Where Science and Faith Converge

Helium Diffusion in Zircon: A Response to Questions by the RATE Team

By Guest Writer - April 22, 2009

Source of the Dispute

Radiometric dating methods have long been disputed by young-earth creationists, and for good reason. Rock ages obtained by these dating methods, usually ranging from millions to billions of years, contradict the notion of a 6,000-year-old earth. An eight-year young-earth research program, called Radioisotopes and the Age of The Earth (RATE) proposed a solution to this dilemma: nuclear decay rates were accelerated in the recent past. If this proves true, then conventional radiometric measurements could be reconciled with the 6,000-year date. The results of this study were published in two parts in 2000 and 2005, respectively.

Although a large part of the RATE program focused on radiometric dating and related phenomena, such as fission tracks and radiohalos, one of their case studies involved a helium diffusion experiment using zircon mineral samples from deep geothermal wells in Fenton Hill, New Mexico.

Think of a radioactive nucleus as a clock that ticks (decays) at a known rate. The RATE team claimed that when they compared the nuclear decay clock with their helium diffusion clock, they found a large discrepancy. The nuclear decay clock recorded an elapsed time of over a billion years, whereas their helium diffusion clock recorded an elapsed time of only a few thousand years. Taking the latter time as the more reliable measurement, the researchers claimed that they had found convincing evidence for accelerated nuclear decay.

Last year Reasons To Believe published a two-part summary of my technical paper critiquing this research program. Recently, Dr. Russell Humphreys, a leading member of the RATE team, responded to my analysis with an article published on the website of Creation Ministries International. Humphreys contends that my old-earth diffusion model is incorrect, whereas the data from the Fenton Hill experiment still support his young-earth RATE model. This article focuses on Humphreys' main criticism of my old-earth diffusion model.

Comparing RATE with Other Models

Humphreys and I disagree on the RATE group's interpretation of the results of their laboratory diffusion experiment. The type of experiment they used was pioneered by H. Fechtig and S. Kalbitzer in the 1960s. Since diffusivity cannot be directly measured, it must be inferred using a model. Fechtig and Kalbitzer's method became popular among other scientists because it used a simple analytic formula to form its calculations. If the prerequisites of this model are not met, the calculated numbers are meaningless. Fechtig and Kalbitzer, well aware of the limitations of their own technique, often recommended the omission of low-temperature data when they deviate from an extrapolation of the high-temperature portion of the curve.

Contrary to this advice, the RATE researchers ignored their high-temperature data and relied instead on the low-temperature data. The validity of their argument hinges upon the correct understanding of only five data points below 300 °C. Since these five heating steps collectively accounted for only 15 parts-per-million of the total helium released, the interpretation is very sensitive to errors in the model assumptions. Although the RATE researchers acknowledged that the behavior in the low-temperature regime was dominated by defects, they appeared to be unaware of how to properly handle defects in a diffusion model.

The rest of the geophysical world, however, is very cognizant of how defects can complicate a diffusion experiment. In recent years, researchers have promoted a two-population or multidomain diffusion model in which the majority of helium is tightly bound to the crystal lattice and the remaining small portion of helium is loosely bound to defect sites. When the results of the RATE diffusion experiment are analyzed using such a model, it is apparent that the miniscule quantity of helium released at low temperatures is not representative of the majority of gas in the crystal. Therefore, the conclusions drawn by the RATE team from this low temperature part of the experiment are unreliable. For technical information on multidomain diffusion models, see the following: Reiners and Farley, Reiners et al. , Shuster, et al., 2003, and Shuster, et al., 2005.

Humphreys agrees that a small, loosely bound fraction of helium atoms exists within these zircons, but claims that it would be completely exhausted after the initial heating ramp of the laboratory experiment. In essence, his assertion is that not enough of the loosely bound fraction would remain after the initial ramp to account for the subsequent low-temperature portion of the diffusivity curve. Apparently, he made this claim without performing any calculations.

Because I was aware of this concern, I had already performed these calculations. In appendix C of my technical paper, I discussed how the diffusion parameters for my multidomain model were extracted from the laboratory data. Although not shown in the paper, my method required the explicit calculation of the gas released by both the tightly bound and loosely bound helium components. Results of this calculation are plotted in the following figure.


The tightly bound component is denoted by the blue circles, and the loosely bound component is denoted by the orange triangles. The initial temperature ramp releases only about 70% of the loosely bound helium fraction. The remaining 30% is sufficient to account for the low-temperature portion of the diffusivity curve. Although the exact gas release values at any given time step are sensitive to the assumptions used in constructing the model, it does demonstrate that it is possible for a fraction of the loosely bound helium to remain throughout the entire experiment, contrary to Humphreys' unsubstantiated claims.

Humphreys argued that retention of the loosely bound helium past an initial heating ramp was not reported in the scientific literature. However, in the references cited, the researchers never took the samples to a low enough temperature for the effect to be noticed. Also, he claimed that the scientist performing the RATE experiments assured him that "the rates he measured were accurate depictions" of only the tightly bound helium. Yet, there is no supporting evidence for this claim in the RATE publications, not even in their conference paper which contains the original laboratory reports as appendices. In these reports, the only effects discussed are the surface depletion of helium and radiation damage.

How Experience in Electronics Applies

Though Humphreys relies heavily upon his understanding of other experts, he draws many of his conclusions without actually consulting with others. Experts' background and experience–including mine–should be taken into consideration.

Many of today's electronic innovations–from personal computers to light-up sneakers–have been made possible by advancements in the semiconductor industry. Although we encounter these things every day, most people have probably never considered how something like a transistor is made. I have. It has been my profession for almost 15 years, and I can tell you from firsthand experience that the processing of a silicon wafer involves hundreds of steps with multiple heating and cooling cycles.

What does experience in the electronics industry have to do with helium diffusion in zircon? The same fundamental principles of physics still apply. The semiconductor industry would not be where it is today without an advanced understanding of the diffusion mechanism, especially as it relates to its interaction with defects. This was one of my areas of responsibility when I began my career. I worked with some of the best diffusion modeling people in the industry, publishing papers and filing patents along the way.

Which Model Passes the Test?

This article answers Humphreys' challenge to my old-earth helium diffusion model that required additional technical information. He made several other criticisms, but did not substantiate them with any solid evidence. The reader is encouraged to consider both sides of the argument for himself, and see which one is supported by the greater weight of evidence. For more information, please see a longer paper that I have written on the subject.

Dr. Gary H. Loechelt

Dr. Gary H. Loechelt

Dr. Loechelt received his doctorate in the science and engineering of materials from Arizona State University in 1995, and currently works as an electrical engineer at ON Semiconductor in Phoenix, Arizona. This work was conducted on his personal time and does not reflect the views or business interests of his employer.

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