Hans Henrik Andersen (May 1, 1937 in

Frederiksberg Frederiksberg () is a part of the Capital Region of Denmark. It is an independent municipality, Frederiksberg Municipality, separate from Copenhagen Municipality, but both are a part of the region of Copenhagen. It occupies an area of less tha ...

Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...

– November 3, 2012) was a professor at the Niels Bohr Institute at the University of Copenhagen (

emeritus ''Emeritus/Emerita'' () is an honorary title granted to someone who retires from a position of distinction, most commonly an academic faculty position, but is allowed to continue using the previous title, as in "professor emeritus". In some c ...

since 2004). He was the founder and subsequently 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 is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. Atomic physics typically refers to the study of atomic structure and the interaction between atoms. It is primarily concerned wit ...

and

solid state physics Solid-state physics is the study of rigid matter, or solids, through methods such as solid-state chemistry, quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state p ...

, especially in the field of the

stopping power Stopping power is the supposed ability of a weapon – typically a ranged weapon such as a firearm – to cause a target (human or animal) to be incapacitated or immobilized. Stopping power contrasts with lethality in that it pertains only to a ...

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 particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...

s is more than four times as large as that for

proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

s. Since the

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (''n''p) or the number of pro ...

(''Z'') of alpha particles is exactly twice as big as that of protons, that means that the stopping power is not exactly proportional to ''Z''², as the simple Bethe formula would have it. That was an additional proof of the existence of the Barkas effect.

Literature

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References

{{DEFAULTSORT:Andersen, Hans Henrik 1937 births 2012 deaths 20th-century Danish physicists Danish nuclear physicists