Resonances and Dissociative Electron Attachment in HNCO.

In a combined experimental and theoretical study, we probe the dissociative electron attachment in isocyanic acid HNCO. The experimental absolute cross section for the NCO^{-} fragment shows a sharp onset and fine structures near the threshold. The autoionizing state responsible for the dissociative attachment is found in both the R-matrix calculation and using analytic continuation in the coupling constant. The involved A^{'} resonance has a mixed π^{*}/σ^{*} character along the dissociating bond and thus combines the effects of nonzero electron angular momentum and dipole-supported states. This leads to unusual behavior of its width at various geometries. Because the potential energy gradient of the autoionizing state points essentially in the direction of the N─H bond, nuclear dynamics can be described by a one-dimensional nonlocal model. The results agree with the experiment both quantitatively and qualitatively. The present system may be a prototype for interpretation of the dissociative electron attachment process in a number of other polyatomic systems.

On a simple way to calculate electronic resonances for polyatomic molecules.

We propose a simple method for calculation of low-lying shape electronic resonances of polyatomic molecules. The method introduces a perturbation potential and requires only routine bound-state type calculations in the real domain of energies. Such a calculation is accessible by most of the free or commercial quantum chemistry software. The presented method is based on the analytical continuation in a coupling constant model, but unlike its previous variants, we experience a very stable and robust behavior for higher-order extrapolation functions. Moreover, the present approach is independent of the correlation treatment used in quantum many-electron computations and therefore we are able to apply Coupled Clusters (CCSD-T) level of the correlation model. We demonstrate these properties on determination of the resonance position and width of the (2)Πu temporary negative ion state of diacetylene using CCSD-T level of theory.

Electron-impact vibrational excitation of cyclopropane.

We report a very detailed test of the ab initio discrete momentum representation (DMR) method of calculating vibrational excitation of polyatomic molecules by electron impact, by comparison of its results with an extensive set of experimental data, covering the entire range of scattering angles from 10° to 180° and electron energies from 0.4 to 20 eV. The DMR calculations were carried out by solving the two-channel Lippmann-Schwinger equation in the momentum space, and the interaction between the scattered electron and the target molecule was described by exact static-exchange potential corrected by a density functional theory (DFT) correlation-polarization interaction that models target's response to the field of incoming electron. The theory is found to quantitatively reproduce the measured spectra for all normal modes, even at the difficult conditions of extreme angles and at low energies, and thus provides full understanding of the excitation mechanism. It is shown that the overlap of individual vibrational bands caused by limited experimental resolution and rotational excitation must be properly taken into account for correct comparison of experiment and theory. By doing so, an apparent discrepancy between published experimental data could be reconciled. A substantial cross section is found for excitation of the non-symmetric HCH twisting mode ν4 of A1 (″) symmetry by the 5.5 eV A2 (') resonance, surprisingly because the currently accepted selection rules predict this process to be forbidden. The DMR theory shows that the excitation is caused by an incoming electron in an f-wave of A2 (') symmetry which causes excitation of the non-symmetric HCH twisting mode ν4 of the A1 (″) symmetry and departs in p- and f-waves of A2 (″) symmetry.

Contrasting Dynamics in Isoelectronic Anions Formed by Electron Attachment.

Cyanogen NCCN and cyanoacetylene HCCCN are isoelectronic molecules, and as such, they have many similar properties. We focus on the bond cleavage in these induced by the dissociative electron attachment. In both molecules, resonant electron attachment produces CN- with very similar energy dependence. We investigate the very different dissociation dynamics, in each of the two molecules, revealed by velocity map imaging of this common fragment. Different dynamics are manifested both in the excess energy partitioning and in the angular distributions of fragments. Based on the comparison with electron energy loss spectra, which provide information about possible parent states of the resonances (both optically allowed and forbidden excited states of the neutral target), we ascribe the observed effect to the distortion of the nuclear frame during the formation of core-excited resonance in cyanoacetylene. The proposed mechanism also explains a puzzling difference in the magnitude of the CN- cross section in the two molecules which has been so far unexplained.

Absolute cross sections for electron scattering from furan.

We report results of measurements and calculations of absolute cross sections for electron scattering from furan molecules (C(4)H(4)O). The experimental absolute differential cross sections (DCSs) for elastic electron scattering were obtained for the incident energies from 50 eV to 300 eV and for scattering angles from 20° to 110°, by using a crossed electron-target beam setup and the relative flow technique for calibration to the absolute scale. The calculations of the electron interaction cross sections are based on a corrected form of the independent-atom method, known as the screening corrected additivity rule (SCAR) procedure and using an improved quasifree absorption model. The latter calculations also account for rotational excitations in the approximation of a free electric dipole and were used to obtain elastic DCSs as well as total and integral elastic cross sections which are tabulated in the energy range from 10 to 10 000 eV. All SCAR calculated cross sections agree very well with both the present and previously published experimental results. Additionally, calculations based on the first Born approximation were performed to calculate both elastic and vibrationally inelastic DCSs for all the modes of furane, in the energy range from 50 eV to 300 eV. The ratios of the summed vibrational to elastic DCSs are presented and discussed. Finally, the present results for furan are compared with previously published elastic DCSs for the tetrahydrofuran molecule and discussed.

CCND1 and ZNF217 gene amplification is equally frequent in BRCA1 and BRCA2 associated and non-BRCA breast cancer.

Breast cancer associated with BRCA1 and BRCA2 gene mutations differs from non-BRCA tumors in several respects. We determined whether there was any difference in CCND1 (11q13) and ZNF217 (20q13) gene amplification with respect to BRCA status. Of 40 breast cancer samples examined, 15 and 9 were from BRCA1 and BRCA2 mutation carriers, respectively, and 16 from patients without mutation. Fluorescence in situ hybridization showed that eight tumors exhibited CCND1 amplification (20%; 3 BRCA1, 3 BRCA2, 2 non-BRCA). ZNF217 amplification was observed in three of 38 cases (8%; 2 BRCA1, 1 non-BRCA). There was no significant difference in CCND1 and ZNF217 amplification between BRCA1, BRCA2 and non-BRCA tumors. CCND1 amplification was associated with decreased disease-free (P = 0.045) and overall survival (P = 0.015). BRCA1 tumors with CCND1 amplification were estrogen receptor negative, in contrast to CCND1 amplified BRCA2 and non-BRCA tumors, suggesting that concurrent CCND1 amplification and estrogen and progesterone receptor negativity may predict germline BRCA1 gene mutation. All ZNF217 amplified tumors were of the medullary histological type (P = 0.002). There was no statistical correlation between CCND1 and ZNF217 amplification and estrogen receptor, progesterone receptor, and ERBB2 expression and TNM classification. CCND1 amplification did not correlate with EGFR expression.

[Alveolar echinococcosis--a new emerging disease?]. / Alveolární echinokokóza--nove se objevující onemocnení?

Alveolar echinococcosis is a rare zoonotic disease caused by the cestode larval stages of Echinococcus multilocularis. The Larva develops as a tumour like cyst (hydatid). Due to a slow cyst development, the early stage of the infection is always asymptomatic and the clinical symptoms develop after years later. In the Czech Republic the disease is still very rare. Only one alveolar echinococcosis case was reported 30 years ago. However, new alveolar echinococcosis cases occurred during last two years and some of them indicate autochtonic character of the transmission. With regard to the recent increasing risk of infection with E. multilocularis in Central Europe, we present two case reports of alveolar echinococcosis in a 33-year old woman and a 24-year old man. The reports show diagnostic process and therapy of the infection.

Endolymphatic sac tumor (aggressive papillary tumor of middle ear and temporal bone): report of two cases with analysis of the VHL gene.

Endolymphatic sac tumor (Heffner tumor) (ELST) is a very rare nonmetastasizing, locally aggressive low-grade adenocarcinoma of endolymphatic sac origin, which is linked to von-Hippel-Lindau disease (VHLD). VHLD is an autosomal dominant disorder characterized by an inherited genetic abnormality of the VHL gene located on the short arm of chromosome 3 (3p26-p25). VHL gene mutations have been shown both in ELSTs associated with VHLD and in sporadic cases. Because of the rarity of ELST, only a small number of cases have been subjected to molecular genetic analysis. We have encountered two patients with ELST, one of whom presented with a medical and family history of VHLD. The second was a sporadic case, the patient having no symptoms of VHLD. The tissues obtained from Heffner tumor and cerebellar hemangioblastoma from the patient with inherited VHLD possess a point mutation in exon 1 of VHL gene. This mutation is a C to T exchange at position 194, resulting in amino acid exchange S65L. No mutation was found in any of the three exons analyzed and in the exon-intron junctions of the VHL gene in the sporadic case.

[Lymphatic mapping in cervical cancer]. / Lymfatické mapování u karcinomu cípku delozního.

BACKGROUND AND AIMS: The aim of the study is to analyze the feasibility of intraoperative sentinel lymph nodes (SLN) detection using gamma detection probe and blue dye in patients with cervical cancer. DESIGN AND SUBJECTS: Prospective clinical study. 106 patients with cervical cancer were included into the study in the period from May 2004 to November 2006. METHODS AND RESULTS: Patients were divided into three groups according to the tumor volume. Lymphoscintigraphy was performed following an injection of 99m Tc-labeled nanocolloid and intraoperatively the SLN were identified visually after marking of lymphatic vessels with blue dye and further detected using a handheld gamma detection probe. The SLN were histologically and immunohistochemically analyzed. Total number of 309 SLN with an average of 2.9 per patient were identified. The SLN detection rate was 94.3% per patient, 84.4 % per side, and depended on the tumor volume. Metastatic disease was detected in 39 patients (36.8%) and micrometastatic disease in 15 patients (14.2%). Sensitivity and negative predictive value calculated were 93.9% and 98.0%, false negative rate reached 5.1. CONCLUSIONS: Intraoperative detection of SLN using combination of technecium-99-labeled nanocolloid and blue dye represents a feasible, safe and accurate technique to identify lymphatic spreading in stages IA2-IB1 of cervical cancer.

PML protein expression in hereditary and sporadic breast cancer.

The PML protein is concentrated in the PML nuclear bodies. Downregulation of the PML protein has been described in various types of cancer and is in accordance with the fact that dysqualification of tumor suppressive functions of the PML protein might promote cancer development. Various differences have been described between sporadic breast cancer and that associated with BRCA1 and BRCA2 gene mutations. Expression of the PML protein has not been studied yet. The aim of this study was to determine if there is any difference in PML protein expression in breast cancer of BRCA1 and BRCA2 gene mutation carriers compared to sporadic breast cancer and if the PML protein can be used as a prognostic marker. There were 47 breast cancer samples included, 14 and 10 from BRCA1 and BRCA2 germline mutation carriers, respectively, and 23 from patients without a BRCA1/BRCA2 germline mutation. Immunofluorescence staining was used. Downregulation of PML protein expression was found in 2 of 14 (14%), 3 of 10 (30%) and 15 of 47 (31%) cases of breast cancer samples from BRCA1, BRCA2 and no BRCA1/BRCA2 mutation carriers, respectively (p(BRCA1) = 0.019; p(BRCA2) = 0.111). There was no correlation between PML protein expression and age, histological types, estrogen and progesterone receptor, c-erbB-2 and PCNA expression, TNM classification, disease-free and overall survival. In conclusion, the PML protein is downregulated in approximately 30% of breast cancers cases. Downregulation of PML protein expression was significantly less frequent in BRCA1 mutation carriers compared to sporadic cases. No correlation was found between PML protein expression and any of the other clinical and laboratory characteristics.

PML and TRF2 protein expression in hereditary and sporadic colon cancer.

The PML (promyelocytic leukemia) protein is concentrated in the PML nuclear bodies. In human cell lines and tumors maintaining their telomeres by alternative lengthening (ALT), the PML protein is colocalized with TRF2 and several other proteins in the so called ALT-associated PML bodies. The aim of this study was to determine if there is any difference in PML protein expression between tumors with stable microsatellites (MSS) and those with high-frequency microsatellite instability (MSI-H), if PML protein expression might be a prognostic factor and if MSI-H tumors more frequently use alternative lengthening of telomeres measured by the presence of ALT-associated PML bodies. Eighty colorectal cancer samples (32 MSI-H and 48 MSS) and 8 human tumor cell lines (Saos-2, U2OS, DU145, LNCaP, U87, HeLa, MCF7 and T98G) were included into the study. Double-colour immunofluorescence staining was used. Downregulation of PML protein expression was found in 7 of 32 (22%) MSI-H and 11 of 48 (23%) MSS tumors (p=0.520). There was no correlation between PML expression and age, histological typing, localization of the tumor in colon, TNM classification, disease-free and overall survival. The Saos-2 and U2OS (ALT using cell lines) and the MCF7 (active telomerase) cell line were characterized by the presence of ALT-associated PML bodies; no such bodies were detected in the DU145, LNCaP, U87, HeLa and T98G cell lines (active telomerase); accumulation of TRF2 was absent or much weaker in these cell lines compared to Saos-2 or U2OS. Accumulation of the TRF2 protein was detected in 16 of 80 (20%) tumors and PML and TRF2 colocalization in 2 MSI-H tumors (6%). In conclusion, the PML protein was downregulated in approximately 20% of tumors; there was no difference between MSS and MSI-H tumors. PML protein expression does not seem to be a prognostic factor.

[Sentinel node detection in early stage of cervical carcinoma using 99mTc-nanocolloid and blue dye]. / Detekce sentinelové uzliny u casných stadií cervikálního karcinomu kombinovanou metodou s uzitím nanokoloidu technecia Tc99 a patentní modri.

OBJECTIVE: The aim of the study was to analyse the feasibility of intraoperative sentinel lymph nodes (SLN) detection using gamma detection probe and blue dye in patients undergoing radical hysterectomy for treatment of early stage of cervical cancer. DESIGN: Prospective case observational study. METHODS: In the period from May 2004 to February 2006 77 patients with early stage of cervical cancer who underwent a radical surgery were included into the study. Patients were divided into three groups according to the tumour volume. First group consists of patients FIGO IA2 and FIGO IB1 with tumour diameter less than 2 cm, second group tumours FIGO IB1 with tumour diameter more than 2 cm and third group stadium IB2. SLN was detected by blue dye and Tc99. Preoperative lymphoscintigraphy was done after Tc99 colloid injection, intraoperative detection was performed by visual observation and by hand-held gamma-detection probe. SLN were histologically and immunohistochemically analysed. RESULTS: A total number of 2764 lymph nodes with an average 36 and 202 SLN with an average 2.6 were identified. The SLN detection rate was 94.8% per patient and 85.1% for the side of dissection and depends on the tumor volume. SLN were identified in obturator area in 48%, in external iliac area in 15%, in common iliac and internal iliac both in 9%, in interiliac region in 8%, in praesacral region in 6% and in parametrial area in 5%. Metastatic disease was detected in 31 patients (40.2%), metastatic involvement of SLN only in 12 patients (15.6%). False negative rate was 2.6%, sensitivity and negative predictive value calculated by patient were 923% and 95.7%. CONCLUSIONS: Intraoperative lymphatic mapping using combination of technecium-99-labeled nanocolloid and blue dye are feasible, safe and accurate techniques to identified SLN in early stage of cervical cancer.

[A rare complication of acute lymphoblastic leukaemia in young patients]. / Neobvyklá komplikace akutní lymfoblastické leukémie u detských pacientu.

The paper presents one of the rather rare complications related to the malignant blood disease in young patients. The treatment of this extremely serious disease should be accompanied not only with number of already described complications which are thus expected but also with rare ones, whose control and treatment is demanding and rather long-term. The immense progress in medical research makes it possible to cope with a variety of serious diseases including leukaemia in young patients with one-year intensive therapy and an overall exhaustion of their organisms, where in spite of a perfect therapeutic protocol new challenges need to be met. The present study describes one of such rare complications, which appeared in two three-year-old girl patients, accidentally during the same time period: namely benign oesophagus stenosis. The condition was caused by several factors - first mycotic infection, histologically proved as Candida Albicans - which in one of the girls lead to septic states and the condition was generalised with more affected organs. Due to the location of the stenosis in the lower third of oesophagus, gastrooesophagus reflux played its role, too and last but not least there was a negative effect of one of the cytostatics - methotrexate - causing mycotic infections (here stomatitis and oesophagitis). For the proper development and overall well-being of a healthy organism, an optimal, sufficient and appropriate per oral reception of food is necessary. Satisfying this need becomes even more crucial in the case of young patient otherwise affected by an immunodeficient condition and an overall impoverishment of their organism. The oesophagus stenosis presents an obstacle manageable using either endoscopic methods or surgery. Although in the cases discussed the treatment was very demanding due to the age of the patients, continuous cytostatic therapy in progress, the primary disease, and the general anaesthesia - it was finally effective and successful.

[Lymphatic mapping and detection of sentinel node in early stages of cervical carcinoma]. / Lymfatické mapováni a detekce sentinelové uzliny u casných stadií cervikálního karcinomu.

OBJECTIVE: The aim of the study was to analyse two methods of intraoperative sentinel node detection using blue dye and blue dye with Tc99 labeled tracer in early stage of the cervical cancer. DESIGN: Prospective case observational study. SETTING: Department of Obstetrics and Gynecology, University Hospital Ostrava. METHODS: From May 2004 to September 2005, 49 patients with cervical cancer who underwent a radical surgery were included into the study. Sentinel lymph node was detected using blue dye in the first group of 23 patients and by blue dye with Tc99 in the second group of 26 patients. Intraoperative sentinel node detection was performed by visual aspection in the first group, and by visual aspection and by hand-held gamma-probe in the second group. RESULTS: Patients were divided according to stage of the disease into three subgroups FIGO IA2, FIGO IB1 and FIGO IB2. A total number of 1561 lymph node with an average 32 and 94 SLN with an average 1.9 were identified. The specific detection rate per site was 63% in the first group and 80.8% in the second group respectively. Metastatic disease was detected in 26 patients (41%) and metastatic involvement of SLN only in 11 patients (17.4%). Sensitivity and negative predictive value were 100% in both groups, false negativity was 0%. CONCLUSION: Detection of SLN by combination of blue dye and Tc99 labeled tracer has a higher detection rate of SLN than detection by blue dye alone.

[The first case of management of the rectovaginal fistule using transanal endocsopic microsurgery]. / První prípad resení rektovaginální pístele pomocí transanální endoskopické mikrochirurgie.

The authors present an unusual and, according to the available literature data, so far unused method--management of the rectovaginal fistule, using a T.E.M. technique (transanal endoscopic microsurgery). In their case-review of a female patient, they present advantages of this technique in a case of a rare disorder - a benign rectovaginal fistule. All of the following employment of a harmonic scalpel in the T.E.M. method, as well as of a tissue adhesive Tissucol and of a surgical rectoscope in the vaginal phase of the procedure, deserve attention of surgeons and gynaecologists.

Chromophobe renal cell carcinoma with microcystic and adenomatous arrangement and pigmentation--a diagnostic pitfall. Morphological, immunohistochemical, ultrastructural and molecular genetic report of 20 cases.

We present clinical, morphological, immunohistochemical, ultrastructural and molecular genetic features of 20 cases of a peculiar form of chromophobe renal cell carcinoma (CRCC) with morphology differing from that of conventional CRCC. Microscopically, the typical features of the tumors were microcystic arrangement and formation of adenomatous structures. Microcystic areas were composed of smaller eosinophilic and bigger pale cells having cytological appearance typical of conventional CRCC. Cytological features of the adenomatous structures were mostly different from those of conventional CRCC. They had a typical columnar arrangement with nuclei positioned at the base of the glandular structures and a small amount of a deeply eosinophilic cytoplasm often endowed with brush border facing the lumen of the glands. In addition, all the tumors showed a brown pigmentation. The pigmentation was located mostly extracellularly, where it formed pools of heavy deposits. Microscopic calcifications present in all cases formed psammoma bodies or else the calcifications were more extensive and amorphous in shape. Ultrastructurally, the cells showed features characteristic of CRCC: typical cytoplasmic vesicles were 100-700 nm in size and mitochondria had tubulovesicular, lamellar or circular cristae. Some tumor cells contained dark, variously sized electron-dense pigment granules. Neither melanosomes nor membrane-bound neurosecretory granules were seen. Using fluorescence in-situ hybridization probes for chromosomes 1, 2, 6, 10, 13, 17 and 21, the tumors revealed massive loss of tested chromosomes typical for conventional CRCC. Monosomy of chromosomes 1, 2, 6, 10, 13 and 21 was found in 100, 36, 91, 82, 82, 82 and 64% of cases, respectively. None of the cases showed mutation of exons 9, 11, 13 and 17 of the c-kit gene. The important feature of pigmented microcystic chromophobe renal cell carcinoma is a relatively benign biological behavior and the absence of distant metastases and sarcomatoid transformation.

[Giant benign mucinous cystadenoma of both ovaries in early puerperium: case report and review of literature]. / Obrovský benigní mucinózní kystadenom obou ovarií v casném puerperiu: Popis prípadu a prehled literatury.

OBJECTIVE: A case report of giant bilateral benign cystadenoma after vaginal delivery. DESIGN: Case report. SETTINGS: Department of Obstetrics and Gynaecology, University Hospital Ostrava. SUBJECT OF STUDY: A 35-year-old woman twelve days after vaginal delivery was presented with symptoms of an acute abdomen. On ultrasonographic examination, the presence of a cyst filling the complete abdominal cavity. Bilateral cystic mass measuring 25 x 30 cm was removed by laparotomy. Subsequent histological examination revealed a benign mucinous cystadenoma. CONCLUSION: A case of giant mucinous cystadenoma is presented with clinical and pathological details. An ovarian cystadenoma was the cause of an acute abdomen in puerperium and led to clinical and therapeutic disconcerment.

Shadow cell differentiation in testicular teratomas. A report of two cases.

Two cases of adult testicular teratoma with shadow cell differentiation (SCD) similar to that seen commonly in pilomatrixoma are presented. The patients aged 21 and 27 years, and both tumors were limited to the testis. The differentiation of squamous epithelium toward shadow cells is well known in cutaneous pilomatrixoma and related lesions, some odontogenic tumors, craniopharyngeoma, and it was recently observed in several visceral carcinomas. In testicular location, SCD was so far described in benign dermoid cyst but not in teratoma, suggesting that the occurrence of shadow cells could help in differential diagnosis between these lesions. This is, however, not the case and the distinction of teratoma from dermoid cyst must be based on other morphological findings.

Spindle cell myoepithelial tumours of the parotid gland with extensive lipomatous metaplasia. A report of four cases with immunohistochemical and ultrastructural findings.

We report four cases of parotid gland tumours composed predominantly of spindle-shaped myoepithelial cells and mature adipocytes. The central portion of one tumour showed extensive adipose differentiation, whereas in the peripheral parts there were small foci of ductal epithelium arranged in cords and tubules within an abundant myxoid stroma. The other cases were adipose spindle cell myoepitheliomas without an obvious glandular component. Under high-power examination, a transition between modified spindle-shaped myoepithelial cells and adipocytes was observed, and this was confirmed with immunohistochemistry. Ultrastructurally, the modified myoepithelial cells showed intracytoplasmic tonofilaments, bundles of actin microfilaments and lipid droplets. A possible pathogenesis is proposed of true metaplastic transformation of myoepithelial cells to adipocytes. This lesion is important to identify correctly, as inadequate surgery can lead to recurrence.

Influence of heavy metals upon the retention and mobilization of polonium-210 in rats.

PURPOSE: To provide information about the tissue retention and mobilization of the alpha-emitting radionuclide, polonium-210 (210Po), in rats under combined exposure to heavy metal ions and the chelating agent, 2, 3-dimercaptopropane-1-sulfonate (DMPS). MATERIALS AND METHODS: Rats were pre-exposed intraperitoneally to either CdCl2 or Pb(CH3COO)2. 9 or 15 h later they received 210Po nitrate intravenously. The retention and excretion of 210Po via the urine and faeces of pre-exposed rats, as well as in pre-exposed rats treated with DMPS, were followed. The radioactivity due to 210Po in a broad spectrum of body tissues and excreta was measured by the liquid scintillation counting after sample digestion in a mixture of perchloric acid and hydrogen peroxide. The immunohistochemical localization of metallothioneins (MT) was studied using a mixture of murine monoclonal antibodies directed against MT I+II. RESULTS: The present study revealed different tissue distributions of polonium-210 in the rats pre-exposed to lead or cadmium ions when compared with that in 210Po only controls. Under combined exposure to Pb or Cd, the spontaneous excretion of 210Po was enhanced and could be further enhanced by treatment with DMPS. Treatment with this chelator was efficient even when its start was postponed until 24h after internal contamination of the body with 210Po. CONCLUSIONS: Polonium-210 is bound in vivo to binding sites on various biomolecules, among them erythrocytic enzymes and MT. This phenomenon explains the different affinity and overall distribution of 210Po in control body tissues. When the appropriate binding sites are occupied by lead or cadmium, enhanced natural excretion of polonium-210 occurs.