Which of the following has highest penetrating power?
Correct Answer: Gamma ray
Description: Ans. b (Gamma ray) (Ref. H - 16th/pg. 1294)IONIZING RADIATIONS# Alpha (a) radiation- Consists of heavy, positively charged particles containing two protons and two neutrons.- Alpha particles are usually emitted from isotopes with an atomic number of >82, such as uranium or plutonium.- Due to their large size, alpha particles have limited (least) penetrating power.- Fine obstacles such as cloth, piece of paper or human skin can usually stop them from penetrating into the body, and they represent a small risk to external exposure due to their limited penetration.- If they somehow are internalized, then alpha particles can cause significant cellular damage within their immediate proximity.# Beta (b) radiation- Consists of electrons, which are small, light, negatively charged particles (about 1/2000 the mass of a neutron or proton).- They can travel only a short finite distance in tissue, depending on their energy.- Exposure to beta particles is common in many radiation accidents. Radioactive iodine, released in nuclear plant accidents, is the best known member of this group.- Plastic layers and clothing can stop most beta particles, and their penetration is measured to be a few millimeters. A large quantum of energy to the basal stratum of the skin can cause a bum that is similar to a thermal burn and is treated as such.- Pure beta emitters (Phosphorous, Strontium, Samarium, Rhenium, Yttrium, and Iodine) are used in systemic radio- therapy (e.g. strontium-89 - 8Gy in single fraction - for palliative treatment of painful bone metastases)# Gamma (y) rays and x-rays (both photons) are similar.- Gamma rays are uncharged electromagnetic radiation (non-particulate) discharged from a nucleus as a wave or photons of energy.- Gamma (y) rays have highest penetrating power and least ionization potential.# X-rays- Are the result of abrupt mechanical deceleration of electrons striking a heavy target such as tungsten.- Gamma and X-rays have similar properties, i.e., no charge and no mass, just energy.- Both travel easily through matter, sometimes called penetrating radiation, and are the principal type of radiation to cause total-body exposure.# Neutrons (N) particles- Are heavy and uncharged, often emitted during nuclear detonation.- They possess a wide energy range; their ability to penetrate tissues is variable, depending upon their energy.- They are less likely to be present in most scenarios of radiation bioterrorism.- Neutron therapy is tried in treatment of brain tumors (e.g., cystic gliomas) - BNCT. Califomum is its importantsource.- The ionization resulting from protons, electrons, and gamma rays is either a direct or indirect (i.e., mediated through water - free radical injury) effect of particles or photons on DNA.- Ionization of DNA resulting from neutrons is secondary to the neutrons knocking electrons out of their atomic orbit and the formation of free radicals, which can also damage DNA directly.RadiationPenetrating PowerIonizationPotentialSourceFormClinical UseAlpha particles (Helium nuclei) He++Least (can be stopped with just a piece of paper)Highest# Uranium# Plutonium-NoneBeta particlesIntermediateIntermediate# P-32# Strontium-89# Samarium# Rhenium# Yttrium# l131Systemic RTPalliative Rx of painful bone metastases with 8 Gy Strontium-89 in single fraction.131l therapy for papillary thyroid cancer.Gamma raysHighestLeast# Tc99m # Co-60 Scintigraphy-is diagnostic use.Teletherapy & Gamma-knife are for therapeutic useX-rays and gamma rays are the most common radiation used for RT.Gamma-imaging (Scintigraphy/ nuclear scan) is investigation ofchoice for many functional diseases.
Category:
Radiology
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