The Single Photon Annihilation Contributions to the Positronium Hyperfine Splitting to Order meα6m_e\alpha^6

The single photon annihilation contributions for the positronium ground state hyperfine splitting are calculated analytically to order $m_e\alpha^6$ using NRQED. Based on intuitive physical arguments the same result can also be determined by a trivial calculation using results from existing literature. Our result completes the hyperfine splitting calculation to order $m_e\alpha^6$. We compare the theoretical prediction with the most recent experimental measurement.Comment: 8 pages, latex, two eps figures include

Notable Radiophysicists and Radiochemists in Croatia by 1945

U ovome preglednom radu dan je uvid u život i rad doajena znanosti o zračenju i zaštite od zračenja u Hrvatskoj do 1945. godine. Efektivni počeci znanosti o zračenju, pa tako i zaštite od zračenja na području Hrvatske sežu čak do kraja 19. stoljeća. Fizičari i kemičari bili su među prvima mogućim žrtvama izloženosti ionizirajućem zračenju, pa su tako i bili prvi koji su upozoravali na štetne učinke radijacije na žive organizme. Pretraživanje dostupnih arhiva i poznate literature nije samo rasvijetlilo život i rad doajena znanosti o zračenju već je omogućilo sistematičan uvid u do sada nepoznate detalje važne za povijest i razvoj znanosti o zračenju, zaštite od zračenja, kao i o medicinskoj fi zici. Sve to pokazuje da Hrvatska od samoga početka ne samo da slijedi najsuvremenije znanstvene spoznaje iz tih područja, već i njima aktivno pridonosi.Physicists and chemists were among the first potential victims of occupational exposure to ionising radiation and they were also the first to warn about the harmful effects of radiation on living organisms. This review presents the work of the first notable scientists in the field of radiation science in Croatia from the discovery of radiation (Henry Becquerel in 1896) to 1945. The beginning of radiation science and radiation protection in Croatia can be traced to the end of the 19th century. Our research of the archived material and literature not only gave a deeper insight to the life and work of some of these notable scientists, but also gave a glimpse of previously unknown facts and details important for the history and development of radiation science, radiation protection, as well as medical physics. Our research has shown that Croatian scientists not only kept pace with contemporary scientific knowledge but also made notable contributions from the very beginning