Sentence:  More than 100 fatalities were recorded among these pioneer <WSD>radiationists</WSD>. One of the earliest and now best known incidents of Industrial radiation injury is that of the radium dial painters. During and immediately after World War I, a number of women worked in a war plant painting luminous watch and instrument dials. The  luminous material was a mixture of a paint containing zinc sulfide, which phosphoresces on exposure to alpha rays, and a radium salt. 
Meaning of the word marked with <WSD> tags:  One whose (medical or scientific) profession is to apply radiation or radioactive material (to someone or something).