Beta burns—caused by
beta particles—are shallow surface burns, usually of skin and less often of
lungs or
gastrointestinal tract, caused by beta particles, typically from
hot particles or dissolved
radionuclides that came to direct contact with or close proximity to the body. They can appear similar to sunburn. Unlike gamma rays, beta emissions are stopped much more effectively by materials and therefore deposit all their energy in only a shallow layer of tissue, causing more intense but more localized damage. On cellular level, the changes in skin are similar to radiodermatitis. The dose is influenced by relatively low penetration of beta emissions through materials. The
cornified keratine layer of
epidermis has enough stopping power to absorb beta radiation with energies lower than 70 keV. Further protection is provided by clothing, especially shoes. The dose is further reduced by limited retention of radioactive particles on skin; a 1 millimeter particle is typically released in 2 hours, while a 50 micrometer particle usually does not adhere for more than 7 hours. Beta emissions are also severely attenuated by air; their range generally does not exceed and intensity rapidly diminishes with distance. The
eye lens seems to be the most sensitive organ to beta radiation, even in doses far below maximum permissible dose.
Safety goggles are recommended to attenuate strong beta. Careful washing of exposed body surface, removing the radioactive particles, may provide significant dose reduction. Exchanging or at least brushing off clothes also provides a degree of protection. If the exposure to beta radiation is intense, the beta burns may first manifest in 24–48 hours by itching and/or burning sensation that last for one or two days, sometimes accompanied by
hyperaemia. After 1–3 weeks burn symptoms appear; erythema, increased
skin pigmentation (dark colored patches and raised areas), followed by
epilation and
skin lesions. Erythema occurs after 5–15
Gy, dry desquamation after 17 Gy, and
bullous epidermitis after 72 Gy. Inhalation of beta radioactive isotopes may cause beta burns of lungs and
nasopharyngeal region, ingestion may lead to burns of gastrointestinal tract; the latter being a risk especially for
grazing animals. • In first degree beta burns the damage is largely limited to epidermis. Dry or wet desquamation occurs; dry
scabs are formed, then heal rapidly, leaving a depigmented area surrounded with irregular area of increased pigmentation. The skin pigmentation returns to normal within several weeks. • Second degree beta burns lead to formation of
blisters. • Third and fourth degree beta burns result in deeper, wet
ulcerated lesions, which heal with routine medical care after covering themselves with dry scab. In case of heavy tissue damage, ulcerated necrotic
dermatitis may occur. Pigmentation may return to normal within several months after wound healing. The acute dose-dependent effects of beta radiation on skin are as follows: As shown, the dose thresholds for symptoms vary by source and even individually. In practice, determining the exact dose tends to be difficult. Similar effects apply to animals, with fur acting as additional factor for both increased particle retention and partial skin shielding. Unshorn thickly wooled sheep are well protected; while the epilation threshold for sheared sheep is between 23 and 47 Gy (2500–5000
rep) and the threshold for normally wooled face is 47–93 Gy (5000–10000 rep), for thickly wooled (33 mm hair length) sheep it is 93–140 Gy (10000–15000 rep). To produce skin lesions comparable with
contagious pustular dermatitis, the estimated dose is between 465 and 1395 Gy.
Energy vs penetration depth The effects depend on both the intensity and the energy of the radiation. Low-energy beta (sulfur-35, 170 keV) produces shallow ulcers with little damage to dermis, while
cobalt-60 (310 keV),
caesium-137 (550 keV),
phosphorus-32 (1.71 MeV),
strontium-90 (650 keV) and its daughter product
yttrium-90 (2.3 MeV) damage deeper levels of the
dermis and can result in
chronic radiation dermatitis. Very high energies from
electron beams from
particle accelerators, reaching tens of megaelectronvolts, can be deeply penetrating. Conversely, megavolt-scale beams can deposit their energy deeper with less damage to the dermis; modern radiotherapy electron beam accelerators take advantage of this. At yet higher energies, above 16 MeV, the effect does not show significantly anymore, limiting the usefulness of higher energies for radiotherapy. As a convention, surface is defined as the topmost 0.5 mm of skin. High-energy beta emissions should be shielded with plastic instead of lead, as
high-Z elements generate deeply penetrating gamma
bremsstrahlung. The electron energies from
beta decay are not discrete but form a continuous spectrum with a cutoff at maximum energy. The rest of the energy of each decay is carried off by an
antineutrino which does not significantly interact and therefore does not contribute to the dose. Most energies of beta emissions are at about a third of the maximum energy. The penetration depth of lower-energy beta in water (and soft tissues) is about 2 mm/MeV. For a 2.3 MeV beta the maximum depth in water is 11 mm, for 1.1 MeV it is 4.6 mm. The depth where maximum of the energy is deposited is significantly lower. The energy and penetration depth of several isotopes is as follows: For a wide beam, the depth-energy relation for dose ranges is as follows, for energies in
megaelectronvolts and depths in millimeters. The dependence of surface dose and penetration depth on beam energy is clearly visible. == Causes ==