Signatures of the Z = 82 shell closure in α-decay process.

In recent experiments at the velocity filter Separator for Heavy Ion reaction Products (SHIP) (GSI, Darmstadt), an extended and improved set of α-decay data for more than 20 of the most neutron-deficient isotopes in the region from lead to thorium was obtained. The combined analysis of this newly available α-decay data, of which the (186)Po decay is reported here, allowed us for the first time to clearly show that crossing the Z = 82 shell to higher proton numbers strongly accelerates the α decay. From the experimental data, the α-particle formation probabilities are deduced following the Universal Decay Law approach. The formation probabilities are discussed in the framework of the pairing force acting among the protons and the neutrons forming the α particle. A striking resemblance between the phenomenological pairing gap deduced from experimental binding energies and the formation probabilities is noted. These findings support the conjecture that both the N = 126 and Z = 82 shell closures strongly influence the α-formation probability.

Low-energy enhancement in the photon strength of 95Mo.

A new experimental technique is presented using proton-γ-γ correlations from (94)Mo(d,p)(95)Mo reactions which allows for the model-independent extraction of the photon strength function at various excitation energies using primary γ-ray decay from the quasicontinuum to individual low-lying levels. Detected particle energies provide the entrance excitation energies into the residual nucleus while γ-ray transitions from low-lying levels specify the discrete states being fed. Results strongly support the existence of the previously reported low-energy enhancement in the photon strength function.

New features of shape coexistence in ;{152}Sm.

Excited states in ;{152}Sm have been investigated with the ;{152}Sm(n,n;{'}gamma) reaction. The lowest four negative-parity band structures have been characterized in detail with respect to their absolute decay properties. Specifically, a new K;{pi} = 0;{-} band has been assigned with its 1;{-} band head at 1681 keV. This newly observed band has a remarkable similarity in its E1 transition rates for decay to the first excited K;{pi} = 0;{+} band at 684 keV to the lowest K;{pi} = 0;{-} band and its decay to the ground-state band. Based on these decay properties, as well as energy considerations, this new band is assigned as a K;{pi} = 0;{-} octupole excitation based on the K;{pi} = 0_{2};{+} state. An emerging pattern of repeating excitations built on the 0_{2};{+} level similar to those built on the ground state may indicate that ;{152}Sm is a complex example of shape coexistence rather than a critical point nucleus.

Lifetime measurement of the first excited 2+ state in 16C.

The lifetime of the 2_+(1) state in 16C has been measured with the recoil distance method using the 9Be(9Be,2p) fusion-evaporation reaction at a beam energy of 40 MeV. The mean lifetime was measured to be 11.7(20) ps corresponding to a B(E2;2_+(1)-->0+) value of 4.15(73)e_2 fm_4 [1.73(30) W.u.], consistent with other even-even closed shell nuclei. Our result does not support an interpretation for "decoupled" valence neutrons.

Nuclear charge radii of neutron-deficient lead isotopes beyond N = 104 midshell investigated by in-source laser spectroscopy.

The shape of exotic even-mass (182-190)Pb isotopes was probed by measurement of optical isotope shifts providing mean square charge radii (delta(r(2))). The experiment was carried out at the isolde (cern) on-line mass separator, using in-source laser spectroscopy. Small deviations from the spherical droplet model are observed, but when compared to model calculations, those are explained by high sensitivity of delta(r(2)) to beyond mean-field correlations and small admixtures of intruder configurations in the ground state. The data support the predominantly spherical shape of the ground state of the proton-magic Z=82 lead isotopes near neutron midshell (N=104).

Identification of mixed-symmetry states in an odd-mass nearly spherical nucleus.

The low-spin structure of 93Nb has been studied using the (n,n'gamma) reaction at neutron energies ranging from 1.5 to 3 MeV and the 94Zr(p,2ngamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at 1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states associated with the pi2p(1/2)-1x(2(1),MS+,94Mo) coupling. These assignments are derived from the observed M1 and E2 transition strengths to the 2p(1/2)-1x(2(1)+,94Mo) symmetric one-phonon states, energy systematics, spins and parities, and comparison with shell model calculations.

Lifetime Measurements in (178)Hf.

Lifetimes of levels from K(π) = 2(+), K(π) = 4(+) and several K(π) = 0(+) bands have been measured in the (178)Hf nucleus using the GRID technique. Lifetimes of the 2(+) and 3(+) levels were measured within the K(π) = 2(+) γ band. A lower limit was established for the lifetime of the 4(+) level of the K(π) = 4(+) band. The resulting upper limits for the absolute B(E2) values exclude collective transitions from the K(π) = 4(+) to the ground state band but not to the K(π)= 2(+) band. Level lifetimes were also measured for several states within three separate K(π)= 0(+) bands. Evidence is presented for a previously unobserved case of two excited K(π)= 0(+) bands being connected via collective E2 transitions.

Acute pancreatitis in a military hospital.

This is a retrospective review of 139 patients who had 152 admissions for acute pancreatitis. Mean patient age was 40 years (range, 1 to 83 years), although the largest percentage (56%) fell between ages 20 and 39 years. There were 92 males and 47 females. Abdominal pain was universal and typically epigastric (88%). Radiologic ultrasound study was used in 80% of patients, which demonstrated pancreatic abnormalities in 37% and gallstones in 16%. Alcohol was the most common cause of acute pancreatitis, accounting for 37% of first attacks and 52% of recurrent attacks. About 15% of patients required intensive care unit management and 23% required operations. Only one patient died (mortality = 0.6%). Among our patients, 58% had at least one of 11 risk factors according to Ranson's criteria, although no one had more than four. Presence of Ranson's risk factors was predictive of need for intensive care unit management (p less than 0.001) and for the need of operation in general (p less than 0.05). Compared to other series reported in the literature, our patients appear to have been diagnosed and admitted earlier.

Improvements in optical methods for measuring rapid changes in membrane potential.

In an effort to increase the utility of optical methods for measuring membrane potential in excitable cells, an additional 369 dyes were tested on giant axons from the squid. Several promising dyes with relatively large absorption and fluorescence signals are described. In addition, a simple modification of the apparatus led to a sixfold increase in the size of dye-related birefringence signals. In preparations with a suitable geometry, these signals are as large as absorption signals but photodynamic damage and bleaching are eliminated when wavelengths longer than the absorption band are used.

Human colonic tumor cell kinetics: potential for therapy.

Using new in vitro techniques developed at the Cancer Research Unit, cell kinetic measurements were obtained in primary and metastatic human colonic tumors, polyps and normal bowel that did not require in vivo 3HTdR and required only single samples of tissue. These techniques included the measurement of the number of cells in DNA synthesis (LI), an estimate of the DNA synthesis time (Ts) and the growth fraction of tissues by means of the primer-available DNA-dependent DNA polymerase assay (PDP). From these data, the potential doubling time and the cell cycle time (Tc) of the tumors were calculated. Early preliminary data on human colonic specimens presented in Tables 1 and 2 indicate that there is an increase in LI from the low polyps to higher adenocarcinomas. There is little difference between primary and metastatic tumor cell kinetics. Growth fraction estimates (PDP) of the various colonic tissue types are also not significantly different and except for villous adenomas, DNA synthesis times are constant. The median 3HTdR labeling indices of 7% primary adenocarcinomas include a number of samples (approximately 20% of all samples) with high labeling indices (in the 10--20% range). These high labeling tumors may be those that show objective response to S-phase active drugs, e.g., 5-FU.

Influence of adriamycin and adriamycin-radiation combination on jejunal proliferation in the mouse.

The influence of adriamycin and adriamycin-radiation combinations on posttreatment proliferative activity of the mouse jejunum was examined by measuring [3H]thymidine incorporation. Single doses of 5 or 10 mg/kg produced a transient reduction in the proliferative activity, while 1 mg/kg had little effect. After 10 mg/kg, there was a rapid decrease in the number of mitotic figures, followed by a gradual decrease in the number of and rate of DNA synthesis in S-phase cells. A compensatory epithelial hyperplasia characterized by an enlarged crypt proliferative population and shortened mitotic cycle duration was observed beginning 48 hr after treatment. Multiple doses of adriamycin totalling 10 mg/kg inhibited cell production to a greater extent than the equivalent single dose. In combination with 1000 R, adriamycin (5 mg/kg) given from 96 hr before to 72 hr after irradiation reduced the amount of postirradiation proliferation.

Combined-modality oncotherapy with cyclophosphamide (NSC-26271) and radiotherapy: control of murine mastocytoma.

We investigated the effects of cyclophosphamide, alone and in combination with a 1,000-R/week radiotherapy schedule, on the growth of solid P815X2 tumors in 12-week-old male DBA/2 mice. Single-dose treatments of 150 mg cyclophosphamide/kg were given to animals bearing tumors of different ages. Such treatment of young tumors resulted in proportionately greater degrees of regression and steeper regrowth curves than did treatment of older tumors. Although slopes of regrowth curves differed greatly, time to regrowth (to pretreatment size) was the same for all age classes of tumors. Graded weekly exposures of 50-250 mg/kg for 4 weeks resulted in dose-dependent increases in incidence of complete remission, duration of remission (time to regrowth), and mean animal life-spans. The combination of radiotherapy to the tumor and 75, 150, or 225 mg cyclophosphamide/kg/week resulted in better local tumor control than occurred with radiotherapy or the drug alone. However, a dose-dependent increase in radiosensitivity of the gastrointestinal mucosa included in radiotherapy fields was observed. A 3-week course of radiotherapy plus 75 mg cyclophosphamide/kg/week (which is tolerated by the mucosa) increased animal lifespans to 165% of those of controls.

The modification of gastrointestinal tolerance and responses to abdominal irradiation by chemotherapeutic agents.

Groups of male DBA/2 mice were irradiated with partial abdominal exposures of x radiation ranging from 100 to 1,600 rads. Concomitant with radiation exposure and at 1 or 4 hours prior to, and at 1, 6, 24, or 48 hours after irradiation, various chemotherapeutic agents were administered, i.e., methotrexate, Cytoxan, adriamycin and BCNU. The results suggest that excessive gastrointestinal toxicity may result if aggressive chemotherapy is closely spaced with radiation exposure for the treatment of abdominal neoplasms. However, adjustment of dose and time patterns based on the proliferative responses of the mucosa may circumvent such toxicity to a large extent.

Treatment of solid P815x2 murine mastocytoma with adriamycin (NSC-1231127): toxity limitations.

The efficacy of adriamycin (NSC-123127), given as weekly or as 5-day-per-week doses, on the control of solid P815X2 murine mastocytomas was severely limited by hematopoietic and gastrointestinal toxicity. Although daily or weekly drug schedules both elicited dose responsiveness in terms of tumor control, no dose level of drug increased the life-span of tumor bearing animals.

Damage and recovery assessment of the mouse jejunum to abdominal X-ray and adriamycin treatment.

The influence of adriamycin on the post-irradiation proliferative response of the mouse jejunum was examined. Doses of either 5 or 10 mg/kg of adriamycin administered immediately after abdominal irradiation reduced the LD50/7 days by 300-400 R. Neither dosage of the drug reduced the number of surviving crypts, as measured by the crypt isolation and microcolony techniques, for a given radiation exposure. However, both drug dosages reduced the amount of post-irradiation compensatory hyperplasia, as measured by 3H-thymidine incorporation.

Proliferative patterns in the mouse jejunal epithelium after fractionated abdominal x-irradiation.

Cell proliferation was studied in the intestinal epithelium of mice exposed to fractionated abdominal X-irradiation. Exposures were separated by 12, 24, 48 or 72 hr. Labelled nuclei and mitotic figures per crypt using the crypt squash technique were determined at closely-spaced time intervals (1 to 96 hr) after 1, 2, 3, 5, 7 and 9 exposures. Cell cycle times including estimates of G-1, S, G-2 and M were determined at 12 and 24 hr. These data show that the intestinal epithelium has a remarkable potential to repair damage and recover following severe injury if sufficient time is allowed for the acceleration in proliferative activity. The damage-repair-recovery pattern, i.e., increase in size of proliferative population and acceleration of the generation cycle, is similar for single and fractionated exposures. The number of 300 R exposures which can be tolerated by a highly organized in vivo cell population is dependent upon time interval between fractions; e.g., when interval between fractions is 12 hr eight 300 R exposures kill all animals, but when the interval is increased to 72 hr some animals survive 20 doses, although time of death is highly variable. The compensatory recovery potential is maintained over a large number of exposures.