N/P ratio

We can use Fig. 17.13 to predict the type of disintegration that a radioactive nuclide is likely to undergo. Nuclei that lie above the band of stability are neutron rich they have a high proportion of neutrons. These nuclei tend to decay in such a way that the final n/p ratio is closer to that found in the band of stability. For example, a l4C nucleus can reach a more stable state by ejecting a (3 particle, which reduces the n/p ratio as a result of the conversion of a neutron into a proton (Fig. 17.15) ... 

Increases in nitrate + nitrite have been well documented in the Great Lakes (19). Relative increases over the past twenty years have been between 30 and 200% with the highest increases in the most populated and agriculturally productive basins of Lakes Ontario and Erie (29). Currently no adverse impacts due to this increase have been observed and concentrations are well below the 10 mg.L maximum acceptable drinking water concentration for the protection of human health. Changing N P ratios, however, can impact phytoplankton community structure (30). 

The moles X/moles P in average plankton is given by a, and b is the surface water concentration in phosphorus free water (water stripped of nutrients). In the case of P itself the surface ocean concentration is close to zero, while the deep Pacific has a concentration of 2.5 pM. For N, the N/P ratio of plankton is 16 and the surface water concentration is 0 pM. The predicted deep sea nitrate is 40 pM. The ratio of (deep)/(surface) is greater than 10. For calcium the Ca/P of... 

Isotope Neutrons Protons Neutrons + Protons n/p Ratio... 

This is a process characteristic of nucleides with high n p ratios, and involving the loss of an electron from the nucleus, which is usually, but not invariably accompanied by the emission of y-photons. A detailed energy balance reveals that the simple picture cannot account for all the energy lost by the nucleus in the decay and the emission of an additional particle - the antineutrino, v is postulated to account for this. The general equation for a negatron emission is... 

A low n p ratio in a nucleus gives a situation which may be stabilized by the conversion of a proton into a neutron. One process which may effect this is positron emission,... 

An unstable, low n p ratio may also be adjusted by the capture of an orbital electron, which would naturally involve the nearest shell, K-shell, of electrons... 

Netherlands significant) (ammonium lactate) 12.4-281 mg kg-1 (means), biomass N/P ratios between 4.5 and 15.9 (means) (2003)... 

Herbaceous terrestrial Sites with intermediate Plant biomass N/P ratios Wassen et al. 

Fens and wet grasslands, Plots with high N/P Plant biomass N/P ratios Gtisewell... 

Increased phosphatase activities and P concentration in Erica multiflora, decreased litter P, soil extractable P and total P in soil No effect on phosphatase activities, plant P concentrations, or N/P ratios Increased microbial P mineralization with... 

Giisewell S (2004) N P ratios in terrestrial plants variation and functional significance. New Phytol 164 243-266. doi http //www.blackwell-synergy.com/doi/abs/10. Ill 1/j. 1469-8137.2004.01192.x Giisewell S, Bailey KM, Roem WJ, Bedford BL (2005) Nutrient limitation and botanical diversity in wetlands can fertilisation raise species richness Oikos 109 71-80. doi http //www.black-well-synergy.com/doi/abs/10.1111/j.0030-1299.2005.13587.x Halsted M, Lynch J (1996) Phosphorus responses of C3 and C4 species. J Exp Bot 47 497-505. 

Sometimes it is difficult to predict if a particular isotope is stable and, if unstable, what type of decay mode it might undergo. All isotopes that contain 84 or more protons are unstable. These unstable isotopes will undergo nuclear decay. For these large massive isotopes, we observe alpha decay most commonly. Alpha decay gets rid of four units of mass and two units of charge, thus helping to relieve the repulsive stress found in the nucleus of these isotopes. For other isotopes of atomic number less than 83, we can best predict stability by the use of the neutron to proton (n/p) ratio. 

A plot of the neutrons (n) versus the protons (p) for the known stable isotopes gives the nuclear belt of stability. (See your textbook for a figure of the belt of stability.) At the low end of this belt of stability (Z < 20), the n/p ratio is 1. At the high end (Z 80), the n/p ratio is about 1.5. We can then use the n/p ratio of the isotope to predict if it will be stable. If it is unstable, then the isotope will utilize a decay mode that will bring it back onto the belt of stability. 

Consider neon-18 or Ne-18. It has lOp and 8n, giving an n/p ratio of 0.8. For a light isotope, like this one, this value is low. A low value indicates that this isotope will probably be unstable. Neutron-poor isotopes, meaning that it has a low n/p ratio do not have enough neutrons (or has too many protons) to be stable. Decay modes that increase the number of neutrons and/or decrease the number of protons are favorable. Both positron emission and electron capture accomplish this by converting a proton into a neutron. As a rule, positron emission occurs with lighter isotopes and electron capture with heavier ones. 

For example, consider Ne-18. It has 10 p and 8 n, giving a n/p ratio of 0.8. That is less than 1, so the isotope is unstable. This isotope is neutron-poor, meaning it doesn t have... 

The stability of the atomic nucleus depends upon a critical balance between the repulsive and attractive forces involving the protons and neutrons. For the lighter elements, a neutron to proton ratio (N P) of about 1 1 is required for the nucleus to be stable but with increasing atomic mass, the N P ratio for a stable nucleus rises to a value of approximately 1.5 1. A nucleus whose N P ratio differs significantly from these values will undergo a nuclear reaction in order to restore the ratio and the element is said to be radioactive. There is, however, a maximum size above which any nucleus is unstable and most elements with atomic numbers greater than 82 are radioactive. 

A nucleus that has an excess of neutrons will undergo neutron to proton transition, a process that may restore the N P ratio but that requires the loss of an electron to convert the neutron to a positively charged proton, and as a result the atomic number increases by one. The particle emitted is a high speed electron known as a negation (P ) and the atom is said to emit beta radiation, e.g. 

An alternative mechanism to positron emission, for the conversion of a proton to a neutron, involves a process known as electron capture (EC) in which the nucleus captures an orbital electron from an inner shell to restore the N P ratio. Subsequently, an electron from another orbital falls into the vacancy left in the inner shell and the energy released in the process is emitted as an X-ray, the atomic number again being reduced by one, e.g. 

The significance of this research showed that they could obtain excellent COD, BOD, TSS and NH3 removals in the effluent of their system with hydraulic residence times between 0.6 and 5 days and they obtained COD/N/P ratios of 167/3.3/1 and 127/2.8/1 which is substantially higher than the Metcalf and Eddy recommended 600 5 1 ratios for anaerobic reactors. Their work was performed at around 35oC + 2Co and their overall reactor treatment train looked like the following Figure 5. 

The wastewater field has more than 100 years of treating difficult waste materials in an aqueous environment. There are sophisticated models for wastewater treatment which can be applied to the remediation field, and the methods and the approaches are also useful. The introduction of a C N P ratio or the introduction of various simple operating parameters has been cost effective, and may be applicable in the remediation field as well. From some of the new reactor designs and applications, it appears that some remediation problems may be those which have already been studied by the wastewater field, and that there are lessons to be learned as well as new and innovative approaches still remaining to be evaluated. 

---