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Mass Analyzing Recoil Appa a us, MARA
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Published e sion
Uusi alo, Juha; Sa én, Jan; Pa anen, Ja i; Hil on, Joshua
Uusi alo, J., Sa én, J., Pa anen, J., & Hil on, J. (2019). Mass Analyzing Recoil Appa a us, MARA.
Ac a Physica Polonica B, 50(3), 319-327. h ps://doi.o g/10.5506/APhysPolB.50.319
2019
Vol. 50 (2019) Ac a Physica Polonica B No 3
MASS ANALYZING RECOIL APPARATUS, MARA∗
J. Uusi alo, J. Sa én, J. Pa anen, J. Hil on
on behal o he Nuclea Spec oscopy G oup
Uni e si y o Jy äskylä, Depa men o Physics
P.O. Box 35, 40014 Jy äskylä, Finland
(Recei ed No embe 30, 2018)
An in- ligh ze o-angle mass sepa a o , MARA, has been ecen ly con-
s uc ed and commissioned a he Uni e si y o Jy äskylä, Finland. MARA
is a double ocusing de ice, consis ing o a quad upole d iple , elec os a ic
de lec o , and magne ic dipole. This sepa a o is buil o nuclea s uc u e
s udies o be pe o med a ound he N∼Zline and a beyond he p o on
d ip line.
DOI:10.5506/APhysPolB.50.319
1. In oduc ion
The gas- illed ecoil sepa a o RITU [1,2] has been in ope a ion since
1994 a Jy äskylä accele a o labo a o y JYFLACCLAB. RITU has been
in a hea y use and he expe imen al p og am pe o med has been e y suc-
ces ull. In a e age, i has yelded mo e han 10 e e eed publica ions pe
yea and i has been a base o nume ous hesis wo ks. O iginally, RITU
was planned o expe imen s whe e he hea y nuclei (Z≥82) a e p oduced
in usion–e apo a ion eac ions using asymme ic kinema ics. In eali y,
howe e , RITU sepa a o has been used o s udies a he p o on d ip line
s a ing om lowe mass egion, as low as 66As [3], up o ansac inide egion
256R [4]. In he egion below 100Sn, symme ic kinema ics has o be used
whe e he gas- illed sepa a o is no an op imal solu ion o be employed.
Al hough he p og am has been success ull, a clea need o a mo e selec i e
sepa a o sys em has been demons a ed. In he hea y-mass egion, he al-
pha and he p o on decays help wi h he selec i i y, bu in he lowe -mass
egion, such a ag is no a ailable. In he egion below Z≤74, he main
∗P esen ed a he Zakopane Con e ence on Nuclea Physics “Ex emes o he Nuclea
Landscape”, Zakopane, Poland, Augus 26–Sep embe 2, 2018.
(319)
320 J. Uusi alo e al.
decay mode is be a ac i i y and o gain in he selec i i y, a p ojec o ob ain
an in- ligh mass sepa a o was s a ed. In his pape , he layou o he e-
cen ly cons uc ed MARA [5] sepa a o will be p esen ed. In addi ion, some
esul s om he commissioning phase o he sepa a o will be gi en. I will
be ollowed by a sho in oduc ion o he pe o med expe imen al p og am
so a and he u u e plans. A mo e de ailed ou look o he MARA sepa a-
o ion-op ics and commissioning phase will be published in he o hcoming
pape [6].
2. The layou o he sepa a o
The con igu a ion o he MARA sepa a a o is QQQEM, whe e Q s ands
o quad upole, E o elec ic dipole, and M o magne ic dipole (Fig. 1).
MARA di e s om he as majo i y o he in- ligh acuum mode sepa a-
o s in ha i is no a symme ic de ice. The combina ion o elec ic dipole
and magne ic dipole p o ides a ixed ene gy ocus. Quad upole iple is
used o ob ain angula ocus o he poin o he ene gy ocus and wha
is hen le is ha he ions wi h di e en m/q a ios a e sepa a ed. In o
he magne ic dipole co ec ion coils ha e been added o in oduce a small
quad upole componen . This will allow he ocal plane o be a ied ±30 cm
along he op ical axis om i s nominal poin . A he en ance o he i s
dipole, poin o pa allel ocusing is used in o de o achie e he bes pos-
sible mass esol ing powe . A he ocal poin , he ocal plane is hea ily
il ed. Mo able ape u e sli s, bo h in dispe si e and non-dispe si e planes,
a e placed a he en ance o he elec ic dipole. Mo able “ene gy” sli s (dis-
pe si e plane) a e placed be ween he wo dipoles. Due o he hea ily il ed
ocal plane, a double-mass sli sys em is in oduced a he ocal plane a he
en ance and a he exi o he MWPC-coun e (see below). The ape u e
and he ene gy sli s can be used o imp o e he inal mass esol ing powe
wi h he cos o accep ance. The mass sli s a e ypically used o allow only
wo cha ge s a es o a gi en mass o be anspo ed in o he implan a ion
de ec o . The ion-op ical elemen s o he sepa a o a e lis ed in Table I.
Fig. 1. Ion-op ical layou o he MARA sepa a o .
Mass Analyzing Recoil Appa a us, MARA 321
TABLE I
The op ical elemen s in MARA sepa a o .
Leng h om a ge o ocal plane [m] 6.90
Dipoles M E
Radius o cu a u e [m] 1.0 4.0
De lec ion angle (deg.) 40 20
E ec i e ield bounda y inclina ion angles (deg.) 8.0 0
E ec i e ield bounda y adii [m] 2.0 —
Gap [cm] 10 14
Maximum igidi y 1.0 Tm 14 MV
Magne ic lenses Q1 Q2, Q3
Bo e diame e [cm] 10 15
E ec i e leng h [cm] 25 35
Maximum ield g adien [T/m] 10 10
The main ion-op ical p ope ies o he sepa a o using he so-called nom-
inal se ings a e shown in Table II. The nominal se ings a e ound o gi e
a good mass esol ing powe wi h high angula and ene gy accep ance. The
quad upole iple gi es a eedom o ha e in ini e numbe o se ing alues
gi ing double ocusing a he ocal plane. Fo example, by a ying hese
se ing alues, i is posible o inc ease he angula accep ance wi h he cos
o mass esol ing powe (o ice e sa).
TABLE II
The main ion-op ical p ope ies o he MARA sepa a o s (nominal se ings).
Con igu a ion QQQEM
Ho izon al magni iga ion −1.55
Ve ical magni ica ion −4.48
m/q dispe sion 8.0 mm/%
Fi s o de esol ing powe (2 mm beam spo diame e ) 259
Solid angle accep ance o cen al m/q and ene gy 10 ms
Ene gy accep ance o cen al m/q and angle −15%–+20%
m/q accep ance ±4%
3. De ec o se up
Sepa a o is no a use ul de ice by i sel and needs an e icien de ec o
se up o each he inal selec i i y. MARA is a mass sepa a o bu i canno
esol e isoba s o o e lapping e apo a ion channels in ol ing alpha-pa icle
322 J. Uusi alo e al.
e apo a ion, called m/q ambigui y. A he a ge posi ion, a pa icle de ec-
o a ay (JYTube) is placed. I consis s o 96 sepa a e scin illa o de ec o s
whi h SiPM (Silicon Pho o Mul iplie ) eadou s. Indi idual de ec o s ha e
been a anged in o wo ba els. In addi ion, bo h ba els a e connec ed o
an end-pla e a ay wi h a hole in he cen e o he ion beam and ecoil p od-
uc s. The a ge is placed be ween hese wo ba el a ays. The geome ical
e iciency o he sys em is a ound 80%. I is used o collec e apo a ed p o-
ons and alphas. I can be used as a e o de ec o o enhance he weak
neu on-e apo a ion channels o i used as a old one a ay, i enhances he
weak pxn-e apo a ion channels.
The m/q spec um is ob ained using a posi ion sensi i e Mul i-Wi e-
P opo ional Coun e (MWPC) a he ocal plane o MARA. I consis s
o h ee wi e planes, x-plane, ca hode, and y-plane. The wi e planes a e
ealized wi h 20 µm hick gold-pla ed ungs en wi es wi h 1 mm spacing.
Final posi ion is ob ained using 2 ns delay lines be ween he wi es and by
measu ing he delays in he signals be ween he wo ends o he wi e planes.
The main de ec o is a double-sided silicon s ip de ec o (DSSD). Models
BB17 and BB20 (Mic on) ha e been in use. BB17 has 1 mm s ip wid h and
in BB20 he s ip wid h is 0.67 mm. The o al amoun o s ips in BB17
is 48+128 and in BB20 is 72+192 (de ec o size is hen 48 mm (y-plane)
×128 mm (x-plane)). In addi ion, behind he DSSD, a second laye o
silicon is used o punch h ough e en s, and in on o he DSSD, a silicon
box a ay is used o escapes. All his can be su ounded wi h an a ay o
Ge-clo e de ec o s o gamma- ay collec ion. All he channels a e connec ed
o a digi al eadou sys em, in which all channels a e igge ed independen ly.
On-line and o -line analysis o he da a is pe o med using so wa e package
called G ain [7].
4. Commissioning phase
The commissioning o he sepa a o was pe o med using di e en a ge
beam combina ions co e ing eac ion ypes om asymme ic, symme ic,
and in e se kinema ics close o he Coulomb ba ie ene gies. The eac ions
used a e lis ed in he ollowing, i s he used beam hen he a ge . In
addi ion, he de ec o s used (mo e and mo e de ec o s added when commis-
sioning phase p og essed) a e lis ed:
—78K + 92Mo, MWPC, BB17,
—40A + 45Sc,na Ca, MWPC, BB17,
—78K + 58Ni, MWPC, BB17, punch- h ough silicon, wo Ge-clo e s,

Mass Analyzing Recoil Appa a us, MARA 323
—40A + 124Sn, as abo e and wo Ge-clo e de ec o s a he a ge po-
si ion, i s ecoil ga ing,
—58Ni + 106Cd, MWPC, BB20, punch- ough and escape silicon de ec-
o s, JYTube-de ec o , ou Ge-clo e de ec o s.
As an example o commissioning uns in igu e 2, a m/q spec um s.
he posi ion di e ence be ween MWPC and DSSD is shown. This posi ion
di e ence co esponds o he incoming angle o he ecoil. Spec um is usion
ecoil ga ed using he ene gy measu ed a he DSSD and ime-o - ligh (ToF)
measu ed be ween he MWPC and he DSSD. F om igu e 2, i can be seen
ha masses a e well-sepa a ed and ha ou cha ge s a es we e collec ed.
Also om his spec um, he second o de abbe a ion om he incoming
angle as well as he e ec o he il ed ocal plane can clea ly be seen.
Fig. 2. m/q spec um measu ed a he ocal plane o MARA. In he x-axis, he
posi ion in he MWPC is shown and in he y-axis, he posi ion di ence be ween
he MWPC and DSSD is shown. The eac ion was 78K + 92Mo.
In ano he example in igu e 3, a spec um is shown whe e in he x-axis
is he co ela ed alpha-pa icle ene gy measu ed a DSSD, and in he y-axis
is he m/q measu ed a he MWPC. Again, i shows he sepa a ion be ween
masses and ha 4–5 cha ges s a es a e collec ed.
324 J. Uusi alo e al.
Fig. 3. Alpha-pa icle ene gy [keV] spec um measu ed a he DSSD s. he m/q
spec um ob ained om MWPC is shown. The eac ion was 58Ni + 106Cd.
5. Expe imen al campaign
A e he commissioning phase an expe imen al campaign has been pe -
o med using MARA. As a esul , o example, i e new iso opes ha e been
iden i ied in hese s udies so a . The da a analysis is ongoing and esul s
om hose s udies will be p esen ed la e . As an example, a s udy on p o on
emi e s is shown in igu e 4. P o on ene gy spec um (a bi a y uni s, ob-
168P
164Os
160W
156H
169Au
165I
78K + 96Ru -> 174Hg*
78K + 92Mo -> 170P *
Fig. 4. Pa icle ene gy spec um measu ed a he DSSD. E en s, which a e ound
o be ollowed by long alpha decay chains, a e shown.
Mass Analyzing Recoil Appa a us, MARA 325
ained om aces) as well as one example o a ace om a signal a e shown.
This ace ep esen s a ecoil signal ollowed by a as decay signal wi hin
5µs ime window. The p o on peaks belong o i idium iso ope 165I and o
a new gold iso ope 169Au [8]. Final iden i ica ion o he decays was based
on long co ela ion chains ollowed, which is also illus a ed in igu e 4.
Some p ope ies o he sepa a o can be ob ained om hose s udies and
will be p esen ed in he ollowing. The p oduc ion c oss sec ion o p o on
emi e s a e a he well-known. In his expe imen al campaign, some o
hese known p o on emi e s we e p oduced. The used eac ions, e apo a-
ion channels, and c oss sec ions a e lis ed below (c oss-sec ion alues gi en
as p o on yield):
—78K + 92Mo →170P * →167,166I + p2n, p3n, 3µb, 0.1 µb [9],
—58Ni + 106Cd →164Os* →160Re + p3n, 1µb [10],
—58Ni + 92Mo →150Yb* →147Tm + p2n, 30 µb [11],
—64Zn + 58Ni →122Ce* →117La + p4n, 240 nb [12].
F om he ob ained yields measu ed a he ocal plane o MARA, i can be
concluded ha MARA ansmission o hese cases has been 30–50%. These
alues ag ee e y well wi h he ion-op ical calcula ions. Also he cleanliness
o he sepa a o has been demons a ed. I he uning o he beam has been
accep able, he po ion o he usion ecoils om all he ecoils i.e. including
sca e ed componen s has been mo e han 70% in all cases p esen ed in his
pape .
6. Fu u e plans and conclusion
MARA sepa a o has al eady been in succes ul use o delayed ocal plane
spec oscopic s udies. The plan is o s a ex ensi e in-beam gamma- ay
spec oscopy Recoild-Decay-Tagging (RDT) s udies using MARA. A sophis-
ica ed ail sys em has been buil o mo e he LN2-cooled and HV-biased
Ge-de ec o a ay (JUROGAMIII) be ween he a ge posi ion o he wo
sep a o s RITU and MARA (see Fig. 5) wi hou ha ing a ull, hea y load-
ing, de ec o annealing p ocess be ween. JUROGAMIII is an a ay o 45
Comp on-supp essed HPGe de ec o s, including Eu ogam clo e s, Eu ogam
Phase I, and GASP- ype de ec o s, p o ided by he GAMMAPOOL Collab-
o a ion.
A p ojec o build a s opping gas cell ollowed by a low-ene gy b anch
LEB behind MARA ocal plane has also been s a ed (see igu e 6[13]). This
se up will be used o measu e masses o exo ic e y p o on ich nuclei as well
as o pe o m a ie y o lase -spec oscopic s udies. In his p ojec , MARA
326 J. Uusi alo e al.
Fig. 5. The ail sys em o anspo he JUROGAMIII a ay be ween he wo
sepa a o s.
will be used o sepa a e he usion p oduc s om he un eac ed beam and
guide he wan ed p oduc s o he ocal plane o MARA whe e he s opping
gas cell will be si ua ed.
Fig. 6. The plan o he gas-cell and MARA-LEB o be connec ed o MARA.