Photon quantum entanglement in the MeV regime and its application in PET imaging.

Positron Emission Tomography (PET) is a widely-used imaging modality for medical research and clinical diagnosis. Imaging of the radiotracer is obtained from the detected hit positions of the two positron annihilation photons in a detector array. The image is degraded by backgrounds from random coincidences and in-patient scatter events which require correction. In addition to the geometric information, the two annihilation photons are predicted to be produced in a quantum-entangled state, resulting in enhanced correlations between their subsequent interaction processes. To explore this, the predicted entanglement in linear polarisation for the two photons was incorporated into a simulation and tested by comparison with experimental data from a cadmium zinc telluride (CZT) PET demonstrator apparatus. Adapted apparati also enabled correlation measurements where one of the photons had undergone a prior scatter process. We show that the entangled simulation describes the measured correlations and, through simulation of a larger preclinical PET scanner, illustrate a simple method to quantify and remove the unwanted backgrounds in PET using the quantum entanglement information alone.

Signatures of the d

We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570 MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the d^{*}(2380) hexaquark.

Neutron skin of (208)pb from coherent pion photoproduction.

Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be c(n)=6.70±0.03(stat.) fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.) fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.) fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of (208)Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

Measurement of the 1H(γ, p)π0 reaction using a novel nucleon spin polarimeter.

We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon. The measurement pioneers a novel polarimetry technique, which can be applied to many other nuclear and hadron physics experiments. The commissioning reaction of 1H(γ, p)π0 in the range 0.4

Investigation of the exclusive 3He(e,e' pn)1H reaction.

Cross sections for the 3He(e,e' pn)1H reaction were measured for the first time at energy transfers of 220 and 270 MeV for several momentum transfers ranging from 300 to 450 MeV/c. Cross sections are presented as a function of the momentum of the recoil proton and the momentum transfer. Continuum Faddeev calculations using the Argonne V18 and Bonn-B nucleon-nucleon potentials overestimate the measured cross sections by a factor 5 at low recoil proton momentum with the discrepancy becoming smaller at higher recoil proton momentum.

Incoherent neutral pion photoproduction on 12C.

We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The 12C(gamma,pi(0))(12)C*(4.4 MeV) reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a pi(0) spectrometer and to detect decay photons from the excited residual nucleus. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. Such data are sensitive to the propagation of the Delta in the nuclear medium and will give the first information on matter transition form factors from measurements with an electromagnetic probe. The incoherent cross sections are compared to two theoretical predictions including a Delta-hole model.

Photoproduction of eta-mesic 3He.

The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma3He-->etaX has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. A resonancelike structure just above the eta production threshold with an isotropic angular distribution suggests the existence of a resonant quasibound state. This is supported by studies of a competing decay channel of such a quasibound eta-mesic nucleus into pi(0)pX. A binding energy of (-4.4+/-4.2) MeV and a width of (25.6+/-6.1) MeV is deduced for the quasibound eta-mesic state in 3He.

The reaction gammap-->pi0gamma'p and the magnetic dipole moment of the Delta+ 1232 resonance.

The reaction gammap-->pi(0)gamma'p has been measured with the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI for energies between sqrt[s]=1221-1331 MeV. The cross section's differential in angle and energy have been determined for the photon gamma' in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the Delta(+)(1232) resonance and, for the first time, a value of mu(Delta(+))=[2.7(+1.0)(-1.3)(stat)+/-1.5(syst)+/-3(theor)]mu(N) has been extracted.

Demographic influences on the hunting behavior of chimpanzees.

We investigated hunting in an unusually large community of wild chimpanzees at Ngogo in the Kibale National Park, Uganda. Aspects of predation were recorded with respect to the prey, the predators, and hunting episodes. During 23 months of observation, the Ngogo chimpanzees caught 128 prey items from four primate and three ungulate species. Chimpanzees preyed selectively on immature red colobus primarily during group hunts, with adult males making the majority of kills. Party size and composition were significant predictors of the probability that chimpanzees would hunt and of their success during attempts. Chimpanzees were more likely to hunt red colobus if party size and the number of male hunters were large; party size and the number of male hunters were also significantly larger in successful compared with unsuccessful hunts. The Ngogo chimpanzees did not appear to hunt cooperatively, but reciprocal meat-sharing typically took place after kills. Hunts occurred throughout the year, though there was some seasonality as displayed by periodic hunting binges. The extremely high success rate and large number of kills made per successful hunt are the two most striking aspects of predation by the Ngogo chimpanzees. We compare currently available observations of chimpanzee hunting behavior across study sites and conclude that the large size of the Ngogo community contributes to their extraordinary hunting success. Demographic differences between groups are likely to contribute to other patterns of interpopulation variation in chimpanzee predation.

Lost or forgotten?

Bonobo, the Forgotten Ape by F. de Waal University of California Press, 1997. £39.95 hbk (210 pages) ISBN 0 520 20535 9.

Strategies of habitat use by mountain gorillas.

Patterns of home range use by a mountain gorilla group are examined here in relation to variation in food abundance and quality, diet quality and rainfall, to interactions between different social units and to the distribution of hazards (poaching risk). Variation in habitat quality influenced both long-term area occupation densities and shorter-term movement parameters (day journey length and the distance moved between consecutive feeding sites). Observed home range use patterns increased the gorillas' foraging efficiency. Rainfall influenced the evenness of home range use slightly, but this was the only seasonal variability. Interactions with other gorillas and poaching risk had proximate effects superimposed on the fundamental influence of food distribution patterns. Data from a larger sample of groups show a positive influence of group size on day journey length, but this was apparent only at very small and relatively large group sizes. The absolute distance travelled per day tends to be short even for large groups. The data support arguments that the costs of social foraging are low for mountain gorillas.

Reproduction in wild gorillas and some comparisons with chimpanzees.

Information was collected over a period of almost 12 years on the gorillas of the Virunga Volcanoes region of Rwanda and Zaire, most of it collected since September 1972. Comparisons were made with the Gombe Stream chimpanzee population (values in parentheses). Gorilla females matured at about 8 years (compared with 9-10 years for the chimpanzee) and first bred at 10-11 years (11-12 years). Males started to breed later, possibly at 15 years (about 13 years). Oestrous periods of female gorillas lasted for about 2 days (10 days) and oestrous cycles for about 30 days (36 days). Gestation in the gorilla lasts 255 days (228 days). Intervals between surviving offspring in the Virunga study groups was about 4 1/2 (5 1/2 years) but in the whole Virunga population was nearer 8 years. Lactational amenorrhoea lasted about 2 1/2 years (3 1/2 years). In gorillas and chimpanzees there were about 3 cycles to conception after parturition and females probably produce in their lifetime about 3 offspring that survive to adulthood. A successful male's productivity is greater. Mortality of immature gorillas was about 40% (50%). Initiation of courtship is generally by the female in gorillas but the male in chimpanzees. Copulation in gorillas lasts for about 1 1/2 min (7 sec) and occurs at a rate of once every 3 h when a female is in oestrus (once in 2 h). Interference in copulation is more common in the chimpanzee than the gorilla, but competition between individual males is more intense in gorilla populations. Females of both species can clearly exercise their preferences for particular males. The observed differences between the species in courtship and mating behaviour can be related to differences in the number of males available to and competing for oestrous females: in the loose multi-male chimpanzee community there is more advantage to males in initiating copulation and mating frequently and efficiently, and to females in advertising oestrus, than in the relatively stable one-male mating system of the gorilla.