Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2020 Sep:163:109216.
doi: 10.1016/j.apradiso.2020.109216. Epub 2020 May 13.

The next generation of current measurement for ionization chambers

R Fitzgerald  1 , D E Bergeron  2 , S P Giblin  3 , D G Jarrett  2 , S M Judge  4 , C Michotte  4 , H Scherer  5 , N M Zimmerman  2
Affiliations

The next generation of current measurement for ionization chambers

R Fitzgerald et al. Appl Radiat Isot. 2020 Sep.

Abstract

Re-entrant ionization chambers (ICs) are essential to radionuclide metrology and nuclear medicine for maintaining standards and measuring half-lives. The requirements of top-level metrology demand that systems must be precise and stable to 0.1 % over many years, and linear from 10-14 A to 10-8 A. Thus, laboratories depend on bespoke current measurement systems and often rely on sealed sources to generate reference currents. To maintain and improve present capabilities, metrologists need to overcome two looming challenges: ageing electronics and decreasing availability of sealed sources. Possible solutions using Ultrastable Low-Noise Current Amplifiers (ULCAs), resistive-feedback electrometers, and (quantum) single-electron pumps are reviewed. Broader discussions of IC design and methodology are discussed. ULCAs show promise and resistive-feedback systems which take advantage of standard resistor calibrations offer an alternative.

Keywords: Current measurement; Gamma-ray; Ionization chambers; Small currents.

PubMed Disclaimer

Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
Schematic diagram of an ionization chamber, showing a radioactive solution (yellow shaded), which emits a γ-ray (orange arrow) that is absorbed in the pressurized gas region. The resulting current is measured with the ammeter.
Figure 2
Figure 2
Ratio of the current produced by two 226Ra sources as a function of time since 1976 at the BIPM, showing that a reproducibility of the order of 0.1 % can be achieved. However, a long-term trend in the ratio can be observed- the origin of this effect is unknown.
Figure 3
Figure 3
Schematic circuit diagrams of (a) an integrating electrometer, and (b) a feedback ammeter.
Figure 4
Figure 4
Example operation of a ULCA in an electrometer mode for current measurements on an IC (left), with ATR = 1 GΩ (using the internal 1 MΩ resistor for current-voltage conversion) and for currents up to ± 5 nA. Note, the IC shown uses an external source, but the principle is the same for re-entrant ICs.
Figure 5
Figure 5
Circuit diagram for calibration of an electrometer used with an ionization chamber. Switch S1 connects the electrometer to the ionization chamber or the voltage source, DVM, and standard resistor. See text for definition of other symbols. A calibrate, measure, calibrate sequence is used to bracket ion chamber measurements with before and after calibrations of the electrometer.
See this image and copyright information in PMC

References

    1. Amiot MN, Chisté V, Fitzgerald R, Juget F, Michotte C, Pearce A, Ratel G, Zimmerman BE, 2015. Uncertainty evaluation in activity measurements using ionization chambers. Metrologia 52, S108–S122.
    1. Callegaro L, Capra PP, D’Elia V, Galliana F, 2014. Generation of reference DC currents at 1 nA level with the capacitance-charging method, IEEE IM Trans 63, 1779–1782.
    1. Bergeron DE, Cessna JT, Coursey BM, Fitzgerald R, Zimmerman BE, 2014. A review of NIST primary activity standards for 18F: 1982 to 2013. J. Res. NIST 119, 371–396. - PMC - PubMed
    1. Bergeron DE, Cessna JT, 2018. An update on ‘dose calibrator’ settings for nuclides used in nuclear medicine. Nucl. Med. Comm 39, 500–504. - PMC - PubMed
    1. CCRI-CCEM, 2020, CCRI-CCEM Task Group on Low Current Measurement, bipm.org/en/communities/cc/wg/ccem-ccri-tg-lcm.html, accessed March 2020.

LinkOut - more resources