Martin Deutsch

Nuclear polarization of Co55

Abstract The angular distribution and linear polarization of the gamma rays emitted from 18-h Co55, polarized at low temperatures in cerium-magnesium nitrate crystals, have been measured. The amplitude mixing ratios δ(E2/M1) of mixed multipole gamma transitions in Fees have been determined. With a spin of 7 2 for Co55, we find a spin sequence of 7 2 → 5 2 → 3 2 in the main decay in Fe66, and for the 0.93S MeV gamma ray a δ of + 0.36±0.11. A possible spin sequence 5 2 → 7 2 → 3 2 in Fe55 has been eliminated by our linear polarization measurements. The ratio of the nuclear g-values of Co58 and Co55 has been found from a simultaneous measurement of the angular distribution of the gamma rays from the two isotopes grown into the same crystals. The magnetic moment of Co65 is 6.3±0.4 n.m., if the 1.03 MeV beta branch is predominantly a G.T. transition, or 4.6±0.4 n.m., if a pure Fermi transition.

A Spherical Drift Chamber Area Detector for X-Ray Crystallography

A multiwire proportional chamber system has been built as an area detector for use in x-ray crystallography with Cu K¿ radiation (1.54Å). The chamber, constructed by Charpak and collaborators at CERN, consists of a 10cm thick spherical interaction region with a radial electric field, a transition from spherical to plane geometry and a 50cm × 50cm multiwire proportional chamber and subtends a 90° opening angle. Two dimensional position information is obtained from orthogonal cathode planes using a high speed analog centroid finding technique. Data on spatial and energy resolution as a function of angle and depth of interaction in the spherical drift region using a collimated, pulsed, x-ray source are presented. Ionization loss as a function of drift distance and field and loss due to field shaping grids has also been measured.

Spins of the isomeric states of Hf178 and Hf180

Abstract The 4.8 sec state of Hf 178 and the 5.5 h state of Hf 180 are shown by angular correlation measurements to have spin J = 8.

Pressurized Xenon-Filled Multiwire Proportional Chamber for Radionuclide Imaging

A pressurized multiwire proportional chamber radionuclide imaging system has been constructed which has operated at pressures of up to 11 atmospheres absolute using a xenon-methane gas mix. The experimental detector has an active imaging area of 25 sq. cm. and an effective depth of 11 cm. An all digital readout system has been constructed with an intrinsic resolution of 1.3 mm FWHM. The FWHM has been measured for various radionuclides: iodine-125 (28 keV), 1.3 mm; thallium - 201 (75 keV), 2 mm; technetium-99 m (140 keV), 3 mm. Our primary goal has been the investigation of properties of such detectors that offer advantages over conventional gamma cameras, including high data rate and improved spatial resolution, particularly for isotopes with photon energies below 100 keV. We have fabricated a gas purification system which permits long term operation of the system without degradation and have investigated construction techniques to produce reliable devices which could be used in a hospital environment.

PIP: a photo-interpretive program for the analysis of spark-chamber data

Sorting techniques using an IBM 1401 with a random access storage device are evaluated.

ANNIHILATION OF POSITRONS

Publisher Summary This chapter discusses the annihilation of positrons. Positrons are generally produced in the laboratory by one of two distinct processes: (1) electromagnetic pair creation by X-rays, gamma rays, swift charged particles, or nuclear transitions; and (2) beta decay. Keeping Diracs hole theory of the positron in mind, transitions from positive to negative energy states without passing through the forbidden intermediate energy region can take place quantum mechanically, although they would be impossible in classical mechanics. This possibility would result, sooner or later, in a complete depopulation of all positive energy states, all electrons dropping into states of negative energy. When an electron collides with a hole represented by a positron, it may make a radiative transition to the unoccupied negative-energy level. Two-quantum annihilation is allowed only for an electron pair state of complete spherical symmetry state. General selection rules for annihilation in different states have been given by Yang (1950) and Landau (1948). Experiments on positron annihilation carried out in recent years have not only verified the predictions of Dirac theory but have also thrown valuable light on the interaction between electrons.

X-Ray Crystallography Using a Spherical Proportional Camera

A wide angle gas proportional detector specifically designed for X-ray crystallography has been instrumented and is being applied in pilot experimental studies. It has essentially complete efficiency, uniform spatial precision of 2 mrad FWHM, acceptance over 90 degrees, and count rate capability to 100,000 per second at less than 10% loss. Comparison of data with conventional measurements indicates satisfactory angular mappings and a relative R-factor for scaled intensities of better than 10%.

An experimental test of position resolution of a lead glass array

Abstract We report on an experiment to examine the use of lead glass Cherenkov counters in a hodoscope to determine the trajectory of incident shower particles, i.e. electrons, positrons, or photons. This tests the accuracy with which an incident positron can be located using only an array of lead glass counters. Twelve lead glass counters were used in each of three counter configurations, at 1.5, 3.1 and 4.2 GeV. For each configuration, the axis of the electromagnetic shower was calculated from the digitized lead glass counter pulse heights, and compared to the trajectory of the incident positron, which was separately measured with spark chambers. For one of the configurations, the one-dimensional discrepancy between the positron trajectory and the calculated shower axis was less than 1.1 cm (fwhm) at 1.5 GeV and 3.1 GeV.

Electric monopole transition rate in Zr90

The mean life of the 1.75 MeV excited state in Zr90 with J = 0, even parity, has been found to be 8.5±3 mμsec by observing delayed coincidences between beta rays from Y90 and annihilation radiation due to internal pair creation. This corresponds to ϱ2 = 0.036, close to the values for the other three known monopole transition probabilities.

Instrumentation of the M.I.T. Cyclotron for the Study of Nuclear Reactions

The emergent beam from the cyclotron has been focused to bombard targets placed in an evacuated chamber behind shielding walls. Heavy charged particle products from the targets can be counted and identified as to charge and mass by three proportional ionization chambers in time coincidence, utilizing the difference in specific ionization near the end of the particle range. Energy spectra at fixed angles are observed with an automatic foil changer which interposes aluminum absorbers between target and detector. Angular distributions can be studied by rotating the detector about the target with a remote‐controlled selsyn drive. Rapid automatic recording of data is accomplished with count storage circuits, a beam current integrator, mechanisms for scanning through a preselected set of absorber foils, and a pen‐recorder.Reactions studied to date include (d,p), (d,t), (d,α), (p,d), and elastic and inelastic scattering of protons, deuterons, and α‐particles. Targets throughout the periodic table have been used,...