Artificial neutrino source based on the 37Ar isotope

In April 2004, a neutrino source was produced by irradiating a 330-kg piece of pressed calcium oxide at the fast-neutron reactor BN-600 (Zarechny, Russia) for six months. The ³⁷Ar isotope was obtained via the (n, α) reaction on ⁴⁰Ca, and ³⁷Ar was extracted from an aqueous solution of nitric acid in which the solid target was dissolved. After that, ³⁷Ar was purified and sealed into a capsule. This source was used to measure the neutrino-capture rate in metalic gallium for neutrinos from ³⁷Ar decay, which have an energy close to that of the main line of solar ⁷Be neutrinos (863 keV). The target of the SAGE Gallium-Germanium Neutrino Telescope was irradiated by using this source at the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences). The source activity was measured by several methods during its production, in the course of irradiation, and after its completion. The weighted mean of the activity for six measurements was 409 ± 2 kCi at the beginning of irradiation of the gallium target (04:00 Moscow time, 30.04.2004). The scatter in the activity values obtained by different methods does not exceed 5%.     

37Ar测量系统的研制与能谱测量方法研究

建立了移动式³⁷Ar测量系统.采用1 L的正比计数探测器和能谱分析方法对³⁷Ar的测量进行了研究.分析了计数管的坪长、坪斜和本底等特点.结果表明，相比传统的计数方法，采用电子能谱法测量³⁷Ar具有直观、坪长长、坪斜小等优点.相比传统的总计数方法，采用峰本底的方法可以将本底降低约一个量级，从而降低³⁷Ar的探测下限.并研究了工作气体中不同甲烷含量对³⁷Ar的测量能谱和计数管工作电压的影响，结果表明，     

Measurement of the response of a Ga solar neutrino experiment to 37Ar source

An intense ³⁷Ar source was produced by the (n, α) reaction on ⁴⁰Ca by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The ³⁷Ar was released from the solid target by dissolution in acid, collected from this solution, purified, sealed into a small source, and brought to the Baksan Neutrino Observatory, where it was used to irradiate 13 t of gallium metal in the Russian—American solar neutrino experiment SAGE. Ten exposures of the gallium to the source, whose initial strength was ∼ 409 ± 2kCi, were carried out during the period from April to September 2004. The ⁷¹Ge produced by the reaction ⁷¹Ga(ν _e, e ⁻)⁷¹Ge was extracted, purified, and counted. The measured production rate was 11.0 _−0.9 ^+1.0 (stat.) ±0.6 (syst.) atoms of ⁷¹Ge/d, which is 0.79 _−0.10 ^+0.09 of the theoretically calculated production rate. The text was submitted by the authors in English.     

37Ar测量系统的研制与能谱测量方法研究

建立了移动式³⁷Ar测量系统.采用1 L的正比计数探测器和能谱分析方法对³⁷Ar的测量进行了研究.分析了计数管的坪长、坪斜和本底等特点.结果表明,相比传统的计数方法,采用电子能谱法测量³⁷Ar具有直观、坪长长、坪斜小等优点.相比传统的总计数方法,采用峰本底的方法可以将本底降低约一个量级,从而降低³⁷Ar的探测下限.并研究了工作气体中不同甲烷含量对³⁷Ar的测量能谱和计数管工作电压的影响,结果表明,     

Positron–neutrino correlations in 32Ar and 33Ar decays: Probes of scalar weak currents and nuclear isospin mixing

The positron–neutrino correlation in the 0⁺→0⁺ β-decay of ³²Ar was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of the narrow proton group following the super-allowed decay. Our result is consistent with the standard model prediction;for vanishing Fierz interference we find a=0.9989±0.0052±0.0039. Our result leads to improved constraints on scalar weak interactions. The positron–neutrino correlation in ³³Ar decay was measured in the same experiment;for vanishing Fierz interference we find a=0.944±0.002±0.003. The ³²Ar and ³³Ar correlations, in combination with precision measurements of the half-lives, super-allowed branching ratios and beta endpoint energies, will determine the isospin impurities of the super-allowed transitions. These will provide useful tests of isospin-violation corrections used in deducing |V_ud| which currently indicates non-unitarity of the KM matrix. This revised version was published online in July 2006 with corrections to the Cover Date.     

Measuring neutrino mass with radioactive ions in a storage ring

We propose a method to measure the neutrino mass kinematically using beams of ions which undergo beta decay. The idea is to tune the ion beam momentum so that in most decays, the electron is forward moving with respect to the beam, and only in decays near the endpoint is the electron moving backwards. Then, by counting the backward moving electrons one can observe the effect of neutrino mass on the beta spectrum close to the endpoint. In order to reach sensitivities for m _ν <0.2 eV, it is necessary to control the ion momentum with a precision better than δ p/p<10⁻⁵, identify suitable nuclei with low Q-values (in the few to ten keV range), and one must be able to observe at least O(10¹⁸)\mathcal{O}(10^{18}) decays.     

Investigation of double-beta decay at the Institute of Theoretical and Experimental Physics (ITEP, Moscow)

Investigation of neutrinoless double-beta (2β0ν) decay is presently being considered as one of the most important problems in particle physics and cosmology Interest in the problem was quickened by the observation of neutrino oscillations. The results of oscillation experiments determine the mass differences between different neutrino flavors, and the observation of neutrinoless decay may fix the absolute scale and the hierarchy of the neutrino masses. Investigation of 2β0ν decay is the most efficient method for solving the problem of whether the neutrino is a Dirae or a Majorana particle, Physicists from the Institute of Theoretical and Experimental Physics (ITEP, Moscow) have been participating actively in solving this problem. They initiated and pioneered the application of semiconductor detectors manufactured from enriched germanium to searches for the double-beta decay of ⁷⁶Ge. Investigations with ⁷⁶Ge provided the most important results. At present, ITEP physicists are taking active part in four very large projects, GERDA. Majorana, EXO, and NEMO, which are capable of recording 2β0ν decay at a Majorana neutrino mass of 〈m _ν〉 ≈ 10^?2 eV.     

Precision nuclear β-decay half-life measurements

Precise measurements of the intensities of superallowed Fermi β decays between 0^?+? analog states provide a demanding test of the electroweak standard model. At ISAC, nuclear β-decay lifetimes are measured with high-precision (<0.05 %) by direct β counting using a 4π continuous flow gas proportional counter coupling to a fast tape transport system. This facility has provided the most precise half-life measurements for several superallowed β emitters including: ²⁶Al^m, ³⁸K^m, ⁶²Ga and ⁷⁴Rb.     

Thermal neutron induced charged particle reactions in radioactive targets of37Ar,109Cd,125Xe,127Xe,and132Cs

Thermal neutron induced charged particle reactions in a radioactive target of³⁷Ar have been studied. Upper limits of the cross-sections for the (n, α) reaction in radioactive targets of¹⁰⁹Cd,^{125, 127}Xe, and¹³²Cs have been obtained. The isotopically pure targets were produced at the ISOLDE facility at CERN and irradiated with thermal neutrons at the high flux reactor of the Institute Laue-Langevin in Grenoble. Charged particles from (n, p) and (n, α) reactions in³⁷Ar were observed with cross-sections of 69±14b and 1970 ±330b, respectively. TheQ-values for these reactions were determined to be 1600 ±12 keV and 4630±7 keV, in agreement with existing mass data. The branching ratio Γ_α/Γ_p of the³⁷Ar capturing state was found to be 28.5±2.7. An upper limit of the cross-section for the (n, γα) reaction in³⁷Ar was obtained.     

Statistical theory of nuclear neutrino capture: (II). Inclusion of first-forbidden transitions

The statistical theory of nuclear neutrino capture is extended to include first-forbidden transitions. A comparison with the theory of Bahcall and Frautschi is made. It is found that the present theory predicts neutrino capture cross sections which are smaller than those of Bahcall and Frautschi by a factor 2–3 for neutrino energies less than 50 MeV when first-forbidden transitions are dominant. Calculation of the cross section is made for the process in which ³⁷Cl nuclei capture electron neutrinos that are emitted in muon decay. The present calculation gives a cross section which is around one half of that of Donnelly and Haxton. Finally the contributions of the highly excited states in ³⁷Ar to the neutrino capture cross section are evaluated. It is shown that the contributions from the highly excited states (E > 6.02 MeV) to the neutrino capture cross section amount to 60% for E_v = 50 MeV.     

Background of external <Emphasis Type="Italic">γ</Emphasis> radiation in the proportional counters of the SAGE experiment

The effect of external γ radiation on the process of counting ⁷¹Ge decays in the proportional counters of the SAGE experiment measuring the solar-neutrino flux is considered. The systematic uncertainty in the SAGE result due to radon decays inside the air volume surrounding the counters is estimated. The background counting rate in the proportional counters that is caused by γ radiation from the enclosing shield is also determined.     

Time-modulation of entangled two-body weak decays with massive neutrinos

In recent experiments at the GSI, Darmstadt, time-modulated orbital Electron Capture (EC) decays of H-like ¹⁴⁰Pr⁵⁸⁺, ¹⁴²Pm⁶⁰⁺, and ¹²²I⁵²⁺ ions with one electron in the K-shell, coasting in the ESR storage ring with velocity β=0.71, were observed. The EC-branches show exponential decay curves time-modulated with period T=7.06(8) s and amplitude a=0.18(3) for ¹⁴⁰Pr decays, T=7.10(22) s and a=0.23(4) for ¹⁴²Pm decays, and T=6.04(6) s and a=0.19(3) for ¹²²I (preliminary) decays in the laboratory frame. The simultaneously measured β⁺ branch of ¹⁴²Pm shows no modulation with a<0.03. We discuss here as origin of the modulation quantum beats produced by the superposition of massive neutrino, mass eigenstates emitted in the entangled two body weak decay. From the modulation frequency a value for the difference of the quadratic mass values is deduced, which is 2.9 times larger than the value derived by the KamLAND antineutrino oscillation experiment. The origin of the small modulation amplitudes is discussed as the result of a partial restoration of the interference terms which are expected to cancel for the usual assumed unitarity of the neutrino flavor mixing matrix.     

Beta-neutrino recoil broadening inβ-delayed proton emission of32Ar and33Ar

In high-resolution measurements of delayed protons following theβ-decays of³²Ar and³³Ar we have observed significant line broadening caused by theβ —gn recoil motion of the daughter nuclei. The measured line shapes agree well with the calculation for both Fermi and Gamow-Teller decays and yield new spectroscopic information on the transitions and excited states involved. For the Gamow-Teller strength in theβ ⁺-decay of³³Ar to the isobaric analogue state in³³Cl an upper limit of B_GT<0.029 was determined.     

Effects of anomalousZ 0 decays on neutrino counting near theZ 0 peak

We study the implications of the anomalousZ ⁰ decays on neutrino counting ine ⁺ e ^? collisions. The \(Z^0 \to l\bar l\gamma \) vertex is parametrized by an effective Lagrangian,L _eff, satisfyingU(1)_em gauge invariance, CP and chirality conservation. The parameters ofL _eff are constrained by the ratio \(\Gamma (Z \to l\bar l\gamma )/\Gamma (Z \to l\bar l)\) , Bhabba scattering, and low energyv _µ e scattering data. We find that the effect on neutrino counting can be significant but depends on the magnitude and relative signs of the parameters inL _eff. We also find that accurate measurements of the cross-section \(\sigma (e^ + e^ - \to v\bar v\gamma )\) at theZ ⁰ peak can be used as a sensitive test for new physics.     

Solar-neutrino variations: A manifestation of nonzero neutrino mass and magnetic moment, and mixing

Time variations of solar neutrino flux are investigated on the basis of available Homestake experimental data for more than two solar cycles (1970–1994). At first, we determine (with the weight-time function by taking into account ³⁷Ar decay), for each solar neutrino run n, the effective Earth’s heliolatitude L _eff(n), the effective Zurich sunspots number Z _eff(n), the effective latitude of sunspots distribution Λ_eff(n), and the effective surfaces of sunspots in different heliolatitude belts. Then, we consider the correlation of solar-electron-neutrino fluxes with these parameters for different periods of solar activity. It is found that correlation coefficients change sign in different periods of solar activity, so that for total period 1970–1994 the correlation coefficient is very small. The obtained information indicates that a neutrino should have nonzero mass and nonzero magnetic moment.     

The Windowless Gaseous Tritium Source of KATRIN

The objective of KATRIN is the determination of the mass of the electron anti-neutrino with a sensitivity of 200 meV by investigating the kinematics of the electrons from tritium β decay. It is currently under construction at KIT (Karlsruhe Institute of Technology).A key component of the KATRIN experiment is the Windowless Gaseous Tritium Source (WGTS), in which molecular tritium decays with an activity of 10¹¹ Bq. A precise understanding of the properties of the WGTS is mandatory for the neutrino mass determination. In particular the gas dynamics is crucial since the measured energy spectrum is influenced by inelastic scattering of the decay electrons with the tritium molecules as well as Doppler broadening of the electron energy. Therefore parameters of the WGTS such as purity, temperature, density and velocity distributions of the tritium gas and the magnetic field strength inside the WGTS have to be modeled in detail.This talk gives an overview of the simulation and modeling program package currently in development which allows us to study the influence of the WGTS parameters on the measured electron energy spectrum.     

A search for decays of heavy neutrinos in the mass range 0.5–2.8 GeV

A search for decays of heavy neutrinos was conducted by the CHARM Collaboration in a prompt neutrino beam produced by dumping 400 GeV protons in a Cu target, and in the CERN wide-band neutrino beam produced by 400 GeV primary protons. No candidate event was found. In the beam-dump experiment heavy neutrinos have been assumed to be produced by mixing in charmed D meson decays. Neutrinos decaying into e⁺e⁻v_e, μ⁺e⁻v_μ, and μ⁺μ⁻v_μ were searched for. Limits of |U_ei|², |U_μi|² < 10⁻⁷ were obtained for neutrino masses around 1.5 GeV. In the wide-band experiment heavy neutrinos were assumed to be produced by neutral-current neutrino interactions in the CHARM calorimeter. Here a search was made for neutrinos decaying into a μ and hadrons. This experiment is sensitive to decays of neutrinos with mass in the range 0.5–2.8 GeV with limits of |U_μi|² < 3 × 10⁻⁴ for masses around 2.5 GeV. These measurements extend our previous results in the mass range 10–400 MeV.     

Review of absolute neutrino mass measurements

The discovery of neutrino flavor oscillations has firmly established that at least two of the three known neutrino mass eigenstates possess a non-vanishing rest mass. Complementary to cosmology and the search for neutrino-less double beta decay laboratory-based measurements of low-energy beta decays provide a direct and model-independent approach to measure the effective electron (anti-)neutrino mass. I have reviewed the recent progress of the field starting from the first molecular tritium spectrum measured with the current state of the art KATRIN experiment before discussing the development of new approaches to achieve the sensitivity required to cover the full neutrino mass parameter range allowed in the inverted mass ordering scheme. The new avenues opened by micro-calorimeteric measurements of the electron capture decay spectrum of ¹⁶³Ho (ECHo, Holmes and Numecs) and by the new technology of cyclotron radiation emission spectroscopy in combination with molecular and atomic tritium sources have been presented.     

Measurement of the 214Po half-life by the DEVIS track setup

Measurement of the ²¹⁴Po half-life with the DEVIS track setup at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) by means of a procedure based on determining lifetimes of individual nuclei is described. The value obtained for the ²¹⁴Po half-life is 163.8 ± 3.0 µs. The possibility of reaching the accuracy of the measurements that is required for testing the statement that the decay of some nuclei has a nonexponential character and the source intensity necessary for this are discussed.