Isotoptech Zrt - ATOMKI: technical background
Low
background γ-detector
Vacuum systems, analytical balances, centrifuges, cryocool systems, hot
plates, magnetic stirrers, stereomicroscopes, temperature controllers,
electromantles, shakers, ultrasonic cleaners, filtration units, cutting
mill with particle separation unit.
1. Static vacuum noble gas mass spectrometer type VG-5400 with sample inlet line and gas cleanup system
The VG-5400 mass spectrometer is suitable for determination of isotope ratios of all noble gases. This is the first noble gas mass spectrometer in Hungary which has the sensitivity, accuracy and resolution required by various important fields of research, like environmental research, nuclear fission safety, waste disposal and geochronology.
The sample inlet line is equipped with pneumatically activated NUPRO valves SS‑4‑BK, controlled by a computer. The line is made of stainless steel with UHV connections (VCR) with copper or aluminium gaskets. Four samples can be analyzed in a row without any manual intervention. The line includes two vacuum units: one ion pump for the inlet section, one turbomolecular pump with its rotary pump for evacuating the purification section. This provides a high vacuum in the system (<10-8 torr). The pressure is controlled manually and via the computer at different stages in the system with Pirani and Penning gauges connected to the computer through an HP-IB interface.
The purification section consists of an unfilled trap and a charcoal trap, placed in the same Dewar filled with liquid nitrogen, the level of which is regulated automatically by thermal sensors and an electrically activated valve connected to a liquid nitrogen tank. These two traps are followed by a SAES getter pump for removing the hydrogen.
The mass spectrometer has a magnet of 90o deflection and 27 cm deflection radius with an extended geometry. The sensitivity is 1x10-3 A/mbar for Ar and 2x10-4 A/mbar for He. The resolution is adjusted to 600 which is sufficient for the resolution of 3He+, H3+ and HD+ beams. The abundance sensitivity measured as contribution from mass 40 at mass 39 is less than 0.5 ppm at 10-7 torr. The static vacuum level in the 1.3 l volume deflection chamber is 1x10-12 cm3 STP/min at mass 40.
2. Stable isotope mass spectrometer
The stable isotope mass spectrometer specially designed for measurement of light environmental stable isotopes D, 13C, 15N, 18O, 34S is a sensitive and selective instrument with application in hydrology, geology, environmental protection, radwaste management. The high precision stable isotope ratio mass spectrometer is provided with two ion sources (H, CNOS sources) and ten separate Faraday cups. Its analyser of 3.7 cm (H) and 13.6-15.1 cm (CNOS) radii and 180o deflection angle provide first order focusing for ion beams diverging in the radial plane.
The sensitivity of the instrument for nitrogen is better than 4x10-4 A/mbar using the ion source adopted for higher masses with an exit slit of 0.2 mm and collector entry slit of 1 mm width. The collector slits are of 1 mm width for nitrogen, carbon, oxygen, sulphur and 2.5 mm for hydrogen, resulting a working resolution of M/DM = 120 (10 % valley) and M/DM = 8 for hydrogen. The slits are width enough to produce flat topped trapezoidal peaks with the shape of about 10-3 top flatness. The H3+contribution of the hydrogen source depends strongly on the operational pressure. It is in the region of 12 ppm (equivalent to 4% contribution to minor current at natural level) for the standard operating major current of 8x10-9 A H3+contribution is compensated by the software.
Trap regulation of a magnetically and electrostatically focused electron beam is used to achieve stable ion production in the ion sources. Ion currents are amplified with low bias-current solid state amplifiers and integrated with voltage to frequency converters and scalers. Mass setting is performed by varying the ion accelerating voltage.
A symmetrical dual viscous inlet system was constructed for measuring the sample and standard gases alternately. Pneumatically actuated bakeable gold sealed metal valves exclude cross mixing between sample and standard gases. The instrument, including the inlet system with variable reservoir volumes, is controlled by computer thus providing automatic and reproducible operation.
3.OmniStar quadrupole mass spectrometer (Balzers Instruments)
The quadrupole mass spectrometer equipped with a capillary inlet system is able to measure the main components of gas samples. Its range of analysis cover the interval from 1 amu to 200 amu. Weighting 45 kg it might be transported easily being applied on in situ measurements. The resolution of the instrument is between 50 and 100 at mass 40. The spectrometer can be supplied with a membrane inlet system, which makes it suitable to measure dissolved gas in liquids.
4. Elemental Analyser – Fisons type NA 1500 NCS
The
instrument is devoted to pre-treatment of samples for stable mass
spectrometry.
The analytical method is based on the complete and instantaneous oxidation of the sample by “flash combustion” which converts all organic and inorganic substances into combustion products. The resulting combustion gases pass through a reduction furnace and are swept into the chromatographic column by the carrier gas (helium). The gases are separated in the column and detected by the thermal conductivity detector (TCD) which gives and output signal proportional to the concentration of the individual components of the mixture.
5. Counter system for high-precision 14C dating + pre-treatment unit (conversion or acidic digestion of samples)
The gas proportional counting system was developed for high precision radiocarbon dating and consists of nine electrolytic copper proportional counters of identical diameters with sensitive volumes of 0.35-0.73 dm3 and filled with CO2 at 1115 mbar and 2 bar. The inner counters are surrounded by an anticoincidence shield consisting of five multiwire proportional flat counters filled with propane. The pulses of the detectors are handled by integrated amplifiers, discriminators and anticoincidence units interfaced to a microprocessor-controlled data evaluation unit. Software is written in BASIC using ASSEMBLER sub-routines. The overall precision of the system for modern carbon samples is better than 4 ‰ after a counting period of seven days.
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|
Counters |
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System parameters |
1 |
2 |
3 |
4 |
5 |
6 |
8 |
9 |
|
Total active volume (dm3) |
0.7 |
0.7 |
0.7 |
0.7 |
0.5 |
0.35 |
0.35 |
0.7 |
|
Standard counting rate (S) (cpm) |
4.9256 |
8.7715 |
4.8603 |
4.7992 |
6.5739 |
4.6498 |
4.7617 |
4.8602 |
|
Background (B) (cpm) |
0.4945 |
0.6074 |
0.5084 |
0.5373 |
0.5328 |
0.4498 |
0.4566 |
0.5828 |
|
Figure of merit (S/ÖB) |
7.00 |
11.25 |
6.82 |
6.55 |
9.00 |
6.93 |
7.05 |
6.34 |
|
Max. measurable age (2 days) (yr) |
33705 |
37516 |
33530 |
33171 |
35724 |
33624 |
33762 |
32909 |
6. LSC instrument (Tri-Carb 3170 TR/SL)
A completely computer controlled benchtop liquid scintillation analyzer, provided by Canberra-Packard Instruments, specially configured for extremely low level radioactivity analysis, featuring:
- The time-resolved liquid scintillation counting circuitry employs a multiparameter multichannel analyzer (effective resolution of 1/10 keV), and three-dimensional analysis of both the prompt and afterpulses to discriminate between true beta events and background pulses.
- The instrument employs a bismuth germanium oxide (BGO) detector guard to lower backgrounds for 3H to 1.0-0.75 CPM, and 14C backgrounds to below 0.3 CPM. High sensitivity is achieved using less cocktail (reducing waste) - the E2/B ratio is about 800 for 3H and 6000 for 14C; limits of detectability are greatly reduced (less than 1 Bq/l of tritium can be measured in water samples in 500 minutes without enrichment).
- The instrument includes a built-in computer, which controls all system functions including sample changer, CRT display and data output. Dynamic color quench correction automatically corrects results for the optical quenching effects of highly colored samples, while the luminescence detection and correction feature automatically detects, quantitates and corrects for unwanted or unexpected luminescence in liquid scintillation samples.
- The LSC analyzer is equipped with a cassette-loaded bidirectional sample conveyor with sample capacity for either 408 standard 20 ml vials or 720 small 4 or 7 ml vials with Varisette sample changer for intermixing large and small vial cassettes without requiring special adapters.
The HPGe γ-ray spectrometer (Canberra Model BE5030) situated in the underground low background laboratory of the Institute is equipped with a preamplifier (Canberra model 2002 CP) and an U-type cryostat. The detector has an active diameter of 80 mm and a carbon epoxy window with 0.5 mm thickness. The γ-ray spectral data are recorded by a multichannel analyzer (DSA-2000) processed by peak search and nuclide identification software (Genie 2000).
|
Energy |
5,9 keV |
59,5 keV |
122 keV |
1332,5 keV |
|
Resolution ev (FWHM) |
500 |
660 |
700 |
2150 |
|
Isotope |
241Am |
55Fe |
57Co |
60Co |
|
Energy (keV) |
59,5 |
5,9 |
122 |
1332,5 |
|
FWHM (eV) |
555 |
437 |
659 |
2025 |
|
FWTM (eV) |
1024 |
- |
1221 |
3799 |