We present a protocol for the generation of an isotopically purified low-energy 229Th ion beam from a 233U source. This ion beam is used for the direct detection of the 229mTh ground-state decay via the internal-conversion decay channel. We also measure the internal conversion lifetime of 229mTh as well.
A methodology is described to generate an isotopically pure 229Th ion beam in the 2+ and 3+ charge states. This ion beam enables one to investigate the low-lying isomeric first excited state of 229Th at an excitation energy of about 7.8(5) eV and a radiative lifetime of up to 104 seconds. The presented method allowed for a first direct identification of the decay of the thorium isomer, laying the foundations to study its decay properties as prerequisite for an optical control of this nuclear transition. High energy 229Th ions are produced in the α decay of a radioactive 233U source. The ions are thermalized in a buffer-gas stopping cell, extracted and subsequently an ion beam is formed. This ion beam is mass purified by a quadrupole-mass separator to generate a pure ion beam. In order to detect the isomeric decay, the ions are collected on the surface of a micro-channel plate detector, where electrons, as emitted in the internal conversion decay of the isomeric state, are observed.
The first excited metastable state in the thorium-229 nucleus, denoted as 229mTh, exhibits a special position in the nuclear landscape, as it possesses the lowest nuclear excitation energy of all presently known ca. 176,000 nuclear excited states. While typical nuclear energies range from keV up to the MeV region, 229mTh possesses an energy of below 10 eV above the nuclear ground state1,2,3. The currently most accepted energy value for this state is 7.8(5) eV4,5. This low energy value has triggered interest from different physical communities and led to the proposal of several interesting applications. Among them are a nuclear laser6, a highly stable qubit for quantum computing7 and a nuclear clock8,9.
The reason that 229mTh is expected to offer a broad variety of applications is based on the fact that, due to its extraordinary low energy, it is the only nuclear state that could allow for direct nuclear laser excitation using currently available laser technology. So far, however, direct nuclear laser excitation of 229mTh was prevented by insufficient knowledge of the metastable state's parameters like its precise energy and lifetime. Although the existence of a nuclear excited state of low energy in 229Th was already conjectured in 197610, all knowledge about this state could only be inferred from indirect measurements, not allowing for a precise determination of its decay parameters. This situation has changed since 2016, when the first direct detection of the 229mTh decay opened the door for a multitude of measurements aiming to pin down the excited state's parameters11,12. Here, a detailed protocol is provided, which describes the individual steps required for a direct detection of 229mTh as achieved in the experiment of 2016. This direct detection provides the basis for a precise determination of the 229mTh energy and lifetime and therefore for the development of a nuclear clock. In the following the concept of a nuclear clock as the most important application for 229mTh will be discussed.
With a relative linewidth of ΔE/E~10-20 the ground-state transition of the thorium isomer potentially qualifies as a nuclear frequency standard ('nuclear clock')8,9. Due to an atomic nucleus about 5 orders of magnitude smaller compared to the atomic shell, the nuclear moments (magnetic dipole and electric quadrupole) are accordingly smaller than the ones in atoms, rendering a nuclear clock largely immune against external perturbations (compared to the present state-of-the-art atomic clocks). Therefore, a nuclear frequency standard promises a highly stable and accurate clock operation. Although the accuracy achieved in the best present atomic clocks reaches about 2.1×10-18 13, corresponding to a deviation of 1 second in a time period considerably longer than the age of the universe, nuclear clocks hold the potential of a further improvement which could become essential for a vast field of applications. Satellite-based navigational systems like the Global Positioning System (GPS), Global Navigation Satellite System (GLONASS) or Galileo presently operate with a positioning precision of a few meters. If this could be improved to the centimeter or even millimeter scale, a plethora of applications could be envisaged, from autonomous driving to freight or component tracking. Besides highly accurate clocks, such systems would require reliable uninterrupted operation, with long-term drift stability that secures long-resynchronization intervals. The use of nuclear clocks could turn out beneficial from this practical point of view. Further practical applications of (synchronized networks of) nuclear clocks could lie in the field of relativistic geodesy14, where the clock acts as a 3D gravity sensor, relating local gravitational potential differences ΔU to measured (relative) clock frequency differences Δf/f via the relation Δf/f=-ΔU/c2 (c denoting the speed of light). The best present clocks are capable of sensing gravitational shifts from height differences of about ±2 cm. Thus, ultra-precise measurements using a nuclear clock network could be used to monitor the dynamics of volcanic magma chambers or tectonic plate movements15. Moreover, the use of such clock networks was proposed as a tool to search for the theoretically described class of topological dark matter16. Extensive discussion can be found in the literature on the application of a 229mTh-based nuclear clock in the quest for the detection of potential temporal variations of fundamental constants like the fine structure constant α or the strong interaction parameter (mq/ΔQCD, with mq representing the quark mass and ΔQCD the scale parameter of the strong interaction), suggested in some theories unifying gravity with other interactions17. The detection of a temporal variation in the ground-state transition energy of 229mTh may provide an enhanced sensitivity by about 2-5 orders of magnitude for temporal variations of the fine structure constant or the strong interaction parameter18,19,20,21,22,23,24,25,26. The current experimental limit for such a variation of α amounts to (dα/dt)/α=-0.7(2.1)10-17/yr27. In the following the experimental approach for the direct detection of the 229mTh ground-state decay will be described.
Evidence for the existence of the 229-thorium isomer until recently could only be inferred from indirect measurements, suggesting an excitation energy of 7.8(5) eV (equivalent to a wavelength in the vacuum ultra-violet spectral range of 160(11) nm)4,5. Our experimental approach, aiming at a direct identification of the isomeric ground-state deexcitation of the 229mTh isomer, builds on a spatial separation of the isomer population in a buffer-gas stopping cell, followed by an extraction, and mass-separated transport towards a suitable detection unit to register the deexcitation products28,29. Thus population and deexcitation of the isomer can be disentangled, resulting in a clean measurement environment, unaffected by prompt background contributions. Population of the isomer is achieved via the α decay from a radioactive 233U source, where a 2% decay branch proceeds not directly to the ground state of 229Th, but populates the isomeric first excited state instead. α-decay recoil nuclei are thermalized in an ultra-pure helium atmosphere of a buffer-gas stopping cell, before being guided by electric radiofrequency (RF) and direct current (DC) fields towards an extraction nozzle, where the emerging supersonic gas jet drags them into an adjacent vacuum chamber, housing a (segmented) radiofrequency quadrupole (RFQ) structure acting as ion guide, phase-space cooler and potentially also as linear Paul trap for bunching the extracted ions. For a detailed description of the buffer-gas stopping cell and extraction RFQ see Refs.30,31,32. Since up to that moment the extracted ion beam contains in addition to 229(m)Th also the chain of α decay daughter products, mass separation is performed using a quadrupole mass separator (QMS) in a subsequent vacuum chamber to finally generate an isotopically pure 229(m)Th beam in selectable charge states (q=1-3). A detailed description of the QMS can be found in Refs.33,34. Detection of the isomeric decay was achieved by impinging the Th ions directly on the surface of a microchannel-plate detector (MCP), where electrons are liberated, accelerated towards a phosphor screen and viewed by a charge-coupled device (CCD) camera. An overview of the experimental setup is shown in Figure 1. A detailed description is given in Ref.35.
Figure 1: Overview of the experimental setup. The thorium-229 isomer is populated via the 2% decay branch in the α decay of uranium-233. 229mTh ions, leaving the 233U source due to their kinetic recoil energy, are thermalized in a buffer-gas stopping cell filled with 30 mbar helium gas. The ions are extracted from the stopping volume with the help for RF and DC fields and a low-energy ion beam is formed with the help of a radio-frequency quadrupole (RFQ). The ion beam is mass-purified with the help of a quadrupole-mass-separator (QMS) and the ions are softly implanted into the surface of a micro-channel-plate (MCP) detector combined with a phosphor screen which allows for spatially resolved detection of any occurring signals. With kind permission of Springer Research, this figure has been modified from11. Please click here to view a larger version of this figure.
The following protocol describes the underlying procedure to generate the 229(m)Th ion beam that enabled the first direct detection of the ground-state decay of the thorium isomer, thus laying the foundation for studying its decay properties as a prerequisite of the ultimately envisaged all-optical control of this exotic nuclear state towards its application as an ultra-precise nuclear frequency standard. For better orientation a schematic overview of the setup used for direct detection of the isomeric decay11 is provided in Figure 2, containing a numerical labelling of the components addressed in the following protocol. Also the components used for lifetime determination12 are contained as an inset.
Figure 2: Schematic sketch of the experimental setup used for isomeric decay detection. The components used for lifetime measurement are shown as an inset. Individual components that will be referenced in the protocol section are numerically labelled. Please click here to view a larger version of this figure.
Note: Numbers given in the Protocol will reference to Figure 2.
1. Direct Detection of Th-229 Isomeric Decay
2. Measurement of the 229m Th Half-Life (Re-arrangement of the Setup)
The method described before allowed for the extraction of α decay products from a 233U source placed inside a buffer-gas stopping cell, operated at ca. 30 mbar ultra-pure helium gas at room temperature. For the first time up to triply charged ions could be extracted from such a device with high efficiency29. Figure 3a displays the mass spectrum of ions extracted from the buffer-gas cell, showing three groups of 233U α-decay products (plus accompanying contaminant adducts) in singly, doubly and triply charged ionic states. Noteworthy is the dominance of 229Th3+ extraction compared to 233U3+, while both species are extracted with about equal intensity when being doubly charged. This fact was used for comparative measurements with 233U ions, which allowed the exclusion of any ionic impact as signal origin.
Figure 3: Identification of the direct decay of the 229-thorium isomer. a) Complete mass scan performed with the 233U source 129. Units are given as atomic mass (u) over electric charge (e). b) Comparison of MCP signals obtained during accumulation of thorium and uranium in the 2+ and 3+ charge states (as indicated by the arrows linking to the mass scan). 233U and 234U sources were used (the source number is given on the right-hand side of each row). Each image corresponds to an individual measurement of 2,000 s integration time (20 mm diameter aperture indicated by the dashed circle). Measurements were performed at -25 V MCP surface voltage in order to guarantee soft landing of the ions. c) Signal of the 229Th isomeric decay obtained during 229Th3+ extraction with source 1. A signal area diameter of about 2 mm (FWHM) is achieved. The obtained maximum signal intensity is 0.08 counts/(s mm2) at a background rate of about 0.01 counts /(s mm2). With kind permission of Springer Research 11. Please click here to view a larger version of this figure.
After transport, cooling and mass separation, the ion beam impinges onto the surface of a microchannel-plate detector, where a low attractive surface potential ensures the suppression of ionic impact signals and leaves only electrons arising from the Internal Conversion (IC) decay channel of the 229mTh isomer to be multiplied in the strong electric field of the detector plate channels. The resulting MCP signals as obtained for three different uranium sources are displayed in Figure 3b. The ion species of doubly or triply charged ions which was selected with the help of the quadrupole mass separator in each individual measurement is indicated by the arrows from the upper panel. Shown are pictures acquired with the CCD camera behind the phosphor screen, onto which the electrons from the MCP were accelerated. The field of view of the CCD camera is indicated by the dashed circles for triply (first two columns) and doubly charged (last two columns) 229Th and 233U ions, respectively. The upper row represents the result obtained for a small-area 233U source (ca. 1000 extracted 229Th3+ ions per second, source 1), while the bottom row shows the same for a stronger source with ca. 10,000 extracted 229Th3+ ions per second (source 3). It is obvious that in both cases a clear signal is obtained for 229Th, while no indication of an electron signal is observed for 233U 11. In order to prove that this signal indeed originates from a nuclear deexcitation and not from an atomic shell process, the middle row shows the resulting camera image when using a 234U source, where the α decay populates the neighboring isotope 230Th, with a comparable electronic, yet different nuclear structure. As expected for 230Th, no indication of a conversion electron signal is found in any of the cases studied. So the strong signal, displayed in Figure 3c with excellent signal-to-background ratio, is clearly correlated with the decay of 229mTh.
Additional verification measurements to support this interpretation are shown in Figure 4. They show two measurements to give further evidence that the registered electron signals indeed originate from the decay of the nuclear isomer: in Figure 4a it is shown that the attractive surface potential of the MCP detector was varied from -100 V (favoring the occurrence of electrons from ionic impact) down to 0 V, comparing the count rates registered with the MCP for extracted 229Th2+ (red) and 233U2+ ions (blue). Clearly the count rate drops down to zero for 233U2+ when realizing a 'soft landing' of the incoming ions with a surface voltage below ca. -40 V, while a considerable count rate remains for 229Th2+ until the threshold of 0 V. In Figure 4b, the blue curve shows the electron count rate registered for extracted ions after strong acceleration towards the MCP detector surface with -2000 V. Ionic impact of 233U2+ and 229Th2+ ions is observed with about equal intensity, as already shown for doubly charged ions in the extracted mass spectrum of Figure 3a. The red curve shows the same scenario, however now for a 'soft landing' of incoming ions with -25 V MCP surface potential. No indication of the ionic impact signal of 233U2+ is visible any more, while for 229Th2+ a signal remains, originating from the isomeric internal conversion decay11.
Figure 4: Isomer decay verification measurements. a) 229Th2+ signal (red) compared to 233U2+ (blue) as a function of the MCP surface voltage. Errors are indicated by shaded bands. b) Signal of extracted ions as a function of the mass-to-charge ratio behind the QMS for MCP surface voltages of -25 V (isomer decay, red) and -2,000 V (ion impact, blue). Note the different integration times and axis scales. In addition to the signal at 114.5 u/e (corresponding to 229Th2+), a further signal at 117.5 u/e occurs, which originates from the isomeric decay of 235U. With kind permission of Springer Research11. Please click here to view a larger version of this figure.
Thus, it can be unambiguously proven (together with additional arguments given in Ref. 11) that the signal observed in Figure 4 originates from the isomeric decay of 229mTh and represents the first direct identification of the deexcitation of this elusive isomer.
Subsequently the segmented extraction-RFQ was operated as a linear Paul trap to create a bunched ion beam, thus allowing for lifetime measurements of the thorium isomer. Since our room-temperature high vacuum does not allow for sufficiently long storage times to investigate the expected radiative lifetime of up to 104 seconds, only a lower limit of t1/2 > 1 minute could be derived for charged 229mTh ions, limited by the maximum achievable ion storage time in the linear Paul trap11. However, using the same detection strategy as applied before for the identification of the isomer decay after neutralization of the thorium ions on the surface of an MCP detector, the expected much shorter lifetime for neutral 229mTh atoms undergoing internal conversion decay provides access to lifetime information12. Figure 5a shows the expected shape of the decay time spectrum as simulated for an ion bunch with a pulse width of 10 μs. While the red curve indicates the ionic impact signal and the signal from an exponential decay with 7 μs half-life is represented by the gray curve with a long decay tail, the expected signal from the decay of the thorium isomer, comprised of both the ionic impact and the exponential isomeric decay, is illustrated by the blue curve. Figure 5b displays the outcome of the corresponding measurement for 233U3+ (red) and 229Th3+ (blue), respectively. While uranium ions only exhibit their ionic impact signal, for 229-thorium clearly the expected decay tail of the isomer decay can be observed12.
Figure 5: Simulated and measured temporal ion impact and decay characteristics. a) Simulation of the isomer decay time characteristics of 229Th bunches. The simulation is based on a measured bunch shape and the assumption that 2 % of the 229Th ions are in the isomeric state with a half-life of 7 μs after neutralization. The electron detection efficiency is assumed to be 25 times larger than the ion detection efficiency. b) Measurement of the isomeric decay with a bunched 229(m)Th3+ ion beam (blue). A comparative measurement with 233U3+ is shown in red. With kind permission of the American Physical Society12. Please click here to view a larger version of this figure.
Fitting the decay tail with an exponential (corresponding to a linear fit to the logarithmic representation in Figure 6) finally results in a half-life of the neutral 229mTh isomer of 7(1) μs12. This value nicely agrees with the theoretically expected lifetime reduction by nine orders of magnitude from the ca. 104 seconds in case of the charged isomer due to the large conversion coefficient of αIC ~ 109 37.
Figure 6: Fit to 229mTh decay curve. Logarithmic plot of the temporal decay characteristics for 229(m)Th2+ ions (a) and 229(m)Th3+ ions (b) together with a fit curve applied to extract the isomeric half-life of 229mTh after charge recombination on the MCP detector surface. With kind permission of the American Physical Society12. Please click here to view a larger version of this figure.
The range of recoiling α decay daughter nuclei in uranium amounts to only about 16 nm. In order to achieve a high efficiency of the source for α-recoil ions for a given source activity, it is mandatory to limit the source material thickness to this range. The α recoil extraction efficiency is strongly affected by the cleanliness of the buffer-gas cell. Contaminations of the stopping gas will lead to charge exchange or molecule formation. Therefore, the gas cell itself has to be built according to ultra-high vacuum standards, in particular to allow for a baking of the cell and avoiding any organic materials inside. The stopping gas has to be purified according to technical state-of-the-art, starting from highest-grade gas purity assisted by catalytic purification and delivery to the gas cell via an ultra-clean gas-supply line, partially surrounded by a cryogenic trap to freeze out impurities. In general, careful alignment of the central axis of the complete setup to the position of the gas cell extraction nozzle is essential for achieving a high transport and detection efficiency29.
Step 1.4.5 is the most critical of the protocol. For efficient ion extraction a high RF amplitude has to be applied to the funnel ring electrode. However, if the amplitude is chosen too high, sparks in the gas cell will occur. The maximum achievable RF voltage amplitude depends critically on the purity of the buffer gas. A successful application of voltage is monitored via the current of the funnel offset voltage. This current will increase in the case of sparks. If sparks have occurred, the bake-out procedure has to be repeated in order to guarantee highest ion extraction efficiency.
A further critical point is the application of the high voltages to the MCP detector (steps 1.6.2-1.6.4). Field emissions can occur on the MCP, leading to the emission of electrons which can lead to artefactual signals.
Optimum ion extraction and (cooled and mass purified) transport towards the detection unit requires careful alignment of the central optical axis. The availability of an optical alignment system (alignment laser or theodolite) is essential. The efficient ion transport through the extraction RFQ and the QMS requires a continuous stabilization of the radio-frequency amplitudes for the two opposite phases applied to each opposite pair of rods29. Identification of extraction or transport problems can be facilitated by an ion diagnostic realized e.g., via a multichannel-plate detector placed either consecutively at different positions along the ion path during the commissioning phase of the setup, or alternatively, e.g., under 90o behind the extraction RFQ with a high negative surface voltage (1-2 kV) to attract all extracted ions towards the detector.
During operation typically two problems can arise. Not all voltages are correctly applied. In this case usually no ions are extracted, and one has to find the place of not correctly applied voltage. Also, impurities are present in the helium buffer-gas. In this case the extraction efficiency for triply charged thorium ions will be drastically reduced and molecule formation occurs. In the worst case, even sparks will show up when the funnel voltage is applied. The reason for insufficient gas purity is typically a leakage in the gas supply line or a not properly closed flange of the buffer-gas stopping cell.
The described method to generate a clean beam of ions containing the energetically low-lying 229mTh isomer can be applied to all comparable cases where the ion of interest can be extracted from the buffer-gas atmosphere in sizeable amounts. Cleanliness of the gas-cell and buffer gas is mandatory, thus the amount of remaining gas impurities is a limitation to the sensitivity of the method. While the employed microchannel-plate detector (MCP) is based on the detection of electrons, as exploited here for the registration of low-energy conversion electrons, this case already lies at the low-energy border of the efficiency curve for MCPs38, while for higher energies the method would significantly gain in detection efficiency.
So far, the described method has provided the only reported direct and unambiguous identification of the de-excitation of the thorium isomer. Alternatively, vacuum ultra-violet (VUV)-transparent crystals (with large bandgaps, exceeding the assumed excitation energy of the isomer) are doped with 229Th. The goal is to place 229Th ions in high (4+) charge state of crystal lattice positions, inhibit de-excitation by the large band gap and aim at an excitation of the isomer using X- rays from synchrotron light sources. Despite the elegant concept of this approach, so far no VUV fluorescence could be observed in a series of experiments reported by several groups worldwide39,40,41,42,43. The same holds for a class of experiments that aims to realize the nuclear excitation of the isomer via the electron shell of 229Th, using a so-called electron-bridge transition. Here a resonant coupling between an electron shell transition and the nuclear isomer should allow for a more efficient isomer population44,45. Other experiments that aim for the investigation of the isomeric properties are based on microcalorimetry46 or the observation of the hyperfine-shift in the atomic shell47. Very recently another method to excite the isomer in a laser-induced plasma was reported48 and is subject to scientific discussion within the community.
The discovery of the internal conversion decay channel of the thorium isomer11 and the determination of the corresponding half-life of neutral 229mTh (7(1) μs)12 can be exploited in the future to realize a first all-optical excitation with a pulsed, tunable VUV laser based on already existing technology. Thus the present paradigm that this would require much better knowledge of the excitation energy and a corresponding customized laser development can be circumvented. In contrast, exploiting the knowledge of internal conversion electron emission, gating the detection of conversion electrons with the laser pulse will provide a high signal-to-background ratio, while allowing for a scan of 1 eV of excitation energy in less than 3 days49.Moreover, a determination of the excitation energy of the isomer, still being work in progress, can be based on the described method of generating the 229mTh beam by sending IC decay electrons into a magnetic-bottle electron spectrometer with retarding field electrode grids50. The same technique will also allow to determine the isomeric lifetime for different chemical environments (e.g., on large band-gap materials like CaF2 or frozen argon) or in 229Th+ as well as in the free, neutral atom.
The described method of generating an isotopically pure thorium ion beam of 3+ charge state can be used as a tool to provide thorium ions for future laser-spectroscopy experiments. In this case the ion beam can be used to load a Paul trap in a stable and efficient way. So far, the only alternative method is to produce 229Th3+ by laser ablation from a solid target. This, however, requires high laser intensities and a large quantity of 229Th, which is an expensive radioactive material and leads to the contamination of used vacuum components. For this reason, the described method can be of significant advantage when it comes to nuclear laser spectroscopy experiments. A first application of this type has already been published51.
The authors have nothing to disclose.
This work was supported by the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 664732 "nuClock", by DFG grant Th956/3-1, and by the LMU department of Medical Physics via the Maier-Leibnitz-Laboratory.
Uranium-233 Source | Institut für Radiochemie Universität Mainz | customized | 290 kBq U-233 deposited onto 90 mm diameter |
RF funnel | Secamus Laserschneidtechnik GmbH | customized | 50 ring electrodes, laser cut and electropolished |
Buffer-gas stopping cell | Workshop of LMU Munich | customized | Vacuuchamber DN200 CF for buffer-gas stopping cell |
Roughing pump | Leybold | Screwline SP 250 | Roughing pump for entire system |
Roughing pump control | Siemens | Micromaster 420 | Control unit for Screwline SP 250 |
Vacuum gauge Prepressure | Pfeiffer | TPR 265 | Pressure control for roughing pump |
Vacuum gauge cell 1 | Pfeiffer | CMR 261 | Pressure control for cell (high-pressure range) |
Vacuum gauge cell 2 | Pfeiffer | PBR 260 | Pressure control for cell (low-pressure range) |
Vacuum gauge RFQ | Pfeiffer | PKR 261 | Pressure control for RFQ pressure read-out |
Pressure gauge QMS | Pfeiffer | PKR 261 | Pressure control for QMS pressure read-out |
Pressure control unit | Pfeiffer | TPG 256 A | Control unit for all pressure gauges |
Control PC 1 | Fujitsu | unknown | Control computer for buffer-gas stopping cell |
Simatic with CPU | Siemens | S7-300 | Simatic for automation and control |
Simatic without CPU | Siemens | ET 200M | Simatic for automation and control |
Vacuum valves | SMC | XLH-40 | Vacuum valves for evacuation control |
UHV gate valve | VAT | 48240-CE74 | Gate valve for cell closing during operation |
Turbo-Molecular pump 1 | Pfeiffer | TMU 400M | Turbo pump for cell |
Control unit for TMP 1 | Pfeiffer | TCM 1601 | Control unit for TMP TMU 400M |
Turbo-Molecular pump 2 | Pfeiffer | HiMag 2400 | Trubo pump for RFQ |
Turbo-Molecular pump 3 | Edwards | STP 603 | Trubo pump for QMS |
Control unit for TMP 3 | Edwards | SCU-800 | Control unit for TMP Edwards STP 603 |
Bypass valve of gas tubing | Swagelok | SS-6BG-MM | Valve to bypass the mass-flow controller |
Heating sleeves | Isopad | customized | Heating sleeves for bake out of cell and RFQ |
Temperature sensors | Isopad | TAI/NM NiCrNi | Temperature sensors for bake-out system |
Heating control unit | Electronic workshop of LMU Munich | customized | Control unit for Isopad heating sleeves |
Catalytic gas purifier | SAES MonoTorr | PS4-MT3-R-2 | Gas purifier for ultra-pure helium supply |
He gas cylinder | Air Liquide | He 6.0, 50 liters | Helium of 99.9999 % purity |
Pressure reducer | Druva | FMD 502-16 | Pressure reducer for He gas cylinder |
Valve of gas supply | Swagelok | SS-6BG-MM | Valve to open or close the gas supply |
Mass flow control | AERA | FC-780CHT | Mass flow control valve for He supply |
control unit for mass flow valve | Electronic workshop of LMU Munich | customized | Control unit for AERA mass flow control |
Gas tubing | Dockweiler | Ultron | electropolished gas tubing for He supply |
Cryogenic trap | Isotherm | unknown | cryogenic trap for He purification (optional) |
DC voltage supply for source | Electronic workshop of LMU Munich | customized | DC offset voltage supply for U-233 source |
DC voltage supply for funnel | Heinzinger | LNG 350-6 | Power supply for DC gradient of funnel |
DC voltage supply for RFQ | Iseg | unknown | DC voltage supply for funnel offset, nozzle and RFQ |
Laval nozzle | Friatec AG | customized | Laval nozzle for He and ion extraction |
DC voltage supply for buncher | Heinzinger | LNG 350-6 | DC supply for bunching electrode |
Trigger module | Electronic workshop of LMU Munich | customized | Trigger module for bunched operation |
RF generator for funnel | Stanford Research Systems | SRS DS 345 | RF generator for funnel |
RF amplifier for funnel | Electronic Navigation Industries | ENI 240L-1301 | Rf amplifier for funnel |
RF phase divider for funnel | Electronic workshop of LMU Munich | customized | RF phase divider for funnel |
RF+DC mixer for funnel | Electronic workshop of LMU Munich | customized | Voltage divider and RF+DC mixer for funnel voltage |
Extraction RFQ | Workshop of LMU Munich | customized | Extraction RFQ for ion-beam formation or storage |
RF generator for RFQ | Stanford Research Systems | SRS DS 345 | RF generator for RFQ |
RF amplifier for RFQ | Electronic workshop of LMU Munich | customized | RF amplifier for RFQ |
RF amplifier for bunch electrode | Electronic workshop of LMU Munich | customized | RF amplifier for bunch electrode |
RF+DC mixer for RFQ | Electronic workshop of LMU Munich | customized | Mixes the RF and DC potentials for RFQ voltage |
RFQ exit electrode | Workshop of LMU Munich | customized | 2-mm diameter exit aperture for differential pumping |
4 Channel DC supply | Mesytec | MHV 4 | DC offset for aperture and triode |
QMS | Workshop of LMU Munich | customized | Quadrupole mass separator for m/q selection |
Brubaker DC offset module | Electronic workshop of LMU Munich | customized | DC offset supply for Brubaker lenses of QMS |
QMS DC offset module | Electronic workshop of LMU Munich | customized | DC offset supply for QMS |
USB-to-Analog converter | EA Elektro-Automatik | UTA12 | to generate signal for QMS HV shifter |
QMS HV shifter | Electronic workshop of LMU Munich | customized | to shift the voltage of the QMS DC module |
QMS DC module | Electronic workshop of LMU Munich | customized | Module to provide DC voltages for QMS |
RF generator for QMS | Tektronix | AFG 3022B | RF generator for QMS |
RF amplifier for QMS | Electronic workshop of LMU Munich | customized | RF amplifier for QMS |
Picoscope | Pico Technology | Picoscope 4227 | Oscilloscope for QMS RF control |
Control PC 2 | Fujitsu | Esprimo P900 | Control computer for QMS |
Triode extraction system | Workshop of LMU Munich | customized | Set of three ring electrodes to guide ions |
MCP detector | Beam-Imaging-Solutions | BOS-75-FO | MCP detector with phosphor sreen |
DC voltage supply for MCP | Keithley Instruments | HV Supply 246 | Voltage supply for MCP front side |
DC voltage supply for MCP | CMTE (NIM module) | HV 3160 | Voltage supply for MCP back side |
DC voltage supply for MCP | Fluke | HV Supply 410B | Voltage supply for phosphor sreen |
CCD camera | PointGrey | FL2-14S3M-C | CCD camera for image recording |
Control PC 3 | Fujitsu | Esprimo P910 | Control computer for CCD camera |
Light-tight housing | Workshop of LMU Munich | customized | Light tight wooden box for CCD camera |
Dewar for LN2 supply | Isotherm | unknown | Dewar to provide dry nitrogen for venting |
Evaporator for LN2 | Workshop of LMU Munich | customized | Evaporator to provide dry nitrogen |
Single anode MCP detector | Hamamatsu | F2223 | Single anode MCP for lilfetime measurement |
DC voltage supply for MCP | Fluke | HV supply 410B | Voltage supply for MCP anode |
Power supply for preamplifier | Delta Elektronika | E 030-1 | Power supply for preamplifier |
Preamplifier for MCP signals | Ortec | VT120A | Preamplifier for MCP signals |
Amplifier for MCP signals | Ortec (NIM module) | Ortec 571 | Amplifier for MCP signals |
CFD | Canberra | 1428A | Constant-fraction-discriminator for MCP signals |
Multichannel Scaler | Stanford Research | SR 430 | Multichannel scaler for signal read-out |
Control PC 4 | Fujitsu | Esprimo P920 | Control computer for scaler read-out |
Labview | National Instruments | various versions | Program used for measurement control |
Matlab | Mathworks Inc. | version 7.0 | Program used for data analysis |