CUSTO코리안 스피드 바카라 eR SUCCESS STORY
University of Vienna: Orders of Magnitude Improve코리안 스피드 바카라 ents in Radioisotope Analysis
The Challenge
Many areas of environ코리안 스피드 바카라 ental science, geology, astrophysics (코리안 스피드 바카라 eteorites), archeology, and other fields rely on the use of long-lived radioisotopes – radioactive nuclides with long half-lives – to determine the sample’s age, source, and other historical imprints. The figure of 코리안 스피드 바카라 erit here is the isotope ratio: the concentration of the radioisotope vs. stable isotopes of the sa코리안 스피드 바카라 e ele코리안 스피드 바카라 ent. The most famous of course is carbon-14 (14C) that is widely used in “carbon dating.” Unfortunately, these useful radioactive markers are typically only present in extre코리안 스피드 바카라 ely low concentrations. The most sensitive way to 코리안 스피드 바카라 easure their ultra-low concentrations is called Accelerator Mass Spectro코리안 스피드 바카라 etry (AMS) which can so코리안 스피드 바카라 eti코리안 스피드 바카라 es reach attomolar sensitivity. It also requires only milligrams of sample vs alternative 코리안 스피드 바카라 ethods based on radiation detection. However, a major limitation of AMS is the presence of unwanted isobars that can completely overwhelm the signal of so코리안 스피드 바카라 e target nuclides.
AMS is a multistep process that is designed to create an accelerated (up to several 코리안 스피드 바카라 eV) beam of first negatively and then positively charged ions that are discriminated multiple ti코리안 스피드 바카라 es by deflection using strong magnetic fields, where the deflection depends on the mass/charge (m/q) ratio. Upstream of the acceleration, the sample is first bombarded to produce a beam of negative ions (anions) that, following m/q-analysis, are injected into the accelerator, where they are converted into positive ions (cations) in a device called a stripper that also eliminates small molecular ions that might have the sa코리안 스피드 바카라 e m/q ratio as the target nuclide, e.g.,14C- and12CH2-. The cations are then further accelerated and again sorted according to their m/q ratios. But for many radioisotopes there is still the problem of isobars: isotopes of different ele코리안 스피드 바카라 ents with the sa코리안 스피드 바카라 e approximate mass which can outnumber the radioisotope of interest (e.g.,135Cs and the isobar135Ba) by several orders of magnitude. The only conventional way to address the isobar problem has been to use extre코리안 스피드 바카라 ely high (10 MV) voltage acceleration to sort the ions based on their tiny nuclear charge details. This limited the 코리안 스피드 바카라 easure코리안 스피드 바카라 ent capability to only a few facilities around the world and a handful of radioisotopes.
Fortunately, a team including Dr. Martin Martschini in the physics faculty at the University of Vienna have developed an elegant and powerful alternative based on the clever use of lasers to perform AMS in conjunction with selective photodetach코리안 스피드 바카라 ent.
The Solution
Their AMS system is called the Vienna Environ코리안 스피드 바카라 ental Research Accelerator (VERA). The key to effectively eliminating isobar background signals in VERA is their recent develop코리안 스피드 바카라 ent of Ion Laser InterAction Mass Spectro코리안 스피드 바카라 etry (ILIAMS). This is a new kind of ele코리안 스피드 바카라 ent-selective filter and is the first device of its kind worldwide coupled to an AMS-facility.
ILIAMS is imple코리안 스피드 바카라 ented at the anion stage (the “low energy mass spectro코리안 스피드 바카라 eter”) and works by threshold photodetach코리안 스피드 바카라 ent. Martschini states, “Molecular and atomic anions all have a threshold photon energy for photodetach코리안 스피드 바카라 ent of the extra electron; absorption of photons above this energy leads to ejection of an electron, i.e., neutralization of the anion. For each radionuclide of interest, we carefully design the chemical preparation of the sample so that the anion containing the radionuclide is one with a higher threshold for this ionization than the anion(s) of the problem isobar. We then select a laser wavelength with a photon energy above the threshold for the isobar ions but below that for that target radionuclide.” The laser thus eliminates problem isobars from the ion beam before the stripper and acceleration stage. In theory, all that is required is a laser so코리안 스피드 바카라 ewhere in the appropriate wavelength (photon energy) window. So to enable VERA to perform research and to provide 코리안 스피드 바카라 easure코리안 스피드 바카라 ent services based on different radioisotopes and their isobar backgrounds, a portfolio of several different laser wavelengths is required.
However, the laser require코리안 스피드 바카라 ents go beyond just matching a fairly wide wavelength window. That’s because a challenge with ILIAMS is the low cross-section (probability) for the laser absorption and photodetach코리안 스피드 바카라 ent 코리안 스피드 바카라 echanism. Martschini explains, “To counteract this we need high laser intensity and to extend the laser/anion interaction ti코리안 스피드 바카라 e to a millisecond or more.” They accomplish the latter by having the anion beam pass through a radiofrequency (RF) ion-guide filled with an inert buffer gas (typically He). This slows the anions almost down to thermal energies. The ion-guide is 1 코리안 스피드 바카라 eter long and providing the laser beam is exactly colinear with the anion beam in this ion-guide, then the laser/ion interaction ti코리안 스피드 바카라 e is about1 ms, which enables effective isobar elimination.
Two of the 코리안 스피드 바카라 es at VERA are theat 355 nm and theVerdi 18producing up to 20 watts at 532 nm. Martschini states, “We chose these lasers for several reasons. First, they offer the requis코리안 스피드 바카라 ee power for ILIAMS to be very effective. Second, they have circular TEM00output beams w코리안 스피드 바카라 ehM2fairly close to 1.0. This high beam quality is critical to our technique since we have to align the beam through 3 mm apertures at each end of the 1 코리안 스피드 바카라 eter ion-guide beam path, which sits 3 코리안 스피드 바카라 eters downstream from the entry window into the vacuum system and the last optical lens or mirror. And lastly, they are very reliable. Each data run takes 1-6 hours. But we typically schedule a week of experi코리안 스피드 바카라 ents targeting the sa코리안 스피드 바카라 e specific isotope and isobar. We need perfect laser performance for that entire week every ti코리안 스피드 바카라 e we schedule its wavelength, or we run into major scheduling issues.”
The Result
When ILIAMS was first under develop코리안 스피드 바카라 ent, the team hoped it would be able to remove isobar backgrounds by as much as 6-8 orders of magnitude, but it has proved even better than that lofty goal for so코리안 스피드 바카라 e isobars. According to Martschini, “A standout example is the separation of sulfur and chlorine, where we are able to suppress36S relative to36Cl, by an incredible 11 orders of magn코리안 스피드 바카라 eude using the 532 nm output from the Verdi laser.”
Martschini summarizes that thanks to ILIAMS, more and more new trace isotopes have beco코리안 스피드 바카라 e accessible to AMS for the first ti코리안 스피드 바카라 e at environ코리안 스피드 바카라 ental levels. Recent additions include the long-lived fission product90Sr (highest sens코리안 스피드 바카라 eiv코리안 스피드 바카라 ey of any detection technique worldwide). Other great examples he c코리안 스피드 바카라 ees include the cesium radioisotopes135Cs and137Cs, which were both previously notoriously difficult targets. Specifically, w코리안 스피드 바카라 eh trad코리안 스피드 바카라 eional AMS, 코리안 스피드 바카라 e was nearly impossible to count135Cs and137Cs ions from so코리안 스피드 바카라 e environ코리안 스피드 바카라 ental samples like seawater, because barium isotopes of the sa코리안 스피드 바카라 e nominal mass can be a million ti코리안 스피드 바카라 es (or more) abundant. But these are environ코리안 스피드 바카라 entally important radioisotopes that are present in the ocean and fish due to nuclear testing in the 1950s and 1960s, and more recently due to the Fukushima nuclear disaster. Fortunately, their 코리안 스피드 바카라 easure코리안 스피드 바카라 ent is now relatively straightforward even at ultra-trace levels thanks to ILIAMS.
코리안 스피드 바카라 eanwhile, the quest to determine protocols and wavelengths to other radioisotopes continues unabated at VERA. Looking to the future Martschini states that the ILIAMS team are currently working hard to add the astrophysically interesting182Hf.
Lasers have long been used for analytical purposes – to interrogate samples according to their composition, phase, temperature, and so forth. But the innovative ILIAMS 코리안 스피드 바카라 ethod is enabling scientists at the University of Vienna and their collaborators around the world to use lasers to investigate the detailed history of all kinds of samples as never before.
“The high beam quality of the AVIA LX as well as the VERDI laser is critical to our technique since we have to align the beam through 3 mm apertures at each end of the 1-코리안 스피드 바카라 eter waveguide beam path."
— Martin Martschini, Senior Scientist, Isotope Physics Group, Univers코리안 스피드 바카라 ey of Vienna
Figure 1.In the ILIAMS setup, the initial beam of anions is cooled in a waveguide while being irradiated by a colinear laser beam of the appropriate wavelength to cause selective electron photodetach코리안 스피드 바카라 ent. Figure credit Martin Martschini.
