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Description
Lithium fluoride (LiF) thermoluminescent dosemeters (TLD) are commonly used for personnel monitoring. When the TL material is enriched in $^6$Li they are sensitive to neutrons via the $^6$Li(n,$\alpha$)$^3$H reaction which has a strong energy dependence. These dosemeters are referred to as albedo dosemeters since they rely on neutrons that are backscattered from the body (or phantom) and these albedo neutrons have a lower average energy than those incident on the body. During calibration, the TLDs are mounted directly on a phantom. The dosemeters should be worn in a similar configuration, but in operational settings, the TLDs may have a small gap between the dosemeter and the body. Thus, the albedo effect may change resulting in different overall response to a neutron field. In this work, the effects of varying gaps between the TLD and phantom were investigated. The MCNP6 radiation transport code was used to tally the number of (n,$\alpha$) reactions within TLD elements of the Harshaw 8806 dosemeter for several configurations. This TLD consists of two $^6$LiF and two $^7$LiF elements, with one pair of $^6$LiF and $^7$LiF elements positioned behind a cadmium shield. These included the TLD mounted directly on the phantom and with air gaps between the dosemeter and phantom ranging from 1 cm to 10 cm. The total response to common neutron calibration spectra (unmoderated $^{252}$Cf, D$_2$O-moderated $^{252}$Cf, AmBe, AmB, and PuBe) was determined by folding these spectra with the energy-dependent responses for each air gap. Results indicated that a 1 cm gap reduced the average response by 20 % while a 10 cm gap lowered the total response by about 50 % for most spectra. Radiation protection programs should ensure that albedo dosimeters are securely positioned against the body when personnel are monitored for neutron radiation.