@misc{9248581,
  abstract     = {{In the event of a radiological or nuclear (R/N) emergency, individuals and/or population groups
may be exposed to radiation. For the average civilian, a potential but not confirmed exposure causes
anxiety, even though it is unlikely that anyone except first responders or those close to the emergency
site receives doses above negligible levels. Thus, there needs to be a way to separate the unexposed
but worried masses from those in need of immediate care, as well as means to conduct long-term
population monitoring for epidemiological purposes. Preferably, such a method should be rapidly
deployable.

A possible way to survey the population would be to distribute NaCl samples, which are easily
mass-produced, and to set up a network of relatively inexpensive, portable optically stimulated
luminescence (OSL) readers. The feasibility of this approach requires readers to be benchmarked
for this purpose beforehand. This work investigates the portable reader Helios, which features two
reader holders (flat and conical) and three LED options for the continuous-wave mode (blue light, IR
light, and a combination of the two), in order to ascertain suitable readout protocols and characterise
luminescent properties. Readout parameters for the Helios reader were determined for salt pellets
and salt grains, based on their OSL/IRSL dosimetric properties. The potential effect of various
laboratory conditions was also studied, including the standard procedure to expose samples to red
light and emulating mishaps by exposing them to other light sources. During irradiation, only one
side of a pellet will be facing the radiation source. This side of the pellet is not necessarily the side
later facing the photomultiplier tube (PMT) and LEDs during readout. Whether or not the side of
the pellet being read out coincided with the side of the pellet facing the source during irradiation
had a significant impact on the intensity of the luminescence signal, according to a Mann-Whitney
U-test. The difference in luminescence signal intensity was not considered large enough to affect
triage during R/N emergencies. However, for research requiring more precise dose estimation, the
dependence on irradiation geometry and readout orientation may have a greater impact.

For pellets, the reader showed a linear response over the dose interval 10 mGy-15 Gy for IRSL, while
for blue light (OSL) and the combination of IR and blue, linearity was observed up to 7 Gy, after
which the PMT was saturated. An overresponse at high doses was found for all readout geometries
except OSL with pellets. When reconstructing doses using the sensitivity from the dose response
curves, pellets read out for OSL yielded the most consistent results, with values never more than 10 %
away from the theoretical dose. Minimum measurable dose (MMD) was 1.5 mGy for IR, 210 µGy for
blue light, and 190 µGy for the combination. After irradiation, the signal stabilised within a matter of
days for IR, indicating that correction for fading may not be necessary for readouts conducted more
than 1 day after irradiation. Readout using OSL showed an inverse fading effect for at least 50 days
after irradiation, suggesting that fading correction is necessary when the time between irradiation
and readout is prolonged. A relatively linear dose response was observed for grains over the dose
interval 50 mGy-5 Gy for both IRSL and OSL, but overresponse at high doses was present. For grains,
dose reconstruction from IRSL measurements was superior, although the MMD was relatively high,
20 mGy. The MMD for OSL was 0.5 mGy. Inverse fading was observed, continuing for the first week
after irradiation, after which the signal stabilised for IRSL but continued to increase for at least 15
days for OSL.

Based on these results, the use of the portable reader Helios, combined with NaCl samples, for dose
monitoring during emergencies seems promising. Salt in pellet form greatly simplified the workflow
compared with grains, but both are feasible options for monitoring due to their easy availability
and favourable luminescent properties. OSL was superior for dose reconstruction with pellets and
measurements of low doses. Its main disadvantage was persistent inverse fading, which could make the
readout of samples stored for a long time more difficult. For grains, IRSL readout was preferable to
OSL for dose reconstruction, but not at low doses. Still, more research is needed before a universal
readout protocol can be devised, especially regarding the impact of environmental factors on the
samples.}},
  author       = {{Borg Djurberg, Tuva}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Investigation of a portable OSL reader for dosimetry applications during radiological or nuclear emergencies using ordinary salt (NaCl)}},
  year         = {{2026}},
}