Crystal growth and scintillation properties of Er-doped Lu3Al5O12 single crystals

Er-doped Lu₃Al₅O₁₂ (Er:LuAG) single crystalline scintillators with different Er concentrations of 0.1, 0.5, 1, and 3% were grown by the micro-pulling-down (μ-PD) method. The grown crystals were composed of single-phase material, as demonstrated by powder X-ray diffraction (XRD). The radioluminescence spectra measured under ²⁴¹Am α-ray excitation indicated host emission at approximately 350 nm and Er³⁺ 4f-4f emissions. According to the pulse height spectra recorded under γ-ray irradiation, the 0.5% Er:LuAG exhibited the highest peak channel among the samples. The γ-ray excited decay time profiles were well fitted by the two-component exponential approximation (0.8 μs and 6-10 μs).     

Determination of the content of radioactive elements in irradiated beryllium

The elemental composition of the material of beryllium blocks of SM reactor reflector in the initial state was determined by inductively coupled plasma atom emission spectrometry (ICP AES). The α-, β-, and Γ-active components of the radiation from Be irradiated to a neutron fluence of 6 × 10²² cm⁻² (E > 0.1 MeV) were determined. Radiochemical analysis revealed the presence in the irradiated Be of ⁶⁰Co, ⁵⁴Mn, ¹³⁷Cs, ¹³⁴Cs, and ⁹⁰Sr. The following α-emitters were revealed: ^238–241Pu, ²⁴¹Am,²⁴³Am, and ²⁴⁴Cm.     

Diffusion of some critical radionuclides in mineral-like ceramic materials

The diffusion coefficients and activation energy of diffusion of ²²Na, ⁹⁰Sr, ¹⁵²Eu, and ²⁴¹Am radionuclides in zirconolite ceramics prepared by cold crucible induction melting (CCIM), of ²²Na, ⁹⁰Sr, ¹³⁷Cs, ¹⁵²Eu, and ²⁴¹Am in Synroc-C ceramics prepared by hot pressing (HP) and CCIM, and of ²²Na and ¹⁵²Eu in the ceramic from the Lawrence Livermore National Laboratory (the United States), synthesized by cold pressing (CP) and sintering, and also the diffusion mobility of ⁹⁰Sr, ¹³⁷Cs, and ²⁴¹Am in the chromium-containing sphene glass ceramic prepared by CCIM were determined by the method of integral residual activity. In the temperature interval 573–923 K, the ²²Na radionuclide is the most mobile and ²⁴¹Am is the least mobile. The differences between the diffusion coefficients reach 4–5 orders of magnitude. The diffusion coefficients of the examined radionuclides in the ceramic depend both on the preparation procedure (HP, CP, or CCIM) and on the initial charge components when the same procedure is used for preparing the ceramic. Negative values of the activation entropy of the diffusion of ²²Na, ⁹⁰Sr, ¹⁵²Eu, and ²⁴¹Am in ceramics suggest that the mass transfer of radionuclides in them occurs not by the vacancy mechanism but by the interstitial mechanism and, probably, in part along the facilitated migration pathways (grain boundaries, pore surfaces, micro- and macrocracks).     

Crystal growth and scintillation properties of Nd-doped Lu3Al5O12 single crystals with different Nd concentrations

Nd 0.1%, 0.5%, 1% and 3% doped Lu₃Al₅O₁₂ (Nd:LuAG) single crystals were grown in the nitrogen atmosphere by the micro-pulling down (μ-PD) method. The grown crystals had a single-phase confirmed by powder XRD analysis. In absorption spectra, some weak absorption lines due to Nd³⁺ 4f-4f transitions were observed and their intensity increased with the increase of Nd concentration. When excited by ²⁴¹Am α-ray, a broad emission peak due to defects in the host lattice at 320 nm and some sharp lines due to Nd³⁺ 4f-4f transitions at wavelength longer than 400 nm were observed. The decay time profiles of Nd:LuAG under γ-ray excitation were well approximated by two exponential function of 340-760 ns and 3-5 μs for each sample. By pulse height measurement using ¹³⁷Cs, Nd 0.5%:LuAG showed the highest light yield of 7600 ± 760 photons/MeV.     

Fluorescent sources for an energy dispersive compton spectrometer

A new version of γ-ray Compton spectrometer has been developed substituting the γ-ray source with an X-ray fluorescent source. The new instrument provides higher intensity with a large variety of incident energies. Using an Au X-ray spectrometry tube operating at 100 kV, 30 mA, fluxes as high as 10⁸ ph/s deg² have been reached for photon energy of about 10 keV of the primary beam in the Compton spectrometer. In the area of γ-rays of energy 59.54 keV that are employed in most of the ²⁴¹Am Compton spectrometers, the flux of the fluorescent source is 5.28 × 10⁶ ph/s deg² in comparison to 6.16 × 10⁵ ph/s deg² of a 5 Ci ²⁴¹Am annular source. To demonstrate the new instrument's applicability on the Compton spectroscopical studies of the condensed matter, it has been employed in measuring the difference Compton profiles for polycrystalline TiH₂ and Ti and the ratio coherent-incoherent scattering cross-section of Al, S, Ti Cr at energies 48.82 keV and 52.00 keV.     

Scintillation properties of Tm-doped Lu3Al5O12 single crystals

Using the micro-pulling-down (μ-PD) method, Tm-doped Lu₃Al₅O₁₂ (Tm:LuAG) single crystals were grown to examine their scintillation properties. In transmittance spectra, they exhibited about 80% transparency in the wavelengths longer than 320 nm and five absorption lines due to Tm³⁺ 4f–4f transitions were observed. ²⁴¹Am α-ray excited radioluminescence spectra were measured and intense 4f–4f emission peaks were observed with the host emission. When excited by ¹³⁷Cs γ-Ray to obtain pulse height spectra, Tm 1% doped LuAG showed the highest light yield coupled with a photomultiplier (PMT) or a silicon avalanche photodiode (Si-APD). The light yield was estimated to be 5800 and 7300 photons/MeV for PMT and Si-APD, respectively. Decay time profiles consist of two exponential components and the fast and slow components are considered to be attributed to the host and the combination of the host and Tm³⁺ 4f–4f emission, respectively.     

Evaluation of spectrum measurement devices for operational use

Several neutron spectrometers manufactured by Bubble Technology Industries (BTI) were tested and evaluated in a variety of neutron fields. Findings and conclusions are presented for the following BTI instruments: a modification of the Rotational Spectrometer (ROSPEC) that includes a thermal and epithermal capability, the Simple Scintillation Spectrometer that is used in conjunction with the ROSPEC to extend its high-energy range, and the MICROSPEC N-Probe which is capable of providing a crude spectrum over the energy range from thermal to 18 MeV. The main objective of these measurements was to determine the accuracy of both the energy spectrum and dose equivalent information generated by these devices. In addition, the dose response of the Wide-Energy Neutron Detection Instrument (WENDI-II) was measured in all neutron fields relative to a bare ²⁵²Cf calibration. The performance of the WENDI-II rem meter was compared to the dose information generated by the neutron spectrometers. The instruments were irradiated to bare ²⁵²Cf and ²⁴¹AmBe sources, and in a series of moderated ²⁵²Cf fields using a standard D₂O sphere and a set of polyethylene spheres. The measured spectra were benchmarked with a set of detailed Monte Carlo calculations with the same energy bin structure as that of the instruments under test. These calculations allowed an absolute comparison to be made with the measurements on a bin by bin basis. The simulations included the effects of room return and source anisotropy.     

Synthesis and X-ray diffraction study of intermetallic compounds of americium with copper

An alloy of americium-241 and copper was prepared by high-temperature deposition of the vapor of metallic Am on a Cu support. The intermetallic compound Cu₅Am (or Cu₇Am) with the hexagonal lattice of the Cu₅Ca (or Cu₇Tb) type was detected in the sample. The effect of α-radiation of ²⁴¹Am on the crystal structure of the intermetallic compound was examined.     

Speciation of artificial radionuclides 60Co, 137Cs, 152Eu, and 241Am in bottom sediments of the Yenisei river

The speciation of artificial radionuclides ⁶⁰Co, ¹³⁷Cs, ¹⁵²Eu, and ²⁴¹Am in surface layers of bottom sediments of the Yenisei river, collected within the near zone of impact of the Mining and Chemical Combine (Rosatom), was studied. In these samples the radionuclides ⁶⁰Co, ¹⁵²Eu, and ²⁴¹Am are mainly associated with fractions of humic and fulvic acids. The fraction of ¹⁵²Eu associated with nonsilicate iron is approximately 92%. The migration capability of radionuclides collected near the Atamanovo settlement decreases in the order ¹⁵²Eu > ²⁴¹Am > ⁶⁰Co > ¹³⁷Cs. For samples collected near Bol’shoi Balchug settlement, this order is as follows: ¹⁵²Eu ≈ ²⁴¹Am > ⁶⁰Co > ¹³⁷Cs. The presence of radionuclide-bearing micro-particles in bottom sediments considerably complicates the distribution of radionuclides, in particular, of ²⁴¹Am and ¹³⁷Cs, among migration forms.     

Growth and characterization of strontium metaborate scintillators

The undoped and 0.5% Ce³⁺-doped strontium metaborate SrB₂O₄ single crystals has been grown successfully by micro-pulling down method with radio frequency (RF) heating system, and scintillation characteristics including optical properties and radiation response were studied for these crystals. The Ce³⁺-doped SrB₂O₄ crystal showed absorption band around 240–320 nm, which is corresponding to the 4f-5d transition of Ce³⁺. Intense emission band at 375 nm due to the Ce³⁺ 5d–4f transition was observed under ²⁴¹Am 5.5 MeV α-ray excitation. The scintillation decay time showed fast (50 ns) and slow (1430 ns) components ascribed to the Ce³⁺ 5d–4f transition and lattice defect in the crystal, respectively. The scintillation light yield of Ce³⁺-doped SrB₂O₄ was calculated to be about 1000 ph/n under ²⁵²Cf irradiation.     

Basic study of Europium doped LiCaAlF6 scintillator and its capability for thermal neutron imaging application

Eu²⁺ 0.1, 0.5, 1, and 2 mol% doped LiCaAlF₆ single crystalline scintillators were grown by the micro-pulling down (μ-PD) method. Eu²⁺ 2 mol% doped LiCaAlF₆ was also prepared using the Czochralski method. In the transmittance spectra, 4f-5d absorption lines appeared around 200-220 and 290-350 nm. An intense emission at 375 nm due to Eu²⁺ 5d-4f transition was observed under ²⁴¹Am α-ray excitation. When ²⁵²Cf excited pulse height spectra were measured, Eu 2% doped one showed the highest light yield of 29,000 ph/n with 1.15 μs decay time. Using the 2 inchφ Czochralski grown one coupled with the position sensitive photomultiplier tube covered by Cd mask with various size (1, 2, 3, and 5 mm) pin holes, thermal neutron imaging was examined. As a result, the spatial resolution turned out to be better than 1 mm.     

Radionuclide composition of fragments of lava-like fuel-containing materials from the CNPP fourth unit

Samples of fuel-containing materials taken inside the CNPP Fourth Unit were analyzed by γ- and α-ray spectrometry. The isotope ratios for Cs, Eu, Pu, Am, and Cm were measured, and the fuel burn-up in the samples was determined. Inconsistencies in theoretical estimations on the production of all the radionuclides over ²⁴¹Am were revealed. The burn-up values determined from data on the Cs isotopes systematically differ from those determined from data on the other radionuclides. The causes of these facts are discussed.     

Speciation of radionuclides in colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

The strength of actinide bonding with colloidal matter of groundwaters from the Lake Karachai contamination area was studied by selective leaching. An α-track analysis showed that the microdistribution of α-emitting radionuclides in the colloidal matter is uniform. Analysis of fission tracks confirms the presence of ²³⁹Pu and ²⁴¹Am in the colloidal material. In the colloidal matter of groundwaters taken from three wells and differing in the chemical composition, radionuclides occur in forms differing in the solubility. U and Np in the colloidal material are associated only with readily soluble and mobile groups of compounds and are not detected in the difficultly soluble residue. Pu and Am, on the contrary, occur in the colloidal material of groundwaters mainly in difficultly soluble forms. Am is bound to a greater extent with surface organometallic complexes. Pu is detected mainly in the fraction of amorphous oxides.     

CsI(Tl)-241Am calibration source for Pb-glass detectors

A light pulser for calibrating Pb-glass detectors has been designed consisting of a 3 mm diameter by 1 mm thick CsI(Tl) scintillation crystal positioned in an Al cup 1 mm from an ²⁴¹Am α-emitting source. Optical coupling to a Pb-glass detector is provided by a glass window and epoxy. Calibration consists of exposing the Pb-glass detector to high-energy electrons, typically 2 GeV, and comparing the Cherenkov pulse with the line from the CsI(Tl)-²⁴¹Am source. The advantages of this source are its expected long-term stability of light output, simplicity, and low cost.     

Model Assessment of the Migration Capability of Transuranium Radionuclides (<Superscript>241</Superscript>Am and Pu Isotopes) and <Superscript>152</Superscript>Eu in the System Bottom Sediments-Yenisei River Water by Chemical Fractionation Technique

Sorption of radiotracers ²⁴¹Am and ²⁴²Pu and weighable amounts of uranium and stable Eu on bottom sediments in the simulated system bottom sediments—Yenisei river water was studied. At a contact time of 40 min these metals are completely sorbed on the bottom sediments, presumably via association with organomineral complexes and hydrated gels. Along with sorption, these metals can form soluble complexes and stable colloids (pseudocolloids). The distribution factors of ²⁴¹Am and ²⁴²Pu, and stable Eu in the simulated system between bottom sediments and liquid phases were calculated from the results of sorption experiments. The introduced ²⁴¹Am and ¹⁵²Eu initially present in radioactively contaminated bottom sediments of the Yenisei river show similar pattern of distribution over differently mobile fractions. The distribution of weighable amounts of stable Eu significantly differs from that of initially present ¹⁵²Eu and tracer ²⁴¹Am due to decelerated sorption of stable Eu and its considerably higher concentration. A significant part of ²⁴²Pu, ²⁴¹Am, and ¹⁵²Eu is associated with mobile fractions of bottom sediments, which, under certain environmental conditions, can pass into river water as migrating species.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 379–384.Original Russian Text Copyright © 2005 by Bondareva, Bolsunovskii, Sukhorukov, Kazbanov, Makarova, Legler.     

In-flight energy calibration for the X-ray and gamma-ray spectrometers on the solar-A satellite

The electronically gated in-flight energy calibration is applied to the X-ray and gamma-ray spectrometers on a SOLAR-A satellite. The NaI X-ray spectrometer covering the 20–400 keV energy band is calibrated by an ²⁴¹Am radioactive source which decays by the simultaneous emission of 60 keV X-rays and 5.48 MeV alpha-particles. The X-ray calibration spectrum is accumulated in coincidence with an event tag pulse generated by the simultaneous detection of an X-ray and an alpha-particle. The BGO gamma-ray spectrometer covering the 0.2–10 MeV energy band is calibrated by a ⁶⁰Co radioactive source which decays by the simultaneous emission of 1.17 and 1.33 MeV gamma-rays and a beta-ray (maximum energy is 313 keV). The gamma-ray calibration spectrum is accumulated in a manner similar to the X-ray spectrometer. Since the present method enables to select the calibration pulse without the disadvantage of introducing extra pulses, it is suitable for a space experiment where external conditions and background counting rates can significantly change.     

A high-resolution neutron spectra unfolding method using the Genetic Algorithm technique

The Bonner sphere spectrometers (BSS) are commonly used to determine the neutron spectra within various nuclear facilities. Sophisticated mathematical tools are used to unfold the neutron energy distribution from the output data of the BSS. This paper highlights a novel high-resolution neutron spectra-unfolding method using the Genetic Algorithm (GA) technique. The GA imitates the biological evolution process prevailing in the nature to solve complex optimisation problems. The GA method was utilised to evaluate the neutron energy distribution, average energy, fluence and equivalent dose rates at important work places of a DIDO class research reactor and a high-energy superconducting heavy ion cyclotron. The spectrometer was calibrated with a ²⁴¹Am/Be (α,n) neutron standard source. The results of the GA method agreed satisfactorily with the results obtained by using the well-known BUNKI neutron spectra unfolding code.     

Transuranium elements in liquid radioactive wastes from the Shelter

The volume activity of ⁹⁰Sr, ¹³⁷Cs, ²³⁸Pu, ^239+240Pu, ²⁴¹Am, and ²⁴⁴Cm in water taken from unorganized water accumulations on lower marks of the Shelter was determined. Separate water accumulations are characterized by their specific radionuclide activity ratios ²³⁸Pu/^239+240Pu, ²⁴¹Am/^239+240Pu, and ²⁴⁴Cm/²⁴¹Am. The activity ratios ²⁴¹Am/^239+240Pu and ²⁴⁴Cm/^239+240Pu in the water accumulations are 5–10 times higher than in the irradiated fuel of the 4th Unit of the Chernobyl NPP and in lava-like fuel-containing materials.     

Coprecipitation of microamounts of radionuclides on chitosans of various molecular weights in solutions

Coprecipitation of ²³³U, ²³⁹Pu, ²⁴¹Am, ¹⁵²Eu, ⁹⁰Sr, ⁹⁰Y, and ⁶⁰Co on chitosans of various molecular weights (MW) was studied. Low-molecular-weight chitosan (LMWC) with MW of 5 kDa (5 × 10³ g mol⁻¹) proved to be a more effective coprecipitant than high-molecular-weight chitosan (HMWC) with MW of 700 kDa (7 × 10⁵ g mol⁻¹). With HMWC, the degree of coprecipitation (α) was 80% for ¹⁵²Eu and ⁹⁰Y, 99% for ²³³U and ²⁴¹Am, and 85% for ²³⁹Pu. For ⁶⁰Co, α monotonically increased with an increase in the chitosan concentration in solution and reached 40% at [HMWC] = 5 g l⁻¹. For ⁹⁰Sr, α did not exceed 3% in the entire examined range of chitosan concentrations. With LMWC, the α values for An, ¹⁵²Eu, and ⁹⁰Y differed insignificantly (92–99%). For ⁶⁰Co and ⁹⁰Sr, α increased to 40% in the range of chitosan concentrations from 0 to 1 g l⁻¹. The presence of inorganic salts in solution considerably decreases α of UO₂²⁺ with chitosans but does not noticeably affect the behavior of Am, Pu, and Eu. The effect of salts on the efficiency of ²³³UO^2/2+ coprecipitation on HMWC decreases in the order Na₂SO₄ > NaCl > Na₂CO₃ > NaNO₃ > Na₃PO₄. Based on the results obtained, a procedure suitable for expedition conditions was developed for preconcentration of Pu from seawater on chitosan, with simultaneous separation of Pu from U, for radioecological monitoring of natural waters. The specific activity of Pu in samples of near-bottom seawater of gulfs of the Novaya Zemlya archipelago was (150–170) ± 20 mBq m⁻³. The results are well consistent with the published data.     

Scintillation properties of Ce-doped LuLiF4 and LuScBO3

The crystals of 1 mol% Ce-doped LuLiF₄ (Ce:LLF) grown by the micro-pulling down (μ-PD) method and 1 mol% Ce-doped LuScBO₃ (Ce:LSBO) grown by the conventional Czochralski (Cz) method were examined for their scintillation properties. Ce:LLF and Ce:LSBO demonstrated ∼80% transparency at wavelengths longer than 300 and 400 nm, respectively. When excited by ²⁴¹Am α-ray to obtain radioactive luminescence spectra, Ce³⁺ 5d-4f emission peaks were detected at around 320 nm for Ce:LLF and at around 380 nm for Ce:LSBO. In Ce:LSBO, the host luminescence was also observed at 260 nm. By recording pulse height spectra under γ-ray irradiation, the absolute light yield of Ce:LLF and Ce:LSBO was measured to be 3600±400 and 4200±400 ph/MeV, respectively. Decay time kinetics was also investigated using a pulse X-ray equipped streak camera system. The main component of Ce:LLF was ∼320 ns and that of Ce:LSBO was ∼31 ns. In addition, the light yield non-proportionality and energy resolution against the γ-ray energy were evaluated.