NOLDOR S.R.L. offers a wide variety of services, studies and developments for industries in general. However its main speciality is industrial applications of radioisotopes with emphasis in utilisation of nuclear gauges and process analysis using radiotracers. 

In this framework, NOLDOR has capabilities to perform mercury inventories in electrolytic cells, determination of residence time distributions (RTD), mixing efficiency evaluations, leak detection and location, flow rate measurements and other applications of nuclear techniques and instruments.

In the field of industrial gauges or nucleonic control systems (NCS) the offer aims to designing of new instruments, maintenance, replacement of radioactive sealed sources, calibration and general assessment.


Industrial nuclear gauges

Sealed sources

Thickness measurement

Density measurement

Level measurement

Concentration measurement

NOLDOR's proposal


Residence time distributions

Leak detection

Dilution analysis

NOLDOR's proposal

Industrial nuclear gauges

Nucleonic gauges or nucleonic control systems (NCS) have been widely used in industries of developed countries to improve the quality of their products, optimise processes and save energy and materials. It is considered that NCS technology is by far the most requested among other industrial nuclear techniques. Their economic benefits have been widely demonstrated and recognised by industries.

There are several hundred thousand nucleonic gauges installed in industries all over the world. Simple, one parameter, static measuring nucleonic gauges are commercially available from several manufacturers. However, a significant number of NCS are not yet in the market as standard products and the development of a new generation of nucleonic devices is ongoing.

The competition from alternative methods shows that NCS have survived and prospered in the past because of their superiority in certain areas to competitive methods. The success of NCS is due primarily to the ability, conferred by their unique properties, to collect data which cannot be obtained by other investigative techniques. Though NCS are continually under pressure from alternative techniques, nevertheless, they continue to make an increasingly important contribution to the better management of natural resources, industrial efficiency and environmental conservation.

Relevant target areas for NCS applications are well defined. Though the technology is applicable across a broad industrial spectrum, the oil, gas and chemical industries, minerals and raw materials exploration, mining and processing industries, iron, steel and metal production plants, civil engineering, paper, pulp, plastics and cement industries have been identified as the most appropriate target beneficiaries of NCS applications. These industries are widespread internationally and are of considerable economic and social impact.

Sealed sources

A radiation sealed source is constituted of some radioactive mass stored in a container in order to prevent the radioisotope from being in direct contact with the environment.

As a general rule, gamma radiation emitters are enclosed in small holders made out stainless steel whose volume is as low as a few cubic millimetres. On the other hand, some beta sources may be stored in quartz tubes and in some cases they may be used as metallic lames.

In any alternative, the sealed source should be stored in a source holder generally made out of lead. The holder plays two roles, shield and collimator, focusing the radiation beam to a specific point according to each particular instrument.

Holders must include a mechanic, electromechanical or pneumatic shutter whose purpose is to shield completely the radiation source when the gauge is transported or when it is non-operative.

Thickness measurement

Different kind of papers, plastic films, fibreglass sheets, rubber plates, adhesive layers, plastic or electrolytic coatings and laminated metals are some examples of materials whose thickness are usually measured by nuclear gauges.

As a general rule transmission instruments are preferred although their installation is not always possible because of geometrical reasons. In the basic configuration of a transmission gauge the media to be measured is placed between the radioactive source and the detector so that the radiation beam can be transmitted through it. The media attenuates the emitted radiation (beta particles or photons) before reaching the sensible volume of the detector. Both source and detector may be collimated. The radiation intensity in the detector is a function of several parameter of the tested material.

Backscattering technique is used every time transmission geometry is inadvisable for any reason. Whenever a radiation beam interacts with matter a fraction of it is transmitted, a fraction absorbed and a fraction is scattered from its original path. If the scattering angle is greater than 90o some photons or particles will come back towards the original emission point. The measurement of this radiation is on the basis of the backscattering method.

In many processes, thickness must be inside some tolerance limits and then comparative measurement is commonly used. Both nuclear and electronic compensation techniques are employed.

Measurement is always dynamic because the material to be measured moves longitudinally in a continuous way while it is produced. The nuclear measurement head may also move laterally in order to get thickness profiles.

The display system can be simply a plotter or an analog instrument (such as a milliammeter) or something more complex such as a CRT or LCD monitor showing graphic and digital information. In this case a personal computer is generally used with a suitable software intended to display information, store statistic data and calibration parameters and control the production process.

Ionization chambers are mainly used as detectors along with beta or gamma radiation sources. Though the latter are in general limited to measuring thickness in metal sheets.

Density measurement

Nuclear gauges are often used to measure density in any kind of liquids flowing within pipes. For this purpose the transmission method is generally preferred. They are also frequently applied for soil density measurements where both transmission and backscattering techniques are used.

Measurements can be absolute or relative, with nuclear or electronic compensation, and static or dynamic.

In case of flowing liquids, the measurement is dynamic if the fluid velocity is "high" when compared with the system response time, otherwise it can be considered as static. Obviously this is the situation for a soil density gauge. Furthermore there are mobile devices designed for density liquid logging in vessels.

The information can be displayed by means of any technique as in the case of thickness gauges. Soil density devices use to be portable and consequently simpler. However some instruments include microprocessors to make simple calculations combining soil density and moisture.

Ionization chambers, Geiger-Müller (GM) tubes and scintillation counters are valid alternatives for detectors depending on each particular assembly. Regarding radioactive sources, gamma emitters are always used, especially 137Cs and 60Co. Portable soil density and moisture gauges need also a fast neutron source, usually 241Am-Be, and a thermal neutron detector.

Level measurement

Level gauges are usually installed in large tanks containing liquids and can be classified as level detectors (on / off) or continuous gauges. The former is used just to know whether the liquid is above or bellow a reference level while the latter is suitable to determine the actual liquid level inside a working interval.

The most important nuclear gauge advantage, not only in this case but in many other situations, is their ability to measure the parameter of interest with no contact with the system under study which could operate at very high temperature or pressure or contain corrosive materials making it difficult to use conventional techniques.

Generally the transmission configuration is preferred using 60Co and 137Cs gamma sources and Geiger Müller or scintillation detectors. However the backscattering technique is sometimes used with 241Am-Be neutron sources and thermal neutrons detectors such as boron trifluoride (F3B) tubes or chambers.

To know whether some liquid is above or bellow a reference level is a very common requirement in industrial processes. The production sequence can follow different stages according to that information. In some cracking catalytic plants the detection of several levels is needed before making a decision.


In such cases the configuration is very simple  including a collimated radiation source and a radiation detector fixed outside the tank and opposed to each other. Whenever the liquid is above the level determined by the horizontal plane containing the source-detector axes, the radiation intensity that reaches the detector sensible volume is strongly attenuated because of the interposed fluid. Hence the output signal goes down abruptly, theoretically following a negative step function. This signal after being amplified and, eventually, modified may be used to operate an electro-valve or any other electromechanical device or to feedback an automatic control loop.

A continuous level gauge is based on a linear sealed source and a radiation detector located in both sides of a vessel containing some liquid. The schematic assembly shown bellow is intended to measure the liquid level inside an interval determined by the source length. It is also possible to work with an inverse configuration, that is to say a punctual source and one or more GM detectors in a parallel connection but in a linear assembly.

In case of working with a linear source, this is made out of an irradiated wire that is coiled on a metal bar with a wide space between consecutive spirals. Geiger- Müller tubes are almost always used.

Concentration measurement

There are two kinds of nuclear concentration gauges: those in which the sample thickness is constant and those in which it is variable. The former refers to instruments that works submerged in a liquid media in which the knowledge of the concentration of some impurity or pollutant is needed. The sample thickness is the gap between source and detector through which the liquid flows freely. This technique is also used in laboratory devices where the sample must satisfy especial conditions related with shape and thickness. On its side variable thickness gauges are used as on-line meters to determine concentration in solid materials.

In this framework, nuclear turbidy-meters are primarily intended to measure sediment concentration in water bodies. Compared with conventional gravimetric instruments they have the typical NCS advantages, that means that no samples are required and the supplied information comes from an average area rather than from isolated points and for these reasons is more representative of the zone under study. Nuclear instruments are a complement for optical and ultrasonic turbidy-meters that have low sensibility at high concentrations.

Another application field for nuclear techniques is coal ash concentration measuring. Coal consists of coal matter and mineral matter. Coal ash is the oxidized incombustible residue from the coal combustion and its concentration is closely correlated with mineral matter content. The knowledge of the coal ash is very important not only for the coal industry (in the control of coal washeries and blending operations) but also in metallurgical industry.

NOLDOR's proposal

NOLDOR S.R.L. provides the following duties related with nuclear industrial gauges:

  • Design of new instruments.

  • Maintenance.

  • Wipe-tests.

  • Determination of isodose curves.

  • Replacement of radioactive sources.

  • Calibration.

  • General assessment.


Tracer is a detectable substance added to a chemical, biological, physical or industrial system by means of some injection or labelling technique in order to study and evaluate the characteristics and the dynamic behaviour of such a process.

Pollutant dispersion in water bodies, aquifer behaviour, mechanism of vegetal nutrition, human tissue dynamic, industrial production processes are all fields where tracers can play an important role. Tracers give a comprehensive knowledge of all these systems and allow to better understand their evolution and dynamic.

Examples of tracers are solids in suspension, dyes, salts, alcohols and radioisotopes. The major advantage of radiotracers is that they can be detected without physical contact and therefore without affecting the system.

The selection of the most suitable tracer for a given process is extremely important. In any case it should satisfy the following conditions:

  • to behave the same way that the material under investigation,

  • to be detected easily and unambiguously,

  • to follow the behaviour of the material without being removed from the process by any way,

  • to be injected and detected by mechanisms that not disturb the process,

  • its residual concentration must be as low as possible.

In case of using radiotracers, they must also satisfy conditions regarding the type and energy of the emitted radiation and their half-life. On the other hand they have the following advantages:

  • Identity: all isotopes of a given element have identical chemical properties, therefore a radioisotope of some element is an ideal tracer for such an element.

  • Specificity: the emission of radiation is a specific property of radiotracers and it is not affected by interferences from other materials.

  • Sensitivity: radioisotopes are measurable with high sensitivity and consequently detected in very low concentrations.

  • Measurement “in situ”: in most cases radiotracers can be detected in the field or in an industrial plant with no physic contact with the process.

Residence time distributions

Radiotracers are the best tool whenever the knowledge of residence time distribution (RTD) in an industrial process is needed. As a matter of fact the system response at an instantaneous tracer injection is precisely the RTD function of this system. The system response is the tracer concentration against time curve in its outlet.

In the simplest case the knowledge of the mean residence time and its standard deviation is enough information to evaluate the process but in more complex systems it is preferred to analyse their transfer function in detail, to evaluate all the statistic parameters and to apply mathematical models. These models allow the engineers to decompose the process in a set of interconnected simple systems. Then the model can be "tuned" modifying some of its parameters aiming to the optimisation of the process and the further increase in the production efficiency.

Ideal systems can be classified in two types: plug flow and total perfect mixers. In the former all the elements making part of the flow moves through the system with the same regime and without mixing, being the output concentration curve identical in shape to the input but delayed. In the case of perfect mixers, the material is mixed instantaneously and uniformly within the volume of the system and the output concentration is identical to the concentration within the reactor.

In a real system,  the response to a tracer impulse is its residence time distribution and can take any arbitrary shape. The first moment of the response curve is the system mean residence time and can be calculated solving the equation shown in the picture above numerically.

Additionally, real systems are usually more o less complex but they can be decomposed in small parts connected in series or in parallel and even including feedback loops to make easier their study. Specialised software is then used to obtain the mathematical model that better approaches the dynamic behaviour of the system.

Tracers techniques allow the engineers to find dead volumes, multiple transport paths, internal feedbacks and many other problems that usually affect industrial processes.

Tracer response analysis also contributes to a better understanding of the system under study and to optimise its working conditions in order to get higher economic benefits.

Leak detection

Leak detection and leak location are the most widespread radiotracer applications in industrial plants. Any undesirable interconnection between isolated parts of a same system or between two different systems may be a leak. A leak is suspected if there is any abnormal behaviour of a system such as loss of pressure, contamination of product or loss of process efficiency.

Detection of a leak, if any, is unambiguously achieved by injecting a radiotracer into the suspected part and measuring for the tracer in the part that should be isolated. Radiotracers are especially useful when the leak is located in underground pipelines since in such cases there is no needs of performing excavations.

Dilution analysis

Mass balance is another radiotracer technique successfully applied for inventory of materials and for evaluation of process efficiency in many branches of industry.

The extend to which a tracer is diluted in a tagged material constitutes a measure of the volume or the inventory of the material. The dilution principle is the basis of methods for material inventory in batch systems or for the determination of separation efficiency in a continuous system or for the estimation of the material fraction which recirculates also in a continuous system.

One of the main applications of dilution analysis is mercury inventory in electrolytic cells where radioactive 203Hg isotope is used as tracer. Since mercury is used to label mercury, the tracer can be considered as "ideal".

NOLDOR's proposal

NOLDOR S.R.L. provides the following duties related with radiotracer techniques:

  • Determination of residence time distributions.

  • Leak detection and location.

  • Flow rate measurements.

  • Dilution analysis.

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