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Automatic apparatus for α-γ angular correlation measurements
NUCLEAR INSTRUMENTS AND METHODS 49 (J967) 6I-7o ; t, NORTH-HOLLAND PUBLISHING CO.
AUTOMATIC APPARATUS FOR a-y ANGULAR CORRELATION MEASUREMENTS* A. R. LEWIS and J. P. MORRIS Radioactivity
Center, Department of Physics, Massachusetts Institute of Technology, Massachusetts,
U.S.A .
Received 15 September 1956 Automatic equipment for the measurement of a-y angular corretations is described . The circuitry far automatic operation is given in detail. Detectors used in the system are a coaxial Ge(Li) crystal for y-rays and a silicon surface barrier detector for
cc-particles. A simple method of determining the relative efficiency o£ the Ge(Li) detector as a function of energy is outlined . The electronics used for coincidence has a resolving time of ti 5 nsec
1. Introduction
To obtain relative efficiency values for energies less than 295 keV a-y-ray singles spectrum of a1-52 Eu source was used. The expected relative intensities were calculated for 8 y-rays (122-1409 keV) from the conversion electron intensities measured by Bobykin and Novik') and the theoretical internal conversion coefficients of Sliv and Bands). The measured areas were then normalized in the same manner as in the 22'Ra case . The relative efficiency curve obtained from ' 52 Eu was normalized to the 22'Ra curve at 1120 keV (fig. 2). The error brackets shown in fig. 2 are due almost entirely to the uncertainty in subtracting the underlying structure. `these limits have been chosen very conservatively and are probably much larger than necessary. There has been some question as to the accuracy of the theoretical internal conversion coefficients for the 2 + -> 0 + rotational transitions in statically deformed nuclei') (e.g., the 122-keV y-ray in " 2 Sm which is used in the efficiency calibration) . However, measurements by Nathan and Waggoner") and by Kelman et al.") (among others), summarized by Bernstein"), indicate that the theoretical internal conversion coefficients of this transition in "2Sm agree with experimental results . "32 Gd (with N = 88), whose y-rays are also used in this calibration, is not considered to be in this group whose internal conversion coefficients are under question . Since there is no geometric correc,ion necessary for the different y-rays, the relative efficiency cat the Gc(Li) detector as a function of energy is obtained directly (fig. 2).
11e apparatus herein described has been used to study the "'Ac decay scheme above actinon. Preliminary results of this work are presented elsewhere'). The apparatus is a modified version of a manually operated angular correlation device described by Cobb2). The advantages of the automatic system are as follows a. Full 24-h/day utilization . b. Short counting times (- 2 h) at each angle can be used to minimize the effects of long-term shifts in the electronics system . This can be done without the necessity for constant supervision. c. The automatic timing of the system makes it possible to apply exact corrections for radioactive decay. This is especially crucial in the case of shortlived nuclides . d. The data can be obtained in a form easily lending itself to computer analysis . 2. Detectors Alpha particles are detected by a silicon surface barrier detector (SSB) fabricated in this laboratory using the basic recipe of Blankenship and Borkowski') as modified by Kraner"). The SSB is mounted in a vacuum chamber with the source (fig. 1). Gamma-rays are detected by a coaxial lithiumdrifted germanium [Ge(Li)] detector also fabricated in this laboratory). The energy resolution of the Gc(Li) detector using a preamplifier with a selected input tube (Amnerex 6922) is 5 keV fwlim. ` In order to determine the relative efficiency of the Gc(Li) detector as a function of y-ray energy the following procedure was adopted, A singles y-ray spectrum was obtained of a settled 22'Ra source, in equilibriuin with its daughter products, and the areas under 11 of the more intense peaks (295-17(A keV) wi~:rc measured. The values so obtained were then normalized to the y-ray intensities measured by Dzhelcpov et al .') .
3. Mechanical description
An over-all view of the system is shown in fig . I . The moving arm is driven, viii a gear train, by a motor
mounted under the aluminum table . Microswitches mounted can the table .it preselected angles are activated by a projection on the moving arrr, . The 7-particle This work was supported in part b3 the U . S Atomic energy Commis%ion under contract AT(30-1)-952 . 61
A. R. LEWIS AND 1. P. MORRIS
AUTOMATIC APPARATUS FOR ANGULAR CORRELATION MEASUREMENTS
(ORTEC model 105-107) . The output of the preamplifier is double-delay-line-amplified (RIDL model 30-23) arid sent. to a zero crossover pickoff discrimi,ater (ZCP, RIDL model 33-10) operated in the differential 'rr-ode. This serves as an energy discriminator for the L" -particles . The discriminator level (i.e., the a-particle energy gate) is set by selfgating the x-particle spectrum. The system is modified for this procedure as shown in fig. 5. An ungated 227Ac a-particle energy spectrum with a typical gate superimposed (in this case the peak is at 5.87 MeV, fwhm = 75 keV) is shown in fig. b. The output of the ZCP is fixed in time with respect to the detection ofthe a-particle inthe SSB, independent of the energy of the a-particle . The ZCP output signal serves as one input to the overlap time-to-height converter .
o
Relative efficiency determined from Ra"e data . Normalized to 100 of 352 keV. o Relative efficiency determined from Euc" dota . Normalized to 12 .1 at 1113 keV. RO 22 e and Eu'sa itoont too close to plot separnt-ly Photoelectric Cross Section for Germanium (normalized to relative efficiency curve at 300 kev
Gomma- ray Enerq.4
(keV )
Fig. 2. Relative efficiency of 5 cm ; active volume coaxial gamma-
ray detector as a function of gamma-ray energy .
dei--ctor remains fixed while the ^y-ray detector mounted on Fhc motor-driven arm is shoved in a circle about the source . The table has bce.n raised on legs to accomodate the motor ; leveling is accomplished by knurled disks held to the bottoms o1` the legs by strews . The 217 Ac source is placed on a platinum backing by the tetracthylene glycol method -"). A rr.onomolecular VYlr1S (polyvinyl-enlorïde-acetate copolymer, 85% chloride, 15% acetate)") film between the source and the SSB prevents recoil contamination of the detector . The 5 cm' coaxial Crc(Li) y-ray detector is held spring clip to a copper plate mounted on the reentrant of a stainless steel liquid nitrogen dewar") (fig. 3) where it is maintained in vacuo at 77'K. 4. Electronic system
A block diagram of the experimental system used is
shown in fig . 4.
4 .1 . ALPHA PARTICLE SIGNAL PROCESSING
63
The signal from the SSB detector is taken from the counting chamber to a charge-integrating preanrplifter
4. 22. Y-RAY SIGNAL PROCESSING The signal is taken out of the dewar via low-capacitance cable to a low-noise charge-integrating preamplifier (ORTEC model 103XL-107) operated in the delay line mode. The output signal from the chargeintegrating preamplifier is buffered by a high input impedance-high bandpass . cascaded emitter-follower circuit based upon a design of Emmer' s) and then capacitor pulse-shaped and scat to a 400-channel puke height analyzer (RIDL model 34-12B) . The output of the preamplifier is also sent through a double-delay line amplifier (RTDL model 30-23) to a zero crossover pickoff (RIDL model 33-10) operated in the integral mode with the baseline set slightly above zero to eliminate noise. The output of this zero crossover pickoff forms the other input to the overlap tineto-height converter. 4 .3 . TIME-TO-HEIGHT-CONVERTER (TUC)
The overlap THC, based upon a design by Simm% has an output signai whose amplitude is proportional to the amount of time overlap of the two input pulses (0 .3 mVJnsec) . The intrinsic time fitter of the TFIC. itself is approximately 0.2 trice (fig. 7) and the tinte jitter of the DDA-ZCP-T E~í+ß system as as unit is approximately 1 .2 nsec (fila . g) . Figs . 7 and 8 aalso sho\% . the linearity of tlac output with rc pcct to flic: icl4àt95 d overlap of the inputs .
The THC output is sent through a single-channel analyzer (WA, St atrrup model 701) which passes only the highest output pulses, i.e., almost complete time overlap (coincidence). The SCA output is used to gate the 44tí-channel pulse-height anaalymr . The resolution of this coincidence c"rcuitry is - 5 nscc .
A. R. LEWIS ANI] I. P. MORRIS Deutsch Connector
Ampttenol 27-45 Subminaz Hermetic (For Ssgnat if Bottom Flange is not used ),
Viton"ti Ring
5"OD G .S Tube 0.0355 Wall
17 'fe "
16 'r's'
ix, Punt
8 Il4 I
MC .^rtet
VOLO SS7ul e 0.065 wall . Remo obte Copper Plate sieff! y Three '4lar~Sc revs
" Amphenol 2 - x'" 45 Subminox Hermetic . Four Brass Legs
Fig. 3a . Dewar -,, , ith germanium detector .
z Germanium Detector Mounted on "Tab" of Copper Plate
1 i i 0
. 1 1
1
,
1nel.00-
t
1 2
L- , .Itt~c . 0 1 2 Inches
.
.
3
Fig. 3b. Dewar with germanium detector. GOME) detedar vacwm chamber Silicon Swfoa ®arriv detector
r
f=ig; . 4 . Block diagram of x- ;, cc'incidcncv %ystcm .
A. R. L E ilS AND J. P. MORRIS
store cycle whose duration is determined, by the analyzer live timer and which is manually set for some predetermined time . When the timer reaches zero, the analyzer switches to the -I"read" mode., and -the,- spectrum js~'read, out destrOctivel~ . (usually onto magnetic. tape). When this occurs, a signal ~ is' . sent -frorn the .&C timer via the . analyzer control, to the relay matrix (fig. 11). This signal does two things : 1 . activ.w.es power , to tlhe~ motor which inoves'the mobile arm to the next'progrdmmed switch ; 1 initiates a delav which in e&,Tt extends the "read" time, The delay is chosen to overlap there4dout time of the print-out device being used, thus inhibiting a new store cycle until ~the end of the delay. time., , The device used is a plug-in tim . e delay reNy which can -6e readily changed . ~o obtain delays compatiblie with different re2d-out devices. This,procedure. continues .until data have been taken at all angles, these~ angles being set on the programming board. The arm then continues forward for a short divance and is reversed by a switch which also disables the ""counting" raicroswitches. The'arm then proceeds counterclockwise until it reaches the "forward direction" microswitch whichstarts it moving clockwise and enables the "counting" micl-Oswitches. By this arrangement the y-ray detector always stops to count
Ac 227 Decay Se, -es Alpha
a -,,c4f-saim# io set alpha particle energy
II
Parttcle Energy Spectr~irn (-I w-th T'mcol Ene.- gy Coincidence Go!e (5 87 MeV~
F NHM - 75 keV
11
discrmunation.
Ne!omflon diagram of the co7triplete automated system 'n i-r, multicharnel nal~wr provides connections exu-ma! cont-i~ of soinc functions may be Tl~~1~oc oL t 1he analyzer is such that nn-.~&~s are used, "q-ore" and "read", the e being the quiescen , mot4 e. Basically, u-nit (fiLe- 1,01 m-netions. cn
to
the set for cr~- C~,Jl will switch to the sek-ted time period . This setting or automatic operation. of a cycle the mobile arm with the ,-,-ay st counterclockwise ,yzer control unit initiates a
-L 4 «S
LJ 50
.
5 .5 6.0 6 .5 Alphn F-e , 4ï (Niev)
70
75
Fig. 6 . -2 21Aoz &-av ~~ricz alph2, particle energy srz-ct .-,vr vvith typical energy P(-., iticidence gate .
AUTOMATIC APPARATUS FOR ANGULAR CORRELATION MEASUREMENTS
67
Fig. ~ Output spectra of overlap time-to-height converter (THQ with split pulser input showing linearity of output and intrinsic time j ituer of the THC ^
Ome s~wm * u=w De=, u e A-=^' W *
m=c~~=
a
'r,ne m me,gh .c arve ' tee m="= ."~ «-'" *v° p ~~ C;vef mn ta
the
s~°~
Do.ble
Delay
L=e
o"w.,t "= r~ e ~.1. ~ .^°° s l,0el,
L°"=,",cf
i R
pw*m =
o
/2 nms
~J __.A
50
o~~m~ v ~~~~~ ./w~" Fig. 8. Output spectra o( ~~ delay line pu!m r input to the double dc~)- hnc mmn! ifiwm vhmw ing linearity or output anti ^mimic unic j it m,"[ the m y%ner ` ,
Deuar utlh
Ge(Li)
l?MOy Matrix 5-~---‘----*-~
AlWlyrbr COMOI
I: I
1 contror
Signal
Mullichonnel
I
&iwlyzat Reaa
Readout
CoiAicncc
Device 1 Fig. 9. Block diagram
of automatic cz-7 angular correlaticm system.
AMPHENOL 67-06618.64P
IURNS I.
r.-
ON MOTOR ._... ~‘--._..l ---1
TO
hELA?
CONTROL
_.-
._ -.-_-.. .__ Ycf c8 1 r
ci>
RESET -vTffKR --
LIVE
-_i
I _I
,,
XESLT -__._ _ ‘IMEH LIVE
ALL RELAYS WOWN A1.t. RELAYS --.-.-ARE __....._.-.-FL
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POTTFRH ._---___._ ANALYZER
DE O&AI&~ RRUMFIFLD ____
RS5D
ONLY
Fig. IO. Analyzer
control.
6V
DC
TO ANALYZER
” f f
z
E ?
i
_. __ - -,
1
/
S!
5’
i’
A. R. LEWIS AND J. P. MORRIS
a clockwise mo:,on . Although dynamic braking is used, there is some small amount of play in the gearing system, plus the inertia of the arm. By stopping from only one direction the possible error in angular positioning is eliminated . from
,uthors *iah to ,thank Professor B.. D. Evans for the useof the facilities t f the M.T.T. Radioactivity
Center, . . . Kraner and W. R. Neal for their encouragement and technical advice and continual V. the Physics machine shop . We are .r. . Yena of Dr. H. N. Wilson for his assistance also indebted to the relay matrix . in the design of Re
I
£) A. R.. Lewis, MIT-952-3 (1966) 334. 2) W. C. Cobb, Nucl . Instr. and Meth . 23 (1963) 353. 3) J. L.. Blankenship and C. J. Borkowski, IRE Trans. Nucl . Sci. NS-7 (1960) M. 4) H. W. Kraner, TID-16349 (1962) 76 ; NYO-9505 (1963) 84 ; Pri-vate communication.
s) H. L. Maim, A. J. Tavendale and I. L. Fowler, Can. J. Phys . 43 (1965) 1173 . 6) B. S. Dzhelepov, N. N. Zhukovskii, 1. F. Uchevatkin and S. A. Shestopalova, Bull . Acad . Sci. USSR Phys . Scr. 22 (1958) 835 (Columbia Techn. Transi .) . 7) B. V. Bobykin and K. M. Novik, Bull . Acad . Sci. USSR Phys . ;Techn. Transl .). Ser. 21 (1958) 1546 (Columbia 8) L. A. Sliv and 1. M. :Hand, Coefficients of internal conversion rif y iadiation (Leningrad Physico-Technical Institute) Pt 1: IC-shell (1957), Pt 2: L=heil (1958). 9) E. M. Bernstein, Phys. Rev. Letters 8 (1962) 100. lo) O. Nathan and M. A. Waggoner, Nucl. Physics 2 (1957) $48. 11) V. M. Kelman, V. A. Romanov, R. Ya. Metskhvarishvili and V. A. Kolyunov, Nucl . Physics 2 (1957) 395. 12) D. L. Hufford and B. F. Scott, Nat. Nuclear Energy Series IV-148 (McGraw-Hill Book Company, Inc., New York, 1949) 1149. 13) B. D. Pate and L. Yaffe, Can. J. Chem . 33 (1955) 15 . 14) H. W. Kraner, J. A . Sovka and W. R. Breckenridge, Nucl . Instr. and Meth. 36 .(1965) 328. 1s) T. L. Emmer, IRE Trans. Nucl . Sci. NS-9 (June, 1962) 308, 16) P. C. Simms, Rev. Sci. Instr. 32 (1961) 894.
AUTOMATIC APPARATUS FOR a-y ANGULAR CORRELATION MEASUREMENTS* A. R. LEWIS and J. P. MORRIS Radioactivity
Center, Department of Physics, Massachusetts Institute of Technology, Massachusetts,
U.S.A .
Received 15 September 1956 Automatic equipment for the measurement of a-y angular corretations is described . The circuitry far automatic operation is given in detail. Detectors used in the system are a coaxial Ge(Li) crystal for y-rays and a silicon surface barrier detector for
cc-particles. A simple method of determining the relative efficiency o£ the Ge(Li) detector as a function of energy is outlined . The electronics used for coincidence has a resolving time of ti 5 nsec
1. Introduction
To obtain relative efficiency values for energies less than 295 keV a-y-ray singles spectrum of a1-52 Eu source was used. The expected relative intensities were calculated for 8 y-rays (122-1409 keV) from the conversion electron intensities measured by Bobykin and Novik') and the theoretical internal conversion coefficients of Sliv and Bands). The measured areas were then normalized in the same manner as in the 22'Ra case . The relative efficiency curve obtained from ' 52 Eu was normalized to the 22'Ra curve at 1120 keV (fig. 2). The error brackets shown in fig. 2 are due almost entirely to the uncertainty in subtracting the underlying structure. `these limits have been chosen very conservatively and are probably much larger than necessary. There has been some question as to the accuracy of the theoretical internal conversion coefficients for the 2 + -> 0 + rotational transitions in statically deformed nuclei') (e.g., the 122-keV y-ray in " 2 Sm which is used in the efficiency calibration) . However, measurements by Nathan and Waggoner") and by Kelman et al.") (among others), summarized by Bernstein"), indicate that the theoretical internal conversion coefficients of this transition in "2Sm agree with experimental results . "32 Gd (with N = 88), whose y-rays are also used in this calibration, is not considered to be in this group whose internal conversion coefficients are under question . Since there is no geometric correc,ion necessary for the different y-rays, the relative efficiency cat the Gc(Li) detector as a function of energy is obtained directly (fig. 2).
11e apparatus herein described has been used to study the "'Ac decay scheme above actinon. Preliminary results of this work are presented elsewhere'). The apparatus is a modified version of a manually operated angular correlation device described by Cobb2). The advantages of the automatic system are as follows a. Full 24-h/day utilization . b. Short counting times (- 2 h) at each angle can be used to minimize the effects of long-term shifts in the electronics system . This can be done without the necessity for constant supervision. c. The automatic timing of the system makes it possible to apply exact corrections for radioactive decay. This is especially crucial in the case of shortlived nuclides . d. The data can be obtained in a form easily lending itself to computer analysis . 2. Detectors Alpha particles are detected by a silicon surface barrier detector (SSB) fabricated in this laboratory using the basic recipe of Blankenship and Borkowski') as modified by Kraner"). The SSB is mounted in a vacuum chamber with the source (fig. 1). Gamma-rays are detected by a coaxial lithiumdrifted germanium [Ge(Li)] detector also fabricated in this laboratory). The energy resolution of the Gc(Li) detector using a preamplifier with a selected input tube (Amnerex 6922) is 5 keV fwlim. ` In order to determine the relative efficiency of the Gc(Li) detector as a function of y-ray energy the following procedure was adopted, A singles y-ray spectrum was obtained of a settled 22'Ra source, in equilibriuin with its daughter products, and the areas under 11 of the more intense peaks (295-17(A keV) wi~:rc measured. The values so obtained were then normalized to the y-ray intensities measured by Dzhelcpov et al .') .
3. Mechanical description
An over-all view of the system is shown in fig . I . The moving arm is driven, viii a gear train, by a motor
mounted under the aluminum table . Microswitches mounted can the table .it preselected angles are activated by a projection on the moving arrr, . The 7-particle This work was supported in part b3 the U . S Atomic energy Commis%ion under contract AT(30-1)-952 . 61
A. R. LEWIS AND 1. P. MORRIS
AUTOMATIC APPARATUS FOR ANGULAR CORRELATION MEASUREMENTS
(ORTEC model 105-107) . The output of the preamplifier is double-delay-line-amplified (RIDL model 30-23) arid sent. to a zero crossover pickoff discrimi,ater (ZCP, RIDL model 33-10) operated in the differential 'rr-ode. This serves as an energy discriminator for the L" -particles . The discriminator level (i.e., the a-particle energy gate) is set by selfgating the x-particle spectrum. The system is modified for this procedure as shown in fig. 5. An ungated 227Ac a-particle energy spectrum with a typical gate superimposed (in this case the peak is at 5.87 MeV, fwhm = 75 keV) is shown in fig. b. The output of the ZCP is fixed in time with respect to the detection ofthe a-particle inthe SSB, independent of the energy of the a-particle . The ZCP output signal serves as one input to the overlap time-to-height converter .
o
Relative efficiency determined from Ra"e data . Normalized to 100 of 352 keV. o Relative efficiency determined from Euc" dota . Normalized to 12 .1 at 1113 keV. RO 22 e and Eu'sa itoont too close to plot separnt-ly Photoelectric Cross Section for Germanium (normalized to relative efficiency curve at 300 kev
Gomma- ray Enerq.4
(keV )
Fig. 2. Relative efficiency of 5 cm ; active volume coaxial gamma-
ray detector as a function of gamma-ray energy .
dei--ctor remains fixed while the ^y-ray detector mounted on Fhc motor-driven arm is shoved in a circle about the source . The table has bce.n raised on legs to accomodate the motor ; leveling is accomplished by knurled disks held to the bottoms o1` the legs by strews . The 217 Ac source is placed on a platinum backing by the tetracthylene glycol method -"). A rr.onomolecular VYlr1S (polyvinyl-enlorïde-acetate copolymer, 85% chloride, 15% acetate)") film between the source and the SSB prevents recoil contamination of the detector . The 5 cm' coaxial Crc(Li) y-ray detector is held spring clip to a copper plate mounted on the reentrant of a stainless steel liquid nitrogen dewar") (fig. 3) where it is maintained in vacuo at 77'K. 4. Electronic system
A block diagram of the experimental system used is
shown in fig . 4.
4 .1 . ALPHA PARTICLE SIGNAL PROCESSING
63
The signal from the SSB detector is taken from the counting chamber to a charge-integrating preanrplifter
4. 22. Y-RAY SIGNAL PROCESSING The signal is taken out of the dewar via low-capacitance cable to a low-noise charge-integrating preamplifier (ORTEC model 103XL-107) operated in the delay line mode. The output signal from the chargeintegrating preamplifier is buffered by a high input impedance-high bandpass . cascaded emitter-follower circuit based upon a design of Emmer' s) and then capacitor pulse-shaped and scat to a 400-channel puke height analyzer (RIDL model 34-12B) . The output of the preamplifier is also sent through a double-delay line amplifier (RTDL model 30-23) to a zero crossover pickoff (RIDL model 33-10) operated in the integral mode with the baseline set slightly above zero to eliminate noise. The output of this zero crossover pickoff forms the other input to the overlap tineto-height converter. 4 .3 . TIME-TO-HEIGHT-CONVERTER (TUC)
The overlap THC, based upon a design by Simm% has an output signai whose amplitude is proportional to the amount of time overlap of the two input pulses (0 .3 mVJnsec) . The intrinsic time fitter of the TFIC. itself is approximately 0.2 trice (fig. 7) and the tinte jitter of the DDA-ZCP-T E~í+ß system as as unit is approximately 1 .2 nsec (fila . g) . Figs . 7 and 8 aalso sho\% . the linearity of tlac output with rc pcct to flic: icl4àt95 d overlap of the inputs .
The THC output is sent through a single-channel analyzer (WA, St atrrup model 701) which passes only the highest output pulses, i.e., almost complete time overlap (coincidence). The SCA output is used to gate the 44tí-channel pulse-height anaalymr . The resolution of this coincidence c"rcuitry is - 5 nscc .
A. R. LEWIS ANI] I. P. MORRIS Deutsch Connector
Ampttenol 27-45 Subminaz Hermetic (For Ssgnat if Bottom Flange is not used ),
Viton"ti Ring
5"OD G .S Tube 0.0355 Wall
17 'fe "
16 'r's'
ix, Punt
8 Il4 I
MC .^rtet
VOLO SS7ul e 0.065 wall . Remo obte Copper Plate sieff! y Three '4lar~Sc revs
" Amphenol 2 - x'" 45 Subminox Hermetic . Four Brass Legs
Fig. 3a . Dewar -,, , ith germanium detector .
z Germanium Detector Mounted on "Tab" of Copper Plate
1 i i 0
. 1 1
1
,
1nel.00-
t
1 2
L- , .Itt~c . 0 1 2 Inches
.
.
3
Fig. 3b. Dewar with germanium detector. GOME) detedar vacwm chamber Silicon Swfoa ®arriv detector
r
f=ig; . 4 . Block diagram of x- ;, cc'incidcncv %ystcm .
A. R. L E ilS AND J. P. MORRIS
store cycle whose duration is determined, by the analyzer live timer and which is manually set for some predetermined time . When the timer reaches zero, the analyzer switches to the -I"read" mode., and -the,- spectrum js~'read, out destrOctivel~ . (usually onto magnetic. tape). When this occurs, a signal ~ is' . sent -frorn the .&C timer via the . analyzer control, to the relay matrix (fig. 11). This signal does two things : 1 . activ.w.es power , to tlhe~ motor which inoves'the mobile arm to the next'progrdmmed switch ; 1 initiates a delav which in e&,Tt extends the "read" time, The delay is chosen to overlap there4dout time of the print-out device being used, thus inhibiting a new store cycle until ~the end of the delay. time., , The device used is a plug-in tim . e delay reNy which can -6e readily changed . ~o obtain delays compatiblie with different re2d-out devices. This,procedure. continues .until data have been taken at all angles, these~ angles being set on the programming board. The arm then continues forward for a short divance and is reversed by a switch which also disables the ""counting" raicroswitches. The'arm then proceeds counterclockwise until it reaches the "forward direction" microswitch whichstarts it moving clockwise and enables the "counting" micl-Oswitches. By this arrangement the y-ray detector always stops to count
Ac 227 Decay Se, -es Alpha
a -,,c4f-saim# io set alpha particle energy
II
Parttcle Energy Spectr~irn (-I w-th T'mcol Ene.- gy Coincidence Go!e (5 87 MeV~
F NHM - 75 keV
11
discrmunation.
Ne!omflon diagram of the co7triplete automated system 'n i-r, multicharnel nal~wr provides connections exu-ma! cont-i~ of soinc functions may be Tl~~1~oc oL t 1he analyzer is such that nn-.~&~s are used, "q-ore" and "read", the e being the quiescen , mot4 e. Basically, u-nit (fiLe- 1,01 m-netions. cn
to
the set for cr~- C~,Jl will switch to the sek-ted time period . This setting or automatic operation. of a cycle the mobile arm with the ,-,-ay st counterclockwise ,yzer control unit initiates a
-L 4 «S
LJ 50
.
5 .5 6.0 6 .5 Alphn F-e , 4ï (Niev)
70
75
Fig. 6 . -2 21Aoz &-av ~~ricz alph2, particle energy srz-ct .-,vr vvith typical energy P(-., iticidence gate .
AUTOMATIC APPARATUS FOR ANGULAR CORRELATION MEASUREMENTS
67
Fig. ~ Output spectra of overlap time-to-height converter (THQ with split pulser input showing linearity of output and intrinsic time j ituer of the THC ^
Ome s~wm * u=w De=, u e A-=^' W *
m=c~~=
a
'r,ne m me,gh .c arve ' tee m="= ."~ «-'" *v° p ~~ C;vef mn ta
the
s~°~
Do.ble
Delay
L=e
o"w.,t "= r~ e ~.1. ~ .^°° s l,0el,
L°"=,",cf
i R
pw*m =
o
/2 nms
~J __.A
50
o~~m~ v ~~~~~ ./w~" Fig. 8. Output spectra o( ~~ delay line pu!m r input to the double dc~)- hnc mmn! ifiwm vhmw ing linearity or output anti ^mimic unic j it m,"[ the m y%ner ` ,
Deuar utlh
Ge(Li)
l?MOy Matrix 5-~---‘----*-~
AlWlyrbr COMOI
I: I
1 contror
Signal
Mullichonnel
I
&iwlyzat Reaa
Readout
CoiAicncc
Device 1 Fig. 9. Block diagram
of automatic cz-7 angular correlaticm system.
AMPHENOL 67-06618.64P
IURNS I.
r.-
ON MOTOR ._... ~‘--._..l ---1
TO
hELA?
CONTROL
_.-
._ -.-_-.. .__ Ycf c8 1 r
ci>
RESET -vTffKR --
LIVE
-_i
I _I
,,
XESLT -__._ _ ‘IMEH LIVE
ALL RELAYS WOWN A1.t. RELAYS --.-.-ARE __....._.-.-FL
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A. R. LEWIS AND J. P. MORRIS
a clockwise mo:,on . Although dynamic braking is used, there is some small amount of play in the gearing system, plus the inertia of the arm. By stopping from only one direction the possible error in angular positioning is eliminated . from
,uthors *iah to ,thank Professor B.. D. Evans for the useof the facilities t f the M.T.T. Radioactivity
Center, . . . Kraner and W. R. Neal for their encouragement and technical advice and continual V. the Physics machine shop . We are .r. . Yena of Dr. H. N. Wilson for his assistance also indebted to the relay matrix . in the design of Re
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£) A. R.. Lewis, MIT-952-3 (1966) 334. 2) W. C. Cobb, Nucl . Instr. and Meth . 23 (1963) 353. 3) J. L.. Blankenship and C. J. Borkowski, IRE Trans. Nucl . Sci. NS-7 (1960) M. 4) H. W. Kraner, TID-16349 (1962) 76 ; NYO-9505 (1963) 84 ; Pri-vate communication.
s) H. L. Maim, A. J. Tavendale and I. L. Fowler, Can. J. Phys . 43 (1965) 1173 . 6) B. S. Dzhelepov, N. N. Zhukovskii, 1. F. Uchevatkin and S. A. Shestopalova, Bull . Acad . Sci. USSR Phys . Scr. 22 (1958) 835 (Columbia Techn. Transi .) . 7) B. V. Bobykin and K. M. Novik, Bull . Acad . Sci. USSR Phys . ;Techn. Transl .). Ser. 21 (1958) 1546 (Columbia 8) L. A. Sliv and 1. M. :Hand, Coefficients of internal conversion rif y iadiation (Leningrad Physico-Technical Institute) Pt 1: IC-shell (1957), Pt 2: L=heil (1958). 9) E. M. Bernstein, Phys. Rev. Letters 8 (1962) 100. lo) O. Nathan and M. A. Waggoner, Nucl. Physics 2 (1957) $48. 11) V. M. Kelman, V. A. Romanov, R. Ya. Metskhvarishvili and V. A. Kolyunov, Nucl . Physics 2 (1957) 395. 12) D. L. Hufford and B. F. Scott, Nat. Nuclear Energy Series IV-148 (McGraw-Hill Book Company, Inc., New York, 1949) 1149. 13) B. D. Pate and L. Yaffe, Can. J. Chem . 33 (1955) 15 . 14) H. W. Kraner, J. A . Sovka and W. R. Breckenridge, Nucl . Instr. and Meth. 36 .(1965) 328. 1s) T. L. Emmer, IRE Trans. Nucl . Sci. NS-9 (June, 1962) 308, 16) P. C. Simms, Rev. Sci. Instr. 32 (1961) 894.