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Flett Research Ltd
440 DeSalaberry Avenue, Winnipeg MB CANADA Phone/Fax: (204) 667-2505 |
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| >> FLETT HOME PAGE >> RADIOISOTOPES >> FREQUENTLY ASKED QUESTIONS |
Flett Research - Radioisotope Frequently Asked Questions Below are answers to some of the questions most frequently asked by our clients. We recommend, however, that you contact us before sample submission. Understanding your project and ensuring samples are submitted in the proper manner helps to ensure the success of your project.
Where is the best location to collect a core from a lake? Sampling Where is the best location to collect a core from a lake? The best location to obtain a core for Pb-210 or Cs-137 dating is probably the deepest part of the lake. The isotope activities will usually be highest and most easily measured at this site, and physical and biological mixing may be reduced, particularly if the deep waters are anoxic. It is not recommended to core near river/stream inflows because the sediment accumulation rate could be irregular and very high in sandy material which is poor in Pb-210. Coring on or near sloped bottoms is also to be avoided because the sediment accumulation could be irregular due to periodic slumping or erosion. In either of the forgoing cases, interpretation of the Pb-210 profiles could be difficult or impossible. What is the desirable core length? We recommend collecting a core that is long enough to contain sediments more than 160 years old at the bottom, or taking the core as deep as you can get. The resolution of core sections depends upon the sediment accumulation rate at the sampling site. Typically, the core is sectioned at 1-cm thickness in the upper 20 cm, 2-cm thickness between 20 and 40 cm and 5-cm thickness below 40 cm depth. If the sediment accumulation rate is very low (e.g. <0.5 mm/yr), then a higher resolution is desired (i.e. 0.5 cm / section). If the sediment accumulation rate is very high (e.g. in a dam or river inlet), the core can be sectioned at 2-cm or 5-cm thickness or even thicker. If these samples are to be analyzed for other analytes (e.g. metals or contaminants), then the resolution may have been defined by the study. Do you have any requirements for sample collection? Samples are best collected in clean jars-heavy walled polypropylene is preferred because of resistance to breakage. The jars should be waterproof so that no water is lost from the samples – try to keep the rims of the jars clean when closing so that no particles are on the sealing surfaces. Avoid loss of water from the core slices as this will affect the bulk density which in turn will affect the Pb-210 dating calculations. The samples do not require special storage conditions for radioisotope analyses. Holding times are unlimited. Also see below "Do you have any preference in sample packing/transportation?" Sample Preparation and Submission Should I send the samples dry or wet? We prefer to receive wet samples from you. If the samples will be submitted wet, we will measure the dry bulk density of the sediment (dry wt./wet volume) before the sediments are dried and analyzed for Pb-210. If you are going to send us wet sub-samples, please avoid any water loss and make sure each sub-sample is representative, i.e. the sample is well homogenized before subsampling, especially for the watery samples. If you are going to send us dry sediment samples and request data modeling and interpretation, we will need dry bulk density data (dry wt./wet volume) from you in order to perform Pb-210 modeling. Please let us know if you have any questions concerning the measurement or calculation of the dry bulk density. These measurements are important. Should I send the entire core? We prefer to receive all sections from you and select the most important samples for analyses to obtain reliable dating results. Alternatively, you can send us every second section, including the surface section and the bottom section. If you are going to send discontinuous sections for dating, we recommend that you confirm with us about choosing samples before you send them to us. If you desire, the remaining sample material could be returned to you by mail. Do you have any requirements for sample submission? Please contact us before submitting your samples. A sample submission form will be emailed to you to fill out, and we would also like to receive a brief description of the core site and any information you believe may be useful for interpretation of the core history. If sending samples from outside Canada, for customs declaration, please mark the samples as ‘Geological samples – no commercial value – non-hazardous’. A commercial invoice is also required. How much sample material do you need? Sample amount required for each radioisotope analysis is listed below: Pb-210: 0.5 – 1.0 g (equivalent dry wt.) per sample Ra-226: 1.0 – 2.0 g (equivalent dry wt.) per sample Cs-137: > 5 g (equivalent dry wt.) per sample * * The desired sample size for Cs-137 analysis will vary depending upon the Cs-137 activity in the sample. For example, it may be possible to measure the Cs-137 activity in some lake sediments which are less than 1 g dry wt. However, for marine sediment samples we would recommend at least 15 g dry wt. It is possible to count Cs-137 in a sample less than 5 g dry wt, but the error will increase and the detection limit will be poorer. The Cs-137 analysis is not destructive (other than freeze drying or oven drying at 50C), therefore, sample material counted for Cs-137 can be returned afterwards. If the available sample size is limited, it may not be sufficient for all three radioisotope analyses. We will discuss the most appropriate strategy of analyses with you. Do you have any preference in sample packing/transportation? For the shipment of wet samples, we prefer wide-mouth polypropylene plastic jars with lined caps. Caps should be tightly closed to prevent water loss during transportation. Whirl-Pac bags are next best for packing wet samples. We have received samples in Ziploc sandwich bags but this is not recommended because they have sometimes leaked and compromised the samples. Ziploc freezer bags are a better choice (double bag the sample if you must use such bags). For the shipment of dry samples, we prefer to receive them in plastic vials. If glass vials are to be used, please make sure each vial is safely packed to avoid cracking during transportation. Analyses and Report How many samples will you analyze for Pb-210 for each core? For each core, it is typical to analyze 10 - 20 samples for Pb-210, covering an accumulation period of about 160 years. We will often start with about 7 analyses of Pb-210, spread along the core length, to determine the basic profile shape, and then fill in where the profile dictates. This is the most cost-efficient way, i.e. the number of analyses will be optimized to obtain reliable dating results. Why do you recommend other radioisotope analyses (i.e. Ra-226 and Cs-137)? Are they necessary? Several (2 – 4) Ra-226 measurements are often required for each core, in order to positively determine the Pb-210 background level(s). After all Pb-210 and Ra-226 analyses are completed, we would recommend 5 – 15 Cs-137 analyses for each core, in order to validate the Pb-210 model(s). These analyses are optional but highly recommended, especially for the cores having an irregular Pb-210 profile. Sometimes the Ra-226 and Cs-137 results can completely change the interpretation of the core history. Why is the dry bulk density measurement important? We need to know the DRY bulk density in order to apply the CRS model to your data. Typically, a KNOWN volume of WET sediment is dried at about 50C and then the dry weight of remaining sediment is determined. This is important because the Pb-210 is measured on dry sample and we have to calculate how much Pb-210 there is in each ml of the original wet core material. After we subtract the Pb-210 background from each ml of sediment, we can calculate the total amount of excess (atmospheric sourced) Pb-210 in the core as DPM/cm2. This total excess Pb-210 inventory, together with the subtotals upon which it is based, are used by the CRS model to calculate accumulation rates and ages for each core section. What are the analytical methods and detection limits for each radioisotope analysis? Please refer to our Methods & Resources page for all the details. What will be included in the final report? Our data and interpretation/modeling are all included in a single Excel 2007 workbook for each core, in a standardized format. The results of each analyte are summarized in individual worksheets, including raw data, calibrations and calculations. If modeling and interpretation are requested, where possible, ages will be assigned to the bottom of each section. Graphs of Pb-210 vs accumulated dry weight/cm2, dry bulk density vs accumulated dry weight/cm2, best fit regression of Pb-210 vs accumulated dry weight/cm2, CRS and linear model age vs depth comparison, CRS sediment accumulation rates vs depth, CRS sediment accumulation rates vs age, and Cs-137 vs depth are included where possible. There is no guarantee that any core can be dated. It very much depends upon the character of the core. Can I get a preliminary report before all analyses are completed? Yes, we can provide preliminary report(s) as requested, and co-decide on additional analyses. Costs and Turnaround Time What are the costs for dating one core? Please refer to our pricing page for unit prices for all the analyses. The costs of dating one core in 2024 could range between CAN $1440 - $5855 (plus taxes, if applicable), or USD $1120 - $4550. The number of analyses required highly depends upon the shape of Pb-210 profile, and the desired number of analyses is not known until we start to see data. After you review the preliminary Pb-210 profile (typically contains 5 - 7 data points) and our comments, we can discuss the data and help you decide how to proceed according to your budget. The above prices are applicable to universities and research organizations. Additional costs for modeling/interpretation will be charged to consulting firms. Will there be any other charges in addition to the analyses? If samples are sent from outside Canada, brokerage charges (~CAN$20 per shipment) may apply. If you request the unconsumed sample material to be returned after all analyses are completed, then the costs will include packing charges and postage or courier charges. If the invoice will be paid by wire transfer or credit card, bank charges may apply. What kind of turnaround time can I expect? Typically, the turnaround time for dating 1 - 2 cores is about 3 months upon sample reception. This can vary with the current workload and the complexity of data. Please contact us if fast service is required. Additional costs may apply. Miscellaneous Can I just send you a few samples for radioisotope analyses instead of dating the core? We can analyze individual samples for radioisotopes, but it is not possible to assign an age to such samples. Ages can only be calculated from a series of samples (usually >10) from a single sediment core. |
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For additional information, contact Dr. Robert Flett at
flett@flettresearch.ca Return to the Flett Research Radioisotope Page. |
Flett Research Ltd - 440 DeSalaberry Ave - Winnipeg Manitoba CANADA R2L 0Y7 |
Phone/Fax: (204) 667-2505 |
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