[en] Recently, an international collaboration in securing and managing radioactive sources, particularly orphan sources, is established. For developing countries such as Indonesia which possesses relatively inadequate resources, an effective approach in dealing with the problem is crucial. In order to deal with this situation, an activity was performed including: 1) assessment of available technical means, 2) car-borne survey during the dry and rainy seasons to identify the impact of Rn daughter washout on the interpretation of search results, 3) search for anomalies in the radioactive exposure map of the Java island, and 4) investigation of anomalies found, using more sophisticated instrument, to detect and secure orphan and illicit radioactive sources. The performance of four selected instruments in a car-borne survey which covers a large area in western part of Java was evaluated. Data series of moving background were divided into two measurement groups; control group and test group. These data series were arranged in, order to determine the value of alarm level. For this purpose, statistic procedures relying on Mann-Whitney U test and a simple moving average test (Moving Background) were applied. Among the four selected survey meters, the most convenient detection system for implementing the activity is Exploranium GR-130. There was little concern on the effect of Rn-daughters washouts on the proposed methods, provided that the operator could recognise the transition period between the clear and rainy weather as it could give rise to false alarm. The Moving Background method was generally superior to Mann-Whitney U test for detecting anomalous radiation level. During the survey, an anomaly in steel industrial area was detected. Using portable gamma spectrometers, it was concluded that the anomaly was generated from naturally occurring radioactive materials (NORM). Analyses upon survey data in the big cities showed anomalies due to concrete structures, especially bridges (elevated high way) and tunnels. With the best approach and technical available means in Indonesia, a 7.4 GBq ¹³⁷Cs test source could be detected at a distance of about 145 m from the road. (author)