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Topic: Neutron reflector

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Nuclear weapon design

Beryllium

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	Are Suitcase Bombs Possible?
		A neutron reflector reduces neutron loss and reduces the critical mass at a constant density.
		A thin beryllium reflector can reduce this by a couple of kilograms, but the necessary high explosive, packaging, triggering system, etc. will add mass, so the true absolute minimum probably lies in the range of 11-15 kg (and is probably closer to 15 than 11).
		Since it was capable of being fielded with a "neutron bomb" (enhanced radiation) option, which is intrinsically more complex than a basic nuclear warhead, and was in addition rocket boosted, the actual minimum nuclear package was substantially lighter than the weight of the complete round.
	nuclearweaponarchive.org /News/DoSuitcaseNukesExist.html (1660 words)

	ASQ Home Page Template
		Since it is essential to minimise neutron absorption in the region of the coolant/moderator in order to obtain a high neutron flux, the part of the target unit extending into the moderator tank is filled with heavy water, except for the rod bundle.
		Thermal neutrons are extracted to the experimental areas in 4 sectors of the target block.
		The vertical and horizontal inserts of the cold neutron source are enclosed in vacuum for thermal insulation and in a protective gas enclosure for prevention of potentially explosive hydrogen-oxygen mixtures in case of a leak in the system.
	asq.web.psi.ch /ASQ/facilities/SINQSYSTEMS.html (1289 words)

	4.3 Fission-Fusion Hybrid Weapons
		This reaction injects fusion neutrons into the core, causing the neutron population to rise faster than it would from fission alone (that is, the effective value of alpha increases).
		The fusion neutrons are extremely energetic, seven times more energetic than an average fission neutron, which causes them to boost the overall alpha far out of proportion to their numbers.
		Since each fission in the trigger releases about one excess neutron (it produces two and a fraction, but consumes one), which can breed one tritium atom, which fuses and release one fusion neutron, which causes one fast fission, the overall gain is to approximately double the trigger yield (perhaps a bit more).
	nuclearweaponarchive.org /Nwfaq/Nfaq4-3.html (3815 words)

	Armour
		This outer double layer is followed by a multicellular metal (Titanium) foam, that acts either as an "energy distributor" on the inner layer of protection, and as a room space to allow the expansion of plasma bolts eventually able to pierce the outer armour, weakening their terminal effect.
		These materials are respectively a neutron reflector and a neutron absorber, and were vastly used because allowed to combine high mechanical characteristics with a very high neutron protection.
		It did the same with the antineutrons of the Minbari beams, enhancing, instead of reducing, their terminal effect, because of the annihilation energy release generated by the collisions of antimatter particles with the matter of the armour, a phenomenon localized and enhanced by the armour materials.
	efni.org /armor.htm (2545 words)

	A University Based Cold Neutron Source: Indiana University Cyclotron Facility
		A new concept for a cold neutron scattering facility is described.A low energy, high intensity proton beam is used to produce the neutrons using (p,xn) reactionsThe advantages of this approach and the neutron source capabilities are outlined.
		Neutrons are a unique probe of the structure and dynamics for a great variety of systems studied today in many scientific disciplines.
		With the construction of the Spallation Neutron Source (SNS) at Oak Ridge, which will be the most intense short-pulsed spallation neutron source (SPSS) in the world when completed in 2006, the US hopes to provide the first state-of-the-art facility for neutron research in North America in decades.
	www.iucf.indiana.edu /materialscience/LENS10-02Abstract1.php (1154 words)

	Neutron transport with MCNP
		Neutron histories in arbitrary geometries are tracked from the instant of creation by the use of evaluated cross sections data libraries for elastic scattering, inelastic scattering and absorption on nuclei present in specified (fixed) materials.
		A radial reflector of 50 thickness consisting of of 80 volume percent steel is required to shield the reactor tanks from neutron damage.
		The spallation neutron source is to be approximated with a point source in the centre of the target, emitting neutrons with an evaporation spectrum.
	www.neutron.kth.se /courses/transmutation/NeutronTransport/NeutronTransport.html (1752 words)

	Encyclopedia :: encyclopedia : Nuclear chain reaction (Site not responding. Last check: )
		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)

	L I P T O N - I don't even know which street Canada is on (Site not responding. Last check: )
		While the effect of a tamper is to increase the efficiency both by reflecting neutrons and by delaying the expansion of the core, the effect on the efficiency is not as great as the effect on the critical mass.
		Neutron reflector A neutron reflector layer is an optional layer commonly found as the closest layer surrounding the fissile material.
		Neutron trigger / initiator One of the key elements in the proper operation of a nuclear weapon is initiation of the fission chain reaction at the proper time.
	www.lipton.frac.dk (6610 words)

	German court shuts down Wikipedia.de
		It was the neutron flux in the core that caused the accident, not a chemical reaction.
		This allowed the graphite moderator to become more effective (water acts as a neutron reflector, as well as a moderator), causing a step insertion of reactivity greater than the effective delayed neutron coefficient...
		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.
	lofi.forum.physorg.com /German-court-shuts-down-Wikipedia.de_4608.html (3992 words)

	Beryllium - Wikipedia, the free encyclopedia
		It is highly permeable to X-rays, and neutrons are liberated when it is hit by alpha particles, as from radium or polonium (about 30 neutrons/million alpha particles).
		At standard temperature and pressures beryllium resists oxidation when exposed to air (although its ability to scratch glass is probably due to the formation of a thin layer of the oxide).
		Because it has a low thermal neutron absorption cross section, the nuclear power industry uses this metal in nuclear reactors as a neutron reflector and moderator.
	en.wikipedia.org /wiki/Beryllium (2258 words)

	Rubrik 1
		With its improved performances (in terms of the quality of the neutron pulse and the source intensity) and the use of both (d,d)- and (d,t)-reactions, it expands the possibilities and improves the quality of the experiments.
		The neutron source is surrounded by a lead “buffer” medium, in order to simulate the diffuse properties of a spallation source.
		Most neutronics computational tools and data libraries have not yet been sufficiently validated for accelerator driven systems coupled to an intense external neutron source.
	clio.neutron.kth.se /EUROTRANS (907 words)

	4.1 Elements of Fission Weapon Design
		the neutron is "absorbed" by the collision; and
		Since neutron leakage occurs at the surface of a critical or supercritical core, the strength of the neutron flux is not constant throughout the core.
		I use the term "neutron injection event" instead of simply talking about neutrons for a specific reason: the major source of neutrons in a fission device is spontaneous fission of the fissile material itself (or of contaminating isotopes).
	nuclearweaponarchive.org /Nwfaq/Nfaq4-1.html (21668 words)

	Epithermal neutron detector having enhanced efficiency - US Patent 5581079
		a neutron moderator substantially surrounding said reflector externally to said shield, said neutron moderator comprising a material having a high concentration of hydrogen nuclei in a chemical structure of said neutron moderator material.
		The detector as defined in any of claims 1, 4, 5, or 6 wherein said neutron reflector has a thickness within a range of 0.5 to 0.9 inches.
		The logging tool as defined in claim 8 wherein said neutron moderator comprises a material having a high concentration of hydrogen nuclei within a chemical structure of said neutron moderator material.
	www.patentstorm.us /patents/5581079-claims.html (427 words)

	A History of the ANS
		Interest in building a major new source of neutrons for neutron scattering experiments in the United States was strongly expressed at a 1974 workshop at Brookhaven National Laboratory (BNL).
		Also proposed for this reactor was a "cold source" to supply low-energy neutrons because of their suitability for studies leading to practical applications.
		In May 1976, Alex Zucker, ORNL associate director for the Physical Sciences, formed the Neutron Source Committee to make recommendations on future neutron sources at ORNL, including an upgrade of the Oak Ridge Electron Linear Accelerator (ORELA) so it could be used for neutron scattering experiments.
	www.ornl.gov /ORNLReview/rev27-12/text/ansside3.html (1573 words)

	4.2 Fission Weapon Designs
		Referring to the Reflector Savings Table 4.1.7.3.2.2-3 we can see that for beryllium thicknesses of a few centimeters, the radius of a plutonium core is reduced by 40-60% of the reflector thickness.
		For this reason reflectors have little value in high yield designs, although by reducing the drop in neutron flux near the surface they help fission this outer layer more efficiently.
		Instead the core reaches thermal equilibrium with the reflector and explosive, diluting the thermal energy with the large mass of material.
	nuclearweaponarchive.org /Nwfaq/Nfaq4-2.html (7444 words)

	MILNET Mirror Document: Ex-Soviet Loose Nukes
		A neutron reflector reduces neutron loss and reduces the critical mass at a constant density.
		A limited exception to this is that a thin beryllium reflector (thickness no more than the core radius) can actually reduce the total mass of the system, although it increases its overall diameter.
		A thin beryllium reflector can reduce this by a couple of kilograms, but the necessary high explosive, packaging, triggering system, etc. will add mass, so the true absolute minimum probably lies in the range of 10-15 kg (probably closer to 15 than 10).
	www.milnet.com /milnet/nukeweap/suitbomb.htm (2436 words)

	PSU Neutron Beam Group (NBG) - Neutron Beam Laboratory Expansion
		The Neutron Beam Laboratory (NBL) is one of the experimental facilities at the RSEC.
		When the reactor core is placed next to a D 2 O tank and graphite reflector assembly near the beam port locations, thermal neutron beams become available for neutron transmission and neutron radiography measurement from two of the seven existing beam ports.
		In steady state operation at 1 MW, the thermal neutron flux is 1x10 13 n/cm 2 sec at the edge of the core and 3x10 13 n/cm 2 sec at the central thimble.
	www.engr.psu.edu /nbg/NeutronBeamPortModeling.htm (1119 words)

	The World & I: Alternative Nuclear Power
		Neutrons released in fission are initially moving so fast that they avoid capture by a heavy metal nucleus; hence, they cannot cause fission.
		In this way the neutrons, in colliding with many of the nuclei, will be slowed, as in each collision they transfer some small part of their kinetic energy to one nucleus without being captured.
		Neutron absorbers are used as needed to control the neutron population and fission rate.
	www.worldandi.com /specialreport/nuclear/nuclear.html (2984 words)

	NRC: Full-Text Glossary
		An isotope of hydrogen with one proton and one neutron in the nucleus.
		Neutrons that escape from the vicinity of the fissionable material in a reactor core.
		Neutrons that leak out of the fuel region are no longer available to cause fission and must be absorbed by shielding placed around the reactor pressure vessel for that purpose.
	www.nrc.gov /reading-rm/basic-ref/glossary/full-text.html (13209 words)

	An Exceptional Nuclear Glossary
		Neutrons emitted by nuclei in a material are capable of inducing reactions which lead to the production of additional neutrons, thereby sustaining the reaction chain.
		Neutrons in one generation that are successfully moderated and that induce further fission reactions produce a new generation of neutrons.
		N, the neutron is the projectile, and the proton is the ejectile.
	www.dataenabled.com /nuclearglossary/abcs/nuclearglossary_N.html (1332 words)

	Built from leftovers, IPNS celebrates 15 years of success
		Neutrons (uncharged particles found in the nuclear core of nearly all matter) are useful for this research because of their penetrating power.
		Neutrons are also uniquely useful for studying materials that contain atoms of the lighter elements, such as hydrogen and oxygen.
		Made of beryllium blocks arrayed around the source, originally a lead brick, the reflector increased the useful neutron beam intensity by containing neutrons that would otherwise escape and be useless to experimenters.
	www.anl.gov /Media_Center/News/History/news960505.html (853 words)

	Pebble bed reactor (Site not responding. Last check: )
		However if the gas from the primary coolant can be made radioactive by the neutrons in the reactor, usually it is brought to a heat exchanger, where it heats another gas, or steam.
		Both Romawa and AAE plan to use neutron reflectors (graphite) and shields (heavy metals) that are bins of balls.
		It slows neutrons very ably, is strong, inexpensive, and has a long history of use in reactors.
	www.freedownloadsoft.com /info/through.html (3434 words)

	Nuclear Weapon Physics and Design
		This persistence of neutrons in subcritical masses further reduces the time window for assembly, and requires that the reactivity of the mass be increased from a value of less than 0.9 to a value of 2 or so within that window.
		A neutron generation rate of 10-100 million neutrons per second is needed to ensure the prompt initiation of the reaction, thus 100-1000 billion alphas per second are required (3-30 curies of radioactive material).
		Only a portion of the neutrons are scattered back, and since it takes on average several shakes for the neutrons that do return to reenter the critical mass, their significance is further reduced through "time absorption" (see section 2.1.3).
	www.avhub.net /nuclearweaponphysicsdesign.htm (9240 words)

	IPPE: OKUYAN System
		The laser module is surrounded by the two rows of neutron reflector elements.
		If required, the NPA could be provided with an internal neutron reflector of up to 7 cm thick.
		Neutrons from the ignition reactor passing through the LM are moderated and induce a chain fission reaction of uranium-235 in the coating of LAEL.
	www.ippe.ru /podr/tpl/device/stb_a.html (479 words)

	Reflections on the heart of an atomic reaction - National - smh.com.au
		It is the neutron reflector vessel, installed yesterday at Lucas Heights, that will be the real heart of the $330 million replacement research reactor.
		Still other neutrons will fly down shafts to be used for everything from analysing aircraft parts to developing new materials.
		Dr Cameron said the reflector, installed yesterday at the bottom of a 13 metre deep silo-shaped "reactor pool" that will be flooded with ordinary water, will stay in place for at least 45 years.
	www.smh.com.au /news/National/Reflections-on-the-heart-of-an-atomic-reaction/2005/06/02/1117568321804.html (454 words)

	SPACE.com -- Astronomers Take Measure of City-Sized Neutron Star
		Astronomers have analyzed X-ray light coming from a super-heavy object called a neutron star well enough to more accurately depict the stars dimensions and confirm that theories about the objects are on track.
		Neutron stars created when old stars explode and some of the core matter typically weighing more than our entire Sun -- collapses into a region just 6 or 7 miles (roughly 10 kilometers) across.
		Neutron stars are thought to be composed almost entirely of neutrons, subatomic particles able to huddle close together on the verge of normal physics.
	www.space.com /scienceastronomy/neutron_star_021106.html (586 words)

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