Compound-Nucleus and Doorway-State Decays of ß-Delayed Neutron Emitters

We investigated decays of ^{51,52,53}K at the ISOLDE Decay Station at CERN in order to understand the mechanism of the ß-delayed neutron-emission (ßn) process. The experiment quantified neutron and γ-ray emission paths for each precursor. We used this information to test the hypothesis, first formulated by Bohr in 1939, that neutrons in the ßn process originate from the structureless "compound nucleus." The data are consistent with this postulate for most of the observed decay paths. The agreement, however, is surprising because the compound-nucleus stage should not be achieved in the studied ß decay due to insufficient excitation energy and level densities in the neutron emitter. In the ^{53}K ßn decay, we found a preferential population of the first excited state in ^{52}Ca that contradicted Bohr's hypothesis. The latter was interpreted as evidence for direct neutron emission sensitive to the structure of the neutron-unbound state. We propose that the observed nonstatistical neutron emission proceeds through the coupling with nearby doorway states that have large neutron-emission probabilities. The appearance of "compound-nucleus" decay is caused by the aggregated small contributions of multiple doorway states at higher excitation energy.

g Factor of the

The gyromagnetic factor of the low-lying E=251.96(9) keV isomeric state of the nucleus ^{99}Zr was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of J^{π}=7/2^{+}, with a half-life of T_{1/2}=336(5) ns. The isomer was produced and spin aligned via the abrasion-fission of a ^{238}U primary beam at RIKEN RIBF. A magnetic moment |µ|=2.31(14)µ_{N} was deduced showing that this isomer is not single particle in nature. A comparison of the experimental values with interacting boson-fermion model IBFM-1 results shows that this state is strongly mixed with a main νd_{5/2} composition. Furthermore, it was found that monopole single-particle evolution changes significantly with the appearance of collective modes, likely due to type-II shell evolution.

[A case of bilateral tubal pregnancy after IVF - ET].

The authors describe a rare case of bilateral tubal pregnancy after IVF. The patient is with secondary infertility. The preceding diagnostic laparoscopy excluded the presence of tubal factor. The results of the spermogram show average to severe form of Oligoasthenozoospermia. Short protocol with GnRH-antagonist was performed and two embryos were transferred on the third day. On the 36th day after the embryo transfer the patient was hospitalized with abdominal pain in the right hypogastric region, clinical and ultrasound indications for hemoperitoneum. Urgent laparotomy was performed followed by salpingectomy dextra due to hemoperitoneum caused by tubal abortion. The examination of the left adnexa reveals uruptured tubal pregnancy in the isthmic part of the tube and the decision for salpingectomy sinistra was taken. Histological examinations confirmed the diagnosis of ectopic pregnancy in both tubes. The frequency of some rare forms and localizations of ectopic as well as heterotopic pregnancies increase after ART.

["Flare up" and modified natural cycle IVF for patients with expected poor response].

UNLABELLED: The aim of this study is to compare the efficiency of the "flare up" protocol (mini-dose GnRH-ag, macro-dose FSH, GnRH-ant, HCG)-gr. A, with a modified natural cycle IVF (GnRH-ant, HCG)-gr. B. RESULTS: In gr. A 140 and in gr. B 17 patients were assessed. The average age is 35.5 in gr. A and 35 years in gr. B. The embryo transfer is realized 48-72 hours after ovarian puncture in 98 cases (70%) in gr. A and 11 cases (64.7%) in gr. B. Clinical pregnancy is registered in 32 cases (22.8% per cycle, 32.6% per transfer) in gr. A and 4 cases (23.5% per cycle, 36.3% per transfer) in gr. B. In gr. A the cancellation rate is 30%-42 cases and in gr. B--35.3%--6 cases. CONCLUSION: The preliminary results indicate that the 2 methods are equal as regards cancellation and success rate. The natural and modified natural cycle IVF have the following advantages: minimization of severe early and late complications and multifetal pregnancies as well as cost-effectiveness and better chance for pregnancy cumulation rate. There is no doubt that the "mild" and natural, resp. modified natural protocols will displace the conventional hyperstimulation regimens.