RSS Radon - CR39 Acquisition & analysis of the tracks

RSS Radon - CR39Acquisition & analysisof the tracks dr. Massimo Vascotto

NOTE ABOUT THE PROJECT • The aim of this project, only for educational purposes, is to propose an itinerary of study on the natural radioactivity, allowing students to measure the radon in their homes, following the same protocols of a real scientific research. • Participation at the measure is voluntary, not mandatory. • Participation in the project includes the compilation of a questionnaire that will be only used for the purposes related to the survey. Participants are responsible for the information provided in the questionnaire. • Personal data, the information contained in the questionnaire and data related to the measure will be kept with any safety standards, in the archives and/or reporting of entities involved in the project, under the privacy laws. Ma. 09/03

EQUIPMENT AND MATERIALS • Microscope: Konus Academy 1000x (Mod. 5304) 40x; • Micro camera: Konus CMOS Camera USB PLUG (Mod. 5829) [~10x]; • Software: Konus Minisee (provided with micro camera); • Resolution: 640x480pixel; • Image dimensions: l=0,361mm h=0,263mm; • Image surface: s=lxh=0,095mmq. Ma. 09/03

IMAGE ACQUISITION • Switch the microscope “on” (pos. 2); • The micro camera is in working condition when the USB is inserted on the computer; • Click 2x on “Minisee” software, previously installed on your PC; • Click on file/import image/select device (select the driver as instructions); • Click on “acquire” icon [or follow the path: file/import image/acquire]; • Select resolution (preference/resolution) on 640x480 (NB: microscope is on); • Insert a slide filled with CR39 on the microscope (note: ID number, is readable); • Try to focus the image. If possible, start from the serial number of CR39, if there is, or something visible, like a corner of CR39 (use focus and fine focus);

IMAGE ACQUISITION • Consider that light deformations like arching or saddling of the slide, may alter the focus, when you move it (note that you are working at 40x!).In that case is indispensable to re-focusing the image every time it is necessary (focus and fine focus); • Move the slide randomly. It is suggested to do this operation avoiding to look on the screen of the PC (this is due to the fact that human eye always try to search for something...). So, it is better to work in two people. One check the microscope, moves the slide and decide when to stop, and the other work on the monitor and on the software commands. Finally, both work on focusing; • Focus the image as best as you can (fine focus). Note that you have often some references to do this, like tracks, impurities, serial number, etc.; • Take the photo by clicking once on "SNAP SHOT";

IMAGE ACQUISITION • Move the slide randomly and repeat the previous steps until you have collected at least ten images; • The images are saved per default on desktop and are numbered progressively (from minisee0000); • Remember to always create a folder named as the CR39 analyzed, and then drag the collected images in; • Repeat the image acquisition for the next CR39, until you finish your working session; • Close the acquisition window by clicking on "exit"; • Close the “Minisee” software. It is suggested to always have a backup copy of all the acquisitions; • Now you may count the tracks on your pictures and determine the radon concentration by means of the file “RSS Rn measurements CR-39.xls”.You may download this file at the link: http://physics.units.it/didattica03/orientamento/laboratori.php.

SOME INFORMATION ABOUT TRACKS • Tracks generated by alpha particles on CR39 surface have dimensions of nanometers (nm) and so, to keep them visible at microscope, you must etch them with caustic soda (NaOH). • By means of chemical etching you may widen the holes leaved by alpha particle up to tenth of micrometers (mm), so they become visible at microscope. • For further information about etching see “CR39 EN.ppt”. You may download this file at the link: http://physics.units.it/didattica03/orientamento/laboratori.php; • It is important now to point out something about the track geometry.This aspect is very important if you consider that you must be able to select “good tracks” from bad or poor ones, as this may affect your results (i.e. influence the final radon concentration).

SOME INFORMATION ABOUT THE TRACKS • This aspect is correlated to different parameters, like: • the incidence angle of alpha particles; • the energy of alpha particles; • The range of alpha particles; • the length of chemical etching; • ... • Normally the alpha particle may have any incidence angle when hits the CR39 surface. So, in most cases the hole leaved will be elliptical. The track will be circular only if the incidence angle will be perpendicular or nearly perpendicular to CR39 surface. • Hole shape is also connected to the length of the chemical etching. For example, a short etching time will not allow to all holes to grow up and become visible. Ma. 09/03

SOME INFORMATION ABOUT THE TRACKS • A good timing etching will allow you to well distinguish the different kind of shape of the tracks and to improve the tracks counting. • A long etching will produce in the transformation of all the elliptical holes in circular holes, as a consequence of the prolonged attach of caustic soda, like in figure. • An super etching may determine the vanishing of almost (or all) the tracks. Ma. 09/03

SOME INFORMATION ABOUT THE TRACKS • Another aspect to be considered is the alpha particle range and energy. It is known that alpha particle range in air is around 10cm. In our case alpha particles, inside the exposure chamber, may range between 0 to 5cm. • As alpha particle loose energy in inverse proportional rule to the range, the damage produced by alpha particle on CR39 will be consequent. • All these considerations help us to understand that it is possible to have thousands of situations in shape and dimensions of the tracks and that counting them is not always so easy. • Anyway, if we consider that the tracks will occupy some surface this, possibly, will be an aspect that we may take in account to decide if consider a track or not. Note that this is also the criteria adopted by the automated optical track reader, used by environmental protection agencies.

SOME INFORMATION ABOUT THE TRACKS • Obviously this may introduce some errors as it is possible to count “as real tracks” something like impurities, scratches, chemical residual, etc. • The eye approach is quite different, as it is able to discern between tracks and impurities. • On contrary, eyes cannot work for a long time, especially if the number of observations is high. This may also introduce some errors, in counting phase. • It is important to train, before start a real measure. • It is important to set up a “boundary” in track dimensions to quickly conclude if a track is good or not. • Anyway, good tracks are always “well shaped”. It doesn’t matter if they are circulars or elliptic.

SOME INFORMATION ABOUT THE TRACKS • Moreover: we always must remember that we calculate radon concentration by means of pictures. • The surface analyzed in a picture is less than dimensions of a CR39. • So, possibly, this may represent a “poor statistic”, especially if compared to that of an optical reader, that is able to measure all the CR39 surface (in less time), apart of the fact that it counts some false track. • Usually this will be a real problem when Rn concentration is low. In this case is better to increase the number of acquisitions (more pictures).

TIME OF ACQUISITION OF TRACKS • Remember to always focusing, the images before take the picture (fine focus). • As said before this is due to the light imperfections on the slide shaping or on its thickness, that are inevitably amplified by the microscope (as we work at 400x). The consequence is that you have a change of the focus (sometimes you go inside or outside of the CR39 surface). • Timing: you need between 3 to 5 minutes to acquire a set of images (about 20 to 30 seconds per image). Obviously you need some training. The timing depends also on the ability, the tiredness and on the accuracy of the operator and may be affected by several inconveniences. • Then you must add the time to create the folder named as the ID of the CR39 (around 20 to 30 seconds) and to drag inside the images. • Never consider this as a “time race”, but try reach the better result as you can.

A BRIEF TRAIN COURSE FOR READ THE TRACKS • In the following slides we show some examples of pictures, in which we may see: • Good tracks; • Bad tracks (that’s to say tracks that we not consider for many causes. For example simply because they are too much small); • Impurities; • Faults; • Scratches; • Chemical residuals; • Other substances; • Bad etching tracks; • … • Finally we show some pictures of the same subject, in different focusing conditions. • Note: all the images are from school works.

SOME EXAMPLES OF TRACKS Ma. 09/03

IMPURITIES, FAULT, AND SCRATCHES Ma. 09/03

IMPURITIES, FAULT AND SCRATCHES Ma. 09/03

YES YES EXAMPLES Ma. 09/03

YES BORDER OF A SERIAL ID OF CR39 EXAMPLES Ma. 09/03

IMPURITY IMPURITY YES IMPURITY IMPURITY EXAMPLES Ma. 09/03

EXAMPLES YES Ma. 09/03

YES YES YES YES YES YES YES YES EXAMPLES Ma. 09/03

IMPURITIES YES EXAMPLES Ma. 09/03

IMPURITY YES EXAMPLES Ma. 09/03

IMPURITY YES IMPURITY EXAMPLES Ma. 09/03

IMPURITY EXAMPLES YES Ma. 09/03

YES YES YES IMPURITY CHEMICAL RESIDUALS EXAMPLES Ma. 09/03

RSS Radon - CR39 Acquisition & analysis of the tracks