Minnesota Accelerator The first section of the University of Minnesota linear accelerator with a proton beam energy of 10 Mev came into operation on February 17. This beam will be used in nuclear scattering experiments, even while work proceeds on getting the accelerator into full scale operation. Stanford Linac Stanford University completed construction of a new microwave laboratory and began assembly of a 20-foot model section of a high energy linear electron accelerator. This accelerator will be used to explore the ultimate limitations of electron linear accelerators in the energy range of billions of electron volts, as well as to improve the performance of components such as the klystron power tubes, injector, and structural members. The 220-foot, 1 Bev electron linear accelerator at Stanford will now be devoted primarily to fundamental nuclear research under joint AEC-Office of Naval Research sponsorship. Caltech Synchrotron The synchrotron at California Institute of Technology was operated on a regular experimental schedule during its first year of operation. The intensity of its electron beam was increased more than ten times and it accelerated electrons to an energy of 500 Mev. Modifications will be made to increase the maximum energy of the accelerated particles to over 1 Bev during 1954. Bevatron The initial attempt to inject particles into the UCRL bevatron was made on February 2. During its first week of operation protons were produced with an energy of about 5 Bev, the highest energy to which protons have been accelerated. No experiments have been performed with the protons produced as yet. However, it is expected that the bevatron will be in almost constant use in research work in the near future. Construction of the bevatron began early in 1949 and its total cost was $9.5 million. Neutron Cross Section Spectrometer The Knolls Atomic Power Laboratory neutron cross section spectrometer, using a 100 million-volt betatron as the neutron source, was improved by extending the neutron flight path from 7 to 20 meters. Since the energy resolution depends directly on the distance a neutron travels from the source, the increased flight path resulted in a threefold improvement. With the present resolution-about 20 times better than the best attainable at the close of World War II-it was possible to obtain extensive new information for the reactor and weapons programs. Fast Neutron Detector Until recently the only satisfactory neutron detector was the GeigerMueller counter tube filled with boron trifluoride. The efficiency of such counters of manageable size, thin density of gas, etc., for detection of neutrons was as low as a few tenths of one percent for moderate energies of neutrons, and was totally inadequate over a large range of higher energies. However, a new detector was developed at the Argonne National Laboratory that raised this efficiency detection to between 50 to 100 percent, over a wide region of energy. It consisted of the usual type of liquid scintillator containing an addition of methyl borate. Neutrons that enter the liquid are slowed down and captured by boron nuclei to produce nuclear explosions, giving characteristic flashes of light that are detected by photomultiplier tubes. This sequence of events is very rapid, so that the response time of this detector tends to be less than the uncertainty in the time of response of an alternative boron fluoride counter. The uncertainty results from the time taken for the neutron to traverse the counter and the uncertainty as to just where it will interact in the counter tube. Unfortunately these counters are very sensitive to gamma rays and cannot be used in experiments where much gamma radiation is present. However, they permitted great improvement in those time-of-flight experiments in which no strong gamma rays are present. Optical Spectroscopy An extremely versatile 30-foot concave grating spectrograph was set up at the Argonne National Laboratory and is being used in investigations of nuclear spins, isotope shifts, isotope assay, and the investigation and determination of electronic energy levels in heavy element spectra. Attention was focused on rare samples of special interest to the atomic energy program. Considerable effort was devoted to the development of light sources which provide sufficient intensity to obtain the data desired using only very small samples. The components of the nucleus (neutrons and protons) manifest the property of angular momentum usually called "spin." Since the rotation of a charged particle produces a magnetic moment, nuclei with spin also have magnetic moments associated with them. Nuclear spins can sometimes be determined from hyperfine structure in atomic spectra. Hyperfine structure arises from the fact that the energy of an atom is slightly different for different orientations between nuclear spin of the nucleus and angular momentum of the electrons because of the interaction between the nuclear magnetic moment and the magnetic field of the electrons. From the number of lines of the hyperfine structure in the spectrum of a given sample, the nuclear spin can be determined. Using the spectrograph at high resolution and with an improved light source, it was possible to investigate the nuclear spin of bismuth 210 with less than 0.1 microgram of material (one ten-millionth of a gram). With another type of light source and photoelectric recording of the spectrum of a mixture of isotopes, it was possible to determine the isotope abundance ratio, using samples of the order of one microgram, with an accuracy which compared favorably with that obtainable with the mass spectrometer. The spectrograph was also used for precision wavelength measurements of heavy element spectra. Gamma Ray and Beta Ray Spectroscopy A program of precision measurements in spectroscopy of nuclear and atomic-energy levels continued at the California Institute of Technology utilizing novel instrumental techniques. A curved crystal gamma ray spectrometer, using the same basic principles of crystal diffraction as have long been applied in the field of X-rays, was perfected to work over the range of much shorter gamma ray wavelengths, from about 500 X-units down to 9 X-units corresponding to quantum energies from about 25 kilovolts to about 1.3 million volts, with extremely high absolute precision. A companion instrument of comparable precision, an axial focusing magnetic beta ray spectrometer with homogeneous field, was also developed in this same group for work coordinated and interdependent with the same program of nuclear spectroscopy. The latter instrument relies upon the former for its calibration, but performs many functions to which the former is not adapted. One of the latest problems to which this equipment was applied is the energy level scheme of tungsten 183, a daughter product of tantalum 183 after beta decay produced by irradiation of natural tantalum in the MTR. Results of this decay scheme are currently of considerable theoretical interest because of their bearing on the new Bohr-Mottleson theory of rotational energy levels in nuclei. The program of this group also involves precision determinations of the physical constants and precision X-ray spectroscopic measurements some of which have a bearing on nuclear physics and some on pure research in the lower energy field. Neutron and Alpha Sources Available Neutron and alpha sources made from polonium 210 are offered for sale by the radioisotope sales department of Oak Ridge National Laboratory.17 Neutron sources are made by mixing polonium with any of the neutron-yielding elements, principally beryllium, boron, fluorine, and lithium. Certain neutron spectra are now produced by mixing target elements in neutron sources. When spectra determinations now in progress are completed, it will be possible to produce neutron spectra which will conform more closely to desired specifications. The use of neutron sources for starting reactors, calibrating instruments, logging of wells, and in research has increased materially. Alpha sources are made with or without covers absorbing 10 to 60 percent of the alpha energy. The sources are made to specifications for individual needs in research and industry. Biology and Medicine The biology and medicine program of the Commission includes research activities relating to the establishment of control measures against harmful exposure to radiation, and to the utilization of radiation sources. Application of close and careful safeguards to control radiation hazards involves the integration of protective procedures and techniques to safeguard the health of workers and the Nation in case of an emergency. Utilization of atomic energy is directed toward exploration and development of the beneficial effects of radiation in medical, biological, and agricultural studies. During the current period, progress was reported on studies of the effects of all types of ionizing and nonionizing radiations on man, animals, and living plants. In particular, emphasis was given to the investigation of the relative biological effectiveness of high energy particles as compared with X- and gamma rays. Data are also included on the development and present status of instrumentation re 17 Inquiries should be addressed to the U. S. Atomic Energy Commission, Isotopes Division, Post Office Box E, Oak Ridge, Tenn. search for improved dosimetry and methods of radiation detection and measurement. RADIATION EXPOSURES IN RECENT WEAPONS TESTS Prior to the recent weapons tests a danger zone was established surrounding the proving grounds; within this area a hazard from radiation might exist to shipping or aviation. Appropriate notices on the boundaries and the establishment of the danger zone were carried in marine and aviation navigational manuals. Before each shot of the series, a careful survey was made of the winds at all elevations up to many thousands of feet, and survey aircraft searched the area for shipping. The purpose was to take every precaution against radiation exposure of inhabitants of the area, the task-force personnel, and crew or passengers of vessels or aircraft. During the tests, radiological monitoring teams were set up and the monitoring network of stations as usual was in operation to collect and measure fall-out-radioactive particles from the explosion descending to the lower atmosphere, the sea, or the earth. Measurements were made of airborne, ground, and water activity. The only fall-out of consequence was that which followed the first detonation of March 1, when a shift of the winds occurring after the detonation carried radioactive particles toward the islands of Rongelap, Rongerik, and Utirik. Thirty-one American test personnel, and 236 Marshallese were exposed to radiation. A Japanese fishing trawler, the Fukuryu Maru (Fortunate Dragon) was also in the path of fall-out. Evacuation of Test Personnel The 31 Air Force, Army, and Navy test personnel were evacuated to Kwajalein for physical examinations and observations. None of the men experienced any symptoms of radiation illness, and medical observations to date do not indicate that any permanent harm has resulted. All of the men included in this group were returned to military duty following complete physical examinations at Tripler General Hospital, Honolulu, T. H. Inhabitants of Marshall Islands The Marshallese from the islands of Rongelap and Utirik within the area of fall-out following the first detonation were evacuated promptly by the Task Force to Kwajalein. It was found that of the 236 evacuated, 74, all from Rongelap, experienced radiation burns, principally |