BNCT research activities at the Granada group and the project NeMeSis: Neutrons for medicine and sciences, towards an accelerator-based facility for new BNCT therapies, medical isotope production and other scientific neutron applications.

The Granada group in BNCT research is currently performing studies on: nuclear and radiobiological data for BNCT, new boron compounds and a new design for a neutron source for BNCT and other applications, including the production of medical radioisotopes. All these activities are described in this report.

Exploring neutron capture therapy with 33S and 10B.

The 33S(n,α)30Si reaction was proposed as cooperative neutron capturer to 10B(n,α)7Li in Neutron Capture Therapy (NCT). At that moment, the available 33S(n,α)30Si cross-section data were scarce and discrepant in key energy ranges for its use in NCT. Since then, three experiments have been carried out at n_TOF facility at CERN and at Institut Laue-Langevin. These new data are used for the calculation of the dose rate on ICRU-4 tissue by using kerma factors, a simplified model of tissue and a 13.45 keV neutron beam, energy of the most important 33S(n,α)30Si resonance. A significant enhancement of the dose rate due to the presence of 33S is shown. In spite of the limitations, the cooperative action of 33S and 10B is an interesting possibility to be studied for accelerator-based neutron sources with non-moderated neutrons.

Using a Tandem Pelletron accelerator to produce a thermal neutron beam for detector testing purposes.

Active thermal neutron detectors are used in a wide range of measuring devices in medicine, industry and research. For many applications, the long-term stability of these devices is crucial, so that very well controlled neutron fields are needed to perform calibrations and repeatability tests. A way to achieve such reference neutron fields, relying on a 3 MV Tandem Pelletron accelerator available at the CNA (Seville, Spain), is reported here. This paper shows thermal neutron field production and reproducibility characteristics over few days.

Bilinear diffusion quantum Monte Carlo methods.

The standard method of quantum Monte Carlo for the solution of the Schrödinger equation in configuration space can be described quite generally as devising a random walk that generates-at least asymptotically-populations of random walkers whose probability density is proportional to the wave function of the system being studied. While, in principle, the energy eigenvalue of the Hamiltonian can be calculated with high accuracy, estimators of operators that do not commute the Hamiltonian cannot. Bilinear quantum Monte Carlo (BQMC) is an alternative in which the square of the wave function is sampled in a somewhat indirect way. More specifically, one uses a pair of walkers at positions x and y and introduces stochastic dynamics to sample phi(i)(x)t(x,y)phi(j)(y), where phi(i)(x) and phi(j)(y) are eigenfunctions of (possibly different) Hamiltonians, and t(x,y) is a kernel that correlates positions x and y. Using different Hamiltonians permits the accurate computation of small energy differences. We review the conceptual basis of BQMC, discuss qualitatively and analytically the problem of the fluctuations in the branching, and present partial solutions to that problem. Finally we exhibit numerical results for some model systems including harmonic oscillators and the hydrogen and helium atoms. Further research will be necessary to make this a practical and generally applicable scheme.