Trace Element Analysis Laboratory @ EAPS - MIT

Instrumental Neutron Activation Analysis (INAA)

Radiometric Analysis



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MIT - EAPS INAA Radiometric Analysis

  • Introduction
  • Frequently Asked Questions about Capability
  • Sample size
  • Errors in determination
  • What else?
  • Low background counting
  • Sensitivities
    • Table 1: Sensitivity expressed in the format
    Counts per hour per gram (or microgram) of the element
  • K Data
  • U Data
  • Th Data
    • Table 2: Sensitivity expressed in the format
    Counts per hour per % (or ppm) of the element
  • K Data
  • U Data
  • Th Data
    		•


    INTRODUCTION

    Since the time of nucleosynthesis, radioisotopes with long half-lives have survived in detectable amounts till today. These primeval or primordial isotopes have been the subject of intense study in geochemistry because of their importance to heat flow studies. Uranium and thorium in nature give rise to radioactive decay chains consisting of several isotopes. Together with the isotope potassium-40, the naturally occurring radioactive materials (NORM) are of interest for many other reasons including for the experiments in paritcle physics.

    Well shielded high purity germanium detectors (HPGe) are used extensively for the quantitative measurment of U, Th and K in NORM. The INAA laboratory at EAPS can be utilized for maximum benefit for the study of NORM as well as for the primary screening and selection of materials low in radioactivity of interest to particle physicists.

    In addition to NORMs, anthropogenic radioactivity consists of many more radioactive isotopes introduced into nature from weapons testing and reactor operations. Many of these isotopes can be readily detected by the same HPGe detectors used for INAA.

    References:
    The Natural Radiation Environment, eds. J.A.S Adams and W.M. Lowder, University of Chicago Press, 1964.
    The Natural Radiation Environment II, Vols 1 and 2, 1972
    The Natural Radiation Environment III, 1978
    Gamma-ray spectrometry of Rocks, J.A.S. Adams and P. Gasparini, Elsevier Publishing Company,1970
    Environmental Radioactivity, M. Eisenbud, 1973
    Measurement of Th, U, and K concentrations in a variety of materials, P. Jagam and J.J. Simpson 1993. Nucl. Instr. Meth. A 324, 389-398.
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    FAQ about CAPABILITY

    What sample size is required?

    For Potassium, the size range is 10 g to 1000 g.
    For Uranium and Thorium, the size range is 400g to 1000 g.

    Can a smaller size be used?

    Size is negotiable depending upon the requirement.

    How long does it take to count one sample?

    A typical counting time is about 10 hours. Counting time depends on sample size, concentration of K, U, and Th in the sample, and the desired statistical precision for the counts detected by gamma-ray counting.

    What is the error in the concentration determination?

    The error in the concentration determination depends upon:
    1. The counting statistics,
    2. The known error in the concentration of the standard used as a comparator relative to which the unknown concentration is determined,
    3. The error in sampling arising from inhomogenieity of the sampling location from where the sample is collected,
    4. The sampling technique used for selecting the sample: grab sampling or homogenized sampling from a large collection,
    5. The contamination in sample preparation.


    What is the error arising from counting statistics using the gamma-ray counting for the concentration determination?

    For Potassium concentration of 1%, for a typical counting time of 10 hours, the 1 sigma error range is 58% to 3% for a sample range of 10 g to 1000 g; for a counting time of 100 hours, the 1 sigma error range is 18% to 1% for a sample of 10 g to 100 g
    For Uranium and Thorium, for a concentration of 1 ppm, for a typical counting time of 10 hours, the 1 sigma error is n the range of 27% to 18% for a sample range of 400 g to 1000 g; for a counting time of 100 hours, the 1 sigma error is better than 15% for U and better than 15% for Th.

    What is the counting sensitivity of your system?

    Click here for a typical set of sensitivity data.

    What else?

    In addition to determining the K, U, Th concentrations, we can provide the NORM actvities as well.

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    Sensitivities TABLE 1


    ********************************

    K - Sensitivities typical data


    ********************************
    "Net" means (Gross Counts - Background).
    "Background" means counts without sample.
    "cp10hg" means counts per 10 hours per gram.
    "cp100hg" means counts per 100 hours per gram.
    "1 Sigma%" error is the standard deviation of the background and the net area as a percentage of the net area.

    Sample Net Error Net Error
    Weight g K % cp10hg 1 Sigma % cp100hg 1 Sigma %
    Geometry 1 10 1 2520 60 25205 19
    Geometry 2 20 1 1330 57 13298 18
    Geometry 3 400 1 624 6 6244 2
    Geometry 4 1000 1 456 4 4560 1
    Background cp10h cp100h
    1143 11428

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    ********************************
    U - Sensitivities typical data

    ********************************
    "Net" means (Gross Counts - Background).
    "Background" means counts without sample.
    "cp10hug" means counts per 10 hours per microgram.
    "cp100hug" means counts per 100 hours per microgram.
    "1 Sigma%" error is the standard deviation of the background and the net area as a percentage of the net area.

    Sample Net Error Net Error
    Weight g U ppm cp10hug 1 Sigma % cp100hug 1 Sigma %
    Geometry 3 400 1 0.43 27 4.30 9
    Geometry 4 1000 1 0.30 16 3.0 5
    Background cp10h cp100h
    988 9887

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    ********************************
    Th - Sensitivities typical data


    ********************************
    "Net" means (Gross Counts - Background).
    "Background" means counts without sample.
    "cp10hug" means counts per 10 hours per microgram.
    "cp100hug" means counts per 100 hours per microgram.
    "1 Sigma%" error is the standard deviation of the background and the net area as a percentage of the net area.
    Sample Net Error Net Error
    Weight g Th ppm cp10hug 1 Sigma % cp100hug 1 Sigma %
    Geometry 3 400 1 Below Determination Level 1.70 30
    Geometry 4 1000 1 0.12 58 1.2 18
    Background cp10h cp100h
    2392 23917

    Sensitivities TABLE 2


    ********************************

    K - Sensitivities typical data


    ********************************
    "Net" means (Gross Counts - Background).
    "Background" means counts without sample.
    "cp10h1%K" means counts per 10 hours per 1%K.
    "cp100h1%K" means counts per 100 hours per 1%K.
    "1 Sigma%" error is the standard deviation of the background and the net area as a percentage of the net area.

    Sample Net Error Net Error
    Weight g K % cp10h1%K 1 Sigma % cp100h1%K 1 Sigma %
    Geometry 1 10 1 252 60 2520 19
    Geometry 2 20 1 266 57 2660 18
    Geometry 3 400 1 2498 6 24976 2
    Geometry 4 1000 1 4560 4 45601 1
    Background cp10h cp100h
    1143 11428

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    ********************************
    U - Sensitivities typical data

    ********************************
    "Net" means (Gross Counts - Background).
    "Background" means counts without sample.
    "cp10hUppm" means counts per 10 hours per U ppm.
    "cp100hUppm" means counts per 100 hours per U ppm.
    "1 Sigma%" error is the standard deviation of the background and the net area as a percentage of the net area.

    Sample Net Error Net Error
    Weight g U ppm cp10hUppm 1 Sigma % cp100hUppm 1 Sigma %
    Geometry 3 400 1 172 27 1719 9
    Geometry 4 1000 1 300 16 3005 5
    Background cp10h cp100h
    988 9887

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    ********************************
    Th - Sensitivities typical data


    ********************************
    "Net" means (Gross Counts - Background).
    "Background" means counts without sample.
    "cp10hThppm" means counts per 10 hours per Th ppm.
    "cp100hug" means counts per 100 hours per Th ppm.
    "1 Sigma%" error is the standard deviation of the background and the net area as a percentage of the net area.
    Sample Net Error Net Error
    Weight g Th ppm cp10hThppm 1 Sigma % cp100hThppm 1 Sigma %
    Geometry 3 400 1 Below Determination Level 680 30
    Geometry 4 1000 1 120 58 1199 18
    Background cp10h cp100h
    2392 23917

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    Created by Pillalamarri Ila
    October 27, 2003
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