Experimental determination of some nuclear decay data in the decays of 177Lu, 186Re and 124I

Applied Radiation and Isotopes 109 (2016) 146–150

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Experimental determination of some nuclear decay data in the decays of 177Lu, 186Re and 124I Aurelian Luca n, Maria Sahagia, Mihail-Razvan Ioan, Andrei Antohe, Beatris Luminita Savu Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, IFIN-HH Bucharest, 30 Reactorului Street, Magurele, Ilfov county, PO Box MG-6, RO 077125, Romania

H I G H L I G H T S








177

Lu, 186Re and 124I studies are necessary for nuclear medicine applications. Accurate nuclear decay data needed for these nuclides were measured. Half-life values were determined using a 4πγ ionization chamber. Photon emission intensities were measured by gamma-ray spectrometry. These new results will be used for future nuclear decay data evaluations.

art ic l e i nf o

a b s t r a c t

Article history: Received 24 March 2015 Accepted 24 November 2015 Available online 2 December 2015

A detailed experimental study of the radionuclides 177Lu, 186Re and 124I was conducted at IFIN-HH, Radionuclide Metrology Laboratory. Absolute photon emission intensities in the decays of these radionuclides were measured by high-resolution gamma-ray spectrometry. Half-life measurements using a well-type ionization chamber were also performed. These new experimental results will be useful for the future updates of the existing nuclear decay data evaluations, offering reliable and accurate data for the users. & 2015 Elsevier Ltd. All rights reserved.

Keywords: Photon emission intensity Gamma-ray spectrometry Half-life 177 Lu 186 Re and 124I

1. Introduction A detailed experimental study of three radionuclides with applications in nuclear medicine, 177Lu, 186Re and 124I, was conducted at IFIN-HH, Radionuclide Metrology Laboratory, in the frame of the joint research project IFA Romania – CEA France no. C2–05/2012 and the national research project CNCS, UEFISCDI, PN-II-ID-PCE2011–3–0070. The main aim of these projects was to obtain new national standards for these emerging pharmaceutical radionuclides. The project IFA-CEA no. C2–05/2012 ended recently and consisted in a successful collaboration with Laboratoire National Henri Becquerel (LNE-LNHB) of CEA-LIST, http://proiecte.nipne.ro/ ifa-cea/3-projects.html. The radioactive solutions used for the studies were purchased from different suppliers: Perkin-Elmer, Netherlands (177Lu), Radioisotope Center POLATOM, Poland (186Re) and ACOM S.p.A., Italy (124I) respectively. The absolute activity standardization of 177Lu, 186Re and 124I radioactive solutions, n

Corresponding author. E-mail address: [email protected] (A. Luca).

http://dx.doi.org/10.1016/j.apradiso.2015.11.072 0969-8043/& 2015 Elsevier Ltd. All rights reserved.

performed using the 4πβ(PC)-γ coincidence method (Ioan et al., 2015; Sahagia et al., 2002, 2016; Kossert et al., 2012; Rezende et al., 2012), allowed the experimental determination of the absolute photon emission intensities for the main gamma-rays and high energy K X-rays in these decays. Half-life measurements were also performed using an ionization chamber. The results obtained are presented below.

2. Photon emission intensity measurements 2.1. Experimental setup The measurements of the photon emission intensities were performed using a calibrated high-resolution gamma-ray spectrometer with a HPGe detector. The experimental system and its calibration, and the software used are described in detail in the article Luca et al. (2012). In each case, from the radioactive solution absolutely standardized in activity, a standard point source – suitable for gamma-ray measurements, was prepared. The 177Lu source was measured in two geometries: directly on

A. Luca et al. / Applied Radiation and Isotopes 109 (2016) 146–150

top of the detector (spectrum acquisition time 15,000 s) and at 94 mm above the detector (27,000 s). The 186Re source was measured at 2 mm above the detector for 18,000 s. The 124I source was measured in two geometries, at 233 mm above the detector, with and without a positron absorber (made of lead and aluminum foils, each one of 1.1 mm thick), with the acquisition times of 19,000 s and 15,000 s, respectively. The second setup was used to determine only the emission intensity of the 511 keV annihilation photons. Besides the impurity correction (described below), other corrections applied to the computations were: background, dead time (pile-up), decay/production of the radionuclide during the measurement time and to the reference time, true coincidence summing and efficiency transfer using GESPECOR – a Monte Carlo simulation software (Sima et al., 2001), fitting process for the deconvolution of the multiplet spectral regions in single peaks (e.g., for K X-rays) and annihilation-in-flight (only for the 511 keV emission intensity – 124I). The pile-up correction was done by the spectrum acquisition software (ORTEC GammaVision) and in all cases it was less than 1.5% (the maximum pile-up corrections for 177 Lu, 186Re and 124I were 1.43%, 1.44% and 0.95%, respectively). The impurity check of the solutions was performed using highresolution gamma-ray spectrometry: while in the 186Re and 124I solutions no impurities were found (within the limits of the Minimum Detectable Activity), the 177Lu solution contained the impurity 177mLu, having a longer half-life, (160.447 0.06) days, according to the evaluation of Kondev (2003). The activity of this impurity was determined by gamma-ray spectrometry, using the specific gamma-ray emission of 228 keV. The activity ratio between 177mLu and 177Lu, R, at the reference time, was: R¼ (0.00012 70.00006). As most of the gamma-ray emissions of 177Lu are common with those of the impurity, the corresponding spectra peaks net areas were corrected before computing the photon emission intensity. 2.2. Results and discussion The measured values of photon emission intensities in the decays of 177Lu, 186Re and 124I are presented in Tables 1, 2 and 3, respectively. These values were computed according to Luca et al. (2012). Relative emission intensities are also given, in order to facilitate the comparison with other published data. The adopted Table 1 Emission intensities (absolute and relative) of the X- and gamma-rays following the 177 Lu decay, measured by using a HPGe gamma-ray spectrometer; the results (absolute values) are compared with the most recent DDEP evaluation published by Kondev (2004). Energy (keV), Radiation

71.64 (γ) 112.95 (γ) 136.72 (γ) 208.37 (γ) 249.67 (γ) 321.32 (γ) 54.61 [XKα2 (Hf)] 55.79 [XKα1 (Hf)] 62.98–63.66 [XK’β1 (Hf)] 64.94–65.32 [XK’β2 (Hf)]

Photon emission intensity-present work

DDEP Evaluation (per 100 disintegrations)

Absolute (per 100 disintegrations)

Relative

0.164 7 0.012 5.9 7 0.6 0.03447 0.0026 10.80 7 0.35 0.1887 0.005 0.2047 0.020 1.56 7 0.20

1.52 (12) 0.1726 (23) 55 (6) 6.20 (7) 0.319 (26) 0.0470 (7) 100 10.38 (7) 1.74 (7) 0.2012 (21) 1.89 (19) 0.216 (8) 59 (10) 1.59 (3)

2.647 0.31

100

0.81 7 0.06

30.7 (42)

0.917 (23)

8.1 (13)

0.245 (8)

0.2157 0.024

2.78 (6)

147

Table 2 Emission intensities (absolute and relative) of the X- and gamma-rays following the 186 Re decay, measured by using a HPGe gamma-ray spectrometer; the results (absolute values) are compared with the most recent DDEP evaluation published by Schönfeld and Dersch (2004). Energy (keV), Radiation

122.33 (γ) 137.16 (γ) 630.32 (γ) 767.48 (γ) 57.98 [XKα2 (W)] 59.32 [XKα1 (W)] 66.95–67.66 [XK’β1 (W)] 69.03–69.48 [XK’β2 (W)] 61.49 [XKα2 (Os)] 63.00 [XKα1 (Os)] 71.08–71.86 [XK’β1 (Os)] 73.32–73.82 [XK’β2 (Os)]

Photon emission intensity-present work

DDEP Evaluation (per 100 disintegrations)

Absolute (per 100 disintegrations)

Relative

0.565 7 0.024 10.127 0.42 0.0265 7 0.0010 0.03127 0.0016 1.617 0.06

5.58 (33) 0.603 (6) 100 9.42 (6) 0.262 (15) 0.0293 (6) 0.308 (20) 0.0327 (6) 59.4 (31) 1.736 (30)

2.717 0.10

100

3.02 (5)

0.8667 0.035

32.0 (17)

1.000 (23)

0.258 7 0.011

9.5 (5)

0.274 (8)

1.0777 0.037

60.8 (29)

1.13 (4)

100

1.94 (6)

1.777 0.06 0.582 7 0.026

32.9 (18)

0.650 (23)

0.202 7 0.009

11.4 (6)

0.182 (8)

energy values are from Kondev (2004), Schönfeld and Dersch (2004) and Katakura and Wu (2008), respectively. In the case of 177Lu, two intensity values for each X-ray/gammaray were computed, based on the measurements performed at close and medium distance from the detector. The adopted intensity values represent the weighted mean of the two experimental values and, together with the assigned standard uncertainties, were calculated using the computer code LWEIGHT version 4 (LNE-LNHB, France). The budget of the individual standard uncertainties included the two types of components, statistic and systematic. For the 177Lu and 186Re photon emission intensity measurements, the most important (relative) uncertainty components are due to the efficiency calibrations (between 2.3% and 5.6%) and counting statistics (peaks net area) – from 0.1% to 6.2%. Other uncertainty components are due to the activity of the standard sources (0.88% for 177Lu and 0.62% for 186Re) and correction factors for decay and true coincidence summing (from 0.01% to maximum 1%). For 124I, the coincidence summing corrections – as multiplicative factors of the efficiency – were computed by GESPECOR, with a number of 107 runs for each set of corrections; these corrections were generally low, in the range from 0.99 to 1.01 (with an estimated standard uncertainty of 0.5%), because the measurements were performed at a higher distance of 233 mm above the detector. As expected for measurements at low distance from the detector, the values of the coincidence summing corrections for 177Lu and 186Re were higher: in the ranges from 0.77 to 1.28 (with one exception stated below) and from 0.87 to 1.09, respectively. Two exceptions must be mentioned, when the coincidence summing corrections (summing-in type) were extremely high, due to the characteristics of the decay schemes: for the gamma-rays of 2294.4 keV (124I decay) and 321.32 keV (177Lu decay), with correction values of 2.04 and 5.60, respectively. The above mentioned standard uncertainties correspond to a coverage factor k ¼1. A similar type of uncertainty budget applies also to the emission intensities of the large number of gamma-rays from the 124I decay, but it must be stated that for very weak emissions, the statistical component of relative uncertainty can go up to 100%.

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Table 3 Emission intensities (absolute and relative) of the gamma-rays following the 124I decay, measured by using a HPGe gamma-ray spectrometer; the results (absolute values) are compared with the experimental values published by Woods et al. (1992). Crt. No. Energy (keV)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

351.47 443.88 511.0 541.19 592.34 602.73 609.92 645.85 662.10 707.46 709.36 713.75 722.78 743.2 776.09 790.76 795.63 876.97 899.43 961.84 968.19 976.35 1045.11 1054.54 1128.58 1205.44 1325.52 1355.20 1368.18 1376.09 1436.64 1445.17 1488.92 1509.36 1560.53 1622.22 1637.43 1675.60 1690.96 1720.21 1752.51 1851.37 1918.56 2038.43 2078.67 2090.94 2098.81 2144.21 2232.03 2283.06 2294.4 2385.10 2453.9 2681.5 2746.9 2987.6

Photon emission intensity-present work Absolute (per 100 disintegrations)

Relative

0.0247 0.010 0.034 7 0.013 41.8 7 1.9 0.202 7 0.012 0.089 7 0.010 62.7 7 2.1 0.1607 0.010 0.9737 0.035 0.049 7 0.007 0.0917 0.010 0.0437 0.007 0.068 7 0.007 10.36 7 0.34 0.0187 0.006 0.0087 0.008 0.0247 0.008 0.0337 0.007 0.022 7 0.009 0.029 7 0.007 0.0137 0.007 0.465 7 0.021 0.1057 0.010 0.436 7 0.022 0.1177 0.015 0.0357 0.011 0.0107 0.006 1.55 7 0.06 0.029 7 0.011 0.2747 0.020 1.80 7 0.07 0.0577 0.016 0.0447 0.015 0.1857 0.018 3.117 0.20 0.1377 0.016 0.0407 0.009 0.1797 0.018 0.1017 0.012 10.8 7 0.8 0.1807 0.017 0.049 7 0.007 0.1887 0.019 0.1737 0.018 0.362 7 0.032 0.326 7 0.028 0.596 7 0.049 0.1467 0.015 0.1037 0.011 0.65 7 0.05 0.667 0.05 0.00777 0.0020 0.01517 0.0049 0.049 7 0.009 0.0322 7 0.0046 0.454 7 0.038 0.00787 0.0030

0.038 (16) 0.054 (21) 66.7 (38) 0.322 (21) 0.142 (16) 100 0.255 (18) 1.55 (8) 0.078 (12) 0.145 (17) 0.069 (11) 0.108 (12) 16.5 (8) 0.029 (9) 0.013 (13) 0.038 (12) 0.053 (12) 0.035 (15) 0.046 (12) 0.021 (11) 0.742 (42) 0.167 (17) 0.695 (42) 0.187 (25) 0.056 (18) 0.016 (9) 2.47 (12) 0.046 (18) 0.437 (35) 2.87 (15) 0.091 (25) 0.070 (24) 0.295 (30) 4.96 (36) 0.219 (26) 0.064 (15) 0.285 (30) 0.161 (21) 17.2 (15) 0.287 (29) 0.078 (12) 0.300 (32) 0.276 (31) 0.58 (6) 0.520 (48) 0.95 (8) 0.233 (24) 0.164 (19) 1.04 (9) 1.05 (9) 0.0123 (32) 0.024 (8) 0.078 (15) 0.051 (8) 0.72 (7) 0.012 (5)

Other values (Woods et al., 1992) [per 100 disintegrations]

0.047 43.2 0.213 0.131 62.9

(11) (8) (4) (8) (6)

0.989(12) 0.055 (8) 0.112 (8) 0.076 (3) 10.34 (13)

0.027 (4) 0.035 (4) 0.020 (4)

0.444 0.103 0.441 0.127 0.050

(7) (4) (11) (8) (6)

1.563 (10) 0.303 1.77 0.09 0.068 0.208 3.23 0.165 0.053 0.214 0.112 11.2 0.17

(9) (2) (3) (13) (6) (5) (6) (3) (10) (8) (3) (4)

The most recent 177Lu and 186Re nuclear decay data evaluations, in the frame of the Decay Data Evaluation Project (DDEP), are available from Kondev (2004) and Schönfeld and Dersch (2004), respectively. Updated evaluations are under preparation, as reported by Kellett (2016). A DDEP data evaluation for 124I is not yet available (August 2015); the ENSDF evaluation by Katakura and Wu (2008) is based on the only two measurements of gamma-ray emission intensities

published: Woods et al. (1992) and Warr et al. (1998) – for absolute and relative values, respectively. Other important experimental results about the 124I nuclear decay scheme were published by Qaim et al. (2007). This work proposes the second dataset of measurements of absolute photon emission intensities in the 124I decay (after Woods et al.), with the advantage that several weak gamma-rays, not reported by Woods et al., are now mentioned. The emission intensity of the main gamma-ray in the 124I decay (602.7 keV) determined was 0.627 70.021, standard uncertainty for k ¼1, in very good agreement with Woods′ value, 0.62970.006 (k ¼1), written in Table 3 as 62.9 (6) per 100 disintegrations. At 1691 keV, the photon interaction by pair production is significant: single and double escape peaks (1180 keV and 669 keV, respectively) were identified in the gamma-ray spectrum. Only a partial correction of this effect was done, and this could be an explanation for the slightly lower result obtained. The experimental points of the efficiency calibration performed in the energy range (59–1408 keV) were fitted with a polynomial curve. The detection efficiency was also calculated by Monte Carlo simulation (MC) in the energy range (351–2987 keV), using the GESPECOR software and the parameters of the HPGe detector, source and measurement geometry. The comparison between the experimental and MC efficiency values has shown an agreement for energies between 351 keV and 1560 keV, within the uncertainties of the experimental values (the experimental values were lower than the MC values with 1% to maximum 10%, the average difference being 6.7%). Based on this comparative study, for gamma-ray energies higher than 1560 keV the authors adopted the efficiencies calculated by Monte Carlo simulation. The corresponding standard uncertainty assigned to the MC efficiency values included a statistical component given by the GESPECOR software (very low, from 0.17% to 0.32%) and a systematic component equal to the uncertainty of the extrapolated experimental efficiency data at 1560.5 keV (fixed value, 7.71%). The Te X-rays peaks were detected with low efficiency in the spectral region (27–32 keV), but the emission intensities were not calculated, because the spectrometer was not calibrated in this low energy region. For future measurements, it is necessary to improve the detection efficiency calibration of the gamma-ray spectrometric system, especially at gamma-ray energies lower than 250 keV. Although characterized by higher standard uncertainties, the absolute photon emission intensities measured during this work are, generally, in good agreement with the DDEP and ENSDF evaluated values and other experimental results published in the literature.

3. Half-life measurements For all three radionuclides, the measurements were done using the ionization chamber (IC) type CENTRONIC IG12/20A, considered the most stable instrument for continuing the measurements for longer periods of time. The half-life was fitted for each data set of the radionuclides using a linear least-squares method (Luca et al., 2012). An equation in a semi-logarithmic presentation was used to fit the experimental data:

log10 (I ) = log10 (I0 ) − 0.30103⋅

t T1/2

(1)

I is the corrected data for the IC ionization current (in pA), recorded at a given time t after the reference time t0, and I0 is the ionization current at the reference time; t and T1/2 (the half-life of the considered radionuclide) are both expressed in days (d).

A. Luca et al. / Applied Radiation and Isotopes 109 (2016) 146–150

3.1.

124

I half-life determination

The published recommended half-life value is: (4.176070.0003) days (Katakura and Wu, 2008). In this case, the half-life was determined starting with the reference date, 28.10.2013, 10:00 UTC. A vial containing 5 ml of solution was measured in the ionization chamber for a 18.04 days period (4.32 half-lives), obtaining 25 experimental points. The ionization current values were calculated as means of 10 readings and background was subtracted; it varied between 661.4 pA and 33.07 pA. No impurity level higher than 0.0001 was found. The determined value of the half-life from the data fitting was T1/2 ¼(4.175870.0014) days. Uncertainty budget: Statistical uncertainty of the fitting: uA ¼0.0012 days; uncertainty due to background: uB ¼0.0007 days. Like in the case of 177Lu and 186 Re (below, in Sections 3.2 and 3.3), two other uncertainty components, due to the time measurement and ionization chamber stability, were estimated to be less than 0.01% and were neglected. The determined value is consistent with the published. 3.2.

177

Lu half-life determination

The published recommended half-life value is: T1/2 ¼(6.647 70.004) days (Kondev, 2004). The measurements started at the arrival of the ampoule in the laboratory (4th of July 2013) and lasted 15 days (more than two half-lives). The ionization current of the chamber varied between 1419 pA and 305 pA, within a 14.8 day interval, with a total number of 23 experimental points registered. The current values were calculated as the means of 10 readings and the background value of 0.1 pA was subtracted. As stated in Section 2.1, the 177mLu impurity content, determined by gamma-ray spectrometry, was ALu  177m/ALu  177 ¼(0.00012 70.00006), on the reference time (10 July 2013 12:00 UTC), corresponding to ALu  177m/ALu-177 ¼(0.000066 7 0.000033), on the start of measurements. The first step was to quantify the influence of the impurity over the ionization current due to 177Lu alone, according to the following relations:

I = ILu − 177 + ILu − 177m = (εN )Lu − 177 ALu − 177 + (εN )Lu − 177m ALu − 177m ILu − 177 =

I 1 + ⎡⎣ (εN )Lu − 177m / (εN )Lu − 177⎤⎦ ⎡⎣ ALu − 177m / ALu − 177 ⎤⎦

(2)

(3)

In Relations (2) and (3), I are the ionization currents in pA, εN are the efficiency values of the CENTRONIC IG12/20 A ionization chamber, expressed in pA MBq  1 and ALu  177m/ALu  177 is the impurity content. The calculated efficiency for 177Lu was ( εN )Lu  177,5ml ¼(1.5727 0.047) pA MBq  1 (Sahagia et al., 2005; Ioan et al., 2015), for a 5 ml solution volume, based on the calibrations of the chamber for other radionuclides, and using the general formula written by Schrader (Schrader, 2007):

εN = pβ εβ +

∑ pi (Ei )εi (Ei ) i

(4)

This calculated value is in good agreement with the experimentally determined calibration factor: FLu  177, 5ml ¼(1.560 70.016) pA MBq  1, Ioan et al. (2015). The efficiency of the chamber for 177mLu was calculated in a similar way as for 177Lu, taking into consideration the decay scheme from Kondev (2003). 177mLu decays by beta minus (78.6%) to 177Hf, with emission of a beta spectrum with mean energy of 40.82 keV, followed by the emission of a very complex gamma-ray spectrum, from 55 keV up to 466 keV, with a mean value of Eγ ¼238.82 keV and total intensity of 3.1647 radiations per decay. It decays also by isomer transition (21.4%) to 177Lu, with the emission

149

of gamma-rays within the interval 115 keV up to 414 keV, with a mean energy Eγ ¼292.66 keV and a total intensity of 0.5348 radiations per decay. Applying the formula (4) and the IC efficiency curve parameters from Sahagia et al. (2012), the following value was found: ( εN )Lu  177m,5ml ¼34.66 pA MBq  1. The estimated uncertainty is maximum uc ¼1.04 pA MBq  1. Relation (3). becomes:

ILu − 177 =

I 1 + 22.05⋅[ALu − 177m /ALu − 177 ]

(5)

Relation (5). shows that the impurity contribution is amplified by the efficiencies’ ratio and grows in time due to the growing of the activities’ ratio. These considerations suggest that by operating impurity corrections, one gets: (i) the calculated half-life values will diminish; (ii) the correct half-life value is obtained when the impurity level is precisely determined. These results agree with the interpretation of the impurity role in the measurement of 57Co by ionization chamber at the BIPM during the key comparison BIPM.RI(II)-K1.Co-57 (Michotte et al., 2012). Taking into account the value ALu − 177m /ALu − 177 ¼ (0.000066 70.000033), the obtained result for the 177Lu half-life was T1/2 ¼6.675 (3) days. The experimental 177Lu decay graph (with linear fitting and regular residuals), according to Eq. (1), is presented in Fig. 1. The activity was re-measured after almost one year, a time long enough for 177Lu to decay completely. Two VYNS sources were measured together by the 4πPC(β)-γ coincidence method. The new determination corresponds to the impurity level on the start of ionization current measurements of ALu  177m/ALu  177 ¼0.0001957 0.000020. The calculation of the half-life was repeated with this impurity content by the use of Relation (5), resulting a value of (6.64570.017) days. The reported half-life was computed as the arithmetic mean of the two values from above. Uncertainty budget: Statistical uncertainty of the fitting: uA ¼ 0.004 days; uncertainty due to impurity determination: uB ¼0.017 days, calculated from uncertainty propagation of the mean impurity content. The final result for 177Lu half-life is: T1/2 ¼(6.660 70.017) days. Comments: This new value differs from the published value by [ þ0.013 days (þ0.20)%], within the limit of comparison uncertainty. From these calculations one may see the importance of precise determination of impurity level when the instrument used in measurement is much more sensitive to their radiations, by comparison with the base radionuclide. Despite the short period of measurements (about 2 half-lives) and the impurity influence, the obtained half-life uncertainty is competitive, mainly because a high number of experimental points were registered. 3.3.

186

Re half-life determination

The published recommended value of the 186Re half-life is T1/2 ¼(3.71867 0.0017) days (Schönfeld and Dersch, 2004). In this case, the half-life was determined starting with the reference date, 28.10.2013, 12:00 UTC. A vial containing 5 ml of solution was measured in the ionization chamber for a 17.8 days (4.79 half-lives) period, in a similar way as in the case of 177Lu, obtaining 24 experimental points. The ionization current values were calculated also as means of 10 readings and background was subtracted; it varied between 74.44 pA and 2.70 pA. No impurity level higher than 0.0001 was found. The determined value of the half life from the fitting of data was: T1/2 ¼ (3.7160 70.0024) days.

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In the case of 177Lu, the 177mLu impurity correction was applied and proved the importance of its precise determination.

Acknowledgments This work was funded by the joint research project IFA Romania – CEA France No. C2-05/2012 and the Romanian National Research Project PN-II-ID-PCE-2011-3-0070, in the frame of the Program IDEI coordinated by CNCS, UEFISCDI. The authors are grateful to Prof. Octavian Sima (University of Bucharest, Romania) for his support regarding the use of the GESPECOR software for this work.

References

Fig. 1. The ionization chamber current intensity data (linear fitting and regular residuals), following the 177Lu source decay corrected for the 177mLu impurity contribution (I, expressed in pA, is the current intensity).

Uncertainty budget: Statistical uncertainty of the fitting: uA ¼0.0017 days; uncertainty due to background: uB ¼0.0017 days. The uncertainty is higher than in the case of 124I due to the lower ionization current measured values. The determined halflife value is consistent, within the combined uncertainties, with the evaluation.

4. Conclusions The photon emission intensity and half-life values (of the order of days), were determined for three radionuclides important for the nuclear medicine, 124I, 177Lu and 186Re, by using a calibrated high-resolution gamma-ray spectrometer and the ionization chamber type CENTRONIC IG12/20A.

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