Secondary Electron Multiplier Research Articles

Application of ATONA Amplifiers to the Measurement of Uranium Isotopic Ratios by Thermal Ionization Mass Spectrometry.

Uranium isotopic composition can provide valuable information about the history and provenance of a nuclear material; therefore, uranium isotopic analyses are frequently made in the nuclear forensics, safeguards, and environmental monitoring communities. These measurements have always presented challenges due to the extreme variability in the relative abundance between the major (235U, 238U) and minor (233U, 234U, 236U) isotopes of uranium. The recently developed ATONA (Atto- to Nano-Amp) amplification system paired with Faraday cup detectors has a large dynamic range and low noise floor making it ideal for measuring uranium isotopic ratios in materials of both natural and anthropogenic origin. A wide variety of certified reference materials were analyzed to investigate the utility of the ATONA amplification system for determining uranium isotopic composition in samples ranging from depleted to highly enriched. The ATONA amplifiers provide nearly an order of magnitude improvement in external reproducibility over 1011 Ω amplifiers when measuring the minor 234U/238U ratio in isotopically natural and depleted samples and when paired with a secondary electron multiplier can measure very low relative abundance uranium isotopes (i.e., 236U).

Influence of polarity mode switching and standby times on signal stability and detection of aspirated droplet signatures in electrospray mass spectrometry

Electrospray ionization plays a central role in modern analytical chemistry. It is often used in combination with an HPLC system and is able to transfer large molecules, such as proteins and complexes, into the gas phase. A liquid solution containing the analyte is sprayed in a strong electric field. Charged droplets generated by this process release the analyte molecules which can ultimately be analyzed by the mass spectrometer system. However, the exact mechanisms of droplet generation and ion release are still not fully understood and are under investigation. Recent literature puts the focus on droplet disintegration and shows that the analyte ions are not exclusively released from the droplets within the ionization chamber but rather in the whole mass spectrometer system. Previous experiments allow the direct observation of the signatures of fragmented droplets within the analyzer region of a time-of-flight mass spectrometer: An oscilloscope was connected to a secondary electron multiplier which serves as an auxiliary ion detector, located downstream of the orthogonal acceleration stage of a time-of-flight mass spectrometer. The oscilloscope is thus able to monitor the time-resolved ion current in the mass analyzer region. Pulses of extraordinarily high ion currents are observable here which are attributed to aspirated charged droplets.This work provides insights into long-term experiments with this experimental setup. There is a focus on signal stability, in the presence of such droplet signatures. It is apparent that the standby time of the instrument between individual measurements and the time since a switch of the polarity mode, has a significant influence on the signal stability. There are also indications that the observations of droplet signatures and the MS signal stability are correlated.

Highly sensitive single-molecule detection of macromolecule ion beams.

The analysis of proteins in the gas phase benefits from detectors that exhibit high efficiency and precise spatial resolution. Although modern secondary electron multipliers already address numerous analytical requirements, additional methods are desired for macromolecules at energies lower than currently used in post-acceleration detection. Previous studies have proven the sensitivity of superconducting detectors to high-energy particles in time-of-flight mass spectrometry. Here, we demonstrate that superconducting nanowire detectors are exceptionally well suited for quadrupole mass spectrometry and exhibit an outstanding quantum yield at low-impact energies. At energies as low as 100 eV, the sensitivity of these detectors surpasses conventional ion detectors by three orders of magnitude, and they offer the possibility to discriminate molecules by their impact energy and charge. We demonstrate three developments with these compact and sensitive devices, the recording of 2D ion beam profiles, photochemistry experiments in the gas phase, and advanced cryogenic electronics to pave the way toward highly integrated detectors.

Simultaneous U and Th isotope measurements for U-series dating using MCICPMS

U-series dating is a well-established tool for determining the ages of secondary carbonates in palaeoclimate science.We present a measurement method and data treatment protocol adapted for simultaneous Th and U isotope measurements with sub-‰ precision by using a combination of Faraday cups and a secondary electron multiplier on a multi-collector inductively coupled plasma mass spectrometer (MCICPMS). We systematically analyse the effect of undetected variations in raw data corrections on the accuracy of the activity ratios and ages using three representative speleothem and coral samples.On masses of 229 and 230 amu, we observe “ghost signals” for which we introduce appropriate correction factors. Not accounting for the “ghost signal” can lead to deviations from reference values of more than 10% for young materials. Other data corrections induce accuracy variability on ε-to ‰-levels. The resulting methodology permits measurements on the ε-level for (234U/238U) and on the (sub) permille-scale for (230Th/238U) determinations.

An algorithm for U–Pb geochronology by secondary ion mass spectrometry

Abstract. Secondary ion mass spectrometry (SIMS) is a widely used technique for in situ U–Pb geochronology of accessory minerals. Existing algorithms for SIMS data reduction and error propagation make a number of simplifying assumptions that degrade the precision and accuracy of the resulting U–Pb dates. This paper uses an entirely new approach to SIMS data processing that introduces the following improvements over previous algorithms. First, it treats SIMS measurements as compositional data using log-ratio statistics. This means that, unlike existing algorithms, (a) its isotopic ratio estimates are guaranteed to be strictly positive numbers, (b) identical results are obtained regardless of whether data are processed as normal ratios (e.g. 206Pb / 238U) or reciprocal ratios (e.g. 238U / 206Pb), and (c) its uncertainty estimates account for the positive skewness of measured isotopic ratio distributions. Second, the new algorithm accounts for the Poisson noise that characterises secondary electron multiplier (SEM) detectors. By fitting the SEM signals using the method of maximum likelihood, it naturally handles low-intensity ion beams, in which zero-count signals are common. Third, the new algorithm casts the data reduction process in a matrix format and thereby captures all sources of systematic uncertainty. These include significant inter-spot error correlations that arise from the Pb / U–UO(2) / U calibration curve. The new algorithm has been implemented in a new software package called simplex. The simplex package was written in R and can be used either online, offline, or from the command line. The programme can handle SIMS data from both Cameca and SHRIMP instruments.

ДОСЛІДЖЕННЯ СПЕКТРУ АТОМІВ Zn I В ТРИПЛЕТНИХ РІДБЕРГІВСЬКИХ СТАНАХ

Purpose: This work aims at investigating the zinc atoms in the triplet preionization – Rydberg states. The energy levels of atoms having two electrons outside the closed shell were studied mainly by the optical spectroscopy methods. However, just using the microwave spectroscopy to measure the frequency of transitions between the two Rydberg states allows to increase the accuracy of measurements in two or more orders of magnitude. Disign/methodology/approach:A line of three dye lasers is used to excite the zinc atoms into the triplet Rydberg states with a predetermined set of quantum numbers. The radiation of the first two of them is transformed into the second harmonic in nonlinear crystals. Dye lasers are excited by the radiation of the second harmonic of one YAG: ND3+ laser. All three radiations are reduced to the zone of interaction with the laser and the microwave radiation, which is located between the plates of the ionization cell, where the pulsed electric field is created. The excited Rydberg atoms are recorded with the field ionization procedure. The beam of neutral atoms is created by an effusion cell under the vacuum conditions, the residual pressure does not exceed 10-5 mm Hg. A pulsed electric field of some certain intensity results inionization of atoms excited by microwave radiation and in acceleration of electrons, which have appeared in the direction of the secondary electron multiplier, though being insufficient for ionization of atoms excited only by the laser radiation and which are initial for interaction with microwaves. By scanning the microwave radiation frequency with the given step and measuring the signal intensity of the secondary electron multiplier, the excitation spectrum of the atoms under study can be obtained. Findings: Using the created laser-microwave spectrometer, the frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured. From the analysis made of the transition frequencies, the quantum defect decomposition constants were obtained by the Ritz formula for the D, F, and G states of zinc atoms. Conclusions: The frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured that allowed obtaining the quantum defect decomposition constants according to the Ritz formula for the D, F and G states of zinc atoms, that in turn had allowed to calculate the energy of these terms and the transition frequencies at least in two orders of magnitude more accurately as against the similar measurements made by the optical spectroscopy. Key words: zinc atom, triplet states of atoms, Rydberg states, laser excitation, microwave radiation

Study on the characteristics of quadrupole mass spectrometer by the UHV partial pressure standard

This study aims to investigate the characteristics of QMG700 quadrupole mass spectrometer (QMS) with use of the ultrahigh vacuum (UHV) partial pressure standard. The research parameters were the sensitivity, linearity, secondary electron multiplier (SEM) detector gain, stability, noise level and minimum detectable partial pressure (MDPP). This work was carried out in the scan and multiple ion detection (MID) operation modes for characterization of the QMS, where both the Faraday cup (FC) and the SEM detector were used, and the dwell time and scan speed were respectively 50 ms, 1 s and 50 ms/amu, 1 s/amu, the SEM voltage was varied from 1100 V to 3000 V. The experiments were performed within the partial pressure range of 10−7 Pa to 10−5 Pa for the FC detector and over the range of 10−9 Pa to 10−7 Pa for SEM using He, N2 and Ar. The results demonstrated a significant correlation between the QMS metrological characteristics and its operation mode as well as ion current detection mode. This study was conducted according to the ISO TS 20175: 2018.

236U/238U Analysis of Femtograms of 236U by MC-ICPMS.

A new analytical method has been developed to determine atomic 236U/238U ratios in samples with only femtograms of 236U using a secondary electron multiplier (SEM) on a multicollector high-resolution inductively coupled plasma mass spectrometer (MC-ICPMS). The abundance sensitivity of the 238U tail at 236 atomic mass unit is reduced from 10-6 to 10-10 with the deployment of a retarding potential quadrupole lens. This method features the reduction of polyatomic interferences from hydride, nitride, lead, and plutonium and the evaluation of nonlinear SEM behavior. The instrument sensitivity is 1-2%, and the estimated methodological detection limit of the 236U/238U atomic ratio is as low as 2 × 10-10. Measurements on reference materials with 236U/238U ratios of 10-7-10-9, including the IRMM-075 series and the ETH Zurich in-house standard ZUTRI, demonstrate the accuracy of our MC-ICPMS technique. The analytical precisions (2σ) are ±4% for 5 fg of 236U at a 236U/238U of 1 × 10-8 and ±8% for 2 fg of 236U at a 236U/238U of 4 × 10-9 level. Compared to state-of-the-art accelerator mass spectrometry techniques and triple quadrupole-based ICPMS, our detection limit is not as low, but the required sample size is 3-40 times lower, and the throughput is as high as 3-4 samples per hour. The new MC-ICPMS-SEM technique is sensitive enough for determining 236U/238U in various small natural samples, such as marine carbonates and seawater.

A gated integration method for the detection of unevenly distributed ions bunches in laser resonant ionization mass spectrometry

In laser resonance ionization mass spectrometry (RIMS) systems, pulsed lasers are usually employed to excite and ionize the elements of interest. Therefore, the laser ion signals are clustered and unevenly distributed at the time of appearance. The characteristics of the ions cause difficulties in the use of traditional ion detection technologies, such as the Faraday cup detection method and ion counting method. The gated integration method was proposed herein to measure pulsed laser ion signals. In this method, the intensity information of unevenly distributed ions is continuously converted to voltage amplitude information. Simulation and experiments demonstrated that the proposed method can effectively measure unevenly distributed ion signals with a high linearity over an operating signal range of 3 × 104–2 × 107 count rate within the duration of the pulsed laser (cps-p). In addition, it also can effectively remove the measurement gap between a Faraday cup detection system and a secondary electron multiplier detection system operating in the ion counting mode in laser RIMS.

Моделирование процессов электронного усиления в каналах умножителей на пористых структурах оксида алюминия

The secondary-emission multiplier of spatial-distributed flows of electrons – microchannel membrane – determines along with the photocathode, luminescent screen, electron-optical system determines the amplifying characteristics of the electron-optical transformers, photoelectronic multipliers. This, in its turn, determines the application areas and the operating range of the items. The actual task is an improvement of the microchannel membrane parameters and the search for new approaches to manufacture on alternative materials of the secondary-emission multipliers. In the paper the use of self-organizing high-ordered porous anode structures of aluminum oxide as the secondary-electronic emitters have been considered. The theoretical and practical approaches to development and the implementation of the computer models of processes of multiplying electrons in the channel of the based on aluminum oxide, have been offered. Based on the results of the calculations, performed using this model, the amplifying ability of such channels has been determined, their optimal caliber is 25, and the supply voltage is 300 V. A comparative analysis of these characteristics of secondary electron multipliers with corresponding parameters of microchannel plates based on lead silicate glass has been performed. It has been determined that that porous anodized alumina may be suitable for the manufacture of secondary electron multipliers. Its secondary emission ability is comparable to lead silicate glass.

A High-Dynamic-Range Counting−Analog Detector System Based on a Secondary Electron Multiplier

A high-dynamic-range counting−analog detector system based on a secondary electron multiplier (SEM) is described. The current-to-voltage converter, which is common to both channels, includes a high-speed transimpedance amplifier (TIA) and an automatic bias-correction circuit. This circuit also rejects 1/f noise of the TIA in the 0−2.3 Hz passband of the digital lowpass filter of a 24-bit analog-to-digital converter (ADC) in the electrometric channel. As a result, the noise-free code resolution of the entire channel, which is 18.5 bits, is determined only by the ADC noise. A number of circuit solutions are proposed to minimize the number of circuit components, which have made it possible to place the detector system board in the measuring head of the SEM and thereby reduce the stray capacitances that limit the response speed of the TIA. The maximum counting rate of the pulse-counting channel is 7 ×107 cps and is determined by the time resolution of the SEM. The problems of optimizing the supply voltages of the circuit and the gain of the SEM in the counting−analog mode are considered. The developed system is one of the units of the mass-spectrometry system for the isotope study of noble gases. The SEM-input-referred measurement ranges of the system are as follows: from 1 × 10–16 to 1.2 × 10−11 A at a resolution of 3 × 10−17 A or better for the electrometric channel; from 5 × 10−2 to 5 × 107 ions/s for the pulse-counting channel without counting losses and with the allowance for the SEM dark current; and from 1 × 10–20 to 1.2 × 10−11 A for the entire system. Due to the wide overlap of the measurement ranges, it is possible to perform mutual verification of data obtained in different modes.

Time stability characterization of quadrupole mass spectrometers

• Time stability of eight QMSs was investigated over 2-years period. • Stability of sensitivity of Faraday cup detector and SEM gain for He and N 2 . • Stability of peak position and peak width of He and N 2 . • Stability of minimum detectable partial pressure for He. • Measurements were carried out according to ISO TS 20175:2018. This study focuses on the time stability of different metrological characteristics of quadrupole mass spectrometers (QMSs). Investigated parameters were the sensitivity, when using a Faraday cup as a detector, the peak position, the peak width, the gain of a secondary electron multiplier, and the minimum detectable partial pressure. Eight different commercial QMSs were investigated at seven national metrology institutes under three different nominal calibration pressures of 5 × 10 −6 Pa, 5 × 10 −5 Pa, and 5 × 10 −4 Pa for N 2 and He. The measurements were carried out using a periodicity of approximately 3 months for a total duration of 2 years. Sensitivity calibrations were conducted either through a comparison method using calibrated ionization gauges or by applying a primary vacuum calibration system. In the case of ionization gauges, they were periodically recalibrated to ensure their stability and traceability to a primary pressure standard.

The first results of isotopic (U-Pb, ID-TIMS) dating of individual zircon grains from dolerite dikes of the Eastern zone of the Urals

Research subject. The article presents the results of dating two dolerite dikes differing in geochemical features from a section along the Iset river in the area of Smolinskoe settlement (the Eastern zone of the Middle Urals). Materials and methods. The dating was performed by an U-Pb ID-TIMS technique for single zircon grains using an artificial 205Pb/235U tracer in the laboratory of geochronology and isotope geochemistry of the Geological Institute of the Kola Science Centre of the Russian Academy of Sciences. The lead isotopic composition and uranium and lead concentrations were measured using a Finnigan-MAT (RPQ) seven-channel mass spectrometer in dynamic mode using a secondary electron multiplier and RPQ quadrupole in ion counting mode. Results. The dikes were dated 330 ± 3 Ma and 240 ± 2 Ma. Conclusions. The research results indicate different ages of dolerite dikes developed within the Eastern zone of the Middle Urals. The oldest of the two established age levels corresponds to the Early Carboniferous era. This fact, along with the proximity of the dolerites to the petrochemical features of the basaltoids of the Early Carboniferous Beklenischevsky volcanic complex, allows these bodies to be considered as hypabyssal comagmates of these volcanics. The youngest obtained age level – Triassic – indicates that the introduction of some dolerite dikes was associated with the final phases of the trapp formation developed rarely within the eastern outskirts of the Urals and widely further east in the foundation (pre-Jurassic basement) of the West-Siberian Plate.

A UHV standard with option to be used as partial pressure standard

Partial pressure measurement has become indispensable for many applications and contributes to the complete characterization of a vacuum system. In this work, an ultrahigh vacuum (UHV) standard was established for calibrating partial pressure analyzers as a partial pressure standard, and a new method was introduced to generate standard partial pressures, which was named ‘the dynamic expansion method based on static expansion vacuum standard injection mode’. The method can produce standard partial pressures in the range from 10–5 Pa to 10–10 Pa. The relative standard uncertainty budgets of generated partial pressures (k = 1) were in the range from 2.8% up to 5.0% from 10–5 Pa to 10–9 Pa for nitrogen. Employing this method, the sensitivity calibrations of quadrupole mass spectrometry (QMS) were performed in the partial pressure range of 8.62 × 10−5 Pa to 1.51 × 10−10 Pa with single inert He, Ar, and Kr gas in secondary electron multiplier (SEM) mode. Similarly, the calibrations were carried out using active gases (H2, CH4, N2, O2, and CO2) in the range 8.56 × 10−5 Pa to 1.50 × 10−9 Pa. Additionally, the SEM gains were calibrated for these high-purity gases, on the basis of SEM gain coefficients. QMS sensitivities equivalent to Faraday cup mode were attained, and it was found that the results were approximately consistent with those of previous studies. The data were also in agreement with our theoretical calculation values excluding CH4.

High‐Precision Measurement of 187Os/188Os Isotope Ratios of Nanogram to Picogram Amounts of Os in Geological Samples by N‐TIMS using Faraday Cups Equipped with 1013 Ω Amplifiers

N(187Os)/N(188Os) ratios of six geological reference materials were measured using static Faraday cups (FCs) with 1013 Ω amplifiers by N‐TIMS. Our results show that the repeatability precision was 2–3‰ (2 RSD, n = 3), when taking ~ 1 g of BHVO‐2 with 76 pg g−1 of Os mass fraction and ~ 2 g of BCR‐2 with 21 pg g−1 of Os mass fraction for each sample, whether measured by FCs or by secondary electron multiplier. The repeatability precision measured by FCs was 1–0.2‰ (2 RSD, n = 3) when taking ~ 1 g of BIR‐2 with 350 pg g−1 of Os mass fraction, ~ 1 g of WGB‐1 with 493 pg g−1 of Os mass fraction or ~ 0.5 g of WPR‐1 with 13.3 ng g−1 of Os mass fraction for each sample, which is much better than those measured by secondary electron multiplier. Instead, when taking ~ 2 g of AGV‐2 with 4 pg g−1 Os mass fraction, the repeatability precision measured by secondary electron multiplier is 3–4‰ (RSD, n = 3), which is better than those measured by FCs. Of the six reference materials analysed, WPR‐1 and BIR‐1a are the most homogeneous with regard to Os isotopic composition (2 RSD of 0.08% and 0.23%, respectively) when test portion masses are 0.5–1 g.

Optimizing MC-ICP-MS with SEM protocols for determination of U and Th isotope ratios and 230Th ages in carbonates

Abstract We have optimized techniques to measure uranium and thorium isotopic compositions using secondary electron multiplier (SEM) and peak-jumping protocols on a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Thermo Scientific Neptune Plus). This instrument is equipped with an advanced interface pump, X-skimmer cone, Jet sample cone, and desolvating nebulizer system (CETAC Aridus II) that enables overall ionization and transmission efficiency up to 3% for both U and Th. Approximately 50 fg 234U or 230Th can routinely yield a precision of 1–2‰ (2σ) for abundance and isotopic measurements. Non-linear behavior was not observed in the MasCom SEM with a retarding potential quadrupole in our MC-ICP-MS system when the beam intensity was limited to

Interfacing of a Coordinate-Sensitive Detector Based on Charge-Coupled Devices for Recording Ions with a Portable Static Mass Spectrograph

An IDS 2030 IonCCD coordinate-sensitive detector (Analytical/CMS Field Products) is interfaced with a small-sized mass spectrograph developed at the Ioffe Physical Technical Institute, Russian Academy of Sciences. The measurement data obtained with the mass spectrograph using an IonCCD detector and a Magnum-5901-37029PS channel secondary electron multiplier (Photonics USA Inc., United States) are compared. The results of measurements are discussed, and the prospects for using the IonCCD coupled with a microchannel plate are assessed.

Collisional dampening for improved quantification in single particle inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) is a powerful method for detection and quantification of nanoparticles. Unfortunately, the linear dynamic range of single particle analysis is hindered by “unruly” transient signals, momentary pulse pile-ups at the electron multiplier detector. This study seeks to extend the dynamic range of ICP-MS nanoparticle quantification via addition of a collision gas in the collision cell of the ICP-MS. The collision gas temporally broadens the nanoparticle signal resulting in decreased pulse pile-up and increased integrated intensity, up to a point where scattering losses begin to dominate. We tested collisional broadening with a dual mode simultaneous secondary electron multiplier (pulse counting switching to analog) and the same detector configured for pulse counting only operation. With no collision gas and the detector operating in its standard dual mode, the data shows a linear response for gold nanoparticles from 20 nm (smallest measured size) to 150 nm. With the addition of helium as a collision gas in the cell, the linear range extends up to 250 nm. The data collected exclusively from the pulse counting mode shows that with no collision gas there is a linear response for gold nanoparticles from 20 nm to 60 nm. While the signal slightly improves with the addition of a collision gas, the linear range fails to extend up to 80 nm, the next largest nanoparticle size in this study. The addition of a collision gas used together with the dual mode detector shows a promising path forward towards mitigating unruly transient signals, improving the dynamic range of nanoparticle quantification.

Magnetic and electric deflector spectrometers for ion emission analysis from laser generated plasma

The pulsed laser-generated plasma in vacuum and at low and high intensities can be characterized using different physical diagnostics. The charge particles emission can be characterized using magnetic, electric and magnet-electrical spectrometers. Such on-line techniques are often based on time-of-flight (TOF) measurements. A 90° electric deflection system is employed as ion energy analyzer (IEA) acting as a filter of the mass-to-charge ratio of emitted ions towards a secondary electron multiplier. It determines the ion energy and charge state distributions. The measure of the ion and electron currents as a function of the mass-to-charge ratio can be also determined by a magnetic deflector spectrometer, using a magnetic field of the order of 0.35 T, orthogonal to the ion incident direction, and an array of little ion collectors (IC) at different angles. A Thomson parabola spectrometer, employing gaf-chromix as detector, permits to be employed for ion mass, energy and charge state recognition. Mass quadrupole spectrometry, based on radiofrequency electric field oscillations, can be employed to characterize the plasma ion emission. Measurements performed on plasma produced by different lasers, irradiation conditions and targets are presented and discussed. Complementary measurements, based on mass and optical spectroscopy, semiconductor detectors, fast CCD camera and Langmuir probes are also employed for the full plasma characterization. Simulation programs, such as SRIM, SREM, and COMSOL are employed for the charge particle recognition.

Сопряжение координатно-чувствительного детектора на основе приборов с зарядовой связью для регистрации ионов с портативным статическим масс-спектрографом

AbstractAn IDS 2030 IonCCD coordinate-sensitive detector (Analytical/CMS Field Products) is interfaced with a small-sized mass spectrograph developed at the Ioffe Physical Technical Institute, Russian Academy of Sciences. The measurement data obtained with the mass spectrograph using an IonCCD detector and a Magnum-5901-37029PS channel secondary electron multiplier (Photonics USA Inc., United States) are compared. The results of measurements are discussed, and the prospects for using the IonCCD coupled with a microchannel plate are assessed.