About NPL …The UK’s national standards laboratory

• World leading National Measurement Institute

• 450+ specialists in Measurement Science

• State-of-the-art laboratory facilities

• The heart of the UK’s National Measurement System to support business and society

What do we do

Develop & disseminate UK’s measurement standards, ensure they are internationally accepted

Multidisciplinary R&D and technical services for public and private sector

Knowledge transfer and advice between industry, government and academia

Promotion of science and engineering

Realising the Bq- The principle of coincidence counting

dates back to 1924 in visual observation of scintillations on a screen (Geiger)

- Rutherford later wrote: ‘…by an ingenious treatment of the observations they were able to obtain the true number of scintillations.’

NPL’s coincidence counting system in 1954

o

o

c o

Count Rates

N = N

N = N

N = N

b

g

: oc

N NActivity N =

N

Idea: Use gamma-ray coincidence array for radioactive source decay measurement for: a) Standardisation and use as a traceable primary radiation standard.

b) Use for nuclear assay and identification of which radionuclides are present and in what amounts (activity).

c) Use for nuclear structure / decay data measurements to improve nuclear decay and energy level scheme knowledge based for specific radionuclides (e.g 223Ra)

– Alpha-emitting radionuclides have great potential for treating diffuse tumours

– 223RaCl2 (Xofigo) is the first a-emitting drug to be approved by the FDA and it was licensed in the EC in November 2013.

– Xofigo is used to treat patients with castration-resistant prostate cancer and symptomatic bone metastases.

New Primary Standard of a-emitting radiopharmaceuticals.

Courtesy: John Keightley et al.,

Alpha decay can also leave daughter in excited states which can then decay by (characteristic) gamma emission.

Can use (Eg , Eg ) ‘prompt’ coincidences to select unambiguous decay paths

Idea:Build an array of LaBr3 (Ce) detectors for best combination of

1) Energy resolution ;

2) ‘Fast-timing’ coincidences;

3) Detection efficiency;

…and cost.

Use experience developed by use of other (recent) arrays of LaBr3 detectors for (nuclear) gamma-ray spectroscopy/spectrometry

• FATIMA (‘Fast Timing Array)– STFC funded large array for decay spectroscopy of radionuclide

decays with unusual proton to neutron ratios (nuclear structure physics).

– 36 LaBr3 detectors (1.5” x 2” cylinders in three rings of 12 detectors)

• Other detector arrays including LaBr3(Ce) detectors for nuclear spectroscopy studies. e.g.,:– ROSPHERE (IFIN-HH, Romania)– EURICA array with 18 LaBr3(Ce) at RIKEN, Japan– EXILL-FATIMA (Nuclear structure studies of prompt fission fragments

at ILL-Grenoble).

FATIMA detector module• 1.5” x 2” LaBr3(Ce) crystal, coupled to a fast-

timing PMT. Housed in aluminium can.

R9779 PMTs from Hamamatsu

The Future: FATIMA for DESPEC• FATIMA = FAst TIMing Array = State of the art gamma-ray detection array for precision measurements of nuclear

structure in the most exotic and rare nuclei. Part of the ~ £8M STFC NUSTAR project grant (runs 2012-16).

– Good energy resolution (better than 3% at 1 MeV).

– Good detection efficiency (between than 5% Full-energy peak at 1 MeV).

– Excellent timing qualities (approaching 100 picoseconds).

• Use to measure lifetimes of excited nuclear states & provide precision tests of theories of nuclear structure, uses a fully-digitised Data Acquisition System.

• Collaboration with NPL (Radioactivity group) through NMO project on ‘Nuclear Data’ (Judge, Jerome, Regan et al.,) on parallel development of NPL-based array for use in traceable radioactive standards and traceability to the Bq.

New (gamma) detection devices:LaBr3 detectors for gamma-spec.

Expected, E1/2 dependence of FWHM on gamma-ray energy.

T.Alharbi et al., Applied Radiation and Isotopes, 70, 1337 (2012)

138La, T1/2=1.02x1011 yearsA.A.Sonzogni, NDS 98 (2003) 515

5+ 138La

1435.8138Ba82

2+

0+

ec (66%)

0+

2+

138Ce80

788.7

b- (34%)

137Cs source gives (initial) testenergy resolution of ~3.5% at 662 keV.Note presence of internal radioactivity in detector.PMT HV range ~1300 V

1436 keV EC(2+→ 0+ in 138Ba)789 keV + b-

In 138Ce

Ba x-rays from 137Cs & EC from 138La decay

Coincidence requirements (either gamma-gamma or beta-gated gamma coincidences) remove most problems associated with intrinsic radioactive background of LaBr 3(Ce) detectors.

Typical activities are the order of 1 Bq/cc.

Typical coincidence requirements for true coincidences are usually between picoseconds (for prompt -g g in a cascade) to tens of microseconds (for delayed or isomeric cascades).

Tests with 152Eu source (measure lifetime of Ip=2+ 121 keV level in 152Sm)

Measurement of lifetimes of excited nuclear states?

• HpGe coincidences struggle to measure direct coincidence lifetimes much less than 1 ns.

• LaBr3(Ce) coincidences allow lifetimes to be determined down to the tens of picoseconds.

• Accurate measurements of nuclear excited state lifetimes are of interest for nuclear structure.

• The inform on nuclear shapes, underlying nuclear spectroscopic configurations and geometrical symmetries of nuclear charge distributions.

Fast-timing Techniques

Gaussian-exponential convolution to account for timing resolution

Annual Review of Nuclear Science (1968) 18 p265-290

T1/2 = 1.4ns

Tests with 152Eu source to measure lifetime of Ip=2+ 122 keV level in 152Sm.

EURICA at RIBF, Japan,18 LaBr3(Ce) detectors plus 12 x 7 element HpGe Cluster detectors.

Beta-delayed LaBr3(Ce) coincs from EURICA: Excited state lifetimes in (defrormed) 102Zr

(following 102Y decay)

F.Browne, A.M.Bruce et al., Acta Physica Polonica B (2015)

The ROSPHERE Gamma-ray Spectrometer array (at IFIN-HH Bucharest)

• 14 HPGe detectors (AC) are used to detect coincident γ rays:– 7x HPGe dets. @ 37o

– 4x HPGe dets. @ 64o

– 3x HPGe dets. @ 90o

• 11 LaBr3(Ce:5%) detectors– 7x ø2”x2” and 4x ø1.5”x2”

(Cylindrical) @ 37, 64 and 90o w.r.t. the beam axis.

(h11/2)-2 only

N=80 Isotones

0+

2+

4+

6+

8+

10+isomer

Primarily(d5/2)2

Primarily(g7/2)2

• N = 80 isotones above Z = 50 display 10+ seniority isomers from coupling of (h11/2)-2

• 6+ level decays also usually ‘hindered’ e.g., in 136Ba, T1/2 = 3.1(1)ns.

• Thought to be due to change in configuration and seniority.

N=80 Isotones• Neighbouring N=80 nuclei, 138Ce and 140Nd expected to show

similar 6+ → 4+ hindrance.

• Competing transitions to negative parity states

130Te(12C,4n)138Ce @ 56 MeV

T.Alharbi et al., Phys. Rev. C87 (2013) 014323

138Ce80

S.-J. Zhu et al. Chin.Phys.Lett. 16, 635 (1999)

T1/2 = 140(11)ps

Using “delayed” HPGe gate

Typical -g g analysis, massive increase in signal to noise by coincidence requirement

NANA:The NAtional Nuclear Array

Compact, high-efficiency, good granularity, acceptable resolution gamma-ray spectrometer array.

Gamma-ray detection both in g-g coincidence mode (and later) for use in beta-gamma

Current design, 12 LaBr3(Ce) in close geometry,

Space for additional ‘gating’ detectors (HpGe, or Si beta-detector) to be added later,

Courtesy:R.ShearmanNDA / NNL funded PhD Student at NPL &U. Surrey

Conceptual design, for NANA.

Initial design:12 detectors in fixed geometry with source in central position.

Cylindrical LaBr3(Ce)Scintillation crystals, 1.5” diameter and 2.0” in length.

Digital time stamped DAQUsing CAEN 1 GHzDigitisers.

Acknowledgements

• Zsolt Podolyák, Peter Mason, Thamer Alharbi, Christopher Townsley (Surrey)

• Steven Judge, Robert Shearman (NPL)

• Alison Bruce, Oliver Roberts (Brighton)

• Nicu Marginean et al., (Bucharest)

• Funding for detectors and DAQ from STFC UK and UK NMO (for NANA funding).