Hur snabbt påverkas och nollställs luminiscenssignaler under naturliga ljusförhållanden?
Author
Summary, in English
Optically stimulated luminescence, OSL, is a dating method applicable to geological material with an
age of ca. 1 year-200 000 years. The dating method is based on the mineral grains reaction to natural, radioactive
background radiation, and their ability to accumulate energy within themselves, a process that takes place continuously
during dark/cool conditions. This energy may be released by subjecting the mineral grain to light, either in
nature or under controlled forms, in laboratories. When the energy is released, it is converted into photons, luminescence.
Since the accumulation is only taking place during dark/cool conditions and the amount of accumulated
energy increases over time, it is possible to measure the amount of emitted luminescence and thus determine how
long the sample has been buried. Through measurements and calculations of the luminescence, the age of the sample
is determined. If the mineral grains are exposed to sufficient energy, all accumulated radiation is released and
the grain gets bleached. The grain may also become incompletely bleached, which means that only a part of the
accumulated energy has been released.
By exposing sand samples of various origin to three different types of light conditions during different exposure
times, it was possible to examine how long it takes before the luminescence signal is affected, thus before the samples
start to emit light, and if, or after how long, they get fully bleached. The purpose of this study was to provide
information and thus also provide a better understanding of how quickly luminescence signals are affected and
bleached. The experiments were performed by attaching the samples in the bottom of opaque metal cans. The covers
of the cans was then removed for a fixed amount of time, from five seconds to three hours, and therefore the
samples were exposed to light during three types of light conditions: a sunny day, a cloudy day and twilight/
nightlight.
The results show that the samples, regardless of origin, are affected already after a short amount of time in exposure
to light during sunny and cloudy conditions. The result of the experiment that was made during twilight/
nightlight did not show the same kind of downward trend as the others samples, thus that the remaining luminescence
signal in the material decreased gradually as the time of exposure increased. This means that sediments transported
and buried at night do not bleach. It is important to take into account that these experiments was of fundamental
character whilst the natural processes are more complex and therefore the results should be used as a guidance.
It can be noted that continued caution when sampling is required since exposure to sunlight can result in inaccurate
results when dating of material is applied. Nevertheless, rapid impact and bleaching of luminescence signals
is desirable to avoid incorrect dating of sediments.
age of ca. 1 year-200 000 years. The dating method is based on the mineral grains reaction to natural, radioactive
background radiation, and their ability to accumulate energy within themselves, a process that takes place continuously
during dark/cool conditions. This energy may be released by subjecting the mineral grain to light, either in
nature or under controlled forms, in laboratories. When the energy is released, it is converted into photons, luminescence.
Since the accumulation is only taking place during dark/cool conditions and the amount of accumulated
energy increases over time, it is possible to measure the amount of emitted luminescence and thus determine how
long the sample has been buried. Through measurements and calculations of the luminescence, the age of the sample
is determined. If the mineral grains are exposed to sufficient energy, all accumulated radiation is released and
the grain gets bleached. The grain may also become incompletely bleached, which means that only a part of the
accumulated energy has been released.
By exposing sand samples of various origin to three different types of light conditions during different exposure
times, it was possible to examine how long it takes before the luminescence signal is affected, thus before the samples
start to emit light, and if, or after how long, they get fully bleached. The purpose of this study was to provide
information and thus also provide a better understanding of how quickly luminescence signals are affected and
bleached. The experiments were performed by attaching the samples in the bottom of opaque metal cans. The covers
of the cans was then removed for a fixed amount of time, from five seconds to three hours, and therefore the
samples were exposed to light during three types of light conditions: a sunny day, a cloudy day and twilight/
nightlight.
The results show that the samples, regardless of origin, are affected already after a short amount of time in exposure
to light during sunny and cloudy conditions. The result of the experiment that was made during twilight/
nightlight did not show the same kind of downward trend as the others samples, thus that the remaining luminescence
signal in the material decreased gradually as the time of exposure increased. This means that sediments transported
and buried at night do not bleach. It is important to take into account that these experiments was of fundamental
character whilst the natural processes are more complex and therefore the results should be used as a guidance.
It can be noted that continued caution when sampling is required since exposure to sunlight can result in inaccurate
results when dating of material is applied. Nevertheless, rapid impact and bleaching of luminescence signals
is desirable to avoid incorrect dating of sediments.
Department/s
Publishing year
2017
Language
Swedish
Publication/Series
Examensarbeten i geologi vid Lunds universitet
Full text
Document type
Student publication for Bachelor's degree
Topic
- Earth and Environmental Sciences
Keywords
- optiskt stimulerad luminiscens
- OSL
- datering
- luminiscens
- nollställning
Report number
501
Supervisor
- Helena Alexanderson (professor)
Scientific presentation