Conversion Electron Measurements Research Articles

Direct observation of E0 transitions in 188Pb through in-beam spectroscopy

Competing configurations, assigned with three different shapes, are mixed at low angular momentum in the neutron-deficient 188Pb nucleus. Here, we present a simultaneous conversion electron and γ-ray in-beam spectroscopic precision measurement employing the sage spectrometer. The level energy of the first excited state, 02+, has been determined at 591(1)keV through direct measurement of conversion electrons. By using the intensity of the observed 02+→01+ transition to the ground state, the feeding of the 02+ state has been determined for the first time, which suggests the 02+ state is the head of the predominantly prolate band. The compositions of the 42+→41+ and 22+→21+ inter-band transitions have been determined, indicating configuration mixing between the bands.

Three-dimensional surface analysis of iron-based materials using synchrotron Mössbauer source

A novel three-dimensional surface analysis system for iron-based solid materials has been developed. This system is composed of a synchrotron Mössbauer source, an X-ray focusing device, a precision stage, a gas flow proportional counter for conversion electron measurements, and multiple multichannel scalers. The performance was evidenced by determining the spatial distribution of the iron oxide abundance on a laser-ablated iron foil surface. This system can be widely utilized as a powerful analytical tool in steel science for corrosion, welding, and laser surface modification.

The LSU-Argonne conversion electron spectrometer: A new detector for the X-Array and SATURN decay station

A new conversion electron detector has been commissioned at the ATLAS/ CARIBU facility at Argonne National Laboratory. The LSU-Argonne Conversion Electron Spectrometer (LACES) is a LN2-cooled Si(Li) detector system designed to be incorporated into a decay station that comprises the dedicated HPGe clover array with a box geometry (X-Array) and the Scintillator and Tape Using Radioactive Nuclei (SATURN) device. This integration enables simultaneous measurements of conversion electrons and gamma-rays in decay experiments, yielding novel information on transition multipolarities, electric monopole transitions, and isomeric states that decay mostly via conversion electrons. A measurement of the energy resolution of LACES yielded 2.3-keV FWHM at 975 keV for electrons and 1.3-keV FWHM at 75 keV for X-rays. A detailed study of the absolute detection efficiency (at 5 mm from the source) was performed, where this quantity was determined experimentally in the range of electron transition energies between 25.5 keV and 1047.8 keV and subsequently simulated using the GEANT4 code. Measurement and simulations are found to be in excellent agreement. A precise characterization, for this type of detector system, of the absolute detection efficiency for such a wide energy range is reported for the first time.

Electric monopole transitions and structure of low-spin states in Pd106

Structures in the $^{106}\mathrm{Pd}$ nucleus have been studied in the $\mathrm{EC}/{\ensuremath{\beta}}^{+}$ decay of $^{106}\mathrm{Ag}$ at the INFN Legnaro National Laboratories using the Spes Low-energy Internal Conversion Electron Spectrometer (SLICES). The K-conversion coefficients and the electric monopole transition strengths, between low-lying ${2}^{+}$ and ${0}^{+}$ states, have been studied. These experimental data combined with the results from conversion electron measurement on $^{104}\mathrm{Pd}$ previously performed by the Florence spectroscopy group were compared with the theoretical values calculated in the framework of the interacting proton-neutron boson model. Good agreement between experimental and theoretical values is found when interpreting the ${0}_{3}^{+}$ level as an intruder state.

The mini-orange magnetic β-spectrometer

The brief review available the mini-orange type beta- spectrometers have been made. The various methods for determination of the mini-orange efficiency are discussed. On an example of off-line mini-orange beta-spectrometer of a Department of Nuclear spectroscopy and radiochemistry of Laboratory for Nuclear Problems of JINR, the mini-orange beta-spectrometer as perspective installation for measurement of conversion electrons' spectra from the short-lived neutron- deficient isotopes has been shown.

High-resolution spectroscopy of gaseous 83mKr conversion electrons with the KATRIN experiment

In this work, we present the first spectroscopic measurements of conversion electrons originating from the decay of metastable gaseous 83mKr with the Karlsruhe Tritium Neutrino (KATRIN) experiment. The obtained results represent one of the major commissioning milestones for the subsequent direct neutrino mass measurement with KATRIN. The successful campaign demonstrates the functionalities of the KATRIN beamline. Precise measurement of the narrow K-32, L3-32, and N2,3-32 conversion electron lines allowed to verify the eV-scale energy resolution of the KATRIN main spectrometer necessary for competitive measurement of the absolute neutrino mass scale.

Electron spectrometer for electric monopole (E0) transition studies in nuclei

The study of electric monopole (E0) transitions between two 0+ states is important because the monopole strength carries vital information about the nuclear structure due to its direct link with the mean squared charge radius r2 and quadrupole deformation parameter β. Therefore, the measurement of internal conversion electrons (ICE) or internal pair formation (IPF) is crucial for E0 transition studies. Transitions between 0+ states do not change angular momentum. Hence, single-photon emission is forbidden, but can decay by conversion electrons or pair formation and two-photon emission which is mostly negligible. In order to implement E0 studies at iThemba LABS, an electron spectrometer that uses a solenoidal magnetic field acting as a lens and a Si(Li) detector has been refurbished and characterized using calibration sources of ICE. Figures of merit have been extracted and compared with simulations. The spectrometer coupled with an array of LaBr3:Ce detectors and Low Energy Photon Spectrometers (LEPS) was successfully implemented for in-beam experiments. Measurements of internal conversion coefficients (ICC) and monopole strengths extracted from in-beam measurements of 72As, 72Ge, and 72Se are presented.

The SPEDE spectrometer

The electron spectrometer, SPEDE, has been developed and will be employed in conjunction with the Miniball spectrometer at the HIE-ISOLDE facility, CERN. SPEDE allows for direct measurement of internal conversion electrons emitted in-flight, without employing magnetic fields to transport or momentum filter the electrons. Together with the Miniball spectrometer, it enables simultaneous observation of {\gamma} rays and conversion electrons in Coulomb-excitation experiments using radioactive ion beams.

Mini-orange spectrometer at CIAE**Supported by National Natural Science Foundation of China (11305269, 11375267, 11475072, 11405274, 11205068, 11175259)

A mini-orange spectrometer used for in-beam measurements of internal conversion electrons, consisting of a Si(Li) detector and different sets of SmO5 permanent magnets for filtering and transporting the conversion electrons to the Si(Li) detector, has been developed at the China Institute of Atomic Energy. The working principles and configuration of the mini-orange spectrometer are described. The performance of the setup is illustrated by measured singles conversion electron spectra using the mini-orange spectrometer.

Shape coexistence at low spin in the Z = 50 region and its spectroscopic signatures

Nuclei in the Z = 50 region provide excellent examples of shape coexistence, the establishment of which occurred through the use of detailed spectroscopy, based not only on γ-ray spectroscopy but also conversion electron, particle transfer, Coulomb excitation, and lifetime measurements. The evidence to date strongly suggests that the presence of coexisting shapes arises from the promotion of protons across the Z = 50 closed shell and the strong correlations arising from interplay of the pairing and quadrupole interactions. The evidence for the presence of shape coexistence in the Z = 50 region, at low spin and low excitation energies, will be presented and clues for the microscopic origin explored.

Far From ‘Easy’ Spectroscopy with the 8π and GRIFFIN Spectrometers at TRIUMF-ISAC

The 8π spectrometer, installed at the TRIUMF-ISAC facility, was the world's most sensitive γ-ray spectrometer dedicated to β-decay studies. A description is given of the 8π spectrometer and its auxiliary detectors including the plastic scintillator array SCEPTAR used for β-particle tagging and the Si(Li) array PACES for conversion electron measurements, its moving tape collector, and its data acquisition system. The recent investigation of the decay of 124Cs to study the nuclear structure of 124Xe, and how the β-decay measurements complemented previous Coulomb excitation studies, is highlighted, including the extraction of the deformation parameters for the excited 0+ bands in 124Xe. As a by-product, the decay scheme of the (7+) 124Cs isomeric state, for which the data from the PACES detectors were vital, was studied. Finally, a description of the new GRIFFIN spectrometer, which uses the same auxiliary detectors as the 8π spectrometer, is given.

Measurement of internal conversion electrons from Gd neutron capture

Gadolinium (Gd) is a suitable material for neutron conversion because of its superior neutron absorption cross-section. However, the principal secondary particles that generate electron-hole pairs in a semiconductor detector after Gd neutron capture are low-energy internal conversion (IC) electrons. We measured the IC electron spectrum due to Gd neutron capture by using a thermal neutron beam and a digitizer-based multidetector spectroscopy. We also discussed the effective use of the IC electrons in the context of a twin-detector design and the associated gamma-ray rejection issues. Extensive simulations of the spectra of IC electrons and gamma rays agreed well with the experimental results; both types of results support the feasibility of the proposed n–γ separation method.

Conversion electron measurements and determination of rotational parameters in 177Lu and 177Hf

Conversion electron and gamma spectroscopic measurements were carried out on the 160.44d 177mLu decay with a mini-orange electron transporter coupled to a Si(Li) detector and a large-volume HPGe detector. Conversion electron intensities and internal conversion coefficients of 32 transitions in the two nuclei were obtained by the Normalized Peak to Gamma method. Of these, many are being reported for the first time. Mixing ratios were determined for the M1 + E2 transitions of the rotational bands 7/2+[404] in 177Lu , 7/2−[514] and 9/2+[624] in 177Hf populated by the isomer’s decay. The value of the rotational parameter |(gK − gR)/Q0| was calculated for all the three bands. A revised decay scheme is proposed for 177mLu .

The SAGE spectrometer: A tool for combined in-beam γ-ray and conversion electron spectroscopy

The SAGE spectrometer allows simultaneous in-beam γ-ray and internal conversion electron measurements, by combining a germanium detector array with a highly segmented silicon detector and an electron transport system. SAGE is coupled with the ritu gas-filled recoil separator and the great focal-plane spectrometer for recoil-decay tagging studies. Digital electronics are used both for the γ ray and the electron parts of the spectrometer. SAGE was commissioned in the Accelerator Laboratory of the University of Jyväskylä in the beginning of 2010.

Combined in-beam electron andγ-ray spectroscopy ofHg184,186

By exploiting the SAGE spectrometer a simultaneous measurement of conversion electrons and {gamma} rays emitted in the de-excitation of excited levels in the neutron-deficient nuclei {sup 184,186}Hg was performed. The light Hg isotopes under investigation were produced using the 4n channels of the fusion-evaporation reactions of {sup 40}Ar and {sup 148,150}Sm. The measured K- and L-conversion electron ratios confirmed the stretched E2 nature of several transitions of the yrast bands in {sup 184,186}Hg. Additional information on the E0 component of the 2{sub 2}{sup +}{yields}2{sub 1}{sup +} transition in {sup 186}Hg was obtained.

Electron-gamma spectroscopic measurements in 131Cs

The decay of 131Ba to levels of 131Cs has been studied using an HPGe detector for gamma-ray and a mini-orange electron spectrometer for conversion electron measurements. Our experiment identifies 76 gamma transitions in this decay, including 15 new gamma rays and 6 new K-conversion electron lines. The results also include M2 multipolarity assignment for the 269 keV transition, E2 assignment to two newly observed transitions, M 1 + E 2 for the 406 and 417 keV transitions and M3 for the 533.67 keV transition. A revised 131Cs level scheme is proposed. While confirming the existence of 15 well-established levels, we present strong evidence from our beta decay study for five levels at 496, 764, 775, 1044 and 1258 keV which were earlier observed in reaction studies. Spin–parity assignments to a few other levels are also suggested. The level structure of 131Cs is discussed in the light of the intermediate coupling model.

Observation of M3 isomeric transition from 156mPm through the βdecay of 156Nd

An M3 transition in a doubly odd nucleus of 156Pm was identified by internal conversion electron measurement through the β-decay of 156Nd which was separated from the fission products of 235U using the on-line mass separator KUR-ISOL. The isomeric state at 150.3keV de-excites to the ground state with the M3 transition, and the spin-parity is considered to be 1-. Nilsson configurations are also discussed on the basis of the systematics.

Precision electron-gamma spectroscopic measurements in 75As

The decay of 75Se to levels of 75As has been studied using an HPGe detector for gamma-ray and a mini-orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 18 gamma rays and 16 conversion electron lines reported for the first time. New results also include E2 multipolarity assignment for the 81 keV transition, M1 assignment to three newly observed transitions and M1 + E2 for the 617 keV transition. A revised 75As level scheme is constructed using the Ritz combination principle through the computer code GTOL. While confirming the existence of 10 well-established levels, two levels at 587 and 859 keV are newly placed into the decay scheme of 75Se. The interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly placed 586.8 keV 1/2- and 859.9 keV 1/2+ levels are studied in the light of the Interacting Boson-Fermion Model.

Low-energy conversion electron detection in superfluid 3He at ultra-low temperature

We report on the first results of the MACHe3 (MAtrix of Cells of Helium 3) prototype experiment concerning the measurement of low-energy conversion electrons at ultra-low temperature. For the first time, the feasibility of the detection of low-energy electrons is demonstrated in superfluid 3He-B cooled down to 100 μ K . Low-energy electrons at 7.3 keV coming from the K shell conversion of the 14.4 keV nuclear transition of a low-activity 57Co source are detected, opening the possibility to use a 3He-based detector for the detection of Weakly Interacting Massive Particles (WIMPs) which are expected to release an amount of energy higher-bounded by 5.6 keV.

In-beam electron spectrometer used in conjunction with a gas-filled recoil separator

The conversion-electron spectrometer SACRED has been redesigned for use in conjunction with the RITU gas-filled recoil separator. The system allows in-beam recoil-decay-tagging (RDT) measurements of internal conversion electrons. The performance of the system using standard sources and in-beam is described.