The Cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen. The image may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets and others.
CRTs can emit a small amount of X-ray radiation as a result of the electron beams bombardment of the shadow mask/aperture grille and phosphors. The amount of radiation escaping the front of the monitor is widely considered un-harmful. The Food and Drug Administration regulations in 21 C.F.R. 1020.10 are used to strictly limit, for instance, television receivers to 0.5 milliroentgens per hour (mR/h) (0.13°C/(kg°h) or 36 pA/kg) at a distance of 5 cm (2 in) from any external surface; since 2007, most CRTs have emissions that fall well below this limit.
Radiation poisoning can show a number of symptoms which should be watched for. These symptoms can be dividied into three main sections: Hematopoietic, gastrointestinal and neurological/vascular. These symptoms may or may not be preceded by a prodrome. The speed of onset of symptoms is related to radiation exposure with greater doses resulting in a shorter delay in symptom onset.
Hematopoietic syndrome is marked by a drop in blood cells which results in infections due to low white blood cells, bleeding due to low platelets, and anemia due to low red blood cells.
Gastrointestinal syndrome typically occurs at exposure doses of 600-1000 rad (6-10 Gy). Nausea, vomiting, loss of appetite, and abdominal pain are usually seen within one to two hours.
Neurovascular syndrome typically occurs at exposure doses greater than 1000 rad (10 Gy). It presents with neurological symptoms such as dizziness, headache, or decreased level of consciousness with an absence of vomiting.
The prodrome associated with ARS typically includes nausea and vomiting, headaches, fatigue, fever and short period of skin reddening. These symptoms may occur at radiation doses as low as 35 rad (0.35 Gy) and thus may not be followed by acute radiation sickness.