A+few+Definitions+used+in+this+exercise

Back to Main These definitions are for the lab exercise Natural Occurring Radioactivity

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, dimension 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 contains10 kBq 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 59 Fe and 10 kBq of 51 Cr. P3: A 1L aqueous solution with 100 g dissolved FeCl 3 and 100 g dissolved CrCl 3. This corresponds to 35 g dissolved Fe and 31.6 g dissolved Cr. The solution contains 10 kBq 51 Cr and 10 kBq 59 Fe. For sample P1 we then have: As( 59 Fe) = 10 kBq/kg Fe Ac( 59 Fe) = 10 kBq/kg sample For sample P2: A s ( 59 Fe) = 10 kBq/0.7kg = 14.3 kBq/kg Fe A s ( 51 Cr) = 10 kBq/0.1kg = 100 kBq/kg Cr A c ( 59 Fe) = 10 kBq/kg sample A c ( 51 Cr) = 10 kBq/kg sample AcT = 20 kBq/kg sample For sample P3: As( 59 Fe) = 10 kBq/0.035 kg Fe = 285.7 kBq/kg Fe As( 51 Cr) = 10 kBq/0.0316 kg Cr = 216.5 kBq/kg Cr Ac( 59 Fe) = 10 kBq/1.2 kg sample = 8.33 kBq/kg sample and/or 10 kBq/l sample. Ac( 51 Cr) = 10 kBq/1.2 kg sample = 8.33 kBq/kg sample and/or 10 kBq/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.