WD. ''0?0 MDDC-1090 UNITED STATES ATOMIC ENERGY COMMISSION OAK RIDGE TENNESSEE CLOUD CHAMBER STUDY OF THE PARTICLES IN THE NEUTRON BEAM OF THE 184 1 ' CYCLOTRON by Wilson Powell Published for use within the Atomic Energy Commission. Inquiries for additional copies and any questions regarding reproduction by recipients of this document may be referred to the Technical Information Division, Atomic Energy Commission, P. O. Box E, Oak Ridge, Tennessee. Inasmuch as a declassified document may differ materially from the original classified document by reason of deletions necessary to accomplish declassification, this copy does not constitute authority for declassification of classified copies of a similar document which may bear the same title and authors. Date of Manuscript: July 11, 1947 Document Declassified: September 9, 1947 This document consists of 6 pages. MDDC-1090 CLOUD CHAMBER STUDY OF THE ^ARTICLES IN THE NEUTRON BEAM OF THE 184 CYCLOTRON By Wilson Powell The 200 million electron volt deuterons made by the 184-inch cyclotron strike an inter- nal target and produce a beam of neutrons which come out through the 1.25 inch thick steel wall of the vacuum chamber of the cyclotron. This beam of neutrons drops to half-value at an angle of five degrees from the tangent to the deuteron beam striking the target. A large Wilson cloud chamber was placed in the neutron beam at a point 35 feet from the target. The recoil protons produced by the neutrons in matter surrounding the cloud chamber were observed with the purpose of finding the maximum energy of the protons and thereby the maximum energy of the neutrons in the neutron beam. The circular cloud-chamber 15 3/4 inches in diameter is equipped with a pulsed mag- netic field of 9400 oersteds produced by a pair of Helmholtz coils. The cloud chamber tim- ing circuit turns on the field, expands the chamber, turns on the cyclotron oscillator and pulses the arc source of deuteron ions in the proper sequence. The tracks produced in the chamber are very sharp and free from turbulence so that the energies of 200 Mev protons can be determined to within plus or minus ten percent. A double camera 52 inches from the cloud chamber with lenses separated by 4.5 inches takes two pictures of the chamber. These are reprojected together on a ground glass screen the plane of which can be rotated and placed at proper distance to recombine the tracks. The projector is indentical with the camera so that the reprojected tracks are life size. The curvatures of the tracks are measured directly on the ground glass by matching them with circles drawn on lucite. The error in measurement for a track amounts to plus or minus five percent for an arc of two meter radius and twelve inches in length. The films were examined with the purpose of finding the highest energy particles. Out of approximately 8000 tracks four were discovered which had energies between 150 and 200 Mev. A thorough examination of all the photographs has not yet been made and at present the high energy protons are being sent through several centimeters of lead as a check on these pictures. It is quite possible that more particles of this energy will be found as the search continues. Qualitatively it is possible to account for these high energies by the following argument. When the deuterons strike the target the proton is knocked off and remains inside the cyclotron. The remaining neutron continues on and passes through the cloud-chamber. How- ever the neutron may, at the instant the proton is stripped off, possess a velocity with re- spect to the center of mass of the deuteron. This velocity can be in such a direction as to add to the velocity corresponding to half the kinetic energy of the deuteron (which is 195 Mev.), and give a neutron with considerably more energy than 1/2 x 195 Mev. MDDC-1090 Thus, although at first sight these results appeared difficult to explain it is reasonable to hope that more detailed calculations and more accurate measurements will be in agree- ment. 3 - MDDC-1090 CL6tf»C 33 Figure i Cloud Chamber and magnet assembly. Figure 2 Projector used in analyzing cloud chamber pictures. - 4 - MDDC-1090 Figure 3 Three stars in oxygen at 1/2 atmosphere pressure. The stars have 5, 4 and 3 prongs. No field. Figure 4 A proton scatter in which a short recoil track is visible. Magnetic field of 9,000 oersteds. - 5 MDDC-1090 Figure 5 A 4 particle star in oxygen. Magnetic field of 9,000 oersteds. ^A S-. ■ ■■ y ; . , i ~ ? ~*- 1 \ 1 l. TV " 1 -. v *^a"v. : 7 v - mm ^v'-V*/ , l ^ pr Figure 6 First high energy tracks found in the cloud chamber photographs. Visible only after some search. If a proton, this track has an energy of 150 Mev ± 15%. Energy of the deuteron beam in the cyclotron was 170 Mev. Magnetic field of 9,000 oersteds. MDDC-1090 Figure This picture contains a track which, if proton, has ar. energy of 190 Mev ± 15%. Energy of the deuteron beam in the cyclotron was 190 Mev. Gas used in the chamber was oxygen, and the 4 particle star shown is a common type in oxygen. Figure 8 This exceptionally good ,ngh energy track crosses the chamber completely. If a proton, it has an energy of 165 Mev 1 15%. Energy of the deuteron beam in the cyclotron was 190 Mev. Magnetic field of 9,000 oersteds. UNIVERSITY OF FLORIDA 3 1262 08907 9536 .