Improvements of electrospraying technique

NUCLEAR ITSSTRUTAENTS AND METHODS

32 (ig6s) 355-356 ; C(.) NORTII-HOLLANI) PtIBLISUING CO .

IMPROVEMENTS OF ELECTROSPRAYING TECHNIQVITIF G. BERTOLINI, G . DE PASQUALI* and R. FANTECHI Nuclear Chemistry Lab., Euratom C.C.R ., Ispra, Italy Received 7 December 1964

Thin uniform deposits of radioisotopes for beta spectrometry or alpha-gamma angular correlation are in general made by vacuum evaporation or electrospraying. We have tried to improve the electrospraying technique first proposed by Carswell and Milsted') and developed afterwards by Bruninx and Rudstam'). We use hypodermic needles') instead of glass capillaries and a coneshaped electrostatic collimator, developed from the wire-ring collimator first proposed by Bertolini and Fantechi') . This modification was due to the necessity of a better focusing . As an intermediate step a system of two or three wire loops was tried and discarded because of difficulties of having the loops perfectly coaxial. With the new device we were able to concentmte radioactive deposits within a controlled, circular arev,. The size of the sprayed area depends on the flow rato and the applied field at the needle and at the collimator . Using a constant applied voltage the area of the depos,t is proportional to the flow rate of the liquid thr~,ugh the needle . To regulate the flow of the liquid we were using a tungsten wire having a carefully electroshaped and polished tip. The wire was fitted into the hollow of the needle : lowering or raising it by means of a screw (fig . 1) made it possible to a4just the flow. The end of the hypodermic needle was ground flat and polished, since it was observed that pointed needles and needles having a rough surface gave raise to discharges. The connection of the glass part ofthe apparatus to the hypodermic needle was niade by grinding tile glass wall to a cone and fitting the cone with a polyethylene sleeve . The collimator consists of a lucite screen having a Cn conc-shlatpeU, gollup'lateu holle. 'it iS i111pul-tuill to Iidvu the collimator weil centred with respect to the ground plate. Otherwise the deposits are off centre and on rotating the ground plate inhomogeneous deposits are obtaino-i. Under our conditions the homogeneity of the dcposits is only slightly improved by rotating the ground plate. To check the performance of the spraying apparatus we used as an emitting isotope Pa 233 in a methanol

-1

On leave of absence from the university of Illinois .

L1.1 _el 1 -7777 LUCITE - COLLIMATOR VYNS FOIL METAL

OR

DISC

GRQUND

PLAT.-E

Fig . 1 . Sketch of the apparatLIS.

solution . The glass container of the apparatus was first filled with clean methanol and the rate of flow adjusted so that the recording amp&emeter displayed a steady current . Then a measured amount of the Pa solution, usually 50 pl . was added . After the active solution had A -- I - -

-I - __ __

-- - - I-

-- -I

Lil ill IICU 41ACZ 1,11 HIC1.11dilul xvash

could

&)kvii

the

observe

dispersion

methanol

of

inside

wd~~

retained

the

the

- - ---

__ _!

and

beginning C_

active the

A - A .-

absorbed

and

solution

glass

_1

dukilcu i it

:

the

when

container

po! k lvlf~

activitv .

ending

of

the volume

and

inside

tv

We the

of

the

needle ~vas totally dispersed, a step raise, from 0.02 to 0.05 yA, was evidenced on the recorder. Likewise when tile clean wash solution was beginning to be dispersed . the current dropped to the original value. Since we were using solutions of Pa 213 obtained by

355

0. BERTOLiNi

et al.

Fig., 2. Some profiles of sources -

not sewrated Rom me target 0 and iO%, depe-,nding .pn the : am~o t.,of methwftol I

raise must be relate.4 . to the~ usedfor draining'and desorbing the actiyfty.,~ in the s6lution. Experiments To test 4hei homogeneity -and the extension of the on to try to find a correlation active area or~ the,- fbils. 4, spedMy, built pr, portiotW the ionic concentration of the counter was used, - by - wAf - fhe activit~ of the source WIVti was measured along a diameter of the VYNS foil W collected on a 10 jjg/cm2 VYNS through a I mm hole in a brass plate tbick 4 mm. VI Ma Oth 10 P"2 gold . Some results are shown in fig. 2. Radioautoradio . ~_ing an applied voltage of 6500 V on the needle, a graphy, also tested, gave poor results. ,e of 4200 V and a flow rate such as of a=15 a, the obtained pa 233 RefereUM Wamear of 3 to 4 mm . Varying the

coffimator thw size,, -of the , vmed withincertain hinifs we;t thf-

an

at-t4u;tu die

ICIG

*

kn

14 varied betwee

I

D. J. Cars~vel~ and J. Milsted, J. Nuclear Energy 4 (1957) 51 . ~) E.Bruniax~arI4 0. Rudstam, Nucl. Instr. and Meth. 13 (1961) ') AVA. r% ; A~ULWUU Unq a- %Y4 MMOII"'f 'j . 4. 1 G Dertolin 'P Cap "an 0

4

;

;

Instr. and MeOL 27 (1964) 281 .

110IG b , L5 tly3a) IV'7. A r-- )o-m xt i