alpha particles

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the first letter of the Greek alphabet, α; used to denote the first position in a classification system; as, in names of chemical compounds, to distinguish the first in a series of isomers, or to indicate the position of substituent atoms or groups; also used to distinguish types of radioactive decay, brain waves or rhythms, adrenergic receptors, and secretory cells that stain with acid dyes, such as the alpha cells of the pancreas.
alpha-adrenergic blocking agent (alpha-blocker) (alpha-blocking agent) any of a group of drugs that selectively inhibit the activity of alpha receptors in the sympathetic nervous system. As with beta-adrenergic blocking agents, alpha-blocking agents compete with the catecholamines at peripheral autonomic receptor sites. This group includes ergot and its derivatives, and phentolamine.
alpha chain disease the most common heavy chain disease, occurring predominantly in young adults in the Mediterranean area, and characterized by plasma cell infiltration of the lamina propria of the small intestine resulting in malabsorption with diarrhea, abdominal pain, and weight loss, or, exceedingly rarely, by pulmonary involvement. The gastrointestinal form is immunoproliferative small intestine disease.
alpha-fetoprotein (AFP) a plasma protein produced by the fetal liver, yolk sac, and gastrointestinal tract and also by hepatocellular carcinoma, germ cell neoplasms, and other cancers in adults; elevated levels may also be seen in benign liver disease such as cirrhosis and viral hepatitis. The serum AFP level is used to monitor the effectiveness of cancer treatment.

During pregnancy some AFP crosses from the amniotic fluid to the mother's blood. If the fetus has a neural tube defect, large amounts of AFP will be found in the amniotic fluid and maternal blood. Blood screening tests for serum AFP can thus be done as a first step in the screening process; if test results are positive, further testing is indicated to diagnose the defect.
alpha particles a type of emission produced by the disintegration of a radioactive substance. The atoms of radioactive elements such as uranium and radium are very unstable, continuously breaking apart with explosive violence and emitting particulate and nonparticulate types of radiation. The alpha particles, consisting of two protons and two neutrons, have an electrical charge and form streams of tremendous energy when they are released from the disintegrating atoms. These streams of energy (alpha rays) can be used in treatment of various malignancies. See also radiation and radiation therapy.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

alpha particles

, alpha rays
Radioactive, positively charged particles, equivalent to a helium nucleus (two protons and two neutrons), ejected at high speeds in certain atomic reactions.
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References in periodicals archive ?
The researchers could then calculate the rate of the inverse reaction, given how often slower alpha particles - and by proxy, the splitting of O-16 atoms - occurred.
Alpha particles consist of two protons and two neutrons.
As a result, given the potential repulsion of two protons (~ 0.6 MeV at a specified distance 2.38 fm on the scheme), we obtain: [E.sub.a] = 0.511 x (4.3 x 8 + 10.75 x 2) -0.6 = 28.0 MeV, which corresponds well to the actual alpha particles binding energy (28.2 MeV).
The upper region above the [sup.3]H cut-off covers the LS response NLS attributed principally to alpha particles and includes the "anomalous bumps" [6] on the low energy shoulder.
this is done by special filters for absorbing radon inside the counter machine and the alpha particles emitted from it are counted by ionization chamber in counter machine.
"What we do is strip the inner electrons out of the atom, by getting close to the sample and hitting it with either an alpha particle or an X-ray.
[.sup.210]Po presents a radiation hazard only if taken into the body because its alpha particles have a range of only 40-50 [micro]m in biological tissue and are easily stopped by surface layers of the skin (Jefferson et al.
As for the radiation cookies, the cookie emitting alpha particles can be held safely in one's hand, since the particles don't penetrate the skin.
* Alpha particles. Alpha particles (helium nuclei) capture electrons from nearby atoms; if the electrons are shared by two atoms forming a molecule, then the molecule is broken.
Unlike conventional radiation therapy, which bombards the body with gamma rays from outside, the alpha particles diffuse inside the tumour, spreading further and further before disintegrating, a university statement quoted Keisari as saying.
The highest peak on the plot is a result of the XASW interaction with the alpha particles oscillating at the first cyclotron harmonic of helium.
Alpha particles, beta particles and gamma rays emerged as the prime carriers of radioactivity's energy.