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Topic: Background radiation


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  Background radiation - Wikipedia, the free encyclopedia
A particular example of this is the cosmic microwave background radiation, a nearly uniform glow that fills the sky in the microwave part of the spectrum; stars, galaxies and other objects of interest in radio astronomy stand out against this background.
This background rate, which must be established as a stable value by multiple measurements, usually before and after sample measurement, is subtracted from the rate measured when the sample is being measured.
Background radiation for occupational doses measured for workers is all radiation dose that is not measured by radiation dose measurement instruments in potential occupational exposure conditions.
en.wikipedia.org /wiki/Background_radiation   (836 words)

  
 Cosmic microwave background radiation - Wikipedia, the free encyclopedia
The cosmic microwave background was predicted by George Gamow, Ralph Alpher, and Robert Hermann in 1948.
The interpretation of the cosmic microwave background was a controversial issue in the 1960s with some proponents of the steady state theory arguing that the microwave background was the result of scattered starlight from distant galaxies.
The period after the emission of the cosmic microwave background and the observation of the first stars is semi-humorously referred to by cosmologists as the dark age, and is a period which is under intense study by astronomers (See 21 centimeter radiation).
en.wikipedia.org /wiki/Cosmic_microwave_background_radiation   (3754 words)

  
 Blackbody Radiation
A uniform background radiation in the microwave region of the spectrum is observed in all directions in the sky.
The discovery of the 3K microwave background radiation was one of the crucial steps leading to the calculation of the standard "Big Bang" model of cosmology, its role being that of providing estimates of relative populations of particles and photons.
The scale of the fluctuations is larger than the horizon at the time the background radiation was emitted, indicating that the fluctuations are primordial, dating from a time before the separation of radiation and matter, the transparency point.
hyperphysics.phy-astr.gsu.edu /hbase/bkg3k.html   (913 words)

  
 The Microwave Background Radiation
The microwave background radiation is a messenger from this primordial soup.
The microwave background radiation was created in approximately the same environment everywhere (remember that it came from an epoch in which everything was a very homogeneous hot mixture of nuclei and electrons) and because of this we expect it to look the same in every direction.
The horizontal axis corresponds to the frequency of the radiation, the vertical axis to the intensity.
phyun5.ucr.edu /~wudka/Physics7/Notes_www/node118.html   (1011 words)

  
 The Cosmic Background Radiation
This radiation is the strongest evidence for the validity of the hot big bang model.
The cosmic background radiation (sometimes called the CBR), is the afterglow of the big bang, cooled to a faint whisper in the microwave spectrum by the expansion of the Universe for 15 billion years (which causes the radiation originally produced in the big bang to redshift to longer wavelengths).
As shown in the adjacent intensity map of the background radiation in different directions taken by the Differential Microwave Radiometer on NASA's COBE satellite, it is not completely uniform, though it is very nearly so (Ref).
csep10.phys.utk.edu /astr162/lect/cosmology/cbr.html   (660 words)

  
 NIH - What We Know About Radiation   (Site not responding. Last check: 2007-10-20)
Radiation is used in monitoring the response of tumors to treatment and in distinguishing malignant tumors from benign ones.
Radiation, surgery, and chemotherapy are the major ways in which cancer is treated; they are used singly or in combinations depending on the cancer.
The effectiveness of radiation in killing cancer cells--and, at the same time, the potential for harm to normal tissues--depends on several things, including the type of radiation used, the extent of the body that is treated, and the patient's age or other medical problems.
www.nih.gov /health/chip/od/radiation   (2978 words)

  
 Cosmology
The uniformity of the background radiation is evidence for the cosmological principle.
This background radiation is interpreted to be the relic of the early universe.
Notice that the background appears completely uniform at a temperature of 2.728 K. The colors for the temperatures range from blue for 2.724 K to red for 2.732 K. The double-lobe pattern shows the doppler effect from the motion of the Sun with respect to the background radiation.
www.astronomynotes.com /cosmolgy/s5.htm   (1289 words)

  
 Background Radiation
Background radiation varies over a range of concentrations and exposure rates from a variety of causes.
Understanding the characteristics of background, and the wide range of background values encountered in the field is beneficial when designing and conducting surveys.
This type of background refers to both the primary energetic particles of extraterrestrial origin that strike the earth's atmosphere and to the secondary particles generated by their interaction with the atmosphere.
www.tenorm.com /bkgrnd.htm   (1217 words)

  
 Wikinfo | Cosmic microwave background radiation   (Site not responding. Last check: 2007-10-20)
The Cosmic Microwave Background Radiation is a form of electromagnetic radiation that fills the whole of the universe.
This radiation is regarded as the best available evidence of the Big Bang theory -- it gives a snapshot of the Universe when the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thus making the universe transparent to radiation.
Of these experiments, the Cosmic Background Explorer (COBE) satellite that was flown in 1989-1996 is probably the most famous and which made the first detection of the large scale anisotropies (other than the dipole).
www.wikinfo.org /wiki.php?title=Cosmic_microwave_background_radiation   (747 words)

  
 UIC - Radiation and Life
The amount of ionising radiation, or 'dose', received by a person is measured in terms of the energy absorbed in the body tissue, and is expressed in gray.
The highest known level of background radiation affecting a substantial population is in Kerala and Madras States in India where some 140,000 people receive doses which average over 15 millisievert per year from gamma radiation in addition to a similar dose from radon.
Radiation protection standards are based on the conservative assumption that the risk is directly proportional to the dose, even at the lowest levels, though there is no evidence of risk at low levels.
www.uic.com.au /ral.htm   (3438 words)

  
 I 4 2 Cosmic Background Radiation   (Site not responding. Last check: 2007-10-20)
The existence of the background of matter provides a much more direct cause and effect explanation for the source of the cosmic microwave background radiation than does the more far fetched explanation that the cosmic microwave background radiation is the afterglow of the creation of the Universe.
The cosmic microwave background radiation is, to the very fine degree measured, a perfect match to a thermal flbody radiation curve of a body of matter at 2.7 degrees Kelvin, which would normally indicate that there is a body of matter at a temperature of 2.7 degrees Kelvin.
The deduction of the existence of the background of matter provided a much more direct cause for the cosmic microwave background radiation, which is that the cosmic microwave thermal flbody radiation is the flbody radiation of the background of matter.
www.starlight-pub.com /Matter/PartI/I4/I43Cosmic.html   (346 words)

  
 The Cosmic Microwave Background Radiation
It was soon determined that the radiation was diffuse, emanated unifromly from all directions in the sky, and had a temperature of approximately 3 Kelvin (2.73K).
Initially, the two young scientists were berefit of a satisfactory explanation for their observations, and considered the possibility that the CMB may have been due to some undetermined systematic noise.
The fact that the spectrum (see figure) of the radiation is almost exactly that of a fl body implies that it could not have had its origin through any prosaic means.
aether.lbl.gov /www/science/cmb.html   (827 words)

  
 The Background Radiation Survey Project
This project is an ongoing survey of the background radiation counts as determined by geiger counters at locations throughout the world.
The background radiation count should be taken and averaged over a period of time.
Some possibilities are correlating the background counts with disease statistics gathered from other sources or with the variables of location and time (observers may submit additional background counts if they are found to vary significantly with the date or time).
www.geocities.com /Athens/1555/backrad1.html   (622 words)

  
 Press Release: The 1978 Nobel Prize in Physics
The radiation is emitted in various ways; for example, hydrogen clouds in the Galaxy radiate when excited, and cosmic ray electrons radiate when spiralling in the weak magnetic fields of interstellar space.
The composition and origin of this background were for a long time not well understood; it was assumed to consist of the integrated radiation from a great number of sources, both galactic and extragalactic.
The study of cosmic microwave radiation, and especially of the weak background radiation, obviously requires the use of a very sensitive receiver.
nobelprize.org /physics/laureates/1978/press.html   (1477 words)

  
 Cosmology: A Research Briefing
The cosmic microwave background radiation (CMBR), discovered in 1964, is a telltale remnant of the early universe.
Currently, the radiation temperature is 2.73 K, which means that most of the CMBR exists now as radio energy in the microwave band.
The illustration on the cover of this report is the resulting COBE map of the intensity of microwave radiation arriving from various directions in the sky.
www.nap.edu /readingroom/books/cosmology/2.html   (2628 words)

  
 Cosmic Microwave Background - FAQs
All of the forms of electromagnetic radiation travel at the same speed, the speed of light, which is 300,000 km/s.
Microwaves are the name given to radiation between the infra-red and radio region, with wavelengths typically in the 1mm to 10cm range.
The focussed radiation is transported to the receivers by means of "wave-guides", which are pipes specially tuned to transmit microwave signals.
www.astro.ubc.ca /people/scott/faq_basic.html   (1466 words)

  
 Natural Radiation: High Background Radiation Areas (HBRAs) of Ramsar, Iran
The annual effective radiation dose from natural and man-made sources for the world's population is about 3 mSv, which includes exposure to alpha radiation from radon and its progeny nuclides.
The radioactivity of the high background radiation areas (HBRAs) of Ramsar is due to Ra-226 and its decay products, which have been brought to the surface by the waters of hot springs.
urrent radiation protection recommendations are based on the predictions of an assumption on linear, no-threshold dose-effect relationship (LNT).Beneficial effects and lack of detriment after irradiation with low levels of ionizing radiation, including a prolonged exposure to high levels of natural radiation of the inhabitants of HBRAs, are inconsistent with LNT (Mortazavi et al.
www.angelfire.com /mo/radioadaptive/ramsar.html   (1151 words)

  
 Background Radiation Measurements near Port Chicago
The elevated background radiation is downwind across Suisun Bay from the Concord Naval Weapons Center (formerly known as Port Chicago.) Residents of the Bay Area, particularly Contra Costa and Solano Counties, and the media have reason to ask what has happenned there that could explain elevated background radiation levels downwind from the base.
The first expedition to measure background radiation in the area was also a shakedown trip for the software, which I had just completed that day.
This is the script which draws the raw map image of the background radiation measured on the drive.
ian.kluft.com /pc44   (4139 words)

  
 Cosmic Microwave Background
He inaccurately predicted the temperature of this radiation to be about 50 K (-267°C), but his students later re-calculated the temperature to be 5 K. However, there was still no empirical proof of the existence of the radiation, so Gamow's theory fell somewhat into obscurity.
So as a result of the continual expansion of the universe, the light waves of this radiation have stretched out to longer wavelengths which today exist in the microwave region of the electromagnetic spectrum (which is why we call it the Cosmic "Microwave" Background).
Astronomers and physicists suspected that the Cosmic Microwave Background might display very slight fluctuations in temperature, but this data could not be accurately recorded until the flight of COBE because it was the first satellite experiment to gather information from outer space, where all of the background noise from water vapor could be eliminated.
cmb.physics.wisc.edu /tutorial/cmb.html   (1431 words)

  
 Cosmic Background Radiation   (Site not responding. Last check: 2007-10-20)
This radiation, which is detectable by sensitive radio frequency detectors, is the afterglow of the Big Bang, cooled to a faint whisper in the radio spectrum by the expansion of the Universe for 15 billion years.
As shown in the adjacent intensity map of the background radiation in different directions taken by the Differential Microwave Radiometer on NASA's Cosmic Background Explorer (COBE) Satellite, it is not completely uniform (though it is very nearly so).
A small lack of uniformity in the background radiation is probably essential to the ultimate formation of the galaxies.
csep10.phys.utk.edu /guidry/violence/bang2.html   (289 words)

  
 WMAP Cosmology 101: Cosmic Microwave Background   (Site not responding. Last check: 2007-10-20)
The existence of the CMB radiation was first predicted by George Gamow in 1948, and by Ralph Alpher and Robert Herman in 1950.
Today, the CMB radiation is very cold, only 2.725° above absolute zero, thus this radiation shines primarily in the microwave portion of the electromagnetic spectrum, and is invisible to the naked eye.
In addition to this cosmic microwave background radiation, the early universe was filled with hot hydrogen gas with a density of about 1000 atoms per cubic centimeter.
map.gsfc.nasa.gov /m_uni/uni_101bbtest3.html   (1150 words)

  
 A Science Odyssey: People and Discoveries: Penzias and Wilson discover cosmic microwave radiation
He had elaborated on existing theory to suggest that if there had been a big bang, the residue of the explosion should by now take the form of a low-level background radiation throughout the universe.
This was partly because, as Steven Weinberg wrote, "in the 1950s, the study of the early universe was widely regarded as not the sort of thing to which a respectable scientist would devote his time." Since Penzias, Wilson, and Dicke's work, all that has changed.
The measurement of cosmic background radiation (as the Holmdel telescope's noise is now called), combined with Edwin Hubble's much earlier finding that the galaxies are rushing away, makes a strong case for the big bang.
www.pbs.org /wgbh/aso/databank/entries/dp65co.html   (690 words)

  
 Footprints of Creation
In 1989, an instrument aboard the Cosmic Background Explorer (COBE) satellite measured the cosmic background radiation with unprecedented accuracy.
COBE measured a cosmic background radiation spectrum that fits perfectly with the predicted flbody spectrum at 2.735 degrees Kelvin.
Until 1992, the cosmic background radiation was thought to vary by no more than one part in 10,000.
archive.ncsa.uiuc.edu /Cyberia/Cosmos/Footprints.html   (791 words)

  
 ESA - Space Science - Home - Cosmic Microwave Background (CMB) radiation
The Cosmic Microwave Background (CMB) is the cooled remnant of the first light that could ever travel freely throughout the Universe.
Penzias and Wilson, two radio astronomers in the United States, registered a signal in their radio telescope that could not be attributed to any precise source in the sky.
Since the time when that radiation was released, the Universe has expanded, becoming at the same time cooler and cooler.
www.esa.int /esaSC/SEMB3AR1VED_index_0.html   (611 words)

  
 Cosmic Microwave Background Radiation   (Site not responding. Last check: 2007-10-20)
They calculated that this radiation should still be visible but because of the expansion of the universe would by now have been red-shifted to the microwave part of the spectrum.
It was important to establish that the radiation was consistent with that from a fl-body.
The COBE (Cosmic Background Explorer) satellite was developed to measure the diffuse infrared and cosmic microwave background radiation from the early Universe.
www.schoolsobservatory.org.uk /study/sci/cosmo/internal/microwav.htm   (1051 words)

  
 EPA - Calculate Your Radiation Dose? (EPA's Radiation Protection Programs: Perspectives)   (Site not responding. Last check: 2007-10-20)
The amount of radiation exposure is usually expressed in a unit called millirem (mrem).
The primary sources of information we relied on are the National Council on Radiation Protection and Measurements Reports #92-#95, and #100.
Please remember that the values used in the calculator are general averages and do not provide precise individual dose calculations.
www.epa.gov /radiation/students/calculate.html   (316 words)

  
 Cosmic Microwave Background - Introduction
It was soon determined that the radiation was diffuse, emanated unifromly from all directions in the sky, and had a temperature of approximately 2.7 Kelvin (ie 2.7 degrees above absolute zero).
The fact that the spectrum (see figure) of the radiation is almost exactly that of a "fl body" (a physicists way of describing a perfect radiator) implies that it could not have had its origin through any prosaic means.
The pattern of this temperature variation on the sky is known as a "dipole", and is exactly what is expected if we are moving through the background radiation at high speed in the direction of the hot part.
www.astro.ubc.ca /people/scott/cmb_intro.html   (1634 words)

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