1999 Helmholtz Prizes awarded

Today was an important day for seven Braunschweig scientists. Helmholtz Prizes have been awarded to two PTB working groups for their scientific work. These prizes are awarded every three years by the Helmholtz Fonds for excellent work in the field of metrology, the science of measurement. Within the framework of a session in the PTB's lecture hall in Braunschweig, Ruprecht von Siemens, the treasurer of the Helmholtz Fonds, presented the awards, each of which is endowed with DM 12 000 this year. The money for one of the awards has been made available by the Stifterverband für die Deutsche Wissenschaft. The prizes have been awarded for work in the fields "Highly precise measurement of physical quantities" and "Metrology in medicine and environmental protection".

Among the tasks of the Helmholtz Fonds is the promotion of research and development in metrology. For this purpose, the Helmholtz Prize was created in 1973. The Helmholtz Fonds publicly invites to the prize contest in various fields of metrology. Scientific papers from the fields specified can then be submitted for the competition, prerequisite being that they have not yet been published. Two panels of five judges each then choose the prizewinners. The following papers have been recognized by a prize this year:

Looking for tracks
Measuring instrument for the investigation of radiation effects

Radiating Castor containers, the occurrence of leukaemia in the vicinity of nuclear power plants - such incidents again and again stimulate public discussions about the effects of radioactive radiation on the organism. The debatable point is above all the radiation dose which can cause damage. In order to explain radiation damage and to optimize radiation protection, exacter knowledge is required of how cells and cell structures react with charged particles.

Radiation passes through matter; during this process, energy is transferred from charged particles to the atoms and molecules of the material concerned. The rays leave a particle track along their path. This track is photographed by a camera for the development of which the scientists Uwe Titt, Volker Dangendorf and Helmut Schuhmacher have been awarded the Helmholtz Prize "Metrology in medicine and environmental protection". An image is formed of the spatial distribution of the places of energy transfer, i.e. the ionization points. It is the particular feature of the prizewinning measuring instrument that it allows for the first time the transferred energy to be made visible in the micro- and nanometer range, i.e. in the range of cellular structures. The ionization tracks are measured in a detector cell containing triethylamine (TEA), a gas. The energy of the charged particles stimulates the gas to emit light in the UV region. With the aid of CCD camera with image intensifier the PTB physicists then obtain a two-dimensional picture of the particle tracks. Also the development of the light signal with time is measured by means of an arrangement of photomultipliers. These data provide the scientists with additional information about the energy distribution along the third spatial dimension. The scientists have used TEA for their analyses for yet another reason: its composition is almost identical to that of tissue. Even if a direct measurement of particle tracks in the cell is not yet possible, experts can transfer the data obtained in this way to biological structures.

For the moment, the newly developed measuring instrument will allow fundamental information to be obtained about the effect of radiation on the organism. This will lead to better understand the radiation effect. In the long run, experts hope for improvements in the field of radiation protection and also in radiation therapy. The newly gained information will possibly also lead to new findings concerning the evolution of life on this planet, which has always been exposed to certain natural radiation.

Useful play of light of the atoms
Atomic interferometry for highly precise measurements

Understanding sometimes means not to be surprised any longer. And the scientists of the PTB's "Unit of Length" section are no longer surprised that they can treat atoms as if they were pure light. In a so-called "atomic interferometer", the physicists Fritz Riehle, Harald Schnatz, Tilmann Trebst and Jürgen Helmcke have made optimum use of the light character - or rather wave character - of calcium atoms so that they succeeded in developing an optical frequency standard of a quality not achieved to date. This development, for which the scientists were awarded this year's Helmholtz Prize for the "Highly precise measurement of physical quantities", allows the frequency - and thus the wavelength - of a laser to be kept constant and measured with an accuracy which can be indicated in tenths of a billionth fraction only (a few 10^-13).

With their wavelength stability, such lasers now are the most precise length standards, and their frequency stability might in future lead to even more precise clocks. At the same time, such atomic interferometers make it possible to design highly sensitive sensors for acceleration and gravitation forces, since the atomic waves, because of their mass, are also subject to gravity. For example, oil fields or iron-ore deposits could be tracked down in this way, because the sensitivity of such "atom-interferometric" sensors today is already sufficiently high to detect local variations of the earth's graviational attraction as are caused, for instance, by oil fields or iron-ore deposits.

The physical basis of all these applications is the wave character also of material particles such as atoms. Although this wave character has been known for about three quarters of a century, since the first interpretations of quantum mechanics, it is only this decade's technology which is able to usefully exploit it - for highly precise measurements. By means of pulses from highly stable lasers, PTB scientists split the atomic waves, inside atomic interferometers, like a zip-fastener and then join them again. And as in a zip-fastener these atomic waves can be joined again only if the "small teeth" of the two halves fit exactly. At PTB, displacements of this "zip-fastener" are measured by counting the "spacings between the small teeth". The technological benefit of this zipper principle: The scientists have at their disposal an extremely finely ruled scale, because - depending on the atoms' velocity - their wavelength lies in the range of some picometers (10^-12 meters).

Additional information to be obtained from:
Prof. Dr. Uwe Keyser
telephone: ++49 531 592-8500/1