Pilot experiments on retrospective thoron measurements by CDs/DVDs

► A new concept for retrospective measurements of thoron by CDs/DVDs is tested. ► The results of two pilot experiments are presented - with bare and packed disks. ► The sensitivity of bare disks is dependent on nearby objects close to their surface. ► The diffusion resistance of different kinds of jewel cases is different. ► Measuring thoron in houses can prevent false “high radon” alarms.