Germanium is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon.
In gamma spectroscopy, germanium is preferred due to its atomic number being much higher than silicon and which increases the probability of gamma ray interaction. Moreover, germanium has lower average energy necessary to create an electron-hole pair, which is 3.6 eV for silicon and 2.9 eV for germanium. This also provides the latter a better resolution in energy.
Protons and Neutrons in Germanium
Germanium is a chemical element with atomic number 32 which means there are 32 protons in its nucleus. Total number of protons in the nucleus is called the atomic number of the atom and is given the symbol Z. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10-19 coulombs.
The total number of neutrons in the nucleus of an atom is called the neutron number of the atom and is given the symbol N. Neutron number plus atomic number equals atomic mass number: N+Z=A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N – Z = A – 2Z.
For stable elements, there is usually a variety of stable isotopes. Isotopes are nuclides that have the same atomic number and are therefore the same element, but differ in the number of neutrons. Mass numbers of typical isotopes of Germanium are 70; 72; 73; 74.
Main Isotopes of Germanium
Germanium occurs in 5 natural isotopes: 70Ge, 72Ge, 73Ge, 74Ge, and 76Ge. Of these, 76Ge is very slightly radioactive, decaying by double beta decay with a half-life of 1.78×1021 years. 74Ge is the most common isotope, having a natural abundance of approximately 36%.
Germanium-70 is composed of 32 protons, 38 neutrons, and 32 electrons.
Germanium-72 is composed of 32 protons, 40 neutrons, and 32 electrons.
Germanium-73 is composed of 32 protons, 41 neutrons, and 32 electrons.
Germanium-74 is composed of 32 protons, 42 neutrons, and 32 electrons.
Germanium-76 is composed of 32 protons, 44 neutrons, and 32 electrons.
Electrons and Electron Configuration
The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. Therefore, the number of electrons in neutral atom of Germanium is 32. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom.
Since the number of electrons and their arrangement are responsible for the chemical behavior of atoms, the atomic number identifies the various chemical elements. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
Electron configuration of Germanium is [Ar] 3d10 4s2 4p2.
Possible oxidation states are +2,4.
Elemental germanium starts to oxidize slowly in air at around 250 °C, forming GeO2 . Germanium is insoluble in dilute acids and alkalis but dissolves slowly in hot concentrated sulfuric and nitric acids and reacts violently with molten alkalis to produce germanates ([GeO3]2−). Germanium occurs mostly in the oxidation state +4 although many +2 compounds are known.
Most Common Application of Germanium
High-purity germanium detectors (HPGe detectors) are the best solution for precise gamma and x-ray spectroscopy. In comparison to silicon detectors, germanium is much more efficient than silicon for radiation detection due to its atomic number being much higher than silicon and due to lower average energy necessary to create an electron-hole pair, which is 3.6 eV for silicon and 2.9 eV for germanium. Due to its higher atomic number, Ge has a much lager linear attenuation coefficient, which leads to a shorter mean free path. Moreover silicon detectors cannot be thicker than a few millimeters, while germanium can have a depleted, sensitive thickness of centimeters, and therefore can be used as a total absorption detector for gamma rays up to few MeV.
|Number of protons||32|
|Number of neutrons (typical isotopes)||70; 72; 73; 74|
|Number of electrons||32|
|Electron configuration||[Ar] 3d10 4s2 4p2|
Properties of other elements