Based on Bayesian statistics, characteristic limits such as decision threshold, detection limit and confidence limits can be calculated taking into account all sources of experimental uncertainties. This approach separates the complete evaluation of a measurement according to the ISO Guide to the Expression of Uncertainty in Measurement from the determination of the characteristic limits. Using the principle of maximum entropy the characteristic limits are determined from the complete standard uncertainty of the measurand.
In order to interpret cosmogenic radionuclides in extraterrestrial matter one has to differentiate between p- and α-induced
reactions with solar (SCR) and with galactic (GCR) cosmic rays. Our earlier studies have shown that for a satisfactory description
of GCR-interactions with dense matter rather few but characteristic high energy cross sections are required. In contrast,
for the low and medium energy SCR-production a detailed knowledge of the respective nuclear reactions is needed. In the present
study, excitation functions are presented for 39 p-induced reactions on Ni, Fe, Mn, Cr and Ti, which contribute to SCR-produced
radionuclides (44≤A≤59) at energies up to 200 MeV. The excitation functions are based mainly on our own cross section measurements,
partly on hybrid model predictions and to a lesser extent on experimental data from other authors. Based on these excitation
functions, depth profiles for the proton induced SCR-production of46Sc,44Ti,48V,51Cr,52Mn,53Mn,54Mn,55Fe,56Co,57Co,58Co,60Co and59Ni from the 5 major targets mentioned before in extraterrestrial matter are calculated, assuming normal lunar surface conditions.
Typical rigidities were adopted for the solar proton fluxes, ranging from 50 to 150 MV, which cover the rigidity values commonly
observed in solar flares. In order to derive depth dependent p-fluxes from calculations of the energy loss of incoming particles,
rather large differences in the respective chemical compositions had to be considered. The theoretical profiles are compared
with experimental data from lunar samples, and several cosmochemical applications are discussed. They range from the study
of single solar flare events by short-lived radioisotopes to the investigation of supposed long-term variations of the solar
flare activity on a large times-cale of millions of years. The latter is possible by comparing the production rates of very
long-lived nuclides (as for example53Mn with T=3,8·106 y) with that of short- or medium-lived nuclides. In this respect, the particular importance of44Ti (T-47.3 y) for measuring today's mean solar flare activity is pointed out. In general, the depth dependent production rates
established in this work enable one to estimate the SCR-contributions to cosmogenic radionuclides from the respective target
elements, thus providing a basis for a better understanding of the solar cosmic ray interaction with extraterrestrial matter.
Determination of chromium at naturally occuring levels in biological materials requires very low detection limits and dust-free conditions during sampling. These levels are of interest in order to distinguish from enhanced levels which may be carcinogenic. To this purpose a radiochemical separation technique which includes extraction of Cr(VI) into tribenzylamine/chloroform and reextraction into alkaline solution has been improved. Without time-consuming precipitation of BaCrO4 the detection limit has been decreased by a factor of 1.7 compared to earlier, work (to values like 1 ppb) in samples of typically 35 mg by increase of decontamination of65Zn by a factor of up to 1000. Formation of65Zn(OH)2 is shown as the reason for this result. Yield determination was carried out by ICP-AAS-measurements and UV/VIS-spectroscopy. The accuracy of the radiochemical procedure has been proved by analysis of NBS-SRM 1577 Bovine Liver.
Light metal alloys, as aluminium- and titanium based alloys, are of great interest to aerospace industry but thermodynamic
information, mainly heat capacity, is often missing.
Then we measured on heating the heat content of seven industrial titanium alloys from room temperature to 600°C with the help
of a high-temperature Calvet calorimeter (drop method). Their heat capacities were deduced by derivation of the enthalpy with
respect to temperature. The departures from Kopp-Neuman law were calculated.
Authors:R. Michel, U. Herpers, H. Kulus, and W. Herr
On applique l'activation neutronique aux mesures d'abondance isotopique du rhénium dans les matériaux lunaires. On y parvient
en comparant les activités induites par (n, γ) de186Re et188Re au moyen des raies γ de respectivement 137 et 155 keV. Afin d'éviter les interférences, (spécialement celles de199Au et99mTc) on a besoin d'un procédé conduisant à une grande pureté radiochimique. De plus, on détermine les teneurs en rhénium et
tungstène. On a remarqué une anomalie isotopique du rhénium dans les échantillons d'Apollo-14, montrant un enrichissement
remarquable en187Re (de 1,4 à 1,8% dans les sols et jusqu'à 29% dans les brèches). On montre enfin que cet enrichissement est partiellement
dû à l'irradiation neutronique sur la surface lunaire par la réaction186W(n,γ)187W
187Re. Cependant, l'anomalie observée, causée principalement par les neutrons intermédiaires, n'est pas produite uniquement par
les neutrons lunaires. L'activation d'un réacteur y contribue aussi par la réaction:186W(n,γ)187W
187Re(n,γ)188Re, qui peut être corrigée par l'analyse d'étalons de tungstène irradiés simultanément. On estime que la contribution lunaire
à l'enrichissement du187Re est de 20 à 60% de l'excès total observé.
Authors:O. Elmokhtar, H. Said, M. Michel, M. Ganteaume, and R. Castanet
We report in this paper the results of our thermal and thermodynamic investigation on lithium cyclohexaphosphate, Li6P6O18·5H2O between 298 and 1007 K. The different transitions with respect to temperature (successive dehydrations, solid-solid transition
and melting) were studied with the help of differential thermal analysis and thermogravimetry. The different phases were characterized
by X-ray diffraction and by infrared absorption. Finally, the enthalpy of these phasesvs. temperature was measured by isothermal drop calorimetry. Their heat capacities as well as the enthalpies of dehydration,
of solid-solid transition and of melting were deduced.
We pointed out that the lithium cyclohexaphosphate loses a molecule of water at 333 K (54.3 kJ·mol−1), three molecules of water at 413 K (151 kJ·mol−1) and the last one at 488 K (50.6 kJ·mol−1). The anhydrous lithium cyclohexaphosphate, Li6P6O18, give the polyphosphate, LiPO3, at 708 K (second order transition) and melt at 933 K (24.6 kJ·mol−1).
Authors:R. Michel, F. Löer, M. Nolte, M. Reich, and J. Zilkens
In order to describe the impact of corrosion of medical implants on the trace element balance of man samples of blood, serum and of a variety of tissues and organs were analysed for their trace element composition using instrumental neutron activation techniques. By the analysis of blood and serum the trace element status after long-term implantation as well as its dependence on time after implantation was investigated. Using autopsy samples of human organs such as heart, spleen, liver, of aorta and of lymphatic tissue from the lower pelvis transport and storage of the corrosion products was studided. These investigations were supplemented by a comprehensive study of normal human blood, serum, tissues and organs from patients without implants. The results demonstrate that there are high enrichments of corrosion products in several tissues and organs and that also blood and serum reveal the presence of the metal implants in the trace element levels, increasing shortly after implantation and pertaining during the entire implantation time. Thus the corrosion of metallic implants is a process not only affecting tissues from the vicinity of the implants but also influencing the trace element balance of the entire organism.
Authors:S. Szidat, A. Schmidt, J. Handl, D. Jakob, R. Michel, H.-A. Synal, and M. Suter
The long-lived radionuclide 129I (T1/2 = 15.7 My) occurs in the nature in very low concentrations. Since the middle of our century the environmental levels of 129I have been dramatically changed as a consequence of civil and military use of nuclear fission. Its investigation in environmental materials is of interest for environmental surveillance, retrospective dosimetry and for the use as a natural and man-made fracers of environmental processes. We are comparing two analytical methods which presently are capable of determining 129I in environmental materials, namely radiochemical neutron activation analysis (RNAA) and accelerator mass spectrometry (AMS). Emphasis is laid upon the quality control and detection capabilities for the analysis of 129I in environmental materials. Some applications are discussed.
Authors:A. Büling, C. Carl, P. Englert, U. Herpers, W. Herr, R. Michel, P. Ney, and H. Weigel
In a large number of alpine rocks and respective mineral separates the beryllium distribution was studied via “non-destructive”
photon activation. The detection limit of the assembly was ∼20 ppb. The existence of Be-rich areas was revealed. A selection
of individual rocks was analysed by instrumental as well as by radiochemical neutron activation analysis for main and trace
elements as: Na, K, Sc, Cr, Mn, Fe, Co, Rb, Cs, La, Eu, Yb, Ta, W, Au, and U. The latter was determined by counting the235U-fission tracks. The data supply an insight into the complex processes leading to the formation of metamorphic rocks. The
hardware and the computer evaluation of the γ-spectra is described in some detail. A further application is the determination
of traces of53Mn (in the order of 10−12 g/g) produced by the interaction of cosmic rays with stony meteorites. From a comparison of the26Al- and53Mn-values it is concluded that the depth dependent production of these two radionuclides differs slightly.
Authors:R. Michel, M. Lüpke, U. Herpers, R. Rösel, D. Filges, P. Dragovitsch, W. Wölfli, B. Dittrich, and H. Hofmann
A thick spherical target (R=25 cm) made of gabbro was irradiated isotropically with 1.6 GeV protons at the Saturne cyclotron at Laboratoire National Saturne (LNS)/CEN Saclay in order to simulate the interaction of galactic cosmic ray (GCR) protons with meteoroids in space. During a 2 weeks irradiation a proton-dose of 1.32 · 1014 cm–2 was received, which is equivalent to a cosmic-ray exposure age of 1.4 Ma. Production rates were measured by X- and gamma-spectrometry, by low-level counting and by conventional and accelerator mass spectrometry (AMS). Up to now, more than 200 target-product combinations were investigated. Theoretical production rates were derived on the basis of spectra of primary protons, secondary protons and secondary neutrons calculated by Monte Carlo techniques and thin-target cross sections of the underlying nuclear reactions. The model calculations excellently describe the production depth profiles in the artificial meteoroid, if reliable crosss sections are available. The thus validated model calculations allow for the interpretation of cosmogenic nuclide abundances in stony meteorites and lunar samples in terms of their exposure history and of the history of the radiation itself.