A multi-stop time-of-flight spectrometer for the measurement of positron annihilation-induced electrons in coincidence with the Doppler-shifted annihilation gamma photon.

In this study, we describe an advanced multi-functional, variable-energy positron beam system capable of measuring the energies of multiple "positron-induced" electrons in coincidence with the Doppler-shifted gamma photon resulting from the annihilation of the correlated positron. The measurements were carried out using the unique characteristics of the digital time-of-flight spectrometer and the gamma spectrometer available with the advanced positron beam system. These measurements have resulted in (i) the first digital time-of-flight spectrum of positron annihilation-induced Auger electrons generated using coincident signals from a high-purity Ge detector and a micro-channel plate, (ii) a two-dimensional array of the energy of Doppler-broadened annihilation gamma and the time-of-flight of positron-annihilation induced Auger electrons/secondary electrons measured in coincidence with the annihilation gamma photon, and (iii) the time-of-flight spectra of multiple secondary electrons ejected from a bilayer graphene surface as a result of the impact and/or annihilation of positrons. The novelty of the gamma-electron coincidence spectroscopy has been demonstrated by extracting the Doppler-broadened spectrum of gamma photons emitted due to the annihilation of positrons exclusively with 1s electrons of carbon. The width of the extracted Doppler-broadened gamma spectrum has been found to be consistent with the expected broadening of the annihilation gamma spectrum due to the momentum of the 1s electrons in carbon.

Effect of hydroquinone on meiotic segregation in Drosophila melanogaster females.

The induction of sex chromosomes meiotic nondisjunction (ND) by hydroquinone (HQ) given orally was investigated in Drosophila melanogaster 2-7, 8-22, 24, 48, 72 and 96 h-old females. ND was assessed by a system where exceptional females (XXY) and only 1/4 of the expected regular progeny are viable. Oocytes were treated at different stages of development. 4% HQ tested only in 72 h-old females induced ND in oocytes sampled in brood I (mostly mature oocytes at metaphase I). 6% HQ increased ND in brood I of 8-22 h-old females, while other broods, (including cells treated at early prophase) were also affected in older flies, the highest significance being attained in the 48 h-old series. Newly hatched females (2-7 h-old) were refractory to the treatment, though oocytes sampled in the first three subcultures are comparable to cells showing enhancement of ND in series run with older females. Toxicity of 2, 4 and 6% HQ increased with concentration and females' age: (a) 2% was not toxic; (b) 4% was toxic only to 72 h-old females; (c) 6% was increasingly toxic to females 24, 48 and 72 h-old. The results indicate that age plays a significant role on both chromosomal segregation and toxicity and suggest that in Drosophila HQ is metabolized to its reactive species. The lack of toxic and aneugenic effect in very young females could reflect a more efficient detoxification due to the known high specific activity of glutathione-S-transferase (GST) after eclosion. The decline in GST activity around day 2 of adult life coincides with the high effect of HQ in 48 h-old females.

Genetic damage induced by methylglyoxal and methylglyoxal plus X-rays in Drosophila melanogaster germinal cells.

The effect of methylglyoxal (MG) and MG administered prior to X-irradiation was investigated in Drosophila melanogaster germinal cells using the sex-linked recessive lethal (s.l.r.l.), II-III autosomal translocation (AT) and X-chromosome nondisjunction (ND) tests. For the s.l.r.l. test the males were either injected with MG (0.5 M, 0.75 M or 1.7 M) or fed for 24 h (1 M) and two 24 h broods (A and B) were obtained. For the AT test the males were injected with MG 1.7 M and the same brooding scheme was followed. ND was tested in females fed on MG 1 M. The only effect observed after MG treatment was a significant increase on the yield of s.l.r.l. with MG 1.7 M. In the combined treatments MG was administered prior to irradiation with 20 Gy of X-rays and the induction of s.l.r.l. and AT was assessed. Pre-treatment with MG 0.75 M and 1.7 M enhanced the frequency of s.l.r.l. in cells sampled in brood B, consisting mainly of the rather hypoxic late spermatids. It is suggested that this radiosensitizing effect could be ascribed to a decrease in the level of glutathione due to the metabolization of MG.

Comparative study of the clastogenic efficiency of ethyl methanesulfonate and diethyl sulfate in Drosophila melanogaster mature sperm.

Chromosome loss and translocation tests were carried out in Drosophila melanogaster sperm, stored in untreated females for up to 24 days, to compare the clastogenicity of ethyl methanesulfonate (EMS) and diethyl sulfate (DES). The sex-linked recessive lethal test was used as a "biological dosimeter" and the following results were obtained: The yield of 2-3 translocations induced by both mutagens increased steadily with storage, being significantly higher after EMS than after DES treatment. The frequencies of partial losses induced by EMS and DES were similar and increased with storage. With up to 11 days' storage, the frequency of complete loss induced by DES was higher than that induced by EMS and remained unchanged when storage was extended to 24 days. Complete loss induced by EMS increased significantly with further storage (12-24 days). With DES, complete (but not partial) loss was detected with a dose at which EMS failed to modify the control values. These data suggest that the lower recovery of II-III translocations after treatment with DES does not result from a low breaking capacity but from a diminished or delayed rejoining of the induced breaks. This could be due to a physiological impairment of the treated cells by the high toxicity of DES or to an actual lower rejoinability of the broken ends. The differential recovery of complete and partial losses after DES treatment further suggests that the mechanisms leading to the fixation of both types of damage are somehow different, and that processes intervening in the recovery of partial losses are less affected, or not at all, by the proposed reduced rejoining of chromosome breaks.

Modification of radiation-induced genetic damage in Drosophila melanogaster male germ cells by butylated hydroxytoluene.

The effects of butylated hydroxytoluene (BHT) on genetic damage induced by ionizing radiation were studied in post-meiotic male cells of Drosophila melanogaster. Prior to submitting Samarkand males to 2 krad of X-rays, BHT was administered (a) with the food (0.2 per cent final concentration) from emergence of the imago for 7 days or (b) by intra-abdominal injection (0.05 per cent) to 7-day-old adults. Dominant lethality (embryonic and total), II-III translocations and sex-linked recessive lethals were recorded. The only effect of BHT observed was a decrease in the frequency of recessive lethals induced, detected in early spermatids. Since oxygen plays an important role in the high radiosensitivity of these cells, it is suggested that the sparing action of BHT was due to its antioxidative and radical scavenging properties.