The energy dependent conversion factors from measured photon pulse height spectra to ambient dose equivalent (H*(10)) of three different detectors based on the scintillation materials CeBr_3, LaBr3 and SrI2 were simulated with the three Monte Carlo Codes, GEANT4, MCNP and PENELOPE, respectively. The performance of the detection systems, using the calculated conversion factors (fitted to response functions), is demonstrated for different scenarios ranging from laboratory conditions (i.e. a precisely defined radiation field in a calibration facility) to a free-field irradiation scenario produced by the natural radioactivity at a large lawn. With very simple geometric models of the detector systems, the response function of scintillation based dosemeters can be derived from the aforementioned Monte Carlo simulations with an accuracy of the measured doses in H*(10) of ±10% in an photon energy range from 100 keV to 3000 keV, as being typical for natural environmental gamma radiation.

In cases of nuclear or other radiologically relevant incidents or accidents (“radiological event”), including terrorist attacks, appropriate protection of the public against ionising radiation and radioactive contamination is of major importance. In such scenarios, radiation protection authorities and other decision-makers quickly need reliable information based on sound radiological data in order to determine and optimize countermeasures. The nuclear accidents in Chernobyl (1986) and Fukushima (2011) are major examples where radiation protection measures were crucial for preserving a tremendous number of human lives. However, certain smaller events have also caused severe problems, e.g., the Tokaimura nuclear criticality accident (1999). According to the IAEA Safety Standard No. GSR Part 7, “Preparedness and Response for a Nuclear or Radiological Emergency” (1), safety and security measures have the shared aim of protecting human life and health as well as protecting the environment. This document also emphasises the importance of adequate protective measures following nuclear and radiological emergencies. Reliable radiological data, available at the earliest possible stage, are a prerequisite for effectively protecting people from such unexpected but potentially highly dangerous events. Therefore, the European joint research project 16ENV04 named “Preparedness”, funded by the European Metrology Programme for Innovation and Research (EMPIR), is meant to develop reliable instrumentation and methods needed in the field of radiation protection in the aftermath of a nuclear or radiological emergency. The goal is to quickly gather quantitative data on the activity concentrations of contaminated areas and dose rate levels by aerial measurements, and analyse these air contaminations by flexible and transportable air sampling systems. For large-area ground contaminations, surveillance by unmanned airborne monitoring systems (UAMSs), specifically unmanned aerial vehicles (UAVs) equipped with spectrometric detectors, is the best solution to protect first responders and other task forces against contaminations and hazards due to ionising radiation. However, advanced calibration procedures based on reference materials and standard radionuclide sources must be elaborated for these systems and verified by Monte Carlo simulations. For airborne radioactivity monitoring, transportable air sampling field stations equipped with high-resolution spectrometric detectors and appropriate shielding is needed to allow the measurement of radioactivity concentration levels in the air of affected areas. After the release of a radioactive plume to the atmosphere, the levels of the ambient dose equivalent rate and activity concentrations in air provide essential information about the progression of the radioactive cloud. This information is important for decision-makers to be able to take timely and adequate countermeasures to protect the members of the public against the dangers of ionising radiation. After a major release of radionuclides, short-term decontamination may not always be possible. Hence, concepts for long-term measurements have to be developed. Metrologically sound data is needed in this field as well, because decisions on e.g. decontamination measures or release of restricted areas are of vital importance. Passive dosimeters must therefore be studied with regard to their applicability for this purpose. Furthermore, the “Preparedness” project addresses the question whether non‐governmental networks could support official dose rate data or undermine them because of insufficient quality.

In the event of a radiological emergency, early and reliable knowledge of radioactivity concentrations is important information for organising countermeasures to protect the general public and emergency workers. This is ensured by all European countries in operating airborne radioactivity and dose rate early warning networks. To increase the provided information, the development of new secondary standards based on scintillation detectors for the measurement of ambient dose rate equivalent was initiated in 2014. This paper shows the state-of-the-art of uncertainties and characteristic limits of low dose rate measurement that can be achieved by scintillation-based detector (CeBr3) and gas-based detectors (a high-pressure ionization chamber, HPIC). The comparison of the devices shows the performance and the metrological potential of the CeBr3 detector: Its uncertainty is already very close to the uncertainty of reference values. Looking at the question how to select a reference instrument, the CeBr3 detector with a special data evaluation is even superior to the HPIC and qualifies therefore as a modern secondary standard: Providing both, dose rate and nuclide information.

A new generation of dosemeters, based on the scintillators LaBr3, CeBr3 and SrI2, read out with conventional photomultipliers, to be used in the field of environmental gamma-radiation monitoring, was investigated. The main features of these new instruments and especially their outdoor performance, studied by long-term investigations under real weather conditions, are presented. The systems were tested at the reference sites for environmental radiation of the Physikalisch-Technische Bundesanstalt. The measurements are compared with that of well characterized classical dose rate reference instruments to demonstrate the suitability of new spectrometers for environmental dose rate monitoring even in adverse weather conditions. Their potential to replace the (mainly Geiger Müller based) dose rate meters operated in about 5000 European early waning network stations as well as in environmental radiation monitoring in general is shown.

The responses of electronic dose rate meters were investigated in a large volume radon chamber at PTB in a wide range of radon activity concentrations. The measurements were conducted under controlled laboratory conditions and measured dose rate data are compared with Monte-Carlo simulations. Consequences concerning environmental monitoring are described. A further result is that the direct measurement of the dose rates produced by radon progeny in air is hardly possible in radon atmospheres with high activity concentrations, because the major contribution of measured dose rates is produced by radon progeny on the housing of the dose rate instruments. The latter effect largely depends on the ability of surfaces to absorb radon progeny. The Monte-Carlo simulations revealed quantitative results on the height of the single contributions to the total dose rate measured in the radon chamber. When environmental dose rate measurements are performed, the plate-out on detectors can be neglected.

Short-term pronounced increases of the ambient dose equivalent rate, due to rainfall are a well-known phenomenon. Increases in the same order of magnitude or even below may also be caused by a nuclear or radiological event, i.e. by artificial radiation. Hence, it is important to be able to identify natural rain events in dosimetric early warning networks and to distinguish them from radiological events. Novel spectrometric systems based on scintillators may be used to differentiate between the two scenarios, because the measured gamma spectra provide significant nuclide-specific information. This paper describes three simple, automatic methods to check whether an Ḣ*(10) increase is caused by a rain event or by artificial radiation. These methods were applied to measurements of three spectrometric systems based on CeBr3, LaBr3 and SrI2 scintillation crystals, investigated and tested for their practicability at a free-field reference site of PTB.

For the upgrade of existing dosimetric early warning networks in Europe spectrometric detectors based on CeBr3, LaBr3, SrI2, and CdZnTe are investigated as possible substitutes for the current detector generation which is mainly based on gas filled detectors. The additional information on the nuclide vector which can be derived from the spectra of gamma-radiation is highly useful for an appropriate response in case of a nuclear or radiological accident. The measured gamma-spectra will be converted into ambient dose equivalent H*(10) using a method where the spectrum is subdivided into multiple energy bands. For each band the conversion coefficients from count rate to dose rate is determined. The derivation of these conversion coefficients is explained in this work. Both experimental and simulative approaches are investigated using quasi -mono -energetic gamma-sources and synthetic spectra from Monte -Carlo simulations to determine the conversion coefficients for each detector type. Finally, precision of the obtained characterization is checked by irradiation of the detectors in different well-known photon fields with traceable dose rates.

To detect radiological incidents, all members of the European Union have installed nationwide radiological early warning networks. Most of the installed detector systems supply only dosimetric information. Novel spectrometry systems are considered to be good candidates for a new detector generation for environmental radiation monitoring because they will supply both nuclide-specific information and ambient dose equivalent rate values. Four different detector types were chosen and compared with each other (LaBr3, CeBr3, SrI2 scintillation detectors, and CdZnTe, a semiconductor detector). As a first step, the inherent background of these detectors was measured in the low background underground laboratory UDO II of PTB. As a second step, the relative detection sensitivity between the various detectors was determined at different energies. Finally, the detectors were exposed to a 4 pi-radiation field of radon progeny in PTB's radon chamber. The obtained results show that the investigated detectors are well suited for environmental radiation monitoring.

Applications of nanomaterials rely on their tunable properties with large-scale integration feasibility. Advantages can be envisaged by merging nanostructures with thin film technologies, where ion implantation can be used as an integrated part of the processes. Still, ion implantation carries along with its benefits undesired intrinsic defects. Two examples of studies were performed by Barbosa et al. (pp. 801–808) with the nanoscopic perturbed angular correlations (PAC) technique that probes the charge density distribution in the surroundings of chosen radioactive nuclei, thus allowing characterizing the probe's real environment at the atomic scale. The chosen studies were ZnO and CdxZn1−xO thin films – aimed to cover luminescence wavelengths from UV to yellow - with implanted 111mCd/111Cd probe, and the technologically relevant high k-factor Ga2O3 nanostructures and Ga2O3 pellets, where Cd is a potential p-type dopant. For each case, the Cd lattice site occupancies and how and to which extent the local environment of the implanted Cd is reconstructed are studied as a function of annealing temperature.

Time differential perturbed angular correlation (TDPAC) spectroscopy in beryllium, zinc, rhodium, antimony, hafnium and rhenium was performed with the 100Pd/100Rh probe using four-detector arrays with relative detector orientations of 90° and 180°. The probe was synthesized using the 92Zr(12C,4n)100Pd fusion evaporation reaction, with evaporation residues recoiling into specimens of the metals. The quadrupole coupling constant for 100Rh has been determined for the first time for antimony, hafnium and rhenium, while results for the other elements agree with known values. The coupling constants for the measured hexagonal lattices of the period VI transition metals, hafnium and rhenium, show the same trend with increasing atomic number as those of period V.

The versatility of perturbed angular correlations (PAC) in the study of nanostructures and thin films is demonstrated, namely for the specific cases of ZnO/CdxZn(1-x)O thin films and Ga2O3 powder pellets and nanowires, examples of transparent conductive oxides. PAC measurements as a function of annealing temperature were performed after implantation of Cd-111m/Cd-111 (T-1/2 48 min) and later compared to density functional theory simulations. For ZnO, the substitution of Cd probes at Zn sites was observed, as well as the formation of a probe-defect complex. The ternary CdxZn(1-x)O (x = 0.16) showed good macroscopic crystal quality but revealed some clustering of local defects around the probe Cd atoms, which could not be annealed. In the Ga2O3 samples, the substitution of the Cd probes in the octahedral Ga-site was observed, demonstrating the potential of ion-implantation for the doping of nanowires. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The II-VI semiconductor ZnO has many potential applications in optoelectronic and sensor devices. When used as a transparent conducting contact it is often grown epitaxially onto a different substrate with the consequence that the layers are biaxially strained due to lattice mismatch. Similarly, impurity-implanted layers can lead to the development of local strain fields. Strain usually changes the electronic properties of layers and/ or implanted crystal regions. Detailed knowledge about local strain and its influence on the crystal fields is therefore helpful in predicting changes in crystal properties. The perturbed angular correlation technique was applied to study the electric field gradient (EFG) at the site of implanted In dopants in ZnO under uniaxial and biaxial strain. The observed linear change of the EFG with pressure and a change in symmetry due to compression perpendicular to the c-axis could be well reproduced by theoretical calculations using the point charge model.

The possible presence of a large magnetic field due to spin polarization of a Cd nucleus (decay product of 111In) at an Al substitutional site in AlN is investigated with perturbed angular correlation (PAC) spectroscopy. The PAC spectra of 111In/111Cd in AlN show two probe environments: a weak quadrupole interaction (quadrupole interaction constant, \(\nu _{\rm Q}^{\,\,\,\rm lattice} = 30\) MHz) due to 111In probes at a defect free Al substitutional site and an unknown large interaction (\(\nu _{\rm Q}^{\,\,\,\rm complex} = 300\) MHz) tentatively attributed to a nearest neighbour pair between 111In and a nitrogen vacancy (VN) aligned along the c-axis. Surprisingly, in density functional theory (DFT) calculations, such a large electric field gradient (EFG) could not be reproduced. However, an inclusion of spin polarization in the calculations indicates a strong magnetic field at ~50 % of the 111In/111Cd site. An attempt to verify the presence of the strong magnetic field and to explain the origin of the strong interaction is made. Orientation measurements show, the large interaction is not characterised by a magnetic interaction and is predominantly due to the EFG. However, in the presence of an external magnetic field, the strong interaction probe environment becomes more uniform and the EFG increases by ~10 %. This definitely hints towards some sort of magnetic interaction at the strong interaction probe site.

GaN and AlN thin films were implanted with cadmium (Cd) or silver (Ag), to fluences ranging from 1x10(13) to 1.7 x 10(15) at/cm(2). The implanted samples were annealed at 950 degrees C under flowing nitrogen. While implantation damage could be fully removed for the lowest fluences, for higher fluences the crystal quality was only partially recovered. For the high fluence samples the lattice site location of the ions was studied by Rutherford Backscattering/channelling (RBS/C). Cd ions are found to be incorporated in substitutional cation sites (Al or Ga) while Ag is slightly displaced from this position. To further investigate the incorporation sites, Perturbed Angular Correlation (PAC) measurements were performed and the electric field gradients at the site of the probe nuclei were determined. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

AlN with a wide bandgap of 6.2 eV is a promising candidate for ultraviolet light-emitting diodes and laser diodes. However, the production of the required p-type AlN is still challenging. As a possible dopant Cd was suggested among other Group II atoms (Be, Mg, and Zn). In this study the annealing condition of implanted Cd in AlN was investigated with the method of the perturbed angular correlation (PAC). Therefore radioactive Cd-117 or Cd-111m ions were implanted into thin AlN films on sapphire substrate with an energy of 30 keV and fluences in the range of 10(11) ions/cm(2).After thorough annealing with a proximity cap of the same material most of the Cd-probes occupy substitutional lattice sites and almost all implantation damage can be annealed. This results in a distinct frequency in the PAC spectra which increases with temperature. In contrast to the formation of an indium nitrogen-vacancy complex observed with the probe In-111 on substitutional Al-sites no defects are bound to substitutional Cd impurities. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Time differential perturbed angular correlation spectroscopy of Rh in zinc, rhodium, antimony, hafnium and rhenium has confirmed expectations for zinc and rhodium and provided the first measurements of quadrupole coupling constants for the three other transition metals with preliminary values of νQ = 4.3 MHz, 5.7 MHz, and 3.2 MHz, respectively. The three results appear to be consistent with published results for zirconium and ruthenium.

Wide band gap semiconductors, mainly GaN, have experienced much attention due to their application in photonic devices and high-power or high-temperature electronic devices. Especially the synthesis of InxGa1-xN alloys has been studied extensively because of their use in LEDs and laser diodes. Here, In is added during the growth process and devices are already very successful on a commercial scale. Indium in nitride ternary and quaternary alloys plays a special role; however, the mechanisms leading to more efficient light emission in In-containing nitrides are still under debate. Therefore, the behaviour of In in GaN and AlN, the nitride semiconductor with the largest bandgap is an important field of study. In is also an important impurity in another wide band gap semiconductor – the II-VI compound ZnO where it acts as an n-type dopant. In this context the perturbed angular correlation technique using implantation of the probe 111In is a unique tool to study the immediate lattice environment of In in the wurtzite lattice of these wide band gap semiconductors. For the production of GaN and ZnO based electronic circuits one would normally apply the ion implantation technique, which is the most widely used method for selective area doping of semiconductors like Si and GaAs. However, this technique suffers from the fact that it invariably produces severe lattice damage in the implanted region, which in nitride semiconductors has been found to be very difficult to recover by annealing. The perturbed angular correlation technique is employed to monitor the damage recovery around implanted atoms and the properties of hitherto known impurity – defect complexes will be described and compared to proposed structure models.

The present addendum to project IS481 will allow accomplishing the work of the running project which was not possible due to technical problems. Furthermore, the scope of the project will be extended from binary GaN and AlN to ternary AlGaN semiconductors. β−γ Perturbed Angular Correlation (PAC) measurements using the Cd(In) probe in GaN will allow the determination of the sign of the quadrupole interaction, an important parameter when comparing experimental results with density functional calculations of the electric field gradient. γ−γ PAC using the probes Cd(Cd) and Cd(In) will be used to investigate AlGaN ternaries. Special focus will lie on the investigation of implantation damage and alloy disorder. The presence and characteristics of In-VN complexes in these alloys will be studied and compared to our previous results in binary nitrides. Requested shifts: 12 shifts, (split into two runs over one year)

GaN and ZnO are possible candidates for dilute magnetic semiconductors with Curie temperatures above room temperature. Doping with transition metals like Co, Mn or Fe could be a simple way to create such systems. The perturbed angular correlation (PAC) probe 100Pd/100Rh is isoelectronic to cobalt and therefore a perfect tool to investigate the incorporation of transition metals into these compounds as well as the influence of other impurities on internal magnetic fields. The (0001) and (10\(\bar{1}\)10) surfaces of ZnO single crystals, freestanding GaN films, and GaN thin films (6 μm) on sapphire substrates were recoil-implanted with the 100Pd/100Rh probe. The probe was produced using the fusion evaporation reaction 92Zr(12C, 4n)100Pd at a beam energy of 69 MeV. Subsequently, the incorporation of the probe was studied by PAC spectroscopy during an isochronal annealing program. First results without and with an applied external magnetic field are indicative of a strongly disturbed lattice vicinity of Pd impurities in both hosts. No signs of spontaneous ferromagnetic ordering were observed.

Time Differential Perturbed Angular Correlation measurements were performed in intrinsic germanium with the 100 Pd/ 100 Rh probe. The probe was produced via 92 Zr( 12 C, 4n) 100 Pd and recoil-implanted into samples. Parallel measurements with the 111 In/ 111 Cd probe confirmed the quality of the germanium studied. The measurements with the 100 Pd/ 100 Rh probe show a modulation pattern in the ratio function with a quadrupole interaction frequency of 8.3(2) Mrad/s. The pattern depends on sample orientation and it is most pronounced after annealing at 500°C. After annealing at 700°C the effect vanishes due to strong damping of the ratio function. The pattern may be caused, similar to what has been observed for highly doped n-type silicon, by the pairing of the Pd-atom with a vacancy located in the < 111 > direction. The disappearance of the pattern would indicate the dissociation of this pair. Pair formation and dissociation may be relevant to palladium-induced-crystallization processing of germanium.