Gamma+Spectroscopy+of+NORM+and+TENORM

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Determination of source strength of 241 Am in fire alarms
//Experimental procedure://
 * 1) Mount a metal plate-supported 241 Am fire alarm source on an aluminum ring covered with transparent tape on both sides.
 * 2) Mount the standard source of 241 Am on an aluminum ring with adhesive tape only on one side.
 * 3) Use the two sources and find a suitable counting distance between source and detector (start with a distance of about 5 cm) so that the counting rate is kept at a reasonable and not too high level,
 * 4) Mount the fire alarm source at the decided distance and count the source for 300 s (live-time).
 * 5) Store the spectrum in a dedicated folder on the PC.
 * 6) Mount the standard source in the same position and count for 300 s (live-time).
 * 7) Store the spectrum in the same folder.
 * 8) Use the Maestro program and integrate the photo peaks in both spectra to derive at their respective peak areas.

//Calculations:// The standard source has a known activity **A**s,i at a certain defined date. Let us denote the time from this date until today with **t**d (decay time, in days). One finds the standard source strength today, **A**s,t, by the formula: A_{s,t}=A_{s,i}\cdot e^{-\lambda_t} math || (1) || where λ = ln2/T1/2 for 241Am. Since both sources may be regarded as “mass-less” point sources and the counting geometry is the same for both sources, the total counting efficiencies are identical. Hence, since we in addition perform comparative analysis where the activity of one source is known, knowledge of this total counting efficiency is not needed. We can then put up the following simple relation:
 * math

\frac{S_s}{S_x}=\frac{A_{s,i}\cdot e^{-\lambda_t}}{A_{x,t}} math || (2) ||
 * math

Solved with respect to **A** x ,t,we have: A_{x,t}=\frac{S_x\cdot A_{s,i}\cdot e^{-\lambda t_d}}{S_s} math || (3) ||
 * math

For the calculations Look up the half-life of 241Am from the nuclide chart and obtain the certified activity of the standard source and the certification date from the lab-assistant.


 * ~ Table 1: Data handling and calculations for 241 Am ||
 * Source || Recorded number of counts per 300 s, S || Original decay rate at certification time (Bq) || Decay rate today (Bq) ||
 * Standard || S s = || A s,i = || A s,t = ||
 * Fire alarm || S x = ||  || A x,t = ||

Determination of concentration of KCl in so-called “health salt” – SELTIN
SELTIN is a popular table salt in Norway. It contains substantial amounts of KCl instead of NaCl. In this section we shall determine the specific activity and the activity concentration of 40 K and the fraction of KCl in weight % in SELTIN

M K (g/mol) || Avogadro’s number N A || Natural abundance of 40;K Y K-40 (%) || Branching ratio of 1462 keV, Iabs (%) || Half-life of 40 K T 1/2 (years) ||
 * ~ Table 2: Some physical parameters for 40 K ||
 * Molweight of KCl M KCl (g/mol) || Atomic weight of K
 * 74.551 || 39.1 || 6.023[[image:https://wiki.uio.no/mn/safe/nukwik/images/math/3/6/f/36f8ae4c86b69d52d037a6802d91cc4a.png]]1023 || 0.0117 || 10.7 || 1.28[[image:https://wiki.uio.no/mn/safe/nukwik/images/math/3/6/f/36f8ae4c86b69d52d037a6802d91cc4a.png]]109 ||

Remember in addition that the following relation is generally valid:

D=\lambda\cdot N math || Eqn. 4 || where D = D K-40, N = N K-40 and λ = λ K-40 = ln2/(T 1/2 ) K-40. The general relation between total counting efficiency, decay rate and counting rate is: R=\epsilon_T\cdot D math || Eqn. 5 || ε T is composed of several sub-efficiencies like the intrinsic detector efficiency for this gamma energy ( ε D ), the efficiency due to the sample shape and distance to detector ( ε G ), called geometrical factor efficiency) and the fact that the branching ratio, Iabs, may be less than 100%, i.e. that only a fraction of the decay events leads to emission of the detected gamma ray. For the 1462 keV gamma ray from 40 K, Iabs is found in Table 9. The total counting efficiency for //the gamma energy// 1462 keV, ε D'G //**,**//is independent of the nuclide. Here, we shall use 40 K to determine this efficiency and has to take into account the value of Iabs. Then:
 * math
 * math

\epsilon_T=I_{abs}\cdot\epsilon_{DG} math || Eqn. 6 || When calculating the total counting efficiency for the 1462 keV gamma energy on the basis of recorded counting rate, one has to consider the fact that only 10.7% of the decays result in emission of a gamma ray for the 40K 1462 keV gamma energy (Iabs = 10.7%). The counting efficiency is found from Eqn.6. Since the sample weight and geometry are nearly identical for the two samples, we can suppose that the total counting efficiency, ε//T//, is also the same for both samples. Therefore, the decay rate of 40 K in SELTIN is calculated by the formula:
 * math

\frac{R_{KCl}}{R_s}=\frac{D_{KCl}}{D_s} math || Eqn. 7 || Solving this equation for DS gives: D_s=\frac{D_{KCl}\cdot R_{s}}{R_{KCl}} math || eqn. 8 ||
 * math
 * math

Practical Procedures Since the sample weight and geometry are nearly identical for the two samples, we can suppose that the counting efficiency is also the same for both samples.
 * 1) Start the spectrometer with a preset live-time of 30 min for recording of background.
 * 2) Weigh in a counting sample of KCl (wKCl) in a suitable lid-covered plastic box.
 * 3) Weigh a similar sample of SELTIN (wS) in an identical counting box.
 * 4) If the background counting has not finished already, stop the spectrometer, note the counting time (live-time) tB and store the spectrum in a dedicated file.
 * 5) Mount the KCl-sample, count for a preset time tKCl and store the spectrum in a dedicated file after the spectrometer has stopped.
 * 6) Mount the SELTIN sample, count for a preset time tS and store the spectrum in a dedicated file after end of counting.

Spectra Handeling and Calculations

Determine the net area (S ±σ S) for the 1462 keV gamma peak in the three recorded spectra. Then carry out the calculations to fill into the table below:


 * ~ Table 3. Data handling and calculations for 40 K ||
 * Operations || Result of Operations ||
 * Net area of 1462 keV in background spectrum, S B ±σ SB ||  ||
 * - Counting time t B ||  ||
 * - Background counting rate, R B ±σ SB ||  ||
 * Net area of 1462 keV in KCl spectrum, S KCl ±σ S KCl ||  ||
 * - Counting time t KCl ||  ||
 * - Background-corr. KCl sample counting rate, R KCl ±σ R KCl ||  ||
 * Net area of 1462 keV in SELTIN spectrum, S S ±σ SS ||  ||
 * - Counting time t S ||  ||
 * - Background corr. SELTIN sample counting rate, R S ±σ RS ||  ||
 * Net weight of the KCl-sample, w KCl ||  ||
 * - Weight of K in the KCl sample, w K,KCl ||  ||
 * - Number of K-atoms in the KCl-sample, N K,KCl ||  ||
 * - Number of 40 K atoms in the KCl sample, N K-40,KCl ||  ||
 * - Calculated decay rate of 40 K in the KCl sample, D K-40,KCl ||  ||
 * - Specific activity of 40 K in the KCl sample, A s,KCl ||  ||
 * - Activity concentration of 40 K in the KCl sample, A c,KCl ||  ||
 * - Total counting efficiency of 40 K in KCl sample, ε T,KCl ||  ||
 * - Total counting efficiency of 1462 keV in KCl sample, ε DG,KC l ||  ||
 * Net weight of the SELTIN sample, w S ||  ||
 * - Decay rate of 40 K in the SELTIN sample, D K-40,S ||  ||
 * - Activity concentration of 40 K in the SELTIN sample, A c,S ||  ||
 * - Number of 40 K-atoms in the SELTIN sample, N K-40,S ||  ||
 * - Number of K-atoms in the SELTIN sample, N K,S ||  ||
 * - Weight% of KCl in SELTIN ||  ||
 * - Number of K-atoms in the SELTIN sample, N K,S ||  ||
 * - Weight% of KCl in SELTIN ||  ||

Gamma Spectroscopy on Thorium and Uranium and Progeny

//Procedure:// > a. Uranium oxide of natural uranium isotope composition. > b. Uranium with about 1.5% enrichment in 235 U. > c. Uranium with about 20% enrichment in 235 U. > d. Th(NO 3 ) 2.
 * 1) Record gamma spectra with the NaI(Tl) detector for the following samples and store the spectra in dedicated files:
 * 1) Determine the energies of the strongest peaks and find the corresponding radionuclei. Use the attached spectra and tables.
 * 2) Plot the spectra and attach the plots to this report with energies and radionuclides indicated on the plot.
 * 3) Determine the energy counting efficiency, ε DG, for the energies in the range around 600 keV for a certain counting geometry (ask lab supervisor) by using a standard source of 137 Cs (661.6 keV).
 * 4) Prepare a small piece of native radioactive rock, record its weight and accumulate a gamma spectrum in this counting geometry.
 * 5) Plot the spectrum and find the corresponding radionuclei. Use the attached spectra and tables. Attach the plot to this report.
 * 6) If the activity in the rock is predominantly from 238 U and progeny: Integrate the peak at 609 keV (belonging to 214 Bi) and determine the activity concentration of 214 Ra in the rock. Find necessary data for Iabs in the attached tables.
 * 7) If the activity in the rock is predominantly from 232 Th and progeny: Integrate the peak at 583 keV (belonging to 208 Tl) and determine the activity concentration of 208 Bi in the rock. Find necessary data for Iabs in the attached tables.
 * 8) Make a table of data used and the results achieved for the rock sample.
 * 9) Prepare a counting sample of scale from the North Sea petroleum operations in a small lid-covered plastic container, and determine the net weight.
 * 10) Accumulate a gamma spectrum of the scale sample and determine the energies of the strongest peaks. Attach spectrum.
 * 11) Integrate the 609 keV peak of 214 Bi and determine the activity concentration of 214 Bi in the sample.
 * 12) Make a table of data used and the results achieved for the scale sample.
 * 13) Perform an energy calibration of a HPGe-semiconductor detector. Let the lab supervisor demonstrate the superior energy resolution of this detector for some of the samples analysed with the NaI(Tl)-detector. Determine the gamma energies and the corresponding nuclei. Attach the plots.
 * 14) Compare the HPGe-and NaI(Tl)-spectra: Describe the main differences and indicate advantages and disadvantages with the two detectors for TENORM-containing scale analysis for the petroleum industry.