Translartion. Region: Russians Fedetion –
Source: Novosibirsk State University – Novosibirsk State University –
Researchers of the Center for Collective Use “Accelerator Mass Spectrometry of NSU-NNC” have tested for the first time an ion detector based on a low-pressure VPK on the MICADAS accelerator spectrometer and obtained the first results. This device was installed instead of the native MICADAS detector (ionization chamber), in which the ions of the C14 isotope are counted, based on the results of which the dating of the studied sample is performed.
In 2023, this time-projection chamber was installed for the first time on a domestic accelerator mass spectrometer, which is made and maintained by the G.I. Budker Institute of Nuclear Physics SB RAS and is located in the Cenozoic Geochronology Shared Utility Center of the Institute of Archeology and Ethnography SB RAS. It was successfully tested on a beam of 14C ions with an energy of 4 MeV and proved to be operational. Later, this chamber was tested on a beam of 14C ions with an energy of 0.4 MeV at the MIKADAS UMS. If the experiments are successful, a smaller VPK will be created in the future for installation on the prototype of the first domestic low-voltage universal accelerator mass spectrometer, which is being created by NSU scientists within the framework of the Priority-2030 program.
Time-projection chamber (TPC) — in application to accelerator mass spectrometry, this is a method of identifying low-energy heavy ions based on measuring their path lengths in gas. The principle of operation is as follows: ions fly into the chamber through a thin entrance window. Then they lose energy due to ionization losses. As a result, a trail of gas ions and electrons is formed along the track. These electrons, under the influence of an external electric field, drift in the gas at a constant speed in the direction of the GEM, where they are amplified. At the end, the amplified electrons are collected on a collector and digitized by the data acquisition system. Thus, the electron collection time corresponds to the ion path length.
— Previously, the time-projection chamber was developed for the INP UMS to separate ions with the same atomic masses and different nuclear charges. This gas detector will separate Be10 (beryllium) ions from B10 (boron). Since the nuclei of boron and beryllium have different charges, with equal initial energies, their path lengths in a gas environment are different and the VPK will separate them. Be10 has a longer half-life (1.39 million years) compared to 14C (5730 years), so measuring the 10Be content will allow scientists to date geological samples, — explained Ekaterina Parkhomchuk, Director of the UMS NSU-NNC Collective Use Center.
The MICADAS accelerator mass spectrometer, unlike the domestic multiisotope, is aimed only at detecting and determining the amount of the rare isotope C14 in the samples being studied. C14 ions pass through the entire accelerator mass spectrometer and then enter the gas detector, where they are identified and counted.
— Accelerator mass spectrometers are equipped with various types of detectors. For example, the MICADAS UMS has an ionization chamber. We replaced it with a time-projection chamber. One of the important parts of the MICADAS ionization chamber is the preamplifier. If it fails, MICADAS will stop, and we will have to either buy a new preamplifier, which is very difficult in the current circumstances, — said Alexey Petrozhitsky, engineer at the Center for Collective Use “Accelerator Mass Spectrometry NSU-NNC”.
It is important that ionization chambers have one significant drawback – they operate in a mode where the signal-to-noise ratio is far from optimal. In addition, the preamplifier is very demanding of electronics, unlike the gas analyzer, which is equipped with a time-projection chamber.
— In our detector, we amplify the signal using a gas electron multiplier, which significantly reduces the requirements for the electronics of the data acquisition system. In addition, our VPK produces a much better signal-to-noise ratio, is easy to manufacture, operate and repair. We needed to find an answer to the question: is it possible to use the VPK as a detector of 14C ions with an energy of 0.4 MeV? And in the course of our work, we came to a positive answer. We are confident that the time-projection chamber we have developed can be used as the final detector in the first domestic universal low-voltage accelerator mass spectrometer, which we are currently working on. The experiments we are currently conducting are aimed precisely at testing the detector for the first domestic UMS, and the MICADAS setup acts as an ion beam source available to us. This can be called the first brick for building our own setup. When a project already has a detector that registers particles, it means that a significant area of problems has already been covered and other specialists can join in the creation of a new UMS, ensuring the execution of work at the next stage, commented Tamara Shakirova, a junior researcher at the Institute of Nuclear Physics SB RAS, the Center for Collective Use “Accelerator Mass Spectrometry NSU-NNC”.
Currently, tests of the time-projection chamber at MICADAS are carried out on two types of samples: the ANU standard sample (IAEA-C6, sugar) with a 14C content close to the modern level and a “blank” (polyethylene CH – Elemental Microanalysis B2024 standard) with a 14C content of 0.002 of the modern level. The purpose of the tests is to optimize the operating parameters: working gas pressure, gain, electron drift velocity.
— We have collected a sufficient amount of data, and are currently processing and analyzing it. The main thing is that we have made sure that the time-projection chamber works in the mode we expect and produces clearly readable signals above background values. We can certainly say that we can read C14 from them, which is quite suitable for conducting radiocarbon analysis of samples, — said Alexey Petrozhitsky.
Reference:
Accelerator mass spectrometry is a method for measuring the concentration of rare long-lived cosmogenic isotopes in a sample: 10Be, 14C, 26Al, 36Cl, 41Ca, 129I. It is based on the extraction of atoms from the sample with subsequent “piece by piece” counting of the isotopes of interest. The high accuracy of AMS analysis allows measuring the concentration of a rare isotope. This method is used in many sciences, for example, in archeology, geology, biomedicine, ecology, astrophysics. It is most widely used in radiocarbon dating of archaeological objects, that is, recording the concentration of the carbon-14 isotope. The time interval of dating for 14C goes back as far as 50 thousand years. Determining the concentration of another cosmogenic nuclide 10Be is also of interest, since the time interval of dating is much wider – up to 10 million years.
Currently, the NSU-NSC Accelerator Mass Spectrometry Shared Utility Center has two UMS installations. The first was created by scientists from the Budker Institute of Nuclear Physics SB RAS more than 10 years ago. The second Swiss-made MICADAS accelerator mass spectrometer was purchased in 2019. Scientists from Novosibirsk State University, the Budker Institute of Nuclear Physics SB RAS, the Institute of Archeology and Ethnography SB RAS, and the Boreskov Institute of Catalysis as part of the Center’s research group are working on creating a domestic low-voltage universal accelerator mass spectrometer that will combine the advantages of the first two installations. The project is designed for five years and is being implemented with the support of the Priority-2030 program.
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