Analysis of a neutron-induced conversion electron spectrum of gadolinium

A 100-nm-thick gadolinium layer deposited on a pixelated silicon sensor was activated in a neutron field to measure the internal conversion electron (ICE) spectrum generated by neutron capture products of ¹⁵⁵Gd and ¹⁵⁷Gd. The experiment was performed at the ISIS neutron and muon facility, using a bespoke version of the HEXITEC spectroscopic imaging camera. Signals originating from internal conversion electrons, Auger electrons, x rays and gamma rays up to 150 keV were identified. The ICE spectrum has an energy resolution of 1.8-1.9 keV at 72 keV and shows peaks from the K, L, M, N+ ICEs of the 79.51 keV and 88.967 keV 2⁺-0⁺ gamma transitions from the first excited states in ¹⁵⁸Gd and ¹⁵⁶Gd, respectively, as well as the K ICEs of the 4⁺-2⁺ transitions at 181.931 keV and 199.213 keV from the respective second excited states. Spectrum analysis was performed using a convolution of a Gaussian with exponential functions at the low and high energy side as the peak shaping function. Relative ICE intensities were derived from the fitted peak areas and compared with internal conversion coefficient (ICC) values calculated from the BrIcc database. Relative to the dominant L shell contribution, the K ICE intensity conforms to BrIcc and the M, N, O+ ICE intensities are somewhat higher than expected.

Standardisation of 241Am activity for a key comparison

The JRC applied six measurement techniques to standardise the activity of an 241Am solution in the frame of the 2003 key comparison CCRI(II)-K2.Am-241. The methods used were alpha-particle counting at a defined small solid angle, high-efficiency particle and photon counting with a windowless 4π CsI(Tl) sandwich spectrometer, 4π alpha counting with a pressurised proportional counter, alpha-gamma coincidence counting and sum counting with a small pressurised proportional counter and a NaI(Tl) well detector, and 4π counting with a liquid scintillation counter. All results were consistent and an unusually low measurement uncertainty of 0.054% was achieved. An overview is presented of the outcome of the key comparison exercise, which demonstrates international equivalence.

Measurement of the 145Sm half-life

The half-life of ¹⁴⁵Sm has been measured by means of the reference source method with a HPGe detector. The long-lived radionuclide ⁴⁴Ti was mixed into the source for reference. The time-dependency of the ¹⁴⁵Sm/⁴⁴Ti activity ratio was followed by assessing the count-rate ratio of their characteristic gamma-ray emissions at 61.2 keV (¹⁴⁵Sm) and 67.9/78.3 keV (⁴⁴Ti) in spectra recorded over periods of typically one day. In total, 220 measurements were performed over a period of 384 days or about one half-life period. The experiment and ensuing uncertainty budget are discussed in detail. Different error propagation is applied for random uncertainties, autocorrelated structures in the fit residuals, and potential systematic errors. The result for the ¹⁴⁵Sm half-life, 345 (16) d, is compatible with the scarce literature values, however the experimental details of the old measurements were barely documented.

On the interpretation of annual oscillations in 32Si and 36Cl decay rate measurements

The 32Si decay rate measurement data of Alburger et al. obtained in 1982-1986 at Brookhaven National Laboratory have been presented repeatedly as evidence for solar neutrino-induced beta decay. The count rates show an annual sinusoidal oscillation of about 0.1% amplitude and maximum at February-March. Several authors have claimed that the annual oscillations could not be explained by environmental influences on the set-up, and they questioned the invariability of the decay constant. They hypothesised a correlation with changes in the solar neutrino flux due to annual variations in the Earth-Sun distance, in spite of an obvious mismatch in amplitude and phase. In this work, environmental conditions at the time of the experiment are presented. The 32Si decay rate measurements appear to be inversely correlated with the dew point in a nearby weather station. Susceptibility of the detection set-up to local temperature and humidity conditions is a likely cause of the observed instabilities in the measured decay rates. Similar conclusions apply to 36Cl decay rates measured at Ohio State University in 2005-2012.

Alpha-particle emission probabilities of 231Pa derived from first semiconductor spectrometric measurements

The nuclide ²³¹Pa is a member of the ²³⁵U decay chain. It is a complex alpha emitter with 25 identified alpha emissions. Formerly published alpha-particle emission probabilities were derived from measurements taken with magnetic spectrometers. This work presents the first measurements made with semiconductor detectors. High-resolution alpha-particle spectrometry was carried out at CIEMAT and JRC using ion-implanted planar silicon detectors. Alpha-particle emission probabilities of 23 transitions were derived from deconvolutions of the spectra. For the major lines, uncertainties are lower than 1%, a significant improvement to existing data. The new data set will allow a more accurate evaluation of the decay scheme of ²³¹Pa.

Conversion electron spectroscopy of the 59.54 keV transition in 241Am alpha decay

A windowless Peltier-cooled silicon drift detector (SDD) was used to measure internal conversion electron (ICE) spectra of thin ²⁴¹Am sources. The ICE peaks associated with the 59.54 keV gamma transition in ²³⁷Np were deconvoluted and relative ICE intensities were derived from the fitted peak areas. Corrections were made for energy dependence of the full-energy-peak counting efficiency, based on Monte Carlo simulations. As expected for this anomalous E1 transition, a significant discrepancy was found with the theoretical internal conversion coefficient (ICC) values calculated from the BrIcc database. Penetration effects are known to cause such anomalies in highly retarded transitions. The measured ICE intensities are in good agreement with a specific combination of literature data obtained with magnetic spectrometers.

Automated optical distance measurements for counting at a defined solid angle

Two optical distance measurement devices have been compared for accurately defining the source-detector geometry of alpha-particle counters. The first consists of a travelling microscope with unifocal lens, to which a linear distance gauge is attached. The focusing is done by human eye. The second is a modern 3D coordinate measurement machine, equipped with a CMOS colour camera as the sensor. Focusing is performed automatically by software. With both devices, distance measurements of various drop-deposited sources on glass and stainless steel disks have been performed. There is a good mutual agreement of results. Even though the new device can sample more reference points, the accuracy of the measurements has not improved drastically due to the imperfect flatness of the sources. The main advantages of the new system are its ease of use and the lower health risk involved due to the larger distance between the performer and the source.

Two-step transplantation with adipose tissue-derived stem cells increases follicle survival by enhancing vascularization in xenografted frozen-thawed human ovarian tissue

STUDY QUESTION

Do adipose tissue-derived stem cells (ASCs) enhance vascularization and follicle survival in xenografted ovarian tissue using a two-step transplantation approach?

SUMMARY ANSWER

Higher rates of oxygenation and vascularization of ovarian tissue, as well as increased follicle survival rates, were detected in the early post-grafting period.

WHAT IS KNOWN ALREADY

ASCs have multilineage differentiation potential, proangiogenic properties and enhance vascularization in a peritoneal grafting site. Some studies suggest that using ASCs may improve ovarian tissue quality by enhancing graft angiogenesis.

STUDY DESIGN, SIZE, DURATION

A total of 15 severe combined immunodeficient (SCID) mice were intraperitoneally grafted with frozen-thawed human ovarian tissue (OT) from five different patients. A peritoneal transplantation site had been previously prepared in a first step using either empty fibrin (Fi+OT group [n = 5]) or ASC-loaded fibrin (Fi/ASCs+OT group [n = 5]) for 14 days prior to grafting. Five mice underwent the standard one-step transplantation procedure and served as controls (OT group). Lithium phthalocyanine (LiPc) crystals were inserted into all grafted human ovarian tissue before transplantation. Levels of partial pressure of oxygen (pO2) in grafts were monitored in vivo by electron paramagnetic resonance (EPR) oximetry on Days 3 and 7. Samples for histology and immunohistochemistry (IHC) were collected after euthanizing the mice on Day 7 following EPR. One piece of ovarian tissue per patient was fixed for analysis to serve as non-grafted controls.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Prospective experimental study conducted at the Gynecology Research Unit, Université Catholique de Louvain. All materials were used to perform pO2 measurements (EPR oximetry), histological (haematoxylin and eosin staining), immunohistochemistry (anti-mouse and human double CD34 and anti-human Ki-67) and TUNEL analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

A significant increase in pO2 was observed in all groups between Days 3 and 7 (P < 0.001). A significantly higher pO2 level was observed in the Fi/ASCs+OT group compared to the OT group on Day 7 (P = 0.028). Total CD34-positive vessel area on Day 7 was greater in the Fi/ASCs+OT group than in any other group (vs non-grafted group: P = 0.0014; vs OT group: P = 0.013; vs Fi+OT group: P = 0.018). Primordial follicle survival rates after grafting were higher in the Fi/ASCs+OT group than in the OT (P = 0.0059) or Fi+OT groups (P = 0.0307). TUNEL-positive follicle percentages after grafting were significantly lower in the Fi/ASCs+OT group than in any other grafted tissue (vs OT group: P = 0.045; vs Fi+OT group: P = 0.0268). Percentages of Ki-67-positive primordial follicles were significantly higher in all grafted groups compared to non-grafted tissue controls (P < 0.01).

LIMITATIONS REASONS FOR CAUTION

As demonstrated by our results, the proposed two-step ovarian tissue transplantation procedure using ASCs enhances vascularization in the early post-grafting period, leading to increased follicle survival rates and decreased apoptosis. However, mechanisms involved in the proangiogenic behavior of ASCs remain to be elucidated.

WIDER IMPLICATIONS OF THE FINDINGS

Our results suggest that the proposed transplantation procedure with ASCs is a promising step towards potentially solving the problem of massive follicle loss after ovarian tissue grafting.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS-PDR Convention T.0077.14, grant Télévie No. 7.6515.16 F to DDM and grant 5/4/150/5 awarded to MMD and CAA is research associate, FRS-FNRS), Fonds Spéciaux de Recherche, Fondation St Luc, and Foundation Against Cancer, and donations from the Ferrero family.

The 55Fe half-life measured with a pressurised proportional counter

The half-life of ⁵⁵Fe has been measured accurately by following the decay curve of three sources with a large pressurised proportional counter. An argon(90%)-methane(10%) mixture was used as counter gas, at atmospheric pressure (∼1 × 10⁵ Pa) and at enhanced pressures of 5 × 10⁵ Pa and 8 × 10⁵ Pa (for 1 source), respectively. The first measurements were performed in 2001, but the experiment was executed more systematically between 2005 and 2018, covering a period of about 5 half-lives. The residuals from an exponential decay curve were of the order of 0.1% to 0.2% at 1 × 10⁵ Pa, and 0.03% at 5 × 10⁵ Pa and 8 × 10⁵ Pa. The gain of stability with increased gas pressure was due to asymptotically reaching the maximum counting efficiency, resulting in lower sensitivity to pressure variations. The deduced half-life value of T_1/2(⁵⁵Fe) = 1006.70 (15) d or 2.7563 (4) a is more accurate than other data in literature, which are mutually discrepant. It is consistent with previous measurements at JRC with an X-ray defined solid angle counter.

Linearity check of an ionisation chamber through 99 mTc half-life measurements

The half-life of ^99 mTc was measured at the JRC using the ionisation chamber 'IC1' (type Centronic IG12). The result, T_1/2(^99 mTc) = 6.00660 (18) h, is in good agreement with literature data. One experiment was performed in IC1's default set-up with the ionisation current being integrated over an air capacitor and read out as a voltage increase over time. This ensured excellent linearity and precision throughout the dynamic range, but the maximum current was limited to 2 nA. In a second test, the current was directly read out with a Keithley 6517 A electrometer. Applying correction factors for the automatic range switching of the electrometer, an acceptable linearity was demonstrated over a range of 12 half-life periods starting at 20 nA. Range switching and autocorrelation of the current readout increase the systematic and random error propagation factors. Piecewise fitting of the decay curve over periods of 6 h yields the same ^99 mTc half-life value within 0.04% (0.0025 h) standard deviation over an activity range spanning at least 10 half-life periods (3 orders of magnitude).

Measurement of absolute γ-ray emission probabilities in the decay of 235U

Accurate measurements were performed of the photon emission probabilities following the α decay of ²³⁵U to ²³¹Th. Sources of highly enriched ²³⁵U were characterised in terms of isotopic composition by mass spectrometry and their activities were standardised by means of alpha-particle counting at a low defined solid angle. The standardised sources were subsequently measured by high-resolution γ-ray spectrometry with calibrated high-purity germanium detectors to determine the photon emission probabilities. Four laboratories participated in this work and reported emission probabilities for 33 γ-ray lines. Most of them agree with previously published evaluated data. In addition, new values are proposed for γ-lines which have been measured only once in the past.

Deconvolution of 238,239,240Pu conversion electron spectra measured with a silicon drift detector

Internal conversion electron (ICE) spectra of thin ^238,239,240Pu sources, measured with a windowless Peltier-cooled silicon drift detector (SDD), were deconvoluted and relative ICE intensities were derived from the fitted peak areas. Corrections were made for energy dependence of the full-energy-peak counting efficiency, based on Monte Carlo simulations. A good agreement was found with the theoretically expected internal conversion coefficient (ICC) values calculated from the BrIcc database.

Is decay constant?

Some authors have raised doubt about the invariability of decay constants, which would invalidate the exponential-decay law and the foundation on which the common measurement system for radioactivity is based. Claims were made about a new interaction - the fifth force - by which neutrinos could affect decay constants, thus predicting changes in decay rates in correlation with the variations of the solar neutrino flux. Their argument is based on the observation of permille-sized annual modulations in particular decay rate measurements, as well as transient oscillations at frequencies near 11 year^-1 and 12.7 year^-1 which they speculatively associate with dynamics of the solar interior. In this work, 12 data sets of precise long-term decay rate measurements have been investigated for the presence of systematic modulations at frequencies between 0.08 and 20 year^-1. Besides small annual effects, no common oscillations could be observed among α, β^-, β⁺ or EC decaying nuclides. The amplitudes of fitted oscillations to residuals from exponential decay do not exceed 3 times their standard uncertainty, which varies from 0.00023 % to 0.023 %. This contradicts the assertion that 'neutrino-induced' beta decay provides information about the deep solar interior.

Direct measurement of alpha emission probabilities in the decay of 226Ra

High-resolution alpha-particle spectrometry was performed to determine the main alpha-particle emission probabilities in the decay of ²²⁶Ra. Thin, homogeneous sources were prepared by electrodeposition on stainless steel disks. Alpha spectra with an energy resolution of 20keV were obtained in three laboratories and analysed with different deconvolution algorithms. In two set-ups, a magnet system was used to deflect conversion electrons to avoid their coincidental detection with the alpha particles. Spectra taken at close range without a magnet system yielded biased results which cannot be fully compensated by statistical corrections for coincidence summing. The derived emission probabilities of the three main alpha decays are 94.07 (1)%, 5.93 (1)%, and 0.0059 (15)%, respectively. They are in excellent agreement with calculated values derived from the P(γ+ce) decay scheme balance, which solves the existing discrepancy problem with two previous direct measurements published in literature.

Evidence against solar influence on nuclear decay constants

The hypothesis that proximity to the Sun causes variation of decay constants at permille level has been tested and disproved. Repeated activity measurements of mono-radionuclide sources were performed over periods from 200 days up to four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and are attributable to instabilities in the instrumentation and measurement conditions. The most stable activity measurements of alpha, beta-minus, electron capture, and beta-plus decaying sources set an upper limit of 0.0006% to 0.008% to the amplitude of annual oscillations in the decay rate. Oscillations in phase with Earth's orbital distance to the Sun could not be observed within a 10^-6 to 10^-5 range of precision. There are also no apparent modulations over periods of weeks or months. Consequently, there is no indication of a natural impediment against sub-permille accuracy in half-life determinations, renormalisation of activity to a distant reference date, application of nuclear dating for archaeology, geo- and cosmochronology, nor in establishing the SI unit becquerel and seeking international equivalence of activity standards.

Fundamental uncertainty equations for nuclear dating applied to the 140Ba-140La and 227Th-223Ra chronometers

Basic equations for age dating through activity ratio measurements are presented and applied to nuclear chronometers based on parent-daughter decay. Uncertainty propagation formulae are derived which relate the relative uncertainty on the half-lives and measured activity ratios with the relative uncertainty on the calculated time of a nuclear event. Particular attention is paid to the case of relatively short-lived radionuclides for which the change in decay rate during the measurement is non-negligible. Mathematical solutions are presented to correct the perceived activity ratio and adapt the uncertainty propagation formulae to complete the uncertainty budget. The formulae have been applied to ¹⁴⁰Ba-¹⁴⁰La chronometry, which is particularly useful for dating a nuclear explosion through measurement of the produced activity ratio of ¹⁴⁰La and ¹⁴⁰Ba in a finite time interval. They were also applied to the ²²⁷Th-²²³Ra parent-daughter pair produced for therapeutic use. The impact of inaccuracies in the nuclear decay data on the performance of these nuclear chronometers is shown and discussed.

Conversion electron spectrometry of Pu isotopes with a silicon drift detector

An electron spectrometry set-up was built at IRMM consisting of a vacuum chamber with a moveable source holder and windowless Peltier-cooled silicon drift detector (SDD). The SDD is well suited for measuring low-energy x rays and electrons emitted from thin radioactive sources with low self-absorption. The attainable energy resolution is better than 0.5keV for electrons of 30keV. It has been used to measure the conversion electron spectra of three plutonium isotopes, i.e. (238)Pu, (239)Pu, (240)Pu, as well as (241)Am (being a decay product of (241)Pu). The obtained mixed x-ray and electron spectra are compared with spectra obtained with a close-geometry set-up using another SDD in STUK and spectra measured with a Si(Li) detector at IRMM. The potential of conversion electron spectrometry for isotopic analysis of mixed plutonium samples is investigated. With respect to the (240)Pu/(239)Pu isotopic ratio, the conversion electron peaks of both isotopes are more clearly separated than their largely overlapping peaks in alpha spectra.

Confirmation of 20% error in the (209)Po half-life

First results of a half-life measurement of (209)Po show 20% discrepancy with the formerly recommended value of 102 (5) years, which was based on a single experiment performed in 1956. After one year of measurement, a statistical uncertainty on T1/2 of 3.5% has been reached and effects of long-term instability are assumed to be less than 5%. The preliminary half-life value obtained in this work, 120 (6) years, supports the newly determined value of 125.2 (33) years by Collé et al. (2014). The 20% error in the half-life has an impact on numerous measurements in which aged (209)Po solutions were used as a tracer.

Improved peak shape fitting in alpha spectra

Peak overlap is a recurrent issue in alpha-particle spectrometry, not only in routine analyses but also in the high-resolution spectra from which reference values for alpha emission probabilities are derived. In this work, improved peak shape formulae are presented for the deconvolution of alpha-particle spectra. They have been implemented as fit functions in a spreadsheet application and optimum fit parameters were searched with built-in optimisation routines. Deconvolution results are shown for a few challenging spectra with high statistical precision. The algorithm outperforms the best available routines for high-resolution spectrometry, which may facilitate a more reliable determination of alpha emission probabilities in the future. It is also applicable to alpha spectra with inferior energy resolution.

Half-lives of 221Fr, 217At, 213Bi, 213Po and 209Pb from the 225Ac decay series

The half-lives of (221)Fr, (217)At, (213)Bi, (213)Po, and (209)Pb were measured by means of an ion-implanted planar Si detector for alpha and beta particles emitted from weak (225)Ac sources or from recoil sources, which were placed in a quasi-2π counting geometry. Recoil sources were prepared by collecting atoms from an open (225)Ac source onto a glass substrate. The (221)Fr and (213)Bi half-lives were determined by following the alpha particle emission rate of recoil sources as a function of time. Similarly, the (209)Pb half-life was determined from the beta particle count rate. The shorter half-lives of (217)At and (213)Po were deduced from delayed coincidence measurements on weak (225)Ac sources using digital data acquisition in list mode. The resulting values: T1/2((221)Fr)=4.806 (6) min, T1/2((217)At)=32.8 (3)ms, T1/2((213)Bi)=45.62 (6)min, T1/2((213)Po)=3.708 (8) μs, and T1/2((209)Pb)=3.232 (5)h were in agreement only with the best literature data.

Decay data measurements on 213Bi using recoil atoms

In this work, (213)Bi has been separated from an open (225)Ac source by collecting recoil atoms onto a glass plate in vacuum. The activity of such recoil sources has been measured as a function of time, using an ion-implanted planar Si detector in quasi-2π geometry. From these measurements, a new half-life value of T1/2((213)Bi)=45.62 (6)min was derived. Additionally, high-resolution alpha-spectrometry measurements were performed at a solid angle of 0.4% of 4πsr, to verify the energies and emission probabilities of the α-emissions from (213)Bi. Using (225)Ac, (221)Fr, (217)At and (213)Po peaks as reference peaks, the measured (213)Bi α-peak energies at Eα,0=5878 (4)keV and Eα,1=5560 (4)keV were about 10keV higher than validated data. The relative α-particle emission probabilities of (213)Bi, Pα,0=0.9155 (11) and Pα,1=0.0845 (11), and the (213)Bi alpha branching factor, Pα=1-Pβ=2.140 (10)%, are compatible with recommended values, but have a higher accuracy.

Measurement of the 225Ac half-life

The (225)Ac half-life was determined by measuring the activity of (225)Ac sources as a function of time, using various detection techniques: α-particle counting with a planar silicon detector at a defined small solid angle and in a nearly-2π geometry, 4πα+β counting with a windowless CsI sandwich spectrometer and with a pressurised proportional counter, gamma-ray spectrometry with a HPGe detector and with a NaI(Tl) well detector. Depending on the technique, the decay was followed for 59-141 d, which is about 6-14 times the (225)Ac half-life. The six measurement results were in good mutual agreement and their mean value is T(1/2)((225)Ac)=9.920 (3)d. This half-life value is more precise and better documented than the currently recommended value of 10.0 d, based on two old measurements lacking uncertainty evaluations.

The use of solid angle for alpha detector efficiency in 226Ra analyses of soil samples

In the frame of proficiency tests organized by IAEA and IRMM, the specific activity concentration of radium-226 in soil has been measured. The BaSO(4) co-precipitation technique has been used. Normally, in this method, the detector efficiency of the alpha spectrometer is determined using a (226)Ra source with known activity. As an alternative to using a (226)Ra standard, we calculated the detector efficiency from the relative solid angle subtended by the detector on the soil samples. The accuracy of this method depends on the uncertainty of geometrical properties and the distribution of activity within the source. An uncertainty budget is provided. The method was applied successfully in the intercomparisons.

Measurement of the 109Cd half-life

The half-life of (109)Cd was measured by following the decay of sources from a radiochemically pure solution with two different measuring systems: an ionisation chamber and a high-purity germanium (HPGe) detector. The measurements were performed over a period of 3.6 years, i.e. about 2.8 half-lives of (109)Cd. The resulting half-life values and detailed uncertainty budgets (k=1) are presented for both systems. The result obtained with the ionisation chamber, 462.36 (33) days, and the one obtained with the HPGe detector, 461.92 (76) days, are mutually consistent. The weighted mean of our measured values, T(1/2)((109)Cd)=462.29 (30) days, is consistent with the currently recommended values of 461.4 (12) days (Schönfeld and Dersch, 2004; IAEA, 2007) and 462.0 (3) days (Xiaolong et al., 2010). From a set of selected experimental values published after 1970, a "partially weighted mean" (Pommé and Spasova, 2008) of T(1/2)((109)Cd)=462.36 (39) days was calculated. More measurements are needed to resolve the discrepancies among literature data and to reduce the final uncertainty on the (109)Cd half-life.

Measurement of the (54)Mn half-life

The half-life of (54)Mn was measured by following the decay of sources from a radiochemically pure solution using three different measuring systems: an ionisation chamber, a high-purity germanium (HPGe) detector and two 7.5 cm (diameter) × 7.5 cm (height) NaI(Tl) scintillation detectors in opposite position. The measurements were performed over a period of 3 years, i.e. about 3.5 half-lives of (54)Mn. The resulting half-life values and detailed uncertainty budgets are presented for the three measuring systems. The half-life obtained with the ionisation chamber, 312.32 (9) days, is consistent with but more precise than the ones obtained with the HPGe detector, 311.9 (5) days and the NaI(Tl) detectors, 311.9 (6) days, respectively. Our final half-life value of 312.32 (9) days is rather consistent with the currently recommended values of 312.29 (26) (IAEA, 2007) and 312.13 (3) days (Helmer and Schönfeld, 2004), even though the uncertainty of the latter may be underestimated. From a partially weighted mean (Pommé and Spasova, 2008) of selected experimental values published after 1970, a new best estimate of T(1/2)((54)Mn)=312.20 (8) days was calculated.

Half-life measurement of 124Sb

The half-life of (124)Sb was determined experimentally by following the decay of a source from a radiopure solution with a Centronic IG12 ionisation chamber. Thousands of measurements were performed over a period of 358 days, i.e. about six half-life periods. However, the data analysis was restricted to the first 221 days, in order to limit the dominant uncertainty component associated with the hypothetical possibility of a systematic error on background subtraction. The resulting value for the (124)Sb half-life, 60.212 (11) days, is found to be in very good agreement with published values, but carries a lower uncertainty. Major uncertainty contributions pertain to possible systematic errors in background correction, long-term changes in source-detector geometry and medium- and long-term instability of the instrument. Additional measurements were performed with a high-purity germanium detector to confirm the above value.

alpha-Particle and gamma-ray spectrometry of a plutonium solution for impurity determination

A highly enriched (240)Pu solution was measured by alpha-particle and gamma-ray spectrometry to determine other radionuclides present in the material as impurities. Low activities of (238)Pu, (241)Am, (243)Cm and (244)Cm were determined by measuring thin sources, made from the original solution, in a high-resolution alpha-particle spectrometer. The sources were prepared by evaporating the plutonium solution on quartz plates in a vacuum chamber. From the ingrowth of (241)Am in the original solution, the amount of (241)Pu could be calculated. After radiochemical separation of (241)Am, the plutonium was measured by high-efficiency alpha-particle spectrometry to determine the amount of (238)Pu. The enriched (240)Pu material was also measured by high-resolution gamma-ray spectrometry, using two different HPGe detectors to determine the impurities of (239)Pu and (241)Am. The preparation of the sources and the measurement methods are described and discussed. The measured impurities, given in % of the (240)Pu activity, are compared with the values on the certificate.

Cascades of pile-up and dead time

Count loss through a cascade of pile-up and dead time is studied. Time interval density-distribution functions and throughput factors are presented for counters with a series arrangement of pile-up and extending or non-extending dead time. A counter is considered, where an artificial dead time is imposed on every counted event, in order to control the length and type of dead time. For such a system, it is relatively easy to determine an average count-loss correction factor via a live-time clock gated by the imposed dead-time signal ('live-time mode'), or otherwise to apply a correction factor based on the inversion of the throughput function ('real-time mode'). However, these techniques do not account for additional loss through pulse pile-up. In this work, counting errors associated with neglecting cascade effects are calculated for measurements in live-time and real-time mode.

The solid angle subtended by a circular detector for a linear source

An exact solution is presented for the solid angle subtended by a circular detector for a linear source. It is based on Conway's equation for a non-coaxial point source, involving an integral of Bessel functions [Conway, J.T., 2006. Generalizations of Ruby's formula for the geometric efficiency of a parallel-disk source and detector system. Nucl. Instrum. Methods A 562, 146-153]. Some numerical examples are calculated and compared with the results obtained with a recently published closed formula (Galiano, E., Pagnutti, C., 2006. An analytical solution for the solid angle subtended by a circular detector for a symmetrically positioned linear source. Appl. Radiat. Isot. 64, 603-607), which is incorrect but can be improved by applying a correction factor.