How many hours/days of EPMA do I need? How many samples can I analyze?
It depends on the number of samples you want to analyze, the number of samples/holders we can fit into the machine, as well as on what you want from your samples (quantitative analyses, WDS element maps etc). Think that you can usually analyze not more than 4 thin sections in 24 hours (e.g. 1 morning session, 1 afternoon session and 1 overnight session). This means a very long evening for you to set automate ca 150-200 analyses for the night, to take relevant BSE images for every site of interest, etc. We can fit no more than 4 thin sections in the EPMA holder at the time. If using 1 inch (25 mm) diameter round blocks we can fit 6 to 9 blocks at the time. If you have blocks of 30 mm diameter, we can fit 2, only. No matter how many samples fit in, you will be limited to a max of 100-200 analysis for major elements per day and overnight (depending on the number of different phases and number of elements to be analyzed). In budgeting your EPMA time also keep in mind that you might want to run element maps, which, depending on size and resolution, number of maps etc can take 2 to 10 hour or more.
How should I prepare my thin sections for EPMA session? Analysis planning – Sample navigation
For a better estimation of the EPMA use, the following information is needed:
- The number of samples to be analyzed
- The type of samples (thin sections, round blocks of 1’, 5 mm brass/aluminum pins etc)
- The type of material (e.g. rock sample, mounted mineral aggregate, mounted experimental products, bone, fossil, etc)
- The type of material/mineral/phases you want to analyse (e.g. unknown glass, unknown mineral, known silicates, oxides, sulphides etc)
- The elements you want to be analyzed in each phase (e.g. Si, Al, Ti, Cr, Mg, Fe, Mn, Ca, Na, K in all silicates and glasses; Ni in olivine, F and Cl in biotite, Sr in plagioclase etc); Cu, Fe, Ni, Co, S in pentlandite, Zn, Fe, Cd, S, in sphalerite etc. This information is essential for standard calibration.
- Do your Petrography, in order to understand your mineral assemblages. Before coming to the microprobe you have to know: i) what mineral phases you want to analyse (and why) and ii) what elements you want to analyze in each of your phase;
- Polish your samples as good as possible. The quality of the images and quantitative EPMA data is drastically dependent on the quality of the polishing and flatness of your samples. Check the polishing quality before taking any step;
- Scan your sample at high resolution, so that, when enlarging the image to be able to recognize the sites of interest you want to image or analyse at the EPMA. Change brightness/contrast so that to allow recognition of different types of phases present in your sample. Print on Letter or A4 size paper your scanned image (have with you the printed images when at the EPMA);
- Clean the surface of your samples before coming to your EPMA session. Use ethanol and/or ultrasound;
- Mark the sites of interest on the printed scanned image. You need to know exactly what grain you want to analyze and you should be able to identify the grain under Back Scattered Electrons (BSE) image. It is useful (time saving) to know what mineral phase do you expect to be from your microscopic examination. If the grain size is too small and the printed image is not useful to recognize your sites of interest, you can also mark the sample with a circle or/and straight lines, using a thin PERMANENT marker; see example on Figure 1.
- Have with you photomicrographs of the sites of interests for each sample. Use 40x magnification (or higher) for your micrographs. Do not acquire pictures in XPL mode, but in PPL mode, in transmitted and/or reflected light. These photomicrographs will help you to identify the grains you want to analyze;
- Bring the polished sections for carbon coating to the EPMA lab (preferably one day before your EPMA session)
Figure 1. Example on how to mark your scanned image (or sample, if the case) and using detailed photomicrographs. Label each circle or marking.
Our carbon coater (JE-420 can coat 4 thin sections or 6 I inch round block at the time. The time for one coating is ~ 40-50 minutes. We recommend (for Rice users, at least) to do the carbon coating one day before your EPMA session. However, if you have few samples only (one single episode of carbon coating) we can do the coating starting at 8.30 am in the day when your EPMA session starts. This is valid for external users and visitors, as well. A detailed guid for using the coater is available here.
Hours and procedure
The EPMA session, starts at 9 am and ends at 5 pm. After 5 pm the time spent on the EPMA instrument is considered overtime. The user can work overtime the number of hours that he/she needs, at a lower rate (see Rates and Payment). The EPMA overnight session starts at 5 pm and ends at 8 am. If more than 4 hours are used during the overnight session, then a full “overnight session” will be charged.
How do I get my EPMA reports/data?
If you are a student from Rice and have a computer linked to Earth Science Network, you will find your data on the network. Look up for a computer called “EPMA2” and double click on it. The password required to access the EPMA2 computer is “epma” (case sensitive). Once you have access, go to the Folder called “ Rice Data”, look for the folder having your name and copy your data.
If you have no access to our network, don’t worry. If you were not able to collect your reports at the end of your EPMA session, the data will be sent to you via e-mail (be sure you sign in in our Logbook). For large files, a link will be provided to download your data. If present to collect your data, a DVD will be burned with your data.
When can I have my samples back?
We are not responsible for the users’ samples left into our lab more than a week. Please make arrangements with the Lab manager to get your samples back. It is not the responsibility of the lab to arrange the return of your analyzed samples. This is especially valid for the external users.
Can I use my cell phone in the EPMA Lab?
The electromagnetic field emitted by your phone, especially when you make a call or you receive a call, can slightly deflect the electron beam. Therefore, you can use the phone but not during the acquiring of the images and analyses. If you still need to use the phone, be sure that you are at a distance of at least 6 ft. away from the electron gun.
Can I bring food and drinks in the lab?