I am working on sediment hosted radioactive mineralisation. I've recorded few locations and that samples were analysed through HPGe detector for identification of radionuclei and the amount present in it. I did proper sheilding, background corrections, calibration, statistical treatment for activity and for total elemental concentration with two methods but both of them are showing almost similar results. The conc. of K40 goes in 300's of percentage. So what could be the reason?? Calculation, calibration and background subtaction and everything i had check thrice.
Take measurements with another spectrometer or radiometer to make sure that the semiconductor spectrometer is working properly.
How did you determine the total potassium or potassium concentration?
Did you take the same time scale for the 'mariage' of the measured (= sample +background) spectrum and the background spectrum itself?
Measurement of the background spectrum is often taken in a long run;
e.g. 10 to 100 times the acquisition time of the sample spectrum.
How did you calibrate? Did you use a 40K reference source with the same geometry as your samples? (e.g. solution of KCl in pure water, or pure KCl powder).
Sandeepkumar Z. Patel Your statement, "The conc. of K40 goes in 300's of percentage." I assumed you referred to the abundance of K40 in the sample compared to total potassium.
Please show how you arrived at '300's of percentage.' What is K40 a percentage of?
It’s possible that the high K-40 values are the result of an efficiency mismatch rather than an actual anomaly in the sample. If your efficiency calibration was built using a point source and then applied directly to a volumetric sample (especially with different density, height, or container geometry), the detector’s true efficiency for that setup can be significantly different. In such cases, the calibration will underestimate the real efficiency, which in turn overestimates the calculated activity.
For accurate results, the efficiency curve must be specific to the exact geometry and matrix you’re measuring, same container type (e.g., Marinelli beaker), fill height, density, and even moisture content, since all these factors affect self-attenuation of gamma rays. Sample preparation is also a very important step: compaction, uniform filling, and consistent density with the calibration standard will help ensure correct attenuation and efficiency. If the density is higher than assumed, attenuation will be stronger, and an uncorrected curve may misreport the activity.
That said, sometimes high K-40 is real, certain materials, including some sediments and even certain foods, naturally have very high potassium content. If you suspect the result might be genuine, you could confirm it using independent analytical chemistry techniques, such as flame photometry, ICP-OES, or XRF, to measure total potassium and cross-check against your HPGe result.
Mismatch between sample geometry and efficiency, peak fitting errors with the Compton background, inadequate background subtraction, and energy calibration drift are common measurement aberrations that cause HPGe detectors to produce abnormally high K-40 values. You can double-check your results by comparing the total potassium content measured by chemical analysis with the expected activity based on the amount of potassium in nature. The high number probably signifies true potassium enrichment from biological or environmental sources, if the outcome is constant. Repeated measurements with appropriate adjustment factors should always precede final interpretation.
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