Beta Decay Spectrum Research Articles

Experimental neutrino physics in a nuclear landscape.

There are profound connections between neutrino physics and nuclear experiments. Exceptionally precise measurements of single and double beta-decay spectra illuminate the scale and nature of neutrino mass and may finally answer the question of whether neutrinos are their own anti-matter counterparts. Neutrino-nucleus scattering underpins oscillation experiments and probes nuclear structure, neutrinos offer a rare vantage point into collapsing stars and nuclear fission reactors and techniques pioneered in neutrino nuclear physics experiments are advancing quantum sensing technologies. In this article, we review current and planned efforts at the intersection of neutrino and nuclear experiments. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'.

Internal Bremsstrahlung, the missing process in beta decay Monte Carlo simulation: The relevance in 32P Dose-Point-Kernel estimation

PurposeIn nuclear medicine, Dose Point Kernels (DPKs), representing the energy deposited all around a point isotropic source, are extensively used for dosimetry and are usually obtained by Monte Carlo (MC) simulations. For beta-decaying nuclides, DPK is usually estimated neglecting Internal Bremsstrahlung (IB) emission, a process always accompanying the beta decay and consisting in the emission of photons having a continuous spectral distribution. This work aims to study the significance of IB emission for DPK estimation in the case of 32P and provide DPK values corrected for the IB photon contribution. MethodsDPK, in terms of the scaled absorbed dose fraction, F(R/X90), was first estimated by GAMOS MC simulation using the standard beta decay spectrum of 32P, Fβ(R/X90). Subsequently, an additional source term accounting for IB photons and their spectral distribution was defined and used for a further MC simulation, thus evaluating the contribution of IB emission to DPK values, Fβ+IB(R/X90). The relative percent difference, δ, between the DPKs obtained by the two approaches, Fβ+IB vs. Fβ, was studied as a function of the radial distance, R. ResultsAs far as the energy deposition is mainly due to the beta particles, IB photons does not significantly contribute to DPK; conversely, for larger R, Fβ+IB values are higher by 30–40% than Fβ. ConclusionsThe inclusion of IB emission in the MC simulations for DPK estimations is recommended, as well as the use of the DPK values corrected for IB photons, here provided.

A Lab-Scale Experiment for keV Sterile Neutrino Search

We developed a simple small-scale experiment to measure the beta decay spectrum of ^{3}H. The aim of this research is to investigate the presence of sterile neutrinos in the keV region. Tritium nuclei were embedded in a 1times1times1 cm^3 LiF crystal from the ^6Li(n,alpha)^3H reaction. The energy of the beta electrons absorbed in the LiF crystal was measured with a magnetic microcalorimeter at 40 mK. We report a new method of sample preparation, experiments, and analysis of ^3H beta measurements. The spectrum of a 10-hour measurement agrees well with the expected spectrum of ^3H beta decay. The analysis results indicate that this method can be used to search for keV-scale sterile neutrinos.

Beta-decay spectrum and Lorentz violation

Relativity theory and its underlying Lorentz and CPT invariance represent key principles of physics and therefore require continued experimental scrutiny across the broadest possible range of energy scales and physical systems. Possibilities for tests of these symmetries in precision β decay experiments with focus on KATRIN are investigated. It is found that countershaded departures from relativity, which represent a particular challenge to detection, are accessible in such experiments. In this context, it is argued that KATRIN would be in an excellent position to conduct the first-ever experimental search for countershaded Lorentz and CPT breaking in neutrinos.

Towards the TRISTAN detector: Characterization of a 47-pixel monolithic SDD array

Multi-pixel Silicon Drift Detectors (SDD), widely employed in X-ray applications, can also be applied to electron spectroscopy experiments. The objective of the TRISTAN project is to equip the KATRIN beam line with a multi-pixel SDD focal plane array. This would allow to extend the physics program of KATRIN, whose main goal is the determination of the neutrino mass via a precise measurement of the tritium beta decay spectrum close to the endpoint. An extension of the measurement interval would enable a sensitive search for physics beyond the standard model, in particular keV-scale sterile neutrinos, a prime dark matter candidate. The SDD technology guarantees excellent energy resolution and high throughput capabilities. A custom 47-pixel prototype, based on a monolithic SDD tile, has been developed and tested for the TRISTAN project. The full functionality of the system has been verified for all 47 channels. Good spectroscopic performance has been observed with a 55Fe X-ray source. This is a crucial step towards the realization of the final 21-fold 166-pixel TRISTAN focal plane detector.

First antineutrino energy spectrum from 235U fissions with the STEREO detector at ILL * * Stereo Collaboration, http://www.stereo-experiment.org.

This article reports the measurement of the 235U-induced antineutrino spectrum shape by the Stereo experiment. 43 000 antineutrinos have been detected at about 10 m from the highly enriched core of the ILL reactor during 118 full days equivalent at nominal power. The measured inverse beta decay spectrum is unfolded to provide a pure 235U spectrum in antineutrino energy. A careful study of the unfolding procedure, including a cross-validation by an independent framework, has shown that no major biases are introduced by the method. A significant local distortion is found with respect to predictions around E ν ≃ 5.3 MeV. A Gaussian fit of this local excess leads to an amplitude of A = 12.1 ± 3.4% (3.5σ).

HUNTER: precision massive-neutrino search based on a laser cooled atomic source

We describe a project that brings together researchers from atomic physics, nuclear physics and sub-atomic particle physics, to develop a high-precision laboratory-scale experiment able to search for very weakly coupled sterile neutrinos in the mass range extending from 5–10 keV/c 2 to several 100 keV/c 2. Observed neutrino flavor eigenstates are known to be quantum mixtures of at least three sub-eV/c 2 mass eigenstates. There is a strong theoretical belief that there may exist further neutrino mass eigenstates at higher mass levels, and which, if in the keV/c 2 mass range, might form all or part of the galactic dark matter. This has led to many searches for anomalous events in both astrophysical and particle physics experiments, and searches for distortions in beta decay spectra. The present experiment will utilize K-capture events in a population of 131Cs atoms suspended in vacuum by a magneto-optical trap (MOT). Using AMO and nuclear physics techniques, individual events will be fully reconstructed kinematically. Normally each event would be consistent with an emitted neutrino mass close to zero, but the existence of a sterile neutrino of keV/c 2 mass that mixes with the electron type neutrino produced in the decay would result in a separated population of events with non-zero reconstructed missing mass (up to the Q = 352 keV available energy of the reaction). Detailed calculations and simulations of all significant background processes have been made, in particular for scattering in the source itself, radiative K-capture, local radioactivity, cosmic ray muons, and knock-out of electrons by x-rays. A phase 1 of the experiment, under construction with funding from the W M Keck Foundation, has the potential to reach sterile neutrino mixing angles down to sin2 θ ∼ 10−4. With further upgrades this technique could be progressively improved to eventually reach much lower coupling levels ∼10−10, in particular reaching the level needed to be consistent with galactic dark matter below the astrophysical x-ray limits.

Ab initio calculations of reactor antineutrino fluxes with exact lepton wave functions

New ab initio calculations of the isotopic reactor antineutrino fluxes are provided with exact numerical calculations of the lepton wave functions, assuming all the decay branches are allowed GT transitions. We illustrate that the analytical Fermi function and finite size effect each could have the largest spectral deviation of O(10%), whereas the effect of their combination could result in spectral deviations at the level of 5%—10%. Meanwhile, we also find that several forms of the extended charge distributions have negligible effects on the spectral variation. Using the state-of-the-art nuclear databases, compared to usual ab initio calculations using the analytical single beta decay spectrum, our new calculation shows sizable but opposite spectral deviations at the level of 2%—4% for the cumulative antineutrino and electron energy spectra which may partially contribute to the observed spectral excess in the high energy antineutrino range. Finally we observe that the bias of analytical beta decay spectrum approximation is rather universal for all the four fissionable isotopes.

TRISTAN measurements at the Troitsk nu-mass experiment

The KATRIN (Karlsruhe Tritium Neutrino) experiment investigates the energetic endpoint of the tritium beta-decay spectrum to determine the effective mass of the electron anti-neutrino with a sensitivity of 200 meV (90 % C.L.) after an effective data taking time of three years. The TRISTAN (tritium beta-decay to search for sterile neutrinos) group aims at detecting a sterile neutrino signature by measuring the entire tritium beta-decay spectrum with an upgraded KATRIN system. One of the greatest challenges is to handle the high signal rates generated by the strong activity of the KATRIN tritium source. Therefore, a novel multipixel silicon drift detector is being designed which is able to handle rates up to 100 Mcps with an excellent energy resolution for electrons of 300 eV (FWHM) at 10 keV. First seven-pixel prototype detectors were successfully installed and operated at the Troitsk nu-mass experiment, one of KATRIN’s technological predecessors. In this work, we present the results of these measurement campaigns.

Hunting keV sterile neutrinos with KATRIN: building the first TRISTAN module

The KATRIN (Karlsruhe Tritium Neutrino) experiment investigates the energetic endpoint of the tritium beta-decay spectrum to determine the effective mass of the electron anti-neutrino. The collaboration has reported a first mass measurement result at this TAUP-2019 conference. The TRISTAN project aims at detecting a keV-sterile neutrino signature by measuring the entire tritium beta-decay spectrum with an upgraded KATRIN system. One of the greatest challenges is to handle the high signal rates generated by the strong activity of the KATRIN tritium source while maintaining a good energy resolution. Therefore, a novel multi-pixel silicon drift detector and read-out system are being designed to handle rates of about 100 Mcps with an energy resolution better than 300 eV (FWHM). This report presents succinctly the KATRIN experiment, the TRISTAN project, then the results of the first 7-pixels prototype measurement campaign and finally describes the construction of the first TRISTAN module composed of 166 SDD-pixels as well as its implementation in KATRIN experiment.

Project 8: Measuring the tritium beta-decay spectrum using Cyclotron Radiation Emission Spectroscopy

The goal of the Project 8 experiment is to measure the absolute neutrino mass using tritium beta decays and a new spectroscopic technique, Cyclotron Radiation Emission Spectroscopy (CRES). CRES has the potential for extremely low backgrounds and high precision. Phase I of Project 8 demonstrated that CRES could be used to detect single-electron cyclotron radiation and perform precision electron spectroscopy. We are in Phase II of the experiment, performing a 2-3-month measurement of the endpoint of the tritium spectrum. We will measure the last ~2 keV of the beta-decay spectrum, demonstrate our understanding of the systematic uncertainties, and explore the background rate at energies just above the endpoint. In Phase III we will demonstrate the ability to scale up the volume of the experiment, and to create a stable atomic tritium source, which will eventually avoid systematic uncertainties from the final states of the molecule. Phase IV will combine the critical factors of precision, size, and well-controlled systematic uncertainties to reach the final sensitivity of 40 meV. I will present the status of Project 8 Phase II and the plans for Phases III and IV.

Status of the Project 8 Phase II

The Project 8 collaboration aims to measure the absolute neutrino mass scale using cyclotron radiation emission spectroscopy on the beta decay of tritium. The second phase of the project will measure a continuous spectrum of molecular tritium beta decays and extract the tritium endpoint value with an eV or sub-eV scale precision. Monoenergetic electrons emitted by gaseous 83mKr atoms are used to determine the relationship between cyclotron frequency and electron energy. This study allows us to optimize both the event reconstruction algorithm and the hardware configuration, in preparation for measuring the tritium beta decay spectrum. Phase II will benefit from a gas system of krypton and tritium that will allow measurement of and offline correction for magnetic field fluctuations. We present the recent progress in understanding the electron kinematics and implementing the magnetic field calibration.

Zero-deadtime processing in beta spectroscopy for measurement of the non-zero neutrino mass

The Project 8 collaboration seeks to measure, or more tightly bound, the mass of the electron antineutrino by applying a novel spectroscopy technique to precisely measure the tritium beta-decay spectrum. The current system produces a single analog signal, which is digitized and processed in several stages before being saved to local disk storage. Online processing includes two stages, an FPGA connected to the analog to digital converter reduces the data down to the region of interest before shipping over the local network for further processing and storage. A normal CPU-based processing stage applies triggering logic to only save data at times when a signal is present, further reducing the total volume of data which needs to be written to disk or transferred for long-term storage. The next stage of the project will need to process many input channels and will integrate a necessary aggregation and combination step prior to applying the event search and triggering logic. We present the online processing system which has successfully been deployed for the current, singlechannel, phase. We also present the status and design for a many-channel platform.

High-availability on-site deployment to heterogeneous architectures for Project 8 and ADMX

Project 8 is applying a novel spectroscopy technique to make a precision measurement of the tritium beta-decay spectrum, resulting in either a measurement of or further constraint on the effective mass of the electron antineutrino. ADMX is operating an axion haloscope to scan the mass-coupling parameter space in search of dark matter axions. Both collaborations are executing medium-scale experiments, where stable operations last for three to nine months and the same system is used for development and testing between periods of operation. It is also increasingly common to use low-cost computing elements, such as the Raspberry Pi, to integrate computing and control with custom instrumentation and hardware. This leads to situations where it is necessary to support software deployment to heterogeneous architectures on rapid development cycles while maintaining high availability. Here we present the use of docker containers to standardize packaging and execution of control software for both experiments and the use of kubernetes for management and monitoring of container deployment in an active research and development environment. We also discuss the advantages over more traditional approaches employed by experiments at this scale, such as detached user execution or custom control shell scripts.

From First Tritium Operation of the Karlsruhe Tritium Neutrino Experiment Toward Precise Determination of the Neutrino Mass

The Karlsruhe Tritium Neutrino Experiment (KATRIN) aims for a model-independent measurement of the neutrino mass scale with a sensitivity of 0.2 eV/c2 (90% confidence limit). This is made possible by using an ultrastable, high-luminosity windowless gaseous tritium source providing 1011 beta decays per second and a high-resolution integrating spectrometer with a resolution of <1 eV. Over the past years, the system was installed at the Tritium Laboratory Karlsruhe and commissioned in various stages while demonstrating the outstanding performance of the magnetic guiding, electron transmission, and stability of individual subsystems. In 2018, the KATRIN beamline was operated with traces of tritium for the very first time. In this campaign, first beta decay spectra could be recorded. This was essential to validate the physics model and the fitting methods of the KATRIN analysis. Furthermore, in the campaign it was demonstrated that the global KATRIN stability of 0.1% in this configuration was successfully reached. Based on these results—as well as those from a subsequent systematic calibration campaign—KATRIN is now performing neutrino mass measurement runs at nominal tritium purity.

Relativistic Theory and Ab Initio Simulations of Electroweak Decay Spectra in Medium‐Heavy Nuclei and of Atomic and Molecular Electronic Structure

AbstractIn this work a novel theoretical and computational method for computing electroweak beta decay spectra of medium and heavy‐mass nuclei, as well as the electronic structure of atomic and molecular systems is developed. In particular, starting from the phenomenological electroweak interaction of the Standard Model (SM) of particles, a general expression of the beta decay rate was derived. Relativistic effects are taken into account by solving the many‐electron Dirac equation from first‐principles. Furthermore, an extension of this approach to include the nucleon‐nucleon interaction at the same level of theory of the electronic correlations has been devised. It is shown that post‐collisional effects, and to a lesser extent the electronic exchange and correlation, can modify significantly the cross‐section only at low energies (&lt;10 keV), while nuclear correlations considerably affect the lineshape of both the absorption and emission spectra particularly in odd‐odd nuclear transitions, where the independent particle approximation, on which the nuclear shell model is framed, is more likely to fail. These findings demonstrate the importance of moving beyond the independent particle picture to obtain an accurate description of the experimental data by adding the many‐body correlations between the spectator and participator hadrons and leptons involved in the decay. The application of our approach to a number of test cases, such as the modeling of beta decay of 36Cl, 63Ni, 129I, 210Bi, 241Pu and of the electron capture of 138La3 + , leads to an extremely good agreement with the relevant experimental data. Finally, the extension of this method to atomic and molecular systems by calculating the electronic structures of 138La3 + and several isomers (MgCN, MgNC) and molecules (HMgCN, MgCNO, and BrCF3) relevant to astrophysical scenarios is presented. This method, which is capable to deal with both nucleonic and electronic degrees of freedom, has far‐reaching implications also in neutrino physics and nuclear astrophysics.

Radiobiological effects of tritiated water short-term exposure on V79 clonogenic cell survival

Purpose: We set out to improve the accuracy of absorbed dose calculations for in vitro measurements of the relative biological effectiveness (RBE) of tritiated water (HTO) for the clonogenic cell survival assay, also considering the influence of the end-of-track linear energy transfer (LET) of low-energy electrons.Materials and methods: The COmputation Of Local Electron Release (COOLER) program was adopted to investigate the cell geometry and the tritium full beta-decay spectrum impact on the S-values and subsequently on the RBE of HTO for clonogenic cell survival at similar high dose rates (HDR).Results: S-values for cells growing in suspension are usually comparable to those for adherent cells. RBEs calculated at the 10% survival fraction through the use of the average energy are almost similar to those obtained with the beta-spectrum. For adherent cells, an RBE of 1.6 was found when HTO cell survival curves were compared to acute γ-ray exposures. Irrespective of the geometrical configuration, the RBE was 2.0 when the comparison was made with similar dose rates.Conclusions: These results underline the importance of irradiating at equal dose rates and cell culture conditions when measuring in vitro RBE-values.

Silicon drift detector prototypes for the keV-scale sterile neutrino search with TRISTAN

The TRISTAN project is an extension of the KATRIN experiment to search for the signature of keV-scale sterile neutrinos in the tritium beta decay spectrum. Sterile neutrinos are hypothetical particles that mix with the active neutrinos and thus affect the spectral shape of the beta decay. For the spectroscopy of electrons from the high-activity tritium source a novel pixelated silicon drift detector (SDD) is in development. In this work the characterization of 7-pixel SDD prototypes equipped with the IDeF-X BD ASIC is presented. The prototype detectors have pixel diameters between 0.5 and 2 mm with 2–12 drift rings. The ASIC noise floor was reached with all designs. A particular focus of the characterization measurements was the study of charge sharing. A very good general performance of the SDD prototypes was demonstrated. In order to reduce charge sharing the detector prototyping continues with SDDs with a pixel diameter of 3 mm. The next prototypes with 160 pixels are in production.

First measurements in search for keV sterile neutrino in tritium beta-decay in the Troitsk nu-mass experiment

We present the first measurements of tritium beta-decay spectrum in the electron energy range 16-18.6 keV. The goal is to find distortions which may correspond to the presence of a heavy sterile neutrinos. A possible contribution of this kind would manifest itself as a kink in the spectrum with a similar shape but with end point shifted by the value of a heavy neutrino mass. We set a new upper limits to the neutrino mixing matrix element U^2_{e4} which improve existing limits by a factor from 2 to 5 in the mass range 0.1-2 keV.

Determining the neutrino mass with cyclotron radiation emission spectroscopy—Project 8

The most sensitive direct method to establish the absolute neutrino mass is observation of the endpoint of the tritium beta-decay spectrum. Cyclotron radiation emission spectroscopy (CRES) is a precision spectrographic technique that can probe much of the unexplored neutrino mass range with resolution. A lower bound of is set by observations of neutrino oscillations, while the KATRIN experiment—the current-generation tritium beta-decay experiment that is based on magnetic adiabatic collimation with an electrostatic (MAC-E) filter—will achieve a sensitivity of . The CRES technique aims to avoid the difficulties in scaling up a MAC-E filter-based experiment to achieve a lower mass sensitivity. In this paper we review the current status of the CRES technique and describe Project 8, a phased absolute neutrino mass experiment that has the potential to reach sensitivities down to using an atomic tritium source.