- Email: [email protected]
Half-life and X-ray emission probabilities of 55Fe
Applied Radiation and Isotopes 53 (2000) 469±472
www.elsevier.com/locate/apradiso
Half-life and X-ray emission probabilities of
55
Fe
Ulrich SchoÈtzig Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116, Braunschweig, Germany Received 13 January 2000; accepted 29 January 2000
Abstract The X-ray emission probabilities of the Mn-Ka and Mn-Kb radiation in the decay of 55 Fe were measured with a calibrated Si(Li) spectrometer, resulting in 0.245(7) and 0.0338(9), respectively. A half-life of 1003.5(21) day was measured using the same detector. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Fe-55; Half-life; X-ray emission probabilities
1. Introduction 55
Fe is used as a calibration nuclide for scintillation and semiconductor detectors and proportional counters; it almost exclusively disintegrates by electron capture decay to the ground state of the stable nuclide 55 Mn: Zlimen et al. (1992) reported on the population of an excited level at 126.0 keV, de-excited by a gamma transition having an emission probability of 1.3(1) 10ÿ9. For the practical work it can thus be assumed that only K X-radiation at about 6 keV from the electron capture process is present, accompanied by emission of Auger electrons and an extremely low portion of inner bremsstrahlung. The L X-rays at about 0.6 keV can usually not be measured by spectrometry with semiconductor detectors. In this work, the K X-ray emission probability was determined spectroscopically with an Si(Li) detector. For this purpose, the activity is needed but dicult to measure, as no gamma radiation is emitted and the usual coincidence counting method cannot be applied. To develop and improve activity measuring techniques for this nuclide, two international comparisons were
E-mail address: [email protected] (U. SchoÈtzig).
carried out. The ®rst was organized by the Bureau International des Poids et Mesures and started in 1979, the results obtained by the various methods beeing published by Smith (1982). As the liquid scintillation technique appeared to become an eective tool for activity determinations, the second comparison was devoted solely to this method and was started in 1996 as the EUROMET 297 project (Cassette et al., 1998). The Radioactivity Group of the PTB participated in both comparisons. Half-life measurements of 55 Fe cannot be carried out with ionization chambers which have an excellent long-term stability, as the radiation of only 6 keV is absorbed in the chamber walls. Detectors with thin entrance windows, like proportional counters or scintillation and semiconductor detectors have therefore to be employed; we used an Si(Li) detector for this measurement. 2. Measurements 2.1. Emission probabilities The Mn K X-ray emission probabilities pKa and pKb at 5.89 and 6.49 keV were determined from the emis-
0969-8043/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 0 0 ) 0 0 1 6 6 - 4
470
U. SchoÈtzig / Applied Radiation and Isotopes 53 (2000) 469±472
sion rates NKi of polyester foil sources with a calibrated Si(Li) spectrometer, the activity A of the radioactive source used and the full energy peak eciencies ei of the spectrometer according to the relation NKi ApKi ei : The speci®c activity of the 55 Fe solution used for the source preparation was determined by liquid scintillation counting according to the CIEMAT/NIST method which is an eciency tracing technique, combining theoretical calculation of the counting eciency and experimental determination of correction factors by means of tracer nuclides, in this case 54 Mn and 3 H: Details of sample composition, scintillator, quenching and the necessary atomic shell data are described in a publication by GuÈnther (1998). With regard to the spread of the results of the international comparison in 1998, referred to in the introduction, the relative standard uncertainty assigned to the activity used in this work was assumed to be nearly 1%. The emission rates were determined from the X-ray spectra by ®tting of a convolution of a Lorentzian and a Gaussian, together with spectral background functions to the Ka =Kb double-peak distribution. The radiative Auger eect (Be et al., 1998) is responsible for additional weak lines in the X-ray spectrum. Searching these lines by ®tting with free parameters did not result in satisfying ®ts, which may also be due to the medium energy resolution of the detector (205 eV at 5.9 keV). Therefore, the portions of the radiative Auger peaks are included in the resulting peak areas. Losses due to dead-time and pile-up eects were corrected for by the pulser method (Debertin and SchoÈtzig, 1977); no correction for real coincidence summing was necessary for this nuclide. Because of the low photon energy, a correction for dierent absorption of the photons in the air between source and detector due to variations of atmospheric pressure, temperature and humidity was necessary; the absorption under normal conditions is included in the eciency calibration. The full-energy peak eciency e of the Si(Li) detector (1.6 cm in diameter, 0.5 cm in length) in the energy region around 6 keV was based on neighbouring eciency points of the K-radiations from the decay of 51 Cr, 54 Mn, 57 Co und 65 Zn, assuming that the self absorption in the dierent sources was nearly identical. The standardization and source preparation of these nuclides was accomplished in our laboratory. The eciency curve was established by ®tting of cubic B-spline functions to the measuring points (Janssen, 1990). The sources were produced by drying of weighed droplets of active solution between two polyester foils (2.2 mg/cm2) sealed by heating. The source-detector distance was 6.5 cm; close to source and detector end cap two Ta collimators (hole diameter 10 mm) were placed, to avoid an unwanted pulse distribution at the low-energy side of the peak due to scattering of the
photons in the source holder. Seven series of measurements were performed, each consisting of six single measurements with measuring times of 30,000 s, yielding the following results for the X-ray emission probabilities per disintegration of 55Fe: p Mn-Ka , 5:89 keV 0:245 7 , ÿ p Mn-Kb , 6:49 keV 0:0338 9 , p Mn-K X, 5:96 keV 0:279 8 : For completeness, the overall K X-ray emission probability pK X is given as the sum of the two single results; the ratio pKb =pKa amounts to 0.138(3). Given in brackets are the standard uncertainties assigned to the results: they include uncertainties from ®t and statistics (1.2%), eciency (2%) and activity measurement (1%). 2.2. Half-life The half-life was determined by spectroscopic measurement of the K X-radiation of three foil sources with the same Si(Li) detector as used for the emission probability measurements. The determination of the area of the Kab double peak was performed by adding up of the channel contents without using a ®t with mathematical functions which yields a lower uncertainty. A preceding auxiliary ®t is necessary only for the determination of the channel-region of interest 23s from the peak centre). Every second month a measurement was performed, each consisting of six single measurements and each with a measuring time of 30,000 s. After three single measurements, the foil sources were positioned upside-down to correct for a possible sag of the polyester foils. The peak areas were determined and corrected for dead-time, pile-up losses and changes of the atmospheric pressure as described in the previous chapter; at the beginning of the measurements in 1987 about 600,000 counts were collected within a single measurement of a measuring time of 30,000 s, and after 12 years, there were still about 30,000 counts. From the peak areas of each of the six single measurements a mean value was formed, so that ®nally 75 measuring points for each of the three sources were available. An exponential function was ®tted to the measured points using the Levenberg± Marquardt algorithm (Janssen, 1995), which resulted in T1=2 1003:5 21 day. The residuals of the ®tting process for one of the three series of measurements are given in Fig. 1. As pointed out in a recent publication (Siegert et al., 1998), the energy-dependent decrease of detector eciencies with time has to be taken into account when
U. SchoÈtzig / Applied Radiation and Isotopes 53 (2000) 469±472
471
Fig. 1. Residuals obtained from a least-squares ®t of Si(Li) spectrometer data taken at 6 keV and using an exponential decay function to calculate the half-life of 55 Fe:
half-lives are determined. For the Si(Li) detector used here, a decrease of about 0.08% per year at an energy of 122 keV was given in that work. A repeated evaluation of 57 Co spectra, taken over a period of 13 years and mentioned in that publication, yielded a decrease of 0.014% per year for the energy of 6.5 keV with an uncertainty being of the same order. This means that an eciency decrease for this energy is not signi®cant; nevertheless all single measurements of 55 Fe were corrected for this nearly negligible eect, resulting in a correction factor of 1.0018 after 12 years. The overall standard uncertainty of 0.21% assigned to the half-life value is calculated by quadratic addition of about 0.1% statistical uncertainty from ®tting of the measured points and from formation of the mean of the series measurements of the three sources, 0.1% from possible changes of the width of the spectral calculation region (region of interest) in the course of time and 0.15% from the correction factor of eciency decrease.
3. Discussion As the decay of 55 Fe is very simple, the K X-ray emission probability pKX can be calculated from the relation pKX PK oK : The K electron-capture probability PK is often determined from a work by Pengra et al. (1972), who measured PL =PK 0:117 1 and PM =PL 0:157 3; according to PEC 1PK 1 PL =PK PL =PK PM =PL , a value of PK 0:8807 9 with a remarkably low uncertainty can be derived. A ®gure of 0.881(4) with a signi®cantly greater uncertainty is extracted from the same publication in a report of the IAEA-TECDOC-619 (1991); we cannot reproduce the calculation leading to this (more realistic) uncertainty value. In a work by SchoÈnfeld (1998), formulae are given to calculate PK from the Q value, binding ener-
gies and tabulated coecients from wave functions, leading to PK 0:8854 16: There are several publications reporting on measurements of the ¯uorescence yield, an evaluated ®gure of oK Mn 0:321 5 is given in a paper by SchoÈnfeld and Janszen (1996). Using this ¯uorescence yield and PK from Pengra et al. (1972) and from SchoÈnfeld (1998), values are obtained which in Table 1 are compared with the measured value. The result of Smith (1982) is extracted from measured data of NKX =A in an international comparison of activity measurements. It should be pointed out that the measured pKX is correlated with the theoretical PK value, as the latter enters into the activity determination; furthermore, a correlation with PK oK values, representing the X-ray emission probabilities of the calibration nuclides which are used for the eciencydetermination process in the 6 keV region (see previous chapter), exists. If the present measured value of pKX is used to calculate the ¯uorescence yield of Mn, a result of 0.315(9) will be obtained when the PK value according to SchoÈnfeld (1998) is used. In the document of IAEA-TECDOC-619 (1991), a 55 Fe half-life of 999(8) day was evaluated and recommended; in the meantime two new measurements were published. The results which are in use today are given in Table 2. The spread of these results is considerable; the dierTable 1 K X-ray emission probability pKX in the decay of
55
Fe
pKX
Comment
0.283(5) 0.283(2) 0.284(5) 0.279(8)
Calculated with PK from Pengra et al. (1972) Calculated by Smith (1982) Calculated with PK from SchoÈnfeld (1998) Measured, this work
472
U. SchoÈtzig / Applied Radiation and Isotopes 53 (2000) 469±472
Table 2 Measurements of the half-life T1=2 of
55
Fe
T1=2 (days)
Author
Method
1000.4(15) 1009.0(17) 977.9(70) 996.8(60) 995(3) 1003.5(21)
Houtermans et al. (1980) Hoppes et al. (1982) Lagoutine and Legrand (1982) Morel et al. (1994) Karmalitsin et al. (1998) This work
PCa PC, Si(Li) PC Planar Ge PC Si(Li)
a
PC = Proportional counter.
ences may possibly be explained by changes of the detection probabilities of the measuring devices with time, or by the presence of unrecognized radioactive impurities which have to be corrected for, when counting integrally. The result determined in this work is compatible within the uncertainty limits with the value given by Houtermans et al. (1980), stating a very low uncertainty, and with that of Morel et al. (1994). Acknowledgements The help of R. DefeÁr in the evaluation of the measurements is acknowledged. References BeÂ, M.-M., LeÂpy, M.-C., Plagnard, J., Duchemin, B., 1998. Measurement of relative X-ray intensity ratios for elements in the 22RZR29 region. Appl. Radiat. Isot. 49, 1367. Cassette, P., Altzitzoglu, T., Broda, R., ColleÂ, R., Dryak, P., De Felice, P., GuÈnther, E., Los Arcos, J.M., Ratel, G., Simpson, B., Verrezen, F., 1998. Comparison of activity concentration measurement of 63 Ni and 55 Fe in the framework of the EUROMET 297 project. Appl. Radiat. Isot. 49, 1403. Debertin, K., SchoÈtzig, U., 1977. Limitations of the pulser method for pile-up corrections in Ge(Li) spectrometry. Nucl. Instr. Meth. 140, 337. GuÈnther, E., 1998. Standardization of the EC nuclides 55 Fe
and 65 Zn with the CIEMAT/NIST tracer method. Appl. Radiat. Isot. 49, 1055. Hoppes, D.D., Hutchinson, J.M.R., Schima, F.J., Unterweger, M.P., 1982. Nuclear data for the eciency calibration of germanium spectrometer systems. NBS Special Publication 626, National Bureau of Standards, Washington, DC. Houtermans, H., Milosevic, O., Reichel, F., 1980. Half-lives of 35 radionuclides. Int. J. Appl. Radiat. Isot. 31, 153. IAEA-TECDOC-619, 1991. X-ray and gamma-ray standards for detector calibration. International Atomic Energy Agency, Vienna. Janssen, H., 1990. Spline techniques for ®tting eciency curves in gamma-ray spectrometry. Nucl. Instr. Meth. Phys. Res. A 286, 398. Janssen H., 1995. FIT9: Ein Dialogprogramm fuÈr die Ausgleichsrechnung nach der Methode der kleinsten Quadrate (A dialog program for ®tting with the leastsquares method). 2nd ed., Laboratory Report PTB-6.31-93 -2/2 (in German), PTB Braunschweig, Germany. Karmalitsin, N.I., Sazanova, T.E., Zanevsky, A.V., Sepman, S.V., 1998. Standardization and half-life measurement of 55 Fe: Appl. Radiat. Isot. 49, 1363. Lagoutine, F., Legrand, J., 1982. PeÂriodes de neuf radionucleÂides. Int. J. Appl. Radiat. Isot. 33, 711. Morel, J., Etcheverry, M., ValleÂe, M., 1994. Emission probabilities of L X-, K X- and g-rays in the 10±130 keV range following the decay of 239 Pu: Nucl. Instr. Meth. A 339, 232. Pengra, J.G., Genz, H., Renier, J.P., Fink, R.W., 1972. Orbital electron-capture ratios in the decay of 55 Fe: Phys. Rev. C 5, 2007. SchoÈnfeld, E., 1998. Calculation of fractional electron capture probabilities. Appl. Radiat. Isot. 49, 1353. SchoÈnfeld, E., Janszen, H., 1996. Evaluation of atomic shell data. Nucl. Instr. Meth. A 369, 527. Siegert, H., Schrader, H., SchoÈtzig, U., 1998. Half-life measurements of Europium radionuclides and the longterm stability of detectors. Appl. Radiat. Isot. 49, 1397. Smith, D., 1982. International comparison of activity measurements of a solution of 55 Fe: Nucl. Instr. Meth. 200, 383. Zlimen, I., Browne, E., Chan, Y., da Cruz, M.T.F., Garcia, A., Larimer, R.M., Lesko, K.T., Norman, E.B., Stokstad, R.G., Wietfeldt, F.E., 1992. Second-forbidden electroncapture decay of 55 Fe: Phys. Rev. C 46, 1136.
www.elsevier.com/locate/apradiso
Half-life and X-ray emission probabilities of
55
Fe
Ulrich SchoÈtzig Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116, Braunschweig, Germany Received 13 January 2000; accepted 29 January 2000
Abstract The X-ray emission probabilities of the Mn-Ka and Mn-Kb radiation in the decay of 55 Fe were measured with a calibrated Si(Li) spectrometer, resulting in 0.245(7) and 0.0338(9), respectively. A half-life of 1003.5(21) day was measured using the same detector. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Fe-55; Half-life; X-ray emission probabilities
1. Introduction 55
Fe is used as a calibration nuclide for scintillation and semiconductor detectors and proportional counters; it almost exclusively disintegrates by electron capture decay to the ground state of the stable nuclide 55 Mn: Zlimen et al. (1992) reported on the population of an excited level at 126.0 keV, de-excited by a gamma transition having an emission probability of 1.3(1) 10ÿ9. For the practical work it can thus be assumed that only K X-radiation at about 6 keV from the electron capture process is present, accompanied by emission of Auger electrons and an extremely low portion of inner bremsstrahlung. The L X-rays at about 0.6 keV can usually not be measured by spectrometry with semiconductor detectors. In this work, the K X-ray emission probability was determined spectroscopically with an Si(Li) detector. For this purpose, the activity is needed but dicult to measure, as no gamma radiation is emitted and the usual coincidence counting method cannot be applied. To develop and improve activity measuring techniques for this nuclide, two international comparisons were
E-mail address: [email protected] (U. SchoÈtzig).
carried out. The ®rst was organized by the Bureau International des Poids et Mesures and started in 1979, the results obtained by the various methods beeing published by Smith (1982). As the liquid scintillation technique appeared to become an eective tool for activity determinations, the second comparison was devoted solely to this method and was started in 1996 as the EUROMET 297 project (Cassette et al., 1998). The Radioactivity Group of the PTB participated in both comparisons. Half-life measurements of 55 Fe cannot be carried out with ionization chambers which have an excellent long-term stability, as the radiation of only 6 keV is absorbed in the chamber walls. Detectors with thin entrance windows, like proportional counters or scintillation and semiconductor detectors have therefore to be employed; we used an Si(Li) detector for this measurement. 2. Measurements 2.1. Emission probabilities The Mn K X-ray emission probabilities pKa and pKb at 5.89 and 6.49 keV were determined from the emis-
0969-8043/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 0 0 ) 0 0 1 6 6 - 4
470
U. SchoÈtzig / Applied Radiation and Isotopes 53 (2000) 469±472
sion rates NKi of polyester foil sources with a calibrated Si(Li) spectrometer, the activity A of the radioactive source used and the full energy peak eciencies ei of the spectrometer according to the relation NKi ApKi ei : The speci®c activity of the 55 Fe solution used for the source preparation was determined by liquid scintillation counting according to the CIEMAT/NIST method which is an eciency tracing technique, combining theoretical calculation of the counting eciency and experimental determination of correction factors by means of tracer nuclides, in this case 54 Mn and 3 H: Details of sample composition, scintillator, quenching and the necessary atomic shell data are described in a publication by GuÈnther (1998). With regard to the spread of the results of the international comparison in 1998, referred to in the introduction, the relative standard uncertainty assigned to the activity used in this work was assumed to be nearly 1%. The emission rates were determined from the X-ray spectra by ®tting of a convolution of a Lorentzian and a Gaussian, together with spectral background functions to the Ka =Kb double-peak distribution. The radiative Auger eect (Be et al., 1998) is responsible for additional weak lines in the X-ray spectrum. Searching these lines by ®tting with free parameters did not result in satisfying ®ts, which may also be due to the medium energy resolution of the detector (205 eV at 5.9 keV). Therefore, the portions of the radiative Auger peaks are included in the resulting peak areas. Losses due to dead-time and pile-up eects were corrected for by the pulser method (Debertin and SchoÈtzig, 1977); no correction for real coincidence summing was necessary for this nuclide. Because of the low photon energy, a correction for dierent absorption of the photons in the air between source and detector due to variations of atmospheric pressure, temperature and humidity was necessary; the absorption under normal conditions is included in the eciency calibration. The full-energy peak eciency e of the Si(Li) detector (1.6 cm in diameter, 0.5 cm in length) in the energy region around 6 keV was based on neighbouring eciency points of the K-radiations from the decay of 51 Cr, 54 Mn, 57 Co und 65 Zn, assuming that the self absorption in the dierent sources was nearly identical. The standardization and source preparation of these nuclides was accomplished in our laboratory. The eciency curve was established by ®tting of cubic B-spline functions to the measuring points (Janssen, 1990). The sources were produced by drying of weighed droplets of active solution between two polyester foils (2.2 mg/cm2) sealed by heating. The source-detector distance was 6.5 cm; close to source and detector end cap two Ta collimators (hole diameter 10 mm) were placed, to avoid an unwanted pulse distribution at the low-energy side of the peak due to scattering of the
photons in the source holder. Seven series of measurements were performed, each consisting of six single measurements with measuring times of 30,000 s, yielding the following results for the X-ray emission probabilities per disintegration of 55Fe: p Mn-Ka , 5:89 keV 0:245 7 , ÿ p Mn-Kb , 6:49 keV 0:0338 9 , p Mn-K X, 5:96 keV 0:279 8 : For completeness, the overall K X-ray emission probability pK X is given as the sum of the two single results; the ratio pKb =pKa amounts to 0.138(3). Given in brackets are the standard uncertainties assigned to the results: they include uncertainties from ®t and statistics (1.2%), eciency (2%) and activity measurement (1%). 2.2. Half-life The half-life was determined by spectroscopic measurement of the K X-radiation of three foil sources with the same Si(Li) detector as used for the emission probability measurements. The determination of the area of the Kab double peak was performed by adding up of the channel contents without using a ®t with mathematical functions which yields a lower uncertainty. A preceding auxiliary ®t is necessary only for the determination of the channel-region of interest 23s from the peak centre). Every second month a measurement was performed, each consisting of six single measurements and each with a measuring time of 30,000 s. After three single measurements, the foil sources were positioned upside-down to correct for a possible sag of the polyester foils. The peak areas were determined and corrected for dead-time, pile-up losses and changes of the atmospheric pressure as described in the previous chapter; at the beginning of the measurements in 1987 about 600,000 counts were collected within a single measurement of a measuring time of 30,000 s, and after 12 years, there were still about 30,000 counts. From the peak areas of each of the six single measurements a mean value was formed, so that ®nally 75 measuring points for each of the three sources were available. An exponential function was ®tted to the measured points using the Levenberg± Marquardt algorithm (Janssen, 1995), which resulted in T1=2 1003:5 21 day. The residuals of the ®tting process for one of the three series of measurements are given in Fig. 1. As pointed out in a recent publication (Siegert et al., 1998), the energy-dependent decrease of detector eciencies with time has to be taken into account when
U. SchoÈtzig / Applied Radiation and Isotopes 53 (2000) 469±472
471
Fig. 1. Residuals obtained from a least-squares ®t of Si(Li) spectrometer data taken at 6 keV and using an exponential decay function to calculate the half-life of 55 Fe:
half-lives are determined. For the Si(Li) detector used here, a decrease of about 0.08% per year at an energy of 122 keV was given in that work. A repeated evaluation of 57 Co spectra, taken over a period of 13 years and mentioned in that publication, yielded a decrease of 0.014% per year for the energy of 6.5 keV with an uncertainty being of the same order. This means that an eciency decrease for this energy is not signi®cant; nevertheless all single measurements of 55 Fe were corrected for this nearly negligible eect, resulting in a correction factor of 1.0018 after 12 years. The overall standard uncertainty of 0.21% assigned to the half-life value is calculated by quadratic addition of about 0.1% statistical uncertainty from ®tting of the measured points and from formation of the mean of the series measurements of the three sources, 0.1% from possible changes of the width of the spectral calculation region (region of interest) in the course of time and 0.15% from the correction factor of eciency decrease.
3. Discussion As the decay of 55 Fe is very simple, the K X-ray emission probability pKX can be calculated from the relation pKX PK oK : The K electron-capture probability PK is often determined from a work by Pengra et al. (1972), who measured PL =PK 0:117 1 and PM =PL 0:157 3; according to PEC 1PK 1 PL =PK PL =PK PM =PL , a value of PK 0:8807 9 with a remarkably low uncertainty can be derived. A ®gure of 0.881(4) with a signi®cantly greater uncertainty is extracted from the same publication in a report of the IAEA-TECDOC-619 (1991); we cannot reproduce the calculation leading to this (more realistic) uncertainty value. In a work by SchoÈnfeld (1998), formulae are given to calculate PK from the Q value, binding ener-
gies and tabulated coecients from wave functions, leading to PK 0:8854 16: There are several publications reporting on measurements of the ¯uorescence yield, an evaluated ®gure of oK Mn 0:321 5 is given in a paper by SchoÈnfeld and Janszen (1996). Using this ¯uorescence yield and PK from Pengra et al. (1972) and from SchoÈnfeld (1998), values are obtained which in Table 1 are compared with the measured value. The result of Smith (1982) is extracted from measured data of NKX =A in an international comparison of activity measurements. It should be pointed out that the measured pKX is correlated with the theoretical PK value, as the latter enters into the activity determination; furthermore, a correlation with PK oK values, representing the X-ray emission probabilities of the calibration nuclides which are used for the eciencydetermination process in the 6 keV region (see previous chapter), exists. If the present measured value of pKX is used to calculate the ¯uorescence yield of Mn, a result of 0.315(9) will be obtained when the PK value according to SchoÈnfeld (1998) is used. In the document of IAEA-TECDOC-619 (1991), a 55 Fe half-life of 999(8) day was evaluated and recommended; in the meantime two new measurements were published. The results which are in use today are given in Table 2. The spread of these results is considerable; the dierTable 1 K X-ray emission probability pKX in the decay of
55
Fe
pKX
Comment
0.283(5) 0.283(2) 0.284(5) 0.279(8)
Calculated with PK from Pengra et al. (1972) Calculated by Smith (1982) Calculated with PK from SchoÈnfeld (1998) Measured, this work
472
U. SchoÈtzig / Applied Radiation and Isotopes 53 (2000) 469±472
Table 2 Measurements of the half-life T1=2 of
55
Fe
T1=2 (days)
Author
Method
1000.4(15) 1009.0(17) 977.9(70) 996.8(60) 995(3) 1003.5(21)
Houtermans et al. (1980) Hoppes et al. (1982) Lagoutine and Legrand (1982) Morel et al. (1994) Karmalitsin et al. (1998) This work
PCa PC, Si(Li) PC Planar Ge PC Si(Li)
a
PC = Proportional counter.
ences may possibly be explained by changes of the detection probabilities of the measuring devices with time, or by the presence of unrecognized radioactive impurities which have to be corrected for, when counting integrally. The result determined in this work is compatible within the uncertainty limits with the value given by Houtermans et al. (1980), stating a very low uncertainty, and with that of Morel et al. (1994). Acknowledgements The help of R. DefeÁr in the evaluation of the measurements is acknowledged. References BeÂ, M.-M., LeÂpy, M.-C., Plagnard, J., Duchemin, B., 1998. Measurement of relative X-ray intensity ratios for elements in the 22RZR29 region. Appl. Radiat. Isot. 49, 1367. Cassette, P., Altzitzoglu, T., Broda, R., ColleÂ, R., Dryak, P., De Felice, P., GuÈnther, E., Los Arcos, J.M., Ratel, G., Simpson, B., Verrezen, F., 1998. Comparison of activity concentration measurement of 63 Ni and 55 Fe in the framework of the EUROMET 297 project. Appl. Radiat. Isot. 49, 1403. Debertin, K., SchoÈtzig, U., 1977. Limitations of the pulser method for pile-up corrections in Ge(Li) spectrometry. Nucl. Instr. Meth. 140, 337. GuÈnther, E., 1998. Standardization of the EC nuclides 55 Fe
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