Activity standards
PTB offers activity standards in the form of solutions and solid sources. For each activity standard, a calibration certificate is issued which states the specific activity (activity divided by mass of solution) and the solution mass or the activity and the assigned uncertainties valid at a defined reference time.
The activity standards are mainly used for the calibration of measuring devices or as reference standards in relative measurements. The user may also prepare on his own special sources (e.g. filter sources) of defined activity from a solution. This is advisable in particular when uniformity of the dimensions and self-absorption of activity standard and sample to be measured are important.
Raw solutions of particular radionuclides which are important for calibrations (e.g. Be-7, Sr-85, Y-88, Ce-139) are no longer, or only occasionally, offered by producers. The dates of delivery for activity standards of such radionuclides are, therefore, undefined. In the tables Activity standards in the form of solutions and Point sources these radionuclides have been specially identified in the column "Availability".
Activity standards of radionuclides which are not stated in the tables may also be obtainable, however at irregular intervals. Deliveries in past years covered, for example, activity standards of the nuclides P-32, Co-56, Co-58, Fe-59, Se-75, Ru-106, Ag-110m, Sb-124, Ce-141, Ta-182, Ir-192 and Hg-203.
Please inform us if you are at long terms interested in certain radionuclides which are not always available by sending us 
this form. For e-mail, telephone, fax, address, see section 
Order and contact above. As soon as activity standards of these nuclides are ready for delivery, you will be informed accordingly.
Calibrations and sources prepared to specification
In addition to delivering activity standards in the form of solutions and solid sources, PTB Working Group 6.11 also determines the activity of radioactive solutions and sources submitted by customers. Moreover, special activity standards may be prepared on request. The customer is, however, requested to inform the PTB by phone about the calibration problem before the order is placed.
It is also possible to obtain other kind of solutions and solid sources than those described here from calibration laboratories of the German Calibration Service (Deutsche Akkreditierungsstelle, DAkkS) or to have activity determinations carried out there. DAkkS calibration laboratories are accredited laboratories of industry and of other institutions, whose personnel and equipment are capable of carrying out measurements of the required accuracy and whose measurement standards are traceable to the national standards held at PTB. Accreditation is granted by PTB after the metrological competence of the laboratory in question has been assessed. The calibration centres carry out the desired calibrations and issue a calibration certificate for the results obtained.
Methods of measurement applied in activity determinations
The measured values stated in the calibration certificates are based on activity determinations carried out by absolute methods, in most cases by 4πβ-γ-coincidence methods and liquid scintillation methods (TDCR, CIEMAT/NIST). The state of the art reached in metrology on the international level is guaranteed by the PTB's participating in international comparison measurements organised by the Bureau International des Poids et Mesures (BIPM), Sèvres, France. Various relative measurement devices, such as 4π-ionization chambers, NaI and semiconductor spectrometers of high reproducibility and constancy with time are available, which have been calibrated against activity standards whose absolute values were measured. They allow the activity to be determined quickly at any time and without a considerable increase in measurement uncertainty.
Activity ranges
The activity ranges stated in the tables give a rough survey of the orders of magnitude of the activity values available. In the case of short-lived radionuclides, the reference time is the date at which the delivery begins. When activity standards of these radionuclides are ordered, the decrease in activity with time is to be taken into account. It is always recommended to indicate a desired range of activity upon placing of the order.
Uncertainties of measurement
The stated uncertainty of a standard covers the uncertainty components of the individual calibration caused by dilution, measuring technique, decay scheme, half-life and many other factors, and, in an appropriate way, the deviations found during international comparison measurements and internal calibrations carried out on different solutions and at different times.
The uncertainty stated in a calibration certificate is the expanded uncertainty of measurement obtained by multiplying the standard uncertainty by a coverage factor k = 2. Standard uncertainties are determined in accordance with the "Guide to the Expression of Uncertainty in Measurement" (ISO, 1995). Normally, the value of a measurand lies within the assigned range of values with a probability of 95 %.
Radionuclide data
The half-lives, energies and emission probabilities per decay stated on these pages have been taken from the following tables:
- Schötzig, U. and Schrader, H.:
Half-lives and photon emission probabilities of frequently used radionuclides.
Report PTB-Ra-16/5, Braunschweig 2000
- IAEA-TECDOC-619:
X-Ray and Gamma-Ray Standards for Detector Calibration
Vienna 1991