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Topic: Delayed neutron

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	Nuclear chain reaction - Wikipedia, the free encyclopedia
		Pu-239 + neutron = fission fragments + 2.95 neutrons + 200 MeV.
		The effective neutron multiplication factor k is the average number of neutrons from these 2.5 or 3 cause another fission reaction, as opposed to neutrons produced by the fission which are being absorbed without causing a new fission, and those travelling out of the system.
		It is usual to split the population of neutrons which are emitted into two sorts - 'prompt neutrons' and 'delayed neutrons' Typically, the 'delayed neutron fraction' is less than 1 % of the whole.
	en.wikipedia.org /wiki/Nuclear_chain_reaction (1254 words)

	Prompt critical - Wikipedia, the free encyclopedia
		Thermal neutrons are neutrons with a speed such that they are capable of initiating further fission events.
		Some are released more or less immediately (and are termed prompt neutrons); other neutrons are released by fission breakdown products as these breakdown products themselves undergo nuclear decay (and these are termed delayed neutrons).
		Prompt neutrons have a lifetime of about 0.0001 s from the fission event that generated them, and delayed neutrons have a "lifetime" (time to be generated plus time before they are absorbed) of about 10 s, so the average neutron "lifetime" is about 0.1 s.
	en.wikipedia.org /wiki/Prompt_critical (970 words)

	Effective Delaved Neutron Fraction
		, the delayed neutron fraction, is the fraction of all fission neutrons that are born as delayed neutrons.
		First, delayed neutrons have a much lower probability of causing fast fissions than prompt neutrons because their average energy is less than the minimum required for fast fission to occur.
		Second, delayed neutrons have a lower probability of leaking out of the core while they are at fast energies, because they are born at lower energies and subsequently travel a shorter distance as fast neutrons.
	www.tpub.com /doenuclearphys/nuclearphysics80.htm (469 words)

	Encyclopedia :: encyclopedia : Nuclear chain reaction (Site not responding. Last check: 2007-11-05)
		The first artificial self-sustaining nuclear chain reaction was initiated by the Metallurgical Laboratory, led by Enrico Fermi, in a racquets court below the bleachers of Stagg Field at the University of Chicago on December 2, 1942 during the Manhattan Project.
		The effective neutron multiplication factor k is the average number of neutrons from a nuclear fission reaction that cause another fission reaction, as opposed to neutrons produced by the fission which are being absorbed without causing a new fission, and those travelling out of the system.
		It is usual to split the population of neutrons which are emitted into two sorts - 'prompt neutrons' and 'delayed neutrons' Typically, the 'delayed neutron fraction' is less than 1 percent of the whole.
	www.hallencyclopedia.com /Nuclear_chain_reaction (605 words)

	SDV Nuclear Glossary (Site not responding. Last check: 2007-11-05)
		Delayed neutrons account for approximately 0.75% of the neutron output from fission and this is an important aspect of controlling the increase in energy output of reactors.
		A neutron emitted as a nuclide undergoes fission.
		Absorption of a neutron by an atomic nucleus.
	glossary.dataenabled.com /sdvglossary_neutrons.html (874 words)

	World Nuclear Association \| Education \| Some Physics of Uranium (Site not responding. Last check: 2007-11-05)
		A neutron is said to have thermal energy when it has slowed down to be in thermal equilibrium with the surroundings (when the kinetic energy of the neutrons is similar to that possessed by the surrounding atoms due to their random thermal motion).
		The delayed neutron release is the crucial factor enabling a chain reacting system (or reactor) to be controllable and to be able to be held precisely critical.
		Neutrons may be captured by non-fissile nuclei, and some energy is produced by this mechanism in the form of gamma rays as the compound nucleus de-excites.
	www.world-nuclear.org /education/phys.htm (3824 words)

	Active neutron plunger (ANP) system -- Mohr Engineering (Site not responding. Last check: 2007-11-05)
		Consequently, the emission probability of delayed neutrons in fission depends on both the fissile nuclide and neutron energy, but this dependence is generally no more than a few per cent.
		Delayed neutron detection commences after the 5 second delay that is required to insert and position the central detector array.
		When a detectable delayed neutron count has been observed for a fissile waste drum, it may be possible to use background neutron measurements to identify the fissile isotope present.
	www.mohr-engineering.com /INEEL_ANPmethod_5_2000/active_neutron_plunger.htm (5114 words)

	REACTOR PERIODS AND REACTIVITY (Site not responding. Last check: 2007-11-05)
		Fundamentally, the neutron lifetime may be divided into two parts: (a) slowing down time, which is the mean time required for fission neutrons to slow to thermal energies and, (b) diffusion time, which is the average time that thermal neutrons will diffuse before absorption.
		Delayed neutrons are a small fraction of all neutrons in the reactor core.
		As positive reactivity is added to the critical reactor, the effects, in terms of time response and generation time, for prompt neutrons is enhanced and the effects for delayed neutrons are diminished.
	www.me.wpi.edu /Nuclear/Reactor/Labs/L-rho.html (627 words)

	NUKEFACTS ... and fictions
		The important distinction between prompt and delayed neutrons is that while prompt neutrons appear at the instant of fission, delayed neutrons appear at some later time, extending from the immediately after the fission to well in excess of 100 seconds following the fission event.
		If the neutron population is changing with time, then it is not possible that both the precursor atoms and the identical number of delayed neutrons make up the same fraction, beta, of different neutron populations.
		The vertical axis is the delayed neutron population fraction, DNF, while the horizontal axis is reactivity.
	www.pipeline.com /~rstater/nuke1a.html (786 words)

	RP Mod 12 Section 4 Page 1
		The delayed neutron fraction can be discussed as both an actual and effective fraction.
		Neutron life-time is the average time from the formation of the precursor until a delayed neutron is emitted, or, that is to say,
		The average neutron life-time of delayed neutrons is about 13 sec, or in other words, this is about the time lapse we must wait for the average delayed neutrons to be released by their precursors.
	www.iaea.org /ns/nusafe/tutors/reactorphysics/module12/learningmaterial/s4p1.htm (252 words)

	German court shuts down Wikipedia.de
		It was the neutron flux in the core that caused the accident, not a chemical reaction.
		To say that the reactor had "extra neutrons" seems to be a way of saying super or prompt critical without "getting specific," other than being generally incorrect way of viewing things; it also implies that the reactor was already in an exponential power growth in the power range.
		There are two forms, average delayed neutron fraction (beta-bar) and effective (beta eff) (neutrons produced and the neutrons absorbed).
	lofi.forum.physorg.com /German-court-shuts-down-Wikipedia.de_4608.html (3992 words)

	Clean And Environmentally Safe Advanced Reactor - Wikipedia, the free encyclopedia
		U fuel rods moderated by liquid water coolant ultimately creates a Maxwellian thermal neutron flux profile, the neutron energy profile from delayed neutrons varies widely.
		Filippone maintains that when steam is used as the moderator, the average neutron speed/energy is increased from that of a liquid water moderated reactor and the delayed neutrons keep going until they hit another nucleus.
		U to create a critical system (one in which the number of neutrons created by fission is equal to the number absorbed).
	en.wikipedia.org /wiki/Clean_And_Environmentally_Safe_Advanced_Reactor (436 words)

	Effective Delayed Neutron Precursor Decay Constant
		The decay constant of a precursor is simply the fraction of an initial number of the precursor atoms that decays in a given unit time.
		, the emission of prompt fission neutrons alone is not sufficient to overcome losses to non-fission absorption and leakage.
		If delayed neutrons were not being produced, the neutron population would decrease as long as the reactivity of the core has a value less than the effective delayed neutron fraction.
	www.tpub.com /doenuclearphys/nuclearphysics81.htm (576 words)

	P4_3
		Comparison of the present data was made with the ENDF/B-VI data in the terms of average half-life of delayed neutron precursors and on the basis of the dependence of reactivity on asymptotic period.
		According to the com-parison of experimental data with our prediction based on correlation properties of delayed neutron characteristics, it is concluded that the value of the total delayed neutron yield near the threshold of (n,f) reaction is not a constant.
		The energy spectrum of the delayed neutrons is the poorest known of all input data required in the calculation of the effective delayed neutron fractions.
	www.ippe.obninsk.ru /podr/cjd/vant01-1.html (1511 words)

	ANS : Store : Electronic Articles
		The effective delayed neutron fraction for a bare critical comprised of a fissile material is comparable with the absolute delayed neutron fraction.
		The effective delayed neutron fraction for a bare critical composed of a fissionable material is reduced by factors of 2 to 10 when compared with the absolute delayed neutron fraction.
		When the effective delayed neutron fraction is small, the difference between delayed and prompt criticality is small, and extreme caution must be used in critical assemblies of these materials.
	www.ans.org /store/index.cgi?i=E120000-nt-128-3-402-408 (163 words)

	Control of Fission Chain Reactions
		Since the continued chain reaction of a nuclear fission reactor depends upon at least one neutron from each fission being absorbed by another fissionable nucleus, the reaction can be controlled by using control rods of material which absorbs neutrons.
		This is modified significantly by inclusion of the delayed neutrons.
		The reproduction constant k for a nuclear fission process is defined as the average number of neutrons from each fission which subsequently cause another fission.
	hyperphysics.phy-astr.gsu.edu /hbase/nucene/control.html (524 words)

	ILL : ANNUAL REPORT 2001 (Site not responding. Last check: 2007-11-05)
		Ni is the most neutron rich doubly magic nucleus, which supposedly can be reached in a nuclear reaction.
		Neutrons are considered here simultaneously as a tool and as the object of investigations.
		Recent and intensive studies of asymmetries in polarised cold neutron induced fission have already yielded big surprises and further exciting physical results are expected soon.
	www.ill.fr /AR-01/p-18.htm (585 words)

	RP Mod 4 Section 2 Page 1
		The neutron emitted is a prompt neutron, but it occurs some time after the original fission, since the Br must decay first.
		As we will see, the proportion of delayed neutrons has a very important effect on the control of the reactor.
		Table-2 displays the characteristics of the delayed neutrons in thermal fission.
	www.iaea.org /ns/nusafe/tutors/reactorphysics/module4/learningmaterial/section2p1.htm (128 words)

	CAARI2002
		Delayed neutrons were detected between pulses by large 3He detectors, and the data were analyzed with the Feynman variance method to determine the number of single- and double-neutron events from the fissions.
		Detector results are providing very useful information regarding the challenges of delayed neutron counting near the photofission threshold energy of 5.5 Ð 6.0 MeV, have identified the possible utilization of prompt neutron emissions to allow enhanced signal-to-noise measurements, and are showing the overall benefits of using slightly higher electron beam energies.
		The primary objective of these tests was to assess the delayed neutron emission responses from different nuclear materials with various shield materials using three nominal electron beam energies: 8-, 10-, and 11-MeV.
	www.jlab.org /~cole/CAARI2002.html (701 words)

	[No title]
		The mass of protons and neutrons is similar, and each is about 1800 times larger than an electron.
		Chemical characteristics are not altered by changes in the number of neutrons, thus all isotopes have the same chemical behavior.
		One of the elements measured by delayed gamma neutron activation is calcium.
	www.bcm.edu /bodycomplab/dgtheorypage.htm (330 words)

	Theory of the angular distribution of beta-delayed protons from oriented nuclei
		Experiments on beta-delayed protons and neutrons [4] studying properties of highly excited particle emitting states, were pursued in the 1970's and 1980's.
		We have explored beta-delayed proton and neutron emission theoretically in detail, building on theory of the process for randomly oriented precursors [6,7] with coverage of the angular distribution properties examining the dependence of the energy spectra and angular distribution upon all variables involved.
		Since neutron emission does not need to overcome a Coulomb barrier, in some cases neutrons are emitted from states in the emitter at lower excitation energy.
	www-nog.physics.ox.ac.uk /www/quantum/quantum.htm (2115 words)

	ANS : Store : Electronic Articles
		The six-group delayed neutron data available in the literature from both macroscopic level experiments and microscopic level calculations for several actinide isotopes are compared.
		Results are also presented from recent experimental measurements of delayed neutron emission and delineates some of the relationships between these measurements and microscopic level predictions.
		In the future, it may be useful to use properties of specific isotopes to replace Keepin's delayed neutron groups 1, 2, 3, and 4 for prescribing delayed neutron data for actinides.
	www.ans.org /store/index.cgi?i=E110000-nse-131-2-208-221 (256 words)

	WSRC-MS-98-00726
		Neutron activation analysis using low-flux isotopic neutron sources is put to use in addressing areas of applied interest in managing the Savannah River Site.
		He-filled proportional counters for delayed neutron counting are located adjacent to the NAA tank in a counting vault with a 1.2-meter wall thickness.
		Despite the low neutron flux, the NAA facility’s sensitivity is adequate for many analytical projects, and it is a more cost-effective choice in many cases because it allows analysis of bulk samples without chemical digestion.
	sti.srs.gov /fulltext/ms9800726/ms9800726.html (2483 words)

	D.html
		DELAYED COINCIDENCE A measurement using a coincidence circuit in which it is required that in order to be recorded, the occurrence of two events be separated by an electronically imposed time delay.
		DELAYED NEUTRON EMISSION Radioactive decay to a daughter product which is unstable towards emitting a neutron and consequently does so in some fraction of decay events.
		Half-lives for delayed neutron emission are long compared to neutron emission associated directly with nuclear reactions or fission.
	www.iupac.org /ACD/V7_karol/D.html (1448 words)

	Energy Citations Database (ECD) - Energy and Energy-Related Bibliographic Citations
		Delayed neutron precursors are expected to appear from the lightest to the heaviest nuclides on the neutron-rich side of the BETA -stability line.
		The short half-lives and the low neutron yield (the latter caused by the rather small branching ratio to the neutronemitting state of the delayed neutron emitter) necessitate that the measurerments start immediately after irradiaiion.
		This requirement was fulfilled by placing the neutron detector at a small radial distance from the irradiated target in the vacuum chamber of the synchro-cyclotron.
	www.osti.gov /energycitations/product.biblio.jsp?osti_id=4113387 (266 words)

	[No title]
		Since the energy of the delayed fission spectrum is lower than that of the prompt fission spectrum, delayed neutrons have a smaller chance to leak out of the system.
		The second set of cases is similar to modeling individual fuel assemblies in the reactor core in which neutron leakage effects are significant.
		Results from pin-cell calculations indicate that there are only minor differences between the original method using the delayed neutron multiplication factor and the new method using adjoint weighting.
	www.twe.com /elib/cpm3-ans_pur9901.html (881 words)

	Fission Neutron Yields (Site not responding. Last check: 2007-11-05)
		The number of neutrons produced in a fission reaction is highly important for fission reactors, explosive fission devices, and the safe storage and processing of fissionable materials.
		Some of the excited fission fragments emit additional neutrons as they decay over the next second or so; these are called "delayed neutrons."
		The format for delayed nu-bar has an additional LIST record giving the decay constants that are used to describe the time history of delayed neutron emission.
	t2.lanl.gov /endf/intro22.html (323 words)

	DJ Morrissey, Decay Studies
		Often the decay leads to the emission of neutrons or protons.
		We have developed a system to detect beta-delayed neutrons and measure their time-of-flight over a one meter flight path.
		This provides a spectroscopic measuremnet of the emitted neutron and allows us to follow the decay of the exotic nuclei in some detail.
	www.cem.msu.edu /~djm/Text/Decay.html (519 words)

	P4_3
		The scheme of parametrization of the energy dependence of delayed neutron yields (DNY) in neutron induced fission is proposed.
		The influence of some experimental factors on the measured quantities in neutron spherical-shell transmission benchmark experiments was estimated by simulating the corresponding components of the set-up (materials near the neutron source, collimator and shield of the detector etc.) as well as the specific measuring technique (time-of-flight spectrometry) in Monte-Carlo calculations.
		To provide support these assumptions it is necessary to investigate the energy-angular photons spectra at neutrons capture end nonelastic neutrons scattering for variety of materials and different neutrons spectra.
	www.ippe.obninsk.ru /podr/cjd/vant97-1.html (1187 words)

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