1. Study of alpha decays obtained by overall scanning method in nuclear emulsion Physics department K.Nakazawa, J.Yoshida, K.T.Tint, M.K.Soe, S.Kinbara, A. Mishina, H.Ito, Y.Endo, H.Kobayashi Aye Moh Moh Theint Gifu University

2. Outlines  Motivation  Events Detection of Overall Scanning method in nuclear emulsion  Detection of alpha decays in nuclear emulsion  Checking Area of Emulsion Plate  Density of alpha decays in nuclear emulsion  Summary

3. Motivation  Overall scanning is a new method that aims for collecting more double-lambda hypernuclear events in nuclear emulsion.  Therefore, we had collected information, alpha decay events that are obtained by overall scanning method in nuclear emulsion to check current detection efficiency.  It is one of the aids to develop our new scanning method.  After developing our new scanning method, we will discover more double-lambda hypernuclear events.  Now, we use overall scanning method to detect events in the nuclear emulsion.

4. Introduction  In the overall scanning, an image process takes hypernuclear events which have multi tracks and vertices.  The detection system of the double-lambda hypernuclear events is the same performance in the case of alpha decays in nuclear emulsion.  Besides, natural radioactive alpha decays are plenty in nuclear emulsion.  Therefore, alpha decays are good samples to check the current detection efficiency of our method in nuclear emulsion.

5. Emulsion plate Detected images from overall-scanning Automatic scanning system Events Detection of Overall Scanning method in nuclear emulsion

6. Mod #49, pl #9 60mm 30mm Checking Area of Emulsion Plate 87alpha decays (45 four tracks, 42 five tracks ) Beam exposed; scan volume => 12.58cm 2 *0.9mm We had checked vertex images from two areas of an emulsion plate; 258 alpha decays (98 four tracks, 160five tracks) No Beam ; scan volume => 8.67cm 2 *0.9mm

7. No beam exposed area Beam exposed area  We can clearly see that there are too much noises in the beam area of the emulsion plate. Under the same condition of microscope, lighting and procedure

8. Detection of alpha decays in nuclear emulsion  We can see the images of alpha obtained from decay chain of thorium and uranium series in nuclear emulsion as shown in figures.  Five tracks alpha decay of Thorium series could be observed in nuclear emulsion.  In the decay chain of uranium, four tracks alpha decay can be seen in nuclear emulsion.

9. Beam exposed (12.58cm 2 ) No Beam (8.67cm 2 ) Density of 5tracks alpha decay Density of 4-tracks alpha decay Density of alpha decays in nuclear emulsion  We had found that the detection efficiency of the beam area and no beam area is different.  Moreover, for 5 tracks alpha decay, detection efficiency of beam exposed area is 5.59 times smaller than that of the no beam exposed area.  Similarly, for 4 tracks alpha decay, detection efficiency of beam exposed area is 3.16 times smaller than that of the no beam exposed area.

10. Summary  These images of beam exposed area and no beam exposed were picked out under the same condition of microscope, lighting and procedure.  After checking alpha decays, we had found that there are different detection efficiencies in these two areas of the emulsion plate.  We had checked the images that are obtained from the two types of areas; beam exposed area and no beam exposed area.  So we concern that we can’t detect some double lambda hypernuclear events in nuclear emulsion as in the case of alpha decay.  We lost the detection of some alpha decay events in the beam exposed area of the emulsion plate.  After developing our method, we will find more double lambda hypernuclear events.