Abstract
In a nuclear or radiological accident scenario, when potentially members of the public can undergo internal contamination by anthropogenic radionuclides released in the atmosphere, effective ...methods that can be used directly in the field to perform a fast scan for internal contamination on a large number of individuals can play a major role to undertake appropriate countermeasures. Specific attention should be paid to the individual monitoring of children since they constitute the sensitive population group with the highest risk of developing cancer. At the ENEA Casaccia Research Center in Rome (Italy), monitoring procedures based on a portable HPGe detector and ratemeters were tested in the field. A total of 170 acquisitions of uncontaminated volunteers for the blank measurements were collected, 105 acquisitions on adult and 65 acquisitions on 10-y/o children. The detection limit calculation, in terms of activity taken up (Bq), was carried out according to the Standard ISO’s 11929 and 28218, whereas the corresponding ‘minimum effective dose’ (mSv) was calculated based on international commission on radiological protection (ICRP) Publications 134, 137 and 141. Results and evaluations of the measurement campaign are presented and discussed in respect to the aspects reported in the current literature.
The results obtained in a measurement campaign concerning internal contamination by the gamma-emitting radionuclides of a large number of individuals are presented in this work. The aim is to assess ...the effectiveness of the spectrometric method in an emergency response following a nuclear power plant accident or a spread of radionuclides in the atmosphere due to an act of terrorism. An HPGe portable spectrometer, deployed in a collective protection apparatus, was used for both whole-body and thyroid measurements. An adult bottle mannequin absorption (BOMAB) and thyroid phantoms were used to evaluate the detector performance. The BOMAB phantom was provided by the Italian Institute of Ionizing Radiation Metrology (INMRI) for the ENEA intercomparison exercise. Thyroid phantoms were provided by the Belgian Nuclear Research Centre for the 'Child and Adult Thyroid Monitoring After Reactor Accident' European intercomparison exercise. The instrument performance was further evaluated by collecting spectral data from healthy volunteers, using acquisition times of 180 s and 100 s, respectively, for the whole-body and thyroid measurements. The detector showed good accuracy in quantifying radionuclide activities in the adult BOMAB and in the thyroids of persons of all ages. The proposed method allows us to detect in vivo activity leading to a committed effective dose E(50) and committed thyroid equivalent doses H
greater than 2 mSv due to all gamma-emitting fission products, if the scan is performed within five days after intake. Assuming, for instance, an acute inhalation of
Cs and
I, the obtained detection limit values for adults lead to a E(50) value equal to 0.08 mSv and an H
value of 0.27 mSv. The E(50) and H
values show that the proposed method can be successfully used when the dose assessment must be rapidly performed for a large number of individuals in the eventuality of the scenarios previously mentioned.
In case of a nuclear reactor accident affecting a large population the internal contamination of the workers and the public can be assessed through in vivo measurements. Since iodine-131 is one of ...the most important releases and since it is of health concern, thyroid monitoring of this radionuclide is of special interest.
Intercomparisons of thyroid in vivo measurements usually focus on the adult case. Here we report about a European intercomparison exercise for spectroscopic devices. Three sets of thyroid phantoms of unknown activity were circulated, representing the following ages: 5 years-old, 10 years-old and the adult.
Nineteen institutions from twelve countries in Europe took part in an intercomparison exercise. Twenty-nine measurement devices have been tested. In the adult case, 5 results were outside the acceptance criteria and 10 in the 10-years old case. In the 5 years-old case, the result was not reported for one measurement device and 11 results were outside the acceptance criteria. Devices that have been tested during this intercomparison now dispose of calibration coefficients for the three age groups.
•Children thyroid measurements are important in case of nuclear reactor accident.•Laboratories could check their ability to measure iodine contamination in thyroid.•Opportunity was given to calibrate for children thyroid measurement.•Measurement capacity in Europe increased from this intercomparison exercises.
In order to properly respond to an emergency caused by an accident in a nuclear power plant with a spread of radionuclides in the atmosphere, we propose a field procedure to perform a large-scale ...individual thyroid monitoring of internal contamination due to inhalation of
I, by means of non-spectrometric equipment, in particular dose rate meters. Specific attention is paid to the individual monitoring of children, because of the very high radiosensitivity of the child's thyroid to the carcinogenic effects of ionising radiation. The device performance was evaluated by measuring mock iodine sources provided in the Child and Adult Thyroid Monitoring After Reactor Accident (CAThyMARA) intercomparison and, just for a scintillator dose rate meter, by means of 60 s acquisitions of healthy volunteers' thyroids. All the devices showed a remarkable accuracy in quantification of equivalent
I activity in the thyroids of persons of all ages. The selected scintillator dose rate meter showed detection limit values resulting in a maximum committed equivalent dose to thyroid H
, assuming an acute
I inhalation occurred five days before the measurement, equal to 10 mSv (related to five-year-old children). Considering the level of H
values associated with the calculated detection limit activities, the proposed procedure has a significant sensitivity to be used for fast internally thyroid monitoring in nuclear or radiological emergencies, allowing daily monitoring a large amount of individuals.
The response to γ-rays of long thin polished or wrapped YAP:Ce scintillator bars read out at both edges by photomultipliers has been studied by means of GEANT4 simulations with the aim to investigate ...the capability of the charge division method to reconstruct the gamma interaction point in the crystal. The GEANT4 simulations took into account the optical properties of the scintillator like absorption, reflection, and diffusion during the passage of the light through the crystal. The simulations were able to reproduce experimental measurements of light yields in polished and wrapped YAP:Ce crystals with dimensions 3.2×3.2×100
mm
3. Once validated, the simulations could show that a particular patterning of the crystal surface, which enhances the surface absorption, should lead to a significant improvement of the reconstruction precision of the charge division method, without compromising the energy resolution.
The effective light attenuation length in thin bars of polished YAP:Ce and LYSO:Ce scintillators with lengths of the order of 10
cm has been studied for various wrappings and coatings of the crystal ...lateral surfaces. This physical parameter plays a key role in a novel 3D PET concept based on axial arrays of long scintillator bars read out at both ends by Hybrid Photodetectors (HPDs) since it influences the spatial, energy and time resolutions of such a device. In this paper we show that the effective light attenuation length of polished crystals can be reduced by wrapping their lateral surfaces with Teflon, or tuned to the desired value by depositing a coating of Cr or Au of well-defined thickness. The studies have been carried out with YAP and LYSO long scintillator bars, read out by standard photomultiplier tubes. Even if the novel PET device will use different scintillators and HPD readout, the results described here prove the feasibility of an important aspect of the concept and provide hints on the potential capabilities of the device.
AX-PET: A novel PET detector concept with full 3D reconstruction Braem, A.; Joram, C.; Séguinot, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2009, Letnik:
610, Številka:
1
Journal Article
Recenzirano
We describe the concept and first experimental tests of a novel 3D axial Positron Emission Tomography (PET) geometry. It allows for a new way of measuring the interaction point in the detector with ...very high precision. It is based on a matrix of long Lutetium-Yttrium OxyorthoSilicate (LYSO) crystals oriented in the axial direction, each coupled to one Geiger Mode Avalanche Photodiode (G-APD) array. To derive the axial coordinate, Wave Length Shifter (WLS) strips are mounted orthogonally and interleaved between the crystals. The light from the WLS strips is read by custom-made G-APDs. The weighted mean of the signals in the WLS strips has proven to give very precise axial resolution. The achievable resolution along the three axes is mainly driven by the dimensions of the LYSO crystals and WLS strips. This concept is inherently free of parallax errors. Furthermore, it will allow identification of Compton interactions in the detector and for reconstruction of a fraction of them, which is expected to enhance image quality and sensitivity. We present the results of proof-of-principle tests and qualification measurements of the various components prepared to build a larger scale demonstrator consisting of two matrices of
8
×
6
LYSO crystals and 312 WLS strips.
The performance of a proximity focusing Ring Imaging Cherenkov detector equipped with a radiator of silica aerogel is presented. The aerogel tile used is a monolith with variable index of refraction. ...Cherenkov photons are detected with high granularity by eight Hamamatsu H9500 flat panel multi anode phototubes.
Scintillator studies for the HPD-PET concept Braem, A.; Chesi, E.; Ciocia, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2007, Letnik:
571, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The spatial, energy, and time resolutions of 10
cm long polished YAP:Ce and LYSO:Ce crystals have been measured. The work is part of the novel HPD-PET concept, based on a full three-dimensional, free ...of parallax errors, reconstruction of the
γ-ray interaction point in 10–15
cm long scintillators. The effective light attenuation length, a key parameter of the HPD-PET concept, and the resolutions have been measured for various wrappings and coatings of the crystal lateral surfaces. Even if the final HPD-PET prototype could use scintillators and/or wrappings different from those tested, the results here presented prove the feasibility of the concept and provide hints on its potential capabilities.
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