Mineral undergoes self-healing of irradiation damage

September 09, 2020

In nature there are quite a few minerals that incorporate uranium and thorium in their crystal structure. This causes radioactive self-irradiation that, over geologic periods of time, may destroy the crystal and transform it into a glassy form. As early as in 1893, the Norwegian mineralogist and geologist introduced the term "metamict" to describe this glassy state.

Self-irradiating minerals are currently in the focus of international research. This is because structural radiation damage may affect significantly the physical and chemical properties of minerals. Understanding the causes of these property changes is crucial for the Earth sciences - one of the most important technique to determine ages of minerals and rocks is based on the radioactive decay of uranium - and in materials sciences, as radioactive minerals are analogues of host ceramics for the immobilization of radioactive waste.

Monazite heals itself

So far it was not understood why some minerals (such as zircon, ZrSiO4) are often found in nature in an irradiation-vitrified state, whereas other species (such as monazite, CePO4) - in spite of even higher self-irradiation - never become metamict but, rather, are always observed in a moderately radiation-damaged state. This is first of all explained by insufficient stability of the monazite structure, resulting in inability to accumulate damage over geologic periods of time. Lutz Nasdala elucidates this, greatly simplified, by a comparison with cheese: "It is easily possible, using a pencil, to prick a hole into a hard ('stable') Emmentaler cheese, whereas analogously produced holes in a soft Camembert cheese would 'heal' in no time", Nasdala said.

Helium ions create and heal radiation damage

It has been supposed in the past already that partial self-healing of monazite is not only caused by the low thermal stability of this mineral, but also related to the action of natural alpha particles (that is, energy-rich helium cores that are emitted by an unstable nucleus in an "alpha-decay event"). The latter, however, was in apparent contrast to the observation that crystalline monazite is prone to alpha-irradiation damage.

In the new study the research team could unravel the causes of the self-healing by conducting irradiation experiments. Helium ions with energies of millions of electron volts (analogues of natural alpha particles) create structural damage in crystalline monazite. In contrast, the same helium ions cause structural recovery of radiation-damaged monazite. Hence crystalline monazite would correspond to "Emmentaler cheese" whereas radiation-damaged monazite becomes "Camembert cheese".

Such strong dependence of mineral properties on small changes in the structural state has never been described before. One consequence for Earth sciences research is that experiments with synthetic (that is, non-radiation-damaged) monazite may yield results that are not necessarily relevant for the behaviour of this (always moderately radiation-damaged) mineral in the Earth's interior.
-end-
Publication in "Scientific Reports":

Nasdala, L., Akhmadaliev, S., Burakov, B.E., Chanmuang N., C. & Škoda, R. (2020): The absence of metamictisation in natural monazite. Scientific Reports. DOI: 10.1038/s41598-020-71451-7.

University of Vienna

Related Radiation Articles from Brightsurf:

Sheer protection from electromagnetic radiation
A printable ink that is both conductive and transparent can also block radio waves.

What membrane can do in dealing with radiation
USTC recently found that polymethylmethacrylate (PMMA) and polyvinyl chloride (PVC) can release acidic substance under γ radiation, whose amount is proportional to the radiation intensity.

First measurements of radiation levels on the moon
In the current issue (25 September) of the prestigious journal Science Advances, Chinese and German scientists report for the first time on time-resolved measurements of the radiation on the moon.

New biomaterial could shield against harmful radiation
Northwestern University researchers have synthesized a new form of melanin enriched with selenium.

A new way to monitor cancer radiation therapy doses
More than half of all cancer patients undergo radiation therapy and the dose is critical.

Nimotuzumab-cisplatin-radiation versus cisplatin-radiation in HPV negative oropharyngeal cancer
Oncotarget Volume 11, Issue 4: In this study, locally advanced head and neck cancer patients undergoing definitive chemoradiation were randomly allocated to weekly cisplatin - radiation {CRT arm} or nimotuzumab -weekly cisplatin -radiation {NCRT arm}.

Breaking up amino acids with radiation
A new experimental and theoretical study published in EPJ D has shown how the ions formed when electrons collide with one amino acid, glutamine, differ according to the energy of the colliding electrons.

Radiation breaks connections in the brain
One of the potentially life-altering side effects that patients experience after cranial radiotherapy for brain cancer is cognitive impairment.

Fragmenting ions and radiation sensitizers
The anti-cancer drug 5-fluorouracil (5FU) acts as a radiosensitizer: it is rapidly taken up into the DNA of cancer cells, making the cells more sensitive to radiotherapy.

'Seeing the light' behind radiation therapy
Delivering just the right dose of radiation for cancer patients is a delicate balance in their treatment regime.

Read More: Radiation News and Radiation Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.