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Hur snabbt påverkas och nollställs luminiscenssignaler under naturliga ljusförhållanden?

Lindvall, Alma LU (2017) In Examensarbeten i geologi vid Lunds universitet GEOL01 20171
Department of Geology
Abstract (Swedish)
Optiskt stimulerad luminiscens, OSL, är en dateringsmetod som går att tillämpa på geologiska material med en ålder på ca 1 år-200 000 år. Dateringsmetoden grundar sig i att mineralkorn påverkas av naturlig, radioaktiv bakgrundsstrålning och därför ackumulerar energi inom sig, en process som endast sker under mörka/ svala förhållanden. Denna energi kan sedan frigöras genom att mineralkornet utsätts för ljus, antingen i naturen eller under kontrollerade former i laboratorier. När energin frigörs omvandlas den till fotoner, luminiscens. Eftersom ackumulationen endast pågår under mörka/svala förhållanden och mängden ansamlad energi ökar med tiden går det att mäta mängden luminiscens och således avgöra hur länge provet legat begravt, d.v.s.... (More)
Optiskt stimulerad luminiscens, OSL, är en dateringsmetod som går att tillämpa på geologiska material med en ålder på ca 1 år-200 000 år. Dateringsmetoden grundar sig i att mineralkorn påverkas av naturlig, radioaktiv bakgrundsstrålning och därför ackumulerar energi inom sig, en process som endast sker under mörka/ svala förhållanden. Denna energi kan sedan frigöras genom att mineralkornet utsätts för ljus, antingen i naturen eller under kontrollerade former i laboratorier. När energin frigörs omvandlas den till fotoner, luminiscens. Eftersom ackumulationen endast pågår under mörka/svala förhållanden och mängden ansamlad energi ökar med tiden går det att mäta mängden luminiscens och således avgöra hur länge provet legat begravt, d.v.s. provet kan dateras. Utsätts mineralkornet för tillräckligt mycket energi frigörs all ackumulerad strålning och kornet blir nollställt. Kornet kan också bli ofullständigt nollställt, vilket betyder att bara en del av den ackumulerade energin har frigjorts.

Genom att utsätta prover från tre olika lokaler, samtliga med olika genes, för tre olika typer av ljusförhållanden under olika exponeringstider undersöktes hur lång tid det tar innan luminiscenssignalen i proverna påverkas, d.v.s. innan de börjar sända ut luminiscens, och om de hinner nollställas helt. Syftet var att bidra med information och således också ge ökad förståelse för hur snabbt luminiscenssignaler påverkas och nollställs. Experimenten utfördes genom att proverna sattes fast i ljustäta burkar. Locken på burkarna togs sedan av under ett bestämt tidsintervall och proverna blev exponerade för ljus en solig dag, en molnig dag samt under skymnings-/nattljus, från fem sekunder till tre timmar.
Resultaten visar att proverna, oavsett ursprung, snabbt påverkas av ljusexponering i dagsljus.

Resultaten från försöken som utfördes i skymnings- och nattljus påvisade ingen tydligt nedåtgående trend, d.v.s. att luminiscenssignalen i materialet minskade efter hand exponeringstiden ökade. Detta betyder att sediment som transporteras och begravs nattetid inte nollställs. Experimenten var av grundläggande karaktär och det bör således tas i beaktning att de naturliga processerna kan vara betydligt mer komplexa varvid resultaten endast bör användas vägledande. Det kan dock konstateras att fortsatt försiktighet vid uttag av prover krävs, då exponering för solljus kan leda till missvisande resultat vid datering. Trots detta är snabb nollställning av luminiscenssignaler något att eftertrakta för att undgå datering som resulterar i att provmaterial får en skenbart för hög ålder. (Less)
Abstract
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... (More)
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. (Less)
Please use this url to cite or link to this publication:
author
Lindvall, Alma LU
supervisor
organization
course
GEOL01 20171
year
type
M2 - Bachelor Degree
subject
keywords
optiskt stimulerad luminiscens, OSL, datering, luminiscens, nollställning
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
501
language
Swedish
id
8916161
date added to LUP
2017-06-19 15:38:10
date last changed
2017-06-19 15:38:10
@misc{8916161,
  abstract     = {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.},
  author       = {Lindvall, Alma},
  keyword      = {optiskt stimulerad luminiscens,OSL,datering,luminiscens,nollställning},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {Hur snabbt påverkas och nollställs luminiscenssignaler under naturliga ljusförhållanden?},
  year         = {2017},
}