R. Collé

Measurement of radon and xenon binding to a cryptophane molecular host

Xenon and radon have many similar properties, a difference being that all 35 isotopes of radon (195Rn–229Rn) are radioactive. Radon is a pervasive indoor air pollutant believed to cause significant incidence of lung cancer in many geographic regions, yet radon affinity for a discrete molecular species has never been determined. By comparison, the chemistry of xenon has been widely studied and applied in science and technology. Here, both noble gases were found to bind with exceptional affinity to tris-(triazole ethylamine) cryptophane, a previously unsynthesized water-soluble organic host molecule. The cryptophane–xenon association constant, Ka = 42,000 ± 2,000 M-1 at 293 K, was determined by isothermal titration calorimetry. This value represents the highest measured xenon affinity for a host molecule. The partitioning of radon between air and aqueous cryptophane solutions of varying concentration was determined radiometrically to give the cryptophane–radon association constant Ka = 49,000 ± 12,000 M-1 at 293 K.

Comparison of activity concentration measurement of 63Ni and 55Fe in the framework of the EUROMET 297 project

Abstract Eleven laboratories participated in an intercomparison of activity concentration measurements using liquid scintillation counting (LSC) for the standardization of 63Ni and 55Fe in the frame of the EUROMET project No. 297 and under the co-ordination of LPRI. The purpose of this action was to compare the main LSC activity concentration measurement methods currently used in radioactive metrology, and to exchange models and ideas on LSC. This paper presents a summary of the results reported by the participant laboratories and an overview of the measurement methods used.

Cocktail volume effects in 4πβ Liquid scintillation spectrometry with 3H-standard efficiency tracing for low-energy β-emitting radionuclides

Abstract The effect of total liquid scintillation (LS) cocktail volume (or mass) in the 4πβ LS spectrometry of β-emitting radionuclides has been investigated. The magnitude of such possible volume effects on the apparent activity of low-energy β-emitting radionuclides, as determined by the CIEMAT/NIST 3H-standard efficiency tracing method, as well as any systematic trends in the relative detection efficiencies of low-ebergy β-emitters were studied. The radionuclides chosen for the study, 63Ni and 36Cl, were traced against 3H. Detection efficiency losses, as a function of total LS cocktail volume, were found to be energy-dependent. Because of the low Eβmax for the decay of 3H and 63Ni, systematic losses in efficiency with increasing cocktail mass, as well as at extremely low (

63NI HALF-LIFE : A NEW EXPERIMENTAL DETERMINATION AND CRITICAL REVIEW

Abstract The 63Ni half-life has been determined to be 101.06 ± 1.97 a based on three independent measurements, conducted over the past 27 years, of the massic activity of gravimetrically-related 63Ni sources. The 63Ni assays were performed initially (in 1968) by microcalorimetry using an assumed mean β− energy per decay, and subsequently (in 1984 and 1995) by 4πβ liquid scintillation spectrometry with 3H-standard efficiency tracing. The present result is the first and only determination of the 63Ni half-life which is based on actually following the radioactive decay of 63Ni. All previously reported determinations were derived from specific activity evaluations. These earlier determinations have been scutinizingly reviewed as part of this work. Some of these previous values can be revised in lieu of more recent nuclear data and on consideration of the experimental details. Based on a critical evaluation of the extant data set, a 63Ni half-life value of T=101.1 ± 1.4 a is recommended.

Systematic effects of total cocktail mass (volume) and H2O fraction on 4πβ liquid scintillation spectrometry of 3H

Abstract Detection efficiencies ϵ of 3 H by 4πβ liquid scintillation (LS) spectrometry systematically vary as a function of both total cocktail mass m and cocktail composition (such as the H 2 O mass fraction f ). Quench indicating parameter (QIP) determinations, such as for the Horrocks number H , are also dependent on m and f . These systematic effects were investigated with a matrix of 33 LS cocktails covering a broad array of m and f values: 3.0 g ⪯ m ⪯ 21.4 g and 0.002 ⪯ f ≤ 0.52. The effects of m and f on the LS background counting rates of matched blanks are also treated in detail. The uncertainties associated with these m - and f -dependent effects on ϵ and on H are particularly given close scrutiny. The systematics clearly demonstrate that efficiency changes cannot be adequately monitored by quench indicating parameters when the quench changes are induced by multiple causal factors (e.g. simultaneously varying cocktail sizes and compositions). The experimental results presented here have significant implications on the critical importance of understanding the systematics of these variable effects for a given LS system (combination of cocktails and spectrometer), and of very closely matching LS cocktail volumes and compositions in order to achieve reproducible and accurate LS counting results.

Cocktail mismatch effects in 4πβ liquid scintillation spectrometry: Implications based on the systematics of 3H detection efficiency and quench indicating parameter variations with total cocktail mass (volume) and H2O fraction

Abstract Detection efficiency changes for 3 H by 4πβ liquid scintillation (LS) spectrometry cannot be adequately monitored by quench indicating parameters when the quench changes are the result of multiple causal factors (e.g. simultaneously varying cocktail sizes and composition). In consequence, some kinds of cocktail mismatches (between LS counting sources) introduce errors that result from efficiency changes that cannot be fully accounted for by quench monitoring compensations. These cocktail mismatch effects are examined for comparative 3 H measurements and for 3 H-standard efficiency tracing methods for the assay of other β-emitting radionuclides. Inherent errors can occur in both types of radionuclidic assays, as demonstrated with realistic case examples, unless cocktails are very closely matched. The magnitude of the cocktail mismatch effect (and attendant errors) can range from being virtually negligible (particularly for high-energy β-emitting nuclides and for slight single-variable cocktail composition mismatches) to be being very significant for high-precision metrology and standardizations (particularly with easily quenched, low-energy β emitters and for mismatches due to both varying cocktail constituents and concentrations). The findins presented here support the need to understand fully the quenching systematics of a given LS system (combination of cocktails and spectrometer) and the need for very careful control of cocktail preparations.

A dual-compensated cryogenic microcalorimeter for radioactivity standardizations

Efforts are underway by our laboratory to develop a microcalorimeter that can be routinely used for radioactivity standardizations of nuclides that decay by pure beta-emission or by low-Z electron capture. The prototype calorimeter consists of a cryostat with two temperature-controlled stages and a base stage that are operated at nominal temperatures of 8 K. A unique aspect of the calorimeters design is the ability to repeatedly engage and disengage the radioactive source from the second stage heat path using a magnetically activated elevator. The measurement of the total power from a radioactive sample is obtained from the difference in the second stage power with and without the source in place. As a result of extensive performance evaluations using 90Sr-90Y and 32P brachytherapy seeds as well as with an internal calibration heater, many initial design flaws have been identified and are being addressed.

Investigation into the standardization of 99Tc.

The standardization of (99)Tc by several primary methods was investigated. This was performed to support a new (99)Tc transfer standard that has been developed and will be disseminated by the National Institute of Standards and Technology (NIST) as Standard Reference Material SRM 4288B. The standardization for the (99)Tc content of the solution was based on 4pibeta liquid scintillation (LS) measurements with (3)H-standard efficiency tracing (CIEMAT/NIST method). Confirmatory determinations were performed by 4pibeta(LS)-gamma(NaI) live-timed anti-coincidence (LTAC) counting and an LS-based 4pibeta triple-to-double coincidence ratio (TDCR) method.

A new primary standardization of 229Th.

The National Institute of Standards and Technology (NIST) has certified a high-purity (229)Th Standard Reference Material as SRM 4328C, based on live-timed 4pialphabeta-gamma anticoincidence counting (LTAC) of the equilibrium solution. The LTAC system was optimized to minimize the uncertainty in the result due to the two short-lived ground-states present in the decay chain. Confirmatory measurements were carried out by four other methods. Furthermore, the present absolute activity and measured gamma-ray emission rates were combined to obtain gamma-ray emission probabilities.

Standards of radium-226: from Marie Curie to the International Committee for Radionuclide Metrology.

In the early part of the 20th century, the pioneers of radioactivity research, led by Marie Curie, Ernest Rutherford and Stefan Meyer, formed a Commission internationale des étalons de radium. The Commission made arrangements for the preparation and intercomparisons of the international standards of radium, which were identified as the Paris standard and the Vienna standard. Otto Hönigschmid from Vienna prepared a first set of international secondary standards in 1912 and a second set in 1934. In both instances, these secondary standards were compared by gamma-ray measurements with the Paris and Vienna standards. The usage of these international standards of radium in the 20th century is described.