A proton-proton bremsstrahlung experiment has been carried out at TRIUMF using a 280-MeV polarized proton beam impinging on a liquid-hydrogen target. All three outgoing particles were detected: the higher-energy proton in a magnetic spectrometer, the lower-energy proton with plastic scintillators, and the photon in lead-glass Cherenkov detectors. The experiment shows the first unambiguous evidence for off-shell effects in the free nucleon-nucleon interaction, in that the analyzing powers disagree strongly with the predictions of the soft-photon approximation (which incorporates only on-shell information) but are consistent with the results of calculations using the Bonn and Paris potentials.

This longitudinal prospective exploratory study used serial measurements in five dogs to evaluate safety and retention of a tin-117 m ( 117m Sn) colloid after intra-articular injection in normal elbow joints. Each dog was deemed healthy based on physical examination, laboratory results, and radiographic evaluation of both elbows. While anesthetized, each received an MRI of both elbows, followed by fluorine-18 fluorodeoxyglucose positron emission tomography scans of both elbow joints and associated lymph nodes. Joint fluid (0.5-1.0 mL) was withdrawn aseptically from the left elbow joint, followed by intra-articular injection of 117m Sn colloid (92.5 MBq; 1-1.5 ml). Postinjection assessments included blood counts, serum chemistry panels, urinalyses, radiographs, joint fluid analyses, MRI/positron emission tomography scans, scintigraphy, and biodistribution scans. On day 45-47, each dog was euthanized and a complete postmortem examination was performed. Tissue samples were submitted for histopathology and radioisotope retention studies.Left elbow joints were decalcified and sectioned for future autoradiography. Scintigraphy, 1 day after injection, indicated slight radioisotope escape from the joint to regional lymph nodes. Serial blood, urine, feces, and organ counts indicated >99.1% of the 117m Sn activity was retained in the joint for 45-47 days. Radiation output levels were below patient release levels the day following injection. Maximum standard uptake value for the injected joint decreased. Joint fluid cytology was unchanged. No dog exhibited lameness during the study. Absence of joint damage and lack of systemic effects after injection of the 117m Sn colloid in normal canine elbow joints indicate that this agent may be safely used for radiosynoviorthesis in dogs with osteoarthritis. K E Y W O R D Sarthritis, radiation therapy, radioisotope, synovectomy

Energy spectra of both protons and deuterons emitted following the capture of negative muons by He nuclei have been measured for energies above 15 MeV. A limited number of proton-neutron pairs emitted in coincidence were also observed. A simple plane wave impulse approximation (PWIA) model calculation yields fair agreement with the measured proton energy spectra, but underpredicts the measured rate of deuteron production above our energy threshold by a large factor. A more sophisticated PWIA calculation for the two-body breakup channel, based on a realistic three-body wave function for the initial state, is closer to the deuteron data at moderate energies, but still is signi6cantly lower near the kinematic end point. The proton-neutron coincidence data also point to the presence of signi6cant strength involving more than one nucleon in the capture process at high energy transfer. These results indicate that additional terms in the capture matrix element beyond the impulse approximation contribution may be required to explain the experimental data. Speci6cally, the inclusion of nucleon-nucleon correlations in the initial or 6nal state and meson exchange current contributions could bring calculations into better agreement with our data. A fully microscopic calculation would thus open the possibility for a quantitative test of multinucleon effects in the weak interaction.Present address: Stanford Linear Accelerator Center, Stanford, CA 94309.Nuclear muon capture Z+p m (Z -1)'+v"normally leads to the emission of an energetic neutrino carrying most of the rest energy of the muon, while the energy transfer to the nucleus q = m& -E"is relatively small.The transferred energy leads to low-lying excitations of the residual nucleus up to the giant resonant region [1] or to the emission of medium energy neutrons (see, e. g., Ref. [2] and references therein). These conditions can be understood in the impulse approximation (IA) picture, in 0556-2813/94/50(4)/

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The treatment of pets, service animals, and pre-clinical research subjects with radionuclides raises concern for the safety of the people who interact with the animals after their treatment. Three treatments of skeletal conditions in dogs are considered in this study: 153Sm-1,4,7,10-tetraazacylcododecanetetramethylenephosphonic acid, which is a bone-seeking radiopharmaceutical; unencapsulated 90Y permanent interstitial implants, which are sometimes called “liquid brachytherapy”; and 117mSn radiosynoviorthesis, which is also called radiosynovectomy. External exposure rate readings of the 153Sm and 117mSn treatments, and Monte Carlo simulations of 117mSn at a distance of 1 m and of all three in direct contact with tissue were analyzed for doses. Dogs that have received any of these treatments using typically administered activities may be released from radiation safety isolation immediately after treatment from the standpoint of external exposure. People should avoid prolonged close proximity, such as sleeping with a treated dog, for three weeks following an 90Y interstitial implant or for a month following 117mSn radiosynoviorthesis. No such avoidance is necessary after treatment with 153Sm-1,4,7,10-tetraazacylcododecanetetramethylenephosphonic acid.

The analyzing power for proton-proton bremsstrahlung has been measured at TRIUMF with 280-MeV polarized protons. All three outgoing particles were detected in coincidence. After appropriate cuts were applied, over 160000 ppy events remained, an order of magnitude more than in previous ppy experiments. The analyzing-power measurements are in good agreement with calculations based on modern potential models of the 7VW interaction, but disagree with the predictions of the soft-photon approximation.PACS numbers: 13.75. Cs, 12.40.Qq, 13.88.+e, 21.30.+y The most direct and unambiguous way of investigating the off-energy-shell behavior of the NN interaction is by measurements of nucleon-nucleon bremsstrahlung. In spite of this, bremsstrahlung experiments have hitherto shown no evidence of off-shell effects, even in kinematic situations where one would expect sensitivity to them. For example, an earlier experiment 1 at TRIUMF gave results for the proton-proton bremsstrahlung (pp y) cross section at 200 MeV which were in better accord with the soft-photon approximation (SPA) than with the predictions of modern potential models of the AW interaction. This is surprising since the SPA contains only on-shell information, potential models should certainly be valid at 200 MeV, and the precision attained in the measurements was apparently sufficient to distinguish between the two approaches. We have therefore measured both the analyzing power (which has not previously been measured) and cross section for pp y in a variety of kinematic situations, in some of which off-shell effects should be negligible and in others of which they should be easily observable. Only the analyzing-power results are reported here.The measurements were carried out at TRIUMF with a proton beam of energy 280 MeV and polarization typically 75%-80% impinging on a 5-mm-thick liquidhydrogen target. The liquid hydrogen was enclosed between thin (7.5 pm) Mylar walls supported by cold hydrogen gas at atmospheric pressure in a 1-m-long container. Shielding prevented the detectors from viewing directly the 0.127-mm-thick stainless-steel end windows of the gas container. With this arrangement the background contribution from the target walls was reduced to less than 5%.All three outgoing particles from the ppy reaction were detected in a coplanar geometry with the apparatus shown in Fig. 1. The momentum and production angle of the higher-energy proton were measured in a spectrometer consisting of a dipole magnet and vertical drift chambers. The drift cell design allowed measurement of track position, angle, and time, giving enough information that extraneous tracks could be eliminated from many of the (ppy) events. Operation at low gas gain (;S10 4 ) and independent time digitization for each wire were necessary to cope with the high elastic-scattering flux. Before the magnet two of the drift chambers mea-LEAD GLASS PHOTON DETECTORS, L.E. PLASTIC SCINTILLATORS! H.E. SCINTILLATOR TELESCOPE AND VETO FIG. 1. Schematic representation of experimental apparatus.