Difference between revisions of "A few definitions in use in KJM5911"

Latest revision as of 10:48, 9 July 2012

Written and developed by Prof. Tor Bjørnstad (IFE/UiO) 

back to Naturally Occuring Radioactivity - NORM and TENORM

N =   number of nuclides
D =   disintegration rate (Bq, Ci, dimension s-1)
A =   activity is disintegration rate D per unit of volume or unit of mass (dimension s-1)
    We distinguish between two notions:
    As(i) = specific activity is activity per unit of mass of that particular element the actual
      radionuclide i belongs to. This notion is also used to express the activity of a
      particular radiolabelled molecule in relation to the total mass of the same molecule
      (labelled and unlabelled) in the sample (for instance when the inactive molecule is present
      as a carrier).
    Ac(i) = activity concentration is the activity of a special radionuclide i or all present
      radionuclides (AcT = A_c(∑i) = total activity) per unit of volume or unit of weight of a radioactive
      sample.

N,D and A may, in addition, have an index t (i.e. N_t, D_t and A_t). This denotes the parameter values at time t relative to a starting time t = 0.
R =   counting rate (cps, cpm or generally cpt where t should be defined, dimention s^-1)
S =   number of counts

N, D, A, R and S may, in addition, have indexes B = background, T = total or N = net. The relations between them are: R_N = R_T - R_B and S_N = S_T - S_B. Other indexes may also be used, for instance S_Cr-51 in order to separate from S_Fe-59.

Examples:

We consider the following three samples:
P1: 1 kg pure iron (Fe). This sample contains10kBq of the radionuclide ⁵⁹Fe.

P2: 1 kg steel consisting of 70 weight% iron and 10 weight% of each of the elements Cr, Ni and Mo. The sample contains 10 kBq of ⁵⁹Fe and 10 kBq of ⁵¹Cr.

P3: A 1L aqueous solution with 100 g dissolved FeCl₃ and 100 g dissolved CrCl₃. This corresponds to 35 g dissolved Fe and 31.6 g dissolved Cr. The solution contains 10kBq ⁵¹Cr and 10 kBq ⁵⁹Fe.

For sample P1 we then have:
      As(⁵⁹Fe) = 10 kBq/kg Fe
      Ac(⁵⁹Fe) = 10 kBq/kg sample

For sample P2:
      A_s(⁵⁹Fe) = 10 kBq/0.7kg = 14.3 kBq/kg Fe
      A_s(⁵¹Cr) = 10 kBq/0.1kg = 100 kBq/kg Cr
      A_c(⁵⁹Fe) = 10 kBq/kg sample
      A_c(⁵¹Cr) = 10 kBq/kg sample
      A_cT         = 20 kBq/kg sample

For sample P3:
      As(⁵⁹Fe) = 10 kBq/0.035 kg Fe = 285.7 kBq/kg Fe
      As(⁵¹Cr) = 10 kBq/0.0316 kg Cr = 216.5 kBq/kg Cr
      Ac(⁵⁹Fe) = 10 kBq/1.2 kg sample = 8.33 kBq/kg sample and/or 10kBq/l sample.
      Ac(⁵¹Cr) = 10 kBq/1.2 kg sample = 8.33 kBq/kg sample and/or 10kBq/l sample
      AcT          = 20 kBq/1.2 kg sample = 16.66 kBq/kg sample and/or 20 kBq/l sample.

Indexes may be omitted when the meaning of the parameters cannot be misunderstood.