Zenon Palacz
What are the parameters required for high precision measurements of small samples? (on Faraday collectors)
- High Sensitivity
- Instrument sensitivity
- Use of activators
- Low noise
- Close to theoretical Johnson noise
- Baseline stability
- Gain stability between detectors
- Required for static analyses
- Multidynamic measurements:
- Eliminates gain and efficiencies
- But can it be used on small samples?
How quiet are Xact amplifier/resistor boards?
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_2-1024x510.png)
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_3-1024x499.png)
Noise comparison between 1e11 and 1T resistors
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_4.png)
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-table_1.png)
How fast are Xact resistors (1e11 ohm)?
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_5.png)
1T baseline in 4 seconds
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_6.png)
Gain stability 5ppm over 1 month no drift
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_7.png)
Day averages
Reduced scatter shows subtle coherent trends. Measured on factory floor with no environmental temperature control.
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_8.png)
Sr dynamic precision 3ppm reproducibility (5volt ion beam)
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_9.png)
Static precision 5ppm no gain corrections between analyses (5 volt ion beam)
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_10.png)
How small a sample of Nd can be measured on Faradays
- Nd+ ion atom efficiency is about 2.5% (triple filament)
- NdO+ is higher than this.
How small an ion beam can we measure with good precision and accuracy?
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_11-1024x615.png)
Errors expand below 1e-13A
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_12-1024x403.png)
10.5% ion/atom efficiency
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_13-1024x595.png)
2ng Nd measured as oxide at 300mv 142Nd16O
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_14.png)
Total evaporation measurements
- Widely used in nuclear applications to overcome mass fractionation by taking the average isotopic composition of the whole evaporation process.
- Baselines , peak centring and focussing at the start of the measurement prior to filament current ramping
- All above must remain stable during the evaporation.
- Used for small Sr in this application
- Potential benefit for micro-drilled samples, ice cores?
Total evaporation (summed isotope ratios)
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_15.png)
Baselines must remain constant throughout analysis
50ng Sr ion beam profile 7v for nearly 2 hours Efficiency 3.5% (No focussing or peak centring)
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_16-1024x476.png)
86Sr/88Sr (summed) 50ng NBS 987
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_17-1024x459.png)
87Sr/86Sr (summed)
![](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_18-1024x460.png)
1ng Sr 3volts 88Sr for 150 minutes Efficiency= 13%
![High Precision Isotope Ratio](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_19-1024x451.png)
Total evaporation measurements of NBS 987 <1ng
![High Precision Isotope Ratio](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-table_2.png)
Ion/Atom detection efficiency for Sr with TaCl activator on rhenium filament
![High Precision Isotope Ratio](https://www.isotopx.com/wp-content/uploads/2022/02/precision-isotope-measurements-image_20-1024x478.png)
Conclusions
- Sub nanogram isotope ratio measurements of Sr can be easily made using total evaporation analyses.
- NdO measurements at the nanogram level produce 20ppm reproducible 143Nd/144Nd
- 1T resistors are 1.5 to 2 times less noisy than 1e11 depending on integration time.
- 1e11 ohm and 1T ohm resistors produce analytically similar data with ion beams >50mv.
- 1T resistors show analytical advantage below 10mv. No benefit to Sr and Nd, Probable benefit for small sample Os, Pb and U isotopes.
- Static Isotope ratio reproducibilities of 5ppm are now possible with new amplifier boards in a temperature controlled environment. (no need for dynamic amplifiers)
- Boards are upgradeable on Sector 54, IsoProbe-T and IsoProbe-P instruments
Download presentation
Download the complete Presentation: 34th IGC Presentation