After returning to Portugal and the University of Lisbon, and still in receipt of scholarships, he devoted himself to investigating nuclear physics and
X-ray spectroscopy. In the initial years he was constrained by a lack of suitable equipment due to funding shortages. In 1936 he started several research studies in the field of X-ray spectrography and radioactivity, but only presented the results some years later. In 1936 all civil servants were required by the Estado Novo to sign the following statement: "I declare on my honour that I am part of the order established by the Political Constitution of 1933, with an active rejection of communism and all subversive ideas". Valadares complied with the request reluctantly, one month after being asked. While in Paris he had collaborated with the
Mainini Institute, which was pioneering the use of X-rays to study works of art, particularly in the
Louvre museum. In 1937 he was given a scholarship to work with
João Couto, director of the
National Museum of Ancient Art in Lisbon to establish a laboratory to investigate works of art through the use of radiographic equipment. In 1940–1941, Valadares went on a scholarship to the
Alessandro Volta Institute in
Pavia, Italy, choosing that institution because it was in the process of assembling a particle accelerator. He was also able to use its Moll microphotometer to study the intensity of spectral streaks of lead. From Pavia, Valadares moved to the Physics Laboratory of the
Instituto di Sanitá Pubblica of
Rome, where he used a spectrograph specially built for him to study the crystalline diffraction of radiation. He then returned to Portugal, where he played an important role in the beginning of atomic and nuclear research at the Physics Laboratory of the Faculty of Sciences of the University of Lisbon, creating, with others, the Centre for Physics Studies (Centro de Estudos de Física) where he guided researchers in nuclear physics and spectrometry. Valadares was awarded a doctorate by the University of Lisbon in 1942. In the same year he was offered a full professorship by the
University of Porto but turned the offer down because he wanted to concentrate on research rather than teaching. This was despite his exceptional teaching skills, a fact that was highlighted when he was awarded an honorary degree at the University of Lisbon in 1981. Meanwhile, he continued to prepare a student manual on atomic physics, which was published in 1947. He was co-founder in 1943 of the journal
Portugaliae Physica. It was intended, through this magazine, both to disseminate the research work done in Portugal, and to also publish foreign scientists. He also contributed in 1946 to the foundation of the magazine
Gazeta de Física, aimed at Portuguese physicists and students, publishing several articles there. The first editor of this was
Lidia Salgueiro, whose PhD thesis he had supervised. ==Dismissal and return to Paris==