A: The ND&M Handmonitor uses a high-gain, proximity focused image intensifier for amplifying scintillation light bursts which are not visible for the human eye. These very faint light burst are amplified to such a high degree that they become visible on the back screen of the intensifier even under daylight conditions. The whole system is built into a small housing, which also contains power supply boards and a battery for convenient, wireless, one-handed operation.
A: The Handmonitor is usually used for aligning neutron beams in a neutron physics experiment. Another application, where our Handmonitor is used for quite often, is finding leaks in neutron shieldings. It is very convenient to have a Handmonitor for this task, because in many cases you can locate the leak and its dimension at the same time by just looking at the screen of the Handmonitor, without performing annoying scanning procedures, remembering numbers, and so on. In most cases, you save a tremendous amount of time if you use our Handmonitor compared to using conventional detectors.
A: Because your time is precious. The Handmonitor saves a lot of time - you don't have to wait until your film is developed, you don't have to build any fixtures or holders four your film cassette. Instead, you can quickly scan over much larger areas of your experiment than you would if you are only eqipped with films - and you won't be the first one who finds unexpected leaks in shieldings, unexpected reflexes from beams or background neutrons from your neighbour's experiment. And - do not forget - you see your beam in real-time! That means that you can quickly discover mechanical instabilities in your setup, or thermal effects, which you would never see on film!
A: That depends on the wavelength, of course - if you work with thermal beams, you can expect to see about 10 to 20% of the neutrons that enter your Handmonitor. At longer wavelenghts - say, about 4 to 5 A, the efficiency increases to about 40 to 50%. At even higher wavelengths, the efficiency drops again to lower values. The reason for this is that the scintillator that is used in Handmonitor is not very tranparent for its own light (you may ask, why don't we use another scintillator then? The reason is, that our scintillator has a very low gamma sensitivity. Other scintillators do not even come close to this low gamma sensitivity.). So, any neutron that is captured close to the entry window of the Handmonitor gives only a weak light spot. The brightest light spots have their origin in neutrons that are captured close to the exit plane of the scintillator. Very cold neutrons are immediately absorbed in the scintillator and such give only a low amount of light. If you mainly work with very cold or ultracold neutrons, we can equip your Handmonitor with a special, very thin scintillator that gives rise to very bright scintillation light spots for longer wavelengths.
A: Beware - keep in mind that any structure that you put in a neutron beam scatters neutrons and/or produces secondary gamma radiation! So, before you try to operate your neutron Handmonitor in any beam, ask your radiation protection staff before to give you advice! Tell them to make measurements for you of the radiation level you will be exposed to! For very intense beams, consider using some form of mechanical expansion of your arm - the Handmonitor is equipped with a standard 1/4'' camera thread for this! So, use some form of a camera tripod, microphone stand or the like to keep distance from the beam and the Handmonitor! Switch the Handmonitor to the lowest gain (gain setting 1) before putting it in the beam! If the gain is not high enough, try gain setting 2 or 3. If the screen of the Handmonitor is very bright even at the lowest gain setting, remove the Handmonitor! Do not use the Handmonitor in this beam then! Caution: The Handmonitor can be activated in a strong beam in a very short time to quite a high degree! So, after using the Handmonitor, put it behind a gamma shielding and let decay for about half an hour. Before you remove the Handmonitor and take it away to a non-radiation- controlled area, measure its activity or tell your radiation protection staff to do so. Do not violate the allowed the allowed activity levels when carrying the Handmonitor.
A: We can equip your Handmonitor with other scintillators, of course. In fact, we have already made a special X-ray Handmonitor for visualizing 6 keV X-rays. For that, we also changed the usual aluminum entrance window. We used a carbon entrance window instead, to get as low absorption as possible.
A: The AFG, together with a ND&M Readout Unit, turns your Handmonitor into a full functioning, computer operated, two-dimensional neutron detector with outstanding resolution. The RCP (Real-time Centroiding Processor) mainly does the same thing, but for a completely different range of applications. The AFG is either good for getting computer readable pictures of your neutron field at HIGH fluxes and LOW resolution (0.1...0.2mm) or for getting images of your neutron fields at LOW fluxes with ULTRA-HIGH resolution (0.04mm).
A: If you want to use the AFG, you have to mount your Handmonitor on a ND&M Readout Unit (the Handmonitor is powered by the Readout Unit then). Inside the Readout Unit sits a CCD camera which looks at the screen of your Handmonitor. The CCD camera delivers 25 pictures per second at a resolution of 512 times 512 pixels to the AFG. The AFG digitizes each picture and removes weak light bursts in each picture. Each new picture is added to the formerly digitized picture then. At the end of the exposure time, you get a matrix of 512 times 512 brightness values with a resolution of 16 bits. This matrix is then read in by the PC. Our AFG software analyzes this matrix then and calculates the center of gravity of each found light burst, which corresponds to the coordinate of an impinging neutron. After this analysis, which usually takes less than a fraction of a second on a Pentium PC, you can save the coordinates of the neutrons in an output file (with a choice of several file formats).
A: The RCP does mainly the same thing as the AFG, but much faster. The AFG has one disadvantage: The light bursts (=neutrons) in the summed up pictures are not allowed to overlap. The calculation of the centers of gravity would become impossible, otherwise. This fact limits the maximum count rate of the AFG to about 100 neutrons per second on the whole detector area. Most neutron experiments that really need the ultra-high resolution of the AFG are experiments where you have to deal with low fluxes, anyway (perfect crystal interferometry, UCN experiments, fundamental physics experiments, to give a few examples). These types of experiments are ideal applications for the AFG. If you are lucky, you can use higher fluxes. Then the RCP is the right thing for you. The RCP also digitizes pictures (50 "half" pictures per second), but these pictures are not summed up for later analysis. Instead, each picture is immediately analyzed for neutron events and the coordinates of each found neutron are also immediately made available to the PC. For this, a really impressive computation speed is needed (about 900 million calculations per second). The RCP has special hardware on board for this task. But, even this high computational speed does not allow to get the same resolution as on the AFG. This is the reason why the RCP has a somewhat lower resolution of about 0.1mm in vertical direction and 0.065mm in horizontal direction.