Experimental Background

Meteorites are extraterrestrial rocks that land on the surface of Earth, rather than meteors that burn before reaching Earth. They play an important role in the evolution of Earth's history. There are many hypotheses about meteorites, and some people believe that the moon was formed from the remnants of a large meteorite colliding with Earth. Some people believe that the water covering the Earth was brought by meteorites. The more well-known theory is that meteorite impacts caused the Cretaceous Paleogene extinction event.

There are many mysteries in meteorites, and their specimens have naturally been sought after by historians, geologists, and extraterrestrial enthusiasts. However, it is quite difficult to determine whether a rock is a genuine meteorite. In general, the basic indicators for identifying rock types include density, magnetism, and composition. However, for example, amorphous rocks mainly composed of iron in terrestrial rocks are also roughly similar in appearance and composition to meteorites. So, we need to use more targeted methods to identify the category of rocks, among which a more effective method is to use laser-induced breakdown spectroscopy (LIBS) technology.

Laser induced breakdown spectroscopy (LIBS) is an atomic emission spectroscopy that uses a pulsed laser as the excitation source. The laser pulse is focused onto the surface of the object being measured, increasing the laser power density on the surface of the material being measured to a certain extent. Under such high laser power density, several micrograms of substance will be ejected from the surface of the tested material, and a short-lived but highly luminous plasma will also be generated on the material surface, with an instantaneous temperature of up to 10000 degrees Celsius. During the cooling process, atoms and ions in an excited state return from a high-energy state to a low-energy stateAt this point, different elements will emit light of their specific wavelengthsAfter being detected by the spectrometer, a spectrum is formed, and peaks representing the wavelengths of each element can be directly observed in the spectrum.Therefore, LIBS has become a spectroscopic technique for identifying the composition of different types of metals and minerals.

Experimental Method

The purpose of this experiment is to use LIBS to identify meteorites and terrestrial rocks in four rock samples.

There are four samples in the experiment, two of which are meteorite samples, namely H5 ordinary chondrite meteorite and nickel iron meteorite. The other two samples are iron oxide (FeO2) and titanium dioxide (TiO2).

In the experiment, we used the Sd mode, which is the original data subtraction dark background mode in AvaSoft. Using this mode can reduce noise and better isolate and identify plasma peaks. We set the integration time to 10ms and the average number of times to 1.

Experimental Configuration

This experiment (Figure 2) used a brand new AvaSThe pec-PCT4096CL mini spectrometer is designed to be compact and easy to integrate into desktop and handheld devices, making it more suitable for OEM users. This spectrometer is equipped with 4096 imagesThe pixel CMOS detector has a resolution of up to 0.09 nm and a stray light level as low as 0.1%.

The other attachments used in the experiment are as follows: Lumibird's DPSS dual pulse Nd: YAG laserThe Quantel control box, model FX002725, is customized with short optical fibers to synchronize laser and spectrometer measurements.

experimental results

The following figure shows the LIBS spectra of each sample in Sd mode.

Figure 3: LIBS spectra of H5 ordinary chondrite samples

Figure 4: LIBS spectra of nickel iron meteorite samples

Figure 5: LIBS spectra of iron oxide samples

Figure 6: LIBS spectrum of titanium dioxide sample

Figure 7: Comparison of LIBS spectra of nickel iron meteorite (orange) and iron oxide (red) samples

Result Analysis

Firstly, let's take a look at three samples: H5 ordinary chondrite meteorite, nickel iron meteorite, and iron oxide. They all show a cluster of peaks in the wavelength range of 230-265 nm (Figure 3-5), indicating that they contain iron elements.

The H5 ordinary chondrite sample has peaks near 280 nm and 288 nm that other samples do not have, indicating that it contains magnesium and silicon elements, respectively. The measurement results correspond to the composition of the H5 ordinary chondrite.

There is not much difference between nickel iron meteorites and iron oxide samples (Figure 7). But a slightly higher peak can be observed in the spectrum of the nickel iron meteorite sample, around 221 nm, indicating that it contains nickel element.

The titanium dioxide sample (Figure 6) has fewer peaks in the wavelength range of 230-265 nm, indicating a lower iron content. Its main peak is in the wavelength range of 300-340 nm, indicating that it contains titanium element.

empirical conclusion

By using LIBS technology to observe specific wavelength peaks of each sample in the spectrum, the elemental composition of the sample can be easily and intuitively determined. The new mini spectrometer PACTO used in this experiment is suitable for various applications. It is compact in size, supports multiple communication protocols, and is easy to integrate into products and systems.