Neutron Spectrometer Operation Manual MIT Department of Physics (Dated: October 16, 2014) This document is for assisting in the understanding and accessing of the technical aspects of the neutron physics experiment currently operated in the NRL (Nuclear Reactor Lab). It is important to note that the apparatus is not located in the Junior Laboratory, but in the Nuclear Reactor Laboratory. Usage of the experiment is scheduled through NRL personnel and Junior lab staff. The best way to access this experiment will be through the remote desktop software to the computer setup in the NRL, which can be done from anywhere on the MIT network. I. EHS SAFETY TRAINING Before the start of the experiment you must complete the EHS web based safety training. The following is how to access the training material that is required to be completed: Go to https://atlas.mit.edu and on the left side of the page click Training. Next you want to click the MIT Learning Center link. You are now on the EHS Training site and you will need to update your activities so that you can find the required training. 1. First go to My profile (On the left side of the site), then Click the My EHS Training Needs Tab. 2. Next you will click Update my EHS profile which will launch a separate window. In that window click Select Activites. 3. In this menu you will want to go down to the Ionizing Radiation section and check off the box next to Use the Nuclear Reactor. Once this is done go to the bottom and click save, then click close to close the separate window. 4. Now go to My Required Training and you should have two different training requirements listed; Radiation Safety: Reactor and Radiation Safety: Reactor Practicum. You will only need to complete the Radiation Safety: Reactor web based course for this experiment. At the end of the semester you can repeat these instructions to remove the activity/training requirements in My Required Training. II. REMOTE DESKTOP: HOW TO CONNECT TO THE EXPERIMENT REMOTELY The experiment is run off of a windows machine in the NRL containment area. During the first day of this experiment you will be escorted by a member of the Junior Lab Staff to visit the experiment. Once you have done this, most of the experiment can be run from any windows machine that has Remote Desktop software which is built-in on Windows XP/7/8. If you currently use Linux or Apple, you may install remote desktop software or use an unused junior lab computer to access the experiment. To connect to the computer, search for the program Remote Desktop Connection or open your remote desktop program. This can be accomplished by going to the start menu and using the built-in windows search function. Once you have it running, use the following information to log-on to the NRL Neutron Scattering computer. DO NOT SHARE THIS INFORMATION: This experiment is used by more than just Junior Lab. Computer: s-spectrometer.mit.edu User Name: student Password: 2209 To access the web cameras that are setup up on the experiment, you will use a standard web browser. The user name and password are the same as the computer and the web addresses are: III. Camera 1: SCC-1.mit.edu Camera 2: SCC-2.mit.edu SPECTROMETER LABVIEW INTERFACE Once connected and logged into the computer you may have to start-up the LabView program. The program is located on the desktop and is named Run Spectrometer. When you first start-up the LabView program an initialization window should appear. This interface will go through a list of checks to make sure all components are in working order. If the initialization is not successful, alert the Technical Staff. The success of the initialization can be determined by the color light that shows up; Green - Successful, Red - Failed. Once the program has initialized, you have the option of 4 different sub-programs.
2 III.1. Common Options and Commands in the spectrometer LabView programs Quit/End Activity: It is important to note that every window has either a quit/logout or end activity button in the window. This allows you to either end the activity/sub-program or quit/logout of the entire labview code which stops the labview code but does not quit labview itself. Never make changes or save the labview code itself. Chopper Wheel: There are two commands that can be toggled in every program; The spinning of the wheel and the position of the wheel. These are important to note, especially since some sub-programs will not run without the wheel down and spinning. Remember to allow time for the wheel to fully spinup before taking measurements. FIG. 1. Screenshot of the experiment initialization Beam Scan: This sub-program is designed to take horizontal beam scans of the neutron beam at any distance. Crystal Angle Scan: This sub-program is designed to take angle scans of the scattered neutrons off of the crystal. Counter: This sub-program is designed to take measurement of counts from both the low efficiency and high efficiency detectors. This program can also control the carousel of materials which you can make the beam pass through. MCS Count: This sub-program is similar to normal counter, but allows you to measure neutron flight time using a MCS/MCA. System Indicators(Power): The power read-out is a direct feed of the current reactor power and should have a stable power reading of about 5.5 5.6 MW. The main concern with this read-out if it reads anywhere lower than about 1 MW: if it does, Inform your Instructor. System Indicators (Initialized state): This is a True/False indicator, If it is green that means that the program has successfully initialized all components it is programmed to check. If it is not green, attempt to reinitialize the program with the initialize button on the man menu. System Indicators(Error Detected): This is a True/False indicator. If it is lit up that means you need to attempt to reinitialize the program. If it is not lit up than all systems should be running correctly. Position Indicators: This chart is the position indicator for all moving components of the experiment. The data displays what position or state it is in and what its target position or state is. III.2. Beam Scan Z Position: This is the distance of the low-efficiency from the chopper wheel. This position will not move during a Bean Scan in this sub-program. X Position: This is the axis that is parallel to the chopper wheel. You have 3 input values: Starting X- position, X Step size, and Final X-position. FIG. 2. Screenshot of spectrometer sub-programs Starting X-position: This is the starting position of the low efficiency detector. X Step size: This is the increment the detector moves per data point.
3 III.3. Crystal Angle Scan FIG. 3. Screenshot of the Beam Scan sub-program Final X-position: This is the target stopping point for the X axis. Count Time: This is the time that the detector counts for each step location. Run: This starts the Beam Scan with the parameters you have selected. Progress: The current state of the run that is in progress. Graph Tab: This tab directly displays the data acquired during the scan in graph form. The scales will automatically adjust depending on the data acquired. Data: This tab displays the data in a list which allows you to directly copy and paste it into a different document. FIG. 4. Screenshot of the Crystal Angle Scan sub-program This sub-program uses a combination of the high efficiency detector and crystal. This allows us to do angle measurements of the neutron scattering from the neutron beam hitting the crystal. Starting Arm Angle: This is the starting position of the arm which holds the high-efficiency detector, measured in degrees. End Arm Angle: This is the ending or target position of the high-efficiency detector, measured in degrees. Arm Step Size: This is the distance the high-efficiency detector moves per scan, measured in degrees. Dwell Time: This is the time the detector sits (or dwells ) at each step position. Crystal Angle: This is the angle of the crystal with reference to the beam, measured in degrees. Graph Tab: This tab directly displays the data acquired during the scan in graph form. The scales will automatically adjust depending on the data acquired. Data: This tab displays the data in a list which allows you to directly copy and paste it into a different document. III.4. Counter This sub-program uses both low and high efficiency detectors. The main purpose of this program is to give you a value for number of counts for each detector depending on the parameters selected. Low-Efficiency Z-Position: This is the position along the beam path of the low-efficiency detector.
4 FIG. 5. Screenshot of the counter sub-program FIG. 6. Screenshot of the MCS Counter sub-program Low-Efficiency X-position: This is the position perpendicular to the beam path of the low-efficiency detector. High-Efficiency Angle: This is the angle position of the high-efficiency detector in degrees. Crystal(Angle and position): This is the angle control for the crystal with reference to the beam. Also this controls whether the crystal is in or out of the beam path. Materials Carousel(type and position): This allows for the selection and positioning of materials to be placed in the beam path. Time Counting(Timer and Remaining): This controls the time the detectors will count for, and gives you an active display of time remaining. Low-Efficiency Counts: This displays the number of counts per second (average) the low-efficiency detector measures. High-Efficiency Counts: This displays the number of counts per second (average) the high-efficiency detector measures. MCS (Pass Length): This is number of channels. MCS (Preset Pass): The number of passes run. Detectors (Lo-Eff/Hi-Eff): The MCS/MCA only takes one input at a time. So you must choose one detector at a time. Other Controls: The rest of the controls are similar to previous sub-programs. IV. WHAT IS AN MCS? An MCS is a Multi-Channel Scaler which records the counting rate of events on the detector as a function of time. At the start of the scan the MCS begins counting events in the first channel. Once the set dwell time has elapsed, the MCS stops and advances to the second channel to begin counting again. This continues till it has completed the full selected range of channels. V. EXPERIMENTAL SETUP This section is a photo-reference of all the components of the experiment. III.5. MCS Counter This sub-program is similar to that of the counter subprogram in that it uses both detectors. But the real difference between the two is the use of a MCA/MCS (Multi-channel scalar/analyzer). This allows you to take counts per-channel which corresponds to the energy level of the neutrons measured. MCS (Dwell Time): This is the time that the counter counts for per channel. MCS (Units): This is the specific units of time for the dwell time, usually in microseconds.
5 FIG. 7. Overview of the whole experiment. FIG. 10. This Lamp indicates whether or not the beam-port is open. FIG. 8. Another overview of the whole experiment. FIG. 9. Overview shot of the low-efficiency detector. FIG. 11. This is what the chopper wheel looks like when not in motion, for reference. FIG. 12. This is a close up shot of where the beam is interrupted, the lead block behind the aluminum chopper has a hole which the beam comes out of.
6 FIG. 13. This is the Carousel wheel with all the samples that can be chosen from. You can also see the track that allows it to move in and out from the beam. FIG. 16. This is the high efficiency detector behind its lead shield with slit. FIG. 14. This is what the detector looks like outside of its housing. (Both the low and high efficiency detector look similar in their respective casing) FIG. 17. This is a picture of the high efficiency detector with a better view of the detector behind the lead. FIG. 15. This is the low efficiency detector in its housing.
7 FIG. 18. This is the crystal on its rotating mount. FIG. 19. This is the crystal and the whole track aparatus for moving it in and out of the beam. FIG. 20. This is the track that the low efficiency detector moves on; Z-Position.