Internal Conversion Electron Spectra Research Articles

New results on the decay spectroscopy of 254No with GABRIELA@SHELS

The structure of the nucleus has been studied for more than 20 years: the last publications on its decay spectroscopy are from LBNL [1], GSI [2], JYFL [3] and ANL [4]. Four decay schemes featuring two isomers have been published and are interpreted differently in terms of excitation energy and decay scheme of the 2 nd isomer and configuration assignments of both K-isomers. These discrepancies have triggered new experiments including this one, performed with the GABRIELA [5, 6] array, at the focal plane of the SHELS [7] separator at the FLNR, Dubna. The first part of this proceeding will present the experimental setup and the analysis techniques used to reveal the electromagnetic decay of the known isomers in 254No. The second part will focus on the new results obtained with more than 1 million 254No nuclei implanted in the focal plane detector. In particular, the internal conversion electron spectrum observed in the decay of the 8− K-isomer has revealed the presence of a strong transition, most likely E0, suggesting low-lying shape coexistence in this nucleus as predicted in [8, 9]. The γ-ray spectrum obtained from the decay of the short-lived 170 μs isomer has revealed new γ-ray lines putting in doubt the previous interpretations about this isomer decay.

Analysis of a neutron-induced conversion electron spectrum of gadolinium

A 100-nm-thick gadolinium layer deposited on a pixelated silicon sensor was activated in a neutron field to measure the internal conversion electron (ICE) spectrum generated by neutron capture products of 155Gd and 157Gd. The experiment was performed at the ISIS neutron and muon facility, using a bespoke version of the HEXITEC spectroscopic imaging camera. Signals originating from internal conversion electrons, Auger electrons, x rays and gamma rays up to 150 keV were identified. The ICE spectrum has an energy resolution of 1.8–1.9 keV at 72 keV and shows peaks from the K, L, M, N+ ICEs of the 79.51 keV and 88.967 keV 2+-0+ gamma transitions from the first excited states in 158Gd and 156Gd, respectively, as well as the K ICEs of the 4+-2+ transitions at 181.931 keV and 199.213 keV from the respective second excited states. Spectrum analysis was performed using a convolution of a Gaussian with exponential functions at the low and high energy side as the peak shaping function. Relative ICE intensities were derived from the fitted peak areas and compared with internal conversion coefficient (ICC) values calculated from the BrIcc database. Relative to the dominant L shell contribution, the K ICE intensity conforms to BrIcc and the M, N, O+ ICE intensities are somewhat higher than expected.

Conversion electron spectroscopy of the 59.54 keV transition in 241Am alpha decay

A windowless Peltier-cooled silicon drift detector (SDD) was used to measure internal conversion electron (ICE) spectra of thin 241Am sources. The ICE peaks associated with the 59.54 keV gamma transition in 237Np were deconvoluted and relative ICE intensities were derived from the fitted peak areas. Corrections were made for energy dependence of the full-energy-peak counting efficiency, based on Monte Carlo simulations. As expected for this anomalous E1 transition, a significant discrepancy was found with the theoretical internal conversion coefficient (ICC) values calculated from the BrIcc database. Penetration effects are known to cause such anomalies in highly retarded transitions. The measured ICE intensities are in good agreement with a specific combination of literature data obtained with magnetic spectrometers.

Measurement of mass stopping power of chitosan polymer loaded with TiO2 for relativistic electron interaction

The Mass Stopping Power (MSP) of relativistic electrons in chitosan loaded with TiO2 of different proportions has been measured by recording the spectrum of internal conversion electrons. The internal conversion electrons of energies 614keV from Cs137, 942keV and 1016keV from Bi207 source are allowed to pass through chitosan-TiO2 alloy and transmitted electrons are detected with a Si (Li) detector coupled to an 8K multichannel analyzer. By knowing the energies of incident electrons and transmitted electrons, the energy loss and the MSP are determined. Thus measured MSP values of the alloys are compared with the values calculated using Braggs additivity rule. The disagreement between theory and experiment is found to increases with increasing TiO2 concentration in chitosan, indicating the influence of chemical environment in the properties of such polymeric membrane.

Deconvolution of 238,239,240Pu conversion electron spectra measured with a silicon drift detector

Internal conversion electron (ICE) spectra of thin 238,239,240Pu sources, measured with a windowless Peltier-cooled silicon drift detector (SDD), were deconvoluted and relative ICE intensities were derived from the fitted peak areas. Corrections were made for energy dependence of the full-energy-peak counting efficiency, based on Monte Carlo simulations. A good agreement was found with the theoretically expected internal conversion coefficient (ICC) values calculated from the BrIcc database.

On the 0+ state with the energy of 681.3 keV in 160Dy

A possibility that the 0+ state with the energy of 681.3 keV exists in the 160Dy nucleus is discussed. Calculations based on the interacting vector boson model show that in addition to the known 0+ states with the number of bosons n = 2, 5, 6, and 7 there should exist other states with the number of bosons n = 1, 3, 4, and 8 in 160Dy. It is shown that the peak at the energy 681.3 keV, which we experimentally observed in the 160Dy internal conversion electron spectrum, can be ascribed to the 0+ state with the number of bosons n = 1 or n = 8.

Modernization of the MAS-1 microscope for use in measurements of the spectra of internal conversion electrons

Efforts to increase the speed with which microscopic objects are measured are described. These efforts include the modernization of the MAS-1 automatic scanning microscope and the development of programs to reach an initial point and for carrying out automatic point-to-point linear transitions with a specified step. The error in realizing a transition to a given point with specified coordinates is shown to amount to 1 μm.

Finding of L 2,3 lines of the 148.16-keV γ transition in the 161Ho nucleus

The preliminary experimental data on the spectrum of internal-conversion electrons of the erbium fraction in the range of electron energies near ∼140 keV are reported. A photographic plate with a spectrogram of erbium fraction, exposed on the spectrometer of the Laboratory of Nuclear Problems (Joint Institute for Nuclear Research), was then measured on the PAVIKOM-1 microscopic complex (Lebedev Physical Institute). Due to the large number of spectral lines in this region, it was previously impossible to determine the intensities of the L2 and L3 lines of internal-conversion electrons for the 148.16-keV transition in the 161Ho nucleus. The use of the PAVIKOM-1 microscopic complex with a resolution of 0.01% made it possible to identify these lines and determine their intensities.

Tissue Absorbed Dose from a Gadolinium Layer Irradiated with Neutrons

A scintillation detector is used to investigate the leakage spectrum of internal conversion electrons produced from gadolinium by the capture of thermal neutrons in a thin layer of gadolinium. Thermoluminescence dosimeters are used to measure the dose of prompt γ-rays from gadolinium. The measurements are performed in the thermal column of a BFS-2 critical assembly and in a thermal-neutron beam extracted from a BR-10 reactor.

Isotopic analysis of plutonium using a combination of alpha and internal conversion electron spectroscopy

A combination alpha and conversion electron spectrometer was developed to quantify 239Pu/240Pu and 238Pu/241Am isotopic ratios of plated sources. The spectrometer was constructed with a commercially available low noise passivated ion-implanted planar silicon (PIPS) detector that was cooled to 77 K with liquid nitrogen. The combination spectrometer was used to quantify alpha-particles, conversion electrons, gamma-rays and X-rays associated with the decay of various plutonium isotopes and 241Am. Two amplifiers operated in parallel with different gains allowed for simultaneous acquisition of the lower energy region (21-60 keV) for internal conversion electrons, gamma-rays and X-rays, and the higher energy region (5050 keV-5550 keV) for alpha-particles. Energy resolutions of 2.2 keV FWHM (full-width at half maximum) for the 38.7 keV M conversion electrons and 11.2 keV for the 5499.2 keV alpha-particles from 238Pu were measured. The energy resolution combined with a spectral deconvolution method was sufficient to be able to quantify the radioactivity using the alpha-spectra as well as the electron spectra; however, quantification of the radioactivity using the internal conversion electron spectra was more problematic because of the presence of X-rays, gamma-rays, Compton scatter electrons and the number of electron peaks present. Deconvolution of the alpha-spectra yielded 239Pu and 240Pu activities (as % of total Pu activity), which differed from expected values by -3.0% to 5.4%. Deconvolution of an internal conversion electron spectrum of a high 239Pu and low 241Am activity sample yielded 239Pu and 240Pu activities, which differed by -17.1 and -35.5% relative to the alpha-measurements, respectively. Determination of the Pu activity using the electron spectra was more problematic in samples where the 241Am activity dominated. Determination of 238Pu and 241Am activity by the electron spectroscopy data was also obtained and compared with the alpha-spectroscopy results. Theoretical investigation of the removal of 241Am or use of a 400 eV electron spectrometer indicated that the internal conversion electron spectra could be used to determine the 238Pu, 239Pu, 240Pu/241Am (when present) activity with and without spectral deconvolution, respectively.

Further evidence on shape coexistence in72As

The 72As nucleus was studied via the (α,nγ) reaction at 14.2 MeV bombarding energy. Single γ−,γγ-coincidence, and internal conversion electron spectra were measured with Ge(HP) γ-ray and superconducting magnetic lens plus Si(Li) electron spectrometers. On the basis of the internal conversion coefficients of72As transitions, parities of the medium-spin levels up to 1.4 MeV excitation energy were determined, resulting in unambiguous parities also for the heads of the bands observed previously. The states observed were assigned to proton-neutron multiplets on the basis of their decay properties. The energy splittings of the observed multiplets are in accordance with the prediction of the previous interacting boson-fermion-fermion model (IBFFM) calculations using a transitional core lying between the vibrational SU(5) and γ-soft O(6) limits, except that of the πg9/2νg9/2 multiplet, which was described using the deformed SU(3) core in the present IBFFM calculations. Such a core structure is in accordance with previous particle-rotor and Hartree-Fock-Bogoliubov calculations.

Low-lying states of 109Sn from the 106Cd( α, nγ) reaction

Measurements of γ-ray, γγ-coincidence and internal conversion electron spectra from the 106Cd( α, nγ) 109Sn reaction were carried out at 15–20 MeV α-particle bombarding energies with Ge(HP) γ-ray and superconducting magnetic lens plus Si(Li) electron spectrometers. The energies, relative intensities, internal conversion coefficients and coincidence relations of the 109Sn transitions were determined, and a more complete, consistent level scheme has been deduced. Spin and parity values have been determined from the internal conversion coefficients, the bombarding-energy dependence of the side-feeding intensities of the states and the available γ-ray angular distribution data. The level scheme was interpreted in the framework of the quasi-particle shell model.

Calibration and interpretation of Mössbauer isomer shift of the 81-keV transition in133Cs

Radioactive ${}^{133}\mathrm{Xe}$ was implanted into five host materials (Al, V, Cr, Rh, Mo) by means of an isotope separator. Internal conversion electron spectra of the 81-keV transition in ${}^{133}\mathrm{Cs}$ were measured with an iron-free magnetic spectrometer and M\"ossbauer spectra were recorded independently. From the correlation between the weighted-mean M\"ossbauer isomer shifts and the intensity ratios of $(O+P)$-shell to ${N}_{1}$-shell conversion electrons, the change of the nuclear charge radius of the 81-keV transition in ${}^{133}\mathrm{Cs}$ was deduced to be $\ensuremath{\Delta}R/R=+(1.5\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for a uniform charge distribution of $R=1.2\ifmmode\times\else\texttimes\fi{}{A}^{1/3}$ fm or, equivalently, $\ensuremath{\Delta}〈{r}^{2}〉=+(6.6\ifmmode\pm\else\textpm\fi{}2.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ ${\mathrm{fm}}^{2}.$ This calibration makes it possible to reasonably interpret the extremely high isomer shifts observed in some refractory metals implanted with ${}^{133}\mathrm{Xe},$ where we take into consideration an increase in s-electron density originated from a decrease in the shielding effect on the s electrons by a removal of the $5p$ electron from the Cs impurity atom, which is attributed to the broadening of the valence band with compression and the resulting increase in overlap between the host and the impurity valence bands.

Proton-neutron multiplet states in112Sb

Excited states of {sup 112}Sb were investigated through the {sup 112}Sn(p,n{gamma}){sup 112}Sb reaction. {gamma}-ray, {gamma}{gamma}-coincidence, and internal conversion electron spectra were measured with Ge(HP) {gamma} and superconducting magnetic lens plus Si(Li) electron spectrometers at 8.5, 8.9, 9.1, and 9.3 MeV bombarding proton energies. A significantly extended level scheme was constructed. Spins and parities have been assigned to the levels from Hauser-Feshbach analysis of reaction cross sections, internal conversion coefficients, angular distribution of the {gamma} rays, and decay properties of the states. The low lying states were assigned to proton-neutron multiplets on the basis of their decay properties. The energy splitting of these multiplets have been calculated using the parabolic rule. {copyright} {ital 1997} {ital The American Physical Society}

Structure of the 73As nucleus

γ-ray, γγ-coincidence and internal conversion electron spectra of the 73Ge(p,nγ) 73As reaction were measured with Ge(HP) γ and a superconducting magnetic lens plus Si(Li) electron spectrometers at 1.92, 2.27, 2.45, 2.75 and 4.0 MeV bombarding proton energies. A complete level scheme was constructed up to an excitation energy of 1.4 MeV. The spins and parities have been assigned to the levels on the basis of the Hauser-Feshbach analysis of reaction cross sections, internal conversion coefficients and decay properties of the states. Energy spectra, electromagnetic moments and transition strengths were calculated in the framework of the interacting boson-fermion model and a reasonable agreement has been obtained between the experimental and theoretical results.

Structure of 72As nucleus

Abstract γ-ray, internal conversion electron and γγ-coincidence spectra of the 72Ge(p,nγ) 72As reaction were measured with Ge(HP) γ and superconducting magnetic lens plus Si(Li) electron spectrometers at eight bombarding proton energies between 5.75 and 6.51 MeV. Energies and relative intensities of 123 (among them 58 new) 72As γ-rays, as well as 51 (including 38 new) internal conversion coefficients have been determined. A more complete level scheme, γ-ray branching ratios, level spin and parity values have been deduced. The energy spectra and electromagnetic properties were calculated using the interacting boson-fermion-fermion model. The calculations reasonably well describe the level spectra and electromagnetic properties of 72As nucleus.

Properties of low-lying states of ^{166}Er

Further investigations of spectra of internal conversion electrons in the {\ }^{166}Tm decay are performed. Calculations in the framework of the phenomenological models taking into account the mixing of low-lying states of {\ }^{166}Er are presented. The branching ratios of E2 and E1 transitions of positive and negative parity states, respectively, having strong deviations from the Alaga rule, are shown. The probability values of dipole electric transitions from the K^{\pi} = O^-_1, 1^-_1 and $^-_1 band levels are calculated.

Structure of the 70As nucleus

γ-ray, γγ-coincidence, internal conversion electron and γ-ray angular distribution spectra of the 70Ge(p,nγ) 70As reaction were measured with Ge(HP) γ and superconducting magnetic lens plus Si(Li) electron spectrometers at eight bombarding proton energies between 7.59 and 8.7 MeV. Energies and relative intensities of 113 (among them 60 new) 70As γ rays, as well as 29 new internal conversion coefficients were determined. The proposed level scheme contains 16 new levels. γ-ray branching and mixing ratios, level spin and parity values have been deduced. The spins and parities have been determined on the basis of decay properties of levels, internal conversion coefficients, Hauser-Feshbach analysis of reaction cross sections, γ-ray angular distribution and other data. The energy spectra and electromagnetic moments were calculated in the framework of the interacting boson-fermion-fermion/truncated quadrupole phonon model for odd-odd nuclei and reasonable agreement has been obtained between the experimental and theoretical results.

Structure of 66Ga from (p, nγ) reaction

γ-ray, γγ-coincidence, and internal conversion electron spectra were measured with Ge(HP), as well as superconducting and traditional magnetic lens plus Si(Li) electron spectrometers at different bombarding proton energies between 6.5 and 7.1 MeV. Energies and relative intensities of 131 (among them 52 new) 66Ga γ-rays have been determined. Internal conversion coefficients of 33 transitions were measured for the first time. A more complete level scheme with new levels, γ-ray branching ratios, level spin and parity values has been deduced. The energy spectrum and electromagnetic properties were calculated on the basis of an interacting boson-fermion-fermion/truncated quadrupole phonon model for odd-odd nuclei. The model calculations reasonably describe the level spectra and electromagnetic properties of 64Zn, 65Ga, 65Zn and 66Ga nuclei with consistent parametrization.

Structure of the 68Ga nucleus from (α, nγ) reaction

Single-γ, γγ-coincidence and internal-conversion electron spectra of the 65Cu(α, nγ) 68Ga reaction were measured with Ge(HP) γ-ray and superconducting magnetic lens plus Si(Li) electron spectrometers at 14.5 MeV α-particle energy. The energies and relative intensities of 98 γ-transitions have been measured. Internal-conversion coefficients were determined for 19 transitions. A more complete level scheme with many new levels, γ-ray branching ratios, level spin and parity values have been deduced. The energy spectrum and electromagnetic moments were calculated on the basis of the interacting boson-fermion-fermion/truncated quadrupole phonon model for odd-odd nuclei (IBFFM/OTQM).