Results from the TARC experiment: spallation neutron phenomenology in lead and neutron-driven nuclear transmutation by adiabatic resonance crossing

Abstract

We summarize here the results of the TARC experiment whose main purpose is to demonstrate the possibility of using Adiabatic Resonance Crossing (ARC) to destroy efficiently Long-Lived Fission Fragments (LLFFs) in accelerator-driven systems and to validate a new simulation developed in the framework of the Energy Amplifier programme. An experimental set-up was installed in a CERN PS proton beam line to study how neutrons produced by spallation at relatively high energy ( E n ≥ 1 MeV) slow down quasi adiabatically with almost flat isolethargic energy distribution and reach the capture resonance energy of an element to be transmuted where they will have a high probability of being captured. Precision measurements of energy and space distributions of spallation neutrons (using 2.5 GeV/ c and 3.5 GeV/ c protons) slowing down in a 3.3 m × 3.3 m × 3 m lead volume and of neutron capture rates on LLFFs 99 Tc, 129 I, and several other elements were performed. An appropriate formalism and appropriate computational tools necessary for the analysis and understanding of the data were developed and validated in detail. Our direct experimental observation of ARC demonstrates the possibility to destroy, in a parasitic mode, outside the Energy Amplifier core, large amounts of 99 Tc or 129 I at a rate exceeding the production rate, thereby making it practical to reduce correspondingly the existing stockpile of LLFFs. In addition, TARC opens up new possibilities for radioactive isotope production as an alternative to nuclear reactors, in particular for medical applications, as well as new possibilities for neutron research and industrial applications.

The thermal neutron capture cross section of 129I

“…It represents a substantial amount of the total radio toxicity of LLFP [1] because of its mobility in the environment [2]. The thermal neutron capture cross section of 129 I is an important quantity to determine the transmutation efficiency in various transmutation facilities such as Accelerator Driven System (ADS) [3,4]. Recently a series of experiments was performed at the GELINA facilities of the JRC Institute for Reference Materials and Measurements (IRMM) to determine the capture cross sections of 127 I and 129 I in the resonance region (RR).…”

The 99Tc(n,γ)100Tc cross section, 99Tc(d,p)100Tc and the 100Tc decay scheme and neutron binding energy

“…This is the basis of transmutation of technetium contained in the nuclear waste [2]. The prompt γ-radiation produced can in principle be used for assaying technetium by prompt gamma activation analysis (PGAA).…”

“…It is, however, not easy to use during the bulk transmutation process. Thus the off line, neutron activation analysis (NAA) technique has been applied in the Transmutation by Adiabatic Resonance Crossing (TARC) experiment performed at the Spallation Neutron Source at CERN [2] for controlling the transmutation process. The calculation of the yield of 100 Tc from NAA measurements requires a knowledge of the absolute gamma decay probabilities, P γ of the states of 100 Ru which are populated in the 100 Tc(β − ) 100 Ru beta decay.…”

Partial and total thermal neutron capture cross sections for non-destructive assay and transmutation monitoring of 99Tc

“…Fortunately, 99 Tc can be transformed by neutron capture into 100 Tc, which decays with a 15 s half-life to stable 100 Ru. This is the basis of transmutation of technetium contained in the nuclear waste [2]. The γ -radiations produced can in principle be used for assaying technetium either by prompt *Author for correspondence (E-mail: molnar@iki.kfki.hu).…”

“…The NAA technique has been applied in the TARC experiment at CERN [2] for controlling the transmutation process. In the present work, accurate partial and total capture cross sections have been determined for the major γ -rays from the 99 Tc(n, γ ) 100 Tc capture reaction and the subsequent beta decay of 15 s 100 Tc at the cold neutron PGAA facility of the Budapest Research Reactor.…”