Detection Of Conversion Electrons Research Articles

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.

Expected yields ofTa181(e,e′)Ta*181in the multi-keV range with a plasma-cathode electron beam

Calculations of the cross sections of inelastic electron scattering $(e,e')$ on a nucleus in the multi-keV energy range strongly depend on the description of the screening of the nuclear Coulomb potential as well as on the deformation of the wave functions of the incoming and outgoing electron in the vicinity of the nucleus. These cross sections are evaluated at values lower than $10^{-30}$ cm$^2$ which vary by several orders of magnitude according to the models. Experimental measurements would be required to constrain the models but it is a real challenge to measure such low cross sections. In this study, we demonstrate that inelastic electron scattering is the main nuclear excitation mechanism in a $^{181}$Ta target irradiated with a new intense 10 - 30 keV electron beam produced with a biased laser-plasma. Calculations show that through the detection of conversion electrons, it should be possible to measure the nuclear excitation yields. The effect of electron beam heating and of plasma deposition on the tantalum target are quantified, thus allowing the dimensioning of a possible experimental configuration to study $(e,e')$ processes in this range of energy for the first time.

Radiation Effects in Amorphous Metallic Alloys as Revealed by Mössbauer Spectrometry: Part II. Ion Irradiation

Due to their excellent magnetic properties, amorphous metallic alloys (AMAs) are considered for the construction of magnetic cores of radio-frequency cavities in accelerators. Here, they might be exposed to ion bombardment. The influence of irradiation by both light and heavy ions featuring low and high energies, respectively, is followed by the techniques of 57Fe Mössbauer spectrometry. Modifications of surface layers in selected Fe-containing AMAs after ion irradiation are unveiled by detection of conversion electrons and photons of characteristic radiation whereas those in their bulk are derived from standard transmission spectra. Rearrangement of microstructure which favors the formation of magnetically active regions, is observed in surface regions bombarded by light ions. Heavy ions caused pronounced effects in the orientation of net magnetization of the irradiated samples. No measurable impact upon short-range order arrangement was observed. Part I of this paper is devoted to radiation effects in Fe-based AMAs induced by neutron irradiation.

Scanning conversion electronic Mössbauer spectroscopy of local surface layers of materials

The method of scanning conversion electron Mössbauer spectroscopy has been proposed, which suggests the anode in the conversion electron detector to be made in the needle form. It has been shown that it is possible to scan the sample surface to obtain information on the structural-phase state of the local near-surface layers of the studied materials. The methods of transmission Mössbauer spectroscopy (MS), integral (ICEMS) and scanning (SCEMS) conversion electron Mössbauer spectroscopy have been used to study the iron nanotubes prepared by template synthesis using the track membranes. According to MS data, ~ 90% of iron in the nanotube structure is in a chemically free state. It follows from the ICEMS and SCEMS results that in the near-surface layers of nanotubes the iron cations are predominantly localized in the structure of hydroxides. The differences in the orientation of the magnetic moments in the bulk and near-surface layers have been established.

Design and Development of a Mini-Orange Magnetic Spectrometer with Multichannel Facility for Conversion Electron Spectroscopy

Background: Conventional magnetic spectrometers used for conversion electron detection are very cumbersome, require strong magnetic fields and the spectra have to be scanned point by point and have very low transmission. A magnetic filter using permanent magnets and an Si(Li) detector would facilitate multichannel analysis with high transmission. The mini-orange is a new type of spectrometer for conversion electrons combining a solid state Si(Li) detector with a filter of permanent magnets around a central absorber of lead.Purpose: An indigenously developed magnetic spectrometer if optimized properly would be of great use in conversion electron spectroscopy for both online and offline experiments. Methods: A Mini-Orange magnetic spectrometer made of small permanent magnets has been designed and developed indigenously and optimized for its best performance condition. The transmission curves for different energy regions are plotted using the conversion electron spectra from the standard gamma transitions from 153Gd, 169Yb and 131Ba decays. The optimized spectrometer facilitates multichannel acquisition of conversion electron spectra for precision electron spectroscopy. The system also can be used in in-beam experiments with minor modifications of the vacuum chamber.Results: The optimized spectrometer was used for precision electron spectroscopy. Experimental transmission curves are then obtained by plotting Transmission (T) against the corresponding electron energy for low energy, medium energy and a broad energy range. Out of the several experiments done the optimum settings for f and g, that resulted in this curve, is identified at f = 7.5 cm and g = 4.5 cm. Conclusions: The optimized spectrometer facilitates multichannel acquisition of conversion electron spectra for precision electron spectroscopy. The system also can be used in in-beam experiments with minor modifications of the vacuum chamber.

The identification and confirmation of isomeric states in 254Rf and 255Rf through conversion electron detection

The neutron-deficient isotopes 254,255Rf were produced in the fusion-evaporation reaction 50Ti+206Pb at the gas-filled recoil separator TASCA. Decay properties of these nuclei were investigated by applying fast digital electronics. A search for isomeric states in both isotopes was performed by using the accompanying conversion electron emissions. Isomeric states with half-lives of 4(1) μs and >30 μs were measured for 254Rf and 255Rf, respectively, which confirm the findings at different separators. The present experimental results demonstrate the great potential of fast digital electronics for measurements of isomeric states in the heaviest nuclei, which are only producible in small quantities.

In-beam conversion-electron spectroscopy of180Hg

Excited states in {sup 180}Hg were populated using the {sup 147}Sm({sup 36}Ar,3n){sup 180}Hg reaction and studied by in-beam conversion-electron spectroscopy. Conversion electrons emitted at the target position were measured using the Silicon Array for Conversion Electron Detection (SACRED) spectrometer and tagged through the characteristic {alpha} decays of {sup 180}Hg detected in a position-sensitive silicon strip detector located at the focal plane of the gas-filled recoil separator Recoil Ion Transport Unit (RITU). Electron conversion of transitions previously assigned to {sup 180}Hg through in-beam {gamma}-ray spectroscopy studies was identified up to the 10{sup +}{yields}8{sup +} transition and the intensities of the conversion-electron transitions were found to be consistent with the previous multipolarity assignments. Evidence was also found for two highly converted transitions in {sup 180}Hg: a 167 keV transition is interpreted as the transition from the newly identified 2{sub 2}{sup +} state at 601 keV to the 2{sub 1}{sup +} state at 434 keV, while a 420 keV transition is assigned as the E0 decay from the 0{sup +} bandhead of the prolate-deformed configuration to the weakly deformed ground state.

Publisher’s Note: Identification of the slowE3transition136Csm→136Cs with conversion electrons [Phys. Rev. C84, 014329 (2011)

We performed at ISOLDE the spectroscopy of the decay of the 8- isomer in 136Cs by and conversion-electron detection. For the first time the excitation energy of the isomer and the multipolarity of its decay have been measured. The half-life of the isomeric state was remeasured to T1/2 = 17.5(2) s. This isomer decays via a very slow 518 keV E3 transition to the ground state. In addition to this, a much weaker decay branch via a 413 keV M4 and a subsequent 105 keV E2 transition has been found. Thus we have found a new level at 105 keV with spin 4+ between the isomeric and the ground state. The results are discussed in comparison to shell model calculations.

Identification of the slowE3transition136Csm→136Cs with conversion electrons

We performed at ISOLDE the spectroscopy of the decay of the ${8}^{\ensuremath{-}}$ isomer in ${}^{136}$Cs by $\ensuremath{\gamma}$ and conversion-electron detection. For the first time the excitation energy of the isomer and the multipolarity of its decay have been measured. The half-life of the isomeric state was remeasured to ${T}_{1/2}=17.5(2)$ s. This isomer decays via a very slow 518-keV $E3$ transition to the ground state. In addition to this, a much weaker decay branch via a 413-keV $M4$ and a subsequent 105-keV $E2$ transition has been found. Thus we have found a new level at 105 keV with spin ${4}^{+}$ between the isomeric and the ground state. The results are discussed in comparison to shell-model calculations.

Absolute measurement of activity of 198Au foils using the 4 - coincidence counting method andcorrections by the Monte Carlo simulation

The thermal neutron fluence rate is determined by the gold activation method. The absolute activity of the irradiated gold foil is measured by a 4πβ-γ coincidence counter. Using this method, corrections for the detection of conversion electrons and gamma rays by a 4πβ counter are very important to obtain accurate absolute activity. In this work, Monte Carlo simulations were performed to derive the correction factor K. The absolute measurement of (198)Au activity for 20-100 μm thickness Au foils were performed to verify the calculating model of the 4πβ-γ coincidence counting system.

Preparation of 235mU targets for 235U(n,n′)235mU cross section measurements

This paper describes the preparation of samples for an experiment to measure the cross-section for 235U(n,n′)235mU in a fast fission spectrum of neutrons provided by a fast pulsed reactor/critical assembly. Samples of 235mU have been prepared for the calibration of the internal conversion electron detector that is used for the 235mU measurement. Two methods are described for the preparation of 235mU. The first method used a U-Pu chemical separation based on anion-exchange chromatography and the second method used an alpha recoil collection method. Thin, uniform samples of 235mU+235U were prepared for the experiment using electrodeposition.

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.

Analysis of Fe valence states in iron-gall inks from XVIth century manuscripts by 57Fe Mössbauer spectroscopy

The charge state of Fe in iron-gall inks was studied by 57Fe Mössbauer spectroscopy. Three ancient manuscripts from the 16th century and a set of model samples were characterized. The chemical fingerprint was found to be well defined for the ancient manuscripts whereas the model samples show a larger spread of chemical states. Two different modes of Mössbauer spectroscopy were used in this work: (1) the detection of γ-quanta in the usual transmission mode and (2) the detection of conversion electrons in backscattering geometry in a special parallel plate avalanche counter. The use of these two measuring modes allowed to reveal differences between the chemical features of the core and the surface of the iron-gall ink structures.

Conversion electron and beta decay spectroscopy at SHIP

Novel methods for internal conversion electron and β-decay spectroscopy at the focal plane of a recoil separator are discussed. As an example the experimental data collected at the focal plane of the velocity filter SHIP (GSI, Darmstadt) are presented and compared with the results of the GEANT Monte Carlo simulations. It is shown that the simultaneous detection of conversion electrons, γ-rays and X-rays is possible, which significantly broadens the range of applications of this and similar systems.

In-trap conversion electron spectroscopy

The Penning trap REXTRAP at ISOLDE was used to test the feasibility of in-trap conversion electron spectroscopy. The results of simulations, experiments with solid conversion electron sources as well as first on-line tests with trapped radioactive ions are presented. In addition to obtaining high-resolution spectroscopic data, the detection of conversion electrons was found to be a useful tool for the diagnostics of the trap operation. The tests proved the feasibility of in-trap spectroscopy but also revealed some potential problems to be addressed in the future.

Laser-induced structural modifications ofFeMoCuB metallic glasses before and after transformation into ananocrystalline state

The effects of laser treatments on the structural and magneticproperties of metallic ribbons have been studied using the melt-spunFe76Mo8Cu1B15 alloy in as-quenched andnanocrystalline states. 57Fe Mössbauer effect techniques,comprising transmission geometry measurements (TM) and detection ofconversion electrons (CEMS), have been employed in addition tomagnetization measurements, differential scanning calorimetry andx-ray diffraction. The Curie temperature of the as-quenched alloy wasabout 70 °C. The distributions of hyperfine magnetic fields aswell as quadrupole splitting obtained from TM and CEM spectra haverevealed the possibility of observing laser-induced structuralmodifications even at room temperature when the system is only weaklymagnetic. Consequently, both types of hyperfine interactions havebeen detected and they are nearly in equilibrium (having the samestrength or occurring to the same extent). After treatments with apulsed XeCl excimer laser (with a homogeneous beam of 5×5 mm2, 308 nm, 55 ns, 1 Hz), the significance of magneticdipole interactions rises as a function of the number of laser pulses(up to 64) and the laser beam fluence (up to 3 J cm-2). Notraces of laser-induced crystallization have been found. In thenanocrystalline Fe76Mo8Cu1B15 alloy, surfacecrystallization was already completely removed after the first pulseof 1 J cm-2.

An improved selective excitation double Mössbauer spectrometer

The design, operation and performance of a selective excitation double Mössbauer (SEDM) spectrometer are described. An innovative drive-mounted conversion electron detector for scattered γ-ray energy analysis provides a three orders of magnitude improvement in counting efficiency over previous SEDM equipment. Simple digital circuitry together with Wissel Mössbauer velocity transducers and electronics supplies energy synchronization for indefinite collection times. Magnetic materials containing resonant Mössbauer nuclei (e.g., Fe57) can now be conveniently studied using SEDM, offering a unique insight into dynamic processes.

Simulation and experimental results for the detection of conversion electrons with gas proportional scintillation counters

The application of gas proportional scintillation counters (GPSC) to the detection and identification of conversion electrons in the medium energy range is investigated. Experimental and Monte Carlo results are presented for the response of a xenon GPSC, filled at atmospheric pressure, to the decay of a 109 Cd source. This source emits 88.0 keV γ-rays, e L=84.6 keV and e K=62.5 keV conversion electrons, as well as fluorescence X-rays and Auger electrons. Good agreement is found between the measured and the calculated energy spectra. The response to higher-energy electrons is investigated by Monte Carlo simulation, by considering a hypothetical GPSC filled with xenon at 10 atm and doped with the 133 m Xe metastable isotope. The calculated energy spectra for the absorption of the 133 m Xe 233.2 keV γ-rays, e K=198.6 keV and e L=228.4 keV conversion electrons, as well as fluorescence X-rays and Auger electrons, are presented and discussed.

Time course of the inflammatory response to histamine and allergen skin prick test in guinea‐pigs

Plasma exudation and vasodilatation are key microvascular features of acute inflammation. Exudation and vasodilatation responses in the weal area after skin prick testing with histamine are essentially completed within 30 min. There is evidence to suggest that vasodilatation lasts considerably longer after provocation with allergen, but there is no information on the duration of plasma exudation. The purpose of this study was to measure the time course of the microvascular inflammatory response in the skin after histamine and allergen provocation. Skin prick tests were performed with histamine, allergen (ovalbumin) or saline (control) on guinea-pigs which were shaved on their backs. Radioactive 113mIn was used to label transferrin as a plasma tracer. Radioactivity was recorded from the superficial part of the skin by external detection of conversion electrons from the decay of 113mIn. The increase in count rate, corresponding to tracer accumulation by vasodilatation and/or plasma exudation, was used as a measure of the microvascular inflammatory response to skin prick test. The microvascular response was studied immediately and up to 30 min after provocation. The largest response to histamine and allergen occurred immediately after provocation. The exudative response then gradually declined to be absent after 25-30 min. Skin prick test with saline resulted in a small response of shorter duration. We conclude that the microvascular reaction to histamine as well as allergen provocation in guinea-pig skin has a rapid onset and a duration of approximately 30 min.

In-beam conversion electron spectroscopy using the SACRED array

Conversion electron studies of medium-heavy to heavy nuclear mass systems are important where the internal conversion process begins to dominate over gamma-ray emission. The use of a segmented detector array sensitive to conversion electrons has been used to study multiple conversion electron cascades from nuclear transitions. The application of the Silicon Array for ConveRsion Electron Detection (SACRED) for in-beam measurements has successfully been implemented.