@Dashty T. Akrawy: But K-40 is irrelevant to humans, because the body maintains a certain level of K, and any K contains the same amount of K-40.

Dear Dr. Dashty, I think the answer of Dr. Erik should take as important because

 the effect of U and Th more harmful. Thank you 

Internal exposures arise from the intake of terrestrial radionuclides by inhalation and ingestion. Doses by inhalation result from the presence in air of dust particles containing radionuclides of the 238Uand 232Th decay chains. The dominant component of inhalation exposure is the short-lived decay products of radon. Doses by ingestion are mainly due to 40K and to the 238U and 232Th series radionuclides present in foods and drinking water.

 http://www.unscear.org/docs/publications/2000/UNSCEAR_2000_Annex-B.pdf

@Florian Glodeanu:

Yes, but as any K contains the same amount of K-40 and K is an essential element, the exposure due to internal K-40 can not be avoided by dietary measures. It will always be the same. In comparison, the uptake of  U-238, Th-232 and their decay products can be influenced or avoided,

you should measure all

Ra is accumulated by plants in a much greater degree than U and Th because of its geochemical nature. Plants have limits on U and Th uptake, while Ra can be accumulated by plants without limits. We investigated the content of naturally occuring radionuclides (NOR) in plants near NOR-contentaining wastes and Ra concentration was linearly correlated with Ra content in soils. But the U content did not increase with U content in soils and was relatively stable.

Concerning Rn, its content varies because of changes in moisture transpiration and its measuring requires high accuracy and can be complex.

Therefore, I think Ra measuring is prefered in this case.

The total effective dose from inhalation and ingestion of terrestrial radionuclides is 310 µSv, of which 170 µSv is from 40K and 140 µSv is from the long-lived radionuclides in the uranium and thorium series.

 Uranium is retained in the body primarily in the skeleton. Following intake by ingestion and inhalation, thorium is mainly deposited on bone surfaces and retained for long periods.

 http://www.unscear.org/docs/publications/2000/UNSCEAR_2000_Annex-B.pdf

alpha spectroscopy  for U

Rad 7 for Radon

In my experience, the concentrations of various radionuclides (U-series) can be made using HPGe detectors with the vegetation inside a Marinelli beaker.  When I worked at the BALUF in Vienna, Austria, we would clean the vegetables as if they were to be eaten; then we would puree them and pour the puree into the beaker for counting.  Low background counting rooms are preferred for these types of environmental measurements.  Depending on the geometry and the pureed density, one could expect efficiencies on the order of 10%.  

Thank you J. Matthew Barnett ,

You right 

Yes,

one solution could be the Gamma spectrometry, but you need a big mass of sample and normally the MDA (Bq/kg) could be to much higher.

Other solution could be the liquid scintillation counting to measure the gross alpha and gross beta activity in sample, but i think if you want know the real concentration of Uranium, Thorium and Radium you must use a radiochemistry method; sequential separation of alla nuclide and measure by alpha spectrometry. Much expansive than Gamma and LS, but with small weight you can obtain a good results in terms of MDA and concentrations.

I don't understand why measure Radon...

Be careful with the K-40 presence if you measure the total activity.

Mattia

Dear Mattia Taroni,

Thank you for your answering, 

  The specific activity  of various radionuclides (U-series)  can done by using HPGe detector with the vegetation inside a Marinelli beaker.

Another alternative way is by using NAA or ICPMS which requires a fractional amount of the sample unlike that of HPGe or NaI(Tl).

Arguably the most sensitive method to determine U (235/8), Th (232), and Ra (226) concentration in vegetation would be by mass spectrometry.  This is due to the extremely low specific activity of U and Th.  And, the issues with K-40 in the sample and terrestrial / cosmic HPGe background contributions will be negated. 

Whole fruit/vegetable can be muffled to ash, then the residue wet ashed in strong acid, and finally the residue brought into solution in dilute acid.  This solution can be nebulized into a ICP-MS for analysis. 

Thank you Dear  Matthew J O'Hara,

The method that use ICP-MS, it is good

Thank you again for your contribution 

I think you can do this with the help of HPGe/NaI detector but you have to take care of the large mass of the samples and some calculations will do the job.

Dear Vimal, thank you so much for your answer,

I think so, this is good way to measure the concentration in vegetables.

نتقدم إليكم بالشكر الجزيل والثناء الجميل على هذه المعلومات العلمية القيمة

Most welcome

Solid state nuclear track detectors CR-39 is the preferred method to determine Radon and Uranium, also gamma ray spectroscopy to measuring Radium and Thorium.  

Thank you Dr. Anees 

Hello , may I ask if it possible to calculate the absorbed dose from K40 if I have the K concentration in some kind of food

Best

Yes, sure u can calculate it

check this paper: Article Estimation of annual effective dose due to natural radioacti...

Thanks for responding I just requested a copy because only abstract is available

You can used HPGe detector or NaI(Tl) to measure Ra-226, Th-232 and K-40

Also the radon concentration can be measure by using Solid Nuclear Track detector and also Uranium concentration

Gamma ray spectroscopy for NORM and SSNTD for radon or RAD7.

You can measure radon and from this you can calculate the annual effective dose

by using passive technique with solid state nuclear track detectors (CR-39, LR-115,......) but if you want to determine U, Th, K you can use scintillation counter like [NaI (Tl)] and HPGe, from the results of gamma you can calculate the all kind of dose.......

*I am agreement with the answer of Dr. Olga Marinich , Dr.Ghassan Saffarini and Dr. Laith Najam and Dr. Anees A. Al-Hamzawi

Use gamma spec with HPGe detector to determine 226Ra and 228Ra radionuclides.

Followed the suggestions of senior colleagues here and already got more publications on guidance.

Ra-226. Ra-228, K-40...u might check the Transfer Factor from the soil to plant as well together with Ingestion Dose Intake. Finally based on the UNSCEAR 2000, u might determine the Radium equivalent, annual effective dose, external hazard index.

Gamma ray spectroscopy for NORM and SSNTD for radon or RAD7.

you may view our contribution

Article Measurement of (40K, 238U and 232Th) and Associated Dose Rat...