Classified Abstracts 344--349

Classified A b s t r a c t s

Abstractmg Editor's Note. The label munedtately following the title oJ each item denotes country o f origin o f pubhcatton, and that at the end o f each abstract mdwates country oJ origin o f u ork (where known).

Genera l V a c u u m Science and Engineer ing

10. V a c u u m Sc ience and Techno logy

lO 21 344. The pumping speed of titanium sputter pumps in ultra-high vacuum. ( Get ma~t~ ) In the pre~sure ranges of lO ~and I0 ~t'torr t h e p u m p l n g s p e e d o l a t i tanium sputter pump is measured by comparr.,on v, lth the k n o ~ n conductance of a dmphragm After s~mple bake-out an ultimate pressure ol 5 10 ~'' torr ts obtained The pumping speed, ho~,,e~er, m tile Io~er pressure range,, [s nouceabb reduced compared to that of a d~ffus~on pump The performance of a sputter pump ~s considerably improved b2, a short mject~on of argon After that t reatment the u lumate pressure drop~ to 3-7 10 ~ t o r r a n d t h e p u m p m g s p e e d c h a r a c t e r ~ t l c t ~ q u a h t a - t l v e l y t h a t o l a diffusion pump A ~trong ume dependence of the pumping speed is observed ~,~hen tile gas m.lectlon i,, kept con- stant In the range of l(I -~' torr, it takes about 24 hours for equlhbr lum to be reached The gas b a c k s t r e a m m g o l the~put te r pump ~s--ln ~_ontrast to a diffusion p u m p ~ b o t h pre.,,sure and time dependent The reduction ot the pumping speed of a pump before it has been argon treated is related to the observed reduction of the intensity, of the ga~, d~scharge belo~ ~ 10 " torr (S~tit_-erlalldl I ~uthor l

E F~scher 2rid Furopean [a~ S3mp. 5-7 June. 1963. 261-265 Rudolph A Lang kerlag, Esch(Taunt t s l

11. Product ion o f L o ~ Pressure

11 21 25 345. Desorptmn experiments m an ultra-high ~acuum s~stem, pumped b) molecular s]ese trapped od diffusion pumps. ( Ge~ m a n ~ ) In an ultra-h~gh ~acuum s~stem pumped by oil d~ffuslon pump~ with molecular siege traps the ~on current of a gauge gt~es no indication of the contaminat ion of the s~sten't b} adsorbed od molecules and their crack product,-, At Io~ coverage the number of backstreamed od molecules Js measured alter a certain pnmplng time b~ isolating tile ~3stem l rom the pumps and b', a thermal desorpuon of the adsorbed molecule~ From a number of such desorpt lon c~,cles a hnear increase of the coverage with oil molecules in the first ~eek,, ~s deduced ~htch gl~es a contamina- tion rate of 10" tool c cm-" da3 for a carefull.~ dega,,sed laborator.,, set-up IGe~man~l ( Author}

S Garbe 2nd Emopean lac Slmp 5-7 June. 1963 295-304. Rudolph A Lang \ e r l a g E~ch(Taunu~)

12. Measurement o f L o w Pressure

12 22 61 Problems in establishing standards for vacuum measurement and m calibrating ~acuum gauges. See Abstr No 449

12 14 16 346. The calculation of the pressure distribution in vacuum systems, taking into account adsorptmn and condensation. (Germany) in a high or ultra-high ~acuum system, the quantlt~ of gas adsor-

bed b.~. or loosely attached to, the ~all~ generalb exceeds by far that r emammg free in the enclosed volume The au thor investigates the influence of the adsorbed ga~ on the pressure distribution existing in long tubes, making use of a simplified form of the d~fferenttal equat ion for the diffusion process Specific solutions are g~ven ~hlch after generahzatton to other s2~stems ot different geometry can be u~ed t\,r the e ' ,a luauon of the time constant of pressure equahzatlon, the calculation of flow impedance and cold trap effic~enc~ ( Germam l w J s

J Neubert , I aAattt~l Techm~ 13 ( I ) Feb 1964, 19-23

12 61 347. Units in ~acuum measurement. (Great BtHam) The term pressure " begins to lose its con,.entlona[ meflnmg s o m e ~ h e r e m t h e , . e r } hJghxac t lumreg lon If ~e could construct an ~ontzatton gauge of absolutel,, known samphng el~c~ency it would be an absolute gauge ~hlch could be cahbrated to read molecules cc From the fact that at a pressure of 760 tort , there are 6 02 IO t-' molecules.mole 1 molecule. M ~ corresponds to a " pressure ol 2 83 10 --'~ torr The au thor suggests the use of a logarithmic dens[t~ scale ~ t h a zero at 1 molecule.'M" A pressure ol 1 10-" torr ~ould then correspond to 16 55 log denstt.,, umts Other ~alues are gt~en belo~

Pressure m tort 760 1 10 ~ 10 ~ 10 -~ 10 -~-' log dens[t'., st.ale 25 4~ 22 55 19 5", 16 55 13 55 10 55

For certain purposes (residual ga,, analys~ ere I a hnear densJt,, scale m~ght be prelerable But ~hate ' .er the final choice, the au thor i% ol the opinion that the basic '.aCt.lum unit in high ".,aduunl ~ork should be one of molecular den~H3 rather than pressure

~A J S F T \~,orrel \atute. 199 (4~921 '~ Aug 1963 476

12 61 348. Units of ~acuum measurement. ( G ~ e a t &tram) The author refers to pre~lou,, proposals ol a logarithmic denslt~ ~cale (see Abstr No 347 abo~e) and proposes a logarithmic pressure scale ot his o ~ n defined by p.t = - l o g , . rpres~ure in atmo,,pheresl Thl~ leads to the follo,~ mg relatl~,e value,,

Pressure m t o r r 760 l 10 a l0 " l0 9 10-t_, p4 0 2 9 59 8 9 119 149

T h ~ scale has the advantage of increasing ~ [th increasing vacuum and being restricted to small numbers Moreover it is related to the simple mercur~ manometer , the readmg~ ot ',~hlch unhke those of the ionization gauge or mass ~pectrometer are Independent of the gas they measure and in~anant from da} to da~ It must be emphasized hov, e~er. that logarithmic ,,tales. ho~e~er convenient and neat they ma~ be m describing the state of a vacuum s~stem are of httle use in vaLuum engineering, conductances, etc In these case.-, the customar2, hnear scale is still m,,aluable

~.~. J s J Cuthbert , Nature, 201(4914) ,4Jan 1964 61

349. Theory of linearity of hot cathode ,onizatton gauge. C Y H'.,.a, ActaPh~s Smtca, 19(2). 1963. 73-82

12 22 ( Clsma )

157