CENIEH - Centro Nacional de Investigación sobre la Evolución Humana
The ESR dating laboratory consists of 4 distinct areas: (1) Sample preparation area, (2) Gamma irradiation facilities, (3) Low Background gamma spectrometry facilities and (4) ESR spectrometry area.
1- Sample preparation area: The samples are prepared following standard protocols that are specific to the kind of material dated. All the equipments needed for an optimal sample preparation are available: circular saws, dentist drill, agate mortar, sieves… Chemical preparations using various products (HCl, HF, H2O2, SPT…) are also performed in routine.
2- Gamma irradiation facili...
2- Gamma irradiation facilities: Sample irradiations are performed using a Gammacell-1000 (Best Theratronics) gamma source (Cs-137, approx. Dose rate = 8 Gy/min).
3- Low Background gamma spectrometry: The natural radioactivity of geological/archaeological samples (sediment, fossil teeth) is assessed with 2 x Canberra high purity germanium detectors (Extended Range Coaxial -XtRa- and well-type detectors).
4- ESR spectrometry area: ESR measurements are performed with an EMXmicro-6/1 (X-band) Bruker ESR spectrometer. The stability of the experimental conditions is ensured by: (i) a ThermoFlex3500 chiller connected to the ESR spectrometer, which controls and precisely stabilizes the temperature (+/- 0.1º) of the water cooling the magnets, and (ii) an air conditioning system regulating the temperature of the room. The ESR spectrometer is equipped to work either at room temperature or at liquid nitrogen temperature (Bruker temperature control system / JEOL finger deware). The programmable goniometer allows the tube rotations inside the resonator to check angular variation of the ESR signal.
Electron Spin Resonance (ESR) dating is an absolute dating method. Depending on the authors, it is usually classified either as a radiation exposure dating method, a trapped charge dating method, a paleodosimetric method, or even as a radiometric method s.l.. Similarly to the methods using luminescence phenomena, the ESR dating is based on the evaluation of the exposure of some materials to natural radioactivity. This exposure is quantified in terms of absorbed radiation dose, which correspond to the energy deposited in a medium by ionizing radiations. Indeed, under the effect of natural radioactivity, some materials acquire or develop a paramagnetic behavior,...
Electron Spin Resonance (ESR) dating is an absolute dating method. Depending on the authors, it is usually classified either as a radiation exposure dating method, a trapped charge dating method, a paleodosimetric method, or even as a radiometric method s.l.. Similarly to the methods using luminescence phenomena, the ESR dating is based on the evaluation of the exposure of some materials to natural radioactivity. This exposure is quantified in terms of absorbed radiation dose, which correspond to the energy deposited in a medium by ionizing radiations. Indeed, under the effect of natural radioactivity, some materials acquire or develop a paramagnetic behavior, which may be detected and quantified by Electron Spin Resonance (ESR) spectroscopy.
The use of this technique for dating purposes was first suggested by Ikeya (1975), after some studies of a stalactite from Akiyoshi cave (Japan). Since then, numerous applications to a wide range of material have been, more or less successfully, attempted (see extensive reviews in Grün, 1989; Ikeya, 1993; Rink, 1997), making nowadays the ESR dating as a landmark in Quaternary Geochronology.
In ESR dating, the sample acts as a dosimeter, i.e. a material that is able to accurately register the energy absorbed when exposed to natural radioactivity. Basically, the interaction of the sample with the ionizing radiations (mainly alpha and beta particles plus gamma and cosmic rays), coming from the radioactive elements (mainly U, Th and K) located within the sample and its surrounding environment, induces some changes in the electronic structure of the material: some electric charges (electrons or holes) are being trapped in the crystalline network by some impurities (i.e., crystalline defects), producing radiation-induced paramagnetic species (free radicals, paramagnetic centers…), which build a characteristic signal that can be detected by ESR spectroscopy. The intensity of the ESR signal is proportional to the amount of trapped charges, which basically depends on three main parameters: the strength of the natural radioactivity, the time of irradiation and the total number of traps available in the sample.
An ESR age is usually derived from the following equation: T = De/D, where T is the age of the sample, De is the equivalent dose, also called paleodose (expressed in Gray – Gy), which is the total absorbed dose by the sample during the time elapsed between the zeroing of the ESR clock (t=0) and the sampling (t=T); D is the dose rate (usually in Gy/ka or μGy/a), or annual dose, i.e. the average dose absorbed by the sample in one year. Further details about the basic principles of the method can be found in Grün (1989, 2007), Ikeya (1993) and Rink (1997).
Reference:Grün, R (1989). Electron spin resonance (ESR) dating. Quaternary International 1: 65-109.Grün, R (2007). Electron Spin Resonance Dating. Encyclopedia of Quaternary Science. A. E. Editor-in-Chief: Scott. Oxford, Elsevier: 1505-1516.Ikeya, M (1975). Dating a stalactite by electron paramagnetic resonance. Nature 255(5503): 48-50.Ikeya, M (1993). New Applications of Electron Spin Resonance Dating, Dosimetry and Microscopy. Singapore, World Scientific.Rink, WJ (1997). Electron spin resonance (ESR) dating and ESR applications in quaternary science and archaeometry. Radiation Measurements 27(5–6): 975-1025.
The equipment in this laboratory consists of:
1) Main facilities- X-band Bruker Electron Spin Resonance (ESR) spectrometer, EMXmicro-6/1 model, connected to a Thermo Scientific NESLAB chiller (ThermoFlex3500 model) to control water cooling temperature.- Gammacell 1000 Elite-I 137Cs gamma irradiation source.- 2 x Canberra high purity germanium detectors (Extended Range Coaxial -XtRa- and well-type detectors) for high-resolution gamma spectrometry of sediments.- Hönle solar simulator (UVACube400 + SOL500).- 2 x Canberra in situ field gamma spectrometers with LaBr3:Ce and NaI:Tl probes and InSpector 1000 multi-channel analysers.
2) Accessories ass...
2) Accessories associated to the ESR spectrometer- Programmable goniometer (ER218PG1)- High sensitivity resonator - Standard resonator (ER4102ST)- Digital Temperature Control System (ER 4141VT-M Metal-Transferline Option) to work close to liquid nitrogen temperature (90-100K)- JEOL Finger Dewar (Insertion type dewar ES-UCD3X, V=150 ml) to work at liquid nitrogen temperature (77K)
For more information, please visit Access and Rates.
Centro Nacional de Investigación sobre la Evolución Humana
Paseo Sierra Atapuerca 3
09002 Burgos - España
Tel:+34 947040800 / Fax:+34 947040810