News 2002

Munich, July 19, 2002

Gastight High-Pressure Compressors in Nuclear medicine

BAUER KOMPRESSOREN GmbH is the technological leader in high-pressure system technologies for air, nitrogen and other inert gases. In the industrial market sector BAUER can profit from over 50 years experience of manufacturing high pressure compressors for breathing air applications as global market and quality leader.

The product portfolio ranges from single compressor units to complete systems, comprising air and gas compression as well as purification, storage and dosage systems. The customer is given professional advice in advance regarding unit dimensioning and final installation at site. BAUER takes over projecting, installation and also certification by societies such as TÜV, Germanischer Lloyd and others upon request as well as maintenance contracts.
BAUER compressor units are used for example to produce the purest air for breathing air, for steering power plant turbines via receivers filled with hydraulic oil and air or various testing procedures.

The turbine steering of the Assuan-Dam and the leackage testing of the carrier rocket ARIANE 4 is realized with compressed air by BAUER compressors.
A typical application for nitrogen units by BAUER is PET- bottle blowing and Gas Injection Technology in the car industry.
A very interesting field of application is nuclear medicine, where gastight helium compressors by BAUER are used in connection with socalled cyclotrons.
Projects of this kind were successfully realized in the polyclinic "Rechts der Isar" in Munich, "Charité" in Berlin, University of Münster, University of Tübingen as well as the AKH in Vienna.

Cyclotrone

"hot cell"

In nuclear medicine in various centers radionuclides for the positrones emission tomography (PET) are produced by means of cyclotrones. It is a fluorine-18, oxygen-15, nitrogen-13 and carbon-11. These radionuclides have very short half-life period of 2 - 110 minutes and are therefore produced with high activities.
In socalled "hot cells" these radio nuclides are modified by chemists to substances such as fluorine-18 marked sugar and injected to the patient.
The following measurements of the spacial and temporal repartition in socalled PET-scanners give information about the sugar metabolism, which may have changes to indicate heart desease, brain desease or cancer.

By modifying of the radio nuclides this way volatile substances are created, which contaminate the air of the hot cells with radioactivity. As those cells are not completely tight, there is danger that radioactivity could escape into the environment.

Acc. to § 47 of radiation protection regulation the limiting values of the yearly discharge activity of the radio nuclides produced on the cyclotron are determined. For these nuclides they are within per mil of the yearly produced activity. Therefore it is necessary to install an effective retension device for the exhaust air of the "hot cells" in order to ensure that these limiting values can be met.
Due to the short period of decay of the radio nuclides it was considered to install rather large hold-up lines in order to make the activity decay as much as possible until it is finally led into the ambient.

This would, however, require very complicated and space consuming exhaust air ducts. It is much easier to store the exhaust of the "hot cells", whose geometric volume per cell is approx. 1 m³ , in storage cylinders up to 350 bar, which can be discharged again after a few hours, in which the activity has decayed.
This has been done successfully in various university hospitals for quite some years.
The advantage is with the high pressure technology, which offers the possibility to compress huge quantities of radioactive contaminated air up to 1/350stel of its volume and to keep the geometric storage volume very small compared to the low pressure treatment.
This procedure however requires that the complete compressor system is gastight.
Such high pressure systems like G 180-18.5 or G 15.1-7.5-5 and G 120-4-5 type by BAUER have been working reliably for many years in nuclear medical centers as stated above.
It is important that the compressor used is completey gastight, although leak rates between 1,2 and 1,6 mbar × l/s are reached. This means a max. leak rate of almost 3 mbar × l/sec. with a storage system (8 cylinders à 50 l).
These leak rates are splendid values for piston compressors of this kind, which are not only appreciated in the low temperature technic for helium regeneration but more and more in the nuclear medicine, too.
As storage 2 × 4 cylinders à 50 l (water volume) capacity are used. The operating pressure is approx. 330 bar. These cylinders can be installed overground or underground, then only the shut off valves of the cylinders are visible. Via an additional SPC unit the complete process can be fully automated from a signal from the compressor, ON / OFF to OPEN / CLOSE of the solenoid shut off valves (mounted at inlet / outlet of storage cylinder group) and setting of decay period.

VERTICUS - G Range for Noble Gases

Ludwig Kühlwein
Sales Project Engineering
BAUER KOMPRESSOREN GMBH