The decay pattern of the Pygmy Dipole Resonance of ¹⁴⁰Ce

The decay properties of the Pygmy Dipole Resonance (PDR) have been investigated in the semi-magic N=82 nucleus ¹⁴⁰Ce using a novel combination of nuclear resonance fluorescence and γ–γcoincidence techniques. Branching ratios for transitions to low-lying excited states are determined in a direct and model-independent way both for individual excited states and for excitation energy intervals. Comparison of the experimental results to microscopic calculations in the quasi-particle phonon model exhibits an excellent agreement, supporting the observation that the Pygmy Dipole Resonance couples to the ground state as well as to low-lying excited states. A 10% mixing of the PDR and the [2+1×PDR]is extracted

Photons fluence to local skin Dose coefficients and benchmark with three Monte-Carlo codes. Application to the computation of radioactive material transport limits

International audienceFluence to Local Skin Dose Conversion Coefficients (LSD-CC) are radiological protection quantities used for external radiation exposures which allow the conversion of particle fluences into local skin equivalent dose. The International Commission on Radiological Protection published LSD-CC for electrons with an energy range from 10 keV to 10 MeV. However, the literature does not address these radiation protection quantities for all particle types, in particular for photons. In this article, computed LSD-CC values for photons are presented which enrich the literature and are of interest for the radiation protection community. As an example for an application of the use of the computed LSD-CC values, the IAEA A1/A2 working group, which supports the review of the international regulation related to the transport of radioactive material, has decided to estimate the dose to the skin using such coefficients. In this publication, LSD-CC for photons are computed and benchmarked using GEANT4, FLUKA and MCNP. In addition, the FLUKA Monte-Carlo calculation code is used to compute the LSD-CC values for electrons and positrons to compare with existing data in the literature and validate the presented models. As one application of these LSD-CC values, the transfer functions for calculating the IAEA A-values are determined using the LSD-CC and are compared to a one-step direct calculation method

Skin dose contamination conversion coefficients. Benchmark with three simulation codes

International audienceHandling of radioactive material by operators can lead to contamination at the surface of the skin in case of an accident. The quantification of the dose received by the skin due to a contamination scenario is performed by means of dedicated dose coefficients as it is the case for other radiation protection dose quantities described in the literature. However, most available coefficients do not match realistic scenarios according to state-of-the-art of science and technology. Therefore, this work deals with dedicated dose conversion factors for skin contamination. Since there is an increasing demand on dose coefficients in general, these specific coefficients can be used for various calculations in radiation protection. In this work a method to evaluate such coefficients for the skin contamination dose related to photons, electrons, positrons, alpha and neutron particles is proposed. The coefficients are generated using Monte-Carlo simulations with three well established calculation codes (FLUKA, MCNP, and GEANT4). The results of the various codes are compared against each other for benchmarking purposes. The new dose coefficients allow the computation of the skin received dose, in the case of skin contamination scenario of an individual, taking into account the decay radiation of the radionuclides of interest. To benchmark the quantity derived here, comparisons of radionuclide contamination doses to the skin using the VARSKIN code available in the literature are performed with the results of this work

Computation of radioactive material transport limits within A1/A2 Working Group at IAEA TRANSSC

IAEA's (International Atomic Energy Agency) publication SSG-26 defines a methodology for calculating A1/A2 values. These values were conceived as limits for the transport of radioactive goods, to limit the public's exposure to radiation in the event of an accident. The limits ensure people involved in an accident receive an effective dose of no more than 50 mSv and a skin equivalent dose no greater than 500 mSv. The current values are based on five exposure scenarios taken from the Q-System, described in 1996. In 2013, the IAEA commissioned an international working group to improve the Q-System and calculate new limits for the transport of radioactive material. Within this working group, CERN has developed a set of models and an associated mathematical framework, and compiled them in a single piece of software. The primary purpose of the software is to compute and compare values produced by the different models under discussion. Later, the software could be distributed in a lighter version which will include the agreed upon regulatory model to determine the A1/A2 values

Review of the A1 and A2 values: final clap?

The A1 and A2 radioactive transport limit values of the Q System described in the advisory material SSG-26 have been developed to provide the maximum allowable contents in packages not designed to withstand accidents, with the objective to limit the accidental exposure of persons below an effective dose of 50 mSv and a skin equivalent dose of 500 mSv. Current values were determined in 1996 according to specific scenarios for five exposure pathways. Since then, the ICRP has published revised radiological data. In addition, progress in computer hardware and software allow the implementation of new Monte Carlo based calculation methods, which are more representative of the physical processes. An international working group involving NRA, PHE, GRS and IRSN was created in 2013 to discuss the improvement of calculation methods described in the Q System. This group later became part of the IAEA TRANSSC Technical Expert Group (TTEG) on Radiation Protection. The first findings and results were presented during the PATRAM 2016 conference, and the progress of the review was described during PATRAM 2019. While most trends on the potential changes in A1 and A2 values were presented, further discussions aimed at consolidating hypotheses and calculation methods were necessary to complete the review and propose to the TRANSSC Member States an update of the Q system consistent with the latest ICRP recommendations and methodologies. This paper describes the work that has been performed since 2019-especially regarding inhalation, contamination, ingestion, alpha and neutron considerations, explains the main changes in the calculation methods as well as the tools that have been developed to evaluate the Q values for any radionuclide, and shows results that could be implemented in the future revision of the IAEA SSR-6 regulations

Review of the A1 and A2 values: development, progress and outcomes

International audienceThe A1 and A2 values of the Q System described in the advisory material SSG-26 have been de-veloped to provide maximum allowable contents in packages not designed to withstand accidents, with the objective to limit the accidental exposure of persons below an effective dose of 50 mSv and a skin equivalent dose of 500 mSv. Current values were determined in 1996 according to spe-cific scenarios for five exposure pathways. Since then, the ICRP has published revised radiologi-cal data. In addition, progress in computer hardware and software allow the implementation of new methods of calculation, which are more complete and accurate. In September 2013, it was decided between NRA, PHE, GRS and IRSN to create an international working group to discuss the improvement of calculation methods described in the Q System. The first findings and results were presented during the PATRAM 2016 conference. The main items considered are the following:1.Using new data from the latest ICRP publications for emission spectra and external dose coef-ficients. 2.Using Monte-Carlo methods to take into account contributions from all radiations. 3.Selecting the irradiation field geometry.4.Selecting the calculation model for beta radiation and neutron emission from (α,n) reactions.5.Developing a specific irradiation scenario to the eye lens and the associated reference dose.6.Dealing with the progeny radionuclides. 7.Reviewing QC (inhalation) and QD (ingestion) values with the updated ICRP intake dose coeffi-cients that introduced new particle sizes and chemical forms.8.Reviewing QD (contamination) and QE (submersion) using Monte-Carlo methods.9.Considering the multi-path cumulative dose principle where simultaneous exposures may oc-cur. The review of items 1 to 4 has been completed; items 5 to 9 are in progress and discussion is pending on further work to be completed in the future.This paper will indicate the status of work that has been performed since 2016, explain the main changes in the calculation methods as well as the tools that have been developed to evaluate the Q values for any radionuclide, show results and describe the actions that are not yet completed. The WG expects the updated A values to be presented to the TRANSSC by 2021

The pygmy quadrupole resonance and neutron-skin modes in 124Sn

We present an extensive experimental study of the recently predicted pygmy quadrupole resonance (PQR) in Sn isotopes, where complementary probes were used. In this study, (α,α' γ ) and (γ , γ') experiments were performed on 124Sn. In both reactions, Jπ = 2+ states below an excitation energy of 5 MeV were populated. The E2 strength integrated over the full transition densities could be extracted from the (γ , γ') experiment, while the (α,α'γ ) experiment at the chosen kinematics strongly favors the excitation of surface modes because of the strong α-particle absorption in the nuclear interior. The excitation of such modes is in accordance with the quadrupole-type oscillation of the neutron skin predicted by a microscopic approach based on self-consistent density functional theory and the quasiparticle-phonon model (QPM). The newly determined γ -decay branching ratios hint at a non-statistical character of the E2 strength, as it has also been recently pointed out for the case of the pygmy dipole resonance (PDR). This allows us to distinguish between PQR-type and multiphonon excitations and, consequently, supports the recent first experimental indications of a PQR in 124Sn

Decay pattern of the pygmy dipole resonance in ¹⁴⁰Ce

The decay behavior of low-lying dipole states in 140Ce was investigated exploiting the γ3-setup at the HIγS facility using quasi-monochromatic photon beams. Branching ratios of individual excited states as well as average branching ratios to low-lying states have been extracted using γ – γ coincidence measurements. The comparison of the average branching ratios to QPM calculations shows a remarkable agreement between experiment and theory in the energy range from 5.0 to 8.5 MeV

Mixed-symmetry octupole and hexadecapole excitations in N=52 isotones

In addition to the well-established quadrupole mixed-symmetry states, octupole and hexadecapole excitations with mixed-symmetry character have been recently proposed for the N = 52 isotones 92Zr and 94Mo. We performed two inelastic proton-scattering experiments to study this kind of excitations in the heaviest stable N = 52 isotone 96Ru. From the combined experimental data of both experiments absolute transition strengths were extracted