Low-energy Conversion Electrons Research Articles

Gamma-ray energies and intensities observed in decay chain 83Rb/83mKr/83Kr

Radioactive sources of the monoenergetic low-energy conversion electrons from the decay of isomeric ^{83textrm{m}}mathrm {{Kr}} are frequently used in the systematic measurements, particularly in the neutrino mass and dark matter experiments. For this purpose, the isomer is obtained by the decay of its parent radionuclide ^{83}mathrm {{Rb}}. In order to get more precise data on the gamma-rays occuring in the ^{83}mathrm {{Rb}}/^{83textrm{m}}mathrm {{Kr}} chain, we re-measured the relevant gamma-ray spectra, because the previous measurement took place in 1976. The obtained intensities are in fair agreement with the previous measurement. We have, however, improved the uncertainties by a factor of 4.3, identified a new gamma transition and determined more precisely energies of weaker gamma transitions.

ETCTN 10437: A single-arm phase II study of bone-targeted sn-117m-DTPA in symptomatic castration-resistant prostate cancer with skeletal metastases.

TPS5095 Background: Most patients with metastatic castration resistant prostate cancer (mCRPC) develop bone metastases with debilitating pain that is itself associated with shorter survival. Several bone-seeking radionuclides have been developed for palliation of metastatic bone pain. To date, radium-223 dichloride is the first and only approved targeted alpha therapy for mCRPC; the major dose limitation is bone marrow toxicity with modest pain relief. Sn-117m-diethylenetriaminepentaacetic acid (DPTA), is a complex of a radioisotope of tin with DTPA. It emits a low-energy conversion electron and also yields a gamma emission. Sn-117m-DPTA localizes selectively in bone, and the limited range (0.2-0.3 mm) of its conversion electrons resulting in deeper tissue penetration with less radiation effects on bone marrow as compared to radium-223 dichloride. Srivastava et al. (1998) reported in a phase I/II study of patients with painful bone metastases from a variety of solid tumors, 45% of patients obtained reduction of pain by at least 50%, and 30% had complete relief of pain for more than two weeks after one injection. Thus, Sn-117m-DTPA has high palliative efficacy with little significant toxicity. Additional evaluation of this agent in mCRPC patients is urgently required. Methods: The study is a phase 2 single-arm clinical trial of Sn-117m-DPTA (20 mCi/70Kg or 0.28 mCi/kg) intravenously every 8 weeks for two injections for patients with mCRPC metastatic to at least two bone sites with at least one clinically meaningful pain site at baseline. Re-treatment with additional two cycles is allowed if patients meet re-treatment criteria. Key eligibility criteria include 1) refractory mCRPC patients who progressed on any lines of therapies 2) self-reported bone pain (≥4 on an 11-point pain intensity scale), and 3) must be on either regular pain medication or have undergone palliative radiation for bone pain within 12 weeks prior to starting study treatment. Key exclusion criteria include 1) visceral metastases and 2) malignant lymphadenopathy exceeding 3cm in short-axis diameter. Twenty-five patients will be enrolled with a primary objective to assess the efficacy of Sn-117m-DTPA on sustained pain response; defined as 1) achieving pain index ≤3 index within a 12-week period and 2) maintaining pain index ≤3 over a 16-week period. Secondary endpoints include patient reported outcomes, adverse events, progression-free survival and overall survival. Correlative aims include assessing blood (systemic inflammatory markers) and tissue biomarkers (gene sequencing and polo-like kinase-1) for association with clinical benefit. An interim analysis will be performed to assess efficacy after 10 patients become evaluable. The study began enrolling patients in December 2021 and is ongoing. Clinical trial information: NCT04616547.

Development of Neutron Detector Based on Gd3Ga3Al2O12:Ce Single Crystals

Single crystals of Gd3Ga3Al2O12:Ce were grown successfully and a slice having thickness lesser than 1 mm was processed from the grown crystals to setup a portable thermal neutron detector. The presence of Gd isotopes having very high thermal neutron capture cross section ensures almost 100% stopping efficiency in such a low thickness. On the other hand, a lower thickness provided a better discrimination from gamma background. In addition to the continuum gamma, Gd isotopes also produce low-energy conversion electrons and X-rays which could be successfully observed in the form of well discriminated photopeaks at 34 and 74 keV. These photopeaks could also be measured in nuclear reactor beam lines with high gamma background.

Absolute standardizations of 99mTc and 57Co by 4π electron-gamma liquid scintillation coincidence counting for SIRTI and SIR comparisons

The radionuclides 99mTc and 57Co were standardized via absolute liquid scintillation counting techniques. We provide the first technical report on the absolute standardization of 99mTc using 4π(LS)e-γ coincidence counting. The low detection efficiency of low-energy conversion electrons translates into a large efficiency extrapolation range. A simulation indicated that the γ-ray interacting with the liquid scintillator introduces curvature to the count rate vs. efficiency relationship, the approximation of the functional form used for extrapolation providing the main measurement uncertainty for 99mTc. A detection efficiency analysis for both radionuclides is presented. Results from the standardizations, and SIRTI and SIR comparison exercises are reported.

Studying the decay of thorium-229 isomer by means of conversion spectroscopy

The design and expected characteristics of an experimental setup for generating a beam of singly, doubly, and triply charged ions of 229mTh isomer are considered. The scheme of ion transport, the preparation of the thin source, and the means of registering low-energy conversion electrons are described.

Uses of alpha particles, especially in nuclear reaction studies and medical radionuclide production

Abstract Alpha particles exhibit three important characteristics: scattering, ionisation and activation. This article briefly discusses those properties and outlines their major applications. Among others, α-particles are used in elemental analysis, investigation and improvement of materials properties, nuclear reaction studies and medical radionuclide production. The latter two topics, dealing with activation of target materials, are treated in some detail in this paper. Measurements of excitation functions of α-particle induced reactions shed some light on their reaction mechanisms, and studies of isomeric cross sections reveal the probability of population of high-spin nuclear levels. Regarding medical radionuclides, an overview is presented of the isotopes commonly produced using α-particle beams. Consideration is also given to some routes which could be potentially useful for production of a few other radionuclides. The significance of α-particle induced reactions to produce a few high-spin isomeric states, decaying by emission of low-energy conversion or Auger electrons, which are of interest in localized internal radiotherapy, is outlined. The α-particle beam, thus broadens the scope of nuclear chemistry research related to development of non-standard positron emitters and therapeutic radionuclides.

Development of an Ultra-Pure, Carrier-Free (209)Po Solution Standard.

Ultra-pure, carrier-free 209Po solution standards have been prepared and standardized for their massic alpha-particle emission rate. The standards, which will be disseminated by the National Institute of Standards and Technology (NIST) as Standard Reference Material SRM 4326a, have a mean mass of (5.169 ± 0.003) g of a solution of polonium in nominal 2.0 mol▪L−1 HCl (having a solution density of (1.032 ± 0.002) g▪ mL−1 at 20 °C) that are contained in 5 mL, flame-sealed, borosilicate glass ampoules. They are certified to contain a 209Po massic alpha-particle emission rate of (39.01 ± 0.18) s−1▪g−1 as of a reference time of 1200 EST, 01 December 2013. This new standard series replaces SRM 4326 that was issued by NIST in 1994. The standardization was based on 4πα liquid scintillation (LS) spectrometry with two different LS counting systems and under wide variations in measurement and counting source conditions. The methodology for the standardization, with corrections for detection of the low-energy conversion electrons from the delayed 2 keV isomeric state in 205Pb and for the radiations accompanying the small 0.45 % electron-capture branch to 209Bi, involves a unique spectral analysis procedure that is specific for the case of 209Po decay. The entire measurement protocol is similar, but revised and improved from that used for SRM 4326. Spectroscopic impurity analyses revealed that no photon-emitting or alpha-emitting radionuclidic impurities were detected. The most common impurity associated with 209Po is 208Po and the activity ratio of 208Po/209Po was < 10−7.

High-resolution alpha-particle spectrometry of 238U

The alpha-particle emission probabilities associated with the three main alpha transitions of 238U were measured by high-resolution alpha-particle spectrometry. Highly enriched 238U material was used and its isotopic composition characterised by mass spectrometry. Source production through electrodeposition was optimised to reconcile conflicting demands for good spectral resolution and statistical precision. Measurements were performed at IRMM and CIEMAT for 1–2 years in three different set-ups. A new magnet system was put into use to largely eliminate true coincidence effects with low-energy conversion electrons. Finally the accuracy and precision of the relative emission probabilities for the three transitions – 77.01 (10)%, 22.92 (10)% and 0.068 (10)%, respectively – have been improved significantly.

Characterization of large area, thick, and segmented silicon detectors for neutron [formula omitted] experiments

The “Nab” and “UCNB” collaborations have proposed to measure the correlation parameters in neutron β-decay at Oak Ridge and Los Alamos National Laboratory, using a novel detector design. Two large area, thick, hexagonal-segmented silicon detectors containing 127 pixels per detector will be used to detect the proton and electron from neutron decay. Both silicon detectors are connected by magnetic field lines of a few Tesla field strength, and set on an electrostatic potential, such that protons can be accelerated up to 30keV in order to be detected. Characteristics of the detector response to low energy conversion electrons and protons from 15keV to 35keV, including the evaluation of the dead layer thickness and other contributions to the pulse height defect for proton detection are presented for Si detectors of 0.5mm and 1mm of thickness.

Preparation of 114 mIn low energy conversion electron sources

The preparation of 114 m In sources of conversion electrons in the energy range 162–190 keV and β continuum with a 1989 keV endpoint via ion implantation of 113In into Al substrates and subsequent irradiation by thermal and epi-thermal neutrons in a nuclear reactor is described.

Estimation of a radiation weighting factor for 99mTc

Decaying (99m)Tc does not only emit a gamma ray (140.5 keV), but also low-energy Auger and conversion electrons. These electrons cause a serious problem in the determination of a radiation weighting factor for (99m)Tc due to their extremely short range in tissue. Therefore, for comparison ultrasoft X rays are used here, which deposit their energy mainly via the photoeffect thus also initiating low-energy photoelectrons. Monte Carlo computer codes provided electron emission spectra of (99m)Tc and subsequent track structure calculations simulated the induction of DNA damage of different degrees of complexity. For the modelling of ultrasoft X rays carbon K photons with an energy of 270 eV were selected, for which experimental results are available from the literature. On average, four electrons were found to be emitted per (99m)Tc decay. Simulation of DNA damage revealed a nearly identical spectrum of primary strand breaks for (99m)Tc and C-K radiation. On this basis, a total radiation weighting factor of 1.2 was evaluated for (99m)Tc.

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.

X-ray Spectroscopic Study of U6p,5f Electronic Levels in γ-UO3

The fine structures of X-ray photoelectron (XPE) spectra of low-energy electrons and conversion electron spectra of γ-UO3 (0-40 eV energy) were analyzed taking into account relativistic calculations based on the Xα discrete variation method of the electronic structure of uranium cluster [(UO2)O4]6- (D4h symmetry group) representing the closest coordination of uranium in γ-UO3. The theoretical and experimental data show that U5f electrons directly participate in the chemical bonding. The density of states of 5f valence electrons in uranium trioxide was calculated. At the same time, U6p electrons participate in formation of both inner and outer valence molecular orbitals, and the density of such 6p states in uranium trioxide was also calculated. The order of the inner valence molecular orbitals in the 13-40 eV range was determined, which is of particular importance for development of a procedure to evaluate the uranium-ligand bond distances in axial and equatorial directions in uranyl compounds using their X-ray photoelectron spectra in the range of inner group) representing the closest coordination of uranium in γ-UO3. The theoretical and experimental data showthat U5f electrons directly participate in the chemical bonding. The density of states of 5f valence electronsin uranium trioxide was calculated. At the same time, U6p electrons participate in formation of both inner andouter valence molecular orbitals, and the density of such 6p states in uranium trioxide was also calculated. The order of the inner valence molecular orbitals in the 13-40 eV range was determined, which is of particular importance for development of a procedure to evaluate the uranium-ligand bond distances in axial andequatorial directions in uranyl compounds using their X-ray photoelectron spectra in the range of innermolecular orbitals.

Therapeutic radiopharmaceuticals.

A variety of radiopharmaceuticals have been introduced for the internal therapy of malignant and inflammatory lesions in nuclear medicine. In order to destroy the diseased tissues radionuclides with high linear energy transfer (LET) such as beta, alpha, Auger or low energy conversion electron emitters are needed. The range of beta particles is in mm's so they are effective for large tumors. The range of alpha particles is short, only a few cell diameters. Thus, they are effective in treating circulating malignant cells and micrometastases. The range of Auger and conversion electrons is <0.1 micro m. They are very effective in cell killing when they are carried across cell membrane into the nucleus to damage DNA. Appropriate ions, molecules and particles are labelled with such radionuclides and used as radiopharmaceuticals in many different applications. For an effective dose to be delivered high target to non target ratios must be attained. Monoclonal antibodies to specific antigens expressed on tumor cells have been developed to increase the uptake by malignant tissues by specific accumulation. Radiolabelled peptides such as somatostatin, small molecules such as metaiodo-benzylguanidine (MIBG) and many different nano-and micro-particles have been investigated. The effectiveness of therapy can be increased by direct locoregional administration of the radiopharmaceutical. This way the radiation effects are confined locally and the normal tissues are spared from radiation effects. In this review article selection criteria and characteristics of radionuclides and carrier ions, molecules and particles for various therapeutic applications will be discussed, including mainly the recent developments.

High-resolution measurements of low-energy conversion electrons

High-resolution measurements of low-energy conversion electrons have been performed in odd and odd–odd nuclei with masses around A=182. The experimental setup, a magnetic spectrograph coupled to a specific tape transport system, is described. Three experiments have been performed and the main results are presented.

Reactor-produced radioisotopes from ORNL for bone pain palliation

The treatment of painful skeletal metastases is a common clinical problem, and the use of therapeutic radionuclides which localize at metastatic sites has been found to be an effective method for treatment of pain, especially for multiple sites for which the use of external beam irradiation is impractical. There are currently several metastatic-targeted agents radiolabeled with various therapeutic radionuclides which are in various stages of clinical investigation. Since neutron-rich radionuclides are produced in research reactors and often decay by emission of β − particles, most radionuclides used for bone pain palliation are reactor-produced. Key examples of radionuclides produced by single neutron capture of enriched targets include rhenium-186 and samarium-153. In addition, generator systems are also of interest which provide therapeutic daughter radionuclides from the decay of reactor-produced parent radionuclides. One important example is rhenium-188, available from generators via decay of reactor-produced tungsten-188. Tin-117m is an example of a reactor-produced radionuclide which decays with the emission of low-energy conversion electrons rather than by β − decay. Each of these agents and/or radionuclides has specific advantages and disadvantages, however, the ideal agent for bone pain palliation has not yet been identified. The goal of this paper is to briefly review the production and use of several reactor-produced radionuclides for bone pain palliation, and to discuss the role of the ORNL High Flux Isotope Reactor (HFIR) for the production of many of these radionuclides.

Air scintillation detector for conversion electrons Mössbauer spectroscopy (CEMS)

A detector for low-energy conversion and Auger electrons used for CEMS are described. It is based on the registration of light pulses produced by microdischarges in rare air caused by electrons under the presence of an electric field. The main parameters of the proposed Air Scintillation Detector (ASD) are comparable with parameters of usual CEMS detectors. However, the contrary to standard detectors, the ASD allows to investigate samples of almost arbitrary shape and size. It extends the field of CEMS applications, in particular, for investigation of tribological problems.

Standardization of 75Se and X-ray emission probability data

A 75Se solution has been standardized by combining the 4π(KX + e)—γ-coincidence measurements at two different γ-ray window settings. The component to the total uncertainty that originated from the correction associated with the metastable level was estimated to be 0.1%. The 4πKX—γ-coincidence method with zero registration of low-energy conversion electrons was also used. The measured activity has been used to determine the 75Se KX-ray emission probability with the aid of a calibrated Si(Li) spectrometer.

Use of Gd in gas counters as neutron detectors in SNO

The Sudbury Neutrino Observatory (SNO) will observe solar neutrino interactions in D 2O. Photomultiplier tubes (PMT) surrounding the D 2O will detect Cherenkov light from these interactions. The neutral current (NC) interactions of the neutrinos disintegrate the deuterons producing neutrons. Cherenkov light from the subsequent capture-gamma-ray shower (CGRS) will register in SNO. The default method uses the Cl of dissolved salt as the neutron capture agent. Since the neutron absorption mean path in D 2O is very long, a small amount of efficient neutron absorber can capture a large fraction of the neutrons. Therefore it is possible to construct discrete neutron counters based on this absorber. We describe the conceptual design of a detection system using Gd in proportional wire chambers (PWCs). Gd neutron capture produces 8 MeV of capture-gamma-ray energy and, with high probability, low energy conversion electrons. The proposed method uses the coincidence between conversion electrons detected in the PWCs, and the CGRS, detected by the SNO PMTs, to register the neutron capture event. This coincidence makes it possible to observe a positively identified background free neutron signal. Further it makes the system insensitive to spurious signals from the PWCs and the PMTs of SNO. We present a conceptual design in which 28% of the neutrons will produce a coincidence. The estimated fraction of neutrons from all sources which will give a detectable signal in the SNO PMTs is 45%. In this design, we require about 6.7 kg of 4 μm natural Gd foils in 870 m long by 6 cm diameter PWCs on a 90 cm lattice. Photon losses due to counter shadowing can be kept to < 20%. We have determined experimentally that the neutron capture conversion electron detection efficiency in Gd foils in a PWC is 85% in the limit of an infinitely thin foil.

Activity concentration of a solution of 133Ba: Results of an international comparison

Nineteen laboratories participated in an international comparison of activity measurements of 133Ba organized by the BIPM. Three trial comparisons were necessary in order to find the best chemical solution for the study. Most participants applied coincidence counting, with proportional counters or liquid-scintillation detectors in the β channel; two laboratories used large well-type scintillation counters. Because of the presence of many low-energy conversion electrons in the decay of 133Ba the extrapolation of efficiency functions obtained by coincidence counting may depend considerably on the γ-channel setting, so most participants used a threshold of at least 200 keV in the γ channel. The mean activity concentration, with its combined uncertainty (lσ) at the reference date, is (1160.8±4.2) Bq mg − with a total range of 1.7 % Results obtained with the International Reference System are also given.