O protótipo de um detector de nêutrons térmicos portátil foi desenvolvido no Instituto de Pesquisa Energéticas e Nucleares (IPEN-CNEN/SP), utilizando um fotodiodo de Si do tipo PIN associado a um filme de boro enriquecido. O filme de boro foi fabricado por meio da técnica de Deposição a Laser Pulsado, considerando duas possibilidades para depositar o boro: deposição direta do boro na face do fotodiodo e deposição na lâmina de vidro. Foram desenvolvidos dois protótipos, no primeiro foi possível ler apenas o sinal elétrico do sistema fotodiodo-boro no qual o filme está depositado na lâmina de vidro. Para aprimorar a resposta do sistema de detecção, outro circuito foi desenvolvido e permitiu contar nêutrons em ambas as situações tanto do filme na lamínula quanto do filme direto no fotodiodo. A caracterização dos protótipos foi feita via irradiação de feixes de nêutrons predominantemente térmicos e frios, por meio de quatro experimentos principais: reposta do sistema ao fluxo de nêutrons, teste de linearidade, resposta angular e o teste de reprodutibilidade. Os protótipos apresentaram uma resposta linear à variação do fluxo, reprodutibilidade, e a resposta angular não foi isotrópica. A eficiência intrínseca em porcentagem do protótipo 1 para um espectro de nêutrons predominantemente térmicos e frios foi (1,17 ± 0,01) % e (1,37 ± 0,01) %, respectivamente. No protótipo 2 foram feitas medições de nêutrons com os dois sistemas fotodiodo-boro (lâmina de vidro, direto no fotodiodo), porém nas medidas com o boro direto no sensor houve um aumento significativo no ruído eletrônico. A eficiência intrínseca do protótipo 2 para os nêutrons frios foi de (5,2 ± 0,4) %. / A portable thermal neutron detector prototype, using a silicon photodiode type PIN coupled to a boron converter, was developed at Nuclear and Energy Research Institute (IPEN-CNEN/SP). The boron layers were made by Pulsed Laser Deposition method using two configurations: directly deposited on the surface of photodiode and at a glass surface. Two prototypes were made in this study using two different associated electronics, in the first prototype is only possible reads signs from the photodiode coupled to boron film and in the second one reads both types of configurations (directly on the photodiode, boron glass). The prototypes were characterized using thermal and cold neutron beam. Four experiments were performed: response of the detection system at neutron beam, linearity test, angular response and repetitive test. The prototypes present a linear behavior, were reproducible and the angular response of the prototypes was not isotropic. The values of intrinsic efficiency from the prototype 1 for thermal and cold neutron were respectively: (1.17 ± 0.01) % e (1.37 ± 0.01) %. In the prototype 2 it was performed an experiment for compare the read out in the detection system for the two possible configuration of system photodiode-boron, in the situation that the boron is part integrant of the system there was an significant increase in the electronic noise, therefore the characterization of this prototype were made using the boron film coupled to the photodiode, and intrinsic efficiency for cold neutron beam was (5.2 ± 0.4) %.

A new set of thermal neutron detectors has been developed as a near term 3He tube replacement. The zinc oxide scintillator is an ultrafast scintillator which can be doped to have performance equal to or superior to 3He tubes. Originally investigated in the early 1950s, this room temperature semiconductor has been evaluated as a thermal neutron scintillator. Zinc oxide can be doped with different nuclei to tune the band gap, improve optical clarity, and improve the thermal neutron detection efficiency. The effects of various dopant effects on the scintillation properties, materials properties, and crystal growth parameters have been analyzed. Two different growth modalities were investigated: bulk melt grown materials as well as thin film scintillators grown by metalorganic chemical vapor deposition (MOCVD). MOCVD has shown significant advantages including precise thickness control, high dopant incorporation, and epitaxial coatings of neutron target nuclei. Detector designs were modeled and simulated to design an improved thermal neutron detector using doped ZnO layers, conformal coatings and light collection improvements including Bragg reflectors and photonic crystal structures. The detectors have been tested for crystalline quality by XRD and FTIR spectroscopy, for scintillation efficiency by photo-luminescence spectroscopy, and for neutron detection efficiency by alpha and neutron radiation tests. Lastly, a novel method for improving light collection efficiency has been investigated, the creation of a photonic crystal scintillator. Here, the flow of optical light photons is controlled through an engineered structure created with the scintillator materials. This work has resulted in a novel radiation detection material for the near term replacement of 3He tubes with performance characteristics equal to or superior to that of 3He.