectors were installed at the CUORICINO site and operated during the final 3 months of the experiment. From these measurements, an upper limit of 0.0021 counts/(keV kg yr) (95% CL) was obtained on the cosmic ray-induced background in the neutrinoless double beta decay region of interest. The measurements were also compared to Geant4 simulations.

Cosmic-ray induced background reduction by means of an anticoincidence shield

The cosmic-ray induced background of a spectrometer is reduced by means of an active veto shielding. Two such spectrometers have been developed: one equipped with a well type Ge detector and the other with a 50% relative efficiency coaxial Ge detector. In both cases, the active veto shielding consists of plastic scintillating plates and an anticoincidence electronic system. Although these devices have lower performances that those placed in an underground laboratory, their advantage is that they can be used in a normal laboratory environment. The background is reduced by 4 or 5 in the whole 30 keV to 2.7 MeV energy range and 5–10 in the energy range below 500 keV. Under these conditions, the count rates are smaller than 10 −4 counts s −1 keV −1.

Automatic analysis of continuum phenomena in gamma spectra

A method to fit the continuum of gamma spectra, developed to determine the baseline below full-energy peaks, is applied to the study of structures contained within the continuum. Specifically, we analyze the two spectral lines which appear in the background spectra of a low-level germanium gamma-ray spectrometer due to the inelastic scattering of cosmic-ray, tertiary fast-neutrons on 72Ge and 74Ge. The automatic analysis of the continuum it makes possible to characterize completely the cosmic-ray induced background and to study the environmental fast-neutron flux.

On the cosmic-ray induced background in neutral pion production measurements with a BaF 2 multidetector

The problem of the cosmic-ray induced background in neutral pion production measurements with barium fluoride multidetectors is discussed. As a reference example, the response to cosmic rays of the MEDEA photon spectrometer is studied. The interaction of the cosmic radiation with the experimental filter has been treated by means of full Monte Carlo computer simulations with the GEANT3 code. The results of the simulations are compared with experimental data and general criteria to minimize the cosmic background are discussed.

Cosmic ray-induced background in Ge-spectrometry

The interaction of hadronic and purely muonic secondary cosmic rays is demonstrated by comparison of Ge-background spectra with a coverage of 1 and 15 meter water equivalent (m.w.e.), respectively. A compilation is given of cosmic-induced background lines, including processes like nuclear and atomic de-excitation and activation. Effects of muonic electron photon showers are investigated using different materials for the inner shield at 15 mw.e. The observed background spectra mainly consist of a bremsstrahlungs-continuum from muonic shower electrons induced in the inner shield and annihilation photons by the same source and partly from stopped positive muons. In general, low activity lead is most effective in background reduction, at least above 90 keV, since it absorbs shower bremsstrahlung best and has the lowest γ-yield for inelastic neutron scattering.

Effects of increased shielding on gamma-radiation levels within spacecraft.

The Shuttle Activation Monitor (SAM) experiment was flown on the Space Shuttle Columbia (STS-28) from 8-13 August, 1989 in a 57 degrees, 300 km orbit. One objective of the SAM experiment was to determine the relative effect of different amounts of shielding on the gamma-ray backgrounds measured with similarly configured sodium iodide (NaI) and bismuth germante (BGO) detectors. To achieve this objective twenty-four hours of data were taken with each detector in the middeck of the Shuttle on the ceiling of the airlock (a high-shielding location) as well as on the sleep station wall (a low-shielding location). For the cosmic-ray induced background the results indicate an increased overall count rate in the 0.2 to 10 MeV energy range at the more highly shielded location, while in regions of trapped radiation the low shielding configuration gives higher rates at the low energy end of the spectrum.

A low background detection system for fragments and neutrons from spontaneous fission sources

A low background system for the detection and characterization of spontaneously fissioning nuclides has been developed. It allows the simultaneous registration of single and coincident fission fragments and their kinetic energies, and of the number of neutrons emitted per fission event together with the time intervals between fission-fragment and neutron pulses. In addition, α-particle spectra can also be measured. The system consists of six pairs of surface barrier detectors surrounded by 30 3He-filled neutron counters embedded in paraffin. It is placed between two large plastic scintillation detectors in order to identify cosmic-ray induced background events. The detector assembly has been used in the search for superheavy elements in reactions of 238U projectiles with 238U and 248Cm targets and of 48Ca with 248Cm at production rates of a few atoms per experiment.

The reduction of cosmic-ray induced background in proportional counter rocket experiments

The reduction of cosmic-ray induced background events in proportional counter rocket experiments is discussed for the energy range 1–20 keV. The results from two Skylark rocket flights are presented, one employing scintillator anti-coincidence and the other proportional guard anti-coincidence, both using rise-time discrimination. The results are analysed in terms of the interactions which produce the background.