Neutron background

H. Wulandari et al. Neutron Background Studies for the CRESST Dark Matter Experiment, hep-... 

Since it will be clearly impossible to reduce the neutron background rigorously to zero, there will always be some chance of predetonation. This is discussed in the following paragraphs in order to see how this affects the firing problem. 

Suppose we had an arrangement in which, for example, v would increase of its own accord from a low value like 0.01 up to a value 10-50 times greater. The firing problem would be simplified by the low initial value of v, and the efficiency would be maintained by the tendency to develop a high value of v as the reaction proceeds. It may be that a method of this kind will be absolutely essential for utilisation of 49 owing to the difficulties of high neutron background from (a, n) reactions with the impurities. 

O Brien K, Sandmeier HA, Hansen GE, Campbell JE (1978) Cosmic ray induced neutron background sources and fluxes for geometries of air over water, ground, iron, and aluminum. J Geophys Res 83 114-120... 

The flux of neutrons normally is proportional to the inverse square of the distance from the source, so for the greatest analytical sensitivity, the sample irradiation position should be near the reactor. This is also where the gamma-ray and neutron backgrounds are highest, so care in optimizing the shielding is needed for good results. Published fluxes of reactor beams that... 

This chemical system is fluorine-free, which reduces the neutron background in the laboratory caused by F(a,n) reactions. The final product consists of small beads of the metal, coated with the CaO reaction product that prevents the formation of a billet. The beads are recovered by treatment with dilute acetic acid, followed by a nitric acid wash. 

Passive calibration curve (using measured doubles versus Pu-effective mass). This calibration curve provides the most accurate results for measurement situations where the singles neutron background has a significant uncertainty. This is especially true for small samples where the neutron multiplication is small. For this mode of calibration, a well-matched set of standards is required and the multiplication is built into the calibration curve. 

The usual neutron beams from a research reactor are contaminated by fast neutrons and y-rays that originate in the core. Filters, collimators, and shielding can reduce these undesirable components to some extent. However, cold neutron beams have a much lower y- and fast-neutron background. Thus, detectors for capture neutron and basic physics experiments can be placed closer to the sample, increasing sensitivity and making coincidence techniques feasible in many more situations. 

The background of delayed neutrons emanating from the assembly had to be subtracted from the measured flux. To determine the magnitude of this delayed-neutron background(Nd)ithe complete time behavior of the neutron density was measured at the base of the re-entrant tube with a small fission counter, and the ratio (A) of the total. number of delayed neutrons to the total number of prompt neutrons was determined, tt can be shown that the appropriate delayed-neutrcm background to subtract is given... 

Passive neutron Total counts Content of even Pu Isotopes relatively simple Instrumentation. Fissile Pu Isotopes not measured directly affected by (o,n) reactions affected by neutron background fuel handling required no HEU fuels. 

During core reloading photon-neutron background was high due to the Be(y,n) reaction. Reactivity measurements using the inverse count rate technique were possible only when criticality was approached. A special procedure was developed to safely reload the core. The main requirement of this procedure was to reload the core in the inverse order of the unloading. 

After a few subcritical runs have been made, the reactor can be brought to delayed critical and pulsed. Care must be taken at this point, since the delayed-neutron background will yield a steady-state neutron level in the reactor. The background will steadily increase each time more neutrons are injected into the system. After enough data have been taken, the pulsing is stopped, and the reactor power level should level off and remain at steady state, since the reactor is in a delayed critical condition. The decay constant calculated for this run will yield the constant of proportionality between the decay constant and the negative reactivity (in dollars) of the system. This constant is equal to jSgff/ip as pointed out in Section II. 

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