In-Situ Chlorine-36

In-Situ Chlorine-In-Situ Chlorine-3636

Nicole DixHWR 696T

OutlineOutline IntroductionIntroduction Production MechanismsProduction Mechanisms Sample Collection MethodsSample Collection Methods Laboratory AnalysisLaboratory Analysis ApplicationsApplications

IntroductionIntroduction Chlorine has three isotopes. Two of which Chlorine has three isotopes. Two of which

are stable (chlorine-35 and 37) and the are stable (chlorine-35 and 37) and the third is a cosmogenic isotope (chlorine-third is a cosmogenic isotope (chlorine-36). 36).

However, for this presentation we will However, for this presentation we will only focus on chlorine-36, which is only focus on chlorine-36, which is produced in the solid materials on the produced in the solid materials on the Earth’s surface.Earth’s surface.

http://www.sahra.arizona.edu/programs/isotopes/chlorine.html

Introduction Continued…Introduction Continued… Because chlorine-36 has a half-life of Because chlorine-36 has a half-life of

310,000 years it is useful in age dating 310,000 years it is useful in age dating ground water and solid materials on the ground water and solid materials on the Earth’s surface.Earth’s surface.

Like all cosmogenic nuclides the production Like all cosmogenic nuclides the production of chlorine-36 depends on the intensity of of chlorine-36 depends on the intensity of incident cosmogenic rays, availability of incident cosmogenic rays, availability of target nuclei in the exposed material, and target nuclei in the exposed material, and the probability with which a nuclear the probability with which a nuclear reaction produces the nuclide of interest.reaction produces the nuclide of interest.

Zreda et al., 2000

Production MechanismsProduction Mechanisms Chlorine-36 is produced in solid materials Chlorine-36 is produced in solid materials

on the Earth’s surface primarily through on the Earth’s surface primarily through cosmic-ray induced reactions with cosmic-ray induced reactions with chlorine-36, potassium-39 and calcium-40.chlorine-36, potassium-39 and calcium-40.

The three mechanisms of formation are: The three mechanisms of formation are: 1) spallation reactions, 2) muon reactions 1) spallation reactions, 2) muon reactions and 3) thermal neutron absorption.and 3) thermal neutron absorption.

Zreda et al., 1991 & http://www.sahra.arizona.edu/programs/isotopes/chlorine.html

Production Mechanisms Production Mechanisms Conti..Conti..

In the top few meters of the Earth’s surface In the top few meters of the Earth’s surface thermal neutron activation of chlorine-35 and thermal neutron activation of chlorine-35 and spallation of potassium-39 and calcium-40 are spallation of potassium-39 and calcium-40 are the dominant means of production for chlorine-the dominant means of production for chlorine-36.36.

Below that depth, slow negative muon capture, Below that depth, slow negative muon capture, by calcium-40, becomes more important than the by calcium-40, becomes more important than the other mechanisms.other mechanisms.

In carbonates chlorine-36 is produced by Ca and In carbonates chlorine-36 is produced by Ca and in silicates it is produced by K, Ca, and Cl.in silicates it is produced by K, Ca, and Cl.

Zreda et al., 1991 & Zreda et al., 2000


Zreda et al., 2000


Zreda et al., 1991

Sample Collection Sample Collection MethodsMethods

First and foremost, determine the rock/mineral First and foremost, determine the rock/mineral type you want to sample, from what surface and type you want to sample, from what surface and how many samples you need to collect.how many samples you need to collect.

Because chlorine-36 is produced from several Because chlorine-36 is produced from several target elements, virtually all rock types are target elements, virtually all rock types are suitable for sampling.suitable for sampling.

The number of samples is related to geological The number of samples is related to geological characteristics of the surface dated, specifically, characteristics of the surface dated, specifically, its history of burial and erosion.its history of burial and erosion.

Zreda et al., 2000

Sample Collection Sample Collection Continued...Continued...

Sampling sites should be assessed due to Sampling sites should be assessed due to their geomorphic stability and geometry.their geomorphic stability and geometry.

Preferably sampling should take place on Preferably sampling should take place on flat, horizontal surfaces that are likely to flat, horizontal surfaces that are likely to have been continuously exposed since the have been continuously exposed since the surfaces formation such as, large tall surfaces formation such as, large tall morainal boulders.morainal boulders.

For chlorine-36 samples should be far For chlorine-36 samples should be far from edges because of a possible leakage from edges because of a possible leakage of thermal neutrons form the sides.of thermal neutrons form the sides.

Zreda et al., 2000

Sample Collection Sample Collection Continued...Continued...

Samples need to be collected from the top Samples need to be collected from the top few centimeters of rock minimizing the few centimeters of rock minimizing the variability of production rates with depth.variability of production rates with depth.

The least weathered surfaces are ideal for The least weathered surfaces are ideal for sampling.sampling.

Once collected samples should be stored Once collected samples should be stored in plastic bags until preparation.in plastic bags until preparation.

Zreda et al., 2000

Laboratory AnalysisLaboratory Analysis First, samples need to cleared of any First, samples need to cleared of any

organic growth.organic growth. They then need to be ground to a size They then need to be ground to a size

fraction smaller than the mean phenocryst fraction smaller than the mean phenocryst size of each rock.size of each rock.

Rock typeRock type CharacteristicCharacteristicss

SizeSize

Granites etc.Granites etc. Coarse-Coarse-crystallinecrystalline

0.5-1.0 mm0.5-1.0 mm

Basalts etc.Basalts etc. Fine-crystallineFine-crystalline 0.25-0.5 0.25-0.5 mmmm

CarbonatesCarbonates 0.25-1.0 0.25-1.0 mmmm

Laboratory Analysis Laboratory Analysis Conti…Conti…

The samples are then leached for 24 hours.The samples are then leached for 24 hours.-Silicates are leached in 5% nitric.-Silicates are leached in 5% nitric.-Carbonates are leached in deionized -Carbonates are leached in deionized water.water.

The leaching is done to remove any The leaching is done to remove any chlorine resulting from handling in the chlorine resulting from handling in the field or secondary carbonates, in the case field or secondary carbonates, in the case of silicates, from the microscopic pore or of silicates, from the microscopic pore or grain boundaries in the rock sample.grain boundaries in the rock sample.


After leaching, the samples are then After leaching, the samples are then dissolved in airtight capsules or “bombs”.dissolved in airtight capsules or “bombs”.

Silicate samples are dissolved using Silicate samples are dissolved using hydrofluoric acid and are incased in the hydrofluoric acid and are incased in the “bomb” for 6 hours, at a temperature of “bomb” for 6 hours, at a temperature of 130 degrees Celsius.130 degrees Celsius.

The carbonate samples are dissolved The carbonate samples are dissolved using concentrated nitric acid and are using concentrated nitric acid and are incase in the “bomb” for 3 hours, at room incase in the “bomb” for 3 hours, at room temperature.temperature.


Once the samples have been digested, Once the samples have been digested, AgNOAgNO33 is added to the solution to is added to the solution to precipitate out AgCl.precipitate out AgCl.

This solution sits overnight.This solution sits overnight. Next, the liquid is removed and NHNext, the liquid is removed and NH44OH is OH is

added to dissolve the solid.added to dissolve the solid. BaNOBaNO33 is added to the solution to remove is added to the solution to remove

any sulfur present.any sulfur present. The solution sits overnight.The solution sits overnight.


The next day HNOThe next day HNO33 is added until a white precipitate is added until a white precipitate forms and again AgNOforms and again AgNO3 3 is added to precipitate AgCl is added to precipitate AgCl out of solution.out of solution.

This solution stands overnight.This solution stands overnight. The above steps, using NHThe above steps, using NH44OH, BaNOOH, BaNO33, and HNO, and HNO33, are , are

repeated two more times.repeated two more times. Finally, the nearly sulfur-free AgCl is rinsed in Finally, the nearly sulfur-free AgCl is rinsed in

deionized water five times, to eliminate any unwanted deionized water five times, to eliminate any unwanted chemicals, and dried in an oven at 60 degrees Celsius.chemicals, and dried in an oven at 60 degrees Celsius.

The resulting sample is then weighed and sent to The resulting sample is then weighed and sent to Purdue University. The amount of chlorine-36 in each Purdue University. The amount of chlorine-36 in each sample will be measured using Accelerator Mass sample will be measured using Accelerator Mass Spectrometry (AMS).Spectrometry (AMS).

In-Situ Chlorine-36

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