Neutron emission rate

Effective half-life Average neutron energy Neutron emission rate Decay heat... 

Precautions must be taken to shield the apparatus because of neutron emission from (a,n) reactions, and the neutron emission rate may be used in a novel fashion to detect reaction. In the reaction of Pa205 with Be (20% xs) in the form of platelets, the T was increased to the mp of Be when a sharp increase in neutron emission showed that reaction had taken place. The mixtures were then maintained at temperature until the neutron emission rate became constant". 

Cf spontaneous fissions have a fast neutron energy spectrum, shown in Figure 3, with an average energy of 2.2MeV. On average, 3.76 neutrons are emitted per spontaneous fission. The neutron emission rate is 2.34 X 10 n/(s-g)... 

It should be emphasized that all isotopes of Pu are sufficiently radioactive so that they must be handled in gloved boxes. However, Pu is formed as a mixture of isotopes, many of which emit neutrons and/or form daughters that emit penetrating radiation resulting from their decay. Neutron emission rates of various Pu isotopes are given in Table IX (203). 

Because of the wide variations in the neutron emission rates shown in Table IX, it is obviously necessary to know the isotopic composition of any particular batch of Pu in order to know how much and what kind of shielding is demanded for biologic safety. 

Neutron Emission Rates for Various Plutonium Isotopes"... 

Cf acts as the basis of a radionuclide neutron source because 3.2% of its decays are by spontaneous bssion, yielding 3.76 neutrons per bssion. The neutron emission rate/Ci of material is quite high and these sources have found widespread use. 

Californium Assay dnd Analyses. Quality control for the californium feedstock is accomplished by measuring the neutron emission rate of an aliquot of the starting material and by performing analyses for isotopic content and chemical purity. Neutron emission rate is measured in a fission counter (9). Isotopic content is measured by mass spectrometry and chemical purity by spark source mass spectrometry. The completed assembly is leak tested, decontaminated, and assayed before packaging and shipping. 

Neutron emission rate 2.34x10 neutrons/sec/gram... 

In cases like D2CO or NO2 comparison with experimental data on a state-specific level are ruled out entirely and one has to retreat to more averaged quantities like the average dissociation rate, (fc), and the distribution of rates, Q(k). If the dynamics is ergodic — the basic assumption of all statistical theories — one can derive a simple expression for Q k), which had been established in nuclear physics in order to describe the neutron emission rates of heavy nuclei [280]. These concepts have since developed into the field of random matrix theory (RMT) and statistical spectroscopy [281-283] and have also found applications in the dissociation of energized molecules [121,284-286]. 

Element Average energy of emitted neutron, MeV Neutron flux required to give 100 mrem in 40 h, l tlKctV -s) Neutron emission rate due to contaminant, to give 1000 mrem/40-h wk exposure at surface of 1-kg sphere of uranium or plutonium metal, n/min per gram of metal... 

Cf (ti 2.73 y) has found several uses. It decays to 3.1% by spontaneous fission (the main decay mode is through a emission) leading to a neutron emission rate of 2.3 X10 n s kg (average n-energy 2.35 MeV). The n-dose rate is 22 kSv h kg Cf is the only nuclide that can provide a useful neutron intensity over a sufficiently long half-life to make it a useful neutron source. The low rates of heat emission (38.5 kW/kg), y-radiation (initially 1.3 x 10 photons s kg, yielding an initial dose rate of 1.6 kGy h kg y-ray intensity increases with time due to fission product build-up) and helium evolution (from a decay) allow fabrication of simple, small Cf sources that require no external power... 

It was relatively recently that heavy cluster emission was observed at a level enormously lower than these estimates. Even so, an additional twist in the process was discovered when the radiation from a 223Ra source was measured directly in a silicon surface barrier telescope. The emission of 14C was observed at the rate of 10-9 times the a-emission rate, and 12C was not observed. Thus, the very large neutron excess of the heavy elements favors the emission of neutron-rich light products. The fact that the emission probability is so much smaller than the simple barrier penetration estimate can be attributed to the very small probability... 

The determination of Pn values is based on the beta saturation counting rate (cP ), the neutron saturation counting rate (C11 ), the beta-neutron coincidence saturation counting rate (dP ), the beta counting efficiency (eg), and the neutron counting efficiency (en). The usual relation for the delayed neutron emission probability is... 

Neutron activation analysis and atomic absorption spectrometry are used to determine the concentrations of Pb, Cd, Cr, As, Al, Zn, Sb and Mn. Although the emission rates are important, the ambient air levels are not altered significantly. The yearly mean deposition rates are increased close to the source for Pb, Cd, Zn and Sb. They are compared to TA-Luft upper limits. Also a toxicity potential" is calculated by comparison with drinking water standards. 

Pu decays through spontaneous fission with a half-life of 6.6 x y. Estimate the number of neutrons emitted per fission if the measured n-emission rate is 1890 n s g. ... 

The second radiation facility was at the Dosimetry Division of Joint Research Centre atlspa-Italy, with the neutron source consisting of americium-beryllium with the following features oxide of metallic Am-Be contained inside a steel capsule 1mm thick (activity of5,994x10 Bq rate neutrons emission of 3.6 x lOV ). 

The two processes are radically different in nature it would indeed be a remarkable coincidence if both these probabilities and their rates of change with energy, were to be so very similar. However, as we have seen in Sect. 8, it is not necessary to assume that the total probability of inelastic neutron emission increases very rapidly with energy. If, as is much more likely, the total neutron width is approximately independent of neutron energy, it follows that the average fission probability is also approximately independent of energy. 

For problems in which reactivity is inserted at a rapid rate, (dpidt) p where t is in seconds, important changes occur in N while the delayed neutron emission 2 changes only by a small fraction. The initial behavior can then be obtained by making the rapid rate approximation... 

Albagli, D., Ballinger, R., Cammarata, V. et al. (1990) Measurements and analysis of neutron and gamma-ray emission rates, other fusion products, and power in electrochemical cells having Pd cathodes. Journal of Fusion Energy, 9, 133-147. 

As before, it is required that A s 0 so as to satisfy boundary condition (5.72a). The constant B is determined by the condition on the source strength. If denotes the rate of neutron emission from the origin (neutrons per unit time), then the total net outflow of neutrons from the source is given by the limit of the product of the net current in the radial direction and the area of a sphere as the radius r — 0. Thus... 

Answer If the delayed neutron effect sets the effective neutron lifetime as 0.1 seconds, it follows that for a reaction that is just barely critical (keff = l.OOO), the rate of neutron population increase or decrease will be determined by the average neutron emission time of 0.1 second. Since the delayed neutron effect is 0.75 per cent, or a fraction 0.0075 of the total, prompt critical can be avoided provided the multiplication factor is kept between 1.0000 and.1.0075-In other words, the control rods should be withdrawn in steps so that at criticality, the keff is less than 1.0075i but greater than 1.0000. If criticality can be attained with keff sli tly in excess of 1.0000, the neutron population can increase only throu the additional contribution from the delayed neutrons. 

Most neutron-activated nuclei decay with beta emission and, since one beta particle is emitted for each disintegration, an absolute beta-emission rate determined for the sample is equal to the disintegration rate. 

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