may be determined by the environment to be monitored. The use of several different materials allows an estimation of the energy/wavelength of the incident radiation. Filters are usually placed on both the back and front of the holder, to ensure operation regardless of orientation. Additionally, the filters need to be sufficiently large (typically 5 mm or more) to minimize the effect of radiation incident at oblique angles causing exposure of the film under an adjacent filter. Usage The badge is typically worn on the outside of clothing, around the chest or torso to represent dose to the "whole body". This location monitors exposure of most vital organs and represents the bulk of body mass. Additional dosimeters can be worn to assess dose to extremities or in radiation fields that vary considerably depending on orientation of the body to the source. The dose measurement quantity, personal dose equivalent Hp(d), is defined by the International Commission on Radiological Protection (ICRP) as the dose equivalent in soft tissue at an appropriate depth, d, below a specified point on the human body. The specified point is specific to the position where the individual’s dosimeter is worn. Tissue depth of interest include the tissue depth of the live layer of skin (0.07 mm), lens of the eye, (0.30 cm), and "deep" dose, or dose to the whole body (1.0 cm). The film badge is still widely used, but is being replaced by thermoluminescent dosimeters (TLDs), aluminium oxide based dosimeters, and the electronic personal dosimeter (EPD). See also Ionization chamber Proportional counter Geiger counter Sievert Semiconductor detector Thermoluminescent dosimeter References Further reading Film Badge Dosimetry in Atmospheric Nuclear Tests (1989) at the National Academies Press Dosimeters Ionising radiation detectors