Angular momentum generation in nuclear fission.

When a heavy atomic nucleus splits (fission), the resulting fragments are observed to emerge spinning1; this phenomenon has been a mystery in nuclear physics for over 40 years2,3. The internal generation of typically six or seven units of angular momentum in each fragment is particularly puzzling for systems that start with zero, or almost zero, spin. There are currently no experimental observations that enable decisive discrimination between the many competing theories for the mechanism that generates the angular momentum4-12. Nevertheless, the consensus is that excitation of collective vibrational modes generates the intrinsic spin before the nucleus splits (pre-scission). Here we show that there is no significant correlation between the spins of the fragment partners, which leads us to conclude that angular momentum in fission is actually generated after the nucleus splits (post-scission). We present comprehensive data showing that the average spin is strongly mass-dependent, varying in saw-tooth distributions. We observe no notable dependence of fragment spin on the mass or charge of the partner nucleus, confirming the uncorrelated post-scission nature of the spin mechanism. To explain these observations, we propose that the collective motion of nucleons in the ruptured neck of the fissioning system generates two independent torques, analogous to the snapping of an elastic band. A parameterization based on occupation of angular momentum states according to statistical theory describes the full range of experimental data well. This insight into the role of spin in nuclear fission is not only important for the fundamental understanding and theoretical description of fission, but also has consequences for the γ-ray heating problem in nuclear reactors13,14, for the study of the structure of neutron-rich isotopes15,16, and for the synthesis and stability of super-heavy elements17,18.

First Direct Measurement of an Astrophysical p-Process Reaction Cross Section Using a Radioactive Ion Beam.

We have performed the first direct measurement of the ^{83}Rb(p,γ) radiative capture reaction cross section in inverse kinematics using a radioactive beam of ^{83}Rb at incident energies of 2.4 and 2.7A MeV. The measured cross section at an effective relative kinetic energy of E_{cm}=2.393 MeV, which lies within the relevant energy window for core collapse supernovae, is smaller than the prediction of statistical model calculations. This leads to the abundance of ^{84}Sr produced in the astrophysical p process being higher than previously calculated. Moreover, the discrepancy of the present data with theoretical predictions indicates that further experimental investigation of p-process reactions involving unstable projectiles is clearly warranted.

Search for Nova Presolar Grains: γ-Ray Spectroscopy of

The discovery of presolar grains in primitive meteorites has initiated a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical ^{33}Cl(p,γ)^{34}Ar reaction is expected to play a decisive role. As such, we have performed a detailed γ-ray spectroscopy study of ^{34}Ar. Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in ^{34}Ar, have been made for the first time. Uncertainties in the ^{33}Cl(p,γ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ=0 resonance at E_{r}=396.9(13) keV dominates the entire rate for T=0.25-0.40 GK. Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected ^{32}S/^{33}S abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain.

5-HT2 receptor binding and 5-HT uptake in mouse brain: developmental changes and the relationship to audiogenic seizure susceptibility in DBA/2J mice.

Abnormal function of serotonergic neurones may be involved in the age-related susceptibility of DBA/2J mice to generalised convulsions induced by auditory stimulation. We have measured 5-HT2 receptor binding sites and synaptosomal 5-HT uptake in 5 brain regions of DBA/2J mice at ages before, during and after their maximal susceptibility to audiogenic seizures and in age-matched C57 B1/6 mice, a strain resistant to audiogenic seizures at all ages. The number of 5-HT2 binding sites was 20% higher in the cerebral cortex of DBA/2J than C57 B1/6 mice at the time of maximal susceptibility of DBA/2J mice to audiogenic seizures but did not differ at other ages. The number of 5-HT2 binding sites did not differ between the two strains at the ages studied in forebrain, mid-brain, hippocampus and pons-medulla. A marked reduction in the number of 5-HT2 binding sites was apparent in the mid-brain, hippocampus and pons-medulla of both strains of mice between 13-15 days of age and 21-23 days of age. Synaptosomal 5-HT uptake did not differ significantly between DBA/2J and C57 B1/6 in any of the brain regions at the ages studied. The higher density of cortical 5-HT2 binding sites in DBA/2J mice may contribute to their susceptibility to sound-induced seizures.

Synaptosomal high-affinity noradrenaline uptake does not differ between mice susceptible (DBA/2J) and resistant (C57 BL/6) to audiogenic seizures.

Abnormalities in noradrenaline-mediated neurotransmission have been advocated as a basis of the age-related susceptibility of DBA/2J mice to generalised convulsions induced by auditory stimulation. We have measured the kinetics of synaptosomal high-affinity noradrenaline uptake in 5 brain regions of DBA/2J mice at ages before, during and after their maximal susceptibility to audiogenic seizures, and age-matched C57 BL/6 mice, a strain resistant to audiogenic seizures at all ages. No differences were found between the two strains of mice in any of the brain regions studied. Abnormalities of high-affinity noradrenaline uptake do not contribute to audiogenic seizure susceptibility of DBA/2J mice.

Cholecystectomy and oesophageal pathology: is there a link?

Symptoms persist in a significant proportion of patients following cholecystectomy, some of which may have an oesophageal aetiology. The oesophagus has not previously been studied in this patient group. In this study all patients who had undergone cholecystectomy over a four year period were invited for review and symptoms were documented. Oesophageal function was examined and compared with normal controls. Patients were subdivided into symptomatic and asymptomatic subgroups and their findings compared. Symptoms were present in 53 percent of the postcholecystectomy group. The mean (sem) DeMeester acid score was higher in the post-cholecystectomy group -20.6 (3.6) than in controls -6.7 (0.9) (p = 0.01). The incidence of oesophagitis and gastritis were also increased in this group. There was a trend towards increased reflux and oesophagitis in the symptomatic compared with the asymptomatic subgroup. Other findings confined to the post-cholecystectomy group included nutcracker oesophagus in 4 and irritable bowel syndrome in 3. It is suggested that cholecystectomy may be associated with changes in oesophageal function which, in turn, may be associated with persistent symptoms.

Helicobacter pylori infection increases following cholecystectomy.

Cholecystectomy is frequently linked with duodenogastric reflux and gastritis but its effect on Helicobacter Pylori (H pylori) infection has not been examined. In a prospective study, twenty two patients with documented cholelithiasis underwent upper gastrointestinal endoscopy and biopsy and 24hr dual channel pH monitoring prior to cholecystectomy and again at 3-6 months post-operatively. The antral biopsies were histologically assessed for H pylori and gastritis and awarded an alkaline reflux score. The number of patients with H pylori infection increased from 7 (32%) preoperatively to 15 (68%) post-cholecystectomy (p < 0.05). Cholecystectomy was also associated with an increase in the incidence of gastritis from 7 to 15 (p < 0.05). The increase in H pylori infection rate occurred in association with an increase in the percentage time gastric pH > 4 in the supine position, from 9.6 (2.2) to 22.2 (4.8) percent, (p < 0.01). The median chemical gastritis score, however, did not change significantly following surgery [8(3-11) vs 7(3-11)]. Seven patients remained symptomatic following cholecystectomy all of whom were H pylori positive and had gastritis. H pylori can survive in the alkaline environment which follows cholecystectomy and may contribute to the post-cholecystectomy syndrome.

[Abscess of the omental bursa (lesser sac)]. / Bursa omentalis (lille saek) absces.

Subphrenic omental bursa abscess is frequently overlooked and the overall mortality is 70%. Early diagnosis and drainage improve the prognosis considerably. In cases with abdominal symptoms followed by pyrexia, possibly with signs of sepsis, and pleural effusion but with no or only slight findings on objective clinical examination, subphrenic abscess should be suspected and a scanning of the abdomen should be performed.

Brain adrenoceptor binding sites in mice susceptible (DBA/2J) and resistant (C57 Bl/6) to audiogenic seizures.

We have examined if the age-related susceptibility of DBA/2J mice to audiogenic seizures is the result of an abnormality in the number or sensitivity of brain adrenoceptors. The binding of alpha 1-, alpha 2-, and beta-adrenoceptor ligands to membranes prepared from whole brain or regions of brain of DBA/2J mice was measured at various ages, corresponding to the periods before, during, and after the maximal sensitivity to audiogenic seizures. For comparison, we have studied concurrently age-matched C57 Bl/6 mice, a strain resistant to audiogenic seizures at all ages. There was no difference in the binding of alpha 2- or beta-adrenoceptor ligands to whole brain membranes between the two strains of mice at any age. The maximal number of alpha 1-adrenoceptor binding sites was lower in whole brains of DBA/2J mice than of C57 Bl/6 mice at all ages studied except 13-15 days of age. The differences were small (maximally 17%) but were statistically significant at 21-23 days of age, the time of maximal sensitivity of DBA/2J mice to audiogenic seizures. No difference between the two strains was found in the number or affinity of alpha 1- or alpha 2-adrenoceptor binding sites at any age in any of the brain regions studied. The age-related susceptibility of DBA/2J mice to audiogenic seizures is not the result of an abnormality in number or sensitivity of alpha 2- or beta-adrenoceptor binding sites, but a reduced number of alpha 1-adrenoceptor binding sites may be involved.

Cholecystectomy and oesophageal reflux: a prospective evaluation.

The effect of cholecystectomy on oesophageal function was examined prospectively. Of 37 patients studied, 17 (46 per cent) were still symptomatic 3-4 months after surgery. Thirteen patients (35 per cent) had abnormal oesophageal pH profiles before cholecystectomy, increasing to 27 (73 per cent) afterwards (P < 0.002). The mean (s.e.m.) DeMeester acid reflux score increased from 15.2(2.1) to 34.2(5.2) (P < 0.001) after operation. Lower oesophageal sphincter function, as measured by the sphincter function index, was significantly reduced in the patients with abnormal pH profiles after operation (P < 0.01). Mean(s.e.m.) supine gastric alkaline shift (proportion of time at pH > 4) increased from 9.2(2.0) to 17.7(3.7) per cent (P < 0.02) and the incidence of gastritis from eight patients (22 per cent) to 23 (62 per cent) (P < 0.001). These data suggest that cholecystectomy results in gastro-oesophageal reflux that appears to be related to compromised sphincter competence.