Biomedical subjects

A K Pearce

Publications and source records attributed to A K Pearce.

5 recordsLinked to original sources

PubMed2006

An approach based on the SIR measurement model for determining the ionization chamber efficiency curves, and a study of 65Zn and 201Tl photon emission intensities.

The measurement model used to determine ionization chamber efficiency curves accounts from the outset for impurity corrections and beta spectrum shapes. The curves are represented by exponentials of polynomials whose coefficients are adjusted using non-linear least-squares minimization. The curves are validated by comparing with SIR key comparison reference values (KCRVs) and other published curves. The associated covariance matrix is also evaluated. Deviations from model predictions for 65Zn and 201Tl using recommended nuclear data are studied.

Algorithms↗

PubMed2001

Integrating stress-response and cell-cycle checkpoint pathways.

The DNA integrity checkpoint and stress kinase (SAPK/JNK and p38) pathways function to modulate cell-cycle, apoptotic and transcriptional responses to stress. Although initially considered to function independently, recent advances indicate a number of links between the stress-response and checkpoint pathways. Here, we consider the relationship between the stress-response and checkpoint pathways and how they interact to modulate cell-cycle control.

Animals↗

PubMedDate not supplied

Primary standardisation of 204Tl using the efficiency tracing method.

The electron-capture and beta(-) -emitting radionuclide 204Tl has been known from previous experience to show discrepancies between different methods of standardisation. Source preparation is also difficult due to the complex chemistry of thallium. The Bureau International des Poids et Mesures (BIPM) intercomparison held in 1997, showed discrepancies of up to 10% between measurements of solid sources and liquid scintillation methods. These problems have been the subject of a BIPM CCRI(II) working group since 1999. This paper presents the results from a primary standardisation of a 204Tl solution using 4pibeta-gamma coincidence counting and liquid scintillation counting. The tracer technique was used for the 4pibeta-gamma coincidence counting, where 204Tl was traced with 134Cs and 60Co. The extrapolation to 100% beta-efficiency was performed by three different approaches: foiling, adding carrier and measuring sources of different initial masses. The results showed that tracing with 60Co and using external foiling gave the same result as obtained by liquid scintillation counting. A comparison of the results achieved by the different methods of measurement, tracers and methods for extrapolation is presented and discussed in this paper.

Algorithms↗

PubMedDate not supplied

Secondary standardisation of 95mTc.

The radionuclide 95mTc, which has a half-life of 61(2)days and emits a number of gamma-rays, may be used in radiochemical analysis as a yield tracer for the long-lived fission product 99Tc. In this work, we present (i) the production of 95mTc via an (alpha, 2n) reaction with stable 93Nb (a method which does not result in the production of any 97mTc, 98Tc or 99Tc), (ii) the chemical separation of 95mTc from niobium via coprecipitation, liquid-liquid extraction and liquid chromatography, and (iii) the secondary standardisation of 95mTc with high-resolution gamma-ray spectrometry and an ionisation chamber system.

Isotope Labeling↗

PubMedDate not supplied

Standardisation of 11C.

The increasing use of positron emission tomography for medical imaging and the availability of short-lived positron emitters has raised concerns about the accuracy of calibration of secondary standard measurement systems and the viability of using a single long-lived positron emitter as a reference calibration source for all positron emitters. Potential problems arise because the 511 keV quanta arising from positron annihilation are not generally produced at the same point as the original disintegration. In addition, the secondary standard may also be responsive to the associated bremsstrahlung radiation. The magnitude of both effects depends on the positron end-point energy. In order to resolve these problems, it is necessary to produce absolute standards of these positron-emitting radionuclides and the work presented here details the results of such work with 11C.

Journal Article↗