The Vita-Ray Detector is a device used to analyze the presence and measure the amount of Vita Radiation.
During an investigation after the war into the theft of a formula for chemical Nitramene from the vault of Howard Stark, Anton Vanko told Peggy Carter that Nitramene emits Vita Radiation. With that information, Carter went to the file room of the Strategic Scientific Reserve New York Office and, in a file box dedicated to Project Rebirth, found the Vita-Ray Detector. While getting the device, Agent Daniel Sousa caught Carter reminiscing, but she did not let him know why she was in the room.
When the SSR learned after the implosion of the Roxxon Refinery that someone who handled the chemical would have been exposed to vita radiation, Chief Roger Dooley got permission from Roxxon Oil Corporation President Hugh Jones to have his employees scanned. Agent Jack Thompson wanted to scan everyone, but regulation would not allow him to scan the females, so Peggy Carter was called upon to help in the investigation.
Realizing that she might be radioactive since she was at the Refinery when it imploded, Carter used the Vita-Ray Detector to scan herself in the ladies' bathroom. She found herself clean except for the watch that her grandmother gave her; she said goodbye to it before putting it in the waste receptacle.
Carter and Thompson took turns scanning the women and men. When Thompson scanned Miles Van Ert with the device, he came up negative. However, Carter knew that he had been in the refinery because she had seen him and blinded him with the Stun Light Device. Since she was independently conducting her own investigation without the consent of the SSR, she could not tell her colleagues this, so Carter suggested that the locker room of the employees be scanned since the employees' lab coats might shield them from the radioactivity. Van Ert grew nervous upon hearing this and tried to escape; Carter helped in his capture.