CA2131784A1 - Particle analysis and sorting - Google Patents
Particle analysis and sortingInfo
- Publication number
- CA2131784A1 CA2131784A1 CA002131784A CA2131784A CA2131784A1 CA 2131784 A1 CA2131784 A1 CA 2131784A1 CA 002131784 A CA002131784 A CA 002131784A CA 2131784 A CA2131784 A CA 2131784A CA 2131784 A1 CA2131784 A1 CA 2131784A1
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- neutron
- isotope
- sample
- gamma
- energy level
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Abstract
ABSTRACT
The invention relates to a method and apparatus for analysing samples for the presence of a particular element or isotope. In the method a pulsed neutron beam is directed at the sample. The beam is at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable gamma spectrum. A gamma detector detects the neutron-induced gamma spectrum. The detector is time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded.
Analysis of the spectrum enables a determination to be made as to whether a spectral peak characteristic of the particular element or isotope is present. The invention also provides apparatus for carrying out the method.
The invention relates to a method and apparatus for analysing samples for the presence of a particular element or isotope. In the method a pulsed neutron beam is directed at the sample. The beam is at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable gamma spectrum. A gamma detector detects the neutron-induced gamma spectrum. The detector is time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded.
Analysis of the spectrum enables a determination to be made as to whether a spectral peak characteristic of the particular element or isotope is present. The invention also provides apparatus for carrying out the method.
Description
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TE~IS ilIve3~tioll r~l~tes to parucle an~lysis ~d sor~g ~el;~on acdqation allalysis is a well~ wn technique ill whi~h, typical~, a s~nple ~Jf a ~ew ~niIligrams m~cs is subjected ro a hi,l~b flux or intensity of ~ermal or low ener~- neu~ons fro~n a nuclca~ T~to}. Ihc radioac~ve sample is ~en ~ansportcd to a mc:as~ement station where a ga~una emiss~o~ ~cLl~ is collected. Each ~vate~ ~sotope m the sample gr~es one or more peilks in ~e spectrum, fi:om whi~ ~he elcmelltal concentr~tions present ~ lhe sample can ~e determ~ed By way of ex~le, US pat~nt ~,340,443 to Clayton et al di~closes a tec~ e fo~ dete~n~n~ng tbe g~ld conterlt a~ allrif.erous ro~ic sampl~s.
In the ~anique, the 5~ le is bon.bardcd w~1;h nentrons a~d there~er the i~tensiy of tbe cmit ed gamma spectrum at an eIler~y level of 279keV is delermi~d to give a me~sure of the gold concen~ n in the : :
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a ~ S ~ a a Sl~l~OR & F' ' Si~ER _ __ _~
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TE~IS ilIve3~tioll r~l~tes to parucle an~lysis ~d sor~g ~el;~on acdqation allalysis is a well~ wn technique ill whi~h, typical~, a s~nple ~Jf a ~ew ~niIligrams m~cs is subjected ro a hi,l~b flux or intensity of ~ermal or low ener~- neu~ons fro~n a nuclca~ T~to}. Ihc radioac~ve sample is ~en ~ansportcd to a mc:as~ement station where a ga~una emiss~o~ ~cLl~ is collected. Each ~vate~ ~sotope m the sample gr~es one or more peilks in ~e spectrum, fi:om whi~ ~he elcmelltal concentr~tions present ~ lhe sample can ~e determ~ed By way of ex~le, US pat~nt ~,340,443 to Clayton et al di~closes a tec~ e fo~ dete~n~n~ng tbe g~ld conterlt a~ allrif.erous ro~ic sampl~s.
In the ~anique, the 5~ le is bon.bardcd w~1;h nentrons a~d there~er the i~tensiy of tbe cmit ed gamma spectrum at an eIler~y level of 279keV is delermi~d to give a me~sure of the gold concen~ n in the : :
., .r i.~ ,g~ ~ggg~g~ V~g ~ r-~
a ~ S ~ a a Sl~l~OR & F' ' Si~ER _ __ _~
.. i ~J i. ~' i3 ~
It is ~mown ~ gamma rays call ~ ernitted prompt3y by carbo4 nuclei irrddia~d wi~h ~eutror~s either ~hen ~he neutron~ a~e captured in the ~bo~ dei or when hi~ ener~y, typic~l~y greater thall 4~5MeV, neutrons are i:~ela~cally scattered at the nuclci In this re~ard, ~outh A~ica~l patem ~/6868 dis~loses the use of hi~h ene~y neutron bomba~dmenl ~o~ the co4rinuous on-llrle evaluation of the q~ty of b~ c coal samples. ~he paten~ discloses the use o~ compo~, te sau~ ion detectors, ie. detector:~ ~ade up of a phlrAli~y of s~ llators t~ detect primary a~d related secondary events. However because thc typc of analys~s disclosed in the patent operates at a low lcvcl of sensitiv~ty~
application ~s probably l~mited ~o evaluation o~ ~al samples w~ere ~ere 3 Is a m~b carbon contellt, typi~:al1y greater tban 505~. It is believed tha~
it would be un~itable for a~ly~is of, say, diarnol~d content i~
l~n~erli~ ores l~e~u;lse of the low G3~00n~dlamond coIItent of t~e san~le.
. ..
Added to ~s~ a problem encountered ~ll thc prior art techniques is that of isolat~ng ~e ch3~acteristic ~cc~um of a paI ticular element or i~otope ~om the back~round ~lo~se~ at least part of whi~h is produced by nehtrons scattered by ~e sall~le und~r ~ ;is.
=~_ ' .
Acco~g to a ~r~t aspect of the înve~tion ~here is pravided a me~hod of aDalysin~ a samyle for the pr~sence therein of a particlllar element or isotope, the method comprising the steps o .
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ll~,'O~ P~ SPi:)~Ji~ ~ ~ ISilLk ~ A ~
- d~re~ting a~ ~:he s~mple a pulsed neu~on beam ~t an energy level c~osen for the neutro~s to interact wit~ the element or 3sotope a;ud produc~ a detectabie gamma spectrum, - detec~ng t~e neu~ro~a-induced gam~a spectmm by n~eallS of gam~nR detection appara~s wl,ich is ~ne~tcd in such a m~er that neu~on-inducca gamn~a radiation is detected wh~e nentrolls scattered by the sa~ple are al leasc substaDtia~ly exe]udcd~ and - determint~ whether a spectr~l pea~c cbaracteristic of the particular elemellt or isotope is prese~t in thc g~mm~ spectrum.
A~ord~g to a seeo~d a~ect of thc i~ven~o l, there is p~ovided appa~tus for ana~ a sample ~or the presence therein of a par~
ele-n~r~ or ~sorope, the ap~a.~dt~s compnsmg - a neutron solLr~e for direc~ at the sample a pulsed neutron be~ at ~n ener~ level c~osen for the ncutrons to i4leract wi~
t~e e~r~er~t or ~otope ~d produce a detectable ga~ma - dete:c~on ~ne~ or de~ecting ^.be neul:ron-indnced g~mma spec~ the detecti~m ~eans being t~me-gated in s~lch a r~nner ~ eutroll-mduced ~mrn~ ~ad~ation is detected while neU~o~s sc:attered by the sa~plc are al lcast subsrantially excl~ded~ aud .~
U~ 5 '~`~ `lY~ SP~ `lSilE~ JU
,~ ~ ;J i i (~ 'J
- me~s for ~eterm~g whether a spe~ral pea~ charae~er ~c of the pa;~cu~ar- clemer~ or isotope is presem irl tbe gamm~
spec~um.
T~e neu~on ~e~ îs prefer~bly mo~o-energetic or at lea~t ~as a well-de~ned ener~y ]~vcl. C~ne ~pplic~tioll oi tbe n:~ethod a~d apparanls of ~Pe inveD~on is ~n the a~ysis of l~m~erli~e samples for the pr~sence of car~o~ dlc~ti~re of a d~ 0nà mclusio~ e sa~ple. ~ this case, the neu~on beam m~y have arl en~rgy level i~L the range 4Me~ to lO~e.V, preferably 6MeV to ~Me~ mo~ pre~erably about 6,3MeV.
The nlet~od ~d appar~n~s of the ~ention ~y fo~ par~ of a p~icle so~ ,ystem i~ wh~ch par~cles are allalysed or~-linc; and partic~e~, for wh~ch the ga~:~la spc~ i:~lcludes a spec~ral pealc characteris~c of the partlc~l~r ~leme~t or isotope are se.parated f~on:~ othe~ pa~ticles.
BRIEF I~CRII~WZNGS
l~e i~Ven~aOL will now be descn~ed in mo~ detail~ by wa~ of exa~ple o~ly, wi~ refere}lce tO t~e accoTnpallyrng drawings"sl which~
Fl~re 1 L~a~atically illustrates the princi~ ; o~ ~}e . in~e~ltion;
ESg~e 2 di~g~Dmalicallyi ustratesclecllonic~mpos~en~y used in the im~le~e~ on oft~e inven~or~ d , O~ 16 :16 ~u l l ~ 8 .SPOOR B~ FISHER 4~' U~
. ~ J.i. i '; -~
- G -s 3a and 3b show gamma spec~a obtamed fo.r a kim~erlite samp~e with a 175% cari~on content b~ ~ss.
~PECIFI~ DE~scR~ o?~
Re~elIill~, ~o Figure 1, a neutron ~n 10 is dile~ed ~om a source 12 onto a ~imberlite sample 14 whicb is to bc analy~cd for thc presen~e of di~smond l~e neutron b--~m is produced by ~ccelera4ll~ a pulsed particle beam and d~rec~n~ it at a deuterium gas target, thereby causing deuteron~ienterorL reaf~tions irl the ta~OeL This gives rise to a pulsed neutron beanL Tbe particle bea~n m~y, for InsT~ce, be accelera~ed usi~g a r~ uency quadrupole (RFQ) accelera~or `: :
~ plas;tice, it i~ desilable for the neutron be~L LO be pulsed in }~ d ~ a~d ~or ~e n~utro~ls to b~ fast, mon{~energe~c ~eutroDs with a hi~;h energy level ~ypically in the r~nge 4MeY lo lOMeV
and mosl prefe~bly in tbe range 6MeV to 8MeY A gas targe~, such a~
the deuten~u ~s ta~get meIltioned above, is co~s~dered preferable to a sol~d tar~et in the produc~ion of a neutron bcam w~th these char~Lcteristics~ The use o~ a de~lteron~euteron reac~on in a gas wget provides a mon~nerg~c neutron beam tha~ can be m~t~hed to gLve a high level of se~ y for ~e cha~acteris~c peak of t}~e ele~ent or ~sotope of interest. Irl the presenr case, where rhe Isotop~ o~ int~resr i~
~oll-12, rese~cb by tbe i~velltors indicates t~at tbe appropriate eut~on be~n ener~ level is ~bout ~,3Me~.
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The incident llentrons pene~ e the k~berlite sal3~ple 14 and iIlteract with ~he nuclei of ca.-bon atoms in a~y diamona p~ides I the sarnple.
A hi~h pL~rity ~ermanium gamma delec~or 18, shielde~ ~om receivillg dire~ r~ ion from the soulce 12 by ~ neutron shield æ. receiq~
~amma radiation 20 emitted by ~he sample 14 and forms a spec~n~n ~om ~he radiation rece*ed wit~Jin a predetermiued time arltelval. The ~pe~um, ~lusb~ated ~iagrarnmatically at 24 in Fi~ure 1, is aDalysed by a cor~u~ (not shown) which compa~s it with standar~ data to det~ine whether the spe~unl Is ~ndicat~ve of the presence of carbon-12, in turn irldi~ive of diamo~ld, in the saulple.
If one or more diamond parucles are present i" the kimb~rlite sample, a chalacteristic pealc w~l be obser~,ed in the dete~ed gs~Tnma spec~
at the a~propriate energy level eor carbo~-~ Le 4,43MeV The spectral pea}; ~ supernnposed on a p,ellera~ bac3;g~owld attr~ ulable at least partially to aeu~ron~ ffered by t~e s~mple 14 whieh reach and interact with th~ g~nma dete~tor 18. The background spectrum detected ~3y -the dete~tor 18 may he such as to immerse t:he charactens~c carbon-12 pe~c i~di~ve of diamon~
'rO reduce the effe~: of backgroLmd radiation in the detected spec~um.
relia~oe ~s p~aced u:pon the differeDt speed~ at ~vhich ~eu~o~ and gamn:~a ra~a~ion travel from ~he sample to ~he detector. Ga~nma r~on ~ravels at the speed of li~ht ~om the sample to the delector w~e neutron~ scar[ered by ~he sa~ple ~owards the detector travel somewhat slower. For e~amplc, thc timc dclay ovcr a distauce of lm for ~mm~ r~dia~o~ and ~eutro~s at an crler~y of 6,~M~V is a~ut 30 r~ds. i.e. 30 x 10-9s.
I!~ U~1 1~ I 1; :1; '~(I I I S~ uh o. t I .S H~. K 1~1 1.11I) ' 8 _ , i.
In accorda~ce ~ith ~h~ Inve~ltio~ Xin, use o~ fast ele~tror.ie pro~essing apparatr~ te gam~ta deLee~ioll sy~ter~ me-~ted ~o ~at the detector is cnabled du~ the ti,~e peri~d that ne~ron-induc~d gamma rays re~cb. the detector, alid the~ disable~d by tht time the ~ca~tered neu~ons amve. In ~his way, ba~kground noise at~uta~le to stray nwtrons sc~tered by the san~le 14 can ~e elin~a~e~, or at least redu ;eL Fgure 12 dia~atically ~ 3strate~ tbe electro~c compo~e~y used lo achieve the rlece~v time~ting, Refer}ing to Fig~ a portion 30 of ~he sign31 produced by the ~e~u~ dctcctor 18 ~s direc~ed via a sig~l amplifier 34 to a lin~3~r gate ~retc~er 48. 'rhe remaindcr 38 of the signal is dLrected ~om ~c detector 18 to a ~imin~ filter a~plifier 40 which in tun~ feeds the signal tG a ~t frdction delay u~i. 4~ '~he unit 4, applies a time delay 44 tO the s~ l wherea~er the ~ignal is fed to a t~e to pulse hei~t corsvert~ 4~.
A~ the same timet a beal:n pick~of~ signal 50 is ini~ated by a beam pi~-off uni~ 5Z which ~irects the 9gllZ.1 to a tirning fi~ter a~npl~fier 54. The ampl~fier ~4 feeds the signal to th~ ~me to pulse height converter 46. I~
~sse~e, ~e be~m p~ ff ~gnal Sta}lS a ciock which controls a ~me ate. The cor~verted signal controls lhe l~ear ~d~e stretche~ 4~, openinO
~he ~me gaIc for admission of an amplified spe~,~osoopv si ,nal 37 fro~
the am~fier 34 to a mul~ch~el analyser 36.
Thus p~lses from the amplifier 34 will oDly be registeI~ed by the ~ltichan~el analyser i~ ~hey ~ppear inside ~e relevant, predetermined timo pe ~od, ... _ _ ______ ...... , .. ,_.. ,,,, ... _ ~
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'J11 t~ J'd S~'IJi~K ~ I!LK 4~iU11 - ~ ? ,! ~ .
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_ g _ Exper~menta~ion by the inventor~ indicates that the time~at~ng techr~q~e de~nrbed above bas the e~ect of Sllpp:le55illg the baekgrouDd radiation or naise l~is is i~ s~ated by a oompa~r~so~ of Figuresi 3a a~d 3b i~ wbi~h logarithmie count ~cquen~y is plot~ed on the ver~ic~ ax:is ag~irst ~h~el valu~s represen~alive of energy level o~ tbe ho~i70ntal a~is. Figure 3a ~lustrates a gamma spectrum in which no time-gating bas been employeLi Tbe 4,43MeV peak 60, inidicatIve of the priesence in the l~mberlite sa~ple of i~rbon-~2 and hence d~nond, ~s m~sked to a large d~ree in the b~:kgrol}~d r.oise. Figure 3b illus~rates a corresponrling gamma sipec~ obt~ ed usirl~ timc~ated detec~on a~paranLs as d~bed. In t s case, a clear spec~l peak 62 is discermble a~ the cha~ac1el~sbc 4,43MeV ~r~y level of carbon-12, ~lear1y showing the suppfession of back~ouIId r~oise that is attri~table to ~me-v,a~g.
Ref~ g again to F~re 1 it wil1 be lloted that the gamma delector 18 i~ positio~ at a }eversc a~gle relative to the incident nelltron 1~ 10.
It is belie~ed ~at ~is geomel!y wflI give nse to an optima! si~nal to ~ois~ ratio. The sha~e and alTan~ement o~ the neutroll shield .Z2 Figure 1 are slso considered ~o be impo~an~ fearures, in that the shield shotlld prevent a~y direct passage of the neutron beam 10 ~om abe ~ource 12 to the detector 18.
At t~e s~me time, as ~uy neutrons as posslb1e ~hat ale scattered l~y the sam~le 14 shonld be divert~ away from the detector rather d~an towards the de~ecr~r. For ~ese reasons, the shield 2~ h~s the illus~ted ~iangllar cross section and the apex 80 ~d3ereof does llot extend fc~wardly i~o the field of v~ew of the dct~tor where it might d~vert neutrons u~wards the detector.
.' I)~ U~ U 5~'0(11~ & I:lS~ '4'1UI.
.
~, ` j `,i,~,'l Spe~G mention has ~een ~ads of analys~ng a kim:~r~i~e sample ~or the pres~nce of carbon-12 and hence of diamon~ Hnwever it will be appr~d tha~ prirlc~ples nf t:he ~vention have ~ar wider a~?plicatio~ Fo~ iu~oe ~e ~echn~qlle of the inven~on could, ie is believed, be used w~2h good e~fect i~ the detection of ~bon and/o~
Q~;ygen în steel samples I~ sho~ld a~o ~e noted that while the abo~e descr~p~io~ is directed to the arlalysis of a single, stauc sample, the pIi~ciples of ~he ~hlvention are ~:q~lly aypl~cable to on-hne analys~s with a sue Lm of partîcles pa~si~
seq~lentially throu~h a detectio~L and analysis station. The ~veIItioIL
could for instanee be en~ployed in a p~r~cle sorting system in which, once a pa~licle has bee~ detected tha~ includes a desirabl~ elem~llt or iSOtOpe, suc~ p3rticl~ is automatic~lly ej~cted from Lhe particle strea~
T~is could ~e achieved usillg ~onventional ejec~on equLpm~nI such as gas blast or other ejectors to remove desir.Lble par~icles from the ~n s~eam ~r colle~on a~t ~ r~ other particles which are bar~en iIL
term~ their conterlt of the des~red element or isotope.
Irl tbe case of ~nberlite arlalysis a m~jor advantag~ of detecting a diamorld mclusior~ 3g ~e technique of the il~ve~ioII is that ~arren l~nberlite particles caII immediately be rejected without the rlecessît y for filrther p~oces~ng. Only p~dcles for whic~ a l?os~iti~ e ~nialysis iS
obmi!od ilr~ scI~d for 511~tOqu~=t pToCCssiD~.
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The :Inono~energe~c Or well~ei~ne~ energy level of th~ pulsed neutron ~e~m is prefe~ed since il enables the selectio~ of the app}opri~te ener~ vel f~Jr ~e elemem ~~ estion, thereby iIr.proving the se~sit~y of ihe sy~em. l~e pulsed na~ure of the ~ n results Lll t~e ac~:lm~on of repeu~ive d~ta whic3~ reduce~ ious backgroulld ef~eces The pu~sing vL 1he beam may ~e achieved in a conven~onal ma~er ~ing a br~m iotrrrllpr~r rf }3!0~ rype.
. I
. .... .... ., ,_ ,._.. _........ ... .
application ~s probably l~mited ~o evaluation o~ ~al samples w~ere ~ere 3 Is a m~b carbon contellt, typi~:al1y greater tban 505~. It is believed tha~
it would be un~itable for a~ly~is of, say, diarnol~d content i~
l~n~erli~ ores l~e~u;lse of the low G3~00n~dlamond coIItent of t~e san~le.
. ..
Added to ~s~ a problem encountered ~ll thc prior art techniques is that of isolat~ng ~e ch3~acteristic ~cc~um of a paI ticular element or i~otope ~om the back~round ~lo~se~ at least part of whi~h is produced by nehtrons scattered by ~e sall~le und~r ~ ;is.
=~_ ' .
Acco~g to a ~r~t aspect of the înve~tion ~here is pravided a me~hod of aDalysin~ a samyle for the pr~sence therein of a particlllar element or isotope, the method comprising the steps o .
: ~:
::
, :
.
..
ll~,'O~ P~ SPi:)~Ji~ ~ ~ ISilLk ~ A ~
- d~re~ting a~ ~:he s~mple a pulsed neu~on beam ~t an energy level c~osen for the neutro~s to interact wit~ the element or 3sotope a;ud produc~ a detectabie gamma spectrum, - detec~ng t~e neu~ro~a-induced gam~a spectmm by n~eallS of gam~nR detection appara~s wl,ich is ~ne~tcd in such a m~er that neu~on-inducca gamn~a radiation is detected wh~e nentrolls scattered by the sa~ple are al leasc substaDtia~ly exe]udcd~ and - determint~ whether a spectr~l pea~c cbaracteristic of the particular elemellt or isotope is prese~t in thc g~mm~ spectrum.
A~ord~g to a seeo~d a~ect of thc i~ven~o l, there is p~ovided appa~tus for ana~ a sample ~or the presence therein of a par~
ele-n~r~ or ~sorope, the ap~a.~dt~s compnsmg - a neutron solLr~e for direc~ at the sample a pulsed neutron be~ at ~n ener~ level c~osen for the ncutrons to i4leract wi~
t~e e~r~er~t or ~otope ~d produce a detectable ga~ma - dete:c~on ~ne~ or de~ecting ^.be neul:ron-indnced g~mma spec~ the detecti~m ~eans being t~me-gated in s~lch a r~nner ~ eutroll-mduced ~mrn~ ~ad~ation is detected while neU~o~s sc:attered by the sa~plc are al lcast subsrantially excl~ded~ aud .~
U~ 5 '~`~ `lY~ SP~ `lSilE~ JU
,~ ~ ;J i i (~ 'J
- me~s for ~eterm~g whether a spe~ral pea~ charae~er ~c of the pa;~cu~ar- clemer~ or isotope is presem irl tbe gamm~
spec~um.
T~e neu~on ~e~ îs prefer~bly mo~o-energetic or at lea~t ~as a well-de~ned ener~y ]~vcl. C~ne ~pplic~tioll oi tbe n:~ethod a~d apparanls of ~Pe inveD~on is ~n the a~ysis of l~m~erli~e samples for the pr~sence of car~o~ dlc~ti~re of a d~ 0nà mclusio~ e sa~ple. ~ this case, the neu~on beam m~y have arl en~rgy level i~L the range 4Me~ to lO~e.V, preferably 6MeV to ~Me~ mo~ pre~erably about 6,3MeV.
The nlet~od ~d appar~n~s of the ~ention ~y fo~ par~ of a p~icle so~ ,ystem i~ wh~ch par~cles are allalysed or~-linc; and partic~e~, for wh~ch the ga~:~la spc~ i:~lcludes a spec~ral pealc characteris~c of the partlc~l~r ~leme~t or isotope are se.parated f~on:~ othe~ pa~ticles.
BRIEF I~CRII~WZNGS
l~e i~Ven~aOL will now be descn~ed in mo~ detail~ by wa~ of exa~ple o~ly, wi~ refere}lce tO t~e accoTnpallyrng drawings"sl which~
Fl~re 1 L~a~atically illustrates the princi~ ; o~ ~}e . in~e~ltion;
ESg~e 2 di~g~Dmalicallyi ustratesclecllonic~mpos~en~y used in the im~le~e~ on oft~e inven~or~ d , O~ 16 :16 ~u l l ~ 8 .SPOOR B~ FISHER 4~' U~
. ~ J.i. i '; -~
- G -s 3a and 3b show gamma spec~a obtamed fo.r a kim~erlite samp~e with a 175% cari~on content b~ ~ss.
~PECIFI~ DE~scR~ o?~
Re~elIill~, ~o Figure 1, a neutron ~n 10 is dile~ed ~om a source 12 onto a ~imberlite sample 14 whicb is to bc analy~cd for thc presen~e of di~smond l~e neutron b--~m is produced by ~ccelera4ll~ a pulsed particle beam and d~rec~n~ it at a deuterium gas target, thereby causing deuteron~ienterorL reaf~tions irl the ta~OeL This gives rise to a pulsed neutron beanL Tbe particle bea~n m~y, for InsT~ce, be accelera~ed usi~g a r~ uency quadrupole (RFQ) accelera~or `: :
~ plas;tice, it i~ desilable for the neutron be~L LO be pulsed in }~ d ~ a~d ~or ~e n~utro~ls to b~ fast, mon{~energe~c ~eutroDs with a hi~;h energy level ~ypically in the r~nge 4MeY lo lOMeV
and mosl prefe~bly in tbe range 6MeV to 8MeY A gas targe~, such a~
the deuten~u ~s ta~get meIltioned above, is co~s~dered preferable to a sol~d tar~et in the produc~ion of a neutron bcam w~th these char~Lcteristics~ The use o~ a de~lteron~euteron reac~on in a gas wget provides a mon~nerg~c neutron beam tha~ can be m~t~hed to gLve a high level of se~ y for ~e cha~acteris~c peak of t}~e ele~ent or ~sotope of interest. Irl the presenr case, where rhe Isotop~ o~ int~resr i~
~oll-12, rese~cb by tbe i~velltors indicates t~at tbe appropriate eut~on be~n ener~ level is ~bout ~,3Me~.
: ~
.
, . .. ,. .... ~
u& ~ 16 ~~ U~ JUK ~ IU~
The incident llentrons pene~ e the k~berlite sal3~ple 14 and iIlteract with ~he nuclei of ca.-bon atoms in a~y diamona p~ides I the sarnple.
A hi~h pL~rity ~ermanium gamma delec~or 18, shielde~ ~om receivillg dire~ r~ ion from the soulce 12 by ~ neutron shield æ. receiq~
~amma radiation 20 emitted by ~he sample 14 and forms a spec~n~n ~om ~he radiation rece*ed wit~Jin a predetermiued time arltelval. The ~pe~um, ~lusb~ated ~iagrarnmatically at 24 in Fi~ure 1, is aDalysed by a cor~u~ (not shown) which compa~s it with standar~ data to det~ine whether the spe~unl Is ~ndicat~ve of the presence of carbon-12, in turn irldi~ive of diamo~ld, in the saulple.
If one or more diamond parucles are present i" the kimb~rlite sample, a chalacteristic pealc w~l be obser~,ed in the dete~ed gs~Tnma spec~
at the a~propriate energy level eor carbo~-~ Le 4,43MeV The spectral pea}; ~ supernnposed on a p,ellera~ bac3;g~owld attr~ ulable at least partially to aeu~ron~ ffered by t~e s~mple 14 whieh reach and interact with th~ g~nma dete~tor 18. The background spectrum detected ~3y -the dete~tor 18 may he such as to immerse t:he charactens~c carbon-12 pe~c i~di~ve of diamon~
'rO reduce the effe~: of backgroLmd radiation in the detected spec~um.
relia~oe ~s p~aced u:pon the differeDt speed~ at ~vhich ~eu~o~ and gamn:~a ra~a~ion travel from ~he sample to ~he detector. Ga~nma r~on ~ravels at the speed of li~ht ~om the sample to the delector w~e neutron~ scar[ered by ~he sa~ple ~owards the detector travel somewhat slower. For e~amplc, thc timc dclay ovcr a distauce of lm for ~mm~ r~dia~o~ and ~eutro~s at an crler~y of 6,~M~V is a~ut 30 r~ds. i.e. 30 x 10-9s.
I!~ U~1 1~ I 1; :1; '~(I I I S~ uh o. t I .S H~. K 1~1 1.11I) ' 8 _ , i.
In accorda~ce ~ith ~h~ Inve~ltio~ Xin, use o~ fast ele~tror.ie pro~essing apparatr~ te gam~ta deLee~ioll sy~ter~ me-~ted ~o ~at the detector is cnabled du~ the ti,~e peri~d that ne~ron-induc~d gamma rays re~cb. the detector, alid the~ disable~d by tht time the ~ca~tered neu~ons amve. In ~his way, ba~kground noise at~uta~le to stray nwtrons sc~tered by the san~le 14 can ~e elin~a~e~, or at least redu ;eL Fgure 12 dia~atically ~ 3strate~ tbe electro~c compo~e~y used lo achieve the rlece~v time~ting, Refer}ing to Fig~ a portion 30 of ~he sign31 produced by the ~e~u~ dctcctor 18 ~s direc~ed via a sig~l amplifier 34 to a lin~3~r gate ~retc~er 48. 'rhe remaindcr 38 of the signal is dLrected ~om ~c detector 18 to a ~imin~ filter a~plifier 40 which in tun~ feeds the signal tG a ~t frdction delay u~i. 4~ '~he unit 4, applies a time delay 44 tO the s~ l wherea~er the ~ignal is fed to a t~e to pulse hei~t corsvert~ 4~.
A~ the same timet a beal:n pick~of~ signal 50 is ini~ated by a beam pi~-off uni~ 5Z which ~irects the 9gllZ.1 to a tirning fi~ter a~npl~fier 54. The ampl~fier ~4 feeds the signal to th~ ~me to pulse height converter 46. I~
~sse~e, ~e be~m p~ ff ~gnal Sta}lS a ciock which controls a ~me ate. The cor~verted signal controls lhe l~ear ~d~e stretche~ 4~, openinO
~he ~me gaIc for admission of an amplified spe~,~osoopv si ,nal 37 fro~
the am~fier 34 to a mul~ch~el analyser 36.
Thus p~lses from the amplifier 34 will oDly be registeI~ed by the ~ltichan~el analyser i~ ~hey ~ppear inside ~e relevant, predetermined timo pe ~od, ... _ _ ______ ...... , .. ,_.. ,,,, ... _ ~
.' ~-.
'J11 t~ J'd S~'IJi~K ~ I!LK 4~iU11 - ~ ? ,! ~ .
~ ~ ~ .J .L
_ g _ Exper~menta~ion by the inventor~ indicates that the time~at~ng techr~q~e de~nrbed above bas the e~ect of Sllpp:le55illg the baekgrouDd radiation or naise l~is is i~ s~ated by a oompa~r~so~ of Figuresi 3a a~d 3b i~ wbi~h logarithmie count ~cquen~y is plot~ed on the ver~ic~ ax:is ag~irst ~h~el valu~s represen~alive of energy level o~ tbe ho~i70ntal a~is. Figure 3a ~lustrates a gamma spectrum in which no time-gating bas been employeLi Tbe 4,43MeV peak 60, inidicatIve of the priesence in the l~mberlite sa~ple of i~rbon-~2 and hence d~nond, ~s m~sked to a large d~ree in the b~:kgrol}~d r.oise. Figure 3b illus~rates a corresponrling gamma sipec~ obt~ ed usirl~ timc~ated detec~on a~paranLs as d~bed. In t s case, a clear spec~l peak 62 is discermble a~ the cha~ac1el~sbc 4,43MeV ~r~y level of carbon-12, ~lear1y showing the suppfession of back~ouIId r~oise that is attri~table to ~me-v,a~g.
Ref~ g again to F~re 1 it wil1 be lloted that the gamma delector 18 i~ positio~ at a }eversc a~gle relative to the incident nelltron 1~ 10.
It is belie~ed ~at ~is geomel!y wflI give nse to an optima! si~nal to ~ois~ ratio. The sha~e and alTan~ement o~ the neutroll shield .Z2 Figure 1 are slso considered ~o be impo~an~ fearures, in that the shield shotlld prevent a~y direct passage of the neutron beam 10 ~om abe ~ource 12 to the detector 18.
At t~e s~me time, as ~uy neutrons as posslb1e ~hat ale scattered l~y the sam~le 14 shonld be divert~ away from the detector rather d~an towards the de~ecr~r. For ~ese reasons, the shield 2~ h~s the illus~ted ~iangllar cross section and the apex 80 ~d3ereof does llot extend fc~wardly i~o the field of v~ew of the dct~tor where it might d~vert neutrons u~wards the detector.
.' I)~ U~ U 5~'0(11~ & I:lS~ '4'1UI.
.
~, ` j `,i,~,'l Spe~G mention has ~een ~ads of analys~ng a kim:~r~i~e sample ~or the pres~nce of carbon-12 and hence of diamon~ Hnwever it will be appr~d tha~ prirlc~ples nf t:he ~vention have ~ar wider a~?plicatio~ Fo~ iu~oe ~e ~echn~qlle of the inven~on could, ie is believed, be used w~2h good e~fect i~ the detection of ~bon and/o~
Q~;ygen în steel samples I~ sho~ld a~o ~e noted that while the abo~e descr~p~io~ is directed to the arlalysis of a single, stauc sample, the pIi~ciples of ~he ~hlvention are ~:q~lly aypl~cable to on-hne analys~s with a sue Lm of partîcles pa~si~
seq~lentially throu~h a detectio~L and analysis station. The ~veIItioIL
could for instanee be en~ployed in a p~r~cle sorting system in which, once a pa~licle has bee~ detected tha~ includes a desirabl~ elem~llt or iSOtOpe, suc~ p3rticl~ is automatic~lly ej~cted from Lhe particle strea~
T~is could ~e achieved usillg ~onventional ejec~on equLpm~nI such as gas blast or other ejectors to remove desir.Lble par~icles from the ~n s~eam ~r colle~on a~t ~ r~ other particles which are bar~en iIL
term~ their conterlt of the des~red element or isotope.
Irl tbe case of ~nberlite arlalysis a m~jor advantag~ of detecting a diamorld mclusior~ 3g ~e technique of the il~ve~ioII is that ~arren l~nberlite particles caII immediately be rejected without the rlecessît y for filrther p~oces~ng. Only p~dcles for whic~ a l?os~iti~ e ~nialysis iS
obmi!od ilr~ scI~d for 511~tOqu~=t pToCCssiD~.
. .....
: ,:
: -:........ . : ':. ,: r, . :,- ' ':::: :: :: .: .. ,.. ::::,:: '` .: :: ::'i :,:,.. '': , ' ' ~10~ '1111 0'~ r~J~ O. r~ r~ JlJ
~ .
The :Inono~energe~c Or well~ei~ne~ energy level of th~ pulsed neutron ~e~m is prefe~ed since il enables the selectio~ of the app}opri~te ener~ vel f~Jr ~e elemem ~~ estion, thereby iIr.proving the se~sit~y of ihe sy~em. l~e pulsed na~ure of the ~ n results Lll t~e ac~:lm~on of repeu~ive d~ta whic3~ reduce~ ious backgroulld ef~eces The pu~sing vL 1he beam may ~e achieved in a conven~onal ma~er ~ing a br~m iotrrrllpr~r rf }3!0~ rype.
. I
. .... .... ., ,_ ,._.. _........ ... .
Claims (25)
1.
A method of analysing a sample for the presence therein of a particular element or isotope, the method comprising the steps of:
- directing at the sample a pulsed neutron beam at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable table gamma spectrum.
- detecting the neutron-induced gamma spectrum by means of gamma detection apparatus which is time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - determining whether a spectral peak characteristic of the particular element or isotope is present in the gamma spectrum.
A method of analysing a sample for the presence therein of a particular element or isotope, the method comprising the steps of:
- directing at the sample a pulsed neutron beam at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable table gamma spectrum.
- detecting the neutron-induced gamma spectrum by means of gamma detection apparatus which is time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - determining whether a spectral peak characteristic of the particular element or isotope is present in the gamma spectrum.
2.
A method according to claim 1 wherein the neutron beam is mono-energetic or with a well-defined energy level.
A method according to claim 1 wherein the neutron beam is mono-energetic or with a well-defined energy level.
3.
A method according to claim 1 wherein the neutron-induced gamma spectrum is detected by a gamma detector which is shielded from the pulsed neutron beam.
A method according to claim 1 wherein the neutron-induced gamma spectrum is detected by a gamma detector which is shielded from the pulsed neutron beam.
4.
A method according to claim 1 wherein the pulsed neutron beam is produced by accelerating a pulsed particle beam and directing at a deuterium gas target.
A method according to claim 1 wherein the pulsed neutron beam is produced by accelerating a pulsed particle beam and directing at a deuterium gas target.
5.
A method according to claim 4 wherein the neutron beam is pulsed in nanosecond bursts.
A method according to claim 4 wherein the neutron beam is pulsed in nanosecond bursts.
6.
A method according to claim 4 when used to detect the presence in a sample of carbon-12.
A method according to claim 4 when used to detect the presence in a sample of carbon-12.
7.
A method according to claim 6 when used to detect the presence of diamond in a kimberlite sample.
A method according to claim 6 when used to detect the presence of diamond in a kimberlite sample.
8.
A method according to claim 7 wherein the neutron beam has an energy level in the range 4MeV to 10MeV.
A method according to claim 7 wherein the neutron beam has an energy level in the range 4MeV to 10MeV.
9.
A method according to claim 8 wherein the neutron beam has an energy level in the range 6MeV to 8MeV.
A method according to claim 8 wherein the neutron beam has an energy level in the range 6MeV to 8MeV.
10.
A method according to claim 9 wherein the neutron beam has an energy level of about 6,3MeV.
A method according to claim 9 wherein the neutron beam has an energy level of about 6,3MeV.
11.
A method according to any one of claim 1 when used to detect carbon and/or oxygen in steel samples.
A method according to any one of claim 1 when used to detect carbon and/or oxygen in steel samples.
12.
A method of sorting particles comprising the steps of:
- analysing each particle for the presence therein of a particular element or isotope, the analysis comprising the steps of:
- directing at each particle a pulsed neutron beam at an energy level chosen for the neutrous to interact with the element or isotope and produce a detectable gamma spectrum, - detecting the neutron-induced gamma spectrum by means of gamma detection apparatus which is time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - determining whether a spectral peak characteristic of the particular element or isotope is present in the gamma spectrum; and - separating from other particles those particles for which the detected gamma spectrum is indicative of the presence of a particular element or isotope.
A method of sorting particles comprising the steps of:
- analysing each particle for the presence therein of a particular element or isotope, the analysis comprising the steps of:
- directing at each particle a pulsed neutron beam at an energy level chosen for the neutrous to interact with the element or isotope and produce a detectable gamma spectrum, - detecting the neutron-induced gamma spectrum by means of gamma detection apparatus which is time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - determining whether a spectral peak characteristic of the particular element or isotope is present in the gamma spectrum; and - separating from other particles those particles for which the detected gamma spectrum is indicative of the presence of a particular element or isotope.
13.
Apparatus for analysing a sample for the presence therein of a particular element or isotope, the apparatus comprising:
- a neutron source for directing at the sample a pulsed neutron beam at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable gamma spectrum, - detection means for detecting the neutron-induced gamma spectrum, the detection means being time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - means for determining whether a spectral peak characteristic of the particular element or isotope is present in the detected gamma spectrum.
Apparatus for analysing a sample for the presence therein of a particular element or isotope, the apparatus comprising:
- a neutron source for directing at the sample a pulsed neutron beam at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable gamma spectrum, - detection means for detecting the neutron-induced gamma spectrum, the detection means being time-gated in such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - means for determining whether a spectral peak characteristic of the particular element or isotope is present in the detected gamma spectrum.
14.
Apparatus according to claim 13 wherein the neutron source is adapted to produce a neutron beam which is mono-energetic or with a well-defined energy level.
Apparatus according to claim 13 wherein the neutron source is adapted to produce a neutron beam which is mono-energetic or with a well-defined energy level.
15.
Apparatus according to claim 14 wherein the neutron-induced gamma spectrum is detected by a gamma detector shielded from the pulsed neutron beam.
Apparatus according to claim 14 wherein the neutron-induced gamma spectrum is detected by a gamma detector shielded from the pulsed neutron beam.
16.
Apparatus according to claim 15 wherein the detection means comprises a germanium gamma detector.
Apparatus according to claim 15 wherein the detection means comprises a germanium gamma detector.
17.
Apparatus according to claim 13 wherein the neutron source comprises means for accelerating a pulsed particle beam and directing it at a deuterium gas target.
Apparatus according to claim 13 wherein the neutron source comprises means for accelerating a pulsed particle beam and directing it at a deuterium gas target.
18.
Apparatus according to claim 17 wherein the neutron source is adapted to produce a neutron beam pulsed in nanosecond bursts.
Apparatus according to claim 17 wherein the neutron source is adapted to produce a neutron beam pulsed in nanosecond bursts.
19.
Apparatus according to claim 17 when used to detect the presence in a sample of carbon.
Apparatus according to claim 17 when used to detect the presence in a sample of carbon.
20.
Apparatus according to claim 19 when used to detect the presence of diamond in a kimberlite sample.
Apparatus according to claim 19 when used to detect the presence of diamond in a kimberlite sample.
21.
Apparatus according to claim 20 wherein the neutron source is adapted to produce a neutron beam having an energy level in the range 4MeV
to 10MeV.
Apparatus according to claim 20 wherein the neutron source is adapted to produce a neutron beam having an energy level in the range 4MeV
to 10MeV.
22.
Apparatus according to claim 21 wherein the neutron source adapted to produce a neutron beam having an energy level in the range 6MeV
to 8MeV.
Apparatus according to claim 21 wherein the neutron source adapted to produce a neutron beam having an energy level in the range 6MeV
to 8MeV.
23.
Apparatus according to claim 22 wherein the neutron source is adapted to produce a neutron beam having an energy level of about 6,3MeV.
Apparatus according to claim 22 wherein the neutron source is adapted to produce a neutron beam having an energy level of about 6,3MeV.
24.
A method according to claim 13 when used to detect carom and/or oxygen in steel samples.
A method according to claim 13 when used to detect carom and/or oxygen in steel samples.
25.
A particle sorting apparatus comprising:
- apparatus for analysing each particle for the presence therein of a particular element or isotope, the analysing apparatus comprising:
- a neutron source for directing at each particle a pulsed neutron beam at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable gamma spectrum, - detection means for detecting the neutron-induced gamma spectrum, the detection means beam time-gate such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - means for determining whether a spectral peak characteristic of the particular element or isotope is present in the detected gamma spectrum; and - means for separating from other particles those particles for which the detected gamma spectrum is indicative of the presence of a particular element or isotope.
A particle sorting apparatus comprising:
- apparatus for analysing each particle for the presence therein of a particular element or isotope, the analysing apparatus comprising:
- a neutron source for directing at each particle a pulsed neutron beam at an energy level chosen for the neutrons to interact with the element or isotope and produce a detectable gamma spectrum, - detection means for detecting the neutron-induced gamma spectrum, the detection means beam time-gate such a manner that neutron-induced gamma radiation is detected while neutrons scattered by the sample are at least substantially excluded, and - means for determining whether a spectral peak characteristic of the particular element or isotope is present in the detected gamma spectrum; and - means for separating from other particles those particles for which the detected gamma spectrum is indicative of the presence of a particular element or isotope.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA93/6657 | 1993-09-09 | ||
| ZA936657 | 1993-09-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2131784A1 true CA2131784A1 (en) | 1995-03-10 |
Family
ID=25583223
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002131784A Abandoned CA2131784A1 (en) | 1993-09-09 | 1994-09-09 | Particle analysis and sorting |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2131784A1 (en) |
| ZA (1) | ZA946966B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101329284B (en) * | 2007-06-21 | 2011-11-23 | 清华大学 | Gamma-ray detector |
| CN117590452A (en) * | 2023-12-13 | 2024-02-23 | 北京锐达仪表有限公司 | Isotope instrument with energy spectrum self-correcting function |
-
1994
- 1994-09-09 CA CA002131784A patent/CA2131784A1/en not_active Abandoned
- 1994-09-09 ZA ZA946966A patent/ZA946966B/en unknown
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101329284B (en) * | 2007-06-21 | 2011-11-23 | 清华大学 | Gamma-ray detector |
| CN117590452A (en) * | 2023-12-13 | 2024-02-23 | 北京锐达仪表有限公司 | Isotope instrument with energy spectrum self-correcting function |
| CN117590452B (en) * | 2023-12-13 | 2024-06-04 | 北京锐达仪表有限公司 | Isotope instrument with energy spectrum self-correcting function |
Also Published As
| Publication number | Publication date |
|---|---|
| ZA946966B (en) | 1995-05-08 |
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