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O line commissioning o a new gas cell o he MARA Low-Ene gy B anch
© 2023 The Au ho (s). Published by Else ie B.V.
Published e sion
Zad o naya, A.; Rome o, J.; E onen, T.; Gins, W.; Kankainen, A.; Moo e, I. D.;
Papadakis, P.; Pohjalainen, I.; Reponen, M.; Rin a-An ila, S.; Sa én, J.; Simono ski,
D.; Uusi alo, J.
Zad o naya, A., Rome o, J., E onen, T., Gins, W., Kankainen, A., Moo e, I. D., Papadakis, P.,
Pohjalainen, I., Reponen, M., Rin a-An ila, S., Sa én, J., Simono ski, D., & Uusi alo, J. (2023).
O line commissioning o a new gas cell o he MARA Low-Ene gy B anch. Nuclea Ins umen s
and Me hods in Physics Resea ch. Sec ion B : Beam In e ac ions wi h Ma e ials and A oms, 539,
33-42. h ps://doi.o g/10.1016/j.nimb.2023.03.016
2023
Nuclea Ins umen s and Me hods in Physics Resea ch B 539 (2023) 33–42
A ailable online 24 Ma ch 2023
0168-583X/© 2023 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/).
Con en s lis s a ailable a ScienceDi ec
Nuclea Ins . and Me hods in Physics Resea ch, B
jou nal homepage: www.else ie .com/loca e/nimb
O line commissioning o a new gas cell o he MARA Low-Ene gy B anch✩
A. Zad o nayaa,∗, J. Rome oa,c, T. E onena, W. Ginsa, A. Kankainena, I.D. Moo ea,
P. Papadakisb, I. Pohjalainena, M. Reponen a, S. Rin a-An ila a, J. Sa én a, D. Simono ski d,e,
J. Uusi aloa
aAccele a o Labo a o y, Depa men o Physics, Uni e si y o Jy äskylä, P.O. Box 35, 40014 Jy äskylä, Finland
bNuclea Physics G oup, STFC Da esbu y Labo a o y, Keckwick Lane, Wa ing on, Cheshi e, WA4 4AD, Uni ed Kingdom
cOli e Lodge Labo a o y, Uni e si y o Li e pool, Li e pool, L69 7ZE, Uni ed Kingdom
dSain Pe e sbu g S a e Uni e si y, 7/9 Uni e si e skaya Emb., 199034, Sain Pe e sbu g, Russian Fede a ion
eKons an ino Pe e sbu g Nuclea Physics Ins i u e (PNPI), Na ional Resea ch Cen e Ku cha o Ins i u e, Ga china, Lening adskaya Oblas , Russian Fede a ion
ARTICLE INFO
Keywo ds:
Gas cell
MARA-LEB
223Ra 𝛼- ecoil sou ce
In-gas lase ioniza ion
ABSTRACT
Resul s o o line commissioning es s o a new dedica ed gas cell o he Mass Analysing Recoil Appa a us
(MARA) Low-Ene gy B anch a e epo ed. E acua ion ime, ion su i al and anspo e iciency in helium
bu e gas we e cha ac e ized wi h a adioac i e 223Ra 𝛼- ecoil sou ce. Supp ession o he ion signal, o igina ing
om non-neu alized species in he gas cell, was explo ed wi h 219Rn ions, he daugh e ecoil o 223Ra, as a
unc ion o ol age applied o one o he ion-collec o elec odes. Two-s ep lase esonance ioniza ion o s able
in iso opes p oduced inside he gas cell om a hea ed b onze ilamen was demons a ed, and b oadening o
he a omic esonances in a gon bu e gas was s udied. These es s indica e he sui abili y o he new gas cell
o u u e in-gas lase spec oscopy s udies o exo ic nuclei a he Accele a o Labo a o y o he Uni e si y o
Jy äskylä.
1. In oduc ion
The MARA Low-Ene gy B anch (MARA-LEB) is a new low-ene gy
adioac i e ion beam acili y unde de elopmen a he Accele a o
Labo a o y o he Uni e si y o Jy äskylä (JYFL-ACCLAB) o he s udy
o exo ic nuclei using high- esolu ion lase spec oscopy, mass measu e-
men s and nuclea decay spec oscopy [1]. MARA-LEB aims o p o ide
a de ailed unde s anding o exo ic nuclea -s uc u e phenomena by
explo ing se e al egions o he nuclea cha , including nuclei wi h
𝑁∼𝑍be ween Z (𝑍=40) and Sn (𝑍=50), nuclei jus abo e
100Sn, as well as hea ie , a e-ea h p o on d ipline nuclei a o ed o
ex eme g ound-s a e p ola e de o ma ion. Nuclei close o he 𝑁=𝑍
line p o ide a e ile landscape o explo e nuclea phenomena including
he e ec s o enhanced p o on–neu on in e ac ions and ela ed pai ing
e ec s, long-li ed isome ic s a es, exo ic nuclea decays and he e olu-
ion o nuclea shapes and sizes. Addi ionally, he as ophysical apid
p o on cap u e ( p) p ocess [2] and he 𝜈𝑝 p ocess [3] a e se h ough
his egion. The iso opic selec i i y o MARA-LEB, in combina ion wi h
a planned high-e iciency decay s a ion, will o e oppo uni ies o
nuclea decay spec oscopy o a e-ea h nuclei (57 ≤𝑍≤71), in pa ic-
ula he s udy o p o on decay ine s uc u e and nuclea shapes. Mo e
✩The esul s p esen ed in his pape a e based on wo k pe o med be o e Feb 24 h 2022.
∗Co espondence o: II. Physikalisches Ins i u , Jus us-Liebig-Uni e si ä Gießen, 35392 Gießen, Ge many.
E-mail add ess: [email p o ec ed] (A. Zad o naya).
ecen ly, mul i-nucleon ans e eac ion s udies a he MARA acuum-
mode ecoil sepa a o ha e been pe o med, and eac ion p oduc s o
ligh ac inide iso opes ha e been iden i ied and hei p oduc ion c oss
sec ions measu ed [4]. Depending on he a ailable p ima y beam in-
ensi ies and expe imen al e iciencies, op ical spec oscopy o ac inide
iso opes may be easible a he new acili y.
The i s phase o MARA-LEB is unde cons uc ion, wi h all majo
pa s o he se up being manu ac u ed [1,5]. S able p ima y beams om
he K130 hea y-ion cyclo on a e deli e ed o MARA wi h in ensi ies o
a leas 200 pnA, impinging on hin oil a ge s moun ed on a o a ing
wheel a he a ge posi ion o he sepa a o . Recoiling ions wi h a
a ie y o mass- o-cha ge a ios a e sepa a ed wi h a combina ion o
s a ic elec ic and magne ic ields. Depending on he eac ion symme-
y, wo o six cha ge s a es co esponding o he mass o in e es a e
anspo ed o he ocal plane de ec ion sys em [6]. MARA has a mass
esol ing powe o oughly 250, and uses se s o mo able mechanical
sli s o imp o e his alue a a cos o accep ance. Fo he ope a ion
o MARA-LEB, a gas cell will be loca ed a he ocal plane. F om he
o iginal cha ge-s a e dis ibu ion, one o h ee cha ge s a es can be
accep ed h ough he gas-cell window. In his manne , mass-selec ed e-
coil ions o in e es , e.g., 94Ag o 102Sn wi h an ene gy o abou 200 MeV
h ps://doi.o g/10.1016/j.nimb.2023.03.016
Recei ed 29 May 2022; Recei ed in e ised o m 12 Feb ua y 2023; Accep ed 16 Ma ch 2023
Nuclea Ins . and Me hods in Physics Resea ch, B 539 (2023) 33–42
34
A. Zad o naya e al.
Fig. 1. A simpli ied h ee-dimensional o e iew o he pa s o he IGISOL acili y ele an o his wo k. The gas cell, no isible in his o e iew, was housed in he a ge
chambe . The dipole magne o mass sepa a ion and de ec o s a ions 1 (silicon de ec o ) and 2 (silicon and MCP de ec o s) a e deno ed.
and yields o a ew ions/s, will be s opped and he malized in ei he
a gon o helium. In he case o a gon, ions will be neu alized, allowing
o subsequen selec i e esonance lase ioniza ion and spec oscopy o
elemen s o in e es ei he ia in-gas cell o in-gas je con igu a ions,
simila o he app oach desc ibed in [7]. Helium on he o he hand is
less conduci e o neu aliza ion, and hus ions ha e a highe su i al
p obabili y. Ne e heless, sho e e acua ion imes can be achie ed in
helium, gi ing access o he s udy o nuclei wi h sho e hal -li es ha
do no equi e lase e-ioniza ion. A e ex ac ion om ei he helium o
a gon gas, ions will be e-accele a ed o 30 keV owa ds he low-ene gy
b anch o downs eam expe imen s.
A p o o ype gas cell has been designed a he In-Gas Lase Ioniza ion
and Spec oscopy (IGLIS) labo a o y o KU Leu en (Belgium) o u u e
use a he online Ra e Elemen in Gas Lase Ion sou ce and Spec oscopy
(REGLIS3) acili y a S3GANIL (F ance) [8]. COMSOL Mul iphysics
so wa e [9] was used o op imize he gas-cell geome y in o de o
minimize he di usion losses and he anspo ime o ions ex ac ed
h ough he gas cell [8]. S udies ha e shown ha o o e come he e ec
o collisional- and empe a u e-b oadening mechanisms o he a omic
line spec al esolu ion, esonance ioniza ion spec oscopy mus be pe -
o med in he low-densi y and low- empe a u e medium o a supe sonic
gas low a he han in he subsonic low inside he gas cell [10].
Fo ma ion o uni o m and spa ially ex ended gas je s is essen ial o
high e iciency and high esolu ion o he in-gas je me hod, and can be
achie ed wi h ca e ully designed and manu ac u ed de La al nozzles o
high Mach numbe s, 𝑀[11].
In his wo k, we p esen an o e iew and esul s om commis-
sioning es s o a new gas cell o MARA-LEB, he design o which is
simila o he gas cell planned o he S3 acili y, GANIL. These es s
we e pe o med a he Ion Guide Iso ope Sepa a o On-Line (IGISOL)
acili y [12] which is b ie ly desc ibed in Sec ion 2. A adioac i e
223Ra 𝛼- ecoil sou ce [13] was ins alled inside he gas cell. The e acua-
ion ime, ion su i al and anspo e iciency we e cha ac e ized using
he daugh e 219Rn ecoil ions s opped in helium bu e gas, discussed
in Sec ion 3. These es s we e ollowed by in-gas cell lase ioniza ion
o s able in iso opes, his ime in an a gon bu e -gas en i onmen
(Sec ion 4). The la e wo k is in an icipa ion o one pa o he
planned science p og am o he MARA-LEB acili y, aiming o s udy he
g ound-s a e elec omagne ic momen s and mean-squa ed cha ge adii
o neu on-de icien in iso opes. Such in o ma ion is no ye a ailable
o iso opes wi h neu on numbe 𝑁 < 58 [14]. We no e ha in-gas
lase ioniza ion o s able in iso opes has ea lie been demons a ed
a he LISOL acili y as pa o he p epa a o y expe imen s owa ds
REGLIS3a S3GANIL [7]. Ou conclusions a e p esen ed in Sec ion 5.
2. Expe imen al me hod
2.1. IGISOL acili y
Commissioning es s wi h he MARA-LEB gas cell we e ca ied ou
a he IGISOL acili y a he Uni e si y o Jy äskylä. Fig. 1 highligh s
he ele an pa s o he acili y used in his wo k. The MARA-LEB
gas cell was ins alled in he a ge chambe o he acili y. Iso opes o
in e es we e p oduced and s opped in he gas cell illed wi h high-
pu i y helium o a gon gas and anspo ed by he gas low owa ds
he ee je nozzle and in o a sex upole ion guide (SPIG) [15]. The
ecombina ion a e coe icien o a gon ions in neu al a gon gas is an
o de o magni ude la ge han ha o helium [16,17]. Fo his eason,
a gon is a o ed as he bu e gas o choice when pe o ming selec i e
esonan lase e-ioniza ion unde online condi ions as he la ge e-
combina ion a e leads o a highe p obabili y o neu aliza ion [18]. I
is impo an o no e, only high-pu i y gases we e used in he ollowing
es s. Pu i ica ion o helium was achie ed wi h liquid ni ogen-cooled
cold aps, while o a gon, a ge e pu i ie was used (Saes MonoTo
PS4-MT15) as desc ibed in de ail in Re . [19]. Subsequen ly, a e
guidance h ough he SPIG, he ions we e accele a ed o 30 keV and
anspo ed owa ds a magne ic dipole mass sepa a o ha ing a mass
esol ing powe 𝑀∕𝛥𝑀 o abou 500.
Two de ec o s a ions we e used in he commissioning es s, as
shown in Fig. 1. De ec o s a ion 1, loca ed be o e he mass sepa a o ,
consis s o a silicon de ec o and was used o de e mine ion su i al
and anspo e iciency by measu ing he numbe o implan ed ions
iden i ied ia hei adioac i e (alpha) decays. De ec o s a ion 2 is
loca ed in he ocal plane a ea o he sepa a o , wi hin he so-called
elec os a ic swi chya d, and consis s o a silicon de ec o and a mi-
c ochannel pla e (MCP) de ec o . The MCP de ec o is used when mass
scans a e pe o med, and o de e mine he e acua ion ime o mass-
sepa a ed ions ex ac ed om he gas cell as i allows o ime- esol ed
ion coun ing. Simila o De ec o s a ion 1, he silicon de ec o a e
he mass sepa a o can be used o de e mine he ion su i al and
anspo e iciency o adioac i e ions, bu canno be used o s able
beams.
A wo-s ep esonan lase ioniza ion scheme o in was ealized
using solid-s a e lase s om he Fas Uni e sal Resonan lase IOn
Sou ce (FURIOS) labo a o y [20]. The Ti anium:sapphi e (Ti:Sa) lase
esona o s, pumped by 10-kHz epe i ion a e Nd:YAG lase s, a e ei he
in-house buil o sou ced om Johannes Gu enbe g Uni e si y Mainz.
The FURIOS labo a o y, loca ed di ec ly abo e he a ge chambe on
he second loo o he acili y, houses wo pump lase s, model Lee Lase
LDP-200, wi h a nominal ou pu powe o abou 100 W a 532 nm
wi h 100 ns empo al pulse wid h. Each Ti:Sa lase is pumped wi h
10–25 W, spli om he main pump beam using hal -wa e pla es and
pola izing beam spli e cubes. The Ti:Sa lase s a e ei he in 𝑍-shaped
o bow ie ca i y con igu a ions, wi h he la e p o iding na owband
ope a ion ia injec ion-locking echniques [21]. In his wo k, only he
b oadband 𝑍-shaped esona o s a e used. The lase s a e equipped wi h
in a-ca i y second ha monic gene a ion capabili y and ha e access o
ex e nal ha monic gene a ion se ups enabling a wa eleng h unabili y
om abou 210–500 nm and 690–1000 nm.
Nuclea Ins . and Me hods in Physics Resea ch, B 539 (2023) 33–42
35
A. Zad o naya e al.
Fig. 2. Cu away iew o he MARA-LEB gas cell. Gas in low and ou low a e indica ed wi h g een and ed a ows, espec i ely. The mass-selec ed seconda y ion beam om he
MARA sepa a o is deno ed wi h a ligh g een a ow. A — p e-chambe o gas- low condi ioning (houses obs acle and honeycomb langes), B — en ance window ( oil window),
C — ilamen eed h oughs, D1 and D2 — lase iewpo s o collinea and ans e se esonan lase ioniza ion con igu a ions, espec i ely, E — ion-collec o elec odes, F — ee
je /de La al nozzle. The en ance window can be eplaced by a lange o which a 223Ra 𝛼- ecoil sou ce can be moun ed in di e en posi ions as shown in he inse on he uppe
igh .
2.2. MARA-LEB gas cell
The geome y o he MARA-LEB gas cell is based on he design o
be used o he REGLIS3 acili y, S3GANIL [8]. A cu away iew o he
gas cell is shown in Fig. 2. A numbe o modi ica ions ha e been imple-
men ed, including an inc ease in he diame e o he en ance window
h ough which he ecoil p oduc s om he MARA sepa a o mus
pass, and he loca ion o he lange housing wo ilamen eed h oughs,
which has been mo ed om he cen al axis o he sepa a o . Th ee
indi idual ope a ional modes a e easible:
•Online mode: he ions om he MARA sepa a o will en e he
gas cell h ough a hin oil window, ypically ha a o myla
wi h a hickness up o ∼10 μm and an open diame e o 64 mm.
The window is suppo ed by a honeycomb ame. Recoils a e
he malized and s opped in a high-pu i y gas.
•O line mode wi h 𝛼- ecoil sou ce: he oil window can be e-
placed by a lange o which a 223Ra 𝛼- ecoil sou ce is moun ed,
as shown in he inse in Fig. 2.
•O line mode wi h ilamen s con aining s able (o long-li ed)
iso opes o in e es : wo ilamen s can be moun ed on a lange,
o se and opposi e o he en ance window. Th ough esis i e
hea ing, a con inuous sou ce o a oms is p oduced (in his wo k,
a b onze ilamen is used o p oduce s able in iso opes).
In his wo k, he MARA-LEB gas cell was ope a ed only in he a o e-
men ioned o line modes. Ion-collec o elec odes (ICs) ins alled be o e
he ee je nozzle o he gas cell a e used o collec non-neu alized ions
anspo ed om he s opping egion, he eby inc easing he selec i i y
when in-gas cell/in-gas je lase ioniza ion is used unde online condi-
ions. S opping and lase ioniza ion olumes a e physically sepa a ed in
o de o educe he e ec s o ecombina ion o pho o-ions. This allows
o mo e e icien low- esolu ion in-gas cell esonance ioniza ion spec-
oscopy (RIS). In-gas lase ioniza ion can be implemen ed in collinea ,
ans e se o c ossed-beam geome ies wi h espec o he a om low
ia lase iewpo s D1 and D2 (see Fig. 2). Finally, iso opes o in e es
and he bu e gas a oms lea e he gas cell ia a ee je o de La al
nozzle, he la e employed o o m collima ed high Mach numbe gas
je s. In his wo k, a ee je nozzle wi h a diame e o 1.65 mm was used.
3. O line es s wi h a 𝟐𝟐𝟑𝐑𝐚 𝜶- ecoil sou ce
Combined e iciency o ion su i al and anspo , as well as e ac-
ua ion ime om he gas cell a e impo an pa ame e s cha ac e izing
gas-cell pe o mance. These pa ame e s ha e been s udied in his wo k
wi h a adioac i e 223Ra 𝛼- ecoil sou ce, ins alled inside he gas cell
ope a ed using helium bu e gas. Fig. 3 shows he gas cell moun ed
inside he a ge chambe o he IGISOL acili y. P io o he es s,
223Ra ions (T1∕2 = 11.4d) we e accumula ed on he ip o a needle
Nuclea Ins . and Me hods in Physics Resea ch, B 539 (2023) 33–42
36
A. Zad o naya e al.
Fig. 3. MARA-LEB gas cell ins alled in he a ge chambe o he IGISOL acili y du ing he commissioning es s. The ee je nozzle canno be seen due o i s close dis ance,
∼2 mm, o he SPIG elec ode (labeled in he pho og aph). Gas ou low is indica ed wi h a ed a ow.
( he ‘‘needle sou ce’’) ins alled in an 𝛼- ecoil gene a o , wi h 227Ac
(T1∕2 = 21.8y) used as he p ima y sou ce. An accumula ed ac i i y
o (4.0±0.4) kBq o 223Ra was measu ed in a sepa a e acuum chambe
be o e ins alling he needle in o he gas cell. Du ing he ollowing
es s, pe o med o e se e al consecu i e days, he sou ce was ins alled
in ou posi ions as shown in he inse in Fig. 2. Fo each posi ion,
𝛼- ecoil spec a o 219Rn ions, he daugh e p oduc o 223Ra wi h a hal -
li e o 3.96 s, we e eco ded a De ec o s a ion 1 o di e en alues
o p essu e 𝑃0inside he gas cell. An example spec um is shown in
Fig. 4 o he sou ce in posi ion I and helium p essu e 𝑃0o 300 mba .
Du ing hese measu emen s, only 50% o he 219Rn ions we e eleased
in o he bu e gas due o he sou ce geome y a a a e o abou
1300 ions/s. The measu ed coun ing a e a De ec o s a ion 1 o his
sou ce posi ion was 160 coun s/s. Analysis o he accumula ed spec a
was pe o med in a manne simila o ha desc ibed in [22], and he
e iciency o ion su i al and anspo o he de ec o s a ion was
ex ac ed. We no e ha helium was chosen as he bu e gas due o he
smalle ecombina ion a e coe icien compa ed o ha o a gon. We
could he e o e an icipa e highe coun ing a es o he de ec ed ecoil
ions. Indeed, such compa isons ha e been s udied a he IGISOL acili y
in he pas and suppo his choice o gas o ion su i al.
To de e mine he e acua ion ime o di e en s a ing coo dina es
inside he gas cell, ol age pulses we e applied o he needle. The sou ce
was connec ed o a powe supply, he ou pu ol age o which could
be p og ammed by using TTL logic. Du ing a eco ding cycle, las ing
0.67 s o helium and 1.34 s o a gon, he ol age a he needle was
main ained a −30 V, excep o sho pe iods o 50 ms o 150 ms
( o helium and a gon, espec i ely) when he ol age was se o 0 V,
hus allowing he elease o 219Rn ions in o he gas low. Time p o iles
o singly-cha ged ions ex ac ed om he gas cell we e subsequen ly
eco ded using a mul i-channel scale (MCS) o ime- esol ed coun ing
o he ion signal om he MCP de ec o a De ec o s a ion 2, loca ed in
he elec os a ic swi chya d as shown in Fig. 1. A iming ca d was used
o p o ide he igge o he MCS o s a eco ding and o change he
Fig. 4. Example o an 𝛼-decay spec um o 219Rn measu ed a De ec o s a ion 1 o
he needle sou ce in posi ion I and a helium p essu e 𝑃0o 300 mba . The 219Rn peak
used o ex ac ing he e iciency is deno ed in ed. The peaks a e labeled acco ding
o he alpha decay om he espec i e iso ope, ene gy o he alpha pa icle and, o
219Rn, he b anching a io.
ol age a he needle sou ce. To imp o e he signal- o-noise a io, ime
p o iles we e accumula ed o e a numbe o eco ding cycles.
3.1. Ion su i al and anspo e iciency
The ion su i al and anspo e iciency was measu ed o all
posi ions o he needle sou ce as a unc ion o helium gas p essu e 𝑃0up

Nuclea Ins . and Me hods in Physics Resea ch, B 539 (2023) 33–42
37
A. Zad o naya e al.
Fig. 5. E iciency o he needle sou ce in posi ions I, II, III and IV a di e en alues
o helium p essu e 𝑃0. (a) Ion su i al and anspo e iciency measu ed a De ec o
s a ion 1. The esul s o posi ion IV a e mul iplied by a ac o o 20. (b) Nume ical
calcula ions o he e iciency o ion su i al agains di usion losses.
o 300 mba , limi ed by he p essu e in he su ounding IGISOL a ge
chambe . We no e ha his limi a ion will be mi iga ed a MARA-LEB
due o he an icipa ed use o a nozzle wi h a smalle diame e o 1 mm
and, he e o e, smalle low a e, o which he pumping capaci y o
MARA-LEB has been ailo ed acco dingly. Mo ing he needle sou ce o
a new posi ion equi ed en ing o he a ge chambe , hus po en ially
exposing he gas cell o he ambien ai . This could de imen ally
a ec he e iciency ia po en ial losses o cha ged ecoils o molecula
adduc s. Fo his eason, a e measu ing a e e y needle posi ion he
gas cell was baked o e nigh using ca idge hea e s (𝑇≈ 100◦C) and
subsequen ly cooled o oom empe a u e wi h a small low o helium
(𝑃0≈50 mba ). The e iciency is shown in Fig. 5(a). As he measu e-
men s we e pe o med using De ec o s a ion 1 he e is no sepa a ion
o di e en mass- o-cha ge (m∕q) alues, no iden i ica ion o po en ial
molecula ions. Howe e , De ec o s a ion 2 was also used o e i y ha
no highe cha ged s a es o hea ie molecula ions we e p esen in he
ex ac ed beam. A maximum e iciency o (12.7±1.3) % was measu ed
o he sou ce in posi ion I o a p essu e 𝑃0o 300 mba . We no e ha
his e iciency includes he anspo e iciency om he exi o he gas
cell o he de ec o s a ion, in addi ion o he ex ac ion h ough he
helium gas. The ip o he needle was un o una ely sc a ched on he
gas-cell su ace while mo ing i om posi ion II o posi ion III, esul ing
in a loss o ac i i y compa ed wi h wha would be expec ed om he
hal -li e alone ( his was con i med a e he gas-cell measu emen s).
The esul s shown in Fig. 5(a) o posi ions III and IV ha e he e o e
been co ec ed o his educ ion ac o o 2.9. Mo eo e , he esul s
o posi ion IV in Fig. 5(a) a e mul iplied by a ac o o 20, o be e
eadabili y o he measu ed da a.
Nume ical calcula ions we e pe o med using he Compu a ional
Fluid Dynamics (CFD) module o COMSOL Mul iphysics so wa e [9].
The eloci y o he gas low inside he gas cell depends on he c oss-
sec ional a ea o he gas ou low and he e o e he diame e o he
a ailable ee je nozzle was accu a ely measu ed o be (1.65±0.07) mm.
The ou pu o he nume ical calcula ions o he eloci y o he helium
gas low and i s s eamlines is shown in Fig. 6. The calcula ions only
include he di usion losses o he simula ed a oms o he inne walls
o he gas cell. The losses a e de ined by he ou low diame e , he
geome y o he gas cell, and he di usion coe icien o he simula ed
a oms in he bu e gas. Due o he absence o a di usion coe icien
o adon in he li e a u e, he coe icien o me cu y (𝐴∼ 200) in
helium a no mal condi ions (273.15 K and 1013 mba ) was used as a
Re . [23], 𝐷𝑟𝑒𝑓 = 5.32×10−5 m2∕s, and scaled o he alue o he helium
p essu e 𝑃0. No signi ican in luence on he calcula ed di usion losses
is expec ed. Resul s o he nume ical calcula ions o he anspo
e iciency in he gas a e shown in Fig. 5(b).
The no able di e ence be ween he absolu e alues o he measu ed
and nume ically calcula ed e iciency is an icipa ed. One ac o ha
may con ibu e is ha ion losses in he gas cell a e de e mined no
only by di usion, bu also by he p esence o impu i ies in he bu e
gas. Po en ial losses due o molecula o ma ion we e no conside ed
in he simula ion, bu a e expec ed o be p esen in he gas, albei
a signi ican ly educed amoun s a e he gas-cell baking. Impu i ies
a e also in ol ed in o he ion-loss mechanisms e.g., neu aliza ion o
ions ia h ee-body ecombina ion in ol ing a ee elec on, dissocia-
i e ecombina ion and cha ge-exchange eac ions [24]. I has been
shown ha an ion su i al and anspo e iciency o up o 30 %
can be eached o 219Rn ions in gas cells ope a ing wi h c yogenic
helium a empe a u es below 90 K [25,26]. This is due o he ul a-
pu e condi ions a ained by eezing ou he impu i ies. Mo eo e , he
e iciency depends on he chemical na u e o he elemen s and he e o e
will be di e en o 219Rn ions in, o example, helium and a gon gas. A
second ac o is he anspo e iciency om he gas cell o he silicon
de ec o ha depends on he uning o he SPIG and mass sepa a o .
The simula ions only include he anspo h ough he gas cell.
Despi e he disc epancy in he absolu e alues, i is encou aging
o see ha he gene al end o he e iciency g ow h as a unc ion
o helium p essu e is ep oduced a he well, in pa icula o needle
sou ce posi ions I and II, o which he simula ions and measu emen s
show a simila sa u a ion abo e 250 mba . In addi ion, he ela i e
e iciencies be ween he sou ce loca ions a e in ag eemen wi h ex-
pe imen , i.e. he highes e iciency is ob ained o posi ion I and he
lowes o posi ion IV. The simula ed e iciency o he la e posi ion is
mos disc epan wi h he expe imen al alues, pe haps indica ing bo h
an unde es ima ed loss due o di usion owa ds he walls o he gas
cell, o o he loss mechanisms no accoun ed o in he simula ion and
ampli ied in egions o slowe gas low close o posi ion IV.
3.2. E acua ion ime
E acua ion ime p o iles o 219Rn+,20Ne+and 40A +ions ex ac ed
om he gas cell we e eco ded and analyzed o all posi ions o he
needle sou ce wi h he MCP de ec o a De ec o s a ion 2. In hese
measu emen s, a gon and in-house ecycled helium bu e gases we e
used. The helium included neon as an impu i y, no p esen in he
comme cially bough a gon [19]. Measu emen s we e pe o med wi h
a p essu e 𝑃0o abou 200 and 100 mba in he cases o helium and
a gon gas, espec i ely, wi h he esul s shown in Fig. 7. Time p o iles
we e i ed using he buil -in Ex eme Peak unc ion om O iginP o
so wa e [27], which allowed he ex ac ion o he peak cen oid 𝑡max
and i s ull wid h a hal maximum 𝛥𝑡, highligh ed in Fig. 7, as well
as he co esponding e o ba s. The i ing esul s, shown in Fig. 8,
we e hen compa ed wi h a mo e sophis ica ed unc ion analy ically
de i ed o he e acua ion ime by sol ing he di usion–con ec ion
equa ions [28] and we e ound o be in good ag eemen wi hin e o
ba s, jus i ying he e o e he use o a simple unc ion. The e o ba s
o he peak cen oids, as well o he wid hs in helium, a e smalle han
he da a poin s shown in Fig. 8.
A highe signal- o-noise a io was achie ed o he 20Ne+ ime p o-
iles accumula ed o e a ewe numbe o eco ding cycles compa ed
o 219Rn+. The ex ac ed peak cen oids o 219Rn+and 20Ne+ions a e
in ag eemen o he needle sou ce in posi ions I and II and ha e a
di e ence o less han 10 % o he needle sou ce in posi ion III. The
e acua ion ime p o ile o 219Rn+ o he needle sou ce in posi ion IV
was no eco ded due o insu icien s a is ics. Mo eo e , peak cen oids
o 219Rn+and 40A +ions a e in ag eemen o he measu emen s
pe o med wi h a gon bu e gas. This leads o he conclusion ha
ioniza ion o bu e gas and i s impu i ies (20Ne+, in case o helium
bu e gas) akes place wi hin a couple o mm a ound he needle ip by
Nuclea Ins . and Me hods in Physics Resea ch, B 539 (2023) 33–42
38
A. Zad o naya e al.
Fig. 6. Ou pu o he nume ical calcula ions o he eloci y and low s eamlines inside he MARA-LEB gas cell. The colo ba indica es he eloci y magni ude wi h he uppe
limi se o 2 m/s o allow isualiza ion o a slowe gas low in he cen al pa o he gas cell. The gas inle (A) is deno ed. The e ec o he honeycomb s uc u e (B) used o
achie e a uni o m low condi ion is clea ly isible. The ions exi he gas cell a posi ion (C). Veloci y p o ile maps om di e en c oss-sec ions o he gas cell a e shown a he
co esponding loca ions.
he 219Rn+ions, eleased in he decay o 223Ra wi h an ene gy o abou
104 keV. On he o he hand, he alpha pa icles eleased wi h an ene gy
o 5.7 MeV, deposi only abou 30 keV pe 1 cm a eled in 200 mba
helium bu e gas. The e o e, o he cases when he ex ac ed ion
signal o 219Rn+is oo small, e acua ion ime p o iles o ions o bu e
gas and/o o i s impu i ies can be used o es ima e he e acua ion
ime. Full wid hs a hal -maximum o ligh e 20Ne+and 40A +ions a e
la ge compa ed o hose o 219Rn+, which can be explained by a la ge
di usion coe icien .
The needle sou ce posi ions I, II and III a e sepa a ed by 24 mm, as
indica ed in he inse in Fig. 2. The co esponding peak cen oids o
20Ne+ions a e delayed by app oxima ely 27 ms o each subsequen
posi ion, allowing he eloci y o he helium gas o be es ima ed
as 0.9 m/s in ha sec ion o he gas cell, in good ag eemen wi h
nume ical calcula ions o he eloci y shown in Fig. 6. Mo eo e , peak
cen oids o 20Ne+coincide o he sou ce in posi ions II and IV, hus
illus a ing ha he gas eloci y is a he cons an in he coo dina e
pe pendicula o he low di ec ion, as he dis ance be ween hese wo
posi ions is also 24 mm.
The a io o he measu ed peak cen oids o 219Rn+ions o he nee-
dle sou ce in posi ion I o a gon and helium bu e gas was calcula ed
o be 2.94 ± 0.02. This alue is easonably close o he es ima e o 3.16,
calcula ed om √𝐴A ∕𝐴He, whe e 𝐴A and 𝐴He a e s anda d a omic
weigh s o a gon and helium gas, espec i ely. This s aigh o wa d
es ima e is based on he ac ha he speed o sound 𝑎∼√1∕𝐴and,
he e o e, does no ake in o accoun sub le de ails such as iscous
e ec s ha sligh ly educe he e ec i e nozzle diame e , he di e en
dynamic iscosi y o helium and a gon, and mino di e ences in low
s uc u e e.g., eloci y s eamlines, be ween he wo gases.
E acua ion ime p o iles o 219Rn+ions o he needle sou ce in
helium and a gon bu e gas we e calcula ed in he CFD module. Resul s
o he calcula ed cen oids ag ee well wi h he expe imen al da a o
all posi ions o he sou ce (see Fig. 8). Howe e , he calcula ed ull
wid hs a hal maximum a e conside ably la ge han he measu ed al-
ues o helium bu e gas. This may be caused by e oneous assessmen
o di usion in ligh e gases and equi es mo e de ailed in es iga ion.
3.3. Ion-collec o es s
The pe o mance o he ion-collec o (IC) elec odes was es ed
wi h he 223Ra 𝛼- ecoil sou ce ins alled in posi ion I. Measu emen s
we e ob ained wi h helium gas a a p essu e 𝑃0o 166 mba . Mass-
sepa a ed 219Rn+ions we e de ec ed as a unc ion o ion-collec o
ol age a De ec o s a ion 2 wi h he MCP de ec o , he esul s a e
shown in Fig. 9. A supp ession o less han 2% o he ini ial amoun
was achie ed wi h a ol age o 5 V con inuously applied o one o he
ICs, while he o he was g ounded. In o de o e i y a pulsed ope a ion
o he ICs, ime p o iles o mass-sepa a ed 219Rn+and 20Ne+ions we e
accumula ed wi h a −20 V ampli ude pulse applied o one elec ode o
100 ms (see he inse in Fig. 9).
4. In-gas cell lase ioniza ion o in
In-gas cell lase ioniza ion o s able in iso opes was pe o med
wi hin a gon gas a a p essu e 𝑃0o 100 mba . The iso opes we e
p oduced by esis i ely hea ing b onze ilamen s (91 % coppe and
9 % in, by mass) ins alled in he gas cell, as shown in Fig. 2. A omic
apo , p oduced in his way, was anspo ed by a high-pu i y a gon
low owa ds he ee je nozzle. Two-s ep b oadband (∼ ew GHz) lase
ioniza ion was used o selec i ely ionize in in a collinea geome y,
in which bo h lase beams we e anspo ed o he in e ac ion egion
Nuclea Ins . and Me hods in Physics Resea ch, B 539 (2023) 33–42
39
A. Zad o naya e al.
Fig. 7. E acua ion ime p o iles o he mass-sepa a ed 219Rn+,20Ne+and 40A +ions.
Time p o iles o 20Ne+we e accumula ed wi hin 400 o 700 eco ding cycles (highe
s a is ics equi ed o he needle sou ce posi ions wi h smalle ion coun ing a es, such
as posi ion IV), while o 219Rn+abou 4 imes longe accumula ion was used. Blue
solid lines show i ing o measu ed da a (black line) using he Ex eme Peak unc ion
discussed in he ex . (a) Vol age pulsed wi h a elease ime o 50 ms applied o
he needle sou ce in he gas cell illed wi h helium bu e gas (𝑃0= 200 mba ). The
coun ing a e o 20Ne+ions was abou an o de o magni ude la ge han ha o 219Rn+.
(b) Vol age pulsed wi h a elease ime o 150 ms applied o he needle sou ce, using
a gon as bu e gas (𝑃0= 100 mba ). The coun ing a e o 40 A +was measu ed o be
app oxima ely he same as ha o 219Rn+.
h ough iewpo D1 (see Fig. 2). The geome y was chosen p ima ily
due o he ease o op ical access ia a window on he a ge chambe .
A mo e e sa ile op ical access ha allows o ans e se and c ossed-
beams geome y, as well as o in-gas je lase ioniza ion will be
a ailable on he a ge chambe o he MARA-LEB acili y.
The lase ioniza ion scheme used in hese es s is shown in
Fig. 10(a), aken om Re . [29]. The Sn a oms we e p omo ed om
he g ound s a e 5s25p2 3P0(J =0) o he in e media e le el 5p6s 1P1
(J = 1), using equency- ipled lase ligh a 254.73 nm (wa eleng h in
acuum). This ansi ion was easily sa u a ed wi h he a ailable a e -
age lase powe o 70 mW measu ed a he op ical able in he FURIOS
labo a o y. The exci ed a oms we e hen ionized ia an au oionizing
s a e abo e he ioniza ion po en ial, a s a e ha co esponds o he
5p7 con igu a ion, using equency-doubled lase ligh a 454.9 nm. By
moni o ing he coun a e o he mos abundan iso ope, 120Sn, a he
MCP o De ec o s a ion 2 as a unc ion o he lase powe , sa u a ion
da a can be ob ained (see Fig. 10(b)). F om a sa u a ion p o ile i
o he da a, a sa u a ion powe P𝑠o 4 mW o he i s s ep was
de e mined. We no e ha all lase powe measu emen s we e made on
he op ical able, oughly 10 m om he a ge chambe . App oxima ely
50% o ene gy losses a e expec ed o he anspo o UV ligh o he
a ge chambe . The second s ep ansi ion was no sa u a ed wi h he
a ailable a e age powe o abou 400 mW.
By independen ly blocking he i s - and second-s ep lase s, we
e i ied ha he ion signal p ima ily comes om wo-s ep ioniza ion.
The coun a e a he MCP d opped o he noise le el when he i s -s ep
lase was blocked. Blocking only he second-s ep lase led o he signal
dec easing o less han 10 % om i s ini ial alue, indica ing only a
small con ibu ion om any non- esonan ioniza ion p ocesses. Wi hou
needing o une he lase equency, he mass sepa a o can be used o
ob ain a mass scan o he lase -ionized in. As can be seen in Fig. 11,
he expe imen al da a is in easonable ag eemen wi h he expec ed
na u al iso opic abundances o all iso opes apa om an unexplained
unde abundance seen a 120Sn. Supp ession o lase -ionized 120Sn o
a ound 40 % o i s ini ial alue was achie ed wi h 5 V applied o one
o he ICs. Fu he supp ession o less han 20 % was achie ed wi h he
ol age highe han 20 V. When 5 V we e applied o bo h ICs, he ion
signal d opped only o a ound 60 % due o a cancella ion e ec o he
ol ages on he ion beam.
F equency scans we e a emp ed o bo h ansi ions in o de o
s udy he e ec o he gas p essu e on he spec al linewid hs and cen-
oids. Un o una ely, he i s -s ep ansi ion was hampe ed by mode
hopping o he b oadband lase , making i impossible o do a smoo h
scan o e he desi ed equency ange. In he u u e his limi a ion will
be add essed by implemen ing an injec ion-locked Ti:Sa lase esona o .
Scanning o he second-s ep ansi ion was howe e achie ed a a gon
p essu e 𝑃0 alues anging om 97 mba o 203 mba , wi h he mass
sepa a o uned o 120Sn. The lase powe was educed o ∼1 mW
and 300 mW o he i s and second s eps, espec i ely, o educe
he e ec o powe b oadening. The esul s o he equency scans a e
shown in Fig. 12. I can be seen ha he spec al line b oadens as he
p essu e inc eases. No ably he e is a s ong asymme y in he da a.
We su mise ha he asymme y a ises due o he geome y o he lase
ioniza ion. The lase beams pass h ough iewpo D1 (Fig. 2) and a e
g adually ocused owa ds he ee je nozzle. Ioniza ion is he e o e
occu ing in a collinea geome y bo h wi hin he gas cell as well as
in he olume a ound he ee je nozzle. The i adia ed gas olume
con ains a con olu ion o di e en collisional and Dopple egions. Fo
example, in he nozzle egion, he Mach numbe , eloci y and densi y
o gas low change apidly o e dis ances as sho as a millime e .
This he e o e complica es any analysis o he spec al p o iles wi h
pa ame ic models o ex ac p essu e b oadening and shi coe icien s
om he da a. A non-pa ame ic me hod o ex ac ing he wid h o he
peaks was used, by de e mining he ange o expe imen al alues ha
a e loca ed abo e he hal maximum o he peak. F om his da a, an
obse ed b oadening o he a omic esonances was ound o be on he
o de o 240 MHz∕mba . In u u e wo k, a c ossed-beam geome y wi h
a well-de ined egion o lase -beam o e lap is p e e able in o de o
minimize complexi ies due o con olu ing egions o di e en gas low.
5. Conclusions
The gas cell designed o he MARA-LEB acili y has been cha ac e -
ized a he Accele a o Labo a o y o he Uni e si y o Jy äskylä using
Nuclea Ins . and Me hods in Physics Resea ch, B 539 (2023) 33–42
40
A. Zad o naya e al.
Fig. 8. (a) Peak cen oids, 𝑡max, and (b) ull wid hs a hal maximum, 𝛥𝑡, ex ac ed om 219Rn+,20Ne+and 40A +e acua ion ime p o iles, shown in Fig. 7. O e lapping da a
poin s a e o se a ound hei X-coo dina es o cla i y.
Fig. 9. No malized signal o 219Rn+ions measu ed a he MCP de ec o (De ec o s a ion 2) wi h di e en ol ages applied o one o he ICs. The inse shows ime p o iles o he
mass-sepa a ed 219Rn+and 20Ne+ions accumula ed in 850 and 130 eco ding cycles, espec i ely, each las ing o 0.67 s, wi h ol age pulses applied o he ion collec o (100 ms
long and −20 V ampli ude). 𝑃0= 166 mba in all measu emen s.
Fig. 10. (a) Two-s ep lase esonance ioniza ion scheme o in. (b) Sa u a ion cu e o he i s -s ep ansi ion. The lase powe (P) was measu ed in he FURIOS labo a o y. The
da a was i ed ( ed cu e) wi h a con en ional sa u a ion unc ion o he o m I(P) = I0+ A P∕P𝑠
(1+P∕P𝑠), whe e I0is an o se pa ame e o accoun o non- esonan pho oioniza ion.