Why is the radium effect measurement by CR39 SSNTDs greater than radium measurement by NaI(TI) gamma spectrometry {the rate (1/10)} in the same water samples?
I'm trying to understand the question. I'm assuming by "radium effect" you're talking about measurements of radium concentration in water. Is that right?
Why radium concentration measured by different methods would give different results would seem to be a question of how those different methods are calibrated. In this case your two detectors measures different radiation.
The SSNTD records tracks from alpha decays, with close to 100% detection of alpha particles crossing the plastic. Because the range of alphas in water will be very short a calibration to activity per unit volume is relatively straightforward.
The NaI(Tl) detector measures gamma rays associated with the radium decays, that would be at 186keV but may also include other decays from radium daughters (though using those to quantify radium will require assumptions about whether these are in equilibrium). The efficiency for the detection of the 186keV, or other, gamma rays will depend on the detector size. And, given the much greater range of gamma rays through water the geometry of the sample container will be important in calibration.
The main question I would ask is how are the two systems calibrated?
Is this basically the same question asked here: https://www.researchgate.net/post/Why_is_the_effective_radium_content_greater_than_the_radium_in_the_foodstuff_sample?_sg=uSnYwKPq5kAC%2B%2FQJOiHYeSJDHpwiOxl2H5773NBhLIl7HsV39pPFyScCxryptQsw ?
don't forget that we have interference between Gamma ray 185.72 KeV of U-235 (probability of Gamma Emission = 57%) with 186.2 KeV of Ra-226 (probability of Gamma Emission = 3.55%) not only NaI(Tl) cannot resolve this problem but also HPGe, you have to correct manually if you have good peak in 143.767 KeV for U-235 so of course the NaI(Tl) is not the good detector for this
I think the best method for this environmental samples (specially water) to measure the Ra-226 is LSC
The effective radium concentration is derived from the actual radium concentration and radon emanation from a sample. The effective radium content is the source term for radon release to the environment.
The effective radium content is a measure of radon emanating from a sample. The radium concentration cannot be smaller than the radon concentration when the two are in equilibrium. It is expected that the effective radium concentration will always be less than the actual radium concentration, because all the radon will not escape the sample matrix. The measured effective radium concentration might be larger than the measured actual radium concentration, but for a well designed measurement system with propagated error of measurement, the values should be within the experimental error.
As noted, this is the same answer as to
https://www.researchgate.net/post/Why_is_the_effective_radium_content_greater_than_the_radium_in_the_foodstuff_sample?ev=tp_feed_post_xview
for determined radium by NaI(tl) we used 214Pb with energy peak (351.9 Kev) in water sample but radium effect measured by passive method (CR-39)
you making an average of 214Pb with energy peak (351.9 Kev) and 214Bi (609 keV)
Assuming that the proper energy & geometry calibrations were performed for both methods & an adequate sample sizes & count times were used, did you allow for proper ingrowth prior to counting via gamma spec? I suggest waiting for at least 3 weeks after sealing the Marinelli beaker before gamma counting so that the Pb/Bi-214 daughters are in equilibrium with the Ra-226.
If you waited for ingrowth, then I would review all the calibrations-
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