80 research outputs found
Monte-Carlo Simulations of Radiation-Induced Activation in a Fast-Neutron and Gamma- Based Cargo Inspection System
An air cargo inspection system combining two nuclear reaction based
techniques, namely Fast-Neutron Resonance Radiography and Dual-Discrete-Energy
Gamma Radiography is currently being developed. This system is expected to
allow detection of standard and improvised explosives as well as special
nuclear materials. An important aspect for the applicability of nuclear
techniques in an airport inspection facility is the inventory and lifetimes of
radioactive isotopes produced by the neutron and gamma radiation inside the
cargo, as well as the dose delivered by these isotopes to people in contact
with the cargo during and following the interrogation procedure. Using MCNPX
and CINDER90 we have calculated the activation levels for several typical
inspection scenarios. One example is the activation of various metal samples
embedded in a cotton-filled container. To validate the simulation results, a
benchmark experiment was performed, in which metal samples were activated by
fast-neutrons in a water-filled glass jar. The induced activity was determined
by analyzing the gamma spectra. Based on the calculated radioactive inventory
in the container, the dose levels due to the induced gamma radiation were
calculated at several distances from the container and in relevant time windows
after the irradiation, in order to evaluate the radiation exposure of the cargo
handling staff, air crew and passengers during flight. The possibility of
remanent long-lived radioactive inventory after cargo is delivered to the
client is also of concern and was evaluated.Comment: Proceedings of FNDA 201
SICANE: a Detector Array for the Measurement of Nuclear Recoil Quenching Factors using Monoenergetic Neutron Beam
SICANE is a neutron scattering multidetector facility for the determination
of the quenching factor (ratio of the response to nuclear recoils and to
electrons) of cryogenic detectors used in direct WIMP searches. Well collimated
monoenergetic neutron beams are obtained with inverse (p,n) reactions. The
facility is described, and results obtained for the quenching factors of
scintillation in NaI(Tl) and of heat and ionization in Ge are presented.Comment: 30 pages, Latex, 11 figures. Submitted to NIM
Measurement and simulation of the neutron response of the Nordball liquid scintillator array
The response of the liquid scintillator array Nordball to neutrons in the
energy range 1.5 < T_n < 10 MeV has been measured by time of flight using a
252Cf fission source. Fission fragments were detected by means of a thin-film
plastic scintillator. The measured differential and integral neutron detection
efficiencies agree well with predictions of a Monte Carlo simulation of the
detector which models geometry accurately and incorporates the measured,
non-linear proton light output as a function of energy. The ability of the
model to provide systematic corrections to photoneutron cross sections,
measured by Nordball at low energy, is tested in a measurement of the two-body
deuteron photodisintegration cross section in the range E_gamma=14-18 MeV.
After correction the present 2H(gamma,n)p measurements agree well with a
published evaluation of the large body of 2H(gamma,p)n data.Comment: 20 pages 10 figures, submitted Nucl. Instr. Meth.
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Neutron-induced gamma-ray production
High resolution Ge detectors coupled with the WNR high-intensity, high-energy, pulsed neutron source at LAMPF recently have been used to measure a variety of reactions including (n,xn) for 1 {le} x {le} 11, (n,n{alpha}), (n,np), etc. The reactions are identified by the known gamma-ray energies of prompt transitions between the low lying states in the final nuclei. With our spallation neutron source cross section data are obtained at all neutron energies from a few MeV to over 200 MeV. Applications of the data range from assisting the interpretation of the planned Mars Observer mission to map the elemental composition of the martian surface, to providing data for nuclear model verification and understanding reaction mechanisms. For example, a study of the Pb(n,xn) reactions for 2 {le} x {le} 11 populating the first excited states of the even Pb isotopes is underway. These data will be used to test preequilibrium and other reaction models. 9 refs., 5 figs
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/sup 3/H(p,n)/sup 3/He differential cross sections below 5 MeV and the n-/sup 3/He cross sections. [2. 5 and 4. 0 MeV]
Complete angular distributions for the /sup 3/H(p,n)/sup 3/He reaction were measured at 2.5 and 4.0 MeV with the /sup 1/H(t,n)/sup 3/He reaction used to obtain the backward yields. Because the distributions are peaked about 17% more strongly in the backward direction than the best previous elevation suggests (based on extrapolated data), the /sup 3/H(p,n)/sup 3/He reaction cross sections below 5 MeV were re-evaluated without the extrapolated data. The results were compared with recent total n-/sup 3/He cross-section results. 3 figures, 4 tables
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