THE APPLICATION OF A NEUTRON IDENTIFICATION CIRCUIT TO THE STUDY OF FAST-NEUTRON INTERACTIONS IN STILBENE

1963 ◽  
Vol 41 (5) ◽  
pp. 793-811 ◽  
Author(s):  
F. A. Johnson
Keyword(s):  
Space Charge ◽  
Fast Neutron ◽  
Excited States ◽  
Light Output ◽  
Particle Spectrum ◽  
Low Light ◽  
Trigger Circuit ◽  
Equivalent Electron ◽  
Selection Of ◽  
Α Particles

A neutron identification circuit is described which has a threshold corresponding to a neutron energy of about 350 kev (50–60 kev equivalent electron energy). The photomultiplier is operated under conditions of space-charge saturation. Selection of pulses due to recoil protons or heavier particles is accomplished by allowing the initial negative-going spike of the space-charge-limited pulse from the last dynode to activate a trigger circuit, the output of which is used to gate the subsequent positive portion of the dynode pulse for presentation to a simple diode discriminator. Separation of pulses due to recoil protons and to α particles is also possible to some extent.The circuit is applied to an investigation of fast-neutron interactions in stilbene. For the case of 14.85-Mev neutrons it is shown that the majority of pulses of low light-output are due to α particles produced by neutron interactions with the carbon and that structure is apparent in this α-particle spectrum. α-Particle groups due to the C12(n, α)Be9 reaction and to the breakup of C12 from its excited states at 7.656 Mev and 9.63 or 10.1 Mev are identified.

Studies of nuclear collisions involving 8 MeV deuterons by the photographic method II. The energy of the excited states of 17 O

1951 ◽  
Vol 209 (1099) ◽  
pp. 478-488 ◽  
Keyword(s):  
Excited States ◽  
Ground State ◽  
Primary Beam ◽  
Photographic Method ◽  
Nuclear Collisions ◽  
Good Agreement ◽  
Α Particles

The apparatus described in part I has been employed to determine the energy of the excited states of the nucleus 17 O by observations on the protons from the reaction 16 O ( d , p ) 17 O, and on the α-particles from the reaction 19 F( d , α) 17 O . The protons from the first reaction were observed a t five angles of emission with respect to the primary beam, and the α-particles from the second at four angles. Thirteen excited states of 17 O were observed, evidence for ten of which was given by both reactions. The values for the energy in the different excited states, derived from both reactions and at different angles of observation, are in good agreement. The Q -values of the reactions 16 O( d , p ) 17 O and 19 F( d , α) 17 O , in which the 17 O nucleus is formed in its ground state, are 1.928 and 10.042 MeV, respectively. The Q -value for the reaction 16 O( d , α) 14 N was found to be 3.09 MeV, and the existence of two excited states of 14 N was established. Ten excited states of 20 F were observed in a study of the proton groups from the reaction 19 F( d , p ) 20 F.

Réactions 3He + 9Be, d + 10B → 3α et excitation du 12C dans la région 29–34 MeV

1977 ◽  
Vol 55 (23) ◽  
pp. 2113-2120 ◽  
Author(s):  
G. Goulard ◽  
R. Roy ◽  
R. J. Slobodrian
Keyword(s):  
Excited States ◽  
Energy Region ◽  
Energy Spectra ◽  
Two Stage ◽  
Final State ◽  
New Information ◽  
Stage Process ◽  
Α Particles

Excited states of 12C between 29 and 34 MeV are studied through the 3He + 9Be and d + 10B reactions leading to three α particles in the final state. Correlated energy spectra are analyzed with a two-stage process and new information is given about the studied excited energy region.

scholarly journals Molecular bases for the selection of the chromophore of animal rhodopsins

2015 ◽  
Vol 112 (50) ◽  
pp. 15297-15302 ◽  
Author(s):  
Hoi Ling Luk ◽  
Federico Melaccio ◽  
Silvia Rinaldi ◽  
Samer Gozem ◽  
Massimo Olivucci
Keyword(s):  
Excited States ◽  
Sequence Divergence ◽  
Evolutionary Transition ◽  
Structure Changes ◽  
Bovine Rhodopsin ◽  
Key Factor ◽  
Pcc 7120 ◽  
Molecular Bases ◽  
Amino Acid Sequence Divergence ◽  
Selection Of

The functions of microbial and animal rhodopsins are triggered by the isomerization of their all-trans and 11-cis retinal chromophores, respectively. To lay the molecular basis driving the evolutionary transition from the all-trans to the 11-cis chromophore, multiconfigurational quantum chemistry is used to compare the isomerization mechanisms of the sensory rhodopsin from the cyanobacterium Anabaena PCC 7120 (ASR) and of the bovine rhodopsin (Rh). It is found that, despite their evolutionary distance, these eubacterial and vertebrate rhodopsins start to isomerize via distinct implementations of the same bicycle-pedal mechanism originally proposed by Warshel [Warshel A (1976) Nature 260:678–683]. However, by following the electronic structure changes of ASR (featuring the all-trans chromophore) during the isomerization, we find that ASR enters a region of degeneracy between the first and second excited states not found in Rh (featuring the 11-cis chromophore). We show that such degeneracy is modulated by the preorganized structure of the chromophore and by the position of the reactive double bond. It is argued that the optimization of the electronic properties of the chromophore, which affects the photoisomerization efficiency and the thermal isomerization barrier, provided a key factor for the emergence of the striking amino acid sequence divergence observed between the microbial and animal rhodopsins.

scholarly journals Correlation between Osmolarity and Luminescence of Symbiotic Vibrio fischeri Strain ES114

2004 ◽  
Vol 186 (9) ◽  
pp. 2906-2908 ◽  
Author(s):  
Eric V. Stabb ◽  
Melissa S. Butler ◽  
Dawn M. Adin
Keyword(s):  
Vibrio Fischeri ◽  
Culture Media ◽  
Light Output ◽  
Euprymna Scolopes ◽  
Low Light ◽  
Luminescence Enhancement ◽  
High Level

ABSTRACT Vibrio fischeri isolates from Euprymna scolopes are dim in culture but bright in the host. We found the luminescence of V. fischeri to be correlated with external osmolarity both in culture and in this symbiosis. Luminescence enhancement by osmolarity was independent of the lux promoter and unaffected by autoinducers or the level of lux expression, but the addition of an aldehyde substrate for luciferase raised the luminescence of cells grown at high and low osmolarities to the same high level. V. fischeri culture media have lower osmolarities than are typical in seawater or in cephalopods, partially accounting for the bacterium's low light output in culture.

scholarly journals Space Charge Fields in the Development of a Townsend Discharge in Nitrogen

1969 ◽  
Vol 22 (4) ◽  
pp. 447 ◽  
Author(s):  
AA Doran
Keyword(s):  
Light Intensity ◽  
Electric Field ◽  
Space Charge ◽  
Applied Electric Field ◽  
Dominant Role ◽  
Light Output ◽  
Exact Relation ◽  
Townsend Discharge ◽  
Discharge Gap ◽  
Infor Mation

As the CUlTent through a spark rises into the milliampere range, ionization due to fields produced by space charge plays an increasingly dominant role. Infor� mation on these fields can be obtained from analysis of the light intensity emitted at different points along the axis of the discharge. In an earlier publication (Doran 1968) photomultiplier records of the light output obtained at various times during the growth of a Townsend discharge in nitrogen (pd = 600 torr cm) were analysed by an approximate method. In the present paper a more exact relation between the light emitted and the variation in local electric field is derived, enabling the previous results to be re.analysed. This has provided a quantitative picture, spatially and temporally resolved, of the development of these fields, which are associated with luminous fronts observed to propagate back and forth across the discharge gap. The magnitude of the field variations is in general about 10-20% of the applied electric field.

Suppression of BaF2 Slow Component of X-RAY Luminescence in Non-Stoichiometric Bao.9R0.1F2.1 Crystals (R=Rare Earth Element)

1994 ◽  
Vol 348 ◽  
Author(s):  
B.P. Sobolev ◽  
E.A. Krivandina ◽  
S.E. Derenzo ◽  
W.W. Moses ◽  
A.C. West
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Earth Element ◽  
Dopant Concentration ◽  
Slow Component ◽  
Light Output ◽  
Fast Component ◽  
Significant Suppression ◽  
Low Light ◽  
X Ray

ABSTRACTA series of BaF2 crystals doped with 10% mole fraction of each rare earth element has been grown, and the effect of these dopants on the slow luminescence (due to anionic self trapped excitons) and fast luminescence (due to core-valence transitions) has been studied. While significant suppression was observed for both components, the best dopants for suppressing the slow component of barium fluoride (up to 25-50%) while maintaining the luminosity of the fast component are La, Y, and Lu. The luminescence of Ba0.9Eu0.1F2.1 is almost entirely fast (>90%), but with low light output. For two rare earth dopants (La and Gd), the effect of slow and fast component suppression was studied as a function of concentration (Ba1-xRxF2+x with x≦0.5 for R=La and x≦0.3 for R=Gd). The suppression is non-linear with dopant concentration, with the relative degree of slow component suppression correlated with the melting point of these samples.

scholarly journals A study of fluorescent lamp stability at very low light output

1991 ◽  
Vol 75 (Appendix) ◽  
pp. 53-53
Author(s):  
Atsushi Ueoka ◽  
Akio Okude ◽  
Yasushi Kanbara ◽  
Masataka Mitani
Keyword(s):  
Light Output ◽  
Fluorescent Lamp ◽  
Low Light

Non L.T.E. Properties of Quasistationary Oxygen Plasmas

1976 ◽  
Vol 31 (3-4) ◽  
pp. 362-368 ◽  
Author(s):  
M. Cacciatore ◽  
M. Capitelli
Keyword(s):  
Excited States ◽  
Cross Sections ◽  
Ground State ◽  
Radiative Recombination ◽  
Local Thermodynamic Equilibrium ◽  
Collisional Radiative Model ◽  
Radiative Model ◽  
Ionization Coefficients ◽  
Selection Of ◽  
The Continuum

The non L.T.E. (local thermodynamic equilibrium) properties of optically thin and thick quasistationary oxygen plasmas have been calculated for the temperature range k T = 0.5 - 1.5 eV and for the electron density interval 108 - 1016 cm-3 , by using the collisional-radiative model of Bates, Kingston and McWhirther. The results include1 the coefficients r0(i) and r1(i), which represent the contribution to the population density of the ith quantum level from the continuum and from the ground state, respectively2 the values of α and S, which are the collisional-radiative recombination and ionization coefficients, respectively. The accuracy of the present results is discussed in connection with the adopted plasma model and with the selection of the collisional cross sections for forbidden and allowed transitions. A discussion is also presented of the influence of the two low lying excited states of oxygen atoms (i.e. the states 2p41D, 2p41S) on the non L.T.E. properties of these plasmas. A satisfactory agreement is found with the calculations of Julienne et al. and with the experimental results of Jones.

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