Nuclear density

{{Short description|Density of the nucleus of an atom}} {{More citations needed|date=July 2021}}

'''Nuclear density''' is the density of the nucleons (neutrons and protons) in the nucleus. For heavy nuclei, it is close to the ''nuclear saturation density'' <math>n_0=0.15\pm0.01</math> nucleons/fm³, which minimizes the energy density of an infinite nuclear matter.<ref name=Horowitz>{{cite journal |last1=Horowitz |first1=C. J. |last2=Piekarewicz |first2=J. |last3=Reed |first3=Brendan |title=Insights into nuclear saturation density from parity-violating electron scattering |url=https://journals.aps.org/prc/abstract/10.1103/PhysRevC.102.044321 |journal=Phys. Rev. C |year=2020 |volume=102 |issue= 4|article-number=044321 |doi=10.1103/PhysRevC.102.044321 |arxiv=2007.07117 |bibcode=2020PhRvC.102d4321H |s2cid=222080305 |access-date=September 7, 2022}}</ref> The ''nuclear saturation mass density'' is thus <math>\rho_0=n_0 m_{\rm u} \approx 2.5\times10^{17}</math> kg/m³, where ''m''_u is the atomic mass constant. The descriptive term ''nuclear density'' is also applied to situations where similarly high densities occur, such as within neutron stars.

== Evaluation == The nuclear density of a typical nucleus can be approximately calculated from the size of the nucleus, which itself can be approximated based on the number of protons and neutrons in it. The radius of a typical nucleus, in terms of number of nucleons, is <math>R=A^{1/3}R_0</math> where <math>A</math> is the mass number and <math>R_0</math> is 1.25 fm, with typical deviations of up to 0.2&nbsp;fm from this value.{{citation needed|date=September 2022}} The number density of the nucleus is thus: :<math>n = \frac{A}{{4\over 3} \pi R^3}</math> The density for any typical nucleus, in terms of mass number, is thus constant, not dependent on ''A'' or ''R'', theoretically:

:<math>n_0^\mathrm{theor} = \frac{A}{{4\over 3} \pi (A^{1/3}R_0)^3} = \frac{3}{4 \pi (1.25\ \mathrm{fm})^3} = 0.122 \ \mathrm{fm}^{-3} = 1.22 \times 10^{44} \ \mathrm{m}^{-3}</math>

The experimentally determined value for the nuclear saturation density is<ref name=Horowitz />

:<math>n_0^\mathrm{exp}=0.15\pm0.01\ \mathrm{fm}^{-3} = (1.5\pm 0.1)\times 10^{44}\ \mathrm{m}^{-3}.</math>

The mass density &rho; is the product of the number density ''n'' by the particle's mass. The calculated mass density, using a nucleon mass of ''m''_n=1.67×10⁻²⁷ kg, is thus:

:<math>\rho_0^\mathrm{theor}=m_\mathrm{n}\,n_0^\mathrm{theor} \approx 2 \times 10^{17} \ \mathrm{kg} \ \mathrm{m}^{-3}</math> (using the theoretical estimate)

or

:<math>\rho_0^\mathrm{exp}=m_\mathrm{n}\,n_0^\mathrm{exp} \approx 2.5 \times 10^{17} \ \mathrm{kg} \ \mathrm{m}^{-3}</math> (using the experimental value).

== Applications and extensions == The components of an atom and of a nucleus have varying densities. The proton is not a fundamental particle, being composed of quark–gluon matter. Its size is approximately 10⁻¹⁵ meters and its density 10¹⁸ kg/m³. The descriptive term ''nuclear density'' is also applied to situations where similarly high densities occur, such as within neutron stars.

Using deep inelastic scattering, it has been estimated that the "size" of an electron, if it is not a point particle, must be less than 10⁻¹⁷ meters.{{citation needed|date=September 2022}} This would correspond to a density of roughly 10²¹ kg/m³.

There are possibilities for still-higher densities when it comes to quark matter. In the near future, the highest experimentally measurable densities will likely be limited to leptons and quarks.{{citation needed|date=September 2022}}

==See also== *{{annotated link|Electron degeneracy pressure}} *{{annotated link|Nuclear matter}} *{{annotated link|Quark–gluon plasma}}

==References== {{Reflist}}

==External links== *{{cite web |url=https://www.cyberphysics.co.uk/topics/atomic/nucleus.htm |title=The Atomic Nucleus |access-date=2014-11-18}} (derivation of equations and other mathematical descriptions)

Category:Mass density Category:Atoms