Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ ~V~ON
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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.r i.~ ,g~ ~ggg~g~ V~g ~ r-~
a ~ S ~ a a Sl~l~OR & F' ' Si~ER _ __ _~
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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.
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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 ~
-- 4 --
- 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
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- 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~
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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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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,
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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.
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I)~ U~ U 5~'0(11~ & I:lS~ '4'1UI.
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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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~10~ '1111 0'~ r~J~ O. r~ r~ JlJ
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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.
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