Direct observation of two protons in the decay of 54Zn

The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope.     

High-resolution measurements of beta-delayed protons from 37Ca and 41Ti

Protons with energies from 870 keV to 5.4 MeV have been observed following bombardment of a ⁴⁰Ca target with ³He at beam energies of 29.5, 36.5 and 60 MeV, as well as from 40 MeV ³He bombardment of an ³⁶Ar gas target. These data, and those resulting from 20 MeV proton bombardment of ⁴⁰Ca, permit accurate identification of proton unbound levels in ⁴¹Sc, ³⁷K, and ⁴⁰Ca fed by allowed beta decay from ⁴¹Ti, ³⁷Ca or ⁴⁰Sc, respectively. Absolute ft values have been determined for beta decay to these levels. The half-life of ⁴¹Ti has been remeasured to be 80±2 ms and the log ft for its superallowed decay branch has been found to be 3.35±0.02, indicating an isospin purity for the lowest $\text{T =}\text{3}\text{2}\text{state in}{}^{41}\text{Sc of}\text{≈ 91 \%}$. The $\text{ft}\text{values for}{}^{37}\text{Ca}\text{β}{}^{\mathrm{+}}$ decay are compared to shell-model calculations for beta-decay in A = 37 nuclei.     

Direct and beta-delayed proton decay of very neutron-deficient rare-earth isotopes produced in the reaction58Ni+92Mo

Using on-line mass separation of evaporation residues from the reaction⁵⁸Ni +⁹²Mo→¹⁵⁰Yb*, a proton line of 1,055±6 keV energy and 0.42±0.10 s half-life was observed at mass number 147. The origin of this activity is very likely the direct proton decay of¹⁴⁷Tm. Beta-delayed protons registered at the same mass position show a pronounced peak structure in their energy distribution. A lower limit of their half-life was set to 1 s.     

Observation of the neutron radiative decay

The aim of this work is the experimental observation of and research into a rare neutron mode, the radiative beta decay, where a new particle, the radiative gamma quantum, is formed along with the expected decay products: a beta electron, a recoil proton, and an antineutrino. The discovery of this rare neutron decay mode was conducted through identification of triple-coincidence events: simultaneous registration of a beta electron, a proton, and a radiative gamma quantum. The ordinary neutron decay was registered by double coincidences of a beta electron and a recoil proton. The statistics collected allow one to deduce the branching ratio (BR) BR = (3.2 ± 1.6) × 10⁻³ (90% C.L.) in the gamma energy region greater than 35 keV. This value of BR is consistent with standard electroweak theory. The text was submitted by the authors in English. An erratum to this article is available at .     

New beta-delayed proton emitters in the lanthanide region

Several new beta-delayed proton emitters have been observed at the on-line mass separator OASIS. They were provisionally identified as:¹²⁵Ce (8.9±0.7 s),¹²⁶pr (3.2±0.6 s),¹²⁷Nd (1.9±0.4 s),¹²⁸Nd (4±2 s),¹³⁷Gd (7±3 s),¹³⁹Gd (4.9±1 s), and¹⁴³Dy (4.1±0.3 s).     

First direct observation of two protons in the decay of 45Fe with a time-projection chamber

The decay of the ground-state two-proton emitter 45Fe was studied with a time-projection chamber and the emission of two protons was unambiguously identified. The total decay energy and the half-life measured in this work agree with the results from previous experiments. The present result constitutes the first direct observation of the individual protons in the two-proton decay of a long-lived ground-state emitter. In parallel, we identified for the first time directly two-proton emission from 43Cr, a known beta-delayed two-proton emitter. The technique developed in the present work opens the way to a detailed study of the mechanism of ground state as well as beta-delayed two-proton radioactivity.     

Observation of trielectronic recombination in Be-like Cl ions

Recombination involving the core excitation of two electrons, which may be termed trielectronic recombination, has been experimentally identified for the first time. Using Cl13+ ions circulating in the TSR heavy-ion storage ring, we have observed surprisingly strong low-energy trielectronic recombination resonances, comparable to the dielectronic process. At higher electron-ion collision energies, trielectronic recombination is suppressed due to the autoionization of the triply excited intermediate state into excited final states. The formation of the intermediate state depends sensitively on configuration mixing, making trielectronic recombination a challenge to atomic-structure calculations.     

Observation of radiative leptonic decay of the tau lepton

Using 4.68 fb(-1) of e(+)e(-) annihilation data collected with the CLEO II detector at the Cornell Electron Storage Ring, we have studied tau radiative decays tau(-)-->nu(tau)&mgr;(-)nu;(&mgr;)gamma and tau(-)-->nu(tau)e(-)nu;(e)gamma. For a 10 MeV minimum photon energy in the tau rest frame, the branching fraction for radiative tau decay to a muon or electron is measured to be (3.61+/-0.16+/-0. 35)x10(-3) or (1.75+/-0.06+/-0.17)x10(-2), respectively. The branching fractions are in agreement with standard model theoretical predictions.     

Observation of nucleon clusters in the spontaneous decay of234U

The emission of Ne and Mg nuclei was detected in the spontaneous decay of²³⁴U with probabilities of, respectively, (3.9 ±1.0) × 10^?13 and (2.3 ±0.7) × 10^?13 relative toα-decay. The upper limits of this kind of decay for²³⁵U and²³⁶U have been established. Systematics of half-lives for cluster emission are found to be similar to the Geiger-Nuttall dependence forα-decay. Some evidence for the presence of hindrance to cluster emission from the odd-mass nuclei²³³U and²³⁵U is obtained.     

A new series of beta-delayed proton precursors

The $\text{T}{}_{\mathrm{z}}\text{=+}\text{1}\text{2}$ beta-delayed proton precursors ⁶⁵Ge, ⁶⁹Se, ⁷³Kr and ⁷⁷Sr have been identified and their decay energies, half-lives and proton branching ratios determined. The half-life of the previously unreported ⁷⁷Sr is 9.0± 1.0 s.     

Observation of the decay instability of a beam plasma wave

The spontaneous decay of a beam plasma wave into an ion acoustic and an electron plasma wave has been observed during the interaction of a monoenergetic electron beam with a helium and a neon plasma.     

Observation of the two-photon decay of a light penetrating particle

Coincident two-photon events, emerging from a 2 m long decay region, and pointing back to the SIN 590 MeV proton beam dump were detected in a thin-foil optical spark chamber. There was a significant excess of photons at small angles (<7°): 19 were observed, whereas (2.0 ± 0.5) were measured with cosmic rays, and additional (2.5 ± 1.0) were accelerator background. The visible γ-ray energies were estimated by multiple scattering to be 〉E_γ1〈 = (83 ± 20) MeV, 〉E_γ2〈 = (84 ± 15) MeV. The invariant 2γ mass is < 1 MeV. The 2γ event rate did not change significantly, when a 20 cm thick iron wall was placed in front of the decay region, but vanished with the wall put at its end. Presumably a light boson χ⁰ comes from the beam dump, penetrates the shielding, and decays: χ⁰ → 2_γ The measured rate of (14.5 ± 5.0) events in 129 Coulomb fixes a combination of production cross section and life-time. If the new boson χ⁰ was the axion, one can solve for the Higgs parameter X = 3.0 ± 0.3, and infer τ_a ≈ 7 ms, and m_a = (250 ± 25) keV.     

Observation of the muonic decay of the charged intermediate vector boson

Muons of high transverse momentum p^μ_T have been observed in the large drift chambers surrounding the UA1 detector at the CERN 540 GeV pp? collider. For an integrated luminosity of 108 nb^?1, 14 isolated muons have been found with p_T > 15 GeV/c. They are correlated with a large imbalance in total transverse energy, and show a kinematic behaviour consistent with the muonic decay of the Intermediate Vector Boson W^± of weak interactions. The partial cross section is in agreement with previous measurements for electronic decays and with muon-electron universality. The W mass is determined to be m_W = 81⁺⁶_?7 GeV/c².