Non-nuclear coating thickness measurement

What you need to know

Introduction to nuclear gauges

Nuclear sources have long been used to conduct coating thickness measurements across a multitude of industries, including coated paper, films, and flexible packaging. And Promethium, Krypton and Strontium nuclear sources have been used in transmission beta gauges and backscatter beta gauges to measure substrates and coatings, ensuring that materials produced adhere to manufacturing guidelines. However, the challenges associated with using – and obtaining – these nuclear sources are becoming insurmountable. So, change is paramount.  

Like many experts within the industry, at Industrial Physics, we’re aware of the ever growing challenges surrounding the nuclear gauge approach. However, what many professionals across these industries are unaware of is that an alternative to this legacy testing approach exists.  

That’s why we created this resource - to support those struggling with this challenge. Within this guidebook, our specialists will highlight the core challenges - giving you the tools to build a case for transitioning, and introducing details regarding an innovative, game-changing alternative approach to coating thickness measurement.

Your guidebook includes:

• A detailed analysis of the challenges posed by a nuclear gauge approach in 2025 

• A short Q&A video summarizing the situation, challenges, and solutions  

• Animations to break down the differences in the nuclear gauge measurement process vs non-nuclear optical interference technology

• A run-down on the Industrial Physics solution by SpecMetrix – including key benefits and specifications

With these resources, we hope to bring insights and relief to those who are facing a mountain of challenges, and those who are simply seeking a more effective way to measure coating thickness in their production lines. 

Vivek Komaragiri, Principal Technologist at Industrial Physics 

Vivek Headshot

The barriers to nuclear measurement in today’s landscape

Challenge one: sourcing nuclear materials  

Traditional gauges rely on nuclear sources such as Promethium, Krypton or Strontium which degrade over time and need to be replaced accordingly. The lifespan for nuclear sources vary with requirement for replacement even every four to five years. During this time the source continually deteriorates which limits the accuracy of measurement. 

In the current geopolitical climate, it is becoming increasingly difficult to source new nuclear material for the gauges. Historically, Ukraine and Russia have been heavily relied upon for the provision of these materials. However, the ongoing global conflict has added complications to this process, creating uncertainty for the manufacturers who rely on the measurement method. Currently, buyers not only face longer procurement times and potential supply shortages, but costs have also risen for the materials themselves and for compliance-related transport or insurance. 

This disruption to the replacement of nuclear gauges poses a real threat to the efficient operations of manufacturers in films and flexible packaging. Not being able to reliably measure coating thickness on products produced can lead to large batch rejections, brand reputation damage and significant costs in materials and wasted energy. Therefore, if the source could not be replaced to ensure accurate measurement, production would likely be halted altogether, with serious negative implications for the company.  

Challenge two: safe disposal

Beyond the measurement itself, nuclear sources must also be disposed of in line with strict guidelines – currently under elevated regulatory scrutiny – to ensure that health or the environment are not put at risk e.g. long-term contamination of water, soil or air.  

Many nuclear regulatory bodies only license a nuclear source if there is already a pre-approved disposal path - this would often involve sending the source back to the original supplier for safe containment in shielding containers.  

Due to the conflict between Russia and Ukraine, nuclear sources are not only harder to obtain, but also harder to dispose of. This creates an additional challenges for manufacturers who persevere with this measurement method.

Challenge three: financial burden and accurate measurement 

Nuclear sources used for these gauges could cost up to $100,000 or more each to replace, which can be as frequent as every couple of years. This is a significant financial burden for companies that are already facing pressures, e.g. rising raw material prices and energy costs. Until favorable alternatives have been made available, professionals have had no choice but to shoulder this burden. However, now that competitive, highly precise systems are available, they can make the switch and vastly improve cost-effectiveness.  

In addition to the cost of the nuclear source vs alternative systems, professionals should also consider the financial impact of inaccurate measurement. The thickness of films and coatings used in these industries is a critical determinant of the product’s efficacy. However, nuclear sources are in a continuous state of decay. This makes it harder for operators to guarantee precise measurements, particularly towards the end of the source’s life. 

Additionally, nuclear gauges are less accurate when the thickness is either in the sub-micron range or in the order of few microns. And as coating technologies and formulations are getting more advanced, the coatings are getting thinner. This is already making nuclear gauges less applicable in those cases. If products are developed with the wrong thickness, then they will not meet the set requirements. As a result, companies will be unable to fill production orders, incurring reputation damage and wasted product costs.

Challenge four: administrative compliance and regulation

Companies across these industries are increasingly looking to optimize their workforces and use skilled operators for more strategic activities. This may be exploring material innovation opportunities or introducing automation to streamline operations. Using nuclear sources in operations involves companies following restrictive and burdensome administrative processes, taking skilled team members away from more valuable projects.  

At a regulatory level, there are currently no global regulations explicitly banning or phasing out nuclear gauges. However, it is clear to see across the world that responsible bodies are trying to reduce industry reliance on nuclear sources when viable, and very effective, alternatives are available. The International Atomic Energy Agency (IAEA) does not prohibit the use of nuclear gauges. However, it encourages justification which is that a radioactive source should only be used if its benefits outweigh the risks. In the United States, the Nuclear Regulatory Commission encourages the use of alternative technologies to nuclear gauges which pose lower risks. Whereas in the EU, Euratom (European Atomic Energy Community) safety directives promote ALARA principles. The principle means that ionizing radiation be kept ‘as low as reasonably achievable’.  

There are significant, growing obstacles to overcome if companies are looking to continue with legacy measurement methods. So, it’s clear to see why professionals need non-nuclear, more precise alternative thickness measurement systems. Solutions available today not only eliminate all the challenges outlined above, but also offer a variety of benefits, helping to make operations more effective and future-proofed. This was a big focus for the development of Industrial Physics’ non-nuclear solution. Decisions were made to ensure that the system could be seamlessly integrated into existing manufacturing operations, strengthening them and providing a wealth of data. To skip ahead to details of our solution, click here: 

The non-nuclear solution

To kick off your introduction to an innovative, non-nuclear solution, watch this short video from our Principal Technologist, Vivek Komaragiri. Here he covers nuclear gauges, the challenges they pose today, and provides information on alternative measurement solutions in short, digestible summaries.

Vivek's Q&A video

The reasons to explore a non-nuclear approach are clear and compelling, and by teaming up with a test and measurement partner such as Industrial Physics, you can identify the best solution for your specific operations. Once selected, you’ll be on the way to reaping the benefits of overcoming regulatory concerns, procurement and disposal challenges, and administrative burden.   

However, if you want to understand more about the difference in measurement methods then continue in this section. 

The animated videos below demonstrate how coating thickness measurement is conducted via nuclear and non-nuclear methods:

• transmission beta gauges (nuclear) 

• backscatter beta gauges (nuclear) 

• ruggedized optical interference technology from SpecMetrix (non-nuclear)

Transmission beta gauge: 

These gauges work by detecting the amount of beta radiation that is transmitted through the sample being measured: The nuclear source emits beta radiation which is directed towards the sample. As this radiation encounters the sample, some of it is absorbed or scattered. The amount of radiation that is absorbed or scattered is proportional to both the thickness of the substrate as well as the thickness of the coating material. The remaining radiation passes through the sample and is detected by a beta radiation detector.  

Since only a difference in emitted radiation and detected radiation is measured, a second beta transmission gauge is required to measure the substrate before it is coated. The measured substrate thickness is then subtracted from the total sample thickness collected by the second beta gauge. Due to how beta radiation interacts with different materials, these gauges must be calibrated with every coating that is run. This is because different materials will absorb and scatter different amounts of radiation for a given thickness.

Backscatter beta gauge:

Backscatter beta gauges work very similarly to transmission beta gauges. The principal difference is that the detector is on the same side of the sample as the source.

As the radiation generated by the nuclear source encounters the sample, it is either absorbed or scattered. The amount scattered is proportional to the thickness of the coating material. The back scattered radiation is scattered towards the source and detector, where it is detected by a beta radiation detector. As with transmission beta gauges, they must be calibrated with every coating too.

SpecMetrix technology:

SpecMetrix measurement technology is based on the principle of optical interference. When a light wave is directed upon a transparent or semi-transparent material, part of the light wave will reflect at each interface. Light is used to illuminate the sample. Some light is reflected at the air-coating surface whereas the remaining light is reflected at the coating-substrate interface where the light can no longer propagate. In some cases light can fully travel through the sample if the substrate is transparent and in that case, light rays further reflect from the substrate-air interface at the bottom allowing to measure the substrate thickness simultaneously along with coating thickness. 

The reflected light waves will interfere with each other, creating an interference wave. The wave is unique to the reflected waves that caused it. Therefore, the specific thickness of the layer(s) between these reflected waves can be calculated.  

The SpecMetrix technology uses a safe, broad-spectrum white light source. It travels through six optical fibers contained in a probe along with a single “read” fiber to illuminate the sample. After these waves reflect and interfere with each other they enter back into the probe and travel through the read fiber to a detector. The detector type is determined by the customer’s coating types and thickness ranges.  

Upon reaching the detector, the interference wave is interpreted and using the proprietary SpecMetrix software, the absolute thickness of the coating or film layer(s) is calculated. As the technology measures the absolute thickness of a material, calibration is not required when a new coating or substrate is used. Instead, a “recipe” may be required to ensure that the interference wave is interpreted correctly. Recipes are easy to make and can be used for multiple coatings and thickness ranges. However, it is recommended to annually verify that the system is still reading correctly using a provided NIST-traceable calibration standard. 

The SpecMetrix technology can measure clear coatings as thick as 350 microns (13.78 mils) and as thin as 0.2 microns (0.0079 mils). Due to how light interacts with materials at different wavelengths, opaque materials can also be measured as they become transparent or semi-transparent at other wavelengths in the visible spectrum. This allows SpecMetrix to measure opaque coatings from 0.7 microns (0.0276 mils) up to 75 microns (2.95 mils). 

Keen to understand how this could work for your operations? Hear from industry peers about their own experiences:

Switching from nuclear gauges to SpecMetrix infrared technology has positively impacted our coating process. The SpecMetrix technology is user-friendly for Operators, Maintenance, and Engineers. Everybody has been happy with this thickness gauge so far since purchased about 2 years ago. 

During the initial phase of setting the thickness gage up, the engineering team was very helpful in training and ensuring that we were able to get the data in a format that was required by the customer. They were even willing to test all of our samples prior to investment and do an on-site demonstration. Even though we have such old software on our site, the thickness gauge performs well and functions as intended. With newer software and communication abilities, we believe that the gauge would enhance our experience and coating operations. We are easily able to communicate any potential improvements to the SpecMetrix engineering team and they take into considerations for future changes.

In terms of maintenance, there is not much, if any, maintenance required. The turnaround for calibrating the sensor or requesting remote services is quick.  Someone is always available to help or answer questions when needed. In addition to the customer service and ease of use, another benefit is that there is no radiation permit or leak tests required for this technology! With nuclear gauges, it is much harder to perform maintenance tasks without having a nuclear technician from the vendor available.

Operators can easily look at the thickness measurements and know what exactly needs to be adjusted on the fly without having to wait to measure an end sample or finish coating an entire roll and then finding out that it was coated to the incorrect thickness. They are easily able to clean the lens of the sensor if needed without having to worry about radiation or any other hazards.

Overall, we are thoroughly impressed with the SpecMetrix technology. It is user-friendly for all groups, easy to maintain, and there are no significant hazards associated with this technology in comparison to nuclear gauges. 

Dhara Prajapati, Manufacturing Technology Process Engineer at DuPont Electronics & Industrial

Industrial Physics 

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