Hans Henrik Andersen
Encyclopedia
Hans Henrik Andersen is Professor at the Niels Bohr Institute of the University of Copenhagen (emeritus
since 2004). He is co-editor of the scientific journal "Nuclear Instruments and Methods in Physics Research B".
He has made important contributions to various fields of atomic physics
and solid state physics, especially in the field of the stopping power
of matter for fast charged particles. The accuracy (0.3–0.5%) of his measurements is unsurpassed even today (2006). They were done by measuring the amount of heat deposited in a foil at the temperature of liquid helium (−269°C).
Together with his collaborators, he succeeded in showing in 1969 that the stopping power for fast alpha particle
s is more than four times as large as that for proton
s. Since the atomic number
(Z) of alpha particles is exactly twice as big as that of protons, that means that the stopping power is not exactly proportional to Z2, as the simple Bethe formula
would have it. That was an additional proof of the existence of the Barkas effect.
Emeritus
Emeritus is a post-positive adjective that is used to designate a retired professor, bishop, or other professional or as a title. The female equivalent emerita is also sometimes used.-History:...
since 2004). He is co-editor of the scientific journal "Nuclear Instruments and Methods in Physics Research B".
He has made important contributions to various fields of atomic physics
Atomic physics
Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and...
and solid state physics, especially in the field of the stopping power
Stopping power (particle radiation)
In passing through matter, fast charged particles ionize the atoms or molecules which they encounter. Thus, the fast particles gradually lose energy in many small steps. Stopping power is defined as the average energy loss of the particle per unit path length, measured for example in MeV/cm...
of matter for fast charged particles. The accuracy (0.3–0.5%) of his measurements is unsurpassed even today (2006). They were done by measuring the amount of heat deposited in a foil at the temperature of liquid helium (−269°C).
Together with his collaborators, he succeeded in showing in 1969 that the stopping power for fast alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s is more than four times as large as that for proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s. Since the atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
(Z) of alpha particles is exactly twice as big as that of protons, that means that the stopping power is not exactly proportional to Z2, as the simple Bethe formula
Bethe formula
In nuclear physics and theoretical physics, charged particles moving through matter interact with the electrons of atoms in the material. The interaction excites or ionizes the atoms. This leads to an energy loss of the traveling particle...
would have it. That was an additional proof of the existence of the Barkas effect.