Wipe tests is a common method to measure surface contaminations with radioactive nuclides, if contamination monitors fail. This may happen, if external radiation levels would be too high, if surfaces would be inaccessible or if the radiation would not be detectable. In these cases activity on the surface is sampled on wipe test smears. They provide an efficient, convenient means of sampling contaminated areas with radioactivity on either wet or dry surfaces. Afterwards the activity on wipe test smears is measured in a counting instrument.

The sample's activity is measured in a counting instrument. In many cases alpha-beta counting is used. But there is also gamma counting. Alpha-Beta counting uses in many cases proportional counter tubes with alpha-beta discrimination, while gamma counting mainly uses scintillation counters, like for instance NaI. In many cases the required detection limits are low or even extremely low. This can be achieved by utilizing special techniques to reduce the internal background of the counting system. Berthold uses shieldings, special low activity material selection of detector materials and anticoincidence techniques to reduce the cosmic ray contribution. To obtain sufficient counting statistics with low activities, measuring periods should be long enough. If relative long measuring times are required, parallel processing of several samples is superior to sample changers with only one detector. This was the basic consideration for the concept of the famous 10-fold low level counter LB770 from Berthold. This instrument is widely used in many laboratories and in nuclear power plants to process large numbers of samples. Both it's low minimum detectable activity (MDA) and it's high throughput with 10 samples in parallel makes it a favourite

The calibration of surface contamination measurement is described in standard ISO 7503-1. The surface contamination is measured in Bq/cm² and it is proportional to the net counting rate and a calibration factor. The calibration factor is a function of the instrument's efficiency for the specified radionuclide, the area wiped, the source efficiency and the removal factor. Frequently the removal factor is unknown. A value of 10% is recommended.